<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a01023-7833-783f-9aa8-4be94ae67ad4,g:ce509e8c-40a0-4ae2-8c8a-37c32ec1ddb5-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://ascentco.com/role/CondensedConsolidatedStatementsofShareholdersEquityUnaudited" xlink:type="simple" xlink:href="acnt-20260930.xsd#CondensedConsolidatedStatementsofShareholdersEquityUnaudited"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/CondensedConsolidatedStatementsofShareholdersEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a01023-7963-7033-ba12-0bef597b6d79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a01023-7963-718f-a612-1d1bd02fd2c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a01023-7963-7033-ba12-0bef597b6d79" xlink:to="loc_us-gaap_StatementTable_01a01023-7963-718f-a612-1d1bd02fd2c5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a01023-7963-76fb-9dae-c601b210f01d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a01023-7963-718f-a612-1d1bd02fd2c5" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a01023-7963-76fb-9dae-c601b210f01d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01023-7963-76fb-9dae-c601b210f01d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01023-7963-76fb-9dae-c601b210f01d" xlink:to="loc_us-gaap_EquityComponentDomain_01a01023-7963-76fb-9dae-c601b210f01d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01023-7963-7e26-820e-5929ae6d07b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01023-7963-76fb-9dae-c601b210f01d" xlink:to="loc_us-gaap_EquityComponentDomain_01a01023-7963-7e26-820e-5929ae6d07b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a01023-7963-7959-ae20-8bd38830830d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01023-7963-7e26-820e-5929ae6d07b0" xlink:to="loc_us-gaap_CommonStockMember_01a01023-7963-7959-ae20-8bd38830830d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a01023-7963-7478-a532-cac6912d6cca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01023-7963-7e26-820e-5929ae6d07b0" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a01023-7963-7478-a532-cac6912d6cca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a01023-7963-7131-be5d-8546309bd4ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01023-7963-7e26-820e-5929ae6d07b0" xlink:to="loc_us-gaap_RetainedEarningsMember_01a01023-7963-7131-be5d-8546309bd4ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_01a01023-7963-71b3-a59d-db730cac7777" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01023-7963-7e26-820e-5929ae6d07b0" xlink:to="loc_us-gaap_TreasuryStockCommonMember_01a01023-7963-71b3-a59d-db730cac7777" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01023-7963-7033-ba12-0bef597b6d79" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a01023-7963-7094-9631-c6ba0aedd6c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_SharesOutstanding_01a01023-7963-7094-9631-c6ba0aedd6c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a01023-7963-7902-a295-a7c5ce85dc90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_StockholdersEquity_01a01023-7963-7902-a295-a7c5ce85dc90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_01a01023-7963-74d1-9470-9459efaab5c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_TreasuryStockCommonShares_01a01023-7963-74d1-9470-9459efaab5c3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a01023-7963-7779-9d87-cffe4312c3be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_NetIncomeLoss_01a01023-7963-7779-9d87-cffe4312c3be" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued_01a01023-7963-7707-b03e-2601d27c6962" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued_01a01023-7963-7707-b03e-2601d27c6962" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_01a01023-7963-78be-8688-f5ece50e897e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_01a01023-7963-78be-8688-f5ece50e897e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_01a01023-7963-7d34-af35-e727e0745d8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_01a01023-7963-7d34-af35-e727e0745d8c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a01023-7963-7799-9b3a-0e76720a98ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a01023-7963-7799-9b3a-0e76720a98ce" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a01023-7963-7ee6-9bd7-2a9c9af635e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a01023-7963-7ee6-9bd7-2a9c9af635e7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a01023-7963-78b4-8a9b-09030afcf537" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a01023-7963-78b4-8a9b-09030afcf537" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a01023-7963-7925-9688-c075663eca22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01023-7963-78b3-9728-c1e75d206c96" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a01023-7963-7925-9688-c075663eca22" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a01023-7963-7038-b6d5-54d0f34a5a02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a01023-7963-7841-8112-fbe3af66fb3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_01a01023-7963-7315-99d0-4494c0370028" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/AcquisitionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7e11-8a81-5d849883318e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7e11-8a81-5d849883318e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7036-93c3-d887505855ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7e11-8a81-5d849883318e" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7036-93c3-d887505855ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7036-93c3-d887505855ef_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7036-93c3-d887505855ef" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7036-93c3-d887505855ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-722c-818e-059e0c4909bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7036-93c3-d887505855ef" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-722c-818e-059e0c4909bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member_01a01023-7963-77d9-9c8e-625cc554d3c2" xlink:href="acnt-20260930.xsd#acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-722c-818e-059e0c4909bd" xlink:to="loc_acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member_01a01023-7963-77d9-9c8e-625cc554d3c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-7963-7e85-95fa-e120ed651542" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7e11-8a81-5d849883318e" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-7963-7e85-95fa-e120ed651542" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01023-7963-7e85-95fa-e120ed651542_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-7963-7e85-95fa-e120ed651542" xlink:to="loc_us-gaap_SegmentDomain_01a01023-7963-7e85-95fa-e120ed651542_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01023-7963-7415-b72a-5a6f9f4df38a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-7963-7e85-95fa-e120ed651542" xlink:to="loc_us-gaap_SegmentDomain_01a01023-7963-7415-b72a-5a6f9f4df38a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_SpecialtyChemicalsSegmentMember_01a01023-7963-757d-ae70-ccbef30b033d" xlink:href="acnt-20260930.xsd#acnt_SpecialtyChemicalsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a01023-7963-7415-b72a-5a6f9f4df38a" xlink:to="loc_acnt_SpecialtyChemicalsSegmentMember_01a01023-7963-757d-ae70-ccbef30b033d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-75d8-9b4b-d682416c8cbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7e11-8a81-5d849883318e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-75d8-9b4b-d682416c8cbc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-75d8-9b4b-d682416c8cbc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-75d8-9b4b-d682416c8cbc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-75d8-9b4b-d682416c8cbc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7026-b068-7d80d4e34c99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-75d8-9b4b-d682416c8cbc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7026-b068-7d80d4e34c99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_01a01023-7963-772b-b710-7cdaaab6ae70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7026-b068-7d80d4e34c99" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_01a01023-7963-772b-b710-7cdaaab6ae70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_01a01023-7963-7b65-9a53-e80fb6e3a1ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7026-b068-7d80d4e34c99" xlink:to="loc_us-gaap_CustomerRelationshipsMember_01a01023-7963-7b65-9a53-e80fb6e3a1ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a01023-7963-75f9-a546-177d898845cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7e11-8a81-5d849883318e" xlink:to="loc_srt_RangeAxis_01a01023-7963-75f9-a546-177d898845cb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01023-7963-75f9-a546-177d898845cb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a01023-7963-75f9-a546-177d898845cb" xlink:to="loc_srt_RangeMember_01a01023-7963-75f9-a546-177d898845cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01023-7963-7918-ab65-2ac2ac7db8d4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a01023-7963-75f9-a546-177d898845cb" xlink:to="loc_srt_RangeMember_01a01023-7963-7918-ab65-2ac2ac7db8d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a01023-7963-709b-9c09-5da9a4cd10b6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01023-7963-7918-ab65-2ac2ac7db8d4" xlink:to="loc_srt_MinimumMember_01a01023-7963-709b-9c09-5da9a4cd10b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a01023-7963-71ca