1、BRITISH STANDARD BS7393:1990 ISO7537:1989 Method for Determination of total acid number in petroleum products by semi-micro colour indicator titrationBS7393:1990 This British Standard, having been prepared under the directionof the Petroleum Standards Policy Committee, waspublished under the authori
2、tyof the Board of BSI andcomes into effect on 31 December1990 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference PTC/13 Draft for comment 85/50442 DC ISBN 0 580 19252 0 Committees responsible for this British Standard The preparation of this British Sta
3、ndard was entrusted by the Petroleum Standards Policy Committee(PTC/-) to Technical Committee PTC/13, upon which the following bodies were represented: Association of Consulting Scientists Association of United Kingdom Oil Independents British Lubricants Federation Limited British Steel plc GAMBICA(
4、BEAMA) Ltd. Institute of Petroleum Ministry of Defence Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd. No. Date CommentsBS7393:1990 BSI 12-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative references
5、1 3 Principle 1 4 Definition 1 5 Reagents and materials 1 6 Apparatus 2 7 Preparation of used oil samples 4 8 Procedure 4 9 Expression of results 5 10 Test report 5 Figure 1 Schematic drawing of typical apparatus 3 Figure 2 Precision curves 6 Table 1 Size of sample 4 Publication(s) referred to Insid
6、e back coverBS7393:1990 ii BSI 12-1999 National foreword This British Standard has been prepared under the direction of the Petroleum Standards Policy Committee. It is identical with ISO7537:1989 “Petroleum products Determination of total acid number Semi-micro colour-indicator titration method”, pr
7、epared by Technical Committee28, Petroleum products and lubricants, of the International Organization for Standardization(ISO) as a result of discussions, in which the United Kingdom participated. The Technical Committee has reviewed the provisions of ISO4263:1986 and ISO6619:1988, to which referenc
8、e is made in the text, and has decided that they are acceptable for use in conjunction with this standard. CAUTION. Attention is drawn to the Health and Safety at Work etc. Act,1974, and the need for ensuring that the method of test specified in this standard is carried out with suitable precautions
9、. The procedure described in this standard method is intended to be carried out by qualified chemists or other suitably trained and/or supervised personnel. Normal safety precautions should be observed throughout the use of the method. A British Standard does not purport to include all the necessary
10、 provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO6353-2:1983 BS6376 Reagents for
11、 chemical analysis Part2:1984 Specifications (first series) (Identical) ISO6618:1987 BS2000 Methods of test for petroleum and its products Part139:1983 Neutralization number of petroleum products and lubricants (colour indicator titration method) (Technically equivalent) Summary of pages This docume
12、nt comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7393:1990 BSI 12
13、-1999 1 1 Scope 1.1 This International Standard specifies a semi-micro colour indicator titration method for the determination of acidic constituents in new or used petroleum products and lubricants soluble in mixtures of toluene and isopropyl alcohol, or capable of existing as suspensions in such m
14、ixtures. The method is especially intended for applications in which the amount of sample available to be analyzed is too small to allow accurate analysis by ISO6619 or ISO6618. It is applicable to the determination of acids having dissociation constants in water larger than10 9 . Extremely weak aci
15、ds having dissociation constants smaller than10 9do not interfere. Salts titrate if their hydrolysis constants are larger than10 9 . 1.2 This method may be used to indicate relative changes in total acid number that occur in an oil during use under oxidizing conditions. Although the titration is mad
16、e under definite equilibrium conditions, the method does not measure an absolute acidic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid number is known. 1.3 Since this test method requires substantially l
17、ess sample than ISO6618 or ISO6619, it provides an advantageous means of monitoring an oxidation test by changes in total acid number by a) minimizing test sample depletion for total acid number analyses and thus minimizing the disturbance of the test or b) allowing additional total acid number anal
18、yses to be made while maintaining the same test sample depletion and thus providing additional data. NOTE 1Some oils, such as many cutting oils, rustproofing oils, and similar compounded oils, or excessively dark-coloured oils, may be more difficult to analyze by this method due to obscurity of the
19、colour indicator end-point. These oils can be analyzed by ISO6619 provided sufficient sample is available. However, this situation is much less likely using this International Standard than using ISO6618, due to the use of a more highly dilute sample during the titration and due to the greater stabi
20、lity of the end-point colour change. The acid numbers obtained by this method may or may not be numerically the same as those obtained by ISO6619, but they should be of the same order of magnitude. NOTE 2The results obtained using this method have been found to be numerically the same as those obtai
