Recyclable Li/NaY zeolite as a heterogeneous alkaline catalyst for biodiesel production: Process optimization and kinetics study

Due to the increasing demand for green and industrial biodiesel production, recyclable and stable catalysts need to be developed. Li/NaY zeolite catalysts with different molar ratios of Li2CO3 to NaY zeolite were synthesized from fly ash by hydrothermal and microemulsion-assisted co-precipitation method, and used to catalyze the transesterification of castor oil with ethanol. The structure, composition and morphology of Li/NaY zeolite catalysts were characterized by thermogravimetric (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area and Fourier transform infrared (FT-IR) spectroscopy. Under the optimized conditions of molar ratio of Li2CO3 to NaY zeolite of 1:1, calcination temperature of 750 °C and calcination time of 4 h for catalyst preparation, the FAEE yield of 98.6% was obtained (catalyst amount with respect to oil of 3 wt%, ethanol/oil molar ratio of 18:1, reaction temperature of 75 °C and reaction time of 2 h). The results show that the catalyst has excellent stability (including air tolerance and reusability) and a certain regenerative capacity (the FAEE yield was increased by 17% after activation treatment), which are crucial for industrial applications. Pseudo-first-order reactions and pseudo-second-order kinetic models were compared to demonstrate the proposed reaction mechanism. The pseudo-first-order reactions kinetic model was fit with experimental data (R2 = 0.9906). Activation energy of 57.37 KJ/mol was required for transesterification of castor oil into biodiesel using Li/NaY zeolite catalyst.