Asymmetric gel-filled microporous membranes

• US 20050011826A1
• Filed: 07/18/2002
• Published: 01/20/2005
• Est. Priority Date: 07/20/2001
• Status: Active Grant

• Current Assignee: Mcmaster University
• Original Assignee: Mcmaster University
• Inventors: Mika, Alieja M., Childs, Ronald F., Ge, Jijun, McCrory, Chris
• Granted Patent: US 7,247,370 B2
• Time in Patent Office: Days
• US Class Current: 210/490
• CPC Class Codes: B01D 2323/30 Cross-linking
• CPC Class Codes: B01D 2323/34 Use of radiation
• CPC Class Codes: B01D 2325/022 Asymmetric membranes
• CPC Class Codes: B01D 2325/28 Degradation or stability over time
• CPC Class Codes: B01D 2325/42 Ion-exchange membranes
• CPC Class Codes: B01D 67/0006 by chemical reactions in-situ polymerisation, polycondensation, cross-linking or reaction for manufacturing composite membranes B01D69/125
• CPC Class Codes: B01D 67/00091 by evaporation
• CPC Class Codes: B01D 67/0088 Physical treatment with compounds, e.g. swelling, coating or impregnation
• CPC Class Codes: B01D 69/10 Supported membranes; Membrane supports
• CPC Class Codes: B01D 71/38 Polyalkenylalcohols; Polyalkenylesters; Polyalkenylethers; Polyalkenylaldehydes; Polyalkenylketones; Polyalkenylacetals; Polyalkenylketals
• CPC Class Codes: B01D 71/40 Polymers of unsaturated acids or derivatives thereof, e.g. salts, amides, imides, nitriles, anhydrides, esters
• CPC Class Codes: B01D 71/44 Polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds, not provided for in a single one of groups B01D71/26-B01D71/42
• CPC Class Codes: Y10T 428/249953 Composite having voids in a component [e.g., porous, cellular, etc.]
• CPC Class Codes: Y10T 428/249961 With gradual property change within a component

Abstract

The invention provides asymmetric membranes composed of a microporous substrate whose pores contain a crosslinked gel, the density of the crosslinked gel being greater at or adjacent to one major surface of the membrane than the density at the other major surface. The membranes are useful for separating matter from liquids and display good flux and good rejection at low pressure.

Claims

1. An asymmetric membrane comprising a microporous membrane substrate, in at least some of whose pores is contained a crosslinked gel which forms a continuous or substantially continuous layer, the density of the crosslinked gel being greater at or adjacent to a first major surface of the membrane than the density at or adjacent to a second major surface of the membrane.

2. A membrane according to claim 1, wherein at least some of the pores contain a cross-linked gel such that it forms a continuous or substantially continuous layer whose thickness is less than that of the support membrane and is adjacent to the first major surface of the microporous membrane substrate.

3. A membrane according to claim 1, wherein the gel forming the continuous pore-filling band is not chemically bonded to the microporous support substrate but is entangled with the structural elements of the support.

4. A membrane according to claim 1, wherein the density of crosslinked gel polymer is at a maximum at or adjacent to the first major surface of the membrane and decreases gradually towards the second major surface of the membrane.

5. A membrane according to claim 1, wherein the membrane substrate is a microporous polyethylene, polypropylene, poly(vinylidenedifluoride), poly(tetrafluoroethylene), cellulose, cellulose acetate, nylon, poly(ester), polysulfone, or polycarbonate, or a porous ceramic or glass membrane support having a thickness of from 1 to 500 μ

m, preferably in the range of 10 to 200 μ

m, more preferably in the range 20 to 150 μ

m, a pore diameter in the range of 0.05 to 20 μ

m, preferably in the range 0.1 to 10 μ

m, more preferably 0.2 to 2 μ

m, and a pore volume of about 25% to about 95%, preferably in the range of 60 to 85%.

6. A membrane according to claim 1, wherein pores are of different sizes, with larger pores adjacent to one of the major surfaces of the substrate and smaller pores adjacent to the other major surface.

