Interference of chloride salts in the determination of total acid number in crude oils using catalytic thermometric titration

Crude oils extracted from reservoirs often contain water with corrosion-causing dissolved salts. Therefore, the residual salt content of crude oils supplied to an oil refinery should be as low as possible. The total acid number (TAN) is an indicator of the corrosive activity of crude oil. However, its determination remains an analytical challenge because of the presence of dissolved salts, mineral matter, or chemicals. Herein, we quantified the impact of chloride salts on the measurement of the TAN of titration solvents and crude oil samples using the American Society for Testing and Materials (ASTM) D8045. Water-in-crude oil (W/O) emulsions (2.4 wt% water) were prepared using light and heavy crude oils mixed with saline solutions, and their TAN was evaluated. The precipitates obtained from the titration solvent were characterized. A chloride salt content of 100 mg kg(-1) in the titration solvent increased the apparent TAN. Analyses of the precipitates indicated that they comprised Ca(OH)(2), Mg(OH)(2), and Sr(OH)(2). The W/O emulsions of samples 1 (API 31.0) and 2 (API 16.7) exhibited an increase in their TAN of up to 89 and 45 wt%, respectively. When using catalytic thermometric titration, CaCl2, MgCl2, and SrCl2 with concentrations above 100 mg kg(-1) interfere with the determination of TAN.