ASTM D664-2018e2 Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration.pdf

1、Designation: D664 182British Standard 4457Designation 177/96Standard Test Method forAcid Number of Petroleum Products by PotentiometricTitration1This standard is issued under the fixed designation D664; the number immediately following the designation indicates the year oforiginal adoption or, in th

2、e 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.1NOTESubsection 13.3.1 and a statement in the Summary of Changes were corrected editorially in Dec

3、ember 2018.2NOTESubsections 16.1.1.1 and 16.1.2.1 were corrected editorially in January 2019.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 This test method covers procedures for the determina-tion of acidic constituents in petroleum products, lubr

4、icants,biodiesel, and blends of biodiesel.1.1.1 Test Method AFor petroleum products and lubricantssoluble or nearly soluble in mixtures of toluene and propan-2-ol. It is applicable for the determination of acids whosedissociation constants in water are larger than 109; extremelyweak acids whose diss

5、ociation constants are smaller than 109do not interfere. Salts react if their hydrolysis constants arelarger than 109. The range of acid numbers included in theprecision statement is 0.1 mgg KOH to 150 mgg KOH.1.1.2 Test Method BDeveloped specifically for biodieseland biodiesel blends with low acidi

6、ty and slightly differentsolubility. This test method requires the use of an automatictitrator with automatic endpoint-seeking capability.NOTE 1In new and used oils, the constituents that may be consideredto have acidic characteristics include organic and inorganic acids, esters,phenolic compounds,

7、lactones, resins, salts of heavy metals, salts ofammonia and other weak bases, acid salts of polybasic acids, and additionagents such as inhibitors and detergents.1.2 The test method may be used to indicate relativechanges that occur in oil during use under oxidizing conditionsregardless of the colo

8、r or other properties of the resulting oil.Although the titration is made under definite equilibriumconditions, the test method is not intended to measure anabsolute acidic property that can be used to predict perfor-mance of oil under service conditions. No general relationshipbetween bearing corro

9、sion and acid number is known.NOTE 2The acid number obtained by this standard may or may not benumerically the same as that obtained in accordance with Test MethodsD974 and D3339. There has not been any attempt to correlate this methodwith other non-titration methods.NOTE 3A few laboratories have ma

10、de the observation that there is adifference in Test Method D664 results when aqueous versus nonaqueousbuffers are used.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 the

11、safety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-

12、dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM

13、Standards:2D974 Test Method for Acid and Base Number by Color-Indicator TitrationD1193 Specification for Reagent WaterD3339 Test Method forAcid Number of Petroleum Productsby Semi-Micro Color Indicator TitrationD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for A

14、utomatic Sampling of Petroleum andPetroleum Products1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.Current edition approved Nov. 1,

15、2018. Published November 2018. Originallyapproved in 1942. Last previous edition approved in 2017 as D664 17a. DOI:10.1520/D0664-18E02.This test method was adopted as a joint ASTM-IP standard in 1964. ASTM TestMethod D4739 has been developed as an alternative to the base number portion ofD664.2For r

16、eferenced 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.*A Summary of Changes section appears at the end of this standardCo

17、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of Interna

18、tional Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1E177 Practice for Use of the Terms Precision and Bias inASTM Test Methods3. Terminology3.1 Definitions:3.1.1 acid number, nthe quantity of a specified base,expressed in mi

19、lligrams of potassium hydroxide per gram ofsample, required to titrate a sample in a specified solvent to aspecified endpoint using a specified detection system.3.1.1.1 DiscussionThis test method expresses the quantityof base as milligrams of potassium hydroxide per gram ofsample, that is required t

20、o titrate a sample in a mixture oftoluene and propan-2-ol to which a small amount of water hasbeen added from its initial meter reading in millivolts to ameter reading in millivolts corresponding to an aqueous basicbuffer solution or a well-defined inflection point as specified inthe test method.3.1

