Catalytic gasification of sewage sludge in near and supercritical water with different catalysts

Catalytic gasification of activated sewage sludge in nearcritical and supercritical water was researched in batch reactor. Different types of commercial catalysts including Ru/C, Raney-iron, Raney-cobalt and different types of Raney-nickel were used. Effects of catalyst type, reaction temperature (350 °C, 400 °C and 450 °C), residence time (5 min–25 min) and catalyst amount were investigated. Temperature was positive for hydrogen yield and Raney-nickel with Mo metal had better catalytic activity. The addition of Raney-nickel-Mo2 promoted the formation of hydrogen better. At 450 °C and 25 min, the maximum hydrogen yield reached to 18.13 mol/kg dry sludge with 1.4 g Raney-nickel-Mo2 catalyst/g dry sludge, and the maximum LHV, GE, CE and HYP achieved 14.3 MJ/Nm³, 92%, 90.1% and 63.5 mol/kg dry sludge respectively. Although the compositions of two Raney-nickel with Mo were similar, Raney-nickel-Mo2 had better catalytic activity because it not only had the spongy structure but also it had larger specific area and better pore space concentration distribution.