Mixed matrix composite membranes for gas separation
So far, the industrial use of technical separation membranes has been largely limited to liquid filtration. Reasons are in particular inadequate separation properties and high membrane costs. Due to their inherent energy efficiency, membranes offer enormous potential for the separation of gases.
In the MEGA project, mixed matrix membranes were developed with great potential for gas separation. Microporous framework compounds (zeolites, MOFs) with defined pore sizes were embedded in polymer matrices and are therefore suitable for the separation of gas molecules by size exclusion. For this purpose, porous PVDF hollow fiber membranes were coated with appropriate polymer dispersions by continuous dip coating. The layer thickness of the mixed matrix layer in the range from 500 nm to 5 μm could be controlled via the viscosity of the dispersion and the coating speed. The use of nanoparticular framework connections (< 100 nm) is decisive for the quality of the layers. By controlling the layer thickness, only small amounts of material are required for the coating.
The mixed matrix membranes show improved separation properties compared to pure polymer coatings. The water vapor permeability of polyvinyl alcohol layers increased about almost 100 percent to 7000 barrers by adding SAPO‑34 particles. By selecting suitable polymer‑MOF combinations, the separation properties of the membranes can be adapted as for partitioning of carbon dioxide in waste gases.