Halar membranes

• US 20050098494A1
• Filed: 08/09/2004
• Published: 05/12/2005
• Est. Priority Date: 02/12/2002
• Status: Active Grant

• Current Assignee: Evoqua Water Technologies LLC
• Original Assignee: Siemen Water Technologies Corporation (Siemens AG)
• Inventors: Mullette, Daniel, Muller, Heinz-Joachim
• Granted Patent: US 7,247,238 B2
• Time in Patent Office: Days
• US Class Current: 210/500.27
• CPC Class Codes: B01D 2323/08 Specific temperatures applied
• CPC Class Codes: B01D 2323/081 Heating
• CPC Class Codes: B01D 2323/18 Pore-control agents or pore formers
• CPC Class Codes: B01D 2323/22 Specific non-solvents or non-solvent system
• CPC Class Codes: B01D 2325/022 Asymmetric membranes
• CPC Class Codes: B01D 2325/0231 Dense layers being placed on the outer side of the cross-section
• CPC Class Codes: B01D 2325/20 Specific permeability or cut-off range
• CPC Class Codes: B01D 2325/36 Hydrophilic membranes
• CPC Class Codes: B01D 2325/38 Hydrophobic membranes
• CPC Class Codes: B01D 67/0018 Thermally induced processes [TIPS]
• CPC Class Codes: B01D 67/0027 by stretching
• CPC Class Codes: B01D 67/003 by selective elimination of components, e.g. by leaching
• CPC Class Codes: B01D 67/0031 by elimination of at least one of the blocks of a block copolymer
• CPC Class Codes: B01D 67/0088 Physical treatment with compounds, e.g. swelling, coating or impregnation
• CPC Class Codes: B01D 69/08 Hollow fibre membranes manufacture of hollow fibres D01D5/24, D01F1/08
• CPC Class Codes: B01D 71/32 containing fluorine atoms
• CPC Class Codes: B29C 67/202 comprising elimination of a solid or a liquid ingredient
• CPC Class Codes: D01D 5/24 with a hollow structure; Spinnerette packs therefor D01D5/38 takes precedence; producing tubes of plastic material B29D; addition of agents forming hollow filaments D01F1/08
• CPC Class Codes: Y10T 428/249958 Void-containing component is synthetic resin or natural rubbers

Abstract

Porous polymeric membranes including Halar (poly (ethylene chlorotrifluoroethylene)) and related compounds and the methods of production thereof which avoid the use of toxic solvents. Preferred solvents, coating agents and pore forming agents are citric acid ethyl ester or glycerol triacetate. The membranes may be in the form of a hollow fibre or flat sheet, and may include other agents to modify the properties of the membrane, such as the hydrophilic/hydrophobic balance. Leachable agents may also be incorporated into the membranes.

Claims

1. A porous polymeric membrane comprising Halar and formed without the use of a toxic solvent.

2. The porous polymeric membrane according to claim 1, comprising a hollow fibre or a flat sheet.

3. The porous polymeric membrane according to claim 1, comprising a microfiltration membrane or an ultrafiltration membrane.

4. The porous polymeric membrane according to claim 1, having an asymmetric cross-sectional pore size distribution defining a large-pore face and a small-pore face.

5. The porous polymeric membrane according to claim 1, wherein the small-pore face of the membrane has a pore size of from 0.01 μ

m to 20 μ

m.

6. The porous polymeric membrane according to claim 1, formed by thermally induced phase separation.

7. The porous polymeric membrane according to claim 1, comprising at least one additional material, wherein the material is compatible with Halar.

8. The porous polymeric membrane according to claim 7, comprising a species adapted to modify a chemical behaviour of the membrane.

9. The porous polymeric membrane according to claim 8, wherein the chemical behaviour of the membrane comprises a hydrophilicity/hydrophobicity balance of the membrane.

10. The porous polymeric membrane according to claim 9, wherein the membrane is hydrophobic.

11. The porous polymeric membrane according to claim 9, wherein the membrane is hydrophilic.

12. The porous polymeric membrane according to claim 1, prepared from a solution comprising at least one compound according to formula I or formula II:

13. The porous polymeric membrane according to claim 12, wherein

R₁, R₂, and R₃ are independently selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, and hexyl;

R₄ is selected from the group consisting of H, OH, COR₅, OCOR₅, methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy; and

R₅ is selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, and hexyl.

14. The porous polymeric membrane according to claim 12, wherein R₁, R₂, and R₃ are each ethyl, and wherein R₄ is H.

15. The porous polymeric membrane according to claim 12, wherein the compound of formula I is citric acid ethyl ester.

16. The porous polymeric membrane according to claim 12, wherein the compound of formula II is glycerol triacetate.

17. The porous polymeric membrane according to claim 12, wherein the compound of formula I or II is at least one of a polymer solvent and a coating agent.

