1、Designation: D664 11a (Reapproved 2017) British 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
2、 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.This standard has been approved for use by agencies of the U.S. Department of D
3、efense.1. Scope1.1 This 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 lubricantssoluble or nearly soluble in mixtures of toluene and propan-2-ol. It is appl
4、icable for the determination of acids whosedissociation constants in water are larger than 10-9; extremelyweak acids whose dissociation constants are smaller than 10-9do not interfere. Salts react if their hydrolysis constants arelarger than 109. The range of acid numbers included in theprecision st
5、atement is 0.1 mgg KOH to 150 mgg 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 co
6、nstituents that may be 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 t
7、est method may be used 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
8、 property that can be 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
9、 D3339. There has not 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
10、 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 t
11、he applica-bility of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations is
12、sued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM 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 Co
13、lor Indicator TitrationD4057 Practice for 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:1This test method is under the ju
14、risdiction 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 May 1, 2017. Published June 2017. Originallyapproved in 1942. Last previous edition approved
15、in 2011 as D664 11a1. DOI:10.1520/D0664-11AR17.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 referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
16、Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed
17、in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.1 acid number, nthe
18、quantity of a specified base,expressed in milligrams 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 hyd
19、roxide per gram ofsample, 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 inflect
20、ion point as specified inthe 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 readin
21、g in millivolts corresponding 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
22、 acids can bevery significantly 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 indi
23、cating electrode and a reference 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 obt
24、ained and for used oils, 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 deg
25、radation products formed 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
26、 the quality control of lubricating 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 corrosionpr
27、operties, the test method 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
28、, a voltmeter or a potentiometer 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 M to20 M. T
29、he meter shall be protected from stray electrostaticfields 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.
30、NOTE 4A suitable apparatus could consist of a continuous-readingelectronic voltmeter designed to operate on an input of less than 5 1012 A, 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 s
31、atisfactory terminal to 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
32、Electrode, filled with 1M3M 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 juncti
33、on on the reference compartment 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
34、third electrode, such as 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 withoutspatt
35、ering and without stirring 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-
36、necting the power to the 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 60.02 mL. Theburette shall have a tip that extends 100 mm to 130 mm beyondthe st
37、opcock and shall be able to 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 othe
38、r suitable material.6.1.7 Titration Stand, suitable for supporting the electrodes,stirrer, and burette.D664 11a (2017)2NOTE 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 syst
39、ems shall be able to carry outthe 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
40、and volume of the addition shallvary 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, Cl
41、ass A.6.2.5 Titration Beaker250 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 o
42、f the commit-tee on Analytical 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 Commer
43、cially available solutions may 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, refe
44、renceto water shall be understood 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
45、 Ethanol, (WarningFlammable and 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).(Warnin
46、gFlammable.) If adequately dry 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
47、 solvent upward through a molecular 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 equi
48、pment such as adispensing bottle, is 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
49、 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, wash away all the salt(if present) with water and then rinse with 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
