MEMBRANE ARRANGEMENT

Abstract

A membrane arrangement for the permeative separation of a gas from gas mixtures has a porous, gas-permeable, metallic support substrate, a membrane formed on the support substrate and selectively permeable for the gas to be separated off. A ceramic, gas-permeable, porous, first intermediate layer is formed between the support substrate and the membrane and directly on the support substrate. A gastight, metallic coupling part is joined by a material-to-material bond to the support substrate. The support substrate and the coupling part are separated by a dividing line. The intermediate layer extends towards the coupling part over the gas-permeable surface of the porous support substrate at least to a distance of 2 mm from the dividing line and extends over the gastight surface of the coupling part by not more than 2 mm beyond the dividing line.

Claims

1-15. (canceled)

16. A membrane arrangement for permeatively separating off a gas from a gas mixture, the membrane arrangement comprising: a porous, gas-permeable, metallic support substrate; a membrane formed on said support substrate, said membrane being selectively permeable for the gas to be separated off; a ceramic, gas-permeable, porous, first intermediate layer arranged between said support substrate and the membrane, and directly on said support substrate; a coupling part joined by a material-to-material bond to said support substrate, said coupling part consisting, at least on a gastight surface thereof, of a gastight, metallic material, where said gas-permeable surface of said support substrate is separated from said coupling part by a dividing line; said first intermediate layer extending over said gas-permeable surface of said porous support substrate in a direction of said coupling part at least to a distance of no more than 2 mm from said dividing line and said first intermediate layer extending in a direction of said coupling part over said gastight surface of said coupling part not more than by a distance of 2 mm beyond said dividing line.

17. The membrane arrangement according to claim 16, wherein said first intermediate layer has a smaller average pore size than said support substrate.

18. The membrane arrangement according to claim 16, wherein said first intermediate layer has an average pore size in a range from 0.20 m inclusive to 2.00 m inclusive.

19. The membrane arrangement according to claim 16, wherein at least one further ceramic, gas-permeable, porous, second intermediate layer which has a smaller average pore size than said first intermediate layer extends between said first intermediate layer and said membrane.

20. The membrane arrangement according to claim 16, wherein said second intermediate layer has an average pore size in a range from 0.03 m inclusive to 0.5 m inclusive.

21. The membrane arrangement according to claim 16, wherein said second intermediate layer extends in a direction of said coupling part beyond said first intermediate layer and ends directly on said coupling part.

22. The membrane arrangement according to claim 16, wherein at least one of said first intermediate layer or said second intermediate layer is a sintered, ceramic layer.

23. The membrane arrangement according to claim 16, wherein a material of said at least one intermediate layer is selected from the group consisting of: zirconium oxide stabilized with yttrium oxide; zirconium oxide stabilized with calcium oxide; zirconium oxide stabilized with magnesium oxide; and aluminum oxide.

24. The membrane arrangement according to claim 16, wherein said first intermediate layer and at least one said second intermediate layer are made of one and the same material.

25. The membrane arrangement according to claim 16, wherein each of said support substrate and said coupling part is tubular.

26. The membrane arrangement according to claim 16, wherein said material-to-material bond is a bond selected from the group consisting of a welded connection, a soldered connection and an adhesive connection.

27. The membrane arrangement according to claim 16, wherein said membrane extends in a direction of said coupling part beyond said at least one intermediate layer and ends directly on said coupling part.

28. The membrane arrangement according to claim 16, wherein: said membrane is made of palladium or a palladium-based, metallic material; and said at least one intermediate layer is made of zirconium oxide stabilized with yttrium oxide; and said support substrate and said coupling part are made of iron-based materials.

29. A method of producing a membrane arrangement for the permeative separation of a gas from a gas mixture, the arrangement including a porous, gas-permeable, metallic support substrate and a coupling part which at least on the surface consists of a gastight, metallic material; the support substrate being joined by a material-to-material bond to the coupling part along a peripheral section of the support substrate and the gas-permeable surface of the support substrate being separated from the gastight surface of the coupling part by a dividing line; the method comprising: applying a ceramic first intermediate layer directly onto the gas-permeable surface of the porous support substrate, where the first intermediate layer extends in the direction of the coupling part over the gas-permeable surface of the porous support substrate at least to a distance of 2 mm from the dividing line and the first intermediate layer extends in the direction of the coupling part over the gastight surface of the coupling part not more than a distance of 2 mm beyond the dividing line; and applying a membrane that is selectively permeable for the gas to be separated off onto the ceramic first intermediate layer, where the membrane extends in a direction of the coupling part beyond the first intermediate layer and ends directly on the coupling part.

30. The method according to claim 29, which comprises applying at least one ceramic, porous, gas-permeable second intermediate layer which has a smaller average pore size than the first intermediate layer onto the first intermediate layer before applying the membrane.

Description

[0045] Further advantages and useful aspects of the invention can be derived from the following description of working examples with reference to the accompanying figures.