-ac29-55282fd173f9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01023-7963-7918-ab65-2ac2ac7db8d4" xlink:to="loc_srt_MaximumMember_01a01023-7963-71ca-ac29-55282fd173f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentAxis_01a01023-7963-70cc-891e-2bc4fcdb52ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrecurringAdjustmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7e11-8a81-5d849883318e" xlink:to="loc_us-gaap_NonrecurringAdjustmentAxis_01a01023-7963-70cc-891e-2bc4fcdb52ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_01a01023-7963-70cc-891e-2bc4fcdb52ce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_01a01023-7963-70cc-891e-2bc4fcdb52ce" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_01a01023-7963-70cc-891e-2bc4fcdb52ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_01a01023-7963-7422-b9f7-3e11837b133c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_01a01023-7963-70cc-891e-2bc4fcdb52ce" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_01a01023-7963-7422-b9f7-3e11837b133c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_IntangibleAssetAmortizationMember_01a01023-7963-7c76-856d-1e71024689d7" xlink:href="acnt-20260930.xsd#acnt_IntangibleAssetAmortizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonrecurringAdjustmentDomain_01a01023-7963-7422-b9f7-3e11837b133c" xlink:to="loc_acnt_IntangibleAssetAmortizationMember_01a01023-7963-7c76-856d-1e71024689d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_01a01023-7963-70e4-ad49-cfcb13864f77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_01a01023-7963-70e4-ad49-cfcb13864f77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a01023-7963-7772-beba-0675866a43cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a01023-7963-7772-beba-0675866a43cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_01a01023-7963-79ab-8647-45a0ace38267" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_Goodwill_01a01023-7963-79ab-8647-45a0ace38267" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_01a01023-7963-797b-8176-677f370f7223" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_01a01023-7963-797b-8176-677f370f7223" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_01a01023-7963-7fbf-acc9-42fba9f09073" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_01a01023-7963-7fbf-acc9-42fba9f09073" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_01a01023-7963-77ff-8e04-63b73a7ad829" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_01a01023-7963-77ff-8e04-63b73a7ad829" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_01a01023-7963-78cf-a7e3-d001dfcd700d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_01a01023-7963-78cf-a7e3-d001dfcd700d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_BusinessCombinationCashInEscrow_01a01023-7963-7df6-9d37-955637a83780" xlink:href="acnt-20260930.xsd#acnt_BusinessCombinationCashInEscrow"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_acnt_BusinessCombinationCashInEscrow_01a01023-7963-7df6-9d37-955637a83780" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_BusinessCombinationCashInEscrowHoldingPeriod_01a01023-7963-76d5-ac27-1bd9441b9d5b" xlink:href="acnt-20260930.xsd#acnt_BusinessCombinationCashInEscrowHoldingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-72b7-89ff-5f2ffc9796bf" xlink:to="loc_acnt_BusinessCombinationCashInEscrowHoldingPeriod_01a01023-7963-76d5-ac27-1bd9441b9d5b" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/AcquisitionsScheduleofFairValueofIdentifiableAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#AcquisitionsScheduleofFairValueofIdentifiableAssetsAcquiredandLiabilitiesAssumedDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/AcquisitionsScheduleofFairValueofIdentifiableAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7a54-b8d4-e46ad65c59e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7a54-b8d4-e46ad65c59e1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7c2f-b8ba-ff87af25b347" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7a54-b8d4-e46ad65c59e1" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7c2f-b8ba-ff87af25b347" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7c2f-b8ba-ff87af25b347_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7c2f-b8ba-ff87af25b347" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7c2f-b8ba-ff87af25b347_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7572-a6d2-34ee02fe85f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7c2f-b8ba-ff87af25b347" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7572-a6d2-34ee02fe85f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member_01a01023-7963-7447-bdb7-343637bd1c7d" xlink:href="acnt-20260930.xsd#acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7572-a6d2-34ee02fe85f5" xlink:to="loc_acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member_01a01023-7963-7447-bdb7-343637bd1c7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_01a01023-7963-78d5-a89b-0251c53e3029" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_01a01023-7963-78d5-a89b-0251c53e3029" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_01a01023-7963-7919-ab3a-9522252b7284" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_01a01023-7963-7919-ab3a-9522252b7284" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_01a01023-7963-771c-b485-71adbab06aed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_01a01023-7963-771c-b485-71adbab06aed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_01a01023-7963-7067-8ada-3d31476d5baf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_01a01023-7963-7067-8ada-3d31476d5baf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_01a01023-7963-7951-8e05-d77196a61ce9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_01a01023-7963-7951-8e05-d77196a61ce9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_01a01023-7963-7860-aa59-82de260a9674" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_01a01023-7963-7860-aa59-82de260a9674" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_01a01023-7963-7fe3-ae5b-b34c4f02f84f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_01a01023-7963-7fe3-ae5b-b34c4f02f84f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherCurrentLiabilities_01a01023-7963-7469-91cf-3d380cd6d893" xlink:href="acnt-20260930.xsd#acnt_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_acnt_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherCurrentLiabilities_01a01023-7963-7469-91cf-3d380cd6d893" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_01a01023-7963-7a64-897e-9fa1de5c161a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_01a01023-7963-7a64-897e-9fa1de5c161a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_01a01023-7963-73c9-96c3-94d0c97b776b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_01a01023-7963-73c9-96c3-94d0c97b776b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a01023-7963-7371-983f-316f645a5fde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a01023-7963-7371-983f-316f645a5fde" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_01a01023-7963-7c17-81d1-45ce3f28c04e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7ac0-9356-1d5e3d4e8738" xlink:to="loc_us-gaap_Goodwill_01a01023-7963-7c17-81d1-45ce3f28c04e" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/AcquisitionsScheduleofProFormaFinancialInformationDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#AcquisitionsScheduleofProFormaFinancialInformationDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/AcquisitionsScheduleofProFormaFinancialInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7800-b8e2-a1d41dd9c7d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7ab7-84a6-f490cfc9f239" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7800-b8e2-a1d41dd9c7d3" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7ab7-84a6-f490cfc9f239" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7cd5-a943-b695df2ce12a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01023-7963-7ab7-84a6-f490cfc9f239" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7cd5-a943-b695df2ce12a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7cd5-a943-b695df2ce12a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7cd5-a943-b695df2ce12a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-7cd5-a943-b695df2ce12a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-72c5-8715-9cb103b32a2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01023-7963-7cd5-a943-b695df2ce12a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-72c5-8715-9cb103b32a2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member_01a01023-7963-7867-9d5b-934b1a335b26" xlink:href="acnt-20260930.xsd#acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01023-7963-72c5-8715-9cb103b32a2c" xlink:to="loc_acnt_MidwestGraphicSalesInc.AndSigmaCoatingsInc.Member_01a01023-7963-7867-9d5b-934b1a335b26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_01a01023-7963-7f17-9f70-e3137ec9625e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7800-b8e2-a1d41dd9c7d3" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_01a01023-7963-7f17-9f70-e3137ec9625e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_01a01023-7963-78d9-b10a-1682ab41387f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01023-7963-7800-b8e2-a1d41dd9c7d3" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_01a01023-7963-78d9-b10a-1682ab41387f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/DiscontinuedOperationsNarrativeDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#DiscontinuedOperationