Asymmetric membranes for use in nanofiltration
AssigneeImperial Innovations Limited
InventorsAndrew Guy Livingston, Yoong Hsiang See-Toh
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Abstract
Improved integrally skinned asymmetric membranes for organic solvent nanofiltration, and their methods of preparation and use are disclosed. Membranes are formed from polyimides by phase inversion and are then crosslinked by addition of amine crosslinking agents that react with the imide groups of the polyimide, creating amide bonds. These stabilize the membranes and allow solvent nanofiltration to be maintained even in the solvents from which the membranes were formed by phase inversion.
Claims41
A membrane, comprising an integrally skinned asymmetric polyimide membrane, wherein:
- (i) the membrane is stable in an organic solvent;
- (ii) at least a fraction of the imide groups of the polyimide are crosslinked;
- (iii) the polyimide is impregnated with a conditioning agent that functions to allow the pore structure to be maintained in a dry state and provides a flexible flat sheet membrane, said conditioning agent being either a low volatility or non-volatile organic liquid;
- (iv) the membrane preferentially rejects solutes having molecular weights in the range of 200-2000 g mol−1 in a feed stream solution comprising an organic solvent and dissolved solutes at ambient temperature.
A process for forming an integrally skinned asymmetric crosslinked polyimide membrane for solvent nanofiltration, comprising:
- (a) preparing a polyimide dope solution comprising:
- (i) a polyimide polymer, and (ii) a solvent system for said polyimide which is water miscible;
- (b) casting a film of said dope solution onto a supporting substrate;
- (c) after an evaporation period, immersing the film cast on the substrate into a coagulating medium;
- (d) treating the resulting asymmetric membrane with a solvent comprising one or more of a mono-, di-, tri-amine and/or a polyamine;
- and
- (e) treating the asymmetric membrane with a wash bath or baths comprising a conditioning agent, said conditioning agent being a low volatility or non-volatile organic liquid.
Dependencies are inferred from the claim text.