Highly permselective MIL-68(Al)/matrimid mixed matrix membranes for CO₂/CH₄ separation

With global appeal to green and efficient utilization of energies, metal-organic frameworks based mixed matrix membranes are standing out in applications such as gas and liquid separation because of the integration of size/shape selectivity of MOFs with processability and mechanical stability of polymers. In the present work, a novel MIL-68(Al) (MIL = Material of Institute Lavoisier) based mixed matrix membrane (MMM) was developed by adding porous MIL-68(Al) into Matrimid for the separation of CO₂/CH₄ mixture. The MIL-68(Al)/Matrimid MMM displays a high CO₂ permselectivity. For the separation of an equimolar CO₂/CH₄ mixture at 373 K and 1 bar, the CO₂ permeability and the CO₂/CH₄ selectivity are 284.3 Barrer and 79.0, respectively, which far exceed the Robeson upper bound limit and those of the previously reported MMMs. Both the operation pressure and temperature have great influence to the separation performance of the MIL-68(Al)/Matrimid MMM. Further, the MIL-68(Al)/Matrimid MMM shows a high stability in the long-term separation of CO₂/CH₄. These properties recommend the MIL-68(Al)/Matrimid MMM as a promising candidate for the purification of natural gases.