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/DiscontinuedOperationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-76ae-aceb-c59d5a992e07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7a07-adbf-4e5ec7be2190" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-76ae-aceb-c59d5a992e07" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7a07-adbf-4e5ec7be2190" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-78df-b765-15f87e003a34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7a07-adbf-4e5ec7be2190" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-78df-b765-15f87e003a34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-78df-b765-15f87e003a34_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-78df-b765-15f87e003a34" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-78df-b765-15f87e003a34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-79d3-993d-c4761b5a0860" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-78df-b765-15f87e003a34" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-79d3-993d-c4761b5a0860" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_BristolMetalsLLCMember_01a01023-7963-738d-b6aa-72cf27f1c609" xlink:href="acnt-20260930.xsd#acnt_BristolMetalsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-79d3-993d-c4761b5a0860" xlink:to="loc_acnt_BristolMetalsLLCMember_01a01023-7963-738d-b6aa-72cf27f1c609" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_AmericanStainlessTubingLLCMember_01a01023-7963-7c51-9fe9-7309ca4d263e" xlink:href="acnt-20260930.xsd#acnt_AmericanStainlessTubingLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-79d3-993d-c4761b5a0860" xlink:to="loc_acnt_AmericanStainlessTubingLLCMember_01a01023-7963-7c51-9fe9-7309ca4d263e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7a28-a368-33ca06247506" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7a07-adbf-4e5ec7be2190" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7a28-a368-33ca06247506" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7a28-a368-33ca06247506_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7a28-a368-33ca06247506" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7a28-a368-33ca06247506_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7f9f-a04b-1c9db353e107" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7a28-a368-33ca06247506" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7f9f-a04b-1c9db353e107" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_01a01023-7963-75c4-8f16-4011218def61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsHeldforsaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7f9f-a04b-1c9db353e107" xlink:to="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_01a01023-7963-75c4-8f16-4011218def61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfProductiveAssets_01a01023-7963-7706-95de-3169c75d2314" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-76ae-aceb-c59d5a992e07" xlink:to="loc_us-gaap_ProceedsFromSaleOfProductiveAssets_01a01023-7963-7706-95de-3169c75d2314" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EscrowDeposit_01a01023-7963-7a38-848b-b2660a353077" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EscrowDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-76ae-aceb-c59d5a992e07" xlink:to="loc_us-gaap_EscrowDeposit_01a01023-7963-7a38-848b-b2660a353077" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_EscrowDepositPaymentPeriod_01a01023-7963-7727-8632-27232323c369" xlink:href="acnt-20260930.xsd#acnt_EscrowDepositPaymentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-76ae-aceb-c59d5a992e07" xlink:to="loc_acnt_EscrowDepositPaymentPeriod_01a01023-7963-7727-8632-27232323c369" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_01a01023-7963-78ac-8a00-3ef3dcffb014" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-76ae-aceb-c59d5a992e07" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_01a01023-7963-78ac-8a00-3ef3dcffb014" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/DiscontinuedOperationsScheduleofResultsofDiscontinuedOperationsDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#DiscontinuedOperationsScheduleofResultsofDiscontinuedOperationsDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/DiscontinuedOperationsScheduleofResultsofDiscontinuedOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-726b-b1df-ccd512def04c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-726b-b1df-ccd512def04c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7419-881c-f314a67d4d0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-726b-b1df-ccd512def04c" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7419-881c-f314a67d4d0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7419-881c-f314a67d4d0d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7419-881c-f314a67d4d0d" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7419-881c-f314a67d4d0d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7192-9d38-42949a0b2a35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7419-881c-f314a67d4d0d" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7192-9d38-42949a0b2a35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_01a01023-7963-729a-a7ae-55d248639c98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsHeldforsaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7192-9d38-42949a0b2a35" xlink:to="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_01a01023-7963-729a-a7ae-55d248639c98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_01a01023-7963-7cb3-8d23-12745f1a0a04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_01a01023-7963-7cb3-8d23-12745f1a0a04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_01a01023-7963-7227-b756-ed0e8e5992de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_01a01023-7963-7227-b756-ed0e8e5992de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss_01a01023-7963-706d-9060-eb58bb8039cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss_01a01023-7963-706d-9060-eb58bb8039cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_01a01023-7963-7be8-9441-d914fc375ef0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_01a01023-7963-7be8-9441-d914fc375ef0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_01a01023-7963-7068-8cea-0abb327041bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_01a01023-7963-7068-8cea-0abb327041bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_DisposalGroupIncludingDiscontinuedOperationAcquisitionCostsAndOther_01a01023-7963-7047-87b2-300ce1a023d5" xlink:href="acnt-20260930.xsd#acnt_DisposalGroupIncludingDiscontinuedOperationAcquisitionCostsAndOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_acnt_DisposalGroupIncludingDiscontinuedOperationAcquisitionCostsAndOther_01a01023-7963-7047-87b2-300ce1a023d5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_01a01023-7963-7fe0-b4ab-f9b3b1680d79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_01a01023-7963-7fe0-b4ab-f9b3b1680d79" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_01a01023-7963-7ec7-8f60-2250272fad64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_01a01023-7963-7ec7-8f60-2250272fad64" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_01a01023-7963-73d3-a993-f988cb1583ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7124-bfce-575e70e03a96" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_01a01023-7963-73d3-a993-f988cb1583ef" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/RevenueRecognitionScheduleofDisaggregatedRevenuebyProductGroupDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#RevenueRecognitionScheduleofDisaggregatedRevenuebyProductGroupDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/RevenueRecognitionScheduleofDisaggregatedRevenuebyProductGroupDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_01a01023-7963-7c23-944a-50e73334d5db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_01a01023-7963-7387-bced-104f1c882b3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a01023-7963-7c23-944a-50e73334d5db" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a01023-7963-7387-bced-104f1c882b3e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a01023-7963-708c-8088-80b1072e00c4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a01023-7963-7387-bced-104f1c882b3e" xlink:to="loc_srt_ProductOrServiceAxis_01a01023-7963-708c-8088-80b1072e00c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a01023-7963-708c-8088-80b1072e00c4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a01023-7963-708c-8088-80b1072e00c4" xlink:to="loc_srt_ProductsAndServicesDomain_01a01023-7963-708c-8088-80b1072e00c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a01023-7963-779a-a9dc-5b5dbec531de" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a01023-7963-708c-8088-80b1072e00c4" xlink:to="loc_srt_ProductsAndServicesDomain_01a01023-7963-779a-a9dc-5b5dbec531de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_CustomManufacturingMember_01a01023-7963-75ba-8f1e-f87f57cbca51" xlink:href="acnt-20260930.xsd#acnt_CustomManufacturingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a01023-7963-779a-a9dc-5b5dbec531de" xlink:to="loc_acnt_CustomManufacturingMember_01a01023-7963-75ba-8f1e-f87f57cbca51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_CoreTechnologyMember_01a01023-7963-7829-af9e-6ed85104fb6c" xlink:href="acnt-20260930.xsd#acnt_CoreTechnologyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a01023-7963-779a-a9dc-5b5dbec531de" xlink:to="loc_acnt_CoreTechnologyMember_01a01023-7963-7829-af9e-6ed85104fb6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