[0046] The figures show:

[0047] FIG. 1: a schematic cross-sectional view of a membrane arrangement according to the invention in the axial direction as per a first embodiment of the invention;

[0048] FIG. 2: a schematic cross-sectional view of a membrane arrangement according to the invention in the axial direction as per a second embodiment of the invention;

[0049] FIG. 2a: an enlarged section denoted by x of the membrane arrangement in FIG. 2;

[0050] FIG. 3: a schematic cross-sectional view of a membrane arrangement according to the invention in the axial direction as per a third embodiment of the invention;

[0051] FIG. 4: a schematic cross-sectional view of a membrane arrangement according to the invention in the axial direction as per a fourth embodiment of the invention;

[0052] FIG. 5: pore size distribution of the first intermediate layer as per an embodiment of the invention;

[0053] FIG. 6: particle size distribution of the first intermediate layer as per an embodiment of the invention;

[0054] FIG. 7: pore size distribution of the second intermediate layer as per an embodiment of the invention; and

[0055] FIG. 8: particle size distribution of the second intermediate layer as per an embodiment of the invention.

[0056] FIGS. 1-4 show various embodiments, which differ from one another in terms of structure, of a membrane arrangement for the permeative separation of a gas to be separated off (e.g. H.sub.2) from a gas mixture (e.g. steam-reformed natural gas containing CH.sub.4, H.sub.2O, CO.sub.2, CO, H.sub.2, etc.), with in each case only the transition region from the support substrate to the coupling part being depicted. In FIG. 1, a tubular, porous, gas-permeable, metallic support substrate 2 (e.g. made of ITM) is joined by a material-to-material bond 3 to a tubular coupling part 4 made of solid metal (e.g. steel) along the (circular) peripheral section of the support substrate. The gas-permeable surface of the support substrate 2a is separated by a dividing line 5 from the gastight surface of the coupling part 2b. A ceramic, gas-permeable, porous, first intermediate layer 6 (e.g. of sintered 8YSZ) is arranged directly on the support substrate and extends over the entire gas-permeable surface of the support substrate. This first intermediate layer has a smaller average pore size than the support substrate 2. A second ceramic, gas-permeable, porous intermediate layer 7 (e.g. of sintered 8YSZ) is arranged on top of this first intermediate layer 6. This second intermediate layer 7 has a smaller average pore size than the first intermediate layer; it extends beyond the first intermediate layer 6 and stops directly on the coupling part 4. Owing to its reduced average pore length compared to the first intermediate layer 6, it can provide a sufficiently smooth substrate for the subsequent membrane 8 (e.g. composed of Pd) which is selectively permeable for the gas to be separated off. The second intermediate layer is made somewhat thicker in the transition region in order to even out the nonuniformity at the periphery of the first intermediate layer and provide a more uniform substrate for the subsequent membrane 8. An additional layer 7 can optionally be provided in the transition region, as depicted in the next working example in FIG. 4, and serves the same purpose, i.e. evening out any nonuniformities. The membrane 8 which directly adjoins the second intermediate layer extends in the direction of the coupling part (a) beyond the two intermediate layers 6 and 7 and stops directly on the coupling part 4 to which it produces a join which is gastight for the gas to be separated off (e.g. H.sub.2).

[0057] In the following description of the second, third and fourth embodiments shown in FIGS. 2, 3 and 4, the same reference symbols are used for the same components. In the present description, only the differences compared to the first embodiment will be discussed. In the second embodiment (FIG. 2 and the enlarged section in FIG. 2a), the material-to-material join is realized by a soldered join 3. The gas-permeable surface 2a of the support substrate merges continually into the gastight surface 4a of the coupling part, with the soldered join 3 forming part of the gastight surface 4a. As shown in the enlarged depiction in FIG. 2a, the first intermediate layer 6 extends over the gas-permeable surface of the support substrate to the dividing line 5 but not beyond the latter. Due to the manufacturing, only a very small region on the gas-permeable surface of the support substrate around the dividing line 5 is not covered by the first intermediate layer 6. According to the invention, the maximum distance d on the gas-permeable surface of the support substrate which is not covered by the first intermediate layer 6 is less than 2 mm. In addition, it is common to all embodiments that the first intermediate layer 6 extends in the direction of the coupling part a over the gastight surface not more than a distance d of 2 mm beyond the dividing line 5. The connection to the coupling part 4 is effected by the second intermediate layer 7 which has a lower porosity, and therefore better adhesion properties, than the first intermediate layer 6 and provides a sufficiently smooth surface for application of the membrane.

[0058] In the third embodiment (FIG. 3), the material-to-material join is formed by a welded join 3, with the welding process bringing about a circumferential depression because of the porosity. In a manner analogous to the second working example, direct contact of the first intermediate layer 6 with the smooth surface of the welding seam is avoided.

[0059] In the fourth embodiment (FIG. 4), the coupling part 4 is made of a porous, gas-permeable base material, in particular the same material as the support substrate 2 (e.g. ITM), and has a gastight surface region 4a only on its exterior surface. The gastight surface region 4a can be produced, for example, by application of a coating or a sealing composition or by surface melting of the porous base material of the coupling part 4. Here too, the first intermediate layer 6 does not extend (apart from an extremely small region around the dividing line) over the gastight surface 4a of the coupling part. The support substrate and the coupling part are preferably configured as an integral component.