7. A membrane according to claim 1, wherein the crosslinked gel is a polyelectrolyte gel.

8. A membrane according to claim 7, wherein the crosslinked polyelectrolyte is based on one or more of 4-vinylpyridine, 2-vinylpyridine, acrylic acid, methacrylic acid, styrenesulfonic acid, vinylsulfonic acid, acrylamidomethylpropanesulfonic acid, diallylamine, N,N-dimethyldiallylamine, allylamine, N(dimethylaminoethyl)-acrylamide, N,N-dimethylaminopropyl-methacrylamide), vinylbenzylamine or polyethyleneimine and their derivatives.

9. A membrane according to claim 1, wherein the crosslinked gel is a hydrogel.

10. A membrane according to claim 9, wherein the crosslinked hydrogel is based on crosslinked poly(vinyl alcohol), poly(acrylamide), poly(N-vinylpyrrolidone), poly(ethylene glycol) or poly(propylene glycol).

11. A membrane according to claim 1, which displays a rejection ratio of 1.5 or greater.

12. A process for preparing an asymmetric membrane according to claim 1, wherein the pores of the microporous substrate are filled with a solution of a polymer, or a polymerizable monomer, that bears functional groups and a crosslinking agent, whereafter some of the solvent is allowed to evaporate and crosslinking or polymerization and crosslinking, is allowed to proceed in the pores to form the asymmetric membrane.

13. A process according to claim 12, wherein the functional groups present on the polymer or on the polymerizable monomer are ionically charged groups or groups that can be rendered ionically chargeable.

14. A process according to claim 12, wherein evaporation from one major surface of the substrate is permitted while the other major surface is sealed to prevent evaporation.

15. A process according to claim 12, wherein the microporous substrate has pores of different sizes, with larger pores adjacent to one major surface of the substrate and smaller pores adjacent to the other major surface of the substrate.

16. A process according to claim 12, wherein evaporation is permitted from that major surface to which the larger pores are adjacent.

17. A process according to claim 15, wherein evaporation from both major surfaces of the microporous substrate is permitted.

18. A process according to claim 12, wherein the polymer is poly(4-vinylpyridine) or poly(acrylic acid) and the solvent is N,N-dimethylformamide or N-methylpyrrolidone.

19. A process according to claim 18, wherein the solvent is N,N-dimethylformamide, in admixture with methanol.

20. A process according to claim 12, wherein the polymer is a polyamine and the crosslinking agent is a dihalide or a diepoxide.

21. A process according to claim 20, wherein the polyamine is poly(4-vinylpyridine) or poly(ethylimine) and the crosslinking agent is α

, α

′

-dibromoxylene, α

, α

′

-dichloroxylene or 1,3-dibromopropane.

22. A process according to claim 20, wherein the polymer is poly(ethyleneimine) and the solvent is an isopropanol/methanol mixture.

23. A process according to claim 12, wherein the polymer is poly(vinylbenzylchloride) and the crosslinking agent is a di- or polyamine.

24. A process according to claim 23, wherein the di- or polyamine is 1,6-diaminohexane, piperazine or 1,4-diazabicyclo[2.2.3]octane.

25. A process according to claim 12, wherein the polymer is poly(vinyl alcohol) and the crosslinking agent is glutaraldehyde.

26. A process for preparing an asymmetric membrane according to claim 1, which comprises filling the pores of the microporous substrate with a solution of a polymerizable monomer that bears functional groups, a crosslinking agent, a photoinitiator for polymerization and a photoblocker, and irradiating to cause polymerization to form the asymmetric membrane.

27. A process according to claim 26, wherein the functional groups are ionically charged groups or groups that can be rendered ionically chargeable.

28. A process according to claim 26, wherein the polymerizable monomer is 4-vinylpyridine or acrylic acid, the photoinitiator is 2,2′

-dimethoxy-2-phenylacetophenone, the photoblocker is 2′

,2-dihydroxy-4,4′

-dimethoxybenzophenone and the solvent is N,N-dimethylformamide.

29. A separation process which comprises passing a liquid containing matter through a membrane according to claim 1 to separate some or all of the matter from the liquid.

30. A process according to claim 29, wherein multivalent cations are separated from the liquid.

31. A process according to claim 29, wherein monovalent cations are separated from the liquid.

32. A process according to claim 29, which is operated at pressure below 300 kPa.

33. A process according to claim 29, which is operated at a pressure below 100 kPa.