Effect of silver ions coordination on morphology and performance of PES/PVP composite membrane in facilitated transport of ethylene

Structural and permeation properties of PES/PVP electrolyte composite membranes including association and dissociation behavior of silver nitrate salt within the polymer structure, structural situation of electron donor groups of membranes, surface and structural charge of membranes, crystalline variation of membrane active layer before and after salt addition and permeation properties of these membranes at different pressures including low pressures were evaluated. Structural evaluation through FTIR analysis revealed that the distributional condition of carrier agents is affected by increasing the AgNO3 concentration. The efficiency of carriers for ethylene transportation is decreased by salt addition at molar concentrations more than 25%. However, according to the results obtained from zeta potential experiment, increasing the salt concentration enhances the surface and structure charge of membranes. Due to the salt crystals formation, the ascending trend of active layer crystallinity stopped at a salt molar concentration more than 25%. These physical and chemical reactions in the active layer structure caused the ethylene selectivity of final membranes to decrease at a salt molar concentration being more than 25%. The separation efficiency of a membrane with the AgNO3 concentration of 25% was the most efficient situation. Adding a very thin and flexible PDMS layer on the surface of PES/PVP membrane in order to increase the real and ideal ethylene selectivity in the separation process was effective. Moreover, blending AgBF4 and AgNO3 salts was a new method for selectivity increament, which was applied in this research. (C) 2011 Elsevier B.V. All rights reserved.