A critical review of recent advancements in continuous flow reactors and prominent integrated microreactors for biodiesel production

Biodiesel is eco-friendly, less toxic and one of the most researched biofuels in recent years to reduce our reliance on fossil fuels and minimize emissions. The various problems associated with batch-type reactors are longer residence time, higher operating costs, and energy consumption with low production efficiency. Researchers are now focusing on continuous flow biodiesel production techniques to overcome problems in batch reactors. This paper highlights various reactors used in continuous flow biodiesel synthesis, catalyst mechanism, hybrid reactors technique and separation methods. Various continuous flow reactors used in biodiesel production have been discussed and the microreactor was intensively elaborated. Compared to traditional reactors, microreactor technology exhibits higher efficiency, improved mixing, high heat and mass transfer rates due to a high surface-area-to-volume ratio and short diffusion distance. The parameters that influence the liquid-liquid phase flow patterns in the microreactors include mixer type, channel size, internal configuration reaction time, reaction temperature, and alcohol to oil ratio. Post-treatment techniques help to improve the quality of the biodiesel and utilization of by-products has been discussed. The limitations and practical implications prevailing in the microreactors help improve the reactor techniques forward in large-scale production. Finally, the review addresses future directions in bridging the gap in current research on microreactors for better yield and high biodiesel quality.