Chiral separation of enantiomers is an essential undertaking throughout discovery given the importance of chirality in the biological response and the difference of biological activity between two enantiomers. Due to their similar physical and chemical properties, separation of enantiomers is a challenging task, but is crucial. While one enantiomers can constitute a cure for a specific disease, the incorrect enantiomer may have no curative effect or may be harmful. Chiral resolution of racemic mixtures has been broadly studied by various methods, among which membranes have potential for large-scale production of single enantiomers and are seen as serious candidates to revolutionise chiral separation processes. The method used in this thesis is based on the incorporation of chiral functional groups into polymeric membranes for the efficient, fast and sustainable separation of enantiomers.
Organic-inorganic membranes containing chiral Metal Organic Frameworks have been investigated. MOFs have shown great potential for use as sorbents, unfortunately this technique did not give a satisfying enantioseparation to date. The fabrication of high-quality membranes containing chiral MOF is still a challenge today because of the difficulty in controlling the MOF growth and the implementation in polymeric membranes.
Another strategy to develop chiral membranes was the use of chiral polymers to induce a chiral environment in the membrane. The performance was tested using different set-ups in order to optimize the process. A pressure driven set-up was compared with the usual preferential adsorption and concentration driven permeation method. Modifying P84 membranes with Polylysine and enhancing the chirality of the membrane via several chemical modifications enabled the separation of Tryptophan enantiomers. As an application of this chapter, a collaboration was established leading to the testing of another type of chiral membranes with the same characterisation set-ups.
Membrane ageing was also investigated as high performance polymer membranes are prone to physical ageing and do not offer long term optimal stability. The anti-ageing performance of several nano-scale additives composite membranes has been studied and evaluated on the basis of crucial performance measures relevant to their real-world usage patterns. Particular focus has been placed on gas permeability, selectivity, and additive compatibility with P84 polymeric membranes. Even after continuous long-term exposure to aqueous solutions of alcohols, the selected composite membranes outperform the state-of-the-art of pervaporation membranes with fluxes higher than the current standard.