Multilayer composite membranes for gas separation based on crosslinked PTMSP gutter layer and partially crosslinked Matrimid^® 5218 selective layer

New multilayer composite membranes for gas separation with enhanced performance were prepared. Membranes consist of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) as the gutter layer deposited on a poly(acrylonitrile) porous support and partially crosslinked Matrimid^® 5218 selective top-layer. Matrimid^® 5218 is an attractive soluble polyimide known for its excellent thermal and mechanical resistance and high selectivities for some gas pairs, e.g. O₂/N₂ or H₂/CH₄. A partial crosslinking of Matrimid^® 5218 using 1,4-xylylenediamine was performed to obtain high-viscous coating solutions exhibiting significantly lower penetration into support pores in comparison with composite membranes where neat commercial Matrimid^® 5218 was used. Because PTMSP is soluble in most organic solvents, including chloroform used for coating of Matrimid^® 5218, a procedure for crosslinking of the PTMSP gutter layer using bis(2-azidophenyl) sulfone was developed. The influence of crosslinking time and crosslinking agent concentration on gas transport properties was determined. The effect of the PTMSP gutter layer on gas transport properties was compared with that of the PDMS sealing layer. It was demonstrated that the gutter layer enhances both gas permeances and selectivities whereas the sealing layer increases selectivities but with a small gas permeance decrease. Long-term performance of prepared multilayer composite membranes showed about 20% reduction of single gas permeances, whereas selectivities remained almost unchanged.