Understanding the Transport Behavior of Gases in Key-Type Polymeric Membranes Via Experimental Mixed-Gas Sorption and Mixed-Gas Diffusion Data

Mixed-gas sorption experiments are required to identify and quantify competitive sorption and polymer/gas1/gas2 interactions occurring during separations via membranes. Moreover, mixed-gas diffusivities can be calculated from the combination of mixed-gas sorption and mixed-gas permeation experiments — to date mixed-gas diffusion has been rarely studied [1-3]. Most commonly, gas transport in polymeric membranes has been investigated based on pure-gas permeation and sorption and less frequently by mixed-gas permeation experiments. Because mixed-gas solubility data were not produced — mainly because these experiments are far more challenging than pure- and mixed-gas permeation — authors have speculated on relevant phenomena affecting membranes for gas separations. To the best of our knowledge, only 12 publications [1, 4-14] exist for mixed-gas sorption experiments and cover a total of 7 polymers (i.e., PDMS, XLPEO, PMMA, PPO/CPPO, 6FDA-TADPO, PTMSP, and PIM-1).

Here, we present the results of CO₂/CH₄ mixed-gas sorption experiments at 35 °C in a series of polymers of interest for membranes for gas separations. To run these experiments, a new barometric mixed-gas sorption system meant to be operator-friendly, accurate and time-efficient was designed, constructed, and employed. Mixed-gas permeation information was retrieved both experimentally (in-house) and from the literature. Hence, we estimated mixed-gas diffusion coefficients from experimental data of mixed-gas permeability and solubility. The combination of mixed-gas permeation, solubility, and diffusion data allows us to quantitatively approach phenomena such as, for example, swelling, plasticization, intrachain rigidity, and aging.

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[7] B.J. Story, W. Koros, Sorption of CO₂/CH₄ mixtures in poly (phenylene oxide) and a carboxylated derivative, Journal of Applied Polymer Science, 42 (1991) 2613-2626.

[8] R.D. Raharjo, B.D. Freeman, E.S. Sanders, Pure and mixed gas CH₄ and n-C₄H₁₀ sorption and dilation in poly(dimethylsiloxane), Journal of Membrane Science, 292 (2007) 45-61.

[9] R.D. Raharjo, B.D. Freeman, E.S. Sanders, Pure and mixed gas CH₄ and n-C₄H₁₀ sorption and dilation in poly(1-trimethylsilyl-1-propyne), Polymer, 48 (2007) 6097-6114.

[10] C.P. Ribeiro Jr, B.D. Freeman, Carbon dioxide/ethane mixed-gas sorption and dilation in a cross-linked poly(ethylene oxide) copolymer, Polymer, 51 (2010) 1156-1168.

[11] O. Vopička, M.G. De Angelis, N. Du, N. Li, M.D. Guiver, G.C. Sarti, Mixed gas sorption in glassy polymeric membranes: II. CO₂/CH₄ mixtures in a polymer of intrinsic microporosity (PIM-1), Journal of Membrane Science, 459 (2014) 264-276.

[12] O. Vopička, M.G. De Angelis, G.C. Sarti, Mixed gas sorption in glassy polymeric membranes: I. CO₂/CH₄ and n-C₄/CH₄ mixtures sorption in poly(1-trimethylsilyl-1-propyne) (PTMSP), Journal of Membrane Science, 449 (2014) 97-108.

[13] A.E. Gemeda, M.G. De Angelis, N. Du, N. Li, M.D. Guiver, G.C. Sarti, Mixed gas sorption in glassy polymeric membranes. III. CO₂/CH₄ mixtures in a polymer of intrinsic microporosity (PIM-1): Effect of temperature, Journal of Membrane Science, 524 (2017) 746-757.

[14] B.J. Story, W.J. Koros, Sorption of CO₂/CH₄ mixtures in poly(phenylene oxide) and a carboxylated derivative, Journal of Applied Polymer Science, 42 (1991) 2613-2626.