Modified membranes

• US 20050029185A1
• Filed: 07/30/2004
• Published: 02/10/2005
• Est. Priority Date: 11/13/2000
• Status: Active Grant

• Current Assignee: Evoqua Water Technologies LLC (Xylem, Inc.)
• Original Assignee: Siemens Water Technologies Corp (Siemens AG)
• Inventors: Muller, Heinz-Joachim
• Granted Patent: US 7,300,022 B2
• Time in Patent Office: Days
• US Class Current: 210/500.240
• CPC Class Codes: B01D 2323/02 Hydrophilization
• CPC Class Codes: B01D 2323/30 Cross-linking
• CPC Class Codes: B01D 2323/36 Introduction of specific chemical groups
• CPC Class Codes: B01D 2325/24 Mechanical properties, e.g. strength
• CPC Class Codes: B01D 67/0018 Thermally induced processes [TIPS]
• CPC Class Codes: B01D 67/00933 by addition of a layer chemically bonded to the membrane
• CPC Class Codes: B01D 69/125 In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
• CPC Class Codes: B01D 71/34 Polyvinylidene fluoride
• CPC Class Codes: B01D 71/403 Polymers based on the polymerisation of maleic acid or derivatives thereof
• CPC Class Codes: B01D 71/48 Polyesters
• CPC Class Codes: B01D 71/56 Polyamides, e.g. polyester-amides
• CPC Class Codes: B01D 71/68 Polysulfones; Polyethersulfones

Abstract

A porous polymeric membrane formed from a blend of a polymeric membrane forming material, such as polyvinylidene fluoride or polysulfone and a polymeric reactivity modifying agent adapted to modify the surface active properties of the porous polymeric membrane. The reactivity modifying agent is preferably a linear polymeric anhydride, such as poly(alkyl vinyl ether/maleic anhydride). The surface activity modifications include modification of the hydrophilicity/hydrophobicity balance of the membrane, or hydrolysis followed by reaction with a polyamine to form a crosslinked polyamide layer. Such modified membranes have use as reverse osmosis membranes.

Claims

1. A method of preparing a porous polymeric membrane, the method comprising the steps of:

blending a reactivity modifying agent with a polymeric membrane forming material whereby a blended material is obtained, wherein the reactivity modifying agent comprises an anhydride; and

casting a porous polymeric membrane from the blended material.

2. The method according to claim 1, wherein the polymeric membrane forming material is blended with the reactivity modifying agent prior to or during the step of casting.

3. The method according to claim 1, wherein the reactivity modifying agent is blended with the polymeric membrane forming material before the step of casting.

4. The method according to claim 1, wherein the reactivity modifying agent is blended with the polymeric membrane forming material in an unreacted form.

5. The method according to claim 1, wherein the reactivity modifying agent is blended with the polymeric membrane forming material in a reacted form.

6. The method according to claim 1, wherein the reactivity modifying agent blended with the polymeric porous membrane forming material is subjected to a chemical modification subsequent to the step of casting.

7. The method according to claim 6, wherein the chemical modification comprises hydrolysis whereby the porous polymeric membrane is rendered hydrophilic.

8. The method according to claim 6, wherein the chemical modification comprises crosslinking.

9. The method according to claim 6, wherein the chemical modification comprises treatment with one or more substances selected from the group consisting of tetraethylenepentamine, tris-(hydroxymethyl) aminomethane, sulfuric acid, polyethylene glycol, and calcium carbonate.

10. The method according to claim 6, wherein the chemical modification comprises treatment with a crosslinking amine to form amide linkages.

11. The method according to claim 10, further comprising the step of selecting a degree of incorporation and an extent of cross linking, whereby the porous polymeric membrane is suitable for reverse osmosis.

12. The method according to claim 1, wherein the reactivity modifying agent is blended into the polymeric membrane forming material before or during the casting step, wherein the reactivity modifying agent is blended in an amount such that a combined precursor to the porous polymeric membrane is a single phase mixture.

13. The method according to claim 1, wherein the porous polymeric membrane comprises a hollow fibre membrane.

14. The method according to claim 1, wherein the porous polymeric membrane comprises a flat sheet membrane.

15. The method according to claim 1, wherein the porous polymeric membrane is cast from a dope solution comprising a polymer.

