Castor oil transesterification catalyzed by a new red mud based LiAlO2-LiFeO2 composite

Abstract

In this study, a new low-cost LiAlO2-LiFeO2 composite (Li/RM) was prepared through a simple solid-state reaction using red mud (RM) as raw material, and the transesterification of castor oil with methanol for biodiesel production was carried out with the prepared Li/RM composite. The optimum preparation parameters of Li/RM composite were obtained, and the optimum preparation parameters were as follows: mass ratio of Li2CO3 to RM 2.5:1, calcination temperature 900 °C and calcination time 3 h. The synthetic catalysts were characterized by Thermogravimetric-Differential Thermogravimetric (TG-DTG), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and CO2-Temperature programmed desorption (CO2-TPD). The biodiesel conversion of 96.32% was obtained under optimal parameters of reaction temperature of 65 °C, catalyst amount of 5 wt%, reaction time of 2.5 h and methanol/oil molar ratio of 15:1. Meanwhile, the kinetics and thermodynamics studies revealed that the transesterification reaction of castor oil obeyed the pseudo-first-order kinetics and was an endothermic, non-spontaneous reaction. The possible catalytic mechanism catalyzed by Li/RM catalyst was further investigated. Besides, the Li/RM composite had an excellent air tolerance and retained its good reusability after four cycles, indicating that Li/RM was an efficient and durable heterogeneous catalyst for biodiesel production.