Direct synthesis of iso-paraffin fuel from palm oil on mixed heterogeneous acid and base catalysts

Abstract

This study focused on the synthesis of hydrocarbon fuel containing a high iso-paraffin and very low oxygen content from palm oil using a mixed acid–base catalyst. The catalysts were characterized by nitrogen adsorption–desorption, X-ray diffraction, hydrogen-temperature programmed reduction, carbon dioxide- and ammonia-temperature programmed desorption as well as thermogravimetric analysis. Solid base (MgO, CaO, SiO2, and Na2SiO3) and solid acid (HY, H-beta, HZSM5, and Al2O3) catalysts were individually evaluated for their catalytic activity in a semi-batch reactor in terms of the deoxygenation level of palm oil product. The best acid and alkali catalyst were then selected for mixing at different weight ratios and re-tested for their tandem catalytic performance in terms of the deoxygenation activity. Finally, the reaction temperature (400–460 °C), pressure in a nitrogen or hydrogen gas atmosphere and residence time were optimized. The main components in the liquid product obtained were normal paraffins, iso-paraffins, olefins and aromatics. For the single base catalysts, a liquid yield of higher than 65 wt% was obtained at a 460 °C using MgO catalyst, which also realized an excellent oxygen removal through decarboxylation and decarbonylation. For the single acid catalysts, the zeolite beta catalysts reached a liquid yield of around 55 wt% with high iso-paraffin content. The optimal MgO:beta zeolite weight ratio for the acid–base hybrid catalyst was 3:1, which resulted in a low oxygen content in the products with a high iso-paraffin (35%) content.