Intensification of synthesis of biodiesel from palm oil using multiple frequency ultrasonic flow cell

Biodiesel is one of the most promising alternatives for fossil fuels but the synthesis of biodiesel is hampered by significant mass transfer and equilibrium limitations along with higher energy requirements especially for the downstream processing. The present investigation focuses on the intensification of transesterification reaction for the generation of biodiesel using palm oil as the feedstock in the presence of KOH as a catalyst. For the first time, a triple frequency ultrasonic reactor (combination of 28-40-70 kHz) has been used for the intensification using palm oil with an objective of reducing the reaction time, molar ratio as well as possibly increasing the yield of biodiesel. The optimized parameters of reaction time, reaction temperature, and the obtained yield (%) in this ultrasound assisted system have been compared with the conventional approach of mechanical stirring. Also, within this ultrasound assisted approach, single, dual and triple frequency modes of operation have been compared to achieve an effective intensification. It has been observed that the cavitation effects were higher for the triple frequency operation as compared to the dual and single frequency operations. The maximum yield of biodiesel obtained with the triple frequency approach, at 3:1 molar ratio of methanol to oil with 1 wt.% potassium hydroxide as catalyst was 93% with a significantly reduced reaction time of 15 min as compared to 3 h required in case of conventional stirring to achieve 75% yield. The results of this investigation support that using multiple frequency ultrasonic irradiation is beneficial in intensifying the transesterification reaction. (C) 2014 Elsevier B.V. All rights reserved.