Removal of Carbon Monoxide in a Post-WGS Gas Stream by Methanation Using Ni-Ru Catalysts

Abstract

Recently, hydrogen energy has received attraction as one of the future renewable energy sources to reduce greenhouse gases. Hydrogen can be produced from fossil fuels, such as natural gas, by hydrocarbon reforming process. Production of high-purity hydrogen is crucial to enhance the long-term stability of PEMFCs. CO is one of the main impurities that need to be removed from the reforming gas. The remaining CO from the hydrocarbon reforming process can be removed with PROX and methanation. The PROX system needs additional units for oxygen supply, cooling system, and a mixing device for the reformate gas and air. These characteristics lead to system expansion and increased costs. Therefore, methanation has been considered as an alternative because it is a low-cost, compact process that is oxygen-free and reuses the produced methane. This study aims to suggest optimal design guidelines of methanation. Ni-Ru/CGO catalysts were used because they tend to promote methanation at low temperatures. Experiments were performed by changing the nickel and ruthenium contents of the Ni-Ru catalysts. The reaction feed gas comprised 50% H2, 20% CO2, 1% CO, 14% N2, and 15% H2O (volume percent). The temperature and GHSV were 200~300°C and 1,000/2,500/5,000/10,000 h-1, respectively. We analyzed the catalysts’ CO selectivity, which indicated whether the catalysts converted more CO than CO2. Low GHSVs clearly led to higher CO conversion and CO selectivity. The Ni-Ru/CGO catalysts achieved a CO concentration less than 100 ppm. The catalyst samples were analyzed to investigate the effects of the metal loading. Through our work, we can produce optimal catalysts for CO methanation and gain insight into designing a methanation reactor on a larger scale.