Carbon dioxide (CO2) comprises ~84% of greenhouse emissions each year in the U.S. To decrease these emissions, polymeric membranes are targeted as efficient means by which CO2 may be separated from other non-greenhouse gases; however, significant advances in membrane performance must be realized. To address this need, we developed a class of alkoxysilyl-substituted vinyl-added polynorbornenes (VAPNBs) that show promising performance for the separation of CO2/N2 – the two most commonly encountered gases in all fossil-fuel fired power plant flue gas emissions. To enhance the performance of these materials, we designed and synthesized a systematic series of monomers and polymers, to determine how 1) alkoxysilyl branching, 2) alkyl chain length, 3) norbornene to alkoxysilane carbon linker length, and 4) inclusion of ethereal linkages impact CO2/N2 gas separation performance. These structure-property relationships reveal that substituents containing ethereal linkages and compact trimethoxysilyl substituents both promote substantial increases in CO2/N2 selectivity with minimal changes in CO2 permeability. Serendipitously, we also found that these membranes exhibit exceptional H2S/CH4 separation performance, as well as good separation capabilities for CO2/CH4. This is intriguing as two of the most prevalent contaminants in crude natural gas are CO2 and H2S. Because both contaminants must be removed to meet pipeline specifications, membranes that simultaneously remove both impurities are desirable. To address this parallel membrane challenge, we have developed a series of fluoroalkoxysilane substituted vinyl-addition polynorbornenes that are highly permeable and selective for CO2/CH4 separation.

Substituted vinyl-addition polynorbornenes as high Tg gas separation membranes

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