Preparation of sulfated zirconia catalyst loaded by copper in 'nano-scale: Green application' to synthesis of biolubricant

Abstract

THIS STUDY investigates the activity of copper-doped catalysts supported on sulfated zirconia (SZ) for the esterification of Free Fatty Acid (FFA). Three catalysts SZ, Cu/SZ (sol) and Cu/SZ (imp) were prepared. The latter two catalysts contain 10% Cu supported on sulfated zirconia (Cu/SZ) prepared by wet impregnation (Cu/SZ/(imp)) and sol-gel method (Cu/SZ/(sol)). The catalysts were characterized by X-ray diffraction (XRD), NH3 Temperature Programmed Desorption (TPD), N2 adsorption, Fourier transform infrared spectroscopy, and imaged by scanning electron microscopy. The XRD analysis showed that, the loading of Cu in the zirconia structure has stabilized the tetragonal zirconia phase, which is the most active phase. Also, the formation of Cu2O and (CuO-ZrO) composite has been proved for the sol-gel preparation technique. The TPD illustrated that the incorporation of Cu ions in the lattice of zirconia via sol-gel technique has lowered the acidity of the catalyst much more than impregnation technique. As a green application, different concentrations of the prepared catalysts were used for preparation of biolubricants by direct esterification of FFAs. The Cu/SZ/(sol) catalyst has the highest activity. The percentage yields of synthesized biolubricants reached 99.8% when 0.3 % from the selected catalyst was utilized. Pour point, Flash point, Viscosity index, Apparent Viscosity and Percentage yield values of synthetic ester oils were evaluated.