1、Designation: D 4739 081An American National StandardStandard Test Method forBase Number Determination by Potentiometric HydrochloricAcid Titration1This standard is issued under the fixed designation D 4739; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n 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.1NOTECorrected isopropyl alcohol references editorially in March 2009.INTRODUCTIONCurrently, t
3、here are two ASTM test methods under the jurisdiction of Committee D02 used fordetermining base number by potentiometric titration: Test Method D 2896 and Test Method D 4739.They are both used throughout the petroleum industry. Test Method D 2896 is for new oils and is usedin setting specifications
4、since it is more accurate than Test Method D 4739. Test Method D 4739 shallbe used exclusively for the purpose of tracking base number loss as an oil proceeds in service. In manycases, the test methods will provide different results. Some comparisons are given in the Scope andthe Significance and Us
5、e sections of this test method to distinguish between the two standards and toprovide guidance to users.1. Scope*1.1 This test method covers a procedure for the determina-tion of basic constituents in petroleum products and new andused lubricants. This test method resolves these constituentsinto gro
6、ups having weak-base and strong-base ionizationproperties, provided the dissociation constants of the morestrongly basic compounds are at least 1000 times than that ofthe next weaker groups. This test method covers base numbersup to 250.1.2 In new and used lubricants, the constituents that can becon
7、sidered to have basic properties are primarily organic andinorganic bases, including amino compounds. This test methoduses hydrochloric acid as the titrant, whereas Test MethodD 2896 uses perchloric acid as the titrant.This test method mayor may not titrate these weak bases and, if so, it will titra
8、tethem to a lesser degree of completion; some additives such asinhibitors or detergents may show basic characteristics.1.3 When testing used engine lubricants, it should berecognized that certain weak bases are the result of the servicerather than having been built into the oil. This test method can
9、be used to indicate relative changes that occur in oil during useunder oxidizing or other service conditions regardless of thecolor or other properties of the resulting oil. The valuesobtained, however, are intended to be compared with the othervalues obtained by this test method only; base numberso
10、btained by this test method are not intended to be equal tovalues by other test methods. Although the analysis is madeunder closely specified conditions, this test method is notintended to, and does not, result in reported basic propertiesthat can be used under all service conditions to predictperfo
11、rmance of an oil; for example, no overall relationship isknown between bearing corrosion or the control of corrosivewear in the engine and base number.1.4 This test method was developed as an alternative for theformer base number portion of Test Method D 664 (lastpublished in Test Method D 66481).1.
12、4.1 Colorimetric test methods for base number are TestMethod D 974, IP 139, and 5102.1 on acid and base number byextraction (color-indicator titration) of Federal Test MethodStandard No. 791b. Test results by these methods may or maynot be numerically equivalent to this test method.1.5 The values st
13、ated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.06 on Analysis of Lubricants.Current ed
14、ition approved Feb. 1, 2008. Published April 2008. Originallyapproved in 1987. Last previous edition approved in 2006 as D 473906a.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, Un
15、ited States.1.6 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.
