Acid value is the amount of alkali used to titrate the sample to the specified endpoint in a specified solvent, measured in KOH, in mg/g.
Acid value mainly reflects the corrosiveness of petroleum and petroleum products to metals during extraction, transportation, processing, and use, as well as the refining depth or degree of deterioration of oil products. It can be used in formula research to control the quality of lubricating oil, and sometimes can also be used to measure the degradation of lubricating oil during use. However, using acid value as a lubricant scrap indicator should be determined through experience.
At present, there are many types of acid value determination methods, one of which is acid-base titration method, such as GB/T264-1983 "Petroleum Products - Determination of Acid Value"; The other is Potentiometric titration, such as GB/T7304-2014 Determination of Acid Value of Petroleum Products - Potentiometric titration. Below are two testing methods for national standards.
1. Acid number of petroleum products - Potentiometric titration
Two methods are introduced in the national standard GB/T7304-2014. Method A: It is mainly applicable to the determination of the acid value of petroleum products and lubricants that can be dissolved or basically dissolved in a mixed solvent of toluene and isopropanol in wastewater. Its precision is established within the range of acid value (calculated as KOH) ranging from 0.1mg/g to 150mg/g; Method B is applicable to the determination of the acid value of biodiesel and biodiesel blended fuels with lower acidity and significant differences in solubility.
The main method is to dissolve the sample in the titration solvent, use potassium hydroxide isopropanol Standard solution as the titrant for potentiometric titration, and the electrodes are glass indicator electrode, reference electrode or composite electrode.
Its advantage lies in the targeted regulations and requirements in sample processing, selection of test conditions, calibration of instruments and equipment, preparation and calibration of reagents, and judgment of test results based on the properties and characteristics of different samples, in order to adapt to the particularity of the samples and achieve more accurate results.
2. Acid value acid-base titration method for petroleum products
GB/T264-1983 is an acid-base titration method mainly used for the determination of the acid value of petroleum products. Extract the acidic components from the sample with boiling ethanol, and then titrate with potassium hydroxide ethanol solution. The acid-base titration operation is simple, but the disadvantage is that it is difficult to observe color changes in oil products with additives or darker colors, resulting in certain errors.