_DistributionMember_01a01023-7963-72e1-8385-09aefee58d5b" xlink:href="acnt-20260930.xsd#acnt_DistributionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a01023-7963-779a-a9dc-5b5dbec531de" xlink:to="loc_acnt_DistributionMember_01a01023-7963-72e1-8385-09aefee58d5b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01023-7963-7513-bfac-e778543a9bea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a01023-7963-7c23-944a-50e73334d5db" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01023-7963-7513-bfac-e778543a9bea" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/RevenueRecognitionScheduleofRevenueRemainingPerformanceObligationExpectedTimingofSatisfactionDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#RevenueRecognitionScheduleofRevenueRemainingPerformanceObligationExpectedTimingofSatisfactionDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/RevenueRecognitionScheduleofRevenueRemainingPerformanceObligationExpectedTimingofSatisfactionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_01a01023-7963-7d83-84ca-611905ac5b5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_01a01023-7963-79ab-87b6-46450f29f4d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a01023-7963-7d83-84ca-611905ac5b5a" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a01023-7963-79ab-87b6-46450f29f4d3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_01a01023-7963-71ec-ac14-964a36444773" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a01023-7963-79ab-87b6-46450f29f4d3" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_01a01023-7963-71ec-ac14-964a36444773" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_01a01023-7963-71ec-ac14-964a36444773_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_01a01023-7963-71ec-ac14-964a36444773" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_01a01023-7963-71ec-ac14-964a36444773_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_01a01023-7963-7bef-8117-dff4144e60ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_01a01023-7963-71ec-ac14-964a36444773" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_01a01023-7963-7bef-8117-dff4144e60ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_01a01023-7963-74e8-891d-8872366b9fed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_01a01023-7963-7bef-8117-dff4144e60ba" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_01a01023-7963-74e8-891d-8872366b9fed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_01a01023-7963-7405-bbae-21335061c3d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_01a01023-7963-7bef-8117-dff4144e60ba" xlink:to="loc_us-gaap_TransferredOverTimeMember_01a01023-7963-7405-bbae-21335061c3d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01023-7963-798e-8be5-f9bf30be6a5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a01023-7963-7d83-84ca-611905ac5b5a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01023-7963-798e-8be5-f9bf30be6a5b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/FairValueofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#FairValueofFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/FairValueofFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7b1a-a3ad-ace4b40dea51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7152-87ca-b2713e3dfee9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7b1a-a3ad-ace4b40dea51" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7152-87ca-b2713e3dfee9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7c20-9c24-5bf2bb003f26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7152-87ca-b2713e3dfee9" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7c20-9c24-5bf2bb003f26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7c20-9c24-5bf2bb003f26_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7c20-9c24-5bf2bb003f26" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-7c20-9c24-5bf2bb003f26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-748f-814c-ac99c6e5b925" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a01023-7963-7c20-9c24-5bf2bb003f26" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-748f-814c-ac99c6e5b925" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_01a01023-7963-733d-9aa9-6e9bf18a6e8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsHeldforsaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a01023-7963-748f-814c-ac99c6e5b925" xlink:to="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_01a01023-7963-733d-9aa9-6e9bf18a6e8e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-7286-9d3b-a8766943c0d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a01023-7963-7152-87ca-b2713e3dfee9" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-7286-9d3b-a8766943c0d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-7286-9d3b-a8766943c0d0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-7286-9d3b-a8766943c0d0" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-7286-9d3b-a8766943c0d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-749b-b293-64555bd24270" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a01023-7963-7286-9d3b-a8766943c0d0" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-749b-b293-64555bd24270" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_MunhallFacilityMember_01a01023-7963-758b-8592-706e34852d91" xlink:href="acnt-20260930.xsd#acnt_MunhallFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a01023-7963-749b-b293-64555bd24270" xlink:to="loc_acnt_MunhallFacilityMember_01a01023-7963-758b-8592-706e34852d91" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseImpairmentLoss_01a01023-7963-782b-9c0a-552fd40ddfaa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a01023-7963-7b1a-a3ad-ace4b40dea51" xlink:to="loc_us-gaap_OperatingLeaseImpairmentLoss_01a01023-7963-782b-9c0a-552fd40ddfaa" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/PropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#PropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/PropertyPlantandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a01023-7963-795e-a7d9-dc0984a4d42d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a01023-7963-795e-a7d9-dc0984a4d42d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a01023-7963-795e-a7d9-dc0984a4d42d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7006-b1c2-1d687ed30904_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7006-b1c2-1d687ed30904_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_01a01023-7963-74b0-9908-0b9e3176270b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_LandMember_01a01023-7963-74b0-9908-0b9e3176270b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandImprovementsMember_01a01023-7963-7084-9ede-c4a9a7330b46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_LandImprovementsMember_01a01023-7963-7084-9ede-c4a9a7330b46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingMember_01a01023-7963-78b9-9311-a35f71b933de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_BuildingMember_01a01023-7963-78b9-9311-a35f71b933de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_01a01023-7963-7913-9e09-5fd25da5a763" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_01a01023-7963-7913-9e09-5fd25da5a763" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_01a01023-7963-79ec-b509-e5ce5984443d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_ConstructionInProgressMember_01a01023-7963-79ec-b509-e5ce5984443d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a01023-7963-79b6-b51f-5d8e6aa4c6d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a01023-7963-795e-a7d9-dc0984a4d42d" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a01023-7963-79b6-b51f-5d8e6aa4c6d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_01a01023-7963-7a83-877a-1c15cbbe1dbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_01a01023-7963-7a83-877a-1c15cbbe1dbc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_01a01023-7963-70c3-a19d-2c028d85899b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_01a01023-7963-70c3-a19d-2c028d85899b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a01023-7963-7ba3-9597-2e485a7e4f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a01023-7963-7ba3-9597-2e485a7e4f9b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_01a01023-7963-71f2-b0f3-50a09e46d58a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_Depreciation_01a01023-7963-71f2-b0f3-50a09e46d58a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/PropertyPlantandEquipmentDetails_1" xlink:type="simple" xlink:href="acnt-20260930.xsd#PropertyPlantandEquipmentDetails_1"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/PropertyPlantandEquipmentDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a01023-7963-795e-a7d9-dc0984a4d42d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a01023-7963-795e-a7d9-dc0984a4d42d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a01023-7963-795e-a7d9-dc0984a4d42d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7006-b1c2-1d687ed30904_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7006-b1c2-1d687ed30904_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a01023-7963-7006-b1c2-1d687ed30904" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_01a01023-7963-74b0-9908-0b9e3176270b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_LandMember_01a01023-7963-74b0-9908-0b9e3176270b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandImprovementsMember_01a01023-7963-7084-9ede-c4a9a7330b46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_LandImprovementsMember_01a01023-7963-7084-9ede-c4a9a7330b46