Efficient production of biodiesel from ionic liquid catalyzed esterification using ultrasonic-microwave combined intensification

A novel approach was developed for producing biodiesel by acid ionic liquid catalyzed esterification of oleic acid and methanol under ultrasonic-microwave combined intensification. Four kinds of acid ionic liquids were synthesized as suitable catalysts. Some key parameters affecting oleic acid conversion were investigated using single factor experiments. Moreover, the production process was optimized via response surface methodology. The results indicated that the ionic liquid 1-(4-sulfobutyl)-3-methylmidazolium hydrosulfate exhibits good catalytic performance because of its double acid sites. The ultrasonic-microwave combined assistance can intensify the process to significantly shorten the reaction time from about 180 min to 15 min, thereby affording good industrial application potential. The specified regression model is accurate, reliable, and adequate for simulating actual production; the oleic acid conversion was 97.85 %, which is close to that achieved with conventional methods.