[0060] In the following, an example of the production of a membrane arrangement according to the invention will be described. A support substrate in the form of a porous tube composed of ITM and having an external diameter of 5-10 mm, a length of 100-300 mm, a porosity of about 40% and an average pore size of <50 m is at one of its axial ends welded to a tubular coupling part made of solid steel and having the same external diameter by laser welding. In order to ensure homogenization of the welded transition, the component obtained is annealed under a hydrogen atmosphere at a temperature of 1200 C. The surface in the region of the welded join is subsequently treated by sand blasting in order to achieve a more uniform surface. Next, the coupling part with the welded seam is covered. In a further step, a suspension suitable for a wet-chemical coating process, for example with addition of dispersant, solvent (e.g. BCA [2-(2-butoxyethoxy)ethyl] acetate, obtainable from Merck KGaA Darmstadt), and binder, is produced for the first intermediate layer produced from an 8YSZ powder, in particular a powder having a d80 of about 2 m (and having a d50 of about 1 m). The first intermediate layer is applied by dip coating, i.e. by dipping the tubular component into the suspension, up to the beginning of the welded seam. After drying, the covering of the gastight surface of the coupling part is removed and the component obtained is subsequently sintered under a hydrogen atmosphere at a temperature of 1300 C., as a result of which the organic constituents are burnt out, sintering of the ceramic layer takes place and the porous, sintered, ceramic first intermediate layer is obtained. A typical pore size distribution and particle size distribution of a first intermediate layer produced in this way are shown in FIGS. 5 and 6. In particular, the pore size distribution is in the range from 0.08 to 12.87 m (with an average pore size of 0.55 m), as can be seen from FIG. 5 (with a few pores having a larger diameter no longer being shown), and the particle size distribution is in the range 0.08-61.37 m (with an average particle size of 1.27 m), as can be seen from FIG. 6 (with a few particles having a larger diameter no longer being shown). In the next step, a suspension of 8YSZ powder for the second intermediate layer is prepared; the information given above for the first intermediate layer applies analogously, except that an 8YSZ powder that is finer overall is used and a somewhat lower viscosity of the suspension than for the first intermediate layer is set. In particular, a mixture or two 8YSZ powders having differing particle sizes, in particular a powder having a d80 of about 2 m (and having a d50 of about 1 m) and a very fine powder having a particle size (crystallite size) of about 25 nm (nanometers), is used as ceramic powder. The second intermediate layer is likewise applied by dip coating. The second intermediate layer covers the first intermediate layer completely and ends directly on the coupling part. Any nonuniformities in the transition region at the periphery of the first intermediate layer are evened out by application (brushing-on) of additional material. The component obtained is subsequently sintered under a hydrogen atmosphere at a temperature of 1200 C., as a result of which the organic constituents are burnt out, sintering of the ceramic layer takes place and the porous, sintered, ceramic second intermediate layer is obtained. The polished section of the second intermediate layer displays, in cross section, a homogeneous profile, even when the material of the second intermediate layer has been applied in a plurality of process steps (dip coating with subsequent brushing-on). A typical pore size distribution and particle size distribution of a second intermediate layer produced in this way are shown in FIGS. 7 and 8. In particular, the pore size distribution is in the range from 0.03 to 5.72 m (with an average pore size of 0.13 m), as can be seen from FIG. 7 (with a few pores having a larger diameter no longer being shown), and the particle size distribution is in the range from 0.03 to 18.87 m (with an average particle size of 0.24 m), as can be seen from FIG. 8 (with a few particles having a larger diameter no longer being shown). A Pd membrane is subsequently applied by means of a sputtering process. It completely covers the second intermediate layer and also the underlying first intermediate layer. Finally, a further Pd layer is applied electrolytically onto the sputtered Pd layer in order to seal the latter and achieve the required gastightness.

[0061] The present invention is not restricted to the embodiments depicted in the figures. In particular, the material-to-material join does not necessarily have to be realized as a welded join. For example, it can also be configured as a soldered join or adhesive bond. Furthermore, the coupling part and the support substrate can also have an integral or monolithic configuration, with the material-to-material join forming the transition between the gas-permeable support substrate and the coupling part which is gastight at least on the surface. For example, a monolithic configuration of the support substrate and the coupling part would also be possible in the fourth embodiment (FIG. 4). Furthermore, the structure described is suitable not only for separating off H.sub.2 but also

for separating off other gases (e.g. CO.sub.2, O.sub.2, etc.). Alternative membranes can also be used, for example microporous, ceramic membranes (Al.sub.2O.sub.3, ZrO.sub.2, SiO.sub.2, TiO.sub.2, zeolites, etc.) or dense, proton-conducting ceramics (SrCeO.sub.3-, BaCeO.sub.3-, etc.).