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingMember_01a01023-7963-78b9-9311-a35f71b933de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_BuildingMember_01a01023-7963-78b9-9311-a35f71b933de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_01a01023-7963-7913-9e09-5fd25da5a763" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_01a01023-7963-7913-9e09-5fd25da5a763" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_01a01023-7963-79ec-b509-e5ce5984443d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a01023-7963-7159-9770-baec137c2667" xlink:to="loc_us-gaap_ConstructionInProgressMember_01a01023-7963-79ec-b509-e5ce5984443d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_01a01023-7963-7a83-877a-1c15cbbe1dbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_01a01023-7963-7a83-877a-1c15cbbe1dbc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_01a01023-7963-70c3-a19d-2c028d85899b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_01a01023-7963-70c3-a19d-2c028d85899b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a01023-7963-7ba3-9597-2e485a7e4f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a01023-7963-7ba3-9597-2e485a7e4f9b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_01a01023-7963-71f2-b0f3-50a09e46d58a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a01023-7963-7f24-be95-42de350b3a79" xlink:to="loc_us-gaap_Depreciation_01a01023-7963-71f2-b0f3-50a09e46d58a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/IntangibleAssetsandDeferredChargesNarrativeDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#IntangibleAssetsandDeferredChargesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/IntangibleAssetsandDeferredChargesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-7510-a375-24558510eb78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_01a01023-7963-7402-b20b-179072f89cd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-7510-a375-24558510eb78" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_01a01023-7963-7402-b20b-179072f89cd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7002-abbb-35dd4abb2bcc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_01a01023-7963-7402-b20b-179072f89cd5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7002-abbb-35dd4abb2bcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7002-abbb-35dd4abb2bcc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7002-abbb-35dd4abb2bcc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7002-abbb-35dd4abb2bcc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7d8a-801d-fa52a0fc7b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7002-abbb-35dd4abb2bcc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7d8a-801d-fa52a0fc7b9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_01a01023-7963-7c0c-8311-8d017a2c5f70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7d8a-801d-fa52a0fc7b9e" xlink:to="loc_us-gaap_CustomerRelationshipsMember_01a01023-7963-7c0c-8311-8d017a2c5f70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a01023-7963-77c1-a22e-838f82589d6e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_01a01023-7963-7402-b20b-179072f89cd5" xlink:to="loc_srt_RangeAxis_01a01023-7963-77c1-a22e-838f82589d6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01023-7963-77c1-a22e-838f82589d6e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a01023-7963-77c1-a22e-838f82589d6e" xlink:to="loc_srt_RangeMember_01a01023-7963-77c1-a22e-838f82589d6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01023-7963-771a-ba94-0d080fd6cc71" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a01023-7963-77c1-a22e-838f82589d6e" xlink:to="loc_srt_RangeMember_01a01023-7963-771a-ba94-0d080fd6cc71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a01023-7963-7788-8a6f-95fab5f95e76" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01023-7963-771a-ba94-0d080fd6cc71" xlink:to="loc_srt_MinimumMember_01a01023-7963-7788-8a6f-95fab5f95e76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a01023-7963-785b-9bd0-d0f8602d6949" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01023-7963-771a-ba94-0d080fd6cc71" xlink:to="loc_srt_MaximumMember_01a01023-7963-785b-9bd0-d0f8602d6949" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_01a01023-7963-7668-96b2-2afe5d988bb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-7510-a375-24558510eb78" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_01a01023-7963-7668-96b2-2afe5d988bb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_01a01023-7963-7ba4-aff5-16af02825406" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-7510-a375-24558510eb78" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_01a01023-7963-7ba4-aff5-16af02825406" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_DeferredChargesAmortizationPeriod_01a01023-7963-7f79-b975-1e4f35a077e4" xlink:href="acnt-20260930.xsd#acnt_DeferredChargesAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-7510-a375-24558510eb78" xlink:to="loc_acnt_DeferredChargesAmortizationPeriod_01a01023-7963-7f79-b975-1e4f35a077e4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/IntangibleAssetsandDeferredChargesScheduleofIntangibleAssetsDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#IntangibleAssetsandDeferredChargesScheduleofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/IntangibleAssetsandDeferredChargesScheduleofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-726b-8f9d-aff5f1ad0641" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_01a01023-7963-72b0-b626-1af4754e2139" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-726b-8f9d-aff5f1ad0641" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_01a01023-7963-72b0-b626-1af4754e2139" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7bc0-b550-0bfd1301b0a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_01a01023-7963-72b0-b626-1af4754e2139" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7bc0-b550-0bfd1301b0a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7bc0-b550-0bfd1301b0a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7bc0-b550-0bfd1301b0a6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-7bc0-b550-0bfd1301b0a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-753b-9148-e0e0863a3a47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01023-7963-7bc0-b550-0bfd1301b0a6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-753b-9148-e0e0863a3a47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelatedIntangibleAssetsMember_01a01023-7963-72f7-9cb7-595cbac119f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelatedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-753b-9148-e0e0863a3a47" xlink:to="loc_us-gaap_CustomerRelatedIntangibleAssetsMember_01a01023-7963-72f7-9cb7-595cbac119f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_01a01023-7963-72ab-88d6-a1b252e1e008" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-753b-9148-e0e0863a3a47" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_01a01023-7963-72ab-88d6-a1b252e1e008" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_01a01023-7963-7fb3-80a8-3e107eec621e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01023-7963-753b-9148-e0e0863a3a47" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_01a01023-7963-7fb3-80a8-3e107eec621e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a01023-7963-77a5-b56b-a02652d0da28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-726b-8f9d-aff5f1ad0641" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a01023-7963-77a5-b56b-a02652d0da28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a01023-7963-74c7-950b-6eb33d5de9cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_01a01023-7963-726b-8f9d-aff5f1ad0641" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a01023-7963-74c7-950b-6eb33d5de9cc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_01a01023-7963-7fc8-ae62-ee1d1db1ab8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_01a01023-7963-7fc8-ae62-ee1d1db1ab8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_01a01023-7963-7fc8-ae62-ee1d1db1ab8b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_01a01023-7963-7fc8-ae62-ee1d1db1ab8b" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_01a01023-7963-7fc8-ae62-ee1d1db1ab8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_01a01023-7963-7ac3-9dd9-4d11e4110c02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_01a01023-7963-7fc8-ae62-ee1d1db1ab8b" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_01a01023-7963-7ac3-9dd9-4d11e4110c02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableToBanksMember_01a01023-7963-7418-834e-31c3f209c122" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableToBanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_01a01023-7963-7ac3-9dd9-4d11e4110c02" xlink:to="loc_us-gaap_NotesPayableToBanksMember_01a01023-7963-7418-834e-31c3f209c122" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a01023-7963-757b-9c89-b48f3d1f003a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:to="loc_us-gaap_CreditFacilityAxis_01a01023-7963-757b-9c89-b48f3d1f003a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a01023-7963-757b-9c89-b48f3d1f003a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a01023-7963-757b-9c89-b48f3d1f003a" xlink:to="loc_us-gaap_CreditFacilityDomain_01a01023-7963-757b-9c89-b48f3d1f003a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a01023-7963-7dfe-8be2-6c343db0c9b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a01023-7963-757b-9c89-b48f3d1f003a" xlink:to="loc_us-gaap_CreditFacilityDomain_01a01023-7963-7dfe-8be2-6c343db0c9