Ionic liquid-functionalized polymeric membranes for separation and catalysis

Abstract

This dissertation focuses on the development of ionic liquid (IL)-functionalized polymeric membranes for advanced applications in simultaneous separation and catalysis, particularly in devices such as membrane reactors. These systems offer a distinct advantage by enabling continuous product removal, thereby shifting reaction equilibria and enhancing overall process efficiency.The work was conducted within the framework of the CO2Refinery doctoral school, which aims to develop and implement innovative technologies for the separation and valorisation of carbon dioxide (CO2). This aligns closely with the overarching goals of carbon capture and utilization (CCU), which involve capturing carbon dioxide and converting it into value-added products such as fuels (including methanol, and synthesis gas) and chemicals (such as cyclic carbonates, polycarbonates, acrylic acid, and urea).The first part of the thesis addresses the development of IL-functionalized membranes for gas separation, with a particular focus on the removal of CO2 from gas mixtures. Hollow fibre membranes coated with imidazolium-based ILs were fabricated and systematically evaluated. These membranes exhibited a CO2 permeance of 23.29 gas permeation units (GPU) and ideal selectivities of 8.7 for CO2/N2 and 12.44 for CO2/CO separations, indicating promising potential for advanced separation processes and establishing a foundation for further optimization.The second part investigates the catalytic conversion capabilities of IL-functionalized membranes, specifically for the esterification of n-butanol with acetic acid to produce n-butyl acetate. Flat sheet composite membranes were developed using dip-coating techniques to apply a thin layer of catalytically active, Brønsted-acidic imidazolium-based ILs. Two ILs, differing only in their anion (hydrogen sulphate and bromide), were examined to assess the influence of anion chemistry on membrane transport and catalytic behaviour. The ILs significantly enhanced water removal via pervaporation, with separation factors increasing to 209.5 for the bromide-based IL and 178.7 for the sulphate-based IL, compared to 82.5 for the unmodified membrane. Catalytic activity was also improved, with the sulphate-based IL demonstrating the highest conversion efficiency.In the final section, the integration of CO2 separation and IL-enhanced catalysis is explored through the conceptual design of a membrane reactor that brings together the key findings of this work. As an outlook, the thesis proposes IL-functionalized membranes for ultra-low temperature water–gas shift (WGS) applications, with the aim of enabling efficient hydrogen production under mild conditions.