CaO-Al₂O₃ calcined aerogels and alcogels for heterogeneous catalytic production of biodiesel from waste cooking oil

Abstract

The depletion of the world’s petroleum reserves, increasing energy demand, and rising greenhouse gas emissions led to the search for an alternative and renewable sources of energy. Biodiesel has become the most promising substitute or additive to diesel fuels since it is renewable, clean, and share similar properties to diesel. In this work, CaO-Al₂O₃ calcined aerogels and alcogels were synthesized for the transesterification of WCO using a rapid epoxide-initiated gelation sol-gel method. All synthesized catalysts were characterized using FTIR spectroscopy, nitrogen adsorption-desorption technique, scanning electron microscopy, X-Ray diffraction, and thermogravimetric analysis. Characterization revealed that the calcined aerogels at low CaO content were not as affected by calcination at 700 oC as their corresponding calcined alcogels. Furthermore, calcined aerogels at low CaO content maintained a different structure than their corresponding calcined alcogels. The 3:1 CaO-Al₂O₃ calcined aerogel showed the best catalytic activity using the minimum amount of material to produce high biodiesel yield and conversion with no soap formation. The effect of CaO content, catalyst loading, methanol to oil ratio, and reaction time on biodiesel production was investigated. After optimization of the parameters, a maximum biodiesel yield (89.84 percent) with highest purity (98.04 percent) was achieved under the following optimum conditions: 1 wt. percent 3:1 CaO-Al₂O₃ calcined aerogel, 11:1 methanol to oil molar ratio, 65°C, and 4 hours. The transesterification reaction followed a pseudo first order kinetics. This work compared the activities of calcined aerogels and alcogels for the production of biodiesel from WCO in an economical and eco-friendly process.