Preparation and Characterization of Mixed Metal Oxides as Solid Catalysts for Transesterification of Triglycerides

Abstract

Energy consumption is essential for the human survival and major portion of the human energy requirement is coming from the non renewable sources such as fossil fuel. In this contest biodiesel has gained significant attention in recent past as renewable alternate for conventional diesel fuel. Chemically, biodiesel is mono alkyl esters of fatty acids which are produced via transesterification of triglycerides in presence of heterogeneous, homogeneous or enzyme catalysts. Traditional homogeneous basic catalysts (NaOH and KOH) are highly effective for industrial scale biodiesel production as they could catalyze the reaction under ambient reaction conditions. However, this process yielded catalyst contaminated biodiesel and glycerol and huge quantity of effluents are generated during their purification. Additionally, homogeneous alkali catalyst due to their sensitivity towards moisture and free fatty acids (FFA) could not be used for the transesterification of waste cottonseed oil and required FFA and moisture free costlier refined oil. In order to circumvent the problem associated with homogeneous catalyst, development of reusable heterogeneous catalysts has gained significant attention in recent past. In present thesis, mixed metal oxides such as KF/CaO/NiO, Li/CaO, Li/NiO, W/Ti/SiO2 and Na/CaO/Fe3O4 were prepared and characterized by powder XRD, BET surface area, FESEM, HRTEM, TPD and Hammett indicators studies. These catalysts were successfully employed for the transesterification of waste cooking (cottonseed) oil to produce biodiesel. CaO/NiO impregnated with 20 wt% KF was found to have the basic strength of 15.0 lt H_lt 18.4 and required 4 h to yield the complete transesterification of waste cottonseed oil (gt 98% FAMEs yield) with methanol under optimized reaction conditions. Further, reusability study of the catalyst has demonstrated that it was able to catalyze four catalytic cycles without significant loss in activity.