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Morphology and gas-permeation analyses for poly(ether sulfone)/poly(vinyl alcohol) electrolyte composite membranes in the facilitated transport process

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Abstract

In this article, we describe the preparation procedure of poly(ether sulfone)/poly(vinyl alcohol) (PVA) composite membranes based on film casting and evaporation methods. The morphology and operation of these membranes in the ethylene/ethane separation process were investigated. AgNO3 and AgBF4 salts were applied in the PVA active layer as carrier agent providers. Salt addition to PVA solution weakened the hydroxyl bond potency and fortified the position of carrier agent in the active layer structure. Scanning electron microscopy with energy-dispersive X-ray spectrometry revealed that the distribution fluctuation of carrier agents in the active layer increased with increasing salt concentration. The glass-transition and α-relaxation temperatures of the salt-containing membranes were lower than those of salt-free membranes. In addition, the polymeric structure of the salt-containing membranes showed crystallinity during the heating process at temperatures higher than 160°C. Atomic force microscopy indicated that the surface roughness of composite membranes with smoother sublayers was greater than that of other membranes. The mechanical strength of membranes containing silver nitrate salt was higher than that of the salt-free membranes. Permeation tests demonstrated an increase in the gas permeation and membrane selectivity after salt incorporation. A performance improvement in the facilitated transport mechanism was associated with increasing salt concentration. However, a higher operational pressure had an inverse impact on it. The saturation of active sites with ethylene molecules at higher pressures and the low plasticity of the created complexes in the membrane structure decreased the performance of the facilitated transport mechanism. The addition of AgBF4 salt, with a lower lattice energy compared to AgNO3, increased the real performance of the membranes. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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