Thin Film Composite Mixed-Matrix Membranes Based on Matrimid and Zeolitic Imidazolate Frameworks for CO2/N2 Separation Performance

Membrane-based gas separation processes are a technology in continuous evolution. Various types of polymer membranes have been developed, many exhibiting high CO2 permeability and selective properties over competing gases such as N2 and CH4. In order to be competitive, membranes must be less-expensive, more stable, and more efficient, and their production must be scalable. One solution is to develop thin-film composites with mixed-matrix membranes (TFC_MMM) that have the potential to boost productivity while maintaining low costs. In this work, TFC_MMMs containing Matrimid mixed with 12 wt % ZIF-94 were prepared by kiss coating on a porous support. The SEM analysis showed that defect-free membranes with a 3 μm selective layer have been obtained. At 1 bar, the addition of ZIF resulted in improved the separation performance for the CO2/N2 pair, with CO2 permeance of 4 GPU and CO2/N2 selectivity of 40, surpassing neat TFC-Matrimid (CO2 permeance ≈ 3 GPU, CO2/N2 selectivity ≈ 29). The use of ZIF-94 also had a stabilizing effect on the membranes against CO2 plasticization at high pressure.

CO2/N2 Gas Separation Using Pebax/ZIF-7-PSf Composite Membranes

In this study, we mixed the zeolitic imidazolate framework-7 (ZIF-7) with poly(ether-b-amide)^® 2533 (Pebax-2533) and used it as a selective layer for a composite membrane. We prepared the composite membrane’s substrate using polysulfone (PSf), adjusted its pore size using polyethylene glycol (PEG), and applied polydimethylsiloxane (PDMS) to the gutter layer and the coating layer. Then, we investigated the membrane’s properties of gases by penetrating a single gas (N₂, CO₂) into the membrane. We identified the peaks and geometry of ZIF-7 to determine if it had been successfully synthesized. We confirmed that ZIF-7 had a BET surface area of 303 m²/g, a significantly high Langmuir surface area of 511 m²/g, and a high CO₂/N₂ adsorption selectivity of approximately 50. Considering the gas permeation, with ZIF-7 mixed into Pebax-2533, N₂ permeation decreased from 2.68 GPU in a pure membrane to 0.43 GPU in the membrane with ZIF-7 25 wt%. CO₂ permeation increased from 18.43 GPU in the pure membrane to 26.22 GPU in the ZIF-7 35 wt%. The CO₂/N₂ ideal selectivity increased from 6.88 in the pure membrane to 50.43 in the ZIF-7 25 wt%. Among the membranes, Pebax-2533/ZIF-7 25 wt% showed the highest permeation properties and the characteristics of CO₂-friendly ZIF-7.