Development of high-performance membranes for CO_2

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Poly(ether impede)segmented copolymers were prepared from polyether diamine and comonomer diamine with acid anhydride. They have microphase-separated structure consisting of microdomaims of rubbery polyether segments and of glassy polyimide segments. The gas permeation occurs through polyether segment microdomains and polyimide segment microdomains contributes to mechanical properties and film-forming ability. The polyethlene oxide(PEO)-based copolymers displayd very high performance for CO_2/N_2 separation, permeability coefficient to CO_2, P_<CO2>=1.4x10^<-8> cm^3(STP)cm^2/(cm scmHg) and permeability ratio of CO_2 over N_2, P_<CO2>/P_<N2>=70 at 298K.Composite hollow fiber membranes, which were composed of surface layr of PEO-based polyimide and supporting sponge layr of BPDA-based polyimide, were prepared by using a double-layred injection nozzle. The outer diameter of the hollow fibers was 300 mum and the thickness of the surface layr was 2mum. Laboratory-scale modules of the hollow fiber membranes displayd high performance for CO_2/N_2 separation, permeation rate to CO2, R_<CO2>=2.9x10^<-5> cm^3(STP)/(cm2 s cmHg) and permeation ratio, RCO_2/RN_2=42 at 323K.BPDA-TrMPD polyimide with high permeability and low permselectivity was brominated and then reacted with aliphatic amine. The chemically modified polyimides thus prepared displayd, P_<CO2>=1x10^<-8> cm^3 (STP) cm^2/(cm s cmHg) and separation factor alpha=35for dry CO_2/N_2 mixtures, and P_<CO2>=0.7x10^<-8> cm^3 (STP) cm^2/(cm s cmHg) and separation factor alpha=50-60 for wet CO_2/N_2 mixtures at 308K.Assymmetric hollow fiber membranes of the chemically modified polyimide are expected to display very excellent performace for wet CO_2/N_2 mixtures.