Predictive calculation of hydrogen and helium solubility in glassy and rubbery polymers

Abstract

Hydrogen sorption isotherms in selected glassy and rubbery polymers, available over a wide range of temperatures (−20 to 70°C) and pressures (0–60atm) have been modeled and correlated using equilibrium and non-equilibrium thermodynamic models based on the lattice fluid theory. A good representation of the experimental data can be obtained for the systems considered over the whole range of pressures and temperatures inspected by using just one fitting parameter, under the fundamental assumption that hydrogen behaves as a non-swelling penetrant. The theoretical estimates of infinite dilution solubility coefficients are in excellent agreement with the experimental data. Remarkably, the model analysis allows a reliable estimate of the isosteric heat of sorption and its dependence on the hydrogen concentration over the whole range of pressures considered. A similar theoretical analysis has been performed by considering the helium sorption data available at 35°C for a series of polymers considered for membrane-based gas separations. Finally, He/H2 solubility–selectivity at 35°C has been correctly predicted: as expected, the glassy Teflon® AF-series perfluorinated copolymers display a higher He/H2 solubility selectivity compared to the hydrocarbon-based polymers.