Novel solvents based on thiocyanate ionic liquids doped with copper(I) with enhanced equilibrium selectivity for carbon monoxide separation from light gases
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This work focuses on the research of novel carbon monoxide (CO) capture solvents to be applied to the separation of CO from other light components contained in gas streams of the process industry, e.g., nitrogen and hydrogen. More specifically, we examine the use of CO-selective capture solutions composed of the ionic liquid 1-ethyl-3-methylimidazolium thiocyanate ([C2mim][SCN]) and the transition metal salt copper(I) thiocyanate (CuSCN) as greener alternatives to the tetrachloroaluminate(III)-aromatic hydrocarbon solutions currently employed for CO separation from gas mixtures. In order to gain insight into the behavior of the selected ionic liquid solutions as chemical solvents for CO, their density and viscosity are characterized with respect to temperature and composition in a wide range of temperatures (273.15-303.15 K), pressures (up to 24 bar) and copper(I) concentrations (0-30 mol%). Moreover, the CO absorption has been assessed and gas-liquid equilibria are successfully described with a thermodynamic model as a function of those variables. The [C2mim]x[Cu]1-x[SCN] solutions exhibit favorable properties in terms of competitive CO sorption capacity and high selectivity towards slightly soluble gases, e.g., 996.1 mmol L-1 and CO/N2 selectivity of ~25 at 283.15 K and 23.3 bar, combined with low heat of absorption (-29.5 kJ mol-1) as well as easiness of regeneration and reuse. Consequently, these copper(I)-containing ionic liquids are promising for the development of novel and greener CO/N2 separation processes alternative to the use of flammable and toxic solvents or energy-intensive cryogenic distillations.