Mechanically robust hollow fiber supported ionic liquid membranes for CO2 separation applications

• Mechanically robust SILMs were spun into hollow fibers using Torlon®.
• Four different types of fibers were made with varying degrees of porosity.
• CT scan technique was used to locate and image the ionic liquid in the membrane.
• Increasing porosity resulted in higher CO2 permeance and selectivity.
• Computer simulation used to explain ionic liquid affinity and mechanical properties.

Polymeric hollow fiber supported ionic liquid membranes (SILMs) were fabricated utilizing Matrimid® and Torlon® as the supporting structure and the ionic liquid (IL) 1-hexyl-3-methylimidalzolium bis(trifluoromethylsulfonyl)imide ([C6mim][Tf2N]) as the gas transport media. This IL served as a baseline while the polymer and the fiber pore morphology were varied in order to optimize the support structure. By using sufficiently high fiber porosity, and thus maximizing the IL content of the membrane, it was found that the permeance and selectivity for CO2/H2 separation were comparable for both Matrimid® and Torlon® supports. However, the mechanical strength of Matrimid® supports was low when saturated with IL. Therefore Torlon® fibers were subsequently investigated because of the higher strength of this material. Molecular modeling was used to investigate the source of the increased strength of Torlon®, and it was found that the polymer chains in Torlon® tend to interlock with each other to a greater degree than Matrimid®. Also, the IL [C6mim][Tf2N] has less interaction with Torlon® than with Matrimid®. In this work the permeance and selectivity for CO2/H2 of these hollow fiber SILMs are reported, as well as the tensile strength, Young׳s modulus, and glass transition temperature. Threshold image analysis was used to determine the volume fractions of polymer, macro-voids, and micro-voids. X-ray computed tomography scanning was used to non-destructively evaluate the location of IL within the fiber wall.