서강대학교

초록/요약

Carbon molecular sieve (CMS) membranes are a promising candidate for large-scale natural gas processing and olefin/paraffin separation since they have high performances and scalability. Formulating ultrathin, defect-free CMS hollow fiber membranes is, however, still challenging due to damage on porous sub-structures induced by thermal relaxation of polymer chains during pyrolysis. Herein, we report a new methodology enabling high separation performance and good plasticization resistance in CMS fiber membranes by uniform integration of ladder-structured polysilsesquioxanes (LPSQ) into the polyimide (PI) matrix. The resulting CMS fiber showed an excellent carbon dioxide permeance with good carbon dioxide/methane selectivity due to a defect-free thin selective layer. Moreover, the PI/LPSQ precursors self-generated fluorinated gases, which possibly lead to the cleavage of double-stranded siloxanes during pyrolysis. At the same time, residual siloxanes underwent thermo-oxidative crosslinking, which resulted in densification into nonporous inorganic silica phases. Such impermeable silica phases adversely affected the gas diffusion, decreasing propylene permeability but contributed to the significantenhancement in the propylene/propane selectivity, because of the substantially enhanced diffusivity selectivity.