ASTM D4739-2006a Standard Test Method for Base Number Determination by Potentiometric Titration《电势滴定法测定碱值的标准试验方法》.pdf

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1、Designation: D 4739 06aAn American National StandardStandard Test Method forBase Number Determination by Potentiometric Titration1This standard is issued under the fixed designation D 4739; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev

2、ision, 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.1. Scope*1.1 This test method covers a procedure for the determina-tion of basic constituents in petroleum pro

3、ducts and lubricants(Note 1). The test method resolves these constituents intogroups having weak-base and strong-base ionization proper-ties, provided the dissociation constants of the more stronglybasic compounds are at least 1000 times that of the next weakergroups.1.1.1 This test method covers ba

4、se numbers up to 70. Whileit can be extended to higher base numbers, the precision of thetest method for base numbers greater than 70 has not beendetermined.NOTE 1In new and used oils, the constituents which can be consid-ered to have basic properties are primarily organic and inorganic bases,includ

5、ing amino compounds, although certain salts of heavy metals, saltsof weak acids, basic salts of polyacidic compounds, and some additivessuch as inhibitors or detergents may show basic characteristics.1.2 This test method can be used to indicate relative changesthat occur in an oil during use under o

6、xidizing or other serviceconditions regardless of the color or other properties of theresulting oil (Note 3). Although the analysis is made underclosely specified conditions, the method is not intended to, anddoes not, result in reported basic properties which can be usedunder all service conditions

7、 to predict performance of an oil;for example, no overall relationship is known between bearingcorrosion or the control of corrosive wear in the engine andbase number.NOTE 2Test Method D 4739 was developed as an alternative for theformer base number portion of Test Method D 664. Base numbersobtained

8、 by this method may or may not be numerically the same as thoseobtained by the former base number portion of Test Method D 664.2NOTE 3A color indicator titration method is also available in the TestMethod D 974 and IP 139. The base numbers obtained by the potentio-metric method may or may not be num

9、erically the same as those obtainedby Test Method D 974 or equivalent color indicator methods such as givenin Federal Test Method Std. No. 791b. Potentiometric methods for basenumber are also available in Test Method D 2896.1.3 The values stated in SI units are to be regarded asstandard. No other un

10、its 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 reg

11、ulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D 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

12、 of Petroleum Prod-ucts by Potentiometric Perchloric Acid Titration2.2 IP Standard:IP 139 Test Method for Acid Number by Color-IndicatorTitration Method, IP Standards for Petroleum and ItsProducts, Part 1. Methods for Analysis and Testing.42.3 U.S. Federal Test Method:Federal Test Method Standard No

13、. 791b Lubricants LiquidFuels and Related Products; Methods of Testing53. 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 sample, dissolved in a specified solvent toa specified end poi

14、nt.3.1.1.1 DiscussionIn this test method, the sample istitrated to a meter reading corresponding to a freshly preparednonaqueous acidic buffer solution.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of Subcommitt

15、eeD02.06 on Analysis of Lubricants.Current edition approved Nov. 1, 2006. Published November 2006. Originallyapproved in 1987. Last previous edition approved in 2006 as D 473906.2The base number portion was last published in the 1981 version.3For referenced ASTM standards, visit the ASTM website, ww

16、w.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.4Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR,U.K.5Available from Standardization Documents O

17、rder Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.1*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.3.2 Definitions of Terms Specific t

18、o This Standard:3.2.1 strong base number, 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

19、to afreshly prepared basic buffer solution.4. Summary of Test Method4.1 The sample is dissolved in a mixture of toluene,propanol-2-ol (isopropyl alcohol), chloroform, and a smallamount of water and titrated potentiometrically with alcoholichydrochloric acid solution. The test results of this procedu

20、reare obtained by titration mode of fixed increment and fixedtime additions of the titrant. An endpoint is selected from atitration curve according to the criteria given in 13.1 and usedto calculate a base number.5. Significance and Use5.1 New and used petroleum products can contain basicconstituent

21、s that are present as additives or as degradationproducts formed during service. The relative amount of thesematerials can be determined by titrating with acids. The basenumber is a measure of the amount of basic substances in theoilalways under the conditions of the test. The base numberis used as

