Hydrotalcite-like compounds containing transition metals as solid base catalysts for transesterification

Abstract

Hydrotalcite-like compounds (HTLCs) containing Mg 2+, Ni 2+ and Al 3+ layered double hydroxide (LDH) were synthesized by co-precipitation method and calcined at 773 K for 10 h performed as heterogeneous base catalysts for transesterification of soybean oil with methanol to produce biodiesel. These four different MgAlNi catalysts were characterized by nitrogen physisorption, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), temperature programmed desorption with CO 2 (CO 2-TPD), nitrogen adsorption–desorption. The Mg/Ni molar ratio varies over the range from 4 to 16 of the MgAlNi catalysts at a constant Al ratio in the hydrotalcite-like structures. The conversion of FAME was related to the basicity and Mg content of the MgAlNi catalysts, with MgAlNi 16 showing the highest basicity, and the lowest surface area due to Mg 2+–O 2− and Al 3+–O 2− pairs. The optimum conditions were obtained with a methanol/oil molar ratio of 21, 0.3% catalyst (w/w, oil), and 1200 rpm stirring speed for 4 h at 338 K, which results in the highest FAME conversion of 87%.