Ti-incorporated SBA-15 mesoporous silica as an efficient and robust Lewis solid acid catalyst for the production of high-quality biodiesel fuels

Abstract

One-pot synthesized Ti-SBA-15 mesoporous materials with various Ti loadings of 0.808–6.78mol% were applied as heterogeneous solid acid catalysts for simultaneous esterification and transesterification of vegetable oils with methanol into high-quality biodiesel fuel (BDF) at 200°C under autogeneous pressure. According to the diffuse-reflectance (DR) UV–vis spectra, diffuse-reflectance infrared Fourier transform (DRIFT) spectra and pulsed ammonia (NH3) chemisorption studies combined with other conventional characterizations, the catalytically active site for high-quality BDF synthesis was mostly related to the tetrahedral Ti4+ species with weak Lewis acid character, which differential heat of NH3 adsorption was lower than 90kJmol−1. Due to that the tetrahedral Ti4+ species were accessible on largely mesoporous framework, the Ti-SBA-15 catalyst gave much higher activity in transesterification of crude Jatropha oil (CJO) with methanol than microporous titanosilicate of TS-1 and commercial TiO2 nanocrystallites. Among them, the 3Ti-SBA-15 catalyst with a Ti loading of 2.46mol% showed a highest fatty acid methyl ester (FAME) content of 90mass% at 200°C for 3h using a methanol-to-oil molar ratio of 27. When the reaction period and methanol-to-oil molar ratio were increased to 3–6h and 108, respectively, a great variety of edible and non-edible vegetable oils with various acid values (0.06–190mgKOHg−l), including refined soybean oil (RSO), refined rapeseed oil (RRO), waste cooking oil (WCO), crude palm oil (CPO), CJO and palm fatty acid distillates (PFAD), was directly transformed into high-quality BDFs, which met with a European standard (EN 14214:2009), over 3Ti-SBA-15 catalyst at 200°C. The used 3Ti-SBA-15 catalyst was easily regenerated by calcination and its high activity was maintained. Most importantly, the 3Ti-SBA-15 catalysts could resist 5wt% of water or 30wt% of free fatty acid (FFA), which tolerance levels were several ten times better than those of homogeneous and heterogeneous catalysts in the current BDF production technology.