CMM assists in elucidating the capabilities of polymeric and zeolite membranes for gas adsorption

© KU Leuven - Xiaoyu Tan

The efficient separation of CO2 and methane or nitrogen gas poses an important industrial challenge, for instance for the purification of biogas or flue gasses. A new mixed-matrix membrane (MMM) developed by the KU Leuven is shown to outperform all existing polymer-based membranes in terms of CO2—CH4 mixed-gas selectivity and CO2 permeability. The role of the Na-SSZ-39 zeolite incorporated in the polymer membrane was elucidated with the aid of computational modelling performed by the CMM. The results of this collaborative study were recently published in Science.

Zeolites are not only used as catalysts in the petrochemical industry, but their high thermal and chemical stability makes them also ideally suited for other applications. In this work, the Na-SSZ-39 zeolite was embedded as a filler in a polymeric membrane, forming a zeolite-filled mixed-matrix membrane (MMM). In this way, a selective zeolite can be combined with less expensive and more processable polymers. Notwithstanding the challenging problem of obtaining an MMM with a high zeolite loading in combination with a defect-free polymer-zeolite interface and a highly selective zeolite, such a membrane was realized by the group of prof. Vankelecom (cMACS), which outperforms all existing polymer-based membranes and even most zeolite-only membranes.

Molecular insight in the gas adsorption behaviour of the zeolite was provided by the CMM. Using grand canonical Monte Carlo (GCMC) simulations, adsorption isotherms were constructed for unary and binary gas adsorption cases. Because of the CO2-philicity of the zeolite, due to the preferential electrostatic interaction between CO2 and the sodium ions in the zeolite, the methane uptake was observed to drastically reduce in the presence of CO2. Furthermore, quantum mechanical calculations of the diffusion barrier also showed a difference of almost 20 kJ/mol between CO2 and methane, thus confirming the experimentally observed difference in diffusivity selectivity.

CMM authorsAran Lamaire, prof. Veronique Van Speybroeck