Metal gas separation membrane module design

An improved metal gas separation membrane for separating hydrogen from a gas steam includes a quantity of metal particles that are bonded together to form a porous body. The porous body may have a porosity that increases from a first surface to an opposite second surface and may additionally include a coating of ceramic particles on the first surface. The metal gas separation membrane may include a coating of a dense precious metal applied thereto that is permeable by hydrogen via chemisorption-dissociation-diffusion. The porous body may include a catalytic enhancement. Also disclosed are three gas separation modules that employ the metal gas separation membrane disposed within a core of the gas separation module for separating hydrogen from a gas stream. The gas separation membranes are each supported on a first mounting member and a second mounting member. The gas separation modules may also include a catalytic enhancement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to gas separation modules and, more particularly, to a gas separation module for the separation of hydrogen gas from a gas stream.

2. Description of the Related Art

Membranes and membrane modules for the separation of hydrogen from other gases are generally known. In particular, useful membranes for hydrogen separation typically can be categorized as being of four general types: (i) polymeric, (ii) porous inorganic, (iii) self-supporting non-porous metal, and (iv) non-porous metal supported on a porous rigid matrix such as metal or ceramic.

Porous inorganic-based membranes are typically fabricated from titania, zirconia, alumina, glass, molecular sieving carbon, silica and/or zeolites. All are fabricated with a narrow pore size distribution, with the porous inorganic membranes exhibiting high hydrogen permeability but low selectivity due to relatively large mean pore diameters. Such materials are brittle and thus susceptible to failure due to cracking, and the sealing and fixturing of such porous inorganic-based membranes limit their use to relatively low temperature applications.

Development of supported metal membranes has focused on the utilization of ceramic tubes coated with a thin adherently bonded film or foil of non-porous or dense palladium (Pd) or Pd-alloys. The ceramic support tube typically is of a graded porosity from one surface thereof to a second opposite surface. More specifically, the porosity of the ceramic support tube typically is at its least at the surface upon which the Pd or Pd-alloy is disposed, and the porosity of the tube increases from this surface to a maximum porosity on the surface opposite the layer of Pd. The layer of Pd or Pd-alloy is selectively permeable to hydrogen gas and is typically capable of withstanding temperatures of 1500-1600° F. (815-870° C.).

Such ceramic-supported metal membranes are typically housed in shell and tube modules and are fitted with compression gaskets to seal the membrane tube into the module to prevent leakage of the feed gas stream into the permeate gas stream. Potential leak paths between the feed and permeate gas streams can exist due to differences in the coefficients of thermal expansion of the ceramic tube and the metal compression fittings. Additionally, the ceramic support tubes are inherently brittle and can experience long-term thermal fatigue due to repetitive process or system start-up and shutdown cycles.

The mechanical adherence of the thin Pd or Pd-alloy layer upon the surface of the ceramic support tube requires secure attachment of the film or foil onto the surface of the ceramic, as well as the absence of pinholes or other mechanical rupturing that can occur during manufacture or use of the ceramic tube membrane.

For porous metal membranes such as porous stainless steel, Knudsen diffusion or combined Knudsen diffusion/surface diffusion are the primary mechanisms by which gas transport occurs across the membrane. For dense metal membranes such as Pd or Pd-alloy foil or film, however, the primary mechanism of gas transport through the metal layer is traditional chemisorption-dissociation-diffusion. Broadly stated, chemisorption-dissociation-diffusion transport involves chemisorption of hydrogen molecules onto the membrane surface, dissociation of hydrogen atoms into protons and electrons, transportation of the protons and electrons through the dense metal, reassociation of the protons and electrons into hydrogen molecules, and desorption of hydrogen molecules from the media. While Knudsen diffusion typically offers greater flow rates across a membrane than chemisorption-dissociation-diffusion, Knudsen diffusion suffers from reduced hydrogen selectivity as compared with chemisorption-dissociation-diffusion.

It is also known that the interaction of a gas stream with catalytic materials can increase the concentration of hydrogen within the reactant or process gas stream. Such catalytic materials enhance the water gas shift reaction whereby carbon monoxide is reacted with water to form carbon dioxide and hydrogen gas. Catalytic materials also promote the decomposition of ammonia which also increases the concentration of hydrogen.

Examples of such catalytic materials include platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), nickel (Ni), iridium (Ir), and the like. While it has been known to apply such catalytic materials to ceramic support substrates to form composite membranes, such composite membranes still suffer from the aforementioned problems associated with the application of Pd and Pd-alloy foils and films to ceramic support tubes.

