UPGRADING OF BIOMASS-DERIVED MOLECULES FOR FUELS VIA HYDRODEOXYGENATION ON SUPPORTED METALS

Abstract

Biomass-derived molecules such as aldehydes and alcohols have been upgraded to more valuable products via hydrogenation and hydrodeoxygenation on supported metals. For unsaturated aldehydes, the competitive hydrogenation of C=C and C=O may result in an unsaturated alcohol, a saturated aldehyde, or a saturated alcohol. Hydrogenation of 2-methyl-2-pentenal has been studied for supported Pt, Pd and Cu catalysts. The activity follows the order Pt>Pd>Cu. While Pt and Pd primarily catalyzed hydrogenation of the C=C bond to 2-methyl-pentanal, Cu catalyzed hydrogenation of both C=C and C=O but more selective for C=O at low space times, and at high space times forming 2-methyl-pentanol which has good fuel property, compared to ethanol or n-butanol.

For coupling reaction to higher carbon chain length, di-methyl-pentyl ethers have been selectively produced from etherification of aldehydes and alcohols on supported Pd catalysts. A yield of 79 % ether with a selectivity of 90% was observed when feeding 2-methyl-pentanal with 2-methyl-pentanol at a molar ratio 1:1 at 125oC. The side product is n-pentane from decarbonylation of the aldehyde. Cross etherification of n-butanol with 2-methyl-pentanal shows a much higher rate than that observed when the alcohol or aldehyde is fed alone. This enhanced activity is consistent with the catalyst requirement for large ensembles that allow surface alkoxide species next to an eta-2 adsorbed aldehyde. The ether yield increases with increased metal loadings and increased reduction temperatures, suggesting etherification is sensitive to metal particle sizes.

Bimetallic Pd-Cu catalysts have been studied for the hydrogenation and deoxygenation of 2-methyl-pentanal. Compared to Pd catalysts, Pd-Cu shows a decrease in conversion of 2-methyl-pentanal. At low space time, 5% Pd-2.5% Cu/SiO2 exhibits high selectivity for hydrogenation to 2-methyl-pentanol and substantially reduces decarbonylation activity compared with pure 5% Pd/SiO2. The bimetallic shows that selectivity for etherification is much greater than Pd alone, since the parallel decarbonylation is reduced. The bimetallic maintains good ether selectivity due to its ability to readily hydrogenate the aldehyde to the intermediate alcohol and continue to form the required surface alkoxide in proximity to the remaining eta-2 sites.