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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

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.

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The invention claimed is: 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 comprising soaking the porous hollow fibre tubes in a s

The invention claimed is: 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 comprising soaking the porous hollow fibre tubes in a solvent solution 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, wherein the structure of the porous fibre tube is modified by soaking the tube in the 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. 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, under controlled temperature and differential pressure conditions. 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 about 10% to 90% acetone and between about 10% to 90% by weight distilled water. 6. A method as claimed in claim 3, 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 claim 1, 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 polling 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 tubas. 9. A method as claimed in claim 1, wherein the modification process is carried out on long lengths of fibre tube wound onto a rectangular frame. 10. A method as claimed in claim 2, 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 claim 1, 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 claim 1, 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 second solvent solution of a selective polymer inside a pressure vessel and on extraction of the second solvent from the second solvent solution a very thin coating of selective polymer is left on the outside surface of the tube. 14. A method as claimed in claim 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, 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, wherein the second solvent is petroleum ether, a liquid hydrocarbon or a chloro-hydrocarbon. 17. A method as claimed in claim 15, wherein the coating of polydimethylsiloxane deposited onto the fibre tube is between about 0.1 to 1 micron thick. 18. A method as claimed in claim 1, 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 a composite, hollow fibre gas separation membrane, wherein external surfaces of the porous hollow fibre tubes used in the construction of the membrane are subjected to a modification technique comprising soaking the porous hollow fibre tubes in a solvent solution before said external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface, said method comprising: packing a plurality of said composite hollow fibre gas separation membranes into a polyurethane polling compound inside said 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; soaking the plurality of said composite hollow fibre gas separation membranes in the solvent solution until the solution has penetrated into the exposed open pores on the outside of the membranes; displacing the solvent solution by distilled water; and then drying the membranes. 20. A method of operating a gas separation module, said gas separation module being formed by a composite, hollow fibre gas separation membrane, wherein external surfaces of the porous hollow fibre tubes used in the construction of the membrane are subjected to a modification technique comprising soaking the porous hollow fibre tubes in a solvent solution before said external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface, said method comprising packing a plurality of said composite hollow fibre gas separation membranes into a polyurethane polling compound inside said 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; wherein said method comprising: applying a positive pressure to the outside of said hollow fibre membranes, thereby forming said differential pressure between the outside walls and the inner cores of the hollow fibre membranes; soaking said hollow fibre membranes in the solvent solution until the solution has penetrated into the exposed open pores on the outside walls of the hollow fibre membranes; displacing the solvent solution by distilled water; and then drying the hollow fibre membranes. 21. A method of operating a gas separation module, said gas separation module being formed by a composite, hollow fibre gas separation membrane, wherein external surfaces of the porous hollow fibre tubes used in the construction of the membrane are subjected to a modification technique comprising soaking the porous hollow fibre tubes in a solvent solution before said external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface, said method comprising packing a plurality of said composite hollow fibre gas separation membranes into a polyurethane potting compound inside said 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, said method comprising: applying a vacuum to the inner core of said membranes such that said differential pressure is formed between the outside walls and the inner cores of the hollow fibre membranes; soaking said hollow fibre membranes in the solvent solution until the solution has penetrated into the exposed open pores on the outside walls of the hollow fibre membranes; displacing the solvent solution by distilled water; and then drying the hollow fibre 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 about 0.3 to 0.8 atmospheres. 24. A method as claimed in claim 21, wherein the application of a vacuum to the inner cores of the modified hollow fibre membranes produces oxygen rich air 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. 26. A method as claimed in claim 21, wherein a plurality of 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 claim 21, 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, and wherein the application of a vacuum to the inner corns of plasma treated hollow fibre membranes produces oxygen rich air containing up to 50% oxygen. 29. A method as claimed in claim 28 wherein a combined multiple module gas separation system containing plasma treated hollow fibre membranes produces up to 100m3/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 of enriching or separating gas mixtures other than oxygen and nitrogen, comprising utilizing the composite hollow fibre gas separation membrane produced by the method of claim 1. 31. A gas separation system consisting of a gas separation module containing composite hollow fibre membranes wherein external surfaces of the porous hollow fibre tubes used in the construction of the membrane are subjected to a modification technique comprising soaking the porous hollow fibre tubes in a solvent solution before said external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface, said composite hollow fibre gas membranes being packed into a polyurethane potting compound inside said 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, said gas separation system comprising: 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, consisting of a gas separation module containing composite hollow fibre membranes wherein external surfaces of the porous hollow fibre tubes used in the construction of the membrane are subjected to a modification technique comprising soaking the porous hollow fibre tubes in a solvent solution before said external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface, said composite hollow fibre gas membranes being packed into a polyurethane potting compound inside said 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, said gas separation system comprising: 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 wherein external surfaces of the porous hollow fibre tubes used in the construction of the membrane are subjected to a modification technique comprising soaking the porous hollow fibre tubes in a solvent solution before said external surfaces are coated with a thin layer of selective polymer so as to increase the number of pores in the fibre surface, said composite hollow fibre gas membranes being packed into a polyurethane potting compound inside said 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, said gas separation system comprising: 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 structure modifying 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 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 external surfaces are coated with a layer of selective polymer, wherein the structure of the porous fibre tube is modified by soaking the tube in the 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. 38. A method according to claim 3, wherein said fibre tube is dried by the application of a vacuum or pressure differential to said fibre tube. 39. The method according to claim 5, wherein said solvent solution has a composition of 50% acetone and 50% water by weight. 40. A method as claimed in claim 23, wherein the vacuum applied to the inner cores of membranes is between about 0.4 to 0.6 atmospheres. 41. A method as claimed in claim 25, wherein the relatively lightweight, albeit pressure resistant, materials comprise a material selected from the group consisting of lightweight metals, rigid plastics, and combinations of such materials. 42. A gas separation system as in claim 32, wherein the enclosed spaces or environments comprise hospital wards or high altitude dormitories.