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A hydrogen permselective membrane, a method of forming a permselective membrane and an apparatus comprising a permselective membrane, a porous substrate and an optional intermediate layer are described. Using chemical vapor deposition (CVD) at low reactant gas concentration, high permselectivities a

A hydrogen permselective membrane, a method of forming a permselective membrane and an apparatus comprising a permselective membrane, a porous substrate and an optional intermediate layer are described. Using chemical vapor deposition (CVD) at low reactant gas concentration, high permselectivities are achieved with minimal reduction in hydrogen permeance.

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1. A permselective asymmetric membrane comprising a surface layer and a porous substrate layer wherein said surface layer is deposited by the chemical vapor deposition of a CVD reactant gas having a concentration of less than 0.03 mole/m3 in a CVD gas stream wherein said deposition is carried out su

1. A permselective asymmetric membrane comprising a surface layer and a porous substrate layer wherein said surface layer is deposited by the chemical vapor deposition of a CVD reactant gas having a concentration of less than 0.03 mole/m3 in a CVD gas stream wherein said deposition is carried out such that said membrane has a hydrogen permeance of at least 5×10?8 mol/m2·s·Pa and a permselectivity of at least 100 for hydrogen relative to argon.2. The permselective asymmetric membrane of claim 1 wherein the surface layer is comprised of a material selected from the group consisting of silica, alumina, zirconia, titania, silicon nitride, silicon carbide and zeolites.3. The permselective asymmetric membrane of claim 1 wherein the porous substrate layer is selected from the group consisting of porous metals, porous ceramics and porous refractory metal oxides.4. The permselective asymmetric membrane of claim 1 wherein the porous substrate layer is selected from the group consisting of porous alumina, porous modified alumina, porous titania, porous carbon and porous stainless steel.5. The permselective asymmetric membrane of claim 1 wherein the surface layer is comprised of silica.6. The permselective asymmetric membrane of claim 5 wherein the CVD reactant gas comprises tetraethyl orthosilicate and the CVD gas stream lacks substantial concentrations of oxygen, ozone and moisture.7. The permselective asymmetric membrane of claim 1 further comprising at least one or more porous intermediate layers.8. The permselective asymmetric membrane of claim 7 wherein at least one of the one or more porous intermediate layers is deposited by chemical vapor deposition.9. The permselective asymmetric membrane of claim 7 wherein at least one of the one or more porous intermediate layers is deposited by sol gel deposition.10. The permselective asymmetric membrane of claim 1 wherein said membrane has a permeance of at least 1×10?7 mol/m2·s·Pa for hydrogen and a permselectivity of at least 300 for hydrogen argon.11. A permselective asymmetric membrane comprising a surface layer, one or more porous intermediate layers and a porous substrate layer wherein said surface layer and at least one porous intermediate layer are deposited by chemical vapor deposition of a CVD reactant gas in a CVD gas stream, such that said membrane has a hydrogen permeance of at least 5×10?8 mol/m2·s·Pa and a permselectivity of at least 100 for hydrogen relative to argon.12. The permselective asymmetric membrane of claim 11 wherein the surface layer is comprised of a material selected from the group consisting of silica, alumina, zirconia, titania, silicon nitride, silicon carbide, and zeolites.13. The permselective asymmetric membrane of claim 11 wherein the porous substrate layer is selected from the group consisting of porous metals, porous ceramics and porous refractory metal oxides.14. The permselective asymmetric membrane of claim 11 wherein the porous substrate layer is selected from the group consisting of porous alumina, porous modified alumina, porous titania, porous carbon and porous stainless steel.15. The permselective asymmetric membrane of claim 12 wherein the surface layer and at least one porous intermediate layer comprise distinct layers of silica.16. The permselective asymmetric membrane of claim 15 wherein the CVD reactant gas is selected from the group consisting of tetraethyl orthosilicate, tetraethyl silicates, tetraisopropyl silicates, tetramethyl silicates, and chlorosilanes including chloro-, dichloro-, and trichloromethyl silanes.17. The permselective asymmetric membrane of claim 16 wherein the CVD gas stream lacks substantial concentrations of oxygen, ozone and moisture.18. The permselective asymmetric membrane of claim 15 wherein the CVD reactant gas is tetraethyl orthosilicate.19. The permselective asymmetric membrane of claim 18 wherein the CVD gas stream lacks substantial concentrations of oxygen, ozone and moisture.20. The permselective asymmetric membrane of claim 18 wherein the concentration of tetraethyl