Morphology and gas permselectivity of blend membranes of polyvinylpyridine with ethylcellulose

Binary blend membranes of poly(4-vinylpyridine) (PVP) with ethylcellulose (EC) have been prepared by a solution casting technique with chloroform as solvent. The membranes appear macroscopically miscible but microscopically immiscible based on wide-angle X-ray diffraction, differential scanning calorimetry and scanning electron microscope investigations. Permeating feature of five pure gases through the blend membranes has been described in detail. The permeability, diffusivity, solubility, and their selectivities of oxygen, nitrogen, carbon dioxide, methane and hydrogen through the blend membranes have been measured over an entire range of blend composition in a time-lag apparatus. A remarkably and continuously enhanced selectivity has been achieved for important gas pairs including oxygen/nitrogen, carbon dioxide/methane, and hydrogen/nitrogen with increasing PVP content from zero to 100 wt%. The highest oxygen over nitrogen, carbon dioxide over methane, and hydrogen over nitrogen selectivity coefficients are, respectively, equal to 6.8, 25, and 70. Experimental permeability was compared with that calculated on the basis of blend composition. The various transport parameters of the five gases through the blends seem normally higher than composition weighted mean computed from pure PVP and pure EC values using semilogarithmic coordinates. The temperature- and pressure-dependences of the permeability of the five gases through a PVP/EC (50/50) blend membrane are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.