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

Abstract

a b s t r a c tHydrogen sorption isotherms in selected glassy and rubbery polymers, available over a wide range of temperatures ( À 20 to 70 1C) and pressures (0-60 atm) 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 1C for a series of polymers considered for membrane-based gas separations. Finally, He/H 2 solubility-selectivity at 35 1C has been correctly predicted: as expected, the glassy Teflon s AF-series perfluorinated copolymers display a higher He/H 2 solubility selectivity compared to the hydrocarbon-based polymers.

Nonequilibrium Lattice Fluid Modeling of Gas Solubility in HAB-6FDA Polyimide and Its Thermally Rearranged Analogues

“…Regardless of the penetrant considered, gas sorption decreases with increasing temperature. This result is consistent with the typical exothermic sorption behavior exhibited by glassy polymers 17,38 . Remarkably, the NELF model captures the temperature dependence of gas solubility.…”

“…Compared to other models for gas sorption in glassy polymers 15,16 , the NELF model exhibits remarkable predictive power 12,14,17,18,19,20 . This model requires, for the penetrant and the polymer, the same characteristic parameters as the corresponding equilibrium model, and it uses the same mixing rules to estimate properties of polymer-penetrant mixture 14 .…”

“…Then, sorption isotherms can be predicted at any other temperature with no additional adjustable parameters 17 .…”

“…In summary, hydrogen, nitrogen and methane solubility isotherms in HAB-6FDA can be predicted at multiple temperatures and up to 6MPa with one adjustable parameter per gas (i.e., k from zero for hydrogen might also be partially due to the uncertainty in the hydrogen sorption data, which is greater than that of other more condensable gases, since hydrogen is only sparingly soluble in polymers 17,25,26 .…”

“…Remarkably, the NELF model captures the temperature dependence of gas solubility. In a recent publication, Galizia et al 17 derived an explicit expression for the infinite dilution enthalpy of sorption:…”