Catalytic esterification and transesterification reaction of high acidic value waste oil by microwave heating

Abstract

In this study, biodiesel production from waste cooking oil was investigated. Esterification and transesterification reactions were carried out under microwave irradiation using heterogeneous (Amberlyst-15) and homogeneous (KOH) catalysts, respectively. The acidity of the oil was reduced from 6.92 to 1.09 mg KOH/g by an esterification reaction to avoid saponification during the transesterification reaction. Optimum esterification reaction conditions were investigated as 75°C, catalyst ratio of 25 wt % Amberlyst-15, 30 min, a 1:12 WCO:methanol molar ratio and stepwise methanol addition. The energy consumption of the biodiesel production under microwave heating was calculated and compared with a conventional heating system. The transesterification reaction was performed at 65°C for 3 min, at a 1:7 oil:methanol molar ratio, and 1 wt % KOH. The methyl ester content of the biodiesel was increased from 25.06% to 97.23% when an esterification reaction was applied prior to transesterification. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 575–581, 2015