Process intensification in biodiesel production using unconventional reactors

[Display omitted] •Biodiesel production in unconventional reactors is critically discussed.•Mixing improved in static and chaotic mixers, cavitation reactor, OFRs, and Microreactor.•Heat and mass transfer are also facilitated by unconventional reactors.•Biodiesel separation was eased in reactive distillation and membrane reactors.•Plasma reactor reduced the reaction time and avoided catalyst for biodiesel production. This review discussed unconventional reactors for biodiesel production including static and chaotic mixers, hydrodynamic cavitation reactor, oscillatory flow reactor (OFR), rotating/spinning-tube reactor, reactive distillation, plasma-, spiral-, membrane-, ultrasonic-, microwave-, and microchannel reactors. Mixers and OFR eased biodiesel production with improved mixing, reduced methanol consumption, and faster reaction time. Cavitation and ultrasound reactor intensified oil/catalyst surface area, mass transfer,and transesterification reaction. Rotary/spinning tube reactors enabled shear stress on oil/alcohol films, providing a high surface area/volume ratio and high interactions between the reactants. Plasma reactor avoided catalyst use and enabled biodiesel production 20 – 25 folds faster than the conventional reactor. Reactive distillation with membrane reactors avoided the separation issue. Spiral reactor facilitated enhanced heat transfer between the reacting mixtures with net energy ratio and energy efficiency of 0.92 and 0.98, respectively. Microwave reactors enabled local heating of reactants and resulted in uniform heating of the reaction mixture. Microreactors enabled short diffusion distance, improved surface area/volume ratio, and enhanced heat and mass transfers than conventional reactors. Thus, the unconventional reactors appeared promising to intensify biodiesel production, however, significant efforts are needed to reach their applications in commercial biodiesel production.