b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_01a01023-7963-797a-ad50-fed00cd81044" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a01023-7963-7dfe-8be2-6c343db0c9b4" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_01a01023-7963-797a-ad50-fed00cd81044" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a01023-7963-7383-9419-d8e902854bc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a01023-7963-7383-9419-d8e902854bc4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01023-7963-7383-9419-d8e902854bc4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01023-7963-7383-9419-d8e902854bc4" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01023-7963-7383-9419-d8e902854bc4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01023-7963-70ee-8299-dc1d524c1ee9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01023-7963-7383-9419-d8e902854bc4" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01023-7963-70ee-8299-dc1d524c1ee9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_TheFacilityMember_01a01023-79f6-7f13-89b4-a0c2236b76c1" xlink:href="acnt-20260930.xsd#acnt_TheFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a01023-7963-70ee-8299-dc1d524c1ee9" xlink:to="loc_acnt_TheFacilityMember_01a01023-79f6-7f13-89b4-a0c2236b76c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_ABLLineOfCreditDueJanuary152025Member_01a01023-79f6-7342-bc7a-aa34e241bfb7" xlink:href="acnt-20260930.xsd#acnt_ABLLineOfCreditDueJanuary152025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a01023-7963-70ee-8299-dc1d524c1ee9" xlink:to="loc_acnt_ABLLineOfCreditDueJanuary152025Member_01a01023-79f6-7342-bc7a-aa34e241bfb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a01023-79f6-7e1f-a2d2-1ed235b68176" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a01023-79f6-7e1f-a2d2-1ed235b68176" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01023-79f6-7e1f-a2d2-1ed235b68176_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01023-79f6-7e1f-a2d2-1ed235b68176" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01023-79f6-7e1f-a2d2-1ed235b68176_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01023-79f6-7d7b-9521-d52354e430fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01023-79f6-7e1f-a2d2-1ed235b68176" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01023-79f6-7d7b-9521-d52354e430fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a01023-79f6-7835-af3e-ab48b739083f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a01023-79f6-7d7b-9521-d52354e430fb" xlink:to="loc_us-gaap_LineOfCreditMember_01a01023-79f6-7835-af3e-ab48b739083f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a01023-79f6-7acf-9c54-0c15c30418d0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:to="loc_srt_RangeAxis_01a01023-79f6-7acf-9c54-0c15c30418d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01023-79f6-7acf-9c54-0c15c30418d0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a01023-79f6-7acf-9c54-0c15c30418d0" xlink:to="loc_srt_RangeMember_01a01023-79f6-7acf-9c54-0c15c30418d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01023-79f6-7abc-ac14-d0c016cb8cd1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a01023-79f6-7acf-9c54-0c15c30418d0" xlink:to="loc_srt_RangeMember_01a01023-79f6-7abc-ac14-d0c016cb8cd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a01023-79f6-7fb9-8662-f20117e16949" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01023-79f6-7abc-ac14-d0c016cb8cd1" xlink:to="loc_srt_MinimumMember_01a01023-79f6-7fb9-8662-f20117e16949" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a01023-79f6-798b-8a36-7e35ccedd6e5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01023-79f6-7abc-ac14-d0c016cb8cd1" xlink:to="loc_srt_MaximumMember_01a01023-79f6-798b-8a36-7e35ccedd6e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_01a01023-79f6-710d-86e3-f6eb021fdfde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a01023-7963-70e1-9f32-d595bb5ed7f3" xlink:to="loc_us-gaap_VariableRateAxis_01a01023-79f6-710d-86e3-f6eb021fdfde" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_01a01023-79f6-710d-86e3-f6eb021fdfde_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_01a01023-79f6-710d-86e3-f6eb021fdfde" xlink:to="loc_us-gaap_VariableRateDomain_01a01023-79f6-710d-86e3-f6eb021fdfde_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_01a01023-79f6-7558-aea9-c38fd3ea9d2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_01a01023-79f6-710d-86e3-f6eb021fdfde" xlink:to="loc_us-gaap_VariableRateDomain_01a01023-79f6-7558-aea9-c38fd3ea9d2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_01a01023-79f6-7fb4-bdc3-f5e3621ceae5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_01a01023-79f6-7558-aea9-c38fd3ea9d2d" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_01a01023-79f6-7fb4-bdc3-f5e3621ceae5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_01a01023-79f6-7249-87a6-6f1e344702f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_01a01023-79f6-7558-aea9-c38fd3ea9d2d" xlink:to="loc_us-gaap_BaseRateMember_01a01023-79f6-7249-87a6-6f1e344702f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_01a01023-79f6-7c94-b1aa-b6a78126a016" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_01a01023-79f6-7c94-b1aa-b6a78126a016" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01023-79f6-7f0a-847e-aa3b79ec71c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01023-79f6-7f0a-847e-aa3b79ec71c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableCurrent_01a01023-79f6-77f3-9168-bfa20c7417c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_NotesPayableCurrent_01a01023-79f6-77f3-9168-bfa20c7417c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_01a01023-79f6-746e-8a3d-842466028a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_01a01023-79f6-746e-8a3d-842466028a80" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a01023-79f6-78bd-ac5e-f436b2c20143" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a01023-79f6-78bd-ac5e-f436b2c20143" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_LineOfCreditFacilityCovenantMinimumAmountOfAvailabilityRequired_01a01023-79f6-7817-bfda-5a8a5db67032" xlink:href="acnt-20260930.xsd#acnt_LineOfCreditFacilityCovenantMinimumAmountOfAvailabilityRequired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_acnt_LineOfCreditFacilityCovenantMinimumAmountOfAvailabilityRequired_01a01023-79f6-7817-bfda-5a8a5db67032" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_LineOfCreditFacilityCovenantRequiredPercentage_01a01023-79f6-7205-ba52-c1d5d6c7d3a1" xlink:href="acnt-20260930.xsd#acnt_LineOfCreditFacilityCovenantRequiredPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_acnt_LineOfCreditFacilityCovenantRequiredPercentage_01a01023-79f6-7205-ba52-c1d5d6c7d3a1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a01023-79f6-77e6-a6ce-29180212eb29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_LineOfCredit_01a01023-79f6-77e6-a6ce-29180212eb29" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_01a01023-79f6-701a-9195-854cbda4a8bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a01023-79f6-77eb-8861-5935c05b8b8c" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_01a01023-79f6-701a-9195-854cbda4a8bc" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/LeasesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_01a01023-79f6-70c4-b6de-b3cd070e4ccf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_01a01023-79f6-742a-94bc-18ed011876be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_01a01023-79f6-70c4-b6de-b3cd070e4ccf" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_01a01023-79f6-742a-94bc-18ed011876be" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermAxis_01a01023-79f6-73b2-88ac-3e4dda3de30d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_01a01023-79f6-742a-94bc-18ed011876be" xlink:to="loc_us-gaap_LeaseContractualTermAxis_01a01023-79f6-73b2-88ac-3e4dda3de30d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_01a01023-79f6-73b2-88ac-3e4dda3de30d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LeaseContractualTermAxis_01a01023-79f6-73b2-88ac-3e4dda3de30d" xlink:to="loc_us-gaap_LeaseContractualTermDomain_01a01023-79f6-73b2-88ac-3e4dda3de30d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_01a01023-79f6-7863-8637-9aa07017a175" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LeaseContractualTermAxis_01a01023-79f6-73b2-88ac-3e4dda3de30d" xlink:to="loc_us-gaap_LeaseContractualTermDomain_01a01023-79f6-7863-8637-9aa07017a175" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_FifthAmendedAndRestatedMasterLeaseAgreementMember_01a01023-79f6-7016-bf03-81c1d1b5008d" xlink:href="acnt-20260930.xsd#acnt_FifthAmendedAndRestatedMasterLeaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_01a01023-79f6-7863-8637-9aa07017a175" xlink:to="loc_acnt_FifthAmendedAndRestatedMasterLeaseAgreementMember_01a01023-79f6-7016-bf03-81c1d1b5008d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_SixthAmendedAndRestatedMasterLeaseAgreementMember_01a01023-79f6-7558-ab3d-5ba0e2efbcb1" xlink:href="acnt-20260930.xsd#acnt_SixthAmendedAndRestatedMasterLeaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_01a01023-79f6-7863-8637-9aa07017a175" xlink:to="loc_acnt_SixthAmendedAndRestatedMasterLeaseAgreementMember_01a01023-79f6-7558-ab3d-5ba0e2efbcb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_SeventhAmendedAndRestatedMasterLeaseAgreementMember_01a01023-79f6-710b-b1b8-d06f12abdb32" xlink:href="acnt-20260930.xsd#acnt_SeventhAmendedAndRestatedMasterLeaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_01a01