Evaluation of catalytic activity of two functionalized imidazolium ionic liquids for biodiesel fuel production by a two-stage process

Abstract

BACKGROUND Today commercial biodiesel processes use mainly homogeneous alkali catalysts when the feedstock is from refined oil with low FFA content. However, acidic catalysts become important when dealing with cheap feedstock that contains high amounts of FFA (>0.5%), such as crude oils and waste oils. Unfortunately, acid catalyst requires extensive and expensive purification steps for recovery from the valuable esters. Hence this study investigated the production of biodiesel from crude palm oil (CPO) containing high FFA content by a two-stage ionic liquid–KOH catalyzed process. To evaluate their catalytic activities, two functionalized imidazolium ionic liquids (ILs) with different anions were tested for esterifying the FFA. RESULTS Among the ILs investigated, 1-butyl-3-(3-sulfopropyl)-imidazolium hydrogensulfate (BSPIMHSO4) was found to be the better catalyst. Based on the experimental results, a BSPIMHSO4 concentration of 4.0 wt%, methanol:CPO molar ratio of 12:1, temperature of 150°C, and agitation speed of 600 rpm offered FFA conversion of 95.7% within 2 h. In the second step, at optimum conditions of 6:1 mole ratio of methanol:esterified CPO, 60°C, 600 rpm and 50 min; 1.0 wt% of KOH was used a catalyst for the transesterification reaction. The results obtained showed that the properties of synthesized biodiesel conform with the international standard specifications. CONCLUSION To understand the catalytic behavior of the IL during biodiesel synthesis, the effect of ionic liquid on the kinetics of esterification catalysis needs to be considered. © 2013 Society of Chemical Industry