The removal of naphthenic acids from dewaxed VGO via esterification catalyzed by Mg–Al hydrotalcite

Abstract

This work focused on deacidification of dewaxed VGO by esterification on solid base hydrotalcite catalyst to achieve the target of lowering the total acid number (TAN) of oil. Mg–Al hydrotalcite with Mg/Al molar ratio of 4 was synthesized via urea method, and followed by calcination and rehydratation. Mg–Al hydrotalcite and its calcined and rehydrated products were characterized by PXRD, BET, CO2-TPD, FTIR, and TG/DTA. The catalytic activity of the prepared catalyst was evaluated using batch reactor for investigating the conversion of naphthenic acids in dewaxed VGO. The effects of various reaction parameters such as mass ratio of glycol to oil, mass ratio of catalyst to oil, temperature, time etc. on the conversion of naphthenic acids were studied and the findings were discussed. The activity of the calcined catalyst was lower than the initial activity of the non-calcined catalytic system. The correlation between the basic properties of the solid catalysts and the activity in the esterification in dewaxed VGO was investigated. The basic Brønsted sites played an important role in the esterification process. The hydrotalcite catalyst rehydrated by water exhibited a slight higher esterification efficiency compared to the as-synthesized one, and the as-synthesized one can be reused several times without significant loss of activity. Therefore, it was verified that Mg–Al hydrotalcite as a heterogeneous catalyst could be used to esterify naphthenic acids to lower TAN value of oil effectively, and Mg–Al hydrotalcite may be a promising catalyst for its sufficient high catalytic activity and stability.