Applied Energy, Vol.185, 2151-2159, 2017
Intensification of transesterification via sonication numerical simulation and sensitivity study
Transesterification is known as slow reaction that can take over several hours to complete. The process involves two immiscible reactants to produce the biodiesel and the byproduct glycerol. Biodiesel commercialization has always been hindered by the long process times of the transesterification reaction. Catalyzing the process and increasing the agitation rate is the mode of intensifying the process additional to the increase of the molar ratio, temperature, circulation that all penalize the overall process metrics. Finding shorter path by reducing the reaction into a few minutes and ensures high quality biodiesel, in economically viable way is coming along with sonication. This drastic reduction moves the technology from the slow batch process into the high throughput continuous process. In a practical sense this means a huge optimization for the biodiesel production process which opens pathways for faster, voluminous and cheaper production. The mechanism of sonication assisted reaction is explained by the creation of microbubbles which increases the interfacial surface reaction areas and the presence of high localized temperature and turbulence as these microbubbles implode. As a result the reaction kinetics of sonicated transesterification as inferred by several authors is much faster. The aim of this work is to implement the inferred rates in a high fidelity numerical reactive flow simulation model while considering the reactor geometry. It is based on Navier-Stokes equations coupled with energy equation for non-isothermal flow and the transport equations of the multiple reactive species in an annular continuous reactor. Following model validation, the spatial reaction rate is evaluated to bring more insight to the reaction progression and species distributions. The two methods (conventional and sonication) then are compared on the basis of their sensitivity to the Alcohol:Oil molar ratio. The spatial distribution of the yield and their favorable sonication method is a key enabler of the development of an optimal process reactor that renders more economy to the process when operating at lower AL:TG ration, catalyst amount, and temperature. (C) 2016 Elsevier Ltd. All rights reserved.