18. A porous polymeric membrane, the membrane comprising a polymer and a leachable agent, wherein the polymer comprises Halar.

19. The porous polymeric membrane according to claim 18, comprising a microfiltration membrane or an ultrafiltration membrane.

20. The porous polymeric membrane according to claim 18, wherein the leachable agent comprises silica.

21. The porous polymeric membrane according to claim 18, wherein the leachable agent is present in the membrane in an amount of from 10 wt. % to 50 wt. % of a total weight of the polymer.

22. The porous polymeric membrane according to claim 18, wherein the leachable agent is present in the membrane in an amount of 30 wt. % of a total weight of the polymer.

23. The porous polymeric membrane according to claim 20, wherein the silica is a hydrophobic silica.

24. The porous polymeric membrane according to claim 23, wherein the hydrophobic silica is a fumed hydrophobic silica.

25. The porous polymeric membrane according to claim 24, wherein the silica is AEROSIL®

R 972 fumed hydrophobic silica.

26. The porous polymeric membrane according to claim 20, wherein the silica is a hydrophilic silica.

27. The porous polymeric membrane according to claim 26, wherein the silica is a fumed hydrophilic silica.

28. The porous polymeric membrane according to claim 27, wherein the silica is AEROSIL®

200 fumed hydrophilic silica.

29. A porous polymeric membrane, the membrane comprising Halar and silica, wherein the porous polymeric membrane further comprises a coating comprising a coating agent comprising at least one compound according to formula I or formula II:

30. The porous polymeric membrane according to claim 29, wherein

R₁, R₂, and R₃ are independently selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, and hexyl;

R₄ is selected from the group consisting of H, OH, COR₅, OCOR₅, methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy; and

R₅ is selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, and hexyl.

31. The porous polymeric membrane according to claim 29, comprising a microfiltration membrane or an ultrafiltration membrane.

32. The porous polymeric membrane according to claim 29, wherein R₁, R₂, and R₃ are each ethyl, and wherein R₄ is H.

33. The porous polymeric membrane according to claim 29, wherein the compound of formula I or formula II is an environmentally friendly pore controlling agent.

34. The porous polymeric membrane according to claim 29, wherein the compound of formula I is citric acid ethyl ester.

35. The porous polymeric membrane according to claim 29, wherein the compound of formula II is glycerol triacetate.

36. The porous polymeric membrane according to claim 29, having a high permeability.

37. The porous polymeric membrane according to claim 29, having a good macroscopic integrity.

38. The porous polymeric membrane according to claim 29, having uniform wall thickness.

39. The porous polymeric membrane according to claim 29, having a high mechanical strength.

40. A method of preparing a porous polymeric material, the method comprising the steps of:

(a) heating a mixture comprising Halar and a solvent system, the solvent system comprising a first component that is a latent solvent for Halar, at an elevated temperature, whereby the Halar dissolves in the solvent system to yield an optically clear solution;

(b) rapidly cooling the optically clear solution such that a non-equilibrium liquid-liquid phase separation takes place, thereby forming a continuous polymer rich phase and a continuous polymer lean phase, wherein the continuous polymer rich phase and the continuous polymer lean phase are intermingled to form a bicontinuous matrix having a large interfacial area;

(c) cooling the bicontinuous matrix until the continuous polymer rich phase solidifies, whereby a solid polymeric material is obtained; and

(d) removing the continuous polymer lean phase from the solid polymeric material, whereby a porous polymeric material is obtained.

41. The method of claim 40, wherein the solvent system further comprises a second component that is a non-solvent for Halar.

42. A method of manufacturing a membrane, the method comprising the step of casting a membrane from a polymer composition, the polymer composition comprising Halar dissolved in a solvent system, wherein the solvent system comprises no toxic solvent.

43. A method of forming a hollow fibre membrane, the method comprising:

forming a blend of Halar with a compatible solvent;

forming the blend into a hollow fibre shape;

contacting an internal lumen surface of the hollow fibre shaped blend with a lumen forming fluid;

inducing a thermally induced phase separation in the hollow fibre shaped blend to form a hollow fibre membrane; and

removing the compatible solvent from the membrane.

44. The method of claim 43, wherein the membrane comprises a microfiltration membrane or an ultrafiltration membrane.

45. The method of claim 43, wherein the blend further comprises a pore controlling agent.

46. The method of claim 45, wherein the pore controlling agent is an environmentally friendly solvent.

47. The method of claim 45, wherein the pore controlling agent is glycerol triacetate.

48. The method of claim 45, wherein the pore controlling agent is citric acid ethyl ester.

49. The method according to claim 43, wherein the blend comprises from 14 wt. % to 25 wt. % Halar.

50. The method according to claim 43, wherein the blend comprises from 16 wt. % to 23 wt. % Halar.

51. The method according to claim 43, wherein the lumen forming fluid comprises digol.

52. The method according to claim 43, wherein the blend is maintained at a temperature of greater than 200°

C.

