Strategies for the Catalytic Conversion of Lignocellulose-Derived Carbohydrates to Chemicals and Fuels.

摘要

Biomass, being the only renewable source of carbon, has the potential to serve as a sustainable platform for the production of energy and chemicals, in this era of diminishing supplies of fossil fuels. The conversion of lignocellulose to fuels and chemicals requires the effective utilization of the hemicellulose and cellulose portions. Catalytic processing strategies for these two portions were developed and studied through key platform molecules.;First, catalytic processing of two cellulose-derived intermediates, glucose and levulinic acid, were investigated. As shown previously, glucose (and sorbitol) could be converted over PtRe/C to monofunctional molecules (alcohols, ketones, carboxylic acids and heterocycles), which could then be upgraded by consecutive C-C coupling reaction steps, i.e., ketonization and aldol condensation, to fuel grade alkanes. In this thesis, the aldol condensation step was studied over Pd dispersed ceria-zirconia mixed oxide catalysts. Among the mixed oxides, Pd/ZrO2 displayed the highest activity, as well as good resistance to inhibition by CO2 and water, two by-products of ketonization. Therefore, Pd/ZrO2 allowed for integration of aldol condensation/hydrogenation step with ketonization in a single reactor dual-bed system. As an alternative, cellulose can be processed through the intermediate formation of levulinic acid. A valuable fuel-precursor, gamma-valerolactone, was obtained from levulinic acid via the formation of levulinate and formate esters for improved management of sulfuric acid. The esters were obtained from the corresponding acids by a reactive extraction step using butene.;Two alternative hemicellulose processing strategies were also developed for the production of furfural. In the first strategy, hemicellulose-derived xylose is converted to furfural in a biphasic system with a novel solvent (2-sec-butyl-phenol, SBP) and use of mineral acids. Increased concentrations of furfural compared to the feed could be obtained due to the exceptionally high partition coefficient of furfural in the SBP-water biphasic system. An alternative strategy involves the conversion of xylose in a monophasic system with another novel green solvent (gamma-valerolactone) using solid acid catalysts (i.e., H-mordenite) with high yields. Importantly, the furfural degradation reactions were found to be dominated by condensation reactions, rates of which could be decreased significantly when gamma-valerolactone was used as the solvent instead of water.