1、Designation: D 664 07Designation 177/96An American National StandardBritish Standard 4457Standard Test Method forAcid Number of Petroleum Products by PotentiometricTitration1This standard is issued under the fixed designation D 664; the number immediately following the designation indicates the year
2、 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 (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Departme
3、nt of Defense.1. Scope*1.1 This test method covers procedures for the determina-tion of acidic constituents in 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 l
4、arger than 10-9; extremelyweak acids whose dissociation constants are smaller than 10-9do not interfere. Salts react if their hydrolysis constants arelarger than 10-9. The range of acid numbers included in theprecision statement is 0.1 mg/g KOH to 150 mg/g KOH.NOTE 1In new and used oils, the constit
5、uents 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 test m
6、ethod 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 prop
7、erty 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 MethodsD 974 and D 3
8、339. There has not been any attempt to correlate thismethod with other non-titration methods.NOTE 3A few laboratories have made the observation that there is adifference in Test Method D 664 results when aqueous versus nonaqueousbuffers are used.1.3 The values stated in SI units are to be regarded a
9、s thestandard. The values given in parentheses are for informationonly.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 th
10、e applica-bility of regulatory limitations prior to use.2. Referenced Documents22.1 ASTM Standards:D 974 Test Method for Acid and Base Number by Color-Indicator TitrationD 1193 Specification for Reagent WaterD 3339 Test Method for Acid Number of Petroleum Prod-ucts by Semi-Micro Color Indicator Titr
11、ationD 4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD 4177 Practice for Automatic Sampling of Petroleum andPetroleum Products3. Terminology3.1 Definitions:3.1.1 acid number, nthe quantity of base, expressed asmilligrams of potassium hydroxide per gram of sample, re-quired to t
12、itrate a sample in a specified solvent to a specifiedend point.3.1.1.1 DiscussionThis test method expresses the quantityof base as milligrams of potassium hydroxide per gram ofsample, that is required to titrate a sample in a mixture of1This test method is under the jurisdiction of ASTM Committee D0
13、2 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.06 on Analysis of Lubricants.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 1942. Last previous edition approved in 2006 as D 66406ae1.This test method was adopted as a joint
14、ASTM-IP standard in 1964. ASTM TestMethod D 4739 has been developed as an alternative to the base number portion ofD 664.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refe
15、r to the standards Document Summary page onthe ASTM website.1*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.toluene and propan-2-ol to which a small amount of water ha
16、sbeen 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.3.1.1.2 DiscussionThis test method provides additionalinformation. The quantity of base, express
17、ed 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 freshlyprepared aqueous acidic buffer solution or a well-definedinflection point as specified in the t
18、est 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. Therefore, the user of this testmethod shall differentiate and report the two, when they arefo
19、und.4. Summary of Test Method4.1 The sample is dissolved in a mixture of toluene andpropan-2-ol containing a small amount of water and titratedpotentiometrically with alcoholic potassium hydroxide using aglass indicating electrode and a reference electrode or acombination electrode. The meter readin
20、gs 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 taken at meterreadings corresponding to those
21、found for aqueous acidic andbasic buffer solutions.5. Significance and Use5.1 New and used petroleum products may contain acidicconstituents that are present as additives or as degradationproducts formed during service, such as oxidation products.The relative amount of these materials can be determi
22、ned bytitrating with bases. The acid number is a measure of thisamount of acidic substance in the oil, always under theconditions of the test. The acid number is used as a guide in thequality control of lubricating oil formulations. It is alsosometimes used as a measure of lubricant degradation inse
23、rvice. Any condemning limits must be empirically estab-lished.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 predict corrosive-ness of oil under service conditions. No general correlat
24、ion isknown between acid number and the corrosive tendency of oilstoward metals.6. Apparatus6.1 Manual Titration Apparatus:6.1.1 Meter, 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 wit
25、h 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 from stray electrostatic fieldsso that no permanent change in the meter readings over theentire operating range is produced by touching, wit
26、h 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 a continuous-readingelectronic voltmeter designed to operate on an input of less than 5 3 1012A, when an electrode system ha
