Studies On Flat Sheet Composite Poly(Amide-b-ethylene Oxide) Membrane

Poly(amide-b-ethylene oxide) copolymers have high CO2 permeability and efficient separation performance for CO2/N2 gas mixture, thus present huge potential for the application of CO2 capture as membrane material. However, there is much difficulty in fabricating it into the composite membrane with high permeance while maintaining its intrinsic selectivity. Two of the key points to solve this problem lie in suppressing the pore penetration of coating solution that causes the decrease of gas permeance and conditioning the properties of substrate membrane to eliminate the defects of coating layer in order to increase the gas selectivity of the composite membrane.In this study, one of the commercial poly(amide-b-ethylene oxide) copolymers -Pebax 1657 was chosen as the separation material, the ratio-optimized ethanol/water mixture as the solvent and polyacrylonitrile (PAN) membrane as the substrate to prepare the flat sheet composite membrane of Pebax. To meet the requirement of gas separation application which demands the substrate mechanically strong, this study targeted at preparing the sponge-like PAN substrate. The influence of polymer concentration, temperature of coagulation bath, evaporation duration and the addition of additives on membrane structure were investigated systematically. The optimized sponge-like PAN substrate was obtained, and its surface roughness was measured with the help of rough meter instead of atomic force microscopy (AFM). The effects of surface roughness of PAN substrate on performance of Pebax composite membrane were investigated. It was found that the surface roughness combined with the concentration of coating solution affected the performance of composite membrane. Within the scope of this study, the CO2/N2 selectivity of Pebax composite membrane decreased with the increase of the surface roughness of substrate as well as the fluctuation of the CO2/N2 selectivityBy means of numerical simulation, the side effect of pore penetration was studied theoretically as well as the gutter layer of hydroxyl siloxane and amino siloxane were investigated to enhance permeance of the Pebax composite membrane. A polymer blend of amino siloxane with cross-linked PDMS (amino-PDMS) was designed, which pioneered a gutter layer with a certain degree of crosslink, hexane resistance, and affinity to Pebax. The influence of concentration, degree of crosslink, composition, and mixing ratio on performance of Pebax composite membrane were investigated systematically. With the help of this gutter layer, the permeance of Pebax composite membrane was promoted significantly while maintaining the selectivity. Based on the application of amino-PDMS gutter layer, polyethylene glycol dimethyl ether (PEGDME) was blended with Pebax to further improve the permeance of the Pebax composite membrane. The influence of ratio and concentration of the blend on membrane performance was studied. As a result, a Pebax composite membrane with CO2/N2 selectivity of 60 as well as CO2 permeance of 410 GPU was obtained.