Investigation, modelling and reviewing the effective parameters in microwave-assisted transesterification

Synthesis of biodiesel using so-called microwave (MW) energy at a frequency of 2.45 GHz is investigated in this work. In this frequency, energy can transfer in the scale of molecular size. Dipolar rotation and ionic conduction are two important mechanisms of energy transformation; Thus, an efficient and localized high temperature is produced that can assist reaction. In this study, we focused on effective parameters during transesterification. It was found that methanol produces a higher yield than the other alcohol types. It is due to methanol reorientation ability under the microwave irradiation, which may result in a better microwave absorption. Furthermore, the requirement for catalyst in this situation was reduced about ten-fold. Besides, an empirical model was generated to analyze and predict the effect of operating parameters. The model was based on fitting a wide range of different experimental results for homogeneous alkalic catalysis. The predictive power of developed model was within the temperature range of 40 and 80 °C, reaction time between 5 and 15 min and alcohol to oil molar ratio between 3 and 12. The optimum values in the mentioned ranges included the alcohol to oil molar ratio of between 1:6 to 1:9 in homogenous catalyst systems and 15:1-18:1 in heterogeneous one, reaction time within 3-5 min and the temperature within 65-90 °C. Finally a very good agreement between the model and experimental data was observed with error of±8% even with the other catalysts types.