Mixed gas hydrogen sulfide permeability and separation using supported polyphosphazene membranes

Three phosphazene polymers were characterized for permeability using a suite of pure gases, including H₂S where high permeabilities were measured with respect to the other gases in the study. Mixed gas selectivities were determined and compared to the ideal gas selectivities for the H ₂S/CH₄, CO₂/CH₄, and Ar/CH ₄ gas pairs. The three phosphazenes represent a set of membrane materials differing by their polarities. Description of the polarity of each was performed using Hansen solubility parameters derived from group contributions for each chemical structure. A good correlation was observed between the polar Hansen parameter (δ_p) and the gas permeabilities of both CO₂ and H₂S. Furthermore, permeant gas critical temperatures were also found to correlate with permeability, with the exception of He and H₂. A comparison of the mixed gas permeabilities with the corresponding pure gas data revealed good agreement in the data. Most surprisingly, permeabilities and separation factors were observed to increase with decreasing glass transition temperature (T_g) for the H ₂S/CH₄ and CO₂/CH₄ gas pairs reaching a maximum of PH2S = 1103 × 10^-10 cm³ (1103 Barrers) with and αH2S/CH4 = 78.8 as derived from a mixed gas experiment.