Mixed matrix and thin-film nanocomposite membranes of PIM-1 and hydrolyzed PIM-1 with Ni- and Co-MOF-74 nanoparticles for CO2 separation: Comparison of blending, grafting and crosslinking fabrication methods
Mustafa Alshurafa, Andrew B. Foster, Sulaiman Aloraini, Ming Yu, Boya Qiu, Patricia Gorgojo, Martin P. Attfield, Peter M. Budd
Abstract
The prototypical polymer of intrinsic microporosity , PIM-1, was synthesized with branched topology, then acid-hydrolyzed to introduce carboxylic acid functional groups (cPIM-1). Self-standing membranes and thin film nanocomposite (TFN) membranes were fabricated from PIM-1, cPIM-1, and Ni- or Co-MOF-74 nanoparticles (NPs), with a particular focus on TFNs for industrial viability. TFN membranes on polyacrylonitrile support were fabricated utilizing the following methods: (i) conventional blending; (ii) a grafting reaction between the hydroxyl group in the MOF-74 NPs and fluoro-groups of the chain-ends during PIM-1 synthesis; and (iii) an in-situ cross-linking reaction between the carboxylic acid groups in cPIM-1 and the metal ions of MOF-74 synthesized in-situ. Both conventional blending and grafting of PIM-1 with MOF-74 showed significant increase in permeance in TFN membranes. A grafted PIM-1 TFN membrane produced a CO 2 permeance of 9600 GPU , which is roughly 170 % higher than a pristine PIM-1 thin film composite (TFC) membrane, while also improving the selectivity . After 28 days of aging, a blended TFN membrane based on PIM-1 showed a CO 2 permeance of 1000 GPU and selectivities of 20.0 and 20.5 for CO 2 /N 2 and CO 2 /CH 4 , respectively. Crosslinked cPIM-1 TFNs showed significant improvement in ideal selectivity from 65 in cPIM-1 to over 90 for CO 2 /N 2 , with permeance almost unchanged after crosslinking with Ni-MOF-74. However, small differences in the polyacrylonitrile support can result in significant changes in gas separation behavior. In mixed gas conditions, crosslinked cPIM-1/Co-MOF-74 produced an impressive 1842 GPU and CO 2 /N 2 selectivity of 33. These results fall within the performance range that is suitable for post-combustion carbon capture.