Truly combining the advantages of polymeric and zeolite membranes for gas separations

Mixed-matrix membranes (MMMs) have been investigated to render energy-intensive separations more efficiently by combining the selectivity and permeability performance, robustness, and nonaging properties of the filler with the easy processing, handling, and scaling up of the polymer. However, truly combining all in one single material has proven very challenging. In this work, we filled a commercial polyimide with ultrahigh loadings of a high–aspect ratio, CO2-philic Na-SSZ-39 zeolite with a three-dimensional channel system that precisely separates gas molecules. By carefully designing both zeolite and MMM synthesis, we created a gas-percolation highway across a flexible and aging-resistant (more than 1 year) membrane. The combination of a CO2-CH4 mixed-gas selectivity of ~423 and a CO2 permeability of ~8300 Barrer outperformed all existing polymer-based membranes and even most zeolite-only membranes. Description Material design maximizes performance Zeolites are able to separate molecules with similar size and shape because of their well-defined, uniform pore size and specific adsorption properties. However, it has been a challenge to retain these features when blending a zeolite with a polymeric matrix support. Tan et al. developed a method to put high loadings of the aluminosilicate SSZ-39, which is known for its attraction of carbon dioxide, into a commercial polyimide selected for its compatibility with the zeolite. The resulting mixed matrix membranes were flexible and defect free, showing excellent separation of carbon dioxide that even exceeded the performance of pure zeolite membranes. —MSL A well-designed zeolite-filled mixed matrix membrane outperforms zeolite-only membranes in gas separation.