orthosilicate in the reactant gas stream is about 0.112 mole/m3 or less during the chemical vapor deposition of at least one layer.21. The permselective asymmetric membrane of claim 18 wherein the concentration of tetraethyl orthosilicate in the reactant gas stream is about 0.03 mole/m3 or less during the chemical vapor deposition of at least one layer.22. The permselective asymmetric membrane of claim 12 wherein the surface layer and at least one porous intermediate layer comprise distinct layers.23. The permselective asymmetric membrane of claim 11 wherein said membrane has a permeance of at least 1×10?7 mol/m2·s·Pa for hydrogen and a permselectivity of at least 300 for hydrogen relative to argon.24. A permselective asymmetric membrane comprising a surface layer and a porous substrate layer, said membrane having a permeance of at least 5×10?8 mol/m2·s·Pa for hydrogen and a permselectivity of at least 100 for hydrogen relative to argon.25. The permselective asymmetric membrane of claim 24 wherein the surface layer is comprised of a material selected from the group consisting of silica, alumina, zirconia, titania, silicon nitride, silicon carbide and zeolites.26. The permselective asymmetric membrane of claim 24 wherein the porous substrate layer is selected from the group consisting of porous metals, porous ceramics and porous refractory metal oxides.27. The permselective asymmetric membrane of claim 24 wherein the porous substrate layer is selected from the group consisting of porous alumina, porous modified alumina, porous titania, porous carbon and porous stainless steel.28. The permselective asymmetric membrane of claim 24 wherein the surface layer is deposited by chemical vapor deposition (CVD) of a CVD gas stream comprising a CVD reactant gas.29. The permselective asymmetric membrane of claim 28 wherein the CVD reactant gas is present in the CVD gas stream at a concentration of less than about 0.112 mole/m3.30. The permselective asymmetric membrane of claim 28 wherein the CVD reactant gas is present in the CVD gas stream at a concentration of less than about 0.03 mole/m3.31. The permselective asymmetric membrane of claim 28 wherein the surface layer is comprised of silica.32. The permselective asymmetric membrane of claim 31 wherein the CVD reactant gas is selected from the group consisting of tetraethyl orthosilicate, tetraethyl silicates, tetraisopropyl silicates, tetramethyl silicates, and chlorosilanes including chloro-, dichloro-, and trichloromethyl silanes.33. The permselective membrane of claim 31 wherein the CVD reactant gas comprises tetraethyl orthosilicate.34. The permselective asymmetric membrane of claim 33 wherein the CVD gas stream lacks substantial concentrations of oxygen, ozone and moisture.35. The permselective asymmetric membrane of claim 28 further comprising one or more porous intermediate layers.36. The permselective asymmetric membrane of claim 35 wherein at least one of the one or more porous intermediate layers is deposited by chemical vapor deposition.37. The permselective asymmetric membrane of claim 36 wherein the surface layer and at least one of the one or more porous intermediate layers are deposited using the same CVD reactant gas under different deposition conditions.38. The permselective asymmetric membrane of claim 37 wherein the CVD reactant gas is tetraethyl orthosilicate and the CVD reactant gas is present in the CVD gas stream at a concentration of less than about 0.112 mole/m3.39. The permselective asymmetric membrane of claim 38 wherein the CVD gas stream lacks substantial concentrations of oxygen, ozone and moisture.40. The permselective asymmetric membrane of claim 35 wherein at least one of the one or more porous intermediate layers is deposited by a sol gel deposition.41. The permselective asymmetric membrane of claim 40 wherein at least one of the one or more porous intermediate layers deposited by a sol gel deposition is selected from the group consisting of alumina, silica, titania and combinations thereof.42. A permselective asymmetric membrane comprising a surface layer and a porous substrate layer, said membrane having a permeance of at least 1×10?7 mol/m2·s·Pa for hydrogen and a permselectivity of at least 300 for hydrogen relative to argon.43. The permselective asymmetric membrane of claim 42 wherein the desired permeate is hydrogen and the one or more undesired permeates are selected from the group consisting of carbon monoxide, methane, carbon dioxide, ammonia, hydrogen sulfide and water.44. The permselective asymmetric membrane of claim 43 wherein the one or more undesired permeates are selected from the group consisting of methane and carbon dioxide.45. The permselective asymmetric membrane of claim 43 wherein the undesired permeates are selected from the group consisting of carbon monoxide, methane, carbon dioxide and water.46. The permselective asymmetric membrane of claim 43 wherein the undesired permeates are selected from the group consisting of ammonia and nitrogen.47. The permselective asymmetric membrane of claim 43 wherein one of the undesired permeates is hydrogen sulfide.