(227f) Mixed Matrix Membranes for Organic Solvent Nanofiltration

Organic liquids are ubiquitous in chemical science based industries, which range in scale from refining to pharmaceutical production. It is generally accepted that 40-70% of capital and operating costs in these industries are dedicated to separations; and a substantial fraction of this cost is related to processing of organic liquids. Membrane technology has the potential to provide game changing alternatives to conventional concentration and purification technologies such as evaporation, liquid extraction, adsorption and chromatography, through Organic Solvent Nanofiltration (OSN). The membranes must offer resistance to organic environments, attractive selectivies and permeabilities. Ideally they should also be resistant to physical aging under use.

This presentation will focus on research into mixed matrix membranes for OSN. Metal-organic frameworks (MOFs) have been used to create mixed matrix membranes in two distinct approaches.

In the first approach, we have used In-Situ-Growth (ISG) to prepare MOFs inside cross-linked polyimide ultrafiltration support membranes. The MOF, in this case HKUST-1, is prepared from the MOF precursors by submerging the pre-formed polyimide membrane in HKUST-1 precursor solutions. ISG is presented as an alternative to mixed matrix membranes (MMMs) in which MOF crystals are fabricated ex-situ of the membrane and added to the polymer dope solution. The presence of HKUST-1 in the ISG membranes was shown to increase the rejection of styrene oligomers on average by 30%, and also reduced pressure-induced flux decline from above 40% flux decline over 24 hours for pure polymer membranes, to less than 2% for the ISG membranes.

In the second approach, thin film nanocomposite (TFN) membranes containing 50-150 nm MOF nanoparticles [ZIF-8, MIL-53(Al), NH₂-MIL-53(Al) and MIL-101(Cr) were employed] have been synthesized via interfacial polymerisation on top of a cross-linked P84 support. MOF nanoparticles were homogeneously distributed in the polyamide layer, and their presence was inferred by a combination of contact angle measurements, FT-IR spectroscopy, SEM, EDX, XPS and TEM. TFN membranes showed dramatically increased MeOH and THF permeances when compared to the same membranes with no MOFs added, without sacrificing rejection. A direct trend was observed between the MeOH permeance and the porosity of the MOFs, suggesting preferential flow paths provided by the MOF pores. The best performance was obtained with the incorporation of nanosized mesoporous MIL-101(Cr), with the largest pore size and surface area. This TFN membrane led to an exceptional increase in permeance, from 1.5 to 3.9 and from 1.7 to 11.1 L·m^−2·h^−1·bar^−1 for MeOH and THF respectively, whereas the rejection remained higher than 90% (molecular weight cut off of 232 g·mol^-1 for MeOH and 295 g·mol^-1 for THF).