1.1 This standard provides a design for the determination of acid content for in-service products that are predominantly hydrophobic in nature. These products are typically lubricants, edible oils and fuels, including biodiesel products. 1.2 The acid content can include total acid, which include organic acid and inorganic acid (measured by difference from the total and organic acids). 1.3 The measure of total acidity is termed Acid Content, expressed as miliequivalents (mEq) of acid per gram of sample. 1.4 It can be qualified by the pKa value of the conjugate acid of the base used - sodium hydrogen cyanamide (pKa ~4.5 for NaHNCN). 1.5 The scope of this method is not restricted by the miscibility (or lack thereof) of the sample with the ethanol reagent solution. The method can compensate for varying degrees of sample miscibility with the reagent solution based by measuring the intensity of an ethanol overtone band in the FTIR spectrum.
New and used petroleum products may contain acidic constituents that are present as additives or degradation products formed during in-service operations, such as oxidation products or ingression constituents. The relative amount of these materials can be determined by titrating with bases. The acid content is a measure of this amount of acidic substance in the oil. The acid content can be used as a guide in the quality control of lubricating oil formulations or used as a measure of the lubricant in-service degradation.
KeywordsAcid Content, Acid number, FTIR
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top
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