Process intensification of transesterification for biodiesel production from palm oil: Microwave irradiation on transesterification reaction catalyzed by acidic imidazolium ionic liquids

In the study, to improve the efficiency of acid-catalyzed biodiesel production process, three acidic imidazolium ionic liquids were synthesized and employed to the production of biodiesel from palm oil under microwave irradiation. The prepared ionic liquids were characterized by NMR, FT-IR and TG-DTG. Among the three ionic liquids, ([HSO3-BMIM]HSO4) was proved to be the most suitable catalyst because of the excellent catalytic performance. Single factor experiments and response surface methodology (RSM) were conducted to investigate various reaction conditions to obtain the optimal condition, and the results indicated that ionic liquid dosage was the most significant variable. A maximal yield of 98.93% was obtained while mole ratio of methanol to oil, ionic liquid dosage, microwave power and reaction time were 11:1, 9.17%, 168 W and 6.43 h, respectively. We also studied the kinetic of transesterification under microwave irradiation, which could be appropriately expressed by the pseudo-first-order kinetic model. Compared with conventional experiments, microwave irradiation can be regarded as an efficient process intensification method for biodiesel production which has the capacity to shorten reaction time and save energy up to more than 44%. In addition, the ionic liquid catalyst showed excellent operational stability with biodiesel yield of 84.76% after six cycles.