023-79f6-7863-8637-9aa07017a175" xlink:to="loc_acnt_SeventhAmendedAndRestatedMasterLeaseAgreementMember_01a01023-79f6-710b-b1b8-d06f12abdb32" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_IncreaseDecreaseInOperatingLeaseRightOfUseAsset_01a01023-79f6-7490-8e7a-9586b5439308" xlink:href="acnt-20260930.xsd#acnt_IncreaseDecreaseInOperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_01a01023-79f6-70c4-b6de-b3cd070e4ccf" xlink:to="loc_acnt_IncreaseDecreaseInOperatingLeaseRightOfUseAsset_01a01023-79f6-7490-8e7a-9586b5439308" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_01a01023-79f6-7500-8aef-d31edac3bd70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_01a01023-79f6-70c4-b6de-b3cd070e4ccf" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_01a01023-79f6-7500-8aef-d31edac3bd70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_GainLossOnOperatingLeaseModification_01a01023-79f6-74d7-bed4-84f8f1425592" xlink:href="acnt-20260930.xsd#acnt_GainLossOnOperatingLeaseModification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_01a01023-79f6-70c4-b6de-b3cd070e4ccf" xlink:to="loc_acnt_GainLossOnOperatingLeaseModification_01a01023-79f6-74d7-bed4-84f8f1425592" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_SaleLeasebackTransactionOperatingLeaseLiability_01a01023-79f6-7432-bd63-acbfa732a57c" xlink:href="acnt-20260930.xsd#acnt_SaleLeasebackTransactionOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_01a01023-79f6-70c4-b6de-b3cd070e4ccf" xlink:to="loc_acnt_SaleLeasebackTransactionOperatingLeaseLiability_01a01023-79f6-7432-bd63-acbfa732a57c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_SaleLeasebackTransactionOperatingLeaseLiabilityPercentOfTotalOperatingLeaseLiabilities_01a01023-79f6-7194-ac03-3fd6045aa5ea" xlink:href="acnt-20260930.xsd#acnt_SaleLeasebackTransactionOperatingLeaseLiabilityPercentOfTotalOperatingLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_01a01023-79f6-70c4-b6de-b3cd070e4ccf" xlink:to="loc_acnt_SaleLeasebackTransactionOperatingLeaseLiabilityPercentOfTotalOperatingLeaseLiabilities_01a01023-79f6-7194-ac03-3fd6045aa5ea" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/ShareholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#ShareholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/ShareholdersEquityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityClassOfTreasuryStockLineItems_01a01023-79f6-7f1e-b253-6a2d3d01e975" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityClassOfTreasuryStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfTreasuryStockTable_01a01023-79f6-77f8-952c-f1ab7cfa074c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfTreasuryStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_01a01023-79f6-7f1e-b253-6a2d3d01e975" xlink:to="loc_us-gaap_ClassOfTreasuryStockTable_01a01023-79f6-77f8-952c-f1ab7cfa074c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_01a01023-79f6-79d7-a10b-005f6b54ad2f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_01a01023-79f6-77f8-952c-f1ab7cfa074c" xlink:to="loc_srt_ShareRepurchaseProgramAxis_01a01023-79f6-79d7-a10b-005f6b54ad2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_01a01023-79f6-79d7-a10b-005f6b54ad2f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_01a01023-79f6-79d7-a10b-005f6b54ad2f" xlink:to="loc_srt_ShareRepurchaseProgramDomain_01a01023-79f6-79d7-a10b-005f6b54ad2f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_01a01023-79f6-7afe-9a43-13fa75a69576" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_01a01023-79f6-79d7-a10b-005f6b54ad2f" xlink:to="loc_srt_ShareRepurchaseProgramDomain_01a01023-79f6-7afe-9a43-13fa75a69576" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_AmendedShareRepurchaseProgramMember_01a01023-79f6-7ecb-a8b9-f12615857eed" xlink:href="acnt-20260930.xsd#acnt_AmendedShareRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_01a01023-79f6-7afe-9a43-13fa75a69576" xlink:to="loc_acnt_AmendedShareRepurchaseProgramMember_01a01023-79f6-7ecb-a8b9-f12615857eed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_01a01023-79f6-78b2-b83a-f15a6f65b68a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_01a01023-79f6-7f1e-b253-6a2d3d01e975" xlink:to="loc_srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_01a01023-79f6-78b2-b83a-f15a6f65b68a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_StockRepurchaseProgramTerm_01a01023-79f6-7e36-8284-094d48e849dc" xlink:href="acnt-20260930.xsd#acnt_StockRepurchaseProgramTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_01a01023-79f6-7f1e-b253-6a2d3d01e975" xlink:to="loc_acnt_StockRepurchaseProgramTerm_01a01023-79f6-7e36-8284-094d48e849dc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/IndustrySegmentsScheduleofSegmentInformationDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#IndustrySegmentsScheduleofSegmentInformationDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/IndustrySegmentsScheduleofSegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01023-79f7-789a-b777-a5fd34bc3ed7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01023-79f7-789a-b777-a5fd34bc3ed7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a01023-79f7-71c1-8d07-8914a5f1eb28" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01023-79f7-789a-b777-a5fd34bc3ed7" xlink:to="loc_srt_ConsolidationItemsAxis_01a01023-79f7-71c1-8d07-8914a5f1eb28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a01023-79f7-71c1-8d07-8914a5f1eb28_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_01a01023-79f7-71c1-8d07-8914a5f1eb28" xlink:to="loc_srt_ConsolidationItemsDomain_01a01023-79f7-71c1-8d07-8914a5f1eb28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a01023-79f7-7782-98c6-13248112067c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_01a01023-79f7-71c1-8d07-8914a5f1eb28" xlink:to="loc_srt_ConsolidationItemsDomain_01a01023-79f7-7782-98c6-13248112067c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a01023-79f7-72ac-ad5a-108c10eaeb72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a01023-79f7-7782-98c6-13248112067c" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a01023-79f7-72ac-ad5a-108c10eaeb72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_01a01023-79f7-7357-9fa1-31dbdc6a2c91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a01023-79f7-7782-98c6-13248112067c" xlink:to="loc_us-gaap_CorporateNonSegmentMember_01a01023-79f7-7357-9fa1-31dbdc6a2c91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-79f7-7332-9bfa-69790414731e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01023-79f7-789a-b777-a5fd34bc3ed7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-79f7-7332-9bfa-69790414731e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01023-79f7-7332-9bfa-69790414731e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-79f7-7332-9bfa-69790414731e" xlink:to="loc_us-gaap_SegmentDomain_01a01023-79f7-7332-9bfa-69790414731e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01023-79f7-7b59-9cae-5740ea94061f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01023-79f7-7332-9bfa-69790414731e" xlink:to="loc_us-gaap_SegmentDomain_01a01023-79f7-7b59-9cae-5740ea94061f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_SpecialtyChemicalsSegmentMember_01a01023-79f7-7e04-b4b8-262138124d62" xlink:href="acnt-20260930.xsd#acnt_SpecialtyChemicalsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a01023-79f7-7b59-9cae-5740ea94061f" xlink:to="loc_acnt_SpecialtyChemicalsSegmentMember_01a01023-79f7-7e04-b4b8-262138124d62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_01a01023-79f7-7547-9cbf-df1f739606a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01023-79f7-789a-b777-a5fd34bc3ed7" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_01a01023-79f7-7547-9cbf-df1f739606a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_01a01023-79f7-7547-9cbf-df1f739606a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentOperatingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_01a01023-79f7-7547-9cbf-df1f739606a6" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_01a01023-79f7-7547-9cbf-df1f739606a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_01a01023-79f7-770c-b0cb-887c3dfe7c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentOperatingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_01a01023-79f7-7547-9cbf-df1f739606a6" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_01a01023-79f7-770c-b0cb-887c3dfe7c0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentContinuingOperationsMember_01a01023-79f7-7723-9ce3-4b2a877b15f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentContinuingOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_01a01023-79f7-770c-b0cb-887c3dfe7c0c" xlink:to="loc_us-gaap_SegmentContinuingOperationsMember_01a01023-79f7-7723-9ce3-4b2a877b15f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_01a01023-79f7-72d8-9d12-1e4183ff5f30" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01023-79f7-789a-b777-a5fd34bc3ed7" xlink:to="loc_srt_StatementGeographicalAxis_01a01023-79f7-72d8-9d12-1e4183ff5f30" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_01a01023-79f7-72d8-9d12-1e4183ff5f30_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_01a01023-79f7-72d8-9d12-1e4183ff5f30" xlink:to="loc_srt_SegmentGeographicalDomain_01a01023-79f7-72d8-9d12-1e4183ff5f30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_01a01023-79f7-72d8-9d12-1e4183ff5f30" xlink:to="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_01a01023-79f7-7a33-bbc4-a980ba42a4eb" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_US_01a01023-79f