Biodiesel production optimization from waste cooking oil using green chemistry metrics

Abstract

Biodiesel is a promising alternative to fossil energy, especially when non edible feedstocks are used in the production process. In the present work, biodiesel was produced from university campus restaurants waste frying soybean oil by means of transesterification reaction.The objective of this study was to reduce the energy and reactants consumption and waste generation to achieve a truly green process. For this purpose, a multiobjective optimization using central composite design (CCD) was performed considering three responses: the reaction conversion, the energy consumption and the green chemistry balance. The last two parameters i.e. the energy consumption and the green chemistry balance were considered as responses for the first time, hence an interesting originality. Temperature, KOH catalyst amount and oil to methanol molar ratio were the CCD independent variables.Five green metrics were used to account for the greenness of the reaction, namely: carbon efficiency, atom economy, reaction mass efficiency, stoichiometric factor and environmental factor.The obtained quadratic models for the prediction of the optimum responses fitted reasonably well the experimental data. The results showed a maximum oil conversion of 100%, minimum energy consumption of 2.69 kJ and maximum green chemistry balance of 77.36% at KOH catalyst concentration of 2 wt%, methanol to oil molar ratio of about 4.73 and a minimum temperature of 45 °C.The physicochemical properties of the produced biodiesel agreed well with the international standards ASTM (American Society for Testing and Materials).