Deoxygenation of Biomass Oxygenates to Hydrocarbon Fuels via Direct Methane Intervention
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One of the most pressing technical challenges in the production of biofuels from biomass is the unavailability of economical processes to remove 30-45% (w/w) of the oxygen that is present in biomass-derived oxygenates. The most promising technology that exists today is hydrodeoxygenation, which requires approximately 132 lb of hydrogen to deoxygenate every ton of biomass. The cost associated with the use of H2 for hydrodeoxygenation has an adverse effect on the economics of biofuels and the long-term sustainability of biorefineries. Therefore, there is a need for an economical and sustainable mechanism for removing oxygen (deoxygenation) from biorenewable feedstock to produce hydrocarbons. The overall objective of this study was to determine whether methane could be used as a direct hydrogen donor (instead of gaseous hydrogen) to deoxygenate biomass-derived oxygenates to produce hydrocarbons over an appropriate metal supported ZSM-5 catalyst. To test this idea and to elucidate the reaction characteristics, six separate studies were conducted, i.e., the proof of the concept, a thermodynamic study, a catalyst screening study, a chemical kinetics study, a catalyst deactivation study, and an economic analysis. It was observed that three separate reaction schemes involving methane and glucose pyrolysis vapor took place, depending on the type of metal or oxide used. The thermodynamic equilibrium analysis provided valuable insights concerning the theoretical limits of the desired products when a substrate reacted under a given set of conditions. At high temperature, it was observed that CO and H2 dominate the equilibrium mixture, with mole fractions of 0.597 and 0.587, respectively. The catalyst screening study indicated that the highest aromatic selectivity, i.e., 5.93%, was obtained for 5% Ga/ZSM-5 and that the highest furan conversion, i.e., 93.3% was obtained for5% Ni/ZSM-5. The chemical kinetics study indicated that the deoxygenation of furan was a first-order reaction with respect to the furan concentration and a second-order reaction with respect to methane concentration. The catalyst deactivation study indicated that at 500 °C coke formation reached a steady state with a coke yield of 8.0 %(w/w). The characterization of bio-oil derived from two types of feedstock, i.e., cellulose and sorghum, indicated that the presence of methane had a significant impact on reducing the oxygen content of bio-oil and increasing its heating value.
Gunawardena, Duminda Anuradh (2014). Deoxygenation of Biomass Oxygenates to Hydrocarbon Fuels via Direct Methane Intervention. Doctoral dissertation, Texas A & M University. Available electronically from