Municipal waste leachate conversion via catalytic supercritical water gasification process

The aim of the paper is to investigate the thermal conversion of Municipal Waste Leachate (MWL) to Synthetic Natural Gas (SNG), based on two step process: gasification with water in supercritical conditions (SCWG) followed by a catalytic upgrading of the resulting gas phase. The proposed combination showed advantages in terms of biomass conversion efficiency with respect to the conventional approaches. As the initial biomass liquid phase includes some carboxylic acids, which are the usual intermediate of biomass decomposition process in SCWG, it is expected that the combined effect of catalysis and SCW leads to an increase of syngas yield, together with an enrichment in hydrogen. Experimental tests, carried out by varying MWL flow rate, showed that SCWG technology allows to produce a syngas with a Higher Heating Value (HHV) of about 15-17 MJ/kg. Hydrogen and methane compositions of the produced syngas varied in the range 25-47%v/v and 11-18%v/v, respectively. Syngas upgrading experimental tests were carried out by using a Nickel based catalyst increasing methane SNG fraction up to 50%v/v.