Textured ion exchange membranes
View Patent ↗A textured water-splitting membrane comprises an anion exchange layer abutting a cation exchange layer to form a heterogeneous water-splitting interface therebetween, and a textured surface having a pattern of texture features comprising spaced apart peaks and valleys. The membranes can also have an integral spacer on the membrane. A cartridge can be fabricated with a plurality of the membranes for use in an electrochemical cell. The electrochemical cell can be part of an electrochemical ion exchange system.
1. A textured water-splitting bipolar membrane comprising:
(a) an anion exchange layer abutting a cation exchange layer to form a heterogeneous water-splitting interface therebetween; and
(b) an exposed textured surface having a pattern of texture features comprising spaced apart peaks and valleys, wherein the texture features comprise a dimension of at least about 10 microns.
2. The membrane of claim 1 wherein the peaks are ridges and the valleys comprise furrows between adjacent ridges.
3. The membrane of claim 2 wherein the ridges and furrows are generally parallel to the direction that a solution will travel across the membrane during use of the membrane.
4. The membrane of claim 1 wherein the texture features are formed on both the anion and cation exchange layers.
5. The membrane of claim 1 wherein the peaks comprise conical protrusions or mesas, and the peaks extend out from a substantially flat surface region which defines the valleys.
6. The membrane of claim 1 wherein a solution traveling across the membrane forms a stagnant layer at the membrane surface, and wherein the texture features of the membrane have a dimension that is greater than the thickness of the stagnant layer.
7. The membrane of claim 1 wherein the texture features have a peak to peak distance dpp of at least about 10 microns.
8. The membrane of claim 1 wherein the texture features have a peak to valley distance dpv of at least about 10 microns.
9. The membrane of claim 1 wherein the texture features have an aspect ratio dpv/dpp of at least about 0.1.
10. The membrane of claim 1 wherein the texture features have an aspect ratio dpv/dpp of at least 0.5.
11. The membrane of claim 1 further comprising channels that cut across the peaks.
12. The membrane of claim 1 wherein the anion exchange layer comprises —NR3A groups and the cation exchange layer comprises —SO3M groups.
13. The membrane of claim 1 wherein the anion exchange layer comprises triethyl ammonium (—N(C2H5)3) groups and the cation exchange layer comprises carboxylic acid (—COOH) groups.
14. The membrane of claim 1 comprising an integral spacer on the exposed textured surface.
15. The membrane of claim 14 wherein the integral spacer comprises filaments on the exposed textured surface.
16. The membrane of claim 14 wherein the integral spacer comprises a polymer coating on the peaks of the texture features.
17. The membrane of claim 14 wherein the integral spacer comprises a thickness of less than about 1000 microns.
18. The membrane of claim 14 wherein the integral spacer comprises a thickness of less than about 500 microns.
19. The membrane of claim 1 that is spiral wrapped.
20. A cartridge comprising a plurality of the membranes of claim 1 abutting each other and spiral wrapped.
21. A cartridge for an ion exchanging electrochemical cell, the cartridge comprising:
(a) a plurality of textured bipolar membranes abutting one another, each membrane having:
(i)an anion exchange layer abutting a cation exchange layer to form a heterogeneous water-splitting interface therebetween; and
(ii) an exposed textured surface having a pattern of texture features comprising spaced apart peaks and valleys.
22. The cartridge of claim 21 wherein the peaks are ridges and the valleys comprise furrows between adjacent ridges, the ridges and furrows being generally parallel to the direction that a solution will travel across the membrane during use of the membrane.
23. The cartridge of claim 21 wherein the texture features have a peak to peak distance dpp of at least about 10 microns, and a peak to valley distance dpv of at least about 10 microns.
24. The cartridge of claim 21 wherein the membranes are spirally wound around a core tube.
25. The cartridge of claim 24 wherein the spirally wound membranes are enclosed by an outer sleeve and two end caps.
26. The cartridge of claim 25 wherein at least one end cap has a hole through which an electrode may pass, and forms a seal with a housing.
27. The cartridge of claim 24 which is absent electrodes.
28. The cartridge of claim 21 wherein the plurality of membranes are spiral wrapped.
29. A cartridge for an ion exchanging electrochemical cell, the cartridge comprising:
a plurality of textured bipolar membranes abutting one another and spiral wrapped, each membrane having:
(i) an anion exchange layer abutting a cation exchange layer to form a heterogeneous water-splitting interface therebetween; and
(ii) an exposed textured surface having a pattern of texture features comprising spaced apart peaks and valleys.
30. The cartridge of claim 29 comprising an integral spacer attached to at least one membrane, the integral spacer comprising filaments on the textured surface or a coating on the peaks.
31. The cartridge of claim 30 wherein the integral spacer comprises a thickness of less than 1000 microns.
32. The cartridge of claim 30 wherein the filaments or coating is composed of a dielectric material.
33. The cartridge of claim 32 wherein the dielectric material comprises polyethylene or polypropylene.
34. The cartridge of claim 29 wherein the texture features comprising peaks are ridges and the valleys comprise furrows between adjacent ridges, the ridges and furrows being generally parallel to the direction that a solution will travel across the membrane during use of the membrane.
35. The cartridge of claim 29 wherein the texture features have a peak to peak distance dpp of at least about 10 microns, and a peak to valley distance dpv of at least about 10 microns.
36. The cartridge of claim 29 wherein the membranes are spirally wound around a core tube.
37. An electrochemical cell for removing or exchanging ions from a solution stream, the electrochemical cell comprising the cartridge of claim 29 , and further comprising a housing comprising first and second electrodes about the cartridge.
38. An electrochemical ion exchange system comprising the electrochemical cell of claim 37 and further comprising:
(a) a power supply for supplying a voltage to the first and second electrodes; and
(b) a pump for flowing a solution stream through the electrochemical cell.
39. An electrochemical ion exchange system according to claim 38 wherein the power supply is capable of maintaining the first and second electrodes at a plurality of voltage levels during an ion exchange stage.
40. An electrochemical ion exchange system according to claim 39 wherein the voltage levels comprise a range of voltage levels that are selected to maintain a predefined ion concentration range in the effluent solution.
41. The electrochemical cell of claim 37 wherein the electrodes comprise titanium or niobium.
42. The electrochemical cell of claim 41 wherein the electrodes comprise an outer coating of a noble metal.
43. The electrochemical cell of claim 37 wherein an electrode is a spiral.
44. The cartridge of claim 29 wherein the plurality of membranes are spiral wrapped.