Physical and chemical analysis of ultrasonic transesterification through numerical simulation

Ultrasound assisted transesterification is increasingly standing out as a highly efficient, reliable and faster way to produce biodiesel from vegetable oil. Applying the same to other feedstock such as used cooking oil, beef tallow or fish oil etc. provides great advantage in terms of yield quality and production time. However, large-scale biodiesel production through ultrasound assisted transesterification is limited by the lack of a continuous sono-chemical reactor, which effectively processes a flow of reactants by simultaneously sonicating them. Design of such a reactor is a complex process since the mechanism is governed by multiple physics such as the ultrasound wave propagation, acoustic cavitation, reactive flow, chemical kinetics etc. In this work a previously designed sono-chemical reactor by the same author is worked upon using numerical simulation to analyze the effectiveness of sonication on the transesterification reaction. The ultrasound mechanism is simulated using the linear wave equation. The acoustic cavitation phenomena which also causes an attenuation of the wave has been accounted for using the complex wave number and impedance. A logical reaction rate coupling model is used to estimate the collective effect of sonication and flow agitation in the reactor. This model system is then applied to study the effect of sonication on the kinetics of reaction and a sensitivity study is carried out. Results show positive effect of alcohol molar ratio in flow agitation case whereas increased molar ratio decreased the sonication rate constant. Biodiesel formation had direct proportionality with applied power and fluid temperature, whereas for frequency sensitivity the results depended on wave number and impedance.