CO2/CH4 and H2S/CO2 Selectivity by Ionic Liquids in Natural Gas Sweetening

CO2 and H2S in natural gas usually lead to low caloric value and corrosion of the transportation pipeline, and hence, separating CO2/CH4, H2S/CH4, and H2S/CO2 is essential for natural gas purification, desulfurization, as well as gas regeneration and reutilization. Trapping H2S, CO2, and CH4 not only eliminates their environmental contamination, but also increases feedstocks for industrial production. In order to avoid the contamination and causticity problems caused by the conventional alkali absorbents, ionic liquids have been proposed as alternatives to absorb and separate different gases for decades. In this paper, the investigations of pure ionic liquids in the selective absorption of CO2/CH4, H2S/CH4, and H2S/CO2 are reviewed. Important influencing factors, including temperature, pressure, functionality, and properties of gas and ionic liquids, were analyzed. Ionic liquids with alkali groups on the cation and anion are promising CO2 and H2S solvents and competent separators for removing CO2 or/and H...