Synthesis of Highly Stable Heterogeneous Acid Based on Co-Doped Mil-100 (Fe) for Biodiesel Production

Abstract

Heterogeneous acids are widely used in catalyzing esterification for biodiesel production due to their low corrosivity and easy separation. While, the catalytic stability is still a challenge on account of active site leaching during successive batch experiments. To this end, the typical metal organic frameworks, MIL-100(Fe) doped with Co was adopted to load ammonium sulfate ((NH4)2SO4) for green and stable heterogeneous acid preparation, which was employed to catalyze the esterification of methanol and oleic acid. Influence of preparation factors of (NH4)2SO4 loading amount and activation temperature on catalytic activity were initially evaluated. Furthermore, to elucidate the effect of Co doping, catalysts were characterized by TG, XRD, FTIR, nitrogen adsorption-desorption, Py-FTIR, XPS, SEM and NH3-TPD. Results indicated that the maximum esterification conversion of 92.56 % was achieved by MS(Fe/Co) with molar ratio of methanol to oleic acid of 8 and catalyst amount of 8 wt.% at 70 °C in 2 h. In comparison to MS(Fe), Co doping significantly improved the reusability, where the catalytic activity of MS(Fe/Co) was increased by 20 % at the fifth cycle. The activation energy and pre-exponential factor of the esterification catalyzed by MS(Fe/Co) were also calculated as 42.06 kJ/mol and 5.24×105 min-1.

Keywords: Biodiesel, Heterogeneous acid, MOFs, Co-doped, stability, kinetics