1、INTERNATIONAL STANDARD IS0 6618 Second edition 1997-02-01 Petroleum products and lubricants - Determination of acid or base number - Colour-indicator titration method Produits p6 troliers et lubrifian ts - DGtermina tion de Iindice d acide ou de Iindice de base - M extremely weak acids or bases whos
2、e dissociation constants are less than IO-9 do not interfere. Salts react if their hydrolysis constants are greater than 10-g. NOTE 1 In new and used oils, the constituents considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, sa
3、lts of heavy metals, and additives such as inhibitors and detergents. Similarly, constituents considered to have basic properties include organic and inorganic bases, amino compounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts of heavy metals, and additives such as inhibitor
4、s and detergents. The method is not suitable for measuring the basic constituents of many basic additive-type lubricating oils, for which IS0 3771 can be used. This International Standard indicates relative changes that occur in an oil during use under oxidizing conditions. Although the titration is
5、 made under definite equilibrium conditions, the method does not measure an absolute acidic or basic property that can be used to predict performance of an oil under service conditions. NOTES 2 No general relationship between bearing corrosion and acid or base number is known. 3 Oils, such as many c
6、utting oils, rustproofing oils, and similar compounded oils, or excessively dark-coloured oils, that cannot be analysed by this method owing to obscurity of the colour-indicator end-point, can be analysed in accordance with IS0 6619. The acid or base numbers obtained by this colour-indicator method
7、may or may not be numerically the same as those obtained by IS0 6619, but they are generally of the same order of magnitude. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of p
8、ublication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain re
9、gisters of currently valid International Standards. IS0 6618:1997(E) 0 IS0 IS0 3696: 1987, Water for analytical laboratory use - Specification and test methods. IS0 3771:1994, Petroleum products - Determination of base number - Perchloric acid po ten tiome tric titration method. IS0 6619:1988, Petro
10、leum products and lubricants - Neutralization number - Po ten tiome tric titration method. NOTES 1 IS0 3771 employs the use of chlorobenzene as a solvent. Alternatives to this solvent are being sought. 2 IS0 6619 is under review, and the scope will be restricted to acid number. 3 Definitions For the
11、 purposes of this International Standard, the following definitions apply. 3.1 acid number: Quantity of base, expressed in milligrams of potassium hydroxide (KOH) per gram of sample, that is required to titrate the acid constituents present in 1 g of sample when titrated under prescribed conditions.
12、 3.2 strong acid number: Quantity of basel expressed in milligrams of potassium hydroxide (KOH) per gram of sample, that is required to titrate the strong acid constituents present in 1 g of sample when titrated under - prescribed conditions. 3.3 base number: Quantity of acid, expressed in terms of
13、the equivalent number of milligrams of potassium hydroxide (KOH) per gram of sample, that is required to titrate the base constituents present in 1 g of sample when titrated under prescribed conditions. 4 Principle To determine the acid number or base number, the test portion is dissolved in a mixtu
14、re of toluene and propan-Z-01 containing a small amount of water, and the resulting single-phase solution is titrated at room temperature with standard alcoholic base or alcoholic acid solution, respectively, to the end-point indicated by the colour change of added pnaphtholbenzein solution (orange
15、in acid and green-brown in base). To determine the strong acid number, a separate portion of the sample is extracted with boiling water and the aqueous extract is titrated with potassium hydroxide solution using methyl orange as indicator. 5 Reagents and materials During the analysis, use only reage
16、nts of recognized analytical grade, and only water in accordance with Grade 3 of IS0 3696. 5.1 Propan-Z-01, anhydrous, maximum water content 0,9 %(V/v) (volume fraction 0,9 %). 5.2 Toluene. 5.3 Titration solvent. Add 500 ml of toluene (5.2) and 5 ml of water to 495 ml of propan-2-01 (5.1). 5.4 Hydro
17、chloric acid, c(HCI) = 0,l mol/l standard volumetric alcoholic solution. Prepare in accordance with 5.4.1 or use commercially available solution. Standardize in accordance with 5.4.2. 0 IS0 IS0 6618:1997(E) 5.4.1 Preparation Mix 9 ml of concentrated HCI 35,4 %( avoid unnecessary exposure to carb on
18、d ioxide during filtration. Store the solution in a chemically resistant dispensing bottle out of contact with cork, rubber or saponifiable stopcock lubricant and protected by a guard tube containing soda lime or nonfibrous soda silicate absorbentl). Glass bottles are not recommended for storage. 5.
