(323a) Catalytic Production and Upgrading of Biomass Derived Monofunctional Hydrocarbons
AIChE Annual Meeting
2009
2009 Annual Meeting
Forest and Plant Bioproducts Division
Production of Fungible Biofuels From Lignocellulose
Tuesday, November 10, 2009 - 3:15pm to 3:40pm
We have studied the deoxygenation/ reforming of biomass derived carbohydrates to yield monofunctional hydrocarbons that can be utilized as fuels, commodity chemicals and solvents. Additionally, we have developed C-C coupling processes to upgrade these monofunctional species into fuel grade components that can be utilized in the current transportation infrastructure.
We have demonstrated the catalytic conversion of biomass-derived carbohydrates, including monosaccharides and sugar alcohols, into hydrophobic mixtures of monofunctional C4-C6 hydrocarbon species containing alcohols, ketones, heterocyclic compounds and carboxylic acids. The conversion occurs over carbon supported Pt-Re catalysts and removes more than 80% of the initial oxygen content of the sugars and polyols, yielding a spontaneously-separating organic phase. This process operates at moderate pressures (20-30 bar) and temperatures (283-523 K) and utilizes highly concentrated aqueous feeds (40-60%) of sorbitol or glucose. At 503 K and 18 bar, Pt-Re/C showed excellent stability for longer than one month time-on-stream and yielded an organic stream containing ~ 50% of the carbon found in the 60 wt% sorbitol feed. A yield of 70% of the maximum possible conversion of the carbon in sorbitol to monofunctional species was obtained, corresponding to the production of 1 kg of organic for every 4 kg of sorbitol.
Furthermore, we have studied catalytic C-C coupling processes to convert functional species (carboxylic acids, alcohols and ketones ) derived from carbohydrate conversion into C7-C12 ketones, that can be converted into diesel grade alkanes via deoxygenation over solid acid supported metal catalysts such as Pt/NbOPO4. These processes include ketonization ? in which two carboxylic acid molecules combine to form a linear ketone, CO2 and water, and aldol condensation/hydrogenation ? in which two ketone or secondary alcohol molecules combine to form a singly-branched ketone. We have studied ketonization of the aforementioned carbohydrate derived organic species over a CeZrOx catalyst at 648-673K and found near 100% conversion of carboxylic acids into C7-C11 linear ketones. The aldol condensation/hydrogenation process occurs on bi-functional catalysts that contain acid/basic functionality as well as metal sites to dissociate hydrogen. Aldol condensation/hydrogenation was studied over a low loading (0.25 wt%) Pd/CeZrOx catalyst at 623K, and was found to convert ~60% of the condensable ketones and alcohols found in the aforementioned carbohydrate-derived mixtures into C8-C12 branched ketones.
Further investigation of the aldol condensation/hydrogenation reaction was performed by examining the reactivity of a representative ketone - 2-hexanone over Pd/CeZrOx and CeZrOx catalysts at temperatures between 573 and 673 K, and pressures of 5 to 26 bar. Reaction kinetics studies show that in addition to the expected C12 condensation product (7-methyl-5-undecaone), the CeZrOx?based catalysts produce C18 and C9 secondary species, along with light alkanes (<C7). Low loadings of Pd (e.g., 0.25 wt. %) lead to optimal activity and selectivity for the production of C12 species. The high activation energy of C9 formation (140 kJ/mol) compared to the formation of C12 and C18 species (15 and 28 kJ/mol, respectively) indicate that these species may be formed as a result of the decomposition of heavier condensation products. The self-coupling of 2-hexanone was found to be positive order in both 2-hexanone and hydrogen. The addition of primary alcohols and carboxylic acids as well as water and CO2 to the feed was found to reversibly inhibit the self-coupling activity of 2-hexanone.