Composite membrane and production method therefor

Details Composite membrane and production method therefor Composite membrane and production method therefor

2003-04-07

2004-07-13

Spitzer, Robert H. (Department: 1724)

Gas separation: apparatus

Apparatus for selective diffusion of gases

Plural layers

C095S056000, C055S524000, C055SDIG005

Reexamination Certificate

active

06761755

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a composite membrane with a flexible, metallic substrate and a layer system arranged on at least one surface of the substrate; the layer system being formed of a rigid, non-self-supporting, nonmetallic inorganic diffusion barrier layer and at least one hydrogen-permeable, nonporous, metallic membrane layer; and the diffusion barrier layer being arranged between the substrate and the at least one membrane layer and being formed by at least one single layer. The invention further relates to a method for the production of such a composite membrane.
Such membranes are known, for example, from European published patent applications EP 783 919 A1. A composite membrane is disclosed therein which has a support of hydrogen-permeable metal or hydrogen-permeable ceramic, wherein the support can be flexible as well as rigid. The support can be made porous, using a fabric of stainless steel. A porous, flexible diffusion barrier layer, which consists of a non-sintered material, such as felt, paper or fiber mats, is situated on this support. It is further disclosed that a rigid diffusion barrier layer can also be used, if the hydrogen-permeable membrane layer arranged above it is textured. Oxides, sulfides, nitrides, carbides and silicides are disclosed as materials for a rigid diffusion barrier layer. It is indicated that these rigid diffusion barrier layers frequently have cracks. The hydrogen-permeable membrane layer arranged over the diffusion barrier layer is textured when a rigid diffusion barrier layer is used, while this is not absolutely required when a porous, flexible diffusion barrier layer is used. The membrane layer is formed from metals of Group VIIb or VIIIb, the metals Fe, Mn, Ni, Pd, Pt and Ru being specifically mentioned here. The hydrogen-permeable membrane layer can be formed, for example, by electrodeposition on the porous, flexible diffusion barrier layer. The textured membrane layer required on the diffusion barrier layer is constituted as a self-supporting, shaped metal sheet for forming the composite membrane.
U.S. Pat. No. 5,393,325 describes a composite membrane with a nonporous, hydrogen-permeable, metal support, on which a non-metallic diffusion barrier layer is arranged. Disclosed therein as materials for the diffusion barrier layer are oxides, sulfides, carbides, nitrides or silicides. Aluminum oxide, lanthanum oxide, molybdenum oxide, silicon dioxide, tungsten oxide, yttrium oxide and vanadium sulfide are mentioned as preferred materials. A non-porous, hydrogen-permeable metallic layer of, for example, Pd, Pt, Fe, Ru, Ni or Mn is arranged on the diffusion barrier layer.
International patent application publication WO 99/33545 discloses a support structure of porous stainless steel, whose surface is sintered with a fine nickel powder. The thus pretreated surface is electroplated with copper and then provided with a further electroplated layer of a hydrogen-permeable metallic alloy as, e.g., a palladium alloy.
European Patent EP 0 348 041 B1 describes a composite membrane with an inorganic support of fibers, whose fiber interstices have a diameter>5 &mgr;m and a length smaller than ten times the diameter. The inorganic support is coated with a porous, inorganic film, which is made of non-metallic, sintered particles and has a pore size of up to 2 &mgr;m. Glass, mineral, or metal fiber materials are disclosed therein as the support materials. For the porous, inorganic film, there are proposed metal oxides, for example, titanium dioxide, aluminum oxide, cerium oxide, zirconium dioxide, mullite, or mixtures thereof. It is mentioned that cracks can appear in the porous, inorganic film due to bending of the membrane.
U.S. Pat. No. 4,468,235 discloses a hydrogen-permeable membrane with a nonporous support made of a titanium alloy, which is coated with a metal or metallic alloy of the group of palladium, nickel, cobalt, iron, vanadium, niobium, or tantalum. This coating is produced on the support by electroplating or by sputtering.
International patent application publication WO 90/09231 describes a hydrogen-permeable membrane with an inorganic support having gaps, wherein the gaps are bridged over by a composite layer of nonmetallic particles and metal. Palladium is disclosed here as the metal.
JP 346824/92 and JP 76738/93 disclose a hydrogen-permeable membrane made of palladium on a porous metallic support, wherein a ceramic barrier layer or a metal oxide barrier layer is arranged between the membrane and the metallic support.
U.S. Pat. No. 5,259,870 describes a hydrogen-permeable composite membrane with a support made of nonporous metal, a diffusion barrier layer made of a metal oxide, and a membrane layer made of palladium or palladium alloy.
Russian Patent RU 1,058,587 discloses a hydrogen-permeable membrane with a metal support, which is bonded by diffusion welding to a layer of palladium or palladium alloy. Ultra-fine metal oxide powder is arranged between the metal support and the layer of palladium or palladium alloy.
Further hydrogen-permeation membranes are known from U.S. Pat. Nos. 4,496,373; 5,094,927; 3,958,391; 3,477,288; 4,699,637; 4,388,479; 3,622,303; 3,350,846; 1,174,631; 2,773,561; and 3,393,098, and European Patent EP 0 242 208 B1, and also the publications H. P. Hsieh, “Inorganic Membrane Reactors,”
Catal. Rev.—Sci. Eng.,
33(1&2):1-70 (1991); J. P. Collins and J. D. Way, “Preparation and Characterization of a Composite Palladium-Ceramic Membrane,”
Ind. Eng. Chem. Res.,
32(12):3006-3013 (1993); and D. T. Hughes and I. R. Harris, “Hydrogen Diffusion Membranes based on some Palladium-Rare Earth Solid Solution Alloys,”
Zeitschrift für Physik. Chemie Neue Folge,
117:185-193 (1979).
BRIEF SUMMARY OF THE INVENTION
The problem is posed of providing an effective composite membrane for separating hydrogen from gas mixtures which attains a separation ratio of hydrogen to nitrogen of greater than about 4,000 at operating temperatures of greater than 300° C.
The separation ratio is determined by separate determinations of the throughflow rates for pure nitrogen and pure hydrogen through the composite membrane, and gives the selectivity of the membrane. The respective volume flows of permeate through the composite membrane are measured. The ratio of the volume flows H
2
/N
2
is above all a measure of the imperviousness of the membrane or for the number of undesired pores and defective places in the membrane layer. For example, a H
2
/N
2
value<about 500 shows that the separating action of the membrane is small and the number of pores or defective places in the membrane layer is high.
The problem is solved in that at least the single layer of the diffusion barrier layer directly adjoining the membrane layer is open-pored and/or has microcracks and on its surface facing away from the substrate has an electrical resistivity of less than about 10 &OHgr;cm at a temperature of 20° C., and wherein the substrate has an open porosity in a range of about 15% to 60% and the at least one membrane layer is electrodeposited on the surface of the at least one diffusion barrier layer facing away from the substrate. By a rigid diffusion barrier layer is understood a brittle, compact layer, firmly adherent to the substrate, which can consist of plural individual layers. Due to the surface of the diffusion barrier layer facing away from the substrate having a low resistivity of less than about 10 &OHgr;cm, a closed membrane layer can be electrodeposited on this surface. It is thus possible to use a multi-layer diffusion barrier layer, which can, for example, also contain electrically insulating single layers, as long as the single layer of the diffusion barrier layer directly adjoining the membrane layer has this low resistivity. If the diffusion barrier layer also has nonporous or crack-free individual layers, these must be formed of a hydrogen-permeable material.
The composite membrane according to the invention has a high permeability for hydrogen, such that a separation ratio of hydrogen to nitrogen of great

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