21、ned using ISO6618, within the precision of the two methods, for new or oxidized lubricants of the type primarily intended for hydraulic or steam turbine type service. The oxidized lubricants were obtained using ISO4263. This correlation is shown by the correlation coefficient r =0,989, with slope s
22、=1,017 and intercept y =+0,029, calculated using the total acid numbers obtained using both titration methods for the samples used for the precision statement(see9.2). 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of th
23、is International Standard. At the time of publication, 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 listed b
24、elow. Members of IEC and ISO maintain registers of currently valid International Standards. ISO4263:1986, Petroleum products Inhibited mineral oils Determination of oxidation characteristics. ISO6353-2:1983, Reagents for chemical analysis Part2: Specifications First series. ISO6618:1987, Petroleum p
25、roducts and lubricants Neutralization number Colour-indicator titration method. ISO6619:1988, Petroleum products and lubricants Neutralization number Potentiometric titration method. 3 Principle Determination of the total acid number by dissolving a sample of the oil in a solvent consisting of tolue
26、ne, isopropyl alcohol, and a small amount of water. The resulting single-phase solution is titrated at room temperature under a nitrogen atmosphere with a standard potassium hydroxide(KOH) solution in isopropyl alcohol, c(KOH)=0,01mol/l, to the stable green colour of the added p-naphtholbenzein indi
27、cator. 4 Definition total acid number the quantity of KOH, expressed in milligrams, required to titrate all acids or salts present in one gram of the sample having dissociation or hydrolysis constants larger than10 9 5 Reagents and materials During the analysis, unless otherwise stated, use only rea
28、gents of recognized analytical grade. All reference to water shall be understood to mean freshly distilled(carbon dioxide free) water. 5.1 p-Naphtholbenzein indicator solution, conforming to the specifications given in Annexes A and B of ISO6618. Prepare a solution containing10g of p-naphtholbenzein
29、 per litre of titration solvent.BS7393:1990 2 BSI 12-1999 5.2 Nitrogen, dry and carbon dioxide free. NOTEIn order to obtain repeatable results and a stable end-point colour change, it is especially important that the nitrogen purge gas be free of carbon dioxide. Prepurified grade nitrogen has been f
30、ound to be satisfactory. 5.3 Phenolphthalein indicator solution Dissolve0,10g of pure, solid phenolphthalein in50ml of water and50ml of95%(V/V) ethanol. 5.4 Titration solvent Add500ml of toluene and5ml of water to495ml of anhydrous isopropyl alcohol. 5.5 Potassium hydroxide, alcoholic solution, stan
31、dard volumetric, c(KOH)=0,01mol/l. 5.5.1 Preparation Add3g of solid KOH to approximately1 litre of anhydrous isopropyl alcohol(containing less than0,9% water) in a2 litre conical flask. Boil the mixture gently on a steam bath for15min while stirring to prevent caking of solids on the bottom of the f
32、lask. Add about1g of barium hydroxide and again boil gently for about10min. Cool to room temperature, stopper to prevent contact with the ambient atmosphere and allow to stand overnight(about16h). Filter the supernatant liquid through a104m polytetrafluoroethylene(PTFE) membrane filter while avoidin
33、g unnecessary exposure to the atmosphere and then dilute the solution(approximately0,05mol/l) with the anhydrous isopropyl alcohol to a total volume of about5litres to obtain a final concentration of0,010mol/l 0,002mol/l. Store the titrant in a chemically resistant dispensing bottle out of contact w
34、ith cork, rubber, or saponifiable stopcock lubricant and protected by a guard tube containing soda-lime. Minimize exposure of the titrant to light by storing in the dark or in an amber bottle or by wrapping the bottle with aluminium foil. NOTEBecause of the relatively large coefficient of cubic expa
35、nsion of organic liquids such as isopropyl alcohol, the standard alcoholic solutions should be standardized at temperatures close to those employed in the titrations of samples. 5.5.2 Standardization Standardize the titrant against dried(at least1h at110 C), pure potassium hydrogen phthalate using t
36、he method specified in8.1 for the total acid number analysis, but using water(40ml 1ml) as the solvent and6 drops of phenolphthalein solution as the indicator. Carry out the blank in the same manner, but omitting the potassium hydrogen phthalate. Standardize the titrant frequently enough to detect v
37、ariations exceeding0,0003 mol/l. Take the mean normality determined by at least duplicate analyses as the titrant concentration for the total acid number calculations. 5.6 Toluene, complying with the requirements ofISO6353-2. 6 Apparatus 6.1 Titration burette, micro-scale, automatic, with0,01ml subd
38、ivisions and at least a2ml burette capacity. 6.2 Titrant reservoir, preferably one which is integral with the automatic burette, such as that shown in Figure 1. If a titrant reservoir separate from the automatic burette is used, the line connecting the reservoir with the burette shall be all glass.
