Permeation, sorption, and diffusion of CO2-CH4 mixtures in polymers of intrinsic microporosity: The effect of intrachain rigidity on plasticization resistance
2019
Genduso, Giuseppe | Wang, Yingge | Ghanem, Bader S. | Pinnau, I. (Ingo)
CO₂-CH₄ mixed-gas sorption and permeation properties of a ladder polymer (PIM-Trip-TB) were measured experimentally at 35 °C to interpret nonideal transport behavior of polymers of intrinsic microporosity (PIMs). Both CH₄ and CO₂ mixed-gas solubilities were lower than those in the pure-gas environment mainly due to competitive sorption. In the range of pressures tested, the CO₂/CH₄ mixed-gas solubility selectivity of PIM-Trip-TB coincided on average with the value at infinite dilution, and at all pressures, it was higher than the pure-gas solubility selectivity. Because CO₂ diffusion coefficient was found insensitive to mixture effects, we inferred that the increased diffusion coefficient of CH₄ and the consequent loss of CO₂/CH₄ permselectivity in mixture environment were correlated to CO₂-induced alteration of the selective diffusion domains of PIM-Trip-TB. Similar effects were also found for PIM-1 by an analysis of pure- and mixed-gas experimental permeation and sorption data. The increase of CH₄ mixed-gas diffusion coefficients from the pure-gas values was more pronounced for both PIMs (PIM-Trip-TB and PIM-1) than for a conventional low-free volume polymer 6FDA-mPDA polyimide reported previously; this indicates that the high intrachain rigidity in PIMs cannot restrain unfavorable mixture effects on CO₂/CH₄ diffusion and permeability selectivity.
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