Catalytic autothermal reforming of biomass to synthesis gas

This thesis examines the catalytic partial oxidation (CPO) of biomass as a potentially more efficient alternative to existing biomass-to-fuel processing techniques. Chapter 2 examines existing literature describing catalytic partial oxidation, its application to gaseous, volatile liquid, and non-volatile liquid fuels, and common catalyst formulations for CPO. It is well documented that Rh-based catalysts provide the most effective and robust catalysts for the partial oxidation of biomass.;Traditional biomass processing technologies suffer from the production of undesired chars and tars resulting from relatively slow reaction rates and heat transfer limitations. Chapter 3 assesses the ability of the catalytic partial oxidation process to overcome these limitations by using the catalytic partial oxidation process to integrate three biomass-to-liquid process steps (volatilization of cellulose, tar-cleaning of organic products, and water-gas-shift of the gaseous effluent) into a single autothermal catalytic reactor for the production of high quality synthesis gas at millisecond residence times (~30 ms).;Chapter 4 focuses on the development of a reactor capable of improving the utilization of biomass-derived carbon during thermochemical conversion to synthesis gas. By co-processing hydrogen-deficient biomass (H/C~2) with hydrogen-rich feedstocks (H/C≥4) through catalytic partial oxidation over Rh based catalysts, it was demonstrated experimentally that 100% of the fuel carbon atoms fed to the reactor can be converted to CO. Such an improvement in carbon efficiency has the potential to double the yield of biofuels from the limited annual biomass supply. In addition to experimental results, reaction equilibrium calculations are presented describing the limits of the reaction system as dictated by thermodynamics.;Chapter 5 focuses on the reforming zone of the reactor, examining in depth the ability of Rh based catalysts to convert undesired tars to equilibrium synthesis gas products. Experiments were performed in a fixed bed reactor at temperatures of 650-850 °C and atmospheric pressure using C6H 6 as a model tar compound. Benzene conversion exhibited a strong dependence on temperature and H2O concentration in the feed. Significantly better catalyst performance was observed upon addition of Ce to the catalyst, which increased Rh dispersion and stability. The concentration of C 6H6 in the feed had very little effect on catalyst performance. CO2, H2, and CO co-feeds had positive, neutral, and negative effects, respectively, on C6H6 conversion.;Chapter 6 uses high speed photography (1000 frames per second) to reveal that direct impingement of microcrystalline cellulose particles (300 mum) with rhodium-based reforming catalysts at high temperature (700 °C) produces an intermediate liquid phase that reactively boils to vapors. The intermediate liquid maintains contact with the porous surface permitting high heat transfer (MW m2) generating an internal thermal gradient visible within the particle as a propagating wave of solid to liquid conversion. Complete conversion to liquid yields a fluid droplet on the catalyst surface exhibiting a linear decrease in droplet volume with time leaving behind a clean surface absent of solid residue (char).;The topics presented in this thesis examine in depth the technical feasibility of using catalytic partial oxidation to convert biomass to a clean synthesis gas product stream. Through extensive performance testing and process characterization, an in depth understanding of how the fuel feed is converted to product gases is described. Although preliminary testing with clean biomass feedstocks show promising performance with a rapid system approach to thermodynamic equilibrium, further studies are needed to examine the effect of biomass-derived inorganics from non-ideal feedstocks (e.g. corn stover) on Rh-based catalysts. Finally, a technical assessment of the economics associated with distributed catalytic partial oxidation of biomass to fuels and chemicals is needed to determine the feasibility of the overall process. (Abstract shortened by UMI.)...