39、Exposure of the titrant to light shall be minimized by the use of amber glass for the reservoir, by wrapping the reservoir with foil such as aluminium foil, or by other suitable means. The tube in the reservoir for titrant withdrawal shall be adjusted so that the end of the tube is about20mm from th
40、e bottom of the reservoir so that any precipitate that may collect on the bottom of the reservoir will not be disturbed. To further avoid disturbing any precipitate in the reservoir, movement of the reservoir shall be minimized. With either type of reservoir all entrances and exits to the burette an
41、d reservoir shall be connected to absorption tubes to remove atmospheric carbon dioxide and water. These tubes may contain, for example,0,71 to1,7mm anhydrous calcium sulfate as desiccant and soda-lime to absorb carbon dioxide. Precautions shall be taken to prevent introduction of any sodalime into
42、the titrant reservoir or burette. 6.3 Titration beaker, 100ml capacity tall-form Berzelius beaker without pouring spout, approximate dimensions51mm inside diameter and71mm high. 6.4 Titration beaker stopper, to seal the titration beaker. The stopper shall be composed of an elastomeric material, such
43、 as neoprene, that is essentially unaffected by the titration solvent. Approximate stopper dimensions are53mm top diameter,45mm bottom diameter, and25mm high. The stopper shall be fitted with a purge gas inlet tube, made of glass and extending15mm 2mm beyond the bottom of the stopper, and pierced by
44、 a7mm1mm diameter purge gas outlet hole. The inlet tube and outlet hole shall be placed on opposite sides of the stopper with a centre-to-centre separation distance of30mm1mm.BS7393:1990 BSI 12-1999 3 Figure 1 Schematic drawing of typical apparatusBS7393:1990 4 BSI 12-1999 6.5 Purge gas flowmeter, v
45、ariable area, capable of indicating a flow rate of10litres/h. 6.6 Stirrer motor, variable speed, magnetically linked. 6.7 Stirring bar, cylindrical, PTFE encased, approximately25mm long and8mm in diameter. 6.8 Pipette, capable of delivering0,100ml 0,002ml of titration indicator solution. 6.9 Titrati
46、on solvent burette, capacity500ml or larger, with5ml subdivisions. The top of the titration solvent burette shall be stoppered and connected with an absorption tube, as in6.2, to remove atmospheric carbon dioxide and water. An alternative means of dispensing the titration solvent may be used, provid
47、ed that a dispensing repeatability within 1ml for40ml is obtainable and the solvent in the dispenser is isolated from atmospheric carbon dioxide and water. 7 Preparation of used oil samples 7.1 Strict observance of the sample preparation procedure specified in7.2 is necessary, since the sediment its
48、elf may be acidic or basic or may have absorbed acidic or basic material from the sample. Failure to obtain a representative sample may lead to erroneous results. 7.2 Heat the sample(seenote1) of used oil to60 C 5 C in the original container and agitate until all sediment is homogeneously suspended
49、in the oil(seealso note2). If the original container is of opaque material, or if it is 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 sample. Transfer all traces of sediment from the original container to the bottle by violent agitation of portions of the sample in the original container. After complete suspension of all sediment, strain the sample or a convenient aliquot of the sample through a1504m screen for the removal of large con
