High-efficiency biodiesel production using rotating tube reactor: New insight of operating parameters on hydrodynamic regime and biodiesel yield

Transesterification is a preferred reaction in biodiesel production using oil and alcohol as feedstocks. The major limitation of biodiesel production is the immiscibility of reactants resulting in the slow reaction rate. The development of an intensification reactor is the main purpose to eliminate the limitation and to increase the production capacity. The present research explored the state of the art for the hydrodynamic regime inside the rotating tube reactor (RTR) to enhance the biodiesel production rate using alkali-catalyzed transesterification based on the design specification. The influence of operating conditions in terms of methanol-to-oil molar ratio, NaOH loading, total flowrate, rotational speed using two dimensionless numbers, i.e. rotating Reynolds number (Rer) and Taylor number (Ta), as well as torque, were originally proposed to determine the optimal operating condition for biodiesel production in this RTR. This was interesting to report that the modulated wavy vortex flow is required to promote biodiesel yield in the RTR. The increment values of Rer, Ta and torque associated with the turbulent Taylor vortex flow regime allowed the high reaction temperature which can generate excessive heat raising the methanol vaporization rate, leading to reduced biodiesel yield. Therefore, the optimal operating condition of this RTR was found to be 6:1 methanol-to-oil molar ratio, total flowrate of 30 mL/min, rotational speed of 1000 rpm at room temperature giving the highest yield of 97.5% with yield efficiency of 3.75×10−3 g/J and the quality of biodiesel met the ASTM specification.