1、Designation: D664 11aDesignation 177/96British Standard 4457Standard 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This
3、 test method covers procedures for the determina-tion of acidic constituents in petroleum products, lubricants,biodiesel and blends of biodiesel.1.1.1 Test Method AFor petroleum products and lubri-cants soluble or nearly soluble in mixtures of toluene andpropan-2-ol. It is applicable for the determi
4、nation of acidswhose dissociation constants in water are larger than 10-9;extremely weak acids whose dissociation constants are smallerthan 10-9do not interfere. Salts react if their hydrolysisconstants are larger than 10-9. The range of acid numbersincluded in the precision statement is 0.1 mg/g KO
5、H to 150mg/g KOH.1.1.2 Test Method BDeveloped specifically for biodieseland biodiesel blends with low acidity 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 b
6、e consideredto have acidic characteristics include organic and inorganic acids, esters,phenolic compounds, 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 use
7、d to indicate relativechanges that occur in oil during use under oxidizing conditionsregardless of the color 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
8、 used to predict perfor-mance of oil under service conditions. No general relationshipbetween bearing corrosion 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
9、 been any attempt to correlate this methodwith other non-titration methods.NOTE 3A few laboratories have made 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
10、 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
11、regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D974 Test Method for Acid and Base Number by Color-Indicator TitrationD1193 Specification for Reagent WaterD3339 Test Method for Acid Number of Petroleum Prod-ucts by Semi-Micro Color Indicator TitrationD4057 Practice for
12、 Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsE177 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 milligra
13、ms of potassium hydroxide per gram ofsample, required to titrate a sample in a specified solvent to aspecified endpoint using a specified detection system.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of Subcomm
14、itteeD02.06 on Analysis of Lubricants.Current edition approved July 15, 2011. Published August 2011. Originallyapproved in 1942. Last previous edition approved in 2011 as D66411. DOI:10.1520/D0664-11A.This test method was adopted as a joint ASTM-IP standard in 1964. ASTM TestMethod D4739 has been de
15、veloped as an alternative to the base number portion ofD664.2For 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.1
16、*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.1.1 DiscussionThis test method expresses the quantityof base as milligrams of potassium hydroxide per gram ofsample,
17、 that is required to 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 in
18、the test method.3.1.1.2 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 correspon
19、ding to a freshlyprepared 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 signifi
20、cantly different. Therefore, 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 re
21、ference electrode or 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,
22、end points are taken 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
23、during service,such 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 l
24、ubricating oilformulations. 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
25、 cannot be used to 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 potent
26、iometer that will 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 to 20MV.The meter shall be protected
27、 from stray electrostatic fieldsso that no permanent change in the meter readings over theentire 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
28、could consist of a continuous-readingelectronic voltmeter designed to operate on an input of less than 5 3 1012 A, when an electrode system having 1000-MV resistance is connectedacross the meter terminals and provided with a metal shield connected tothe ground, as well as a satisfactory terminal to
29、connect the shieldedconnection 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 1
30、M3M LiCl in etha-nol.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 comp
31、artment andshall use 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
32、 a platinum electrode, 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 stirri
33、ng air into the solution.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
34、 motor will not produce 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 6 0.02 mL. Theburette shall have a tip that extends 100 to 130 mm beyond thestopcock and shall be able t
35、o deliver titrant 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.6.1.6 Titration Beaker, 250 mL capacity, made of borosili-cate glass or other suitable material.6.1.7
36、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:D664 11a26.2.1 Automatic titration systems shall be able to carry outthe
37、 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 shallv
38、ary 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 6 0.5 mL.6.2.4 Pipette2.0 mL, Class A.6.2.5 Titration Beaker250 mL,
39、125 mL, or suitable ca-pacity, 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 Rea
40、gents 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 be
41、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 understood
42、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 and tox
43、ic, 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 reagen
44、t 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 molecular s
45、ieve 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 bottle, is
46、near empty and approaching dryness.7.9 Commercial Aqueous pH 4, pH 7 and pH 11 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.
47、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, wash away all the salt(if present) with water and then rinse wit
48、h ethanol. Rinseseveral times with the LiCl electrolyte solution. Finally, replacethe sleeve and fill the electrode with the LiCl electrolyte to thefilling hole. When refitting the sleeve ensure that there will bea free flow of electrolyte into the system. A combinationelectrode shall be prepared in
49、 the same manner. The electrolytein a combination electrode can be removed with the aid of avacuum suction.8.2 Testing of ElectrodesTest the meter-electrode combi-nation when first put into use, or when new electrodes areinstalled, and retest at intervals thereafter. Rinse the electrodeswith solvent then with water, and dip them into a pH 4 aqueousbuffer solution. Read the mV value after stirring one minute.Remove the electrodes and rinse with water. Dip the electrodesinto a pH 7 aqueous buffer. Read the mV value after stirringone minute. Calculate the
