Effect of alumina loading on the properties and activity of SO42-/ZrO2 for biodiesel production: Process optimization via response surface methodology

The key challenges for the production of biodiesel are the utilization of cheap oils, such as waste cooking oil (WCO), and insensitive and active heterogeneous catalysts. Therefore, in this study, an alumina supported sulfated zirconia (SZ) nanocatalyst was synthesized using the solvent-free method and the effect of the optimal percentage of aluminum precursor (Al-P) was examined on its activity in the transesterification of WCO to biodiesel. The catalysts were characterized by XRD, FT-IR, BET surface area, and TEM analyses, and their acidity was determined by the NaOH titration method. The results revealed that SZ supported with 25 mol% of Al-P has the best catalytic properties due to its highest fraction of tetragonal phases of zirconia and lowest crystalline size, well bonded sulfate groups with zirconium and aluminum ions and highest acidity. Moreover, the transmission electron microscopy (TEM) images confirmed the reduction of particle size in SZ from, approximate to 125 nm to approximate to 7 nm by the loading of alumina. Then, transesterification reaction parameters and their interactions were evaluated and optimized using the response surface methodology (RSM). The statistical analysis explained that reaction temperature and time have the most influence on the conversion of WCO. In addition, the interaction of reaction temperature with methanol/WCO ratio and time affected the biodiesel process. The optimum reaction parameters were obtained as 148.5 degrees C, 2.9 wt.% of the catalyst, 12.7 molar ratios of methanol/WCO, and reaction time of 93 min. The yield of 93.5% was attained and the nanocatalyst preserved its activity for at least four times with an only approximate to 10% reduction in the conversion. (C) 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.