Removal of naphthenic acids from a diesel fuel by esterification

The presence of relatively high levels of naphthenic acids in diesel fuels has great influence on petroleum refiners. In this paper, a new method of catalytic esterification was introduced to remove the naphthenic acids from a diesel fuel. The paper used SnO/Al2O3 as the catalyst system, and a fixed bed catalyst was made. The experiments were finished in a fixed bed reactor. The total acid number of the diesel fuel was lowered from 1.7 mg KOH/g to less than 0.1 mg of KOH/g at a methanol/oil ratio of 0.010. This method can attain the effectiveness of aqueous base washing and has no loss of oil. Data indicates that the acid removal is influenced by the reaction temperature, methanol/oil ratio, and space velocity. A high reaction temperature and methanol/oil ratio or low space velocity are favorable for the esterification. The color of the de-acided oils can apparently be improved during the esterification. The optimum reaction temperature is 280 degrees C.