27、ving 1000-MV resistance is connectedacross the meter terminals and provided with a metal shield connected tothe ground, as well as a satisfactory terminal to connect the shieldedconnection wire from the glass electrode to the meter without interferencefrom any external electrostatic field.6.1.2 Sens
28、ing Electrode, Standard pH, suitable for nonaque-ous titrations.6.1.3 Reference Electrode, Silver/Silver Chloride (Ag/AgCl) Reference 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 bod
29、y, which offers the convenience of working withand maintaining only one electrode. The combination electrodeshall have a sleeve junction on the reference compartment andshall use an inert ethanol electrolyte, for example, 1M3MLiCl in ethanol. These combination electrodes shall have thesame response
30、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 electrode, may be usedto increase the electrode stability in certain systems.6.1.4 Variable-Speed Mechanical Stirrer, a suitable t
31、ype,equipped with a propeller-type stirring paddle. The rate ofstirring shall be sufficient to produce vigorous agitation withoutspattering 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 satisf
32、actory.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 produce a permanentchange in the meter reading during the course of the titration.6.1.5 Burette, 10-mL capacity, graduated in
33、0.05-mL divi-sions and calibrated with an accuracy of 60.02 mL. Theburette shall have a tip that extends 100 to 130 mm beyond thestopcock 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 tub
34、e 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 Titration Stand, suitable for supporting the electrodes,stirrer, and burette.NOTE 6An arrangement that allows the removal of the beaker without
35、disturbing the electrodes and stirrer is desirable.6.2 Automatic Titration Apparatus:6.2.1 Automatic titration systems shall be able to carry outthe necessary analyses as prescribed in the method. As aD664072minimum, the automatic titration system shall meet the perfor-mance and specification requir
36、ements 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 shallvary depending on the rate of change of the system. Therecommended maximum volume increment is 0.5 mL and therecommended minimum volume increment
37、is 0.05 mL.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 Reagents of the American Chemical Society,where such specifications are avail
38、able.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 used inplace of laboratory preparations provided the solutions havebeen ce
39、rtified 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 to mean reagent water that meetsthe requirements of either Type I, II, or
40、III of SpecificationD 1193.7.3 Ethanol,(WarningFlammable and toxic, especiallywhen denatured.)7.4 Hydrochloric Acid (HCl)Relative density 1.19.(WarningCorrosive, causes burns.)7.5 Lithium Chloride, LiCl.7.6 Lithium Chloride Electrolyte, Prepare a 1M3M solu-tion of lithium chloride (LiCl) in ethanol.
41、7.7 Methanol,(WarningFlammable. Toxic if swal-lowed.)7.8 Potassium Hydroxide,(WarningCauses severeburns.)7.9 Propan-2-ol, Anhydrous, (less than 0.1 % H2O).(WarningFlammable.) If adequately dry reagent cannot beprocured, it can be dried by distillation through a multiple platecolumn, discarding the f
42、irst 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 sieve columnusing one part of molecular sieve per ten parts of solvent.NOTE 7It has been reported that
43、, 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 near empty and approaching dryness.7.10 Toluene,(WarningFlammable.)7.11 Hydrochloric Acid Solution, S
44、tandard Alcoholic, (0.1mol/L). (WarningSee 7.4 and 7.9.) Mix 9 mL of hydrochlo-ric (HCl, relative density 1.19) acid with 1 L of anhydrouspropan-2-ol. Standardize frequently enough to detect concen-tration changes of 0.0005 by potentiometric titration of ap-proximately 8 mL (accurately measured) of
45、the 0.1-mol/Lalcoholic KOH solution diluted with 125 mL of CO2-freewater.7.12 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 shou
46、ld beobtained from the manufacturer.7.13 Potassium Hydroxide Solution, Standard Alcoholic,(0.1 mol/L). (WarningSee 7.8 and 7.9.)Add6gofpotassium hydroxide (KOH) to approximately 1 L of propan-2-ol. Boil gently for 10 min to effect solution. Allow thesolution to stand for two days and then filter the
47、 supernatantliquid through a fine sintered-glass funnel. Store the solution ina chemically resistant bottle. Dispense in a manner such thatthe solution is protected from atmospheric carbon dioxide(CO2) by means of a guard tube containing soda lime or sodanon-fibrous silicate absorbents and such that
48、 it does not comeinto contact with cork, rubber, or saponifiable stopcock grease.Standardize frequently enough to detect concentration changesof 0.0005 by potentiometric titration of weighed quantities ofpotassium acid phthalate dissolved in CO2-free water.7.14 Titration SolventAdd 5 6 0.2 mL of wat
49、er to 495 65 mLof anhydrous propan-2-ol and mix well.Add 500 6 5mLof toluene. (WarningFlammable.) The titration solventshould be made up in large quantities, and its blank valuedetermined daily by titration prior to use.7.15 Chloroform,(WarningFlammable. Hazardous ma-terial.)8. Electrode System8.1 Preparation of Electrodes:8.1.1 When a Ag/AgCl reference electrode is used for thetitration and it contains an electrolyte which is not 1M3MLiCl in ethanol, replace the electrolyte. Drain the electrolytefrom the electrode, wash away all the salt (if present)
