Poly (amide-6-b-ethylene oxide) multilayer composite membrane for carbon dioxide separation

In this paper, block copolymer poly (amide-6-b-ethylene oxide) Pebax® MH 1657 (PEBA1657) is used to prepare multilayer polyetherimide (PEI)/polydimethylsilicone (PDMS)/PEBA1657/PDMS composite membranes according to dip-coating method. The PDMS gutter layer is mainly used for preventing the pore penetration of PEBA1657 solution and the PDMS protective layer for sealing the defects of PEBA1657 selective layer. The prepared multilayer PEI/PDMS/PEBA1657/PDMS composite membranes display high permeance and high selectivity for CO2 separation. For the nonpolar gases He, H2, O2 and N2, the gas permeance decreases with the increasing molecule size. But for the polar gases CO2, H2S and SO2, their permeance is higher than that of nonpolar gases. Due to CO2 induced plasticization effect, the pressure dependence of CO2 permeance is expressed empirically by an exponential equation. And the temperature dependence of gas permeance is correlated with different Arrhenius equation below and above the melting of PEO segments. Compared with N2, H2 and CH4, CO2 has lower value of the apparent activation energy of permeation (Ep) because of its higher inherent condensability and the special interaction with polymer chain. Due to CO2 induced plasticization effect, the diffusion activation energy (Ed) of CO2 decreases with the increase of CO2 pressure, resulting in the decrease of Ep. As for CO2/N2 gas mixture, the pressure ratio strongly influences the CO2 concentration in the permeate side, and a high pressure ratio is always desirable to obtain high CO2 concentration for flue gas.