ASTM D2274 for oxidation stability of distillate fuel oil (Accelerated method)
4. Summary of Test Method
4.1 A 350-mL volume of filtered middle distillate fuel is aged at 95°C (203°F) for 16 h while oxygen is bubbled through the sample at a rate of 3 L/h. After aging, the sample is cooled to approximately room temperature before filtering to obtain the filterable insolubles quantity. Adherent insolubles are then removed from the oxidation cell and associated glassware with trisolvent. The trisolvent is evaporated to obtain the quantity of adherent insolubles. The sum of the filterable and adherent insolubles, expressed as milligrams per 100 mL, is reported as total insolubles.
5. Significance and Use
5.1 This test method provides a basis for the estimation of the storage stability of middle distillate fuels such as No. 2 fuel oil.
5.2 The test method may not provide a prediction of the quantity of insolubles that will form in field storage over any given period of time. The amount of insolubles formed in such field storage is subject to the specific conditions which are too variable for this test method to predict accurately.
5.3 Test Method D2274 yields results more rapidly than Test Method D4625, the 43°C bottle test. However, as a result of the significantly elevated temperature and the pure oxygen atmosphere, the nature and amount of insolubles may deviate to a greater extent than Test Method D4625 from those formed in field storage.
6. Interferences
6.1 Oxidation is a major chemical process causing adherent and filterable insolubles to form. Any substance such as copper or chromium that catalyzes oxidation reactions will cause greater quantities of insolubles to form. Since the apparatus used in this test can also be used in Test Method D 943, where coils of copper and steel are used, it is important that any residues that could contain these metals be eliminated from the apparatus by thorough cleaning prior to use. Similarly, to preclude the presence of chromium ions, as well as to protect laboratory personnel from potential harm, chromic acid shall not be used for cleaning glassware in the practice of this method.
6.2 It has been found that commercial grades of acetone, if used in the trisolvent, can have impurities which cause an apparently greater level of adherent insolubles to be measured. It is, therefore, critical that only reagent (or higher) grade materials be used in preparing the trisolvent mixture.
6.3 Ultraviolet light exposure has been found to increase the amount of total insolubles. Therefore, the fuel being tested shall be shielded from direct exposure to ultraviolet light (sunlight or fluorescent). Conduct all sampling, measuring, filtration, and weighing away from direct sunlight and in as dark an area as would be compatible with other laboratory operations. Storage before stress, the stress period and cool-down after stressing shall be in the dark.
