Significant parameters and technological advancements in biodiesel production systems

•Continuous mode supercritical biodiesel production offers less energy consumption.•Microwave transesterification should be monitored to keep uniform temperature profile.•Hydrodynamic cavitation provides high efficiency by decreasing the reaction times.•For hydrodynamic cavitation optimum hole to pipe diameter ratio should be taken as 20.•For ultrasonic transesterification amplitude and cycle rate influence the yield. Biodiesel is a mixture of fatty acid esters formed by transesterification of vegetable oil, animal fat, algae oil or waste oil with an alcohol like methanol (CH3OH), ethanol (C2H5OH) or higher alcohols. There are many important catalytic variables like catalyst type and composition, support type and pretreatment conditions (i.e. calcination temperature and time) which are utilized to achieve high yields for the transesterification reaction. In addition, operational conditions such as reaction temperature, alcohol type, alcohol to oil molar ratio and stirring speed have also quite high significance. Moreover, all these variables can be optimized under supercritical conditions by novel techniques like ultrasonic and microwave irradiation or hydrodynamic cavitation. In this work, significant catalytic and operational variables for biodiesel production are reviewed. In addition, dominant parameters together with their limitations during the application of advanced technologies are investigated in detail. Then, it has been concluded that, for better control and higher yields of biodiesel production, future research works should focus on addition of co-solvents, use of longer chain alcohols, bulky structures or ionic liquids, adjustment of mode of irradiation and modification of the instrumentation or the equipment.