Sorption and permeation properties of water and ethanol vapors in poly[bis(trifluoroethoxy)phosphazene] (PTFEP) membranes |
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Authors: | Yi-Ming Sun Chi-Huang Wu Albert Lin |
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Affiliation: | (1) Department of Chemical Engineering, Yuan Ze University, Chung-Li, Taoyung, 32026, Taiwan, ROC |
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Abstract: | The permeability and solubility for water and ethanol in PTFEP membranes were determined experimentally, and the data were
analyzed by the solution-diffusion model. The permeability for water and ethanol ranged from several hundreds to several thousands
Barrers, and they increased exponentially with the vapor activity and increased with temperature. At the same temperature
and vapor activity, the permeability ratio between water and ethanol ranged from 5.7 to 2.3, and it decreased as the vapor
activity increased. The sorption isotherms for water and ethanol were fitted by the Henry’s law relationship. The solubility
decreased as the temperature increased so that the heat of sorption for both water and ethanol was negative. The solubility
for water was more than twice the solubility for ethanol. The solubility seems to be inversely proportional to the molecular
size of the penetrants in such a system. The solubility ratio between water and ethanol is smaller than their molecular volume
ratio possibly due to the slightly stronger nonpolar interaction and the higher degree of plasticization in the ethanol-polymer
system. The diffusivity for water and ethanol ranged from 10−8 to 10−7 cm2/s, and the values for water were larger than those for ethanol at the same temperature and vapor activity. The diffusivity
for water and ethanol also increased exponentially with the vapor activity. The diffusivities for water and ethanol increased
with temperature and their activation energies of diffusion were very similar possibly due to the same energy characteristic
of polymer main chain movement. |
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Keywords: | Membrane Polyphosphazene Permeability Solubility Diffusivity Solution-diffusion model |
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