Effects of Lewis acid on catalyzing gasification of sewage sludge and model compounds in supercritical water

In this work, we investigated how different types and concentrations of Lewis acids effect gas yield and composition from supercritical water gasification (SCWG) of dewatered sewage sludge (DSS). Furthermore, the catalytic mechanism was investigated using AlCl3 as a representative Lewis acid catalyst. Results showed that non-catalytic gasification of DSS produced a hydrogen yield of 0.13 mol/kg organic matter (OM) and total gas yield of 4.82 mol/kg OM; while the addition of 10 wt% Lewis acid resulted in a significantly improved H-2 and total gas yield of 0.77-7.76 mol/kg OM and 7.57-22.88 mol/kg OM, respectively. In addition, the Lewis acids tested herein depicted the following activity trend: AlCl3 > FeCl3 > NiCl2 > ZnCl2. The required temperature for generating hydrogen from SCWG of DSS was greatly reduced when AlCl3 was present during the heating process. Furthermore, AlCl3 significantly increased the hydrogen yield from SCWG of the model compounds. Finally, AlCl3 catalyzed SCWG of guaiacol and glycerol showed the best hydrogen selectivity. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.