Polymeric ionic liquid membranes containing IL–Ag+ for ethylene/ethane separation via olefin-facilitated transport

Abstract

This work focuses on the separation of light olefins from their corresponding paraffins using membranes due to their lower energy consumption and operating costs in comparison to the traditionally used methods which are highly energy intensive. Although polymeric ionic liquids (PILs) have attracted much attention as interesting materials to prepare improved gas separation membranes, their exploitation for light olefin/paraffin separation has never been attempted before. In this work, we propose the use of PILs as alternative polymer matrices for olefin/paraffin separation. A new series of facilitated transport membranes of poly([pyr₁₁][NTf₂]) incorporating different amounts of the ionic liquid ([pyr₁₄][NTf₂]) and the silver salt (AgNTf₂) were prepared by a film casting process and their ethane and ethylene permeation properties were measured at 293 K using a time-lag apparatus. The results show that the preparation of PIL/IL composite membranes increases the permeability of both C₂H₄ and C₂H₆, overcoming the hindered gas diffusion in the pure PIL. Nevertheless, the presence of the IL in the composite membrane promotes reduced C₂H₄/C₂H₆ permselectivity. The addition of the silver salt greatly boosts the solubility of the olefin in the membranes. Furthermore, increasing the silver ion concentration in the PIL/40% IL system leads to enhanced overall C₂H₄/C₂H₆ permselectivity surpassing the upper bound for polymeric membranes, indicating that PILs have interesting potential as polymer matrices for olefin-facilitated transport membranes.