Highly Permeable Matrimid^®/PIM-EA(H₂)-TB Blend Membrane for Gas Separation

The effect on the gas transport properties of Matrimid^®5218 of blending with the polymer of intrinsic microporosity PIM-EA(H₂)-TB was studied by pure and mixed gas permeation measurements. Membranes of the two neat polymers and their 50/50 wt % blend were prepared by solution casting from a dilute solution in dichloromethane. The pure gas permeability and diffusion coefficients of H₂, He, O₂, N₂, CO₂ and CH₄ were determined by the time lag method in a traditional fixed volume gas permeation setup. Mixed gas permeability measurements with a 35/65 vol % CO₂/CH₄ mixture and a 15/85 vol % CO₂/N₂ mixture were performed on a novel variable volume setup with on-line mass spectrometric analysis of the permeate composition, with the unique feature that it is also able to determine the mixed gas diffusion coefficients. It was found that the permeability of Matrimid increased approximately 20-fold with the addition of 50 wt % PIM-EA(H₂)-TB. Mixed gas permeation measurements showed a slightly stronger pressure dependence for selectivity of separation of the CO₂/CH₄ mixture as compared to the CO₂/N₂ mixture, particularly for both the blended membrane and the pure PIM. The mixed gas selectivity was slightly higher than for pure gases, and although N₂ and CH₄ diffusion coefficients strongly increase in the presence of CO₂, their solubility is dramatically reduced as a result of competitive sorption. A full analysis is provided of the difference between the pure and mixed gas transport parameters of PIM-EA(H₂)-TB, Matrimid^®5218 and their 50:50 wt % blend, including unique mixed gas diffusion coefficients.