Preparation and Characterization of Sulfonated CaO Catalyst for Biodiesel Production from Waste Cooking Oil

Abstract

Biodiesel production depends on raw materials. Low-quality oils, such as cooking oil, crude palm oil, and sludge oil, are used to reduce costs, and they contain free fatty acids (FFA) and water. Soap can be produced when using the alkaline catalyst during transesterification. In this work, the sulfonation method prepared the esterification of waste cooking oil by sulfonated CaO as a bifunctional catalyst. The sulfonated CaO catalysts were characterized by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), temperature-programmed desorption of carbon dioxide and ammonia (TPD), BET surface area, and scanning electron microscopy (SEM). It was observed that the specific surface area, pore volume, and pore diameter of the CaO increased after being sulfonated with a 2 M sulfuric acid solution. It showed a high total surface acidity and basicity, 7.22 and 3.86 mmol/g, respectively. The optimal FFA conversion (84.94 %) from the waste cooking oil was acquired at a reaction temperature of 65 ˚C, a 9:1 MeOH: Oil molar ratio, and 5 wt% catalyst loading for a 3 h reaction time. The 2 M sulfonated CaO catalyst can be reused twice with a high FFA conversion without further treatment under optimized reaction conditions. The 2 M sulfonated CaO catalyst has potential treatment for biodiesel production from high-FFA oils due to its lower production cost and high catalytic activity.