16、Referenced Documents2.1 ASTM Standards:2D 664 Test Method forAcid Number of Petroleum Productsby Potentiometric TitrationD 974 Test Method for Acid and Base Number by Color-Indicator TitrationD 1193 Specification for Reagent WaterD 2896 Test Method for Base Number of Petroleum Prod-ucts by Potentiom
17、etric Perchloric Acid TitrationD 4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD 4177 Practice for Automatic Sampling of Petroleum andPetroleum Products2.2 IP Standard:3IP 139 Petroleum products and lubricants Determinationof acid and base number Colour-indicator titrationmetho
18、d2.3 U.S. Federal Test Method:4Federal Test Method Standard No. 791b Lubricants LiquidFuels and Related Products; Methods of Testing3. Terminology3.1 Definitions:3.1.1 base numbers, nthe quantity of acid, expressed inmilligrams of potassium hydroxide per gram of sample that isrequired to titrate a s
19、ample, dissolved in a specified solvent toa specified end point.3.1.1.1 DiscussionIn this test method, the sample istitrated to a meter reading corresponding to aqueous acidicbuffer solution or appropriate inflection point.3.2 Definitions of Terms Specific to This Standard:3.2.1 strong base number,
20、nthe quantity of acid, ex-pressed in terms of the equivalent number of milligrams ofpotassium hydroxide per gram of sample, that is required totitrate a sample dissolved in the specified solvent from theinitial meter reading to a meter reading corresponding to abasic buffer solution.4. Summary of Te
21、st Method4.1 The sample is dissolved in a mixture of toluene,propan-2-ol (isopropyl alcohol), chloroform, and a smallamount of water and titrated potentiometrically with alcoholichydrochloric acid solution. The test results of this procedureare obtained by titration mode of fixed increment and fixed
22、time additions of the titrant. An endpoint is selected from atitration curve according to the criteria given in Section 12 andused to calculate a base number.5. Significance and Use5.1 New and used petroleum products can contain basicconstituents that are present as additives. The relative amountof
23、these materials can be determined by titration with acids.The base number is a measure of the amount of basicsubstances in the oil always under the conditions of the test. Itis sometimes used as a measure of lubricant degradation inservice. However, any condemning limit shall be empiricallyestablish
24、ed.5.2 As stated in 1.2, this test method uses a weaker acid totitrate the base than Test Method D 2896, and the titrationsolvents are also different. Test Method D 2896 uses a strongeracid and a more polar solvent system than Test MethodD 4739. As a result, Test Method D 2896 will titrate salts ofw
25、eak acids (soaps), basic salts of polyacidic bases, and weakalkaline salts of some metals. They do not protect the oil fromacidic components due to the degradation of the oil. This testmethod may produce a falsely exaggerated base number. TestMethod D 4739 will probably not titrate these weak bases
26、but,if so, will titrate them to a lesser degree of completion. Itmeasures only the basic components of the additive packagethat neutralizes acids. On the other hand, if the additivepackage contains weak basic components that do not play arole in neutralizing the acidic components of the degrading oi
27、l,then the Test Method D 4739 result may be falsely understated.5.3 Particular care is required in the interpretation of thebase number of new and used lubricants.5.3.1 When the base number of the new oil is required as anexpression of its manufactured quality, Test Method D 2896 ispreferred, since
28、it is known to titrate weak bases that this testmethod may or may not titrate reliably.5.3.2 When the base number of in-service or at-term oil isrequired, this test method is preferred because in many cases,especially for internal combustion engine oils, weakly basicdegradation products are possible
29、. Test Method D 2896 willtitrate these, thus giving a false value of essential basicity. Thistest method may or may not titrate these weak acids.5.3.3 When the loss of base number value, as the oilsproceed in service, is the consideration, this test method is to bepreferred and all values including
30、the unused oil shall bedetermined by this test method. Base numbers obtained by thistest method shall not be related to base numbers obtained byanother test method such as Test Method D 2896.5.3.4 In ASTM Interlaboratory Crosscheck Programs forboth new and used lubricants, historically Test Method D
31、 2896gives a higher value for base number.6. Apparatus6.1 Potentiometric Titration, automatic or manual, withcapability of adding fixed increments of titrant at fixed timeintervals (see Annex A1).6.1.1 The titrimeter must automatically (or manually) con-trol the rate of addition of titrant as follow
32、s: Delivery of titrantwill be incremental; after delivery of precisely a 0.100-mLincrement (see 6.1.2), the delivery is stopped and a fixed time2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards v
