Treatment of Aqueous Biomass and Waste via Supercritical Water Gasification for the Production of CH4 and H2

The present study targets to convert aqueous fraction of fast pyrolysis oil into methane and hydrogen gases via supercritical water gasification (SCWG). Water above its critical point is referred to as supercritical water, which has unique properties such as a loss of hydrogen bonding, becoming an excellent solvent for organic compounds. In this thesis, SCWG was used to gasify slurry materials into high calorific gases including CH4 and H2. Production selectivity towards more methane or hydrogen was affectively controlled by operational conditions. However, in the absence of catalyst (bank test), gas formation was very minimal. SCWG of glucose as an organic model compound was studied to screen the best catalyst for methane production. Ni20%Ru2%/γ-Al2O3 catalyst was able to convert all carbon in glucose to gases at a temperature of as low as 500 °C and weight-hourly space velocity (WHSV) of 3 h-1. This catalyst significantly promoted methane production and produced 0.5 mol methane per mole of carbon in the glucose feedstock. High stability and activity of this catalyst were observed during 20 hours on stream. It was also found out from this study that nickel loading, temperature, substrate concentration and feeding rate or WHSV greatly affected carbon conversion and yields of CH4 and H2 in SCWG. For instance, higher temperatures favor hydrogen formation while lower temperatures promote methane yield. Moreover, the Ni20%Ru2%/γ-Al2O3 catalyst demonstrated to be active for gasifying the aqueous fraction of fast pyrolysis oil via SCWG. Besides, the aqueous fraction of pyrolysis oil was gasified to a high extent in the presence of this catalyst, and 0.9 mol/mol of carbon in feedstock (2.98 wt.% C) was converted into CH4 and CO2 at 700 °C