Gas separation membranes

• US 20040149127A1
• Filed: 08/07/2003
• Published: 08/05/2004
• Est. Priority Date: 01/17/2003
• Status: Active Grant

• Current Assignee: Smartmembrane Corporation
• Original Assignee: Smartmembrane Corporation
• Inventors: Lyons, Arthur, Van Den Gross, Andrew
• Granted Patent: US 7,166,148 B2
• Time in Patent Office: Days
• US Class Current: 95/45
• CPC Class Codes: B01D 2313/221 Heat exchangers
• CPC Class Codes: B01D 2323/42 Details of membrane preparation apparatus
• CPC Class Codes: B01D 53/22 by diffusion manufacturing semi-permeable membranes B01D67/00; form, structure or properties of semi-permeable membranes B01D69/00; material for semi-permeable membranes B01D71/00
• CPC Class Codes: B01D 53/228 characterised by specific membranes
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: B01D 67/0088 Physical treatment with compounds, e.g. swelling, coating or impregnation
• CPC Class Codes: B01D 67/009 with wave-energy, particle-radiation or plasma
• CPC Class Codes: B01D 67/0095 Drying
• CPC Class Codes: B01D 69/08 Hollow fibre membranes manufacture of hollow fibres D01D5/24, D01F1/08
• CPC Class Codes: B01D 69/12 Composite membranes; Ultra-thin membranes
• CPC Class Codes: B01D 71/70 Polymers having silicon in the main chain, with or without sulfur, nitrogen, oxygen or carbon only
• CPC Class Codes: B01D 71/701 Polydimethylsiloxane
• CPC Class Codes: Y10S 55/05 Methods of making filter

Abstract

A method of producing composite, hollow fibre gas separation membranes, wherein external surfaces of the porous hollow fibre tubes used in the construction of the membranes are subjected to a modification technique before the external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface.

Claims

1. A method of producing composite, hollow fibre gas separation membranes, wherein external surfaces of the porous hollow fibre tubes used in the construction of the membranes are subjected to a modification technique before the said external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface.

2. A method as claimed in claim 1, wherein the fibre tube is manufactured from polyethersulfone polymer.

3. A method as claimed in claim 1, wherein the structure of the porous fibre tube is modified by soaking the tube, preferably under controlled temperature and differential pressure conditions, in a solvent solution until the solution has penetrated into the exposed open pores on the outside of the tube, and wherein the solvent solution is displaced by distilled water and the fibre tube is then dried, preferably by the application of a vacuum or pressure differential to the fibre tube.

4. A method as claimed in claim 3, wherein the solvent solution consists of a mixture of acetone and distilled water.

5. A method as claimed in claim 4, wherein the composition of the solvent solution is between 10% and 90% acetone and between 10% and 90% by weight distilled water, and typically 50% acetone and 50% water by weight.

6. A method as claimed in any of claims 3 to 5, wherein the fibre tube is soaked in the solvent solution for about 200 sec, the process temperature is about 50°

C., and the pressure differential across the tube about 0.9 atmospheres.

7. A method as claimed in any preceding claim, wherein the modification process is carried out on pre-cut lengths of fibre tube located inside a pressure vessel, and wherein each end of each pre-cut fibre tube is fixed in polyurethane potting compound so that the hollow inner cores of the tubes are exposed and open out into a manifold situated at each end of the pressure vessel.

8. A method as claimed in claim 7, wherein a pressure differential is applied inside the pressure vessel between the outside walls and the inner cores of the fibre tubes.

9. A method as claimed in any preceding claim, wherein the modification process is carried out on long lengths of fibre tube wound onto a rectangular frame typically 600 mm long×

500 mm wide×

20 mm thick.

10. A method as claimed in any preceding claim, wherein the application of the modification technique to the polyethersulfone fibre tube results in the modified fibre tube having up to twice as many pores in its structure as unmodified fibre and a gas permeability up to twice that of unmodified fibre.

