Plasticization-enhanced trimethylbenzene functionalized polyethersulfone hollow fiber membranes for propylene and propane separation

Polymeric membranes for gas separations often suffer from plasticization, which leads to the swelling of polymer matrices and thus the loss of the separation selectivity and performance. Such intrinsic and detrimental issues remain challenging and unsolved. Here, we report a newly designed polymer, poly trimethyl phenylene ethersulfone (PTPES) that is a trimethylbenzene-functionalized polyethersulfone and beneficial from the plasticization. When the polymer is fabricated into defect-free hollow fiber membranes, both propylene permeance and propylene/propane selectivity increase exponentially with the feed pressure after plasticization. The PTPES hollow fibers have a propylene permeability and a propylene/propane selectivity about two orders of magnitude higher than their intrinsic values of dense films. The exceptionally plasticization-enhanced phenomena of PTPES hollow fibers might be ascribed to the unique plasticization-enlarged steric-hindrance molecular sieving effect, which happens in the ultra-thin PTPES skin layer and is caused by the trimethylbenzene moieties in the well-oriented polymer chains. Our work provides new insights to the membrane gas transport mechanisms and may inspire the development of new-generation polymeric materials and membranes for propylene/propane and other gas separations.