The problems inherent in forming a highly gas specific membrane that is capable of withstanding elevated temperatures are similarly inherent in designing a module that incorporates such membranes. In order to maintain separation between a feed gas stream and a permeate gas stream, it is necessary to provide seals or sealing structures that effectively isolate the feed gas stream from the permeate gas stream. Mechanical and thermal stresses resulting from different coefficients of thermal expansion and elevated temperatures greatly impair the ability of most known sealing systems to effectively isolate the feed gas stream from the permeate gas stream.

It is thus desired to provide a hydrogen gas separation membrane and module having high hydrogen selectivity that overcomes the aforementioned problems associated with the application of Pd and Pd-alloys to ceramic support tubes. It is also desired to provide such a membrane and module that include a catalytic enhancement incorporated therein.

SUMMARY OF THE INVENTION

In view of the foregoing, an improved gas separation module for separating hydrogen from a gas steam includes a metal gas separation membrane having a quantity of metal particles in the form of fibers and/or powders that are compacted together and bonded with one another to form a porous body that is selectively permeable to hydrogen. The porous body may be of a constant porosity throughout or may have a porosity that is “graded,” i.e., increases from a first surface to a second opposite surface. A porous body having a graded porosity advantageously provides a low porosity (and thus consequent higher hydrogen selectivity) at the first surface without the higher pressure drop that would be experienced by the hydrogen from the second surface to the first surface if the porous body had the same low porosity throughout its cross section. This variation in porosity can result from the use of metal particles in the form of fibers and/or powders that gradually increase in size in going from the first surface to the second surface, or may result from the use of the same size particles that are compacted to a relatively lesser degree in going from the first surface to the second surface.

The metal gas separation membrane may additionally include a coating of ceramic particles on the first surface thereof to further decrease the porosity at the first surface. Alternatively, or in addition thereto, the metal gas separation membrane may include a thin adherently bonded foil or coating of a dense precious metal such as palladium, palladium-alloys, and the like applied thereto that is permeable by hydrogen according to a chemisorption-dissociation-diffusion transport phenomenon.

Still alternatively, or in addition thereto, the gas separation module may include a catalytic enhancement that can interact with a feed gas stream to increase the concentration or quantity of hydrogen in the feed gas stream according to various catalytic reactions such as the water gas shift reaction and the ammonia decomposition reaction. The catalytic enhancement can be in the nature of catalytic materials that are dispersed throughout the porous body, that are supported on scaffold apparatuses such as metal fibers and chemical vapor infiltration silicon carbide (CVI-SiC) reticulated foam, that are coated on the metal particles that make up the porous body, that are in the form of a layer on a surface of the porous body with or without the addition of a ceramic washcoat therebetween, or can be in the form of an application of perovskite, zeolite, or spinel structures to the porous body.

The gas separation module includes a plurality of metal gas separation membranes and a housing having first and second mounting members in the form of tube sheets. The metal gas separation membranes are supported on the first and second mounting members. The metal gas separation membranes can advantageously be fixedly mounted, such as by being welded, to the tube sheets to sealingly mount the metal gas separation members to the tube sheets.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of a metal gas separation membrane4in accordance with the present invention is indicated generally in FIG.1. The metal gas separation membrane4is advantageously configured to separate hydrogen gas from a gas stream8.

The metal gas separation membrane4includes a transmission member6and can be of numerous shapes, such as plates, tubes, honeycomb configurations, and other such shapes. The transmission member6is depicted schematically in cross-sectionFIG. 1, and it includes a porous body10made out of a plurality of metal particles12compressed and bonded together and a metal coating16on the porous body10. The porous body10includes a first surface20and a second surface24opposite one another with the metal coating16being disposed on the first surface20.

The metal particles12that make up the porous body10can be of numerous physical configurations such as metal fibers, metal powder, and other shapes, and the porous body10can be made up of one type of particle or combinations of these different-shaped metal particles12.FIG. 1Aschematically depicts an example of a portion of a porous body10that includes a quantity of metal fibers25. The metal particles12can be fabricated from known metals, superalloys, and/or intermetallic materials to permit the porous body10to withstand high temperatures, meaning not only that the material does not melt at the elevated temperatures but also that the material resists corrosion in the potentially oxidizing or reducing environment in which the membrane4is used.

The metal particles12are compacted and sinter bonded to form a thin, dense member of material that makes up the porous body10. The resultant porous body10has a thickness that is in the range of about 100 microns to 5 millimeters, and preferably in the range of about 0.5 millimeters (500 microns) to 2 millimeters, although other thicknesses may be appropriate depending upon the specific needs of the particular application. In the circumstance where the porous body10is an elongated substantially cylindrical member formed with an elongated void, the outer diameter of the porous body10may be in the range of about 5 to 15 millimeters, and preferably is in the range of about 5 to 8 millimeters.

As can be seen inFIG. 1, the porosity of the porous body10is greater at the second surface24than at the first surface20, meaning that the space between adjacent metal particles12near the second surface24is greater