Valorisation of low fatty acid content waste cooking oil into biodiesel through transesterification using a basic heterogeneous calcium-based catalyst

Abstract

This study presents the valorisation of waste cooking oil (WCO) and marble waste powder (MW) in the synthesis of biodiesel using ultrasonication. The novelty of this study is the development of environmental friendly catalysts from MW for biodiesel synthesis. Performance of five different catalysts such as MW, calcined marble waste powder (MWC), marble waste powder pretreated with acid followed by calcination (MWAC), marble waste powder precalcined followed by acid treatment and calcination (MWCAC) and commercially available CaO were utilized in the synthesis of biodiesel. Characterization of the catalysts was performed using X-ray diffraction (XRD), Transmission Electron Microscope (TEM) with Energy Dispersive X-Ray Analysis (EDX) and Brunauer–Emmett–Teller (BET) surface area analyser. The Box-Behnken method was used to design the sets of experiments followed by the optimization of parameters such as oil to alcohol molar ratio, catalyst concentration and temperature using the response surface methodology (RSM). Thereafter biodiesel synthesis was carried out at the optimized conditions in presence of all catalysts along with ultrasonication. Maximum yield of 95.45 and 98.81% was obtained using MWCAC and CaO in 180 min of reaction time at the optimized conditions of oil to alcohol molar ratio of 1:15.9, catalyst concentration of 6.8 wt% of oil and reaction temperature of 64.8 °C. Biodiesel synthesis carried out using conventional stirring method at the optimum conditions provided a maximum yield of 51.92% only in 180 min of reaction time. The present results delivers that ultrasonication reduced the energy requirement by 1.5 folds in biodiesel production as compared to conventional method.