Hydrodeoxygenation of methyl palmitate over sulfided Mo/Al2O3, CoMo/Al2O3 and NiMo/Al2O3 catalysts

Abstract

The catalytic properties of sulfided Mo/Al₂O₃, CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts in the hydrodeoxygenation of methyl palmitate as a model compound for triglyceride feedstock were studied at 300 °C and 3.5 MPa in the batch reactor using n-tetradecane, m-xylene and hydrotreated straight-run gas oil (HT-SRGO). The comparison of catalyst's performance in n-tetradecane allowed us to see that the sulfided Mo/Al₂O₃, CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts revealed the same rate of the methyl palmitate conversion but the rate of the intermediate oxygenates conversion decreased in order: CoMoS/Al₂O₃ > NiMoS/Al₂O₃ > MoS₂/Al₂O₃. A mixture of linear saturated and unsaturated C₁₅ and C₁₆ hydrocarbons was produced when the oxygenates were fully consumed. The main products obtained over the Mo/Al₂O₃ and CoMo/Al₂O₃ catalysts were C₁₆ hydrocarbons (C₁₆/C₁₅ – 16.1 and 2.79, respectively); however, C₁₅ hydrocarbons were preferentially formed over the NiMo/Al₂O₃ catalyst (C₁₆/C₁₅ – 0.65), highlighting the different contributions of the hydrodeoxygenation (HDO) and decarboxylation/decarbonylation (DeCO_x) pathways during the hydroconversion of methyl palmitate over these catalysts. Investigating the solvent's influence on the activity of the CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts in the methyl palmitate HDO revealed that the reaction rate was decreased in the following order: n-tetradecane > HT-SRGO > m-xylene. The aromatic compounds did not retard the methyl palmitate transformation, but inhibited the conversion of the intermediate oxygenates. Decreased C₁₆/C₁₅ ratios were observed over both catalysts when m-xylene was used as the reaction medium instead of n-tetradecane.