16. The method according to claim 15, wherein the dope solution comprises at least one polymer selected from the group consisting of a polyvinylidene fluoride, a sulfone polymer, and a polyvinylpyrrolidone copolymer.

17. The method according to claim 16, wherein the dope solution comprises about 16.8 to about 17.2% polyvinylidene fluoride.

18. The method according to claim 16, wherein the dope solution comprises about 2.6 to about 2.7% polyvinylpyrrolidone/vinyl acetate copolymer.

19. The method according to claim 1, wherein the porous polymeric membrane is cast from a dope solution comprising an organic solvent.

20. The method according to claim 19, wherein the organic solvent comprises N-methylpyrrolidone.

21. The method according to claim 20, wherein dope solution comprises about 73.7 to about 77.3% N-methylpyrrolidone.

22. The method according to claim 1, wherein the porous polymeric membrane is formed from a dope solution comprising a linear polymeric anhydride.

23. The method according to claim 22, wherein the linear polymeric anhydride comprises poly(methyl vinyl ether/maleic anhydride).

24. The method according to claim 23, wherein the dope solution comprise about 3.1% to about 3.4% poly(methyl vinyl ether/maleic anhydride).

25. The method according to claim 1, wherein the porous polymeric membrane is cast from a dope solution comprising a salt.

26. The method according to claim 25, wherein the salt comprises LiCl.

27. The method according to claim 26, wherein the dope solution comprises about 3.0 to about 3.8% LiCl.

28. The method according to claim 1, wherein the porous polymeric membrane is cast from a dope solution comprising 17% polyvinylidene fluoride;

3.5% LiCl;

2.7% polyvinylpyrrolidone/vinyl acetate copolymer;

3.1% poly(methyl vinyl ether/maleic anhydride); and

73.7% N-methylpyrrolidone.

29. The method according to claim 1, wherein the porous polymeric membrane is formed from a dope solution comprising 16.8% polyvinylidene fluoride;

3.4% poly(methyl vinyl ether/maleic anhydride);

3.8% LiCl; and

76% N-methylpyrrolidone.

30. The method according to claim 1, wherein the reactivity modifying agent and polymeric membrane forming material are selected such that a melt comprising the reactivity modifying agent and polymeric membrane forming material is thermodynamically stable and no demixing process occurs in the melt.

31. The method according to claim 1, wherein the reactivity modifying agent, polymeric membrane forming material, and reaction conditions are selected such that no gelation occurs during casting the membrane.

32. The method according to claim 1, further including the step of mixing the dope solution at about 50°

C. overnight.

33. The method according to claim 1, wherein the dope solution is formed by a diffusion induced phase separation procedure in a precipitation bath comprising water.

34. The method according to claim 1, wherein the dope solution is formed by a diffusion induced phase separation procedure in a precipitation bath comprising polyethylene glycol.

35. The method according to claim 1, wherein the dope solution is formed by a diffusion induced phase separation procedure in a precipitation bath comprising N-methyl pyrrolidone.

36. The method according to claim 1, wherein the dope solution is formed by a diffusion induced phase separation procedure in a precipitation bath comprising 45% polyethylene glycol 200;

45% water; and

10% N-methylpyrrolidone.

43. A porous polymeric membrane prepared according to the method of claim 1.

37. A method of modifying a surface of a porous polymer membrane comprising the steps of:

i) blending a reactivity modifying agent comprising an anhydride with a polymeric membrane forming material; and

ii) casting a modified membrane.

38. The method according to claim 37, further comprising the step of hydrolysing at least a surface portion of the reactivity modifying agent.

39. The method according to claim 38, wherein the step of hydrolysing occurs in the presence of a sodium buffer.

40. The method according to claim 38, wherein the surface portion of the reactivity modifying agent is partially hydrolysed.

41. The method according to claim 37, further comprising the steps of first at least partially hydrolysing at least a surface portion of the reactivity modifying agent, and subsequently reacting resultant hydrolysed groups with a polyfunctional amine.

42. The method according to claim 41, wherein the polyfunctional amine reacts to crosslink the resultant hydrolysed groups.