21、1.2 DiscussionThis test method provides additionalinformation. The quantity of base, expressed as milligrams ofpotassium hydroxide per gram of sample, required to titrate asample in the solvent from its initial meter reading in millivoltsto a meter reading in millivolts corresponding to a freshlypr

22、epared aqueous acidic buffer solution or a well-definedinflection point as specified in the test method shall be reportedas the strong acid number.3.1.1.3 DiscussionThe causes and effects of the so-calledstrong acids and the causes and effects of the other acids can bevery significantly different. T

23、herefore, the user of this testmethod shall differentiate and report the two, when they arefound.4. Summary of Test Method4.1 The sample is dissolved in a titration solvent and titratedpotentiometrically with alcoholic potassium hydroxide using aglass indicating electrode and a reference electrode o

24、r acombination electrode. The meter readings are plotted manu-ally or automatically against the respective volumes of titratingsolution and the end points are taken only at well-definedinflections in the resulting curve. When no definite inflectionsare obtained and for used oils, end points are take

25、n at meterreadings corresponding to those found for aqueous acidic andbasic buffer solutions.5. Significance and Use5.1 New and used petroleum products, biodiesel, and blendsof biodiesel may contain acidic constituents that are present asadditives or as degradation products formed during service,suc

26、h as oxidation products. The relative amount of thesematerials can be determined by titrating with bases. The acidnumber is a measure of this amount of acidic substance in theoil, always under the conditions of the test. The acid number isused as a guide in the quality control of lubricating oilform

27、ulations. It is also sometimes used as a measure oflubricant degradation in service. Any condemning limits mustbe empirically established.5.2 Since a variety of oxidation products contribute to theacid number and the organic acids vary widely in corrosionproperties, the test method cannot be used to

28、 predict corrosive-ness of oil or biodiesel and blends under service conditions. Nogeneral correlation is known between acid number and thecorrosive tendency of biodiesel and blends or oils towardmetals.6. Apparatus6.1 Manual Titration Apparatus:6.1.1 Meter, a voltmeter or a potentiometer that will

29、operatewith an accuracy of 60.005 V and a sensitivity of 60.002 Vover a range of at least 60.5 V when the meter is used with theelectrodes specified in 6.1.2 and 6.1.3 and when the resistancebetween the electrodes falls within the range from 0.2 M to20 M. The meter shall be protected from stray elec

30、trostaticfields so that no permanent change in the meter readings overthe entire operating range is produced by touching, with agrounded lead, any part of the exposed surface of the glasselectrode, the glass electrode lead, the titration stand, or themeter.NOTE 4A suitable apparatus could consist of

31、 a continuous-readingelectronic voltmeter designed to operate on an input of less than 5 1012A, when an electrode system having 1000 M resistance is connectedacross the meter terminals and provided with a metal shield connected tothe ground, as well as a satisfactory terminal to connect the shielded

32、connection wire from the glass electrode to the meter without interferencefrom any external electrostatic field.6.1.2 Sensing Electrode, standard pH, suitable for nonaque-ous titrations.6.1.3 Reference Electrode, silver/silver chloride (Ag/AgCl)reference electrode, filled with 1M to 3M LiCl in ethan

33、ol.6.1.3.1 Combination ElectrodesSensing electrodes mayhave the Ag/AgCl reference electrode built into the sameelectrode body, which offers the convenience of working withand maintaining only one electrode. The combination electrodeshall have a sleeve junction on the reference compartment andshall u

34、se an inert ethanol electrolyte, for example, 1M3MLiCl in ethanol. These combination electrodes shall have thesame response or better response than a dual electrode system.They shall have removable sleeves for easy rinsing andaddition of electrolyte.NOTE 5A third electrode, such as a platinum electr

35、ode, may be usedto increase the electrode stability in certain systems.6.1.4 Variable-Speed Mechanical Stirrer, a suitable type,equipped with a propeller-type stirring paddle. The rate ofstirring shall be sufficient to produce vigorous agitation withoutspattering and without stirring air into the so

