Total Acid Number (TAN) reduction of high acidic crude oil by catalytic esterification of naphthenic acids in fixed-bed continuous flow reactor

Abstract

High acid crude oils contain large amount of naphthenic acids which cause serious corrosion problem in petroleum industry. Therefore, the removal of naphthenic acids becomes a great concern and challenge for oil refineries. In this study, the naphthenic acids in high TAN crude oils were removed by esterification with low consumption of methanol using a solid acid catalyst consisting of 12-tungstophosphoric acid (TPA) supported on γ-Al2O3 (TPA/γ-Al2O3) in a fixed-bed up-flow reactor. The catalyst was prepared by conventional wet impregnation method, and it possessed 25 wt% TPA with high dispersion, and large pore structure. TPA leaching problem from catalyst support was not observed during the reaction. The effect of various reaction parameters such as temperature and liquid hour space velocity (LHSV), and methanol to the crude oil ratio on TAN reduction were investigated in detail to maximize TAN reduction. The results revealed that the TPA/γ-Al2O3 catalyst effectively removed the naphthenic acids via esterification in high TAN crude oils. The TAN decreased with increase in methanol/oil mass ratio, reaction temperature, but it increased with increase in LHSV. In a long-term experiments (up to 100 h) running at a reaction temperature of 250 °C and LHSV of 3 h−1 using 2 wt% methanol in acidic crude oil, the TANs of acidic crude oil reduced from 2.0 mg KOH/g to a value below 0.5 mg KOH/g which is an acceptable TAN value of crude oil to process in the refineries without material upgrades.