Total Acid Number Reduction of Naphthenic Acid Using Subcritical Methanol and 1-Butyl-3-Methylimidazolium Octylsulfate

Abstract

Naphthenic acids (NAs) are naturally occurring organic acids present in crude oil and bitumen as contaminants. Their presence in the crude oil greatly reduces the quality and price of crude oil. NAs also causes corrosion in the production and processing facilities. They are quantified in the petroleum as Total acid number (TAN), which is the amount of KOH required to neutralize one gram of oil. In this study, the TAN of NAs was reduced by using subcritical methanol and then a mixture of 1-butyl-3methylimidazolium octyl sulfate ([BMIM] [C8HSO4]) and subcritical methanol. The experiments were conducted in an autoclave batch reactor at temperatures of 70-150°C, methanol partial pressures of 0.2-2.5MPa and reaction time of 0-120min. TAN value of the reaction was analyzed by ASTM D974 method. The experimental results demonstrate that high temperature and reaction time favors the TAN reduction. Approximately 24% TAN reduction was achieved by using only subcritical methanol at a temperature of 150°C, methanol partial pressure of 0.2MPa and reaction time of 30min. TAN was reduced to 32% by the addition of [BMIM] [C8HSO4] at the same conditions, indicating the capability of this IL to work under the subcritical methanol conditions. Maximum 56% TAN reduction was achieved at a temperature of 150°C, a reaction time of 120min using subcritical methanol. These results show that the subcritical methanol has the ability to lower the reaction time in an environmental-friendly and economical way. The presence of 1-butyl-3-methylimidazolium octyl sulfate [BMIM] [C8HSO4] further help in lowering the TAN.