33、olume information, refer to the standards Document Summary page onthe ASTM website.3Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR,U.K.4Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.D47390812perio
34、d of 90 s is allowed to pass before another 0.100-mLincrement of titrant is delivered. This procedure is repeateduntil the titration is completed.6.1.2 The precision of addition of the 0.100-mL incrementsof titrant must be 60.001 mL for automatic titrators. Formanual buret, it should be 60.005 mL. A
35、 higher incrementalprecision is required for an automatic buret, because the totalvolume to the end point is summed from the individualincrements; it is read from a scale with a manual buret.6.2 Sensing Electrode, standard pH with glass membrane,suitable for non-aqueous titrations.6.3 Reference Elec
36、trode, Silver/Silver Chloride (Ag/AgCl)reference electrode with sleeve junction, filled with 1 to 3 MLiCl in ethanol.6.3.1 Combination ElectrodeSensing electrodes mayhave the Ag/AgCl reference electrode built into the sameelectrode body, which offers the convenience of working withand maintaining on
37、ly one electrode. The combination electrodeshall have a sleeve junction type of reference and shall use aninert ethanol electrolyte, for example, 1 to 3 M LiCl in ethanol.In the reference compartment, the sensing electrode part shalluse a glass membrane designed for non-aqueous titrations.These comb
38、ination electrodes shall have the same response orbetter response than a dual electrode system. They shall haveremovable sleeves for easy rinsing and addition of electrolyte.(WarningWhen a movable sleeve is part of the electrodesystem, ensure that the sleeve is unimpaired before everytitration.)6.4
39、Stirrer, Buret, Stand, Titration Vessel, as specified inAnnex A1, are required.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
40、of the American Chemical Society,where such specifications are available.5Other 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.7.2 Purity of WaterUnless otherwise indicated, refer
41、encesto water shall be understood to mean reagent water that meetsthe requirement of either Type I, II, or III of SpecificationD 1193.7.3 Buffer, Aqueous AcidCommercial pH 3 buffer solutionwith a tolerance of 60.02 pH units at 25C. This solution shallbe replaced at regular intervals consistent with
42、its stability orwhen contamination is suspected. Information related to thestability should be obtained from the manufacturer.7.4 Buffer, Aqueous BasicCommercial pH 10 buffer solu-tion with a tolerance of 60.02 pH units at 25C. This solutionshall be replaced at regular intervals consistent with its
43、stabilityor when contamination is suspected. Information related to thestability should be obtained from the manufacturer.7.5 ChloroformReagent grade. (WarningToxic andsuspected carcinogen.)7.6 Hydrochloric Acid Solution, Standard Alcoholic(0.1 M)Mix 9 mL of reagent grade hydrochloric acid (HCl,sp g
44、r 1.19) (WarningToxic and corrosive), with 1 L ofanhydrous isopropyl alcohol. Standardize frequently enough todetect normality changes of 0.0005 by potentiometric titrationof approximately 8 mL (accurately measured) of the 0.1 Malcoholic KOH solution diluted with 125 mL CO2-free water.7.7 Ethanolrea
45、gent grade. (WarningFlammable andtoxic, especially when denatured.)7.8 Lithium Chloride ElectrolytePrepare a solution of 1 to3 M LiCl in ethanol.7.9 Potassium Hydroxide(WarningCauses severeburns.)7.10 Potassium Hydroxide Solution, Standard Alcoholic(0.1 M)Add6gofreagent grade potassium hydroxide(KOH
46、) (WarningToxic and corrosive), to approximately 1 Lof anhydrous isopropyl alcohol. Boil gently for 10 min to effectsolution. Allow the solution to stand for 2 days, and then filterthe supernatant liquid through a fine sintered-glass funnel.Store the solution in a chemically resistant bottle. Dispen
47、se ina manner such that the solution is protected from atmosphericcarbon dioxide (CO2) by means of a guard tube containingsoda lime or soda non-fibrous silicate absorbent, and such thatit does not come into contact with cork, rubber, or saponifiablestopcock grease. Standardize frequently enough to d
48、etectnormality changes of 0.0005 by potentiometric titration ofweighed quantities of potassium acid phthalate dissolved inCO2-free water.7.11 Propan-2-ol (Isopropyl Alcohol)Anhydrous, (lessthan 0.1 % H2O). (WarningFlammable.) If dry reagentcannot be procured, dry it by distillation through a multipl
49、eplate column, discarding the first 5 % of material distilling overand using the 95 % remaining. Also, drying can be accom-plished using molecular sieves by passing the solvent upwardthrough a molecular sieve column using one part of molecularsieve per ten parts of solvent. (WarningIt has been reportedthat, if not inhibited against it, propan-2-ol can containperoxides. When this occurs, an explosive mixture is possiblewhen the storage vessel or other equipment such as a dispens-ing bottle, are near empty and approaching dryness.7.12 Commercially avail
