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Absorption of H2S and CO2 in Aqueous Solutions of Tertiary-Amine Functionalized Protic Ionic Liquids

Huang, Kuan, Zhang, Jia-Yin, Hu, Xing-Bang, Wu, You-Ting
Energy & fuels 2017 v.31 no.12 pp. 14060-14069
absorbents, absorption, acetic acid, aqueous solutions, carbon dioxide, enthalpy, gases, hydrogen sulfide, ionic liquids, natural gas, neutralization, oil and gas industry, solubility, temperature, thermodynamic models, viscosity
The development of ionic liquid-based absorbents for selective separation of H₂S from CO₂ is of interest to the natural gas industry. In this work, a series of tertiary-amine functionalized protic ionic liquids (TA-PILs) were synthesized by neutralizing one of the tertiary amine groups in diamine compounds with acetic acid, leaving the other tertiary amine group as the functional site for selective absorption of H₂S. To overcome the high viscosity of pure ionic liquids, TA-PILs were dissolved in water to give mixed absorbents. The effects of TA-PIL species, TA-PIL concentration, and experimental temperature on the solubilities of H₂S and CO₂, and absorption kinetics of H₂S and CO₂ in aqueous TA-PILs were investigated systematically. The reaction equilibrium constants and absorption enthalpy of H₂S and CO₂ in aqueous TA-PILs were also calculated by correlating the solubility data with a reaction equilibrium thermodynamic model. Results demonstrated that aqueous TA-PILs have high absorption capacities for H₂S. Although the equilibrium selectivities of H₂S/CO₂ in aqueous TA-PILs are minimized, they still display significant kinetic selectivities for the two gases. More importantly, the TA-PILs designed are featured with low cost and facile synthesis, making them more attractive than other functionalized ionic liquids reported in the literature for application in selective separation of H₂S from CO₂.