Conversion of wastewater containing organic compoundes to hydrogen and methane by the hydrothermal gasification using novel Ni/Carbon catalyst

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A novel Ni/carbon catalyst could be prepared through the carbonization of methacrylic ion exchange resin, which was treated in an aqueous solution of nickel sulfate using NH3 to keep pH at near neutral. The properties of this catalyst are as follows ; Ni content 47 wt%, Particle size of Ni 2〜4 nm, BET surface area 180 m2/g. This catalyst was used for the gasification of water-soluble organic compounds under hydrothermal conditions at 200〜350℃. Acetic acid and sucrose were completely gasified at 300℃, producing methane, hydrogen and carbon dioxide. Aromatic compounds such as benzene are also gasified at 350℃, yielding large amount of hydrogen. The yield of hydrogen surprisingly reached 2.8 mol/mol-C for toluene.Two real wastewaters were used in this study. One is a wastewater from dewatering process of brown coal through hydrothermal treatment. The other is an industrial wastewater from electronic factory. Organic compounds containing in the both wastewaters were completely converted to gaseous product at 300℃. It was found that this catalyst can be used for treating real wastewaters. The product gas contained fairly large amount of combustible gas (CH4 and H2) especially for industrial wastewater. This industrial wastewater was also used for the long-run experiment to examine the life of the catalyst. This catalyst kept complete gasification for 2000 hours when no substances promoting the sintering of Ni particles contained in the wastewater. This result indicates that this catalyst has enough durability for practical use. The energy balance of this proposed process was examined. It was found that 52 % of energy can be recovered as fuel gas from the organic compounds in the wastewater when the heat of exit stream of the reactor was recovered by the heat exchange with the feed steam. This result clearly indicates that this proposed process is promising not only for the wastewater treatment but also for the recovery of energy from wastewater.