Development of epoxy nanofiltration membranes into smart materials for chemical separations

Abstract

Epoxy nanofiltration membranes were synthesized using a diamine and a diepoxide in a one-pot step polymerization. These membranes were stable in organic solvents and used for chemical separations in dichloromethane. The epoxy membranes showed excellent selectivities in chemical separations of over 100:1. The selectivity of the membrane was optimized by adding in a triepoxide to the polymerization to increase the cross-link density. Optimization of the membranes increased the selectivity up to 250:1 for select chemical separations. These epoxy membranes are some of the first nanofiltration membranes used in the separation of important fatty acids such as omega-3 fish oil fatty acid ethyl esters, and saturated fatty acid methyl esters. The epoxy membranes can separate eicosahexaenoic acid ethyl ester from docosahexenoic acid ethyl ester with selectivities up to 1.4:1. The selectivity of saturated fatty acid methyl esters with epoxy membranes were as high as 100:1 for the separation of methyl butyrate from methyl stearate. Epoxy membranes are also the first stimulus-responsive membranes with a disulfide-bond dependent mechanism. The labile disulfide bond is cleaved upon exposure to a chemical stimulus, which cleaves the cross-links within the membrane, and increases the pore size. The flux and selectivity of chemicals through the membrane was controlled before and after exposure to a chemical stimulus. The membranes were implemented in a multicomponent chemical separation to produce three-purity enriched fractions from a three-component mixture. The purity of chemicals improved from 33% up to 82%, with recovery yields as high as 88%. v PUBLIC ABSTRACT Chemical separations account for up to 15% of the global energy usage, and it is important for scientists to explore new technologies that can reduce the cost to purify chemicals. Membrane-based chemical separations are a greener separation technology when compared to the conventional separation techniques such as distillation and chromatography. This thesis describes the fabrication of new epoxy nanofiltration membranes that are highly selective in chemical separations, showing their ability to compete with conventional separation techniques. Epoxy membranes are also used in industrial relevant conditions and offer a potential solution for a multicomponent chemical separation, which is a challenging problem for current industrial membranes. vi