11. A method as claimed in any preceding claim, wherein the modification technique improves the surface characteristics of the fibre tube so that the outer surface of the tube is able to support a very thin, defect free layer of selective polymer material.

12. A method as claimed in any preceding claim wherein a selective polymer material is coated onto the modified surface of the fibre tube.

13. A method as claimed in claim 1, wherein the modified fibre tubes are immersed in a solvent solution of a selective polymer inside a pressure vessel and on extraction of the solvent from the solution a very thin coating of selective polymer is left on the outside surface of the tube.

14. A method as claimed in claim 12 or 13, wherein the pressure vessel used to coat the modified fibre tubes is the same pressure vessel that was originally used to modify the fibre tubes

15. A method as claimed in claim 12, 13 or 14, wherein the selective polymer consists of a mixture of non-cross linked polydimethylsiloxane and cross-linked polydimethylsiloxane.

16. A method as claimed in claim 13, 14 or 15, wherein the solvent is petroleum ether, a liquid hydrocarbon or a chloro-hydrocarbon.

17. A method as claimed in claim 15 or 16, wherein the coating of polydimethylsiloxane deposited onto the fibre tube is between 0.1 and 1 micron thick.

18. A method as claimed in any preceding claim, wherein the outside coated surface of the modified composite hollow fibre membrane is plasma treated to further improve the gas selectivity properties of the membrane.

19. A method of manufacturing a gas separation module wherein composite hollow fibre membranes produced by a method as claimed in any preceding claim are packed into polyurethane potting compound inside a gas separation module so that the inner cores of the membranes are exposed and open out into an evacuation chamber situated at each end of the gas separation module, in a manner whereby a differential pressure can be applied between the outside walls and the inner cores of the membranes.

20. A method of operating a gas separation module produced by the method of claim 19 wherein the differential pressure between the outside walls and the inner cores of the hollow fibre membranes is a positive pressure applied to the outside of the membranes.

21. A method of operating a gas separation module produced by the method of claim 19 wherein the differential pressure between the outside walls and the inner cores of the hollow fibre membranes is a vacuum applied to the inner core of the membranes.

22. A method as claimed in claim 21, wherein the vacuum is applied equally to each evacuation chamber in the gas separation module, so that the vacuum is then applied equally to each open end of the inner cores of the hollow fibre membranes.

23. A method as claimed in claim 22, wherein the vacuum applied to the inner cores of membranes is between 0.3 and 0.8 atmospheres, and more preferably between 0.4 and 0.6 atmospheres.

24. A method as claimed in any of claims 21 to 23, wherein the application of a vacuum to the inner cores of the modified hollow fibre membranes produces oxygen rich air typically containing up to 27% oxygen, and under certain conditions oxygen rich air containing up to 35% oxygen.

25. A method as claimed in claim 19, wherein the gas separation module is manufactured from relatively lightweight, albeit pressure resistant, materials such as lightweight metals, rigid plastics and combinations of such materials.

26. A method as claimed in any of claims 20 to 25 wherein gas separation modules are combined together in multiples and operated in parallel using either a common vacuum pump or a number of vacuum pumps to apply the vacuum to the inner cores of the membranes inside the gas separation modules.

27. A method as claimed in claim 26, wherein a multiple module gas separation system produces up to 150 m³/min, or more, of enriched oxygen air containing 27% oxygen, 73% nitrogen, by the application of a vacuum of about 0.5 atmospheres to the inner cores of the membranes inside the modules, and wherein the energy consumption required to produce the enriched oxygen air is equivalent to about 240 kWhr/tonne of added oxygen.

28. A method as claimed in any of claims 20 to 27 as dependent directly or indirectly upon claim 18, wherein the application of a vacuum to the inner cores of plasma treated hollow fibre membranes produces oxygen rich air containing up to 32% oxygen, and under certain conditions oxygen rich air containing up to 50% oxygen.

