The long-term catalytic performance of mixed oxides in fixed-bed reactors in transesterification

Mg–Al and Mg–Fe mixed oxides with a constant molar ratio (3:1) were tested in the transesterification of rapeseed oil with methanol in a fixed-bed reactor. The mixed oxides were obtained from parent layered double hydroxides by calcination at 500 °C. The synthesized materials were characterized by several experimental techniques such as XRD, TG-MS, TPD-CO2, DRIFT and SEM. The transesterification was carried out at different weight hour space velocities (WHSVs; 1, 2 and 3 h-1) and different reaction temperatures (115, 150 and 200 °C), with every parameter tested for 32 h. Moreover, the stability of the catalysts was tested by the determination of the metal content in the reaction mixture. The ester yield increases with decreasing WHSV and with increasing reaction temperature. The Mg–Al mixed oxides were more active for all WHSVs and for temperatures of 115 °C and 150 °C due to the lower crystallite size and particularly higher concentration of basic species. For the reaction temperature of 200 °C, the catalyst activity was almost the same for both catalysts. A long-term catalytic test (300 h) for the verification of the catalyst lifetime and stability was also carried out with insignificant leaching of metals.