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

Abstract

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