Hydrogen is attracting attention as a clean fuel that produces no carbon dioxide emissions at the stage of use. Hydrogen could be produced from fossil fuels using existing equipment in refineries, but in such production schemes, the hydrogen recovery rate decreases when purity is increased to 99.99% or higher as is required for fuel cells. To solve this problem, we developed a new hydrogen purification system with a hybrid-type membrane that features CO
2 membranes and H
2 membranes arranged alternately, and which utilizes the high temperature and high pressure in the hydrogen production unit. This system achieves increased recovery of high-purity hydrogen compared to existing technologies. Such a system requires a highly stable and CO
2-selective membrane. As ionic liquids (ILs) are known for their negligible volatility, we modified the chemical structure of some ILs to increase their CO
2 selectivity. We thus set out to develop a CO
2 separation membrane incorporating our novel ILs. The membranes we developed show remarkably high CO
2/H
2 selectivity from mixed gases of CO
2 and hydrogen.
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