53. The method according to claim 43, wherein the blend is maintained at a temperature of greater than 220°

C.

54. A method of forming a hollow fibre membrane, the method comprising:

forming a blend of Halar with a compatible solvent;

forming the blend into a hollow fibre shape;

contacting an external surface of the hollow fibre shaped blend with a coating fluid;

contacting an internal lumen surface of the hollow fibre shaped blend with a lumen forming fluid;

inducing a thermally induced phase separation in the hollow fibre shaped blend to form a hollow fibre membrane; and

extracting the compatible solvent from the membrane.

55. The method according to claim 54, wherein the membrane comprises a microfiltration membrane or an ultrafiltration membrane.

56. The method according to claim 54, wherein the coating fluid is selected from the group consisting of glycerol triacetate, citric acid ethyl ester, digol, and mixtures thereof.

57. A method of forming a polymeric hollow fibre ultrafiltration or microfiltration membrane including the steps of:

preparing a Halar dope;

incorporating a leachable pore forming agent into the Halar dope, whereby a leachable pore forming agent-containing Halar dope is obtained;

casting a membrane from the leachable pore forming agent-containing Halar dope; and

leaching the leachable pore forming agent from the membrane with a leachant.

58. The method according to claim 57, wherein the membrane comprises a microfiltration membrane or an ultrafiltration membrane.

59. The method according to claim 57, wherein the leachable pore forming agent comprises an inorganic solid having an average particle size of less than 1 micron

60. The method according to claim 57, wherein the leachable pore forming agent comprises leachable silica.

61. The method according to claim 57, wherein the leachable pore forming agent-containing Halar dope comprises from 3 wt. % to 9 wt. % leachable silica.

62. The method according to claim 57, wherein the leachant comprises a caustic solution.

63. A method of forming a hollow fibre membrane, the method comprising:

forming a blend of Halar with a compatible solvent;

suspending a pore forming agent in the blend;

forming the blend into a hollow fibre shape;

contacting an internal lumen surface of the hollow fibre shaped blend with a lumen forming fluid;

inducing a thermally induced phase separation in the hollow fibre shaped blend to form a hollow fibre membrane; and

extracting the compatible solvent from the membrane.

64. The method according to claim 63, wherein the membrane comprises a microfiltration membrane or an ultrafiltration membrane.

65. The method according to claim 63, wherein the pore forming agent comprises a leachable pore forming agent.

66. The method according to claim 63, wherein the pore forming agent comprises silica.

67. The method according to claim 63, further comprising a step of leaching the pore forming agent from the membrane using a leaching agent.

68. The method according to claim 67, wherein the pore forming agent comprises a leachable silica, and wherein the leaching agent comprises a caustic solution.

69. The method according to claim 63, wherein the blend comprises a nonsolvent for Halar, wherein the nonsolvent comprises digol, and wherein the step of inducing a thermally induced phase separation in the hollow fibre shaped blend to form a hollow fibre membrane comprises contacting the hollow fibre shaped blend with a quench fluid comprising water.

70. The method of forming a hollow fibre membrane, the method comprising:

forming a blend of Halar with a compatible solvent;

suspending a pore forming agent in the blend;

forming the blend into a hollow fibre shape;

contacting an external surface of the hollow fibre shaped blend with a coating fluid;

contacting an internal lumen surface of said blend with a lumen forming fluid;

inducing a thermally induced phase separation in the hollow fibre shaped blend to form a hollow fibre membrane; and

extracting the compatible solvent from the membrane.

71. The method according to claim 70, wherein the membrane comprises a microfiltration membrane or an ultrafiltration membrane.

72. The method according to claim 70, wherein the pore forming agent comprises a leachable pore forming agent.

73. The method according to claim 70, wherein the pore forming agent comprises silica.

74. The method according to claim 70, further comprising a step of leaching the pore forming agent from the membrane using a leaching agent.

75. The method according to claim 70, wherein the pore forming agent comprises a leachable silica, and wherein the leaching agent comprises a caustic solution,

76. The method according to claim 70, wherein the blend comprises a nonsolvent for Halar, wherein the nonsolvent comprises digol, and wherein the step of inducing a thermally induced phase separation in the hollow fibre shaped blend to form a hollow fibre membrane comprises contacting the hollow fibre shaped blend with a quench fluid comprising water.