19、52 Standardization Standardize frequently enough to detect changes of 0,000 5 mol/l, preferably against 0,l g to 0,15 g of pure potassium acid phthalate (5.9) weighed with an accuracy of 0,000 2 g and dissolved in approximately 100 ml of carbon dioxide-free water, using phenolphthalein (5.8) to dete
20、ct the end-point. NOTES 1 To simplify calculations, both the standard potassium hydroxide and hydrochloric acid solutions may be adjusted so that 1 ml is equivalent to 5 mg of KOH. 2 Because of the relatively large coefficient of cubic expansion of organic liquids such as propan-2-01, the standard a
21、lcoholic solutions should be standardized at temperatures close to those employed in the titrations of sample, and close to 20 “C. 56 . Methyl orange, indicator solution. Dissolve 0,l g of methyl orange in 100 ml of water. 5.7 p-naphtholbenzein indicator solution, meeting the specifications given in
22、 annexes A and B. Dissolve I,0 g of pnaphtholbenzein in 100 ml of titration solvent (5.3). NOTE- In a study in 1992, only one co mmercially available sou Careful adhe rence to this requirem ent is t herefore recommended. rce of this indicator met the s pecif ica tion given in annex A*). 1) Ascarite,
23、 Carbosorb and lnde carb are examples of suitable products available commercially. T the convenie nce of users of this I nternational Standa rd and does not cons titute an endorsement by his I IS0 nformation is given of these products. for 2) Solid knaphtholbenzein meeting the specification given in
24、 annex A is available from Distillation Products Industries, Eastman Organic Chemicals Dept., Rochester 3, New York, USA. This information is given for the convenience of users of this International Standard and does not constitute an endorsement by IS0 of the product named. Equivalent products may
25、be used if they can be shown to lead to the same results. IS0 6618:1997(E) 5.8 Phenolphthalein, indicator solution. Dissolve 0,5 g of phenolphthalein in 100 ml propan-2-01 (5.1). 5.9 Potassium acid phthalate. 6 Apparatus Ordinary laboratory apparatus and: 6.1 Burette, capacity 50 ml, graduated in 0,
26、l ml subdivisions, or capacity 10 ml, graduated in 0,05 ml subdivisions. 7 Preparation of used oil sample 7.1 Strictly observe the sampling procedure in 7.2 and 7.3. Failure to obtain a representative test portion causes serious errors. NOTE - Sediment may be acidic or basic, or may have absorbed ac
27、idic or basic material from the sample. As used oil may change appreciably in storage, samples should be tested as soon as possible after removal from the lubricating system; the dates of sampling and testing should be noted. 7.2 Heat the laboratory sample of used oil to 60 “C IfI 5 “C in the origin
28、al container and agitate until all of the sediment is homogeneously suspended in the oil. If the original container is a can, or if it is glass and more than three-quarters full, transfer the entire sample to a clear glass bottle having a capacity at least one-third greater than the volume of the sa
29、mple. Transfer all traces of sediment from the original container to the bottle by violent agitation of portions of the sample in the original container. NOTE - When laboratory samples are visibly free from sediment the heating procedure described may be omitted 7.3 After complete suspension of all
30、sediment, filter the test sample, or a convenient aliquot, through a 150 pm wire mesh filter to remove large contaminating particles. 8 Determination of acid number 8.1 Into a 250-ml conical flask, introduce the appropriate mass of test portion given in table 1. Add 100 ml of the titration solvent (
31、5.3) and 0,5 ml of the indicator solution (5.7) and, without stoppering, swirl until the test portion is completely dissolved by the solvent. If the mixture assumes a yellow-orange colour, proceed as specified in 8.2; if it becomes green or green-black, proceed as specified in clause 9. Table 1 - Ma