29. A method as claimed in any of claims 20 to 28, wherein a combined multiple module gas separation system containing plasma treated hollow fibre membranes produces up to 100 m³/min, or more, of enriched oxygen air containing 32% oxygen, 68% nitrogen, by the application of a vacuum of about 0.5 atmospheres to the inner cores of the membranes inside the modules, and wherein the energy consumption required to produce the enriched oxygen air is equivalent to about 175 kWhr/tonne of added oxygen.

30. A method as claimed in any preceding claim, wherein the composite hollow fibre gas separation membrane is used to enrich or separate gas mixtures other than oxygen and nitrogen.

31. A gas separation system consisting of a gas separation module containing composite hollow fibre membranes manufactured in accordance with the method of any of claims 1 to 18, a low energy fan inside the gas separation module to draw in and then blow normal atmospheric air across the outsides of the membranes, two evacuation chambers inside the gas separation module so that a vacuum can be equally applied to each end of the hollow cores inside the membranes, a vacuum pump to supply the required vacuum to the gas separation module, an oxygen sensor to measure the oxygen concentration in the enriched oxygen air produced by the gas separation module, and a regulating valve to adjust the concentration of oxygen in the enriched oxygen air, when necessary, by admitting normal atmospheric air into the oxygen rich air.

32. A gas separation system for supplying enriched oxygen air to enclosed spaces or environments, such as for example hospital wards or high altitude dormitories, consisting of a gas separation module containing composite hollow fibre membranes manufactured in accordance with the method of any of claims 1 to 18, a low energy fan inside the gas separation module to draw in and then blow normal atmospheric air across the outsides of the membranes, a vacuum pump to supply the required vacuum to the gas separation module, an oxygen sensor to measure the oxygen concentration in the enriched oxygen air produced by the gas separation module, a regulating valve to adjust the concentration of oxygen in the enriched oxygen air, when necessary, by admitting normal air into the enriched oxygen air, and a control system to control and regulate the gas separation module, the vacuum pump, the amount of enriched oxygen air supplied to the enclosed space, and the concentration of oxygen in the enriched oxygen air supplied to the enclosed space.

33. A gas separation system for supplying enriched oxygen air to combustion and industrial processes that require very large volumes of enriched oxygen air, consisting of multiples of gas separation modules connected together in parallel, the modules containing composite hollow fibre membranes manufactured in accordance with the method of any of claims 1 to 18, a low energy fan inside each gas separation module to draw in and then blow normal air across the outsides of the membranes, a vacuum pump or vacuum pumps to supply the required vacuum to the gas separation modules, an oxygen sensor to measure the oxygen concentration in the combined enriched oxygen air stream produced by the gas separation modules, a regulating valve to adjust the concentration of oxygen in the combined enriched oxygen air stream, when necessary, by admitting normal air into the enriched oxygen air, a gas sensor in the exhaust gas coming from the process to monitor pollutants, such as carbon monoxide, emitted from the process, and a control system to control and regulate the gas separation modules, the vacuum pump or pumps, the amount of enriched oxygen air supplied to the process and the concentration of oxygen in the enriched oxygen air supplied to the process.

34. A method of treating the external surface of a hollow fibre gas separation tube prior to application of a selective polymer layer to the external surface of the tube, comprising soaking the surface in a solvent which penetrates into pores in the surface, displacing the solvent with water and then drying the fibre tube.

35. A method as claimed in claim 34 wherein the tube is manufactured from polyethersulfone polymer.

36. A method as claimed in claim 34 or 35 wherein the solvent comprises acetone.

37. A method of producing composite, hollow fibre gas separation membranes, wherein external surfaces of the porous hollow fibre tubes used in the construction of the membranes are subjected to a modification technique that increases the number of pores in the external surfaces of the fibre tubes and improves the surface characteristics of the fibre tubes before the said external surfaces are coated with a layer of selective polymer.