A review of intensification technologies for biodiesel production

Biodiesel is a biodegradable and renewable source fuel and as such it contributes to the reduction of environmental pollution. It is also nontoxic, produces less sulfur oxide emissions and greenhouse gases compared to conventional fossil fuels. Among the chemical reactions, that is, transesterification, esterification, and interesterification reactions, transesterification reaction is the most famous for biodiesel production that is adopted in the industry. The most commonly used technology for biodiesel production is mechanical stirring via transesterification by converting oil with an alcohol to fatty acid alkyl esters and glycerol. The main factors affecting the yield of biodiesel are a molar ratio of oil to alcohol, reaction temperature, catalyst concentration, type of catalysts, reaction time, mixing intensity, and feedstock quality. The main drawback of the transesterification reaction is limited by mass transfer resulting in a much lower reaction rate and also much higher cost compared to diesel fuel. To solve these drawbacks, intensification technologies (i.e., microwave, reactive distillation, ultrasonic cavitation, and hydrodynamic cavitation) have drawn the attention to overcome these aforementioned problems to eliminate the mass transfer resistance of immiscible reactants in shorter reaction time and lower energy consumption against mechanical stirring. In a range of technologies available for intensification, the hydrodynamic cavitation-based approach could be considered as an effective one to assist and intensify the transesterification. The yield efficiency in relation to the method was in the following order: hydrodynamic cavitation > reactive distillation > microwave > ultrasonic cavitation > mechanical stirring. This paper reviews the recent achievements of the different approaches of intensification technologies. The merits and limitations of these various intensification technologies have been discussed in this paper.