Direct Methanation of CO₂ in Biogas with Hydrogen from Water Electrolysis: The Catalyst and System Efficiency
2022
Zhang, Liu | Ma, Fangping | Zeng, Qing | Peng, Fang | Hu, Qiang | Wu, Kejing | Yang, Yixue | Lu, Houfang | Liang, Bin
Methanation of CO₂ in biogas could realize CO₂ utilization; meanwhile, the biogas is upgraded. In this study, a methanation catalyst was designed and the system efficiency considering a solid oxide electrolysis cell (SOEC) was evaluated. A layered nickel silicate catalyst was synthesized and modified by doping with trace amounts of precious metal Pt and alkaline-earth metal Mg. The conversion of CO₂ reached 79% with 100% selectivity toward CH₄ for model biogas with 50 vol % CO₂ and 50 vol % CH₄ over the Pt- and MgO-doped Ni/SiO₂ catalyst at 350 °C. A simulation system consisting of SOEC and methanation of simulated biogas is built with commercial software Aspen Plus. The energy efficiency was analyzed and optimized through a heat exchange network, which achieved about 30% increase in efficiency. The energy utilization efficiency can be greater than 86% when the CO₂ conversion in biogas is greater than 99% by adjusting the methanation temperature and H₂/CO₂ ratio. The energy efficiency in direct methanation of biogas exceeds 8% higher than that in methanation of CO₂ separated from biogas.
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