Transesterification of soybean oil catalyzed by fly ash and egg shell derived solid catalysts

A fly ash supported heterogeneous CaO catalyst has been developed using waste egg shell for transesterification of soybean oil to yield fuel grade biodiesel. The active metal precursor Ca(OH)2 of the catalyst has been economically derived from waste egg shell calcination and the mesoporous, high activity strong base catalyst has been prepared using wet-impregnation method. X-ray diffraction (XRD), scanning electron microscope (SEM), low temperature N2 adsorption–desorption (BET) and BJH method studies manifested the well-dispersed presence of CaO over the fly ash framework. The specific surface area of 0.701 m2/g, pore volume of 0.0044 cm3/g, 5.2 nm pore diameter and 1.6 mmol HCl/g catalyst basicity rendered high catalyst activity which could be demonstrated through high biodiesel yield from refined soybean oil by transesterification with methanol. A three factor–three level face centered central composite design (FCCD) has been used to evaluate the effects of process parameters on yield of fatty acid methyl ester (FAME). Optimal parametric values computed using response surface methodology (RSM) corresponding to maximum (i.e. 96.97%) FAME yield were CaO loading of 30 wt.%, 1.0 wt.% catalyst concentration and 6.9:1 methanol/oil molar ratio. The developed catalyst exhibited higher reusability characteristic and superior catalytic activity compared to unsupported CaO catalyst derived from egg shell. An effective waste valorization avenue could, thus, be procreated through preparation of a novel low cost heterogeneous catalyst from these industrial and municipal wastes for synthesis of fuel grade biodiesel.