Continuous biodiesel production: A review of advances in catalysis, microfluidic and cavitation reactors

Biodiesel production can be achieved through different processes and different reactor types as well as varying reaction parameters such as catalyst dose, oil: alcohol ratio, reaction time, mixing intensity, free fatty acid content (<3% required) and reaction temperature. The present review presents the advances in catalytic biodiesel production with emphasis on the current challenges, and prospects in homogeneous and heterogeneous catalysts. Particularly, alkaline earth metal, metal mixed oxides, carbon-based and biomass-derived catalysts, and ionic liquids are discussed in detail. In addition, microfluidic, and acoustic reactors such as ultrasonic and hydrodynamic cavitation reactors are reviewed. The results from conducted studies revealed calcium oxide (CaO)-based catalysts derived from either residual biomass sources or synthetic chemicals are more favorable for biodiesel synthesis. Hydrotalcite catalysts and ionic liquids require harsh conditions such as higher temperature, higher oil: methanol ratio, and longer reaction time to achieve appreciable yield. The micro-reactors and cavitation reactors provide a faster reaction rate compared to conventional reactors because there is a drastic reduction in the time it takes for miscibility and diffusion of the reactant molecules and hence, eliminates the high energy requirement for mixing. The hydrodynamics reactor presents lower erosion challenges and energy input per unit of reactants when compared with the ultrasonic reactor. It is hoped that this study will provide detailed and recent knowledge on heterogeneous catalysts, microfluidic, and cavitation reactors for biodiesel synthesis.

Automated summary

The use of carbon-based and biomass-derived catalysts for biodiesel production enhances synthesis efficiency. Microfluidic and acoustic reactors can accelerate reaction rates and reduce energy consumption.