32、ss of test portion Type of oil Acid or base number Mass of test portion Accuracy of weighing cl g I New or light-coloured 63 20 + 2 0,05 3 to 25 2 rf: 0,2 0,Ol 25 to 250 0,2 + 0,02 0,001 Used or dark-coloured =s 25 2 Ifr 0,2 0,Ol 25 to 250 I I I 0,2 + 0,02 I 0,001 I NOTE - Light-coloured test portio
33、ns of low acid number permit the use of 20-g test portions to obtain more precise results. The test portion size for dark-coloured oils is limited to the quantity specified to minimize possible interference by the dark colour. 4 0 IS0 IS0 6618:1997(E) 8.2 Titrate immediately at a temperature below 3
34、0 “C. Add the potassium hydroxide solution (5.5) in increments and swirl to disperse the potassium hydroxide as necessary. Shake vigorously near the end-point but avoid dissolving carbon dioxide in the solvent. Consider the end-point definite if the colour change persists for 15 s or if it reverses
35、on addition of two drops of the hydrochloric acid solution (5.4). In the case of acidic oils, the orange colour changes to a green or green-brown as the end-point is approached. To observe the end-point of dark-coloured oil, shake the flask vigorously to produce momentarily a slight foam when the co
36、lour change occurs as the last few drops of titrant are added and observe the titration under a white fluorescent lamp at bench-top level. 8.3 Carry out a blank titration on 100 ml of the titration solvent and 0,5 ml of the indicator solution, adding the potassium hydroxide in 0,05 ml or 0,l ml incr
37、ements. Record the quantity of potassium hydroxide solution required to reach the end-point (orange to green). 9 Determination of base number 9.1 If the titration solvent (5.3) containing the dissolved test portion assumes a green or greenish-brown colour after the indicator is added (8.1) carry out
38、 the titration as specified in 8.2, but use the hydrochloric acid (5.4) as titrant and titrate until the green-brown colour changes to orange. 9.2 Carry out a blank titration as specified in 8.3. NOTE - The titration solvent usually contains weak acid impurities which react with the strongly basic c
39、omponents of the test portion. To correct the base number for the test portion, it is thus necessary to determine an acid number blank of the solvent. 10 Determination of strong acid number 10.1 Introduce approximately 25 g of a representative sample, weighed to within O,O5 g, into a ZSO-ml separati
40、ng funnel, and add 100 ml of boiling water. Shake vigorously and, after phase separation, collect the aqueous phase in a 500-ml beaker. Make two new extractions from the test sample, each time with 50 ml of boiling water, and add the extracts obtained to the same beaker. To the combined extracts add
41、 0,l ml of the methyl orange indicator (5.6) and, if the solution becomes pink or red, titrate with the potassium hydroxide solution (5.5) until the solution becomes golden-brown in colour. If the initial colour is not pink or red, report the strong acid number as zero. IO.2 Into a 250-ml conical fl
42、ask, introduce 200 ml of the boiling water from the same source. Add 0,l ml of the methyl orange indicator solution (5.6). If the indicator solution is yellow-orange, titrate with the hydrochloric acid solution (5.4) to the same depth and shade of colour obtained in the titration of the test portion
43、. If the indicator colour is pink or red, titrate with the potassium hydroxide solution (5.5) to the same end-point as that used in the test portion titration. 11 Calculation 11.1 Acid number Calculate the acid number, AN, in milligrams of KOH per gram of the test sample, from the equation: AN= (VI - Vo)cKoH x 5671 m
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