Acid Number of Petroleum Products According to ASTM D664
Detailed Method for Measurement of Acid Number by Potentiometric Titration
This application note (download below) gives the method and procedure tips for automated acid number determination according to the ASTM D664 standard test. Tips on how to avoid measurement errors are included. The acid number is measured by potentiometric titration with the sample of petroleum product dissolved in a mixture of organic solvents. The sample is titrated against a solution of potassium hydroxide in 2-propanol.
Reaction:
KOH + HA → KA + H2O
Background
New and used petroleum products and biodiesel may contain a variety of acidic compounds. The acids can be present as additives or form by oxidation during the usage of the products. Hence, one of the parameters used to assess the quality of petroleum products or their degradation is the acid number.
Acid number is the measure of the number of acid groups in a substance or a mixture of compounds. It is expressed as the mass (in mg) of potassium hydroxide needed to neutralize 1 g of a sample.
For more applications related to petroleum product analysis see the bromine number determination according to ASTM D1159 and determination of hydrogen sulfide and mercaptans according to UOP 163-10.
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Figure: Experimental setup for automated acid number determination
