Hydrothermal Gasification of Phenol Water on Novel Carbon-Supported Ni Catalysts Prepared by the Sol-Gel Method Using PEG

Abstract

Novel carbon-supported Ni catalysts (Ni/C/Al₂O₃) for wastewater treatment by the hydrothermal gasification were prepared by the sol-gel method using polyethylene glycol (PEG) and aluminium tri-s-butoxide (ASB). Phenol and glycerin aqueous solutions were used as a model wastewater and as a model byproduct of biodiesel, respectively. It was found from XRD patterns that metal Ni in fresh catalysts increased with increasing PEG, and that amorphous Al₂O₃-support was transformed to boehmite during hydrothermal gasification. N₂ adsorption measurement revealed that effect of amounts of PEG on surface area and pore volume was negligibly small for sol-gel derived catalysts, whereas surface area, pore volume and pore diameter of catalyst prepared by impregnation method decreased during impregnation of Ni. The catalysts prepared using more PEG tended to show higher phenol conversion and higher yields of gases (methane and carbon dioxide) for hydrothermal gasification under the same condition. The sol-gel derived catalysts, especially sg-16N63C21A (Figures show 16wt% of Ni, 63wt% of carbon in PEG, 21wt% of Al₂O₃, respectively. Similarly described below. LHSV=48h^-1, phenol water 2-20 g/L), exhibited high catalytic activity compared with (1) catalyst prepared without PEG (sg-16N84A), (2) catalyst prepared by the impregnation method (i-16N/sg-11C73A) and (3) commercial reference Ni catalyst (ref. Ni). In the present case, it is considered that Al₂O₃-support does not play an important role in hydrothermal gasification, because the catalytic activity was stable during the reaction, even if the surface area and pore volume decreased, and the boehmite was formed during hydrothermal gasification. However, introduction of PEG dispersed metal Ni with high loading on carbon derived from PEG. Thus, the sol-gel method using PEG was effective in preparation of catalysts for hydrothermal gasification.