ASTM_D_8031_-_16.pdf

Designation:D803116Standard Test Method forAcid Number of Terephthalic Acid(TA)by AutomaticPotentiometric Titration1This standard is issued under the fixed designation D8031;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of acidnumber in terephthalic acid(TA)by automatic potentiometrictitration.As the index of TA purity,acid number is usuallywithin 674 to 676 mg KOH/g.1.2 In determining the conformance of the test results usingthis method,results shall be rounded off in accordance with therounding-off method of Practice E29.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D664 Test Method for Acid Number of Petroleum Productsby Potentiometric TitrationD1193 Specification for Reagent WaterD4790 Terminology of Aromatic Hydrocarbons and RelatedChemicalsD6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and Related Ma-terialsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE300 Practice for Sampling Industrial ChemicalsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Other Document:3OSHA Regulations,29 CFR paragraphs 1910.1000 and1910.12003.Terminology3.1 Definitions:3.1.1 acid number,nthe quantity of base,expressed asmilligrams of potassium hydroxide per gram of sample that isrequired to titrate a sample in a specified solvent to a specifiedend point.4.Summary of Test Method4.1 ATAsample is dissolved in pyridine,diluted with waterand titrated potentiometrically with standard sodium hydroxidesolution,using a glass indicating electrode and a referenceelectrode or a combination electrode.The meter readings areplotted automatically against the respective volumes of titrat-ing solution and the end points are taken only at well-definedinflections in the resulting curve.The acid number is calculatedas milligrams of KOH per gram of TA sample.Its theoreticalvalue of TA sample is 675.5 mg KOH/g.5.Significance and Use5.1 An estimate of TA purity can be determined by titratingwith KOH.As an index of TA purity,the acid number can beused as a guide in the quality control of TA production.6.Apparatus6.1 Analytical Balance.6.2 Automatic Potentiometric TitratorAutomatic titrationsystems capable of adding fixed increments of titrant at fixedtime intervals(monotonic)or variable titrant increments withelectrode stability between increment additions(dynamic)withendpoint seeking capabilities as prescribed in the method.As aminimum,the apparatus shall meet the performance andspecification requirements as warranted by the manufacturer.1This test method is under the jurisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.02 on Oxygenated Aromatics.Current edition approved March 1,2016.Published June 2016.DOI:10.1520/D8031-16.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Available from U.S.Government Printing Office,Superintendent ofDocuments,732 N.Capitol St.,NW,Washington,DC 20401-0001,http:/www.access.gpo.gov.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.2.1 Amonotonic or dynamic mode of titrant shall be used.During the titration,the speed and volume of the addition mayvary depending on the rate of change of the system.Therecommended maximum volume increment is 0.5 mL and therecommended minimum volume increment is 0.05 mL.6.2.2 Buret,capable of delivering titrant in 0.05 mL orlarger increments.The buret tip should be able to deliver titrantdirectly into the titration vessel without exposure to thesurrounding air.Burets with total capacities of 5 mL,10 mLand 20 mL are typically available from commercial manufac-turers of auto titrators and can be used if their specificationsmeet the criteria of 6.2.1 and 6.2.2.6.2.3 Titration Stand,suitable for supporting the electrode,stirrer and buret tip.6.3 Sensing Electrode,standard pH,suitable for nonaqueoustitrations.6.4 Reference Electrode,silver/silver chloride(Ag/AgCl)refer