Doctor of Philosophy (PhD)


Engineering Science (Interdepartmental Program)

Document Type



Processing biomass in near- and supercritical water has garnered increasing attention because of its ability to accept a variety of wet feedstocks, energy efficiency, and ability to regulate the solubility and separation of components. Very few studies of biomass hydrothermal conversion provide a comprehensive evaluation of multiple process parameters and various additives and their effects on a single product phase. This research examined the influence of temperature, residence time, biomass concentration, and particle size on volatiles production from the hydrothermal conversion of sugarcane bagasse. Temperature had the greatest impact on volatile yields with the largest increase (23 wt %) occurring between 400 and 500 °C. The hydrogen mass yield increased 1000% between 300 and 600 °C. Increasing the residence time from 1 to 60 min resulted in a 49% increase in the mass yield of volatiles and 12.1% increase in the overall conversion of bagasse. The heating value of the volatile products declined after 10 min. Thermal cracking reactions dominated the early gas phase chemistry through 10 min but may have been accompanied by oxygenolysis of intermediate compounds at extended reaction intervals. In general, the use of Li/MgO and MnO2 catalysts improved the hydrothermal conversion of bagasse by 10%. An increased selectivity toward propylene production by both catalysts suggests metal oxide catalysts may promote partial oxidation via hydroxyl radicals. A side by side comparison of runs conducted in a Hastelloy X bomb and a titanium bomb revealed possible wall effects. The titanium bomb run produced 13 times more CO than the Hastelloy X bomb run along with at least 60 ppm of H2S. Lower hydrocarbon yields from the former run also support the theory that Ti is more catalytically active than Fe, Ni, and Cr in hydrothermal media. Chromatographic analysis revealed that methane in the volatile product generated from an experiment conducted using D2O instead of H2O had been perdeuterated, implying that hydrogen from the water medium is a labile participant in hydrothermal reactions. The Arrhenius parameters for bagasse hydrothermal conversion at 500 °C were determined as shown: Ea = 101.4 kJ•mol-1 and A = 1.28 × 109 min-1.



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Committee Chair

Constant, William David