Design and screening of ionic liquids for C2H2/C2H4 separation by COSMO-RS and experiments

Ionic liquids (ILs) have been proposed as promising solvents for separating C 2 H 2 and C 2 H 4 , but screening an industrially attractive IL with high capacity from numerous available ILs remains challenging. In this work, a rapid screening method based on COSMO-RS was developed. We also present an efficient strategy to improve the C 2 H 2 capacity in ILs together with adequate C 2 H 2 /C 2 H 4 selectivity with the aid of COSMO-RS. The essence of this strategy is to increase molecular free volume of ILs and simultaneously enhance hydrogen-bond basicity of anions by introducing flexible and highly asymmetric structures, which is validated by a new class of tetraalkylphosphonium ILs featuring long-chain carboxylate anions. At 298.1 K and 1 bar, the solubility of C 2 H 2 in ILs reaches 0.476 mol/mol IL, very high for a physical absorption, with a selectivity of up to 21.4. The separation performance of tetraalkylphosphonium ILs to the mixture of C 2 H 2 /C 2 H 4 was also evaluated. © 2015 American Institute of Chemical Engineers AIChE J , 61: 2016–2027, 2015