Membranes Based on Polymers of Intrinsic Microporosity for Carbon Dioxide Separation

Abstract

Membrane-based gas separation technologies are of importance for mitigating the rapid increase in greenhouse emissions. Membrane separation demonstrates high potential in replacing conventional technologies such as chemical absorption due to their energy efficiency, simplicity, and cost-effectiveness. Polymeric materials such as polymers of intrinsic microporosity (PIMs) have attracted special attention because of their remarkable gas permeability while maintaining moderate selectivity for different separation processes. Although PIMs exhibit high free volume, they suffer from a decline in gas permeability over time, physical aging, which diminishes their gas separation performance. This research investigates a wide variety of methods to enhance the initial and long-term performance of PIM-1 thin film composite (TFC) membranes. Addition of porous fillers, such as metal organic frameworks (MOFs), via conventional blending is a common strategy to enhance the separation performance of PIM-1. However, this method often suffers from compatibility issues, such as poor dispersion of particles leading to brittle membranes. Grafting and crosslinking of PIM-1 and hydrolyzed PIM-1 (cPIM-1) with MOF-74 were applied to enhance the initial and long-term separation performance. A significant enhancement in CO2/N2 mixed gas separation performance, as well as minimizing the plasticization effect, was observed upon crosslinking of cPIM-1 with MOF-74. Recently, porous substrates have been utilized in the fabrication of TFC membranes for gas separation. A wide range of permeances and selectivities on the same substrate are obtained when utilizing the same polymer. Small microstructural differences in these substrates could lead to a significant difference in the initial and long-term separation performance. These differences are presented and discussed to highlight the importance of substrate choice when fabricating TFC membranes of PIM-1 and cPIM-1. Cardo-PIM-1 polymers were synthesized from 9,9-bis(3,4-hydroxyphenyl)fluorene (BHPF) and 9,9-bis(3,4-dihydroxyphenyl)fluorene (BDPF) monomers to yield colloidal network-rich (CN) cardo-PIM-1 and CN-free cardo-PIM-1. Conventional blending was utilized to fabricate self-standing and TFC membranes at different loadings of CN cardo-PIM-1 and PIM-1. Additional experiments were carried out to examine the impact and relationship of CN and cardo-PIM-1 content in TFN membranes. The TFN membrane blends exhibited a significant enhancement in their initial and long-term gas separation performance.

Date of Award	2 Oct 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Peter Budd (Main Supervisor) & Martin Attfield (Co Supervisor)