Processing of organic waste by catalytic supercritical water gasification

Tapah, Boris Fotso (2014). Processing of organic waste by catalytic supercritical water gasification. University of Birmingham. Ph.D.

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Abstract

The results of the degradation of glycerol in supercritical water show that conversion of pure glycerol (58 % at 550 $^0$ C) without a catalyst can be achieved, but complete conversion of pure glycerol over Fe $_2$ O $_3$ +Cr $_2$ O $_3$ or Fe $_3$ O $_4$ catalysts (at 550 $^0$ C, 250 barg, <15 wt% feed concentration, 10.1 g and 4 mm catalyst particles) can be reached. Crude glycerol conversion decreases from 100 to 67 mole% and 100 to 74 mole% over the same catalysts and conditions. Hydrogen yield was as high as 61 mole% and 49 mole % when crude glycerol was gasified over Fe $_3$ O $_4$ and Fe $_2$ O $_3$ +Cr $_2$ O $_3$ , respectively. 64 mole% of syngas was obtained with minimum 4:1 mole ratio of H $_2$ :CO. Hydrocarbon yields (69 mole% for ethylene and 22 mole% for methane) were obtained and this decreased with temperature as resulted of thermal cracking. Small amounts of char (<3.1 wt%) and carbon deposition on the catalyst surface and inside the reactor wall was observed. Prolonged exposure of Fe $_2$ O $_3$ +Cr $_2$ O $_3$ to 172 h on-stream under supercritical conditions resulted in fragmentation of the surface from metal sintering, which reduced activity for H $_2$ production. 42 mole% of hydrogen was obtained from 2 wt% digestate gasification at the same conditions.