Selective hydrogenation of biomass-derived fatty acid methyl esters to fatty alcohols on RuSn–B/Al2O3 catalysts: analysis of the operating conditions and kinetics

Abstract

Catalyst preparation, reaction process conditions and kinetics of the selective hydrogenation of fatty acid methyl esters (FAME) over a noble metal catalyst were studied. Two catalysts were prepared by impregnation of γ-Al₂O₃ with Ru (1% mass content) as active metal and Sn and B as modifiers (2% mass content), and with different Sn/Ru ratios of 2 and 4. FAME derived from biomass, an environment friendly raw material, was used for the preparation of fatty alcohols by selective hydrogenolysis of the ester group to an alcohol group. The results were analyzed with a simple kinetic model using lumped pseudocomponents. When comparing the two catalysts it was found that the most effective catalyst for producing oleyl alcohol was the one with a Sn/Ru ratio of 2, RuSn2–B. The maximum production of alcohols and alkanes was achieved with this catalyst at 290 °C. At 270 °C a lower production of alkanes was obtained but with a similar yield of alcohols. Both reaction conditions and catalyst composition were found to be important factors influencing alcohol production. Two types of active sites were identified on the studied catalysts: the unmodified Ru⁰ metal for dissociating hydrogen and the modified metal, (Ru⁰–(SnO_x)₂, for adsorbing the C=C carbons. RuSn2–B seemingly exhibited an appropriate balance of these sites. The kinetic model included the reactions of esters, hydrogen, alcohols and deoxygenated hydrocarbons. These were studied with lumped variables with no distinction of individual specific molecules. In spite of this, the model provided a very good fit of the experimental data indicating that the reaction is rather insensitive to secondary features like carbon chain length or group positions.