Supercritical water gasification with Ni/ZrO2 catalyst for hydrogen production from model wastewater of polyethylene glycol

Generation of hydrogen from polyethylene glycol (PEG)-contaminated wastewater by supercritical water gasification (SCWG) with Ni/ZrO2 heterogeneous catalysis was investigated with a continuous flow Inconel 625 reactor at 663 K, 24 MPa and at residence times from 60 s to 300 s. The catalytic activities of Ni, Co and W with ZrO2 support were compared. The catalyst 15%Ni/ZrO2 gave the highest activity and H2 yields, which were 6.1 and 2.4 times higher than those without catalyst and with only ZrO2, respectively. A synergistic effect was found when Co or W was added. The gas yield and gasification efficiency increased with increase in Ni loading and catalyst amount but decreased with an increased PEG concentration. The stability of Ni/ZrO2 was tested with continuous operation for 85 h at 663 K, 24 MPa and 120 s. The gas yield and gasification efficiency were constant throughout the 85 h of gasification reaction. Furthermore, XRD, BET and XRF analyses showed that the crystal type, surface area and Ni loading of the Ni/ZrO2 catalyst were unchanged. This profile of activity and stability suggest that Ni/ZrO2 is a promising heterogeneous catalyst for hydrogen production by SCWG.