22、a guide in the quality control of lubricating oilformulations. It is also sometimes used as a measure oflubricant degradation in service. Any condemning limits mustbe empirically established.6. Apparatus6.1 Potentiometric Titrimeter, automatic or manual, withcapability of adding fixed increments of

23、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 follows: Delivery of titrantwill be incremental; after delivery of precisely a 0.100-mLincrement (see 6.1.2), the delivery is stopped and a fixed timeperiod

24、 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

25、higher incrementalprecision is required for an automatic buret because the totalvolume to the end point is summed from the individualincrements, whereas with a manual buret it is read from a scale.6.2 Glass Indicating Electrode, pH 0 to 14, general purpose.6.3 Reference Electrode, Silver/Silver Chlo

26、ride (Ag/AgCl)reference electrode, filled with 13 M LiCl in ethanol.NOTE 4Certain alternative electrode-electrolyte combinations havebeen found to give satisfactory results although the precision using thesealternatives has not been determined. Combination electrodes may be usedprovided they conform

27、 to 8.3 and have a sufficient fast response time.6.4 Stirrer, Buret, Stand, Titration Vessel, as specified inAnnexA1 are required.Atypical cell assembly is shown in Fig.1.7. Reagents7.1 Buffer, Nonaqueous AcidAdd 10 mL of buffer stocksolution A (see 7.3) to 100 mL of titration solvent. Use within1h.

28、7.2 Buffer, Nonaqueous BaseAdd 10 mL of buffer stocksolution B (see 7.4) to 100 mL of titration solvent. Use within1h.7.3 Buffer Stock Solution AAccurately weigh 24.2 6 0.1g of 2,4,6-trimethyl pyridine (g-collidine), and transfer to a 1-Lvolumetric flask containing 100 mL of anhydrous isopropylalcoh

29、ol. Using a 250-mL graduated cylinder, add to the flask,while continuously stirring its contents, 150/NHCl6 5mLof0.2 M alcoholic HCl solution (NHClbeing the exact molarity ofthe HCl solution found by standardization). Dilute to the1000-mL mark with anhydrous isopropyl alcohol, and mixthoroughly. Use

30、 within 2 weeks.7.4 Buffer Stock Solution BAccurately weigh 27.8 6 0.1gofm-nitrophenol and transfer to a 1-L volumetric flaskcontaining 100 mL of anhydrous isopropyl alcohol. Using a250-mLgraduated cylinder, add to the flask while continuouslystirring its contents, 50/NKOH6 1mLof0.2M alcoholic KOHso

31、lution. (NKOHbeing the exact molarity of the KOH solutionfound by standardization). Dilute to the 1000-mL mark withanhydrous isopropyl alcohol and mix thoroughly. Use within 2weeks.7.5 Chloroform, reagent grade. (WarningToxic and sus-pected carcinogen.)7.6 Chromic Acid Solution(WarningCauses severeb

32、urns. Recognized carcinogen. Strong oxidizer.)7.7 Hydrochloric Acid Solution, Standard Alcoholic (0.1M)Mix 9 mL of reagent grade hydrochloric acid (HCl, sp gr1.19) (WarningToxic and corrosive), with 1 L of anhydrousisopropyl alcohol. Standardize frequently enough to detectnormality changes of 0.0005

33、 by potentiometric titration ofapproximately 8 mL (accurately measured) of the 0.1 Malcoholic KOH solution diluted with 125 mL CO2-free water.7.8 Hydrochloric Acid Solution, Standard Alcoholic (0.2M)Prepare and standardize as described in 7.7, but use 18mL of HCl (sp gr 1.19).FIG. 1 Cell for Potenti

34、ometric TitrationD 4739 06a27.9 Lithium Chloride ElectrolytePrepare a solution of13 M LiCl in ethanol.7.10 m-Nitrophenol, NO2C6H4OH,(WarningToxic),(mol weight 139.11), conforming to the following require-ments:Melting point 96 to 97CColor Pale Yellow7.10.1 Store the reagent in a brown glass bottle.7

