Deoxygenation of beef fat for the production of hydrogenated biodiesel over Pd and NiMo catalysts : effect of catalyst support

Abstract

Hydrogenated biodiesel is one of the biofuels not containing oxygen in its molecules. The absence of oxygen leads to many advantages such as high cetane number, high heating value, and high miscibility with fossil fuels. In this research, the effect of catalyst supports on the production of hydrogenated biodiesel using beef fat as feedstock has been investigated. Pd-based catalysts (Pd/Al₂O₃, Pd/F-Al₂O₃, Pd/SiO₂, Pd/TiO₂, Pd/C, and Pd/KL) and NiMo-based catalysts (i.e. NiMo/Al₂O₃, NiMo/F-Al₂O₃, NiMo/SiO₂, NiMo/TiO₂, NiMo/C, and NiMo/CeO₂-ZrO₂) were prepared by incipient wetness impregnation. The fresh and spent catalysts were characterized by XRD, TPR, BET, and TPO. The prepared catalysts were tested in a continuous flow packed-bed reactor at 500 psig, 325°C, H₂/feed molar ratio of 30, and LHSV 1 h⁻¹. The products obtained from all catalysts were hydrocarbons in diesel specification range. The results showed that by varying catalyst supports the corresponding catalyst had different properties in term of surface area and metal particle size. The triglyceride conversion increased with decreasing Pd crystallite size. However, hydrocarbon selectivity was not significantly changed with catalyst supports. The main products from Pd catalysts were heptadecane and pentadecane, resulting from hydrodecarbonylation. Among Pd catalysts, Pd/TiO₂ exhibited the highest hydrocarbon yield. For NiMo catalysts, octadecane and hexadecane were the main hydrocarbon products, resulting from hydrodeoxygenation.