7-7a33-bbc4-a980ba42a4eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_HN_01a01023-79f7-7353-9749-2c5f951e6b48" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_HN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_HN_01a01023-79f7-7353-9749-2c5f951e6b48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CA_01a01023-79f7-722d-8d83-42d38f4de7b6" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_CA_01a01023-79f7-722d-8d83-42d38f4de7b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_MX_01a01023-79f7-725d-8a3d-fd14983dc787" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_MX"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_MX_01a01023-79f7-725d-8a3d-fd14983dc787" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_AU_01a15276-d3bf-76dd-adbf-31d386e87952" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_AU"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_AU_01a15276-d3bf-76dd-adbf-31d386e87952" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CO_01a01023-79f7-76e2-beb0-8f82580ec54f" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CO"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_CO_01a01023-79f7-76e2-beb0-8f82580ec54f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_NL_01a01023-79f7-74f7-bff9-63b659c68eb8" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_NL"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_NL_01a01023-79f7-74f7-bff9-63b659c68eb8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CR_01a01023-79f7-7001-bdfe-5e6c47878440" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_country_CR_01a01023-79f7-7001-bdfe-5e6c47878440" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_AllOtherCountriesMember_01a01023-79f7-7c65-9660-cb71fe4fd600" xlink:href="acnt-20260930.xsd#acnt_AllOtherCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a01023-79f7-7c59-80ab-121e774add0c" xlink:to="loc_acnt_AllOtherCountriesMember_01a01023-79f7-7c65-9660-cb71fe4fd600" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01023-79f7-7d3c-9d31-f10fed2908be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01023-79f7-7d3c-9d31-f10fed2908be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostDirectMaterial_01a01023-79f7-77ed-9c31-bd669e664d44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostDirectMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_CostDirectMaterial_01a01023-79f7-77ed-9c31-bd669e664d44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_CostOfOtherMaterialAdjusted_01a01023-79f7-732a-9c5c-f76238cc86df" xlink:href="acnt-20260930.xsd#acnt_CostOfOtherMaterialAdjusted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_acnt_CostOfOtherMaterialAdjusted_01a01023-79f7-732a-9c5c-f76238cc86df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciation_01a01023-79f7-76a0-9f3b-d37ab78786e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSoldDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciation_01a01023-79f7-76a0-9f3b-d37ab78786e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_01a01023-79f7-77f8-b439-c8629e94a579" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_GrossProfit_01a01023-79f7-77f8-b439-c8629e94a579" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_01a01023-79f7-74d3-bbfd-14a6bd968a8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_01a01023-79f7-74d3-bbfd-14a6bd968a8c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a01023-79f7-7826-b988-f051724a7ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a01023-79f7-7826-b988-f051724a7ebd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_01a01023-79f7-70a3-8a78-024022adef6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_01a01023-79f7-70a3-8a78-024022adef6d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_01a01023-79f7-7c1a-bee1-b5cdf7ea309a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_01a01023-79f7-7c1a-bee1-b5cdf7ea309a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_01a01023-79f7-71b2-a7e5-b18624ce3fa9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_01a01023-79f7-71b2-a7e5-b18624ce3fa9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_GainLossOnOperatingLeaseModification_01a01023-79f7-7380-88ca-4be35b5911ac" xlink:href="acnt-20260930.xsd#acnt_GainLossOnOperatingLeaseModification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_acnt_GainLossOnOperatingLeaseModification_01a01023-79f7-7380-88ca-4be35b5911ac" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_01a01023-79f7-72b3-b465-fcfc802cd535" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_01a01023-79f7-72b3-b465-fcfc802cd535" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a01023-79f7-7f4d-bddd-ff59bad8eb8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a01023-79f7-7f4d-bddd-ff59bad8eb8a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_OtherOperatingAndNonoperatingIncomeExpense_01a01023-79f7-7a2e-8aa5-d9eaa4b1b010" xlink:href="acnt-20260930.xsd#acnt_OtherOperatingAndNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_acnt_OtherOperatingAndNonoperatingIncomeExpense_01a01023-79f7-7a2e-8aa5-d9eaa4b1b010" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_01a01023-79f7-729d-b794-926d8e51deb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_01a01023-79f7-729d-b794-926d8e51deb0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a01023-79f7-76d9-8fdd-51534b7c2082" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01023-79f7-72c8-bb31-d32e7d5b6458" xlink:to="loc_us-gaap_Assets_01a01023-79f7-76d9-8fdd-51534b7c2082" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://ascentco.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="acnt-20260930.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://ascentco.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_01a05616-83ce-783f-baa8-81aa86455e33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_01a05616-83ce-7fcb-90a3-5ba3b8c96e91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_01a05616-83ce-783f-baa8-81aa86455e33" xlink:to="loc_us-gaap_SubsequentEventTable_01a05616-83ce-7fcb-90a3-5ba3b8c96e91" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a05616-83ce-7244-b6f8-75071d22b9c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_01a05616-83ce-7fcb-90a3-5ba3b8c96e91" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a05616-83ce-7244-b6f8-75071d22b9c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a05616-83ce-7244-b6f8-75071d22b9c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a05616-83ce-7244-b6f8-75071d22b9c7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a05616-83ce-7244-b6f8-75071d22b9c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a05616-83ce-7a7f-8a1d-9c33963ef33d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a05616-83ce-7244-b6f8-75071d22b9c7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a05616-83ce-7a7f-8a1d-9c33963ef33d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a0561b-1a69-7c56-abc7-2a2be9509c87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a05616-83ce-7a7f-8a1d-9c33963ef33d" xlink:to="loc_us-gaap_SubsequentEventMember_01a0561b-1a69-7c56-abc7-2a2be9509c87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a197b8-2a80-71aa-b8ad-c77a4169275f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_01a05616-83ce-7fcb-90a3-5ba3b8c96e91" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a197b8-2a80-71aa-b8ad-c77a4169275f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a197b8-2a80-71aa-b8ad-c77a4169275f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a197b8-2a80-71aa-b8ad-c77a4169275f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a197b8-2a80-71aa-b8ad-c77a4169275f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a197b8-2a80-7a33-943a-d2bf028f48e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a197b8-2a80-71aa-b8ad-c77a4169275f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a197b8-2a80-7a33-943a-d2bf028f48e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_acnt_BristolMetalsLLCMember_01a197b8-6fbf-7a67-9f47-f4e4ad645c52" xlink:href="acnt-20260930.xsd#acnt_BristolMetalsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a197b8-2a80-7a33-943a-d2bf028f48e5" xlink:to="loc_acnt_BristolMetalsLLCMember_01a197b8-6fbf-7a67-9f47-f4e4ad645c52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a19c77-1c14-70a3-b0b4-16e7747a7d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_01a05616-83ce-7fcb-90a3-5ba3b8c96e91" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a19c77-1c14-70a3-b0b4-16e7747a7d1e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a19c77-1c14-70a3-b0b4-16e7747a7d1e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a19c77-1c14-70a3-b0b4-16e7747a7d1e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a19c77-1c14-70a3-b0b4-16e7747a7d1e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a19c77-1c14-7e56-a73c-b40195e7024c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a19c77-1c14-70a3-b0b4-16e7747a7d1e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a19c77-1c14-7e56-a73c-b40195e7024c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_01a19c77-3713-742f-b1ec-9883251999ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a19c77-1c14-7e56-a73c-b40195e7024c" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_01a19c77-3713-742f-b1ec-9883251999ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_01a197b6-ef09-7948-82c1-81a33a33c7b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_01a05616-83ce-783f-baa8-81aa86455e33" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_01a197b6-ef09-7948-82c1-81a33a33c7b1" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
