Esterification of a waste cooking oil using metal-hybrid catalysts for chemoenzymatic reactions

Abstract Waste cooking oil (WCO) serve as a cheap feedstocks for biodiesel production. However, the high acidity of this oil disqualifies it from using alkaline transesterification as the synthesis reaction for biodiesel production. Thus, the integration of enzymatic and chemical catalysts to form a hybrid catalyst for reducing oil acidity is a new option in the biodiesel industry. In the present study, five types of metal oxides and Candida rugosa lipase (CRL) were sequentially co-immobilized on the Alumina (Al2O3) for esterification of free fatty acid (FFA) to fatty acid methyl esters (FAMEs).The lowest FFA content achieved was 1.10% using CRL-CaO-Al2O3 for 24 h esterification reaction, correspond to a conversion rates of 66.94%. The FAMEs conversion of the treated WCO indicates that the hybrid catalyst also can perform transesterification of triglycerides in the oil. Among all the hybrid catalysts, CRL-MgO-Al2O3 shows the highest FAME conversion of 69.10%. The best immobilization time was recorded at 7 h which successfully reduced the FFA content until 1.39%. The application of heterogeneous enzyme-metal hybrid catalysts promise a better insight in the biodiesel industry in terms of its simplicity and catalyst recovery.