Simultaneously enhanced gas permeability, selectivity and aging stability of carbon molecular sieve membranes by the molecule doping of silicon

Simultaneously enhancing the gas permeability, selectivity and aging stability of carbon molecular sieve membrane (CMSM) is extremely difficult. Facing such poser, a novel silicon doped CMSM at molecular level was prepared by copolymerizing siloxane with single Si–O–Si unit into the backbone of polyimide (PI). This can effectively avoid prior separated structure or multiple Si–O–Si structures and strongly alter the chains packing and thermostability of PI, finally determine the pore structure and thermodynamic behavior. The simple design adjustment simultaneously exhibits the triple enhanced effects on the gas permeability, selectivity and aging stability. The best molecule doped CMSM exhibits the ultra-high H2 permeability (12482 Barrer, 87% higher), 26% higher H2/CH4 selectivity, and 32% higher H2/N2 selectivity than pure PI based CMSM. Additionally, such CMSM also has a much better aging stability than pure CMSM and most reported CMSMs. After stabilization, it still maintains a high H2 permeability (8000 Barrer). And the hyper-aging CMSM also exhibits a good aging resistance showing a H2 permeability of 5300 Barrer, as well as high selectivity of H2/CH4 (125) and H2/N2 (106) after 35 days. This work opens a new way on designing CMSM with excellent performance through heteroatom doping to need future application.