35、.11 Potassium Hydroxide Solution, Standard Alco-holic (0.1 M)Add6gofreagent grade potassium hydroxide(KOH) (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

36、 liquid through a fine sintered-glass funnel.Store the solution in a chemically resistant bottle. Dispense 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 (Ascarite,Carbosorb, or I

37、ndicarb), and such that it does not come intocontact with cork, rubber, or saponifiable stopcock grease.Standardize frequently enough to detect normality changes of0.0005 by potentiometric titration of weighed quantities ofpotassium acid phthalate dissolved in CO2-free water.7.12 Potassium Hydroxide

38、 Solution, Standard Alcoholic(0.2 M)Prepare, store, and standardize as directed in 7.11,but use 12 to 13 g of KOH to approximately 1 L of anhydrousisopropyl alcohol.7.13 Propanol-2-ol (Isopropyl Alcohol), Anhydrous, (lessthan 0.1 % H2O) (WarningFlammable). If dry reagentcannot be procured, dry it by

39、 distillation through a multipleplate column, discarding the first 5 % of material distilling overand using the 95 % remaining. Also, drying can be accom-plished using molecular sieves such as Linde Type 4A, bypassing the solvent upward through a molecular sieve columnusing 1 part of molecular sieve

40、 per 10 parts of solvent.(WarningIt has been reported that, if not inhibited against it,propanol-2-ol can contain peroxides. When this occurs, anexplosive mixture is possible when the storage vessel or otherequipment such as a dispensing bottle, are near empty andapproaching dryness.)7.14 Purity of

41、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 available.6Other grades may beused, provi

42、ded it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.14.1 Commercially available solutions may be used inplace of laboratory preparations provided the solutions havebeen certified as equivalent.7.14.2 Altern

43、ate volumes of solutions may be preparedprovided the final solution concentration is equivalent.7.15 Purity of WaterUnless otherwise indicated, refer-ences to water shall be understood to mean reagent water thatmeets the requirement of either Type I, II, or III of Specifica-tion D 1193.7.16 Titratio

44、n SolventIn a brown reagent bottle, add 30mL of water to 1 L of isopropyl alcohol and mix thoroughly.Add 1 L each of toluene and chloroform and mix thoroughly.7.17 Toluene, reagent grade. (WarningExtremely flam-mable.)7.18 2,4,6-Trimethyl Pyridine (g-Collidine), (CH3)3C5H2N,(WarningToxic), (mol weig

45、ht 121.18) conforming to thefollowing requirements:Boiling range 168 to 170CRefractive index ND20 1.4982 6 0.0005Color colorless7.18.1 Store the reagent over activated alumina and keep itin a brown glass bottle.8. Preparation of Electrode System8.1 Maintenance of ElectrodesClean the glass electrode(

46、Note 5) at frequent intervals (not less than once every weekduring continual use) by immersing in cold chromic acidcleaning solution (WarningCauses severe burns. Recog-nized carcinogen. Strong oxidizer). Drain the calomel electrodeat least once each week and refill with fresh LiCl electrolyte asfar

47、as the filling hole. Maintain the electrolyte level in thereference electrode above that of the liquid in the titrationbeaker at all times. When not in use, immerse the lower halvesof the electrodes in either water (glass) or the LiCl in isopropylalcohol electrolyte (reference). Do not allow them to

48、 remainimmersed in titration solvent for any appreciable period of timebetween titrations. While the electrodes are not extremelyfragile, handle them carefully at all times.NOTE 5Cleaning the electrodes thoroughly, keeping the ground-glassjoint free of foreign materials, and regular testing of the e

49、lectrodes areimportant in obtaining repeatable potentials, since contamination canintroduce uncertain, erratic, and unnoticeable liquid contact potentials.7While this is of secondary importance when end points are chosen frominflection points in the titration curve, it is quite serious when end pointsare chosen at artibrarily-fixed cell potentials (that is, the nonaqueousacidic buffer potential).8.2 Preparation of Electrodes, Before and after using,blot-dry the glass electrode thoroughly with a clean cloth or asoft absorbent tissue and rinse with