36、lution.Apropellerwith blades 6 mm in radius and set at a pitch of 30 to 45 issatisfactory. A magnetic stirrer is also satisfactory.6.1.4.1 If an electrical stirring apparatus is used, it shall beelectrically correct and grounded so that connecting or discon-necting the power to the motor will not pr

37、oduce a permanentchange in the meter reading during the course of the titration.6.1.5 Burette, 10 mL capacity, graduated in 0.05 mL divi-sions and calibrated with an accuracy of 60.02 mL. Theburette shall have a tip that extends 100 mm to 130 mm beyondthe stopcock and shall be able to deliver titran

38、t directly into thetitration vessel without exposure to the surrounding air orvapors.The burette for KOH shall have a guard tube containingsoda lime or other CO2-absorbing substance.D664 18226.1.6 Titration Beaker, 250 mL, 125 mL, or suitablecapacity, made of borosilicate glass or other suitable mat

39、erial.6.1.7 Titration Stand, suitable for supporting the electrodes,stirrer, and burette.NOTE 6An arrangement that allows the removal of the beaker withoutdisturbing the electrodes and stirrer is desirable.6.2 Automatic Titration Apparatus:6.2.1 Automatic titration systems shall be able to carry out

40、the necessary analyses as prescribed in the method. As aminimum, the automatic titration system shall meet the perfor-mance and specification requirements listed in 6.1 as war-ranted.6.2.2 A dynamic mode of titrant addition shall be used.During the titration, the speed and volume of the addition sha

41、llvary 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.6.2.3 Graduated Cylinder50 mL, or dispensing devicecapable of delivering 50 mL 6 0.5 mL.6.2.4 Pipette2.0 mL, Class A.6.2.5 Titration Beaker25

42、0 mL, 125 mL, or suitablecapacity, made of borosilicate glass or other suitable material.7. Reagents7.1 Purity of ReagentsReagent-grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the commit-tee on Analytical

43、 Reagents of the American Chemical Society,where such specifications are available.3Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.1.1 Commercially available solutions may

44、 be used inplace of laboratory preparations, provided the solutions havebeen certified as being equivalent.7.1.2 Alternate volumes of the solutions may be prepared,provided the final solution concentration is equivalent.7.2 Purity of WaterUnless otherwise indicated, referenceto water shall be unders

45、tood to mean reagent water that meetsthe requirements of either Type I, II, or III of SpecificationD1193.7.3 Primary StandardWhere specified, these samples, orsamples of commercially available primary standards, are to beused in standardizing the volumetric solutions.7.4 Ethanol. (WarningFlammable a

46、nd toxic, especiallywhen denatured.)7.5 Lithium Chloride, LiCl.7.6 Lithium Chloride Electrolyte, Prepare a 1M3M solu-tion of lithium chloride (LiCl) in ethanol.7.7 Potassium Hydroxide. (WarningCauses severeburns.)7.8 Propan-2-ol, Anhydrous, (less than 0.1 % H2O).(WarningFlammable.) If adequately dry

47、 reagent cannot beprocured, it can be dried by distillation through a multiple platecolumn, discarding the first 5 % of material distilling overheadand using the 95 % remaining. Drying can also be accom-plished using molecular sieves such as Linde Type 4A, bypassing the solvent upward through a mole

48、cular sieve columnusing one part of molecular sieve per ten parts of solvent.NOTE 7It has been reported that, if not originally inhibited against it,propan-2-ol can contain peroxides. When this occurs, an explosion ispossible when the storage of the vessel or other equipment such as adispensing bott

49、le, is near empty and approaching dryness.7.9 Commercial Aqueous pH 4, pH 7, and pH 10 BufferSolutionsThese solutions shall be replaced at regular inter-vals consistent with their stability or when contamination issuspected. Information relating to their stability should beobtained from the manufacturer.8. Electrode System8.1 Preparation of ElectrodesWhen a Ag/AgCl referenceelectrode is used for the titration and it contains an electrolytewhich is not 1M3M LiCl in ethanol, replace the electrolyte.Drain the electrolyte from the electrode