Zn,Al-catalysts for heterogeneous biodiesel production: Basicity and process optimization

Methyl esters produced by transesterification of vegetable oils are the main components of biodiesel, an alternative, biodegradable, non-toxic biofuel produced from renewable resources. The use of solid catalysts allows the development of environmentally friendly processes to produce biodiesel. In this work, Zn,Al-mixed oxides with different Al/(Al + Zn) molar ratios were studied as catalysts for the transesterification of soybean oil with methanol. TPD-CO2 (temperature programmed desorption of CO2) and model reactions such as retroaldolization of diacetone alcohol and 2-propanol transformation were employed to determine the basic properties of the catalysts. The catalytic activity was influenced by the chemical composition of the catalyst and showed a good correlation with basic site density determined by TPD-CO2. The RSM (response surface methodology) was used to select experimental conditions such as alcohol/oil molar ratio, reaction temperature, and catalyst loading that maximize fatty acid methyl esters yield. The best experimental conditions indicated by RSM were reaction temperature of 182.5 °C, catalyst loading of 5.0 wt.%, and alcohol/oil molar ratio of 45, that provided a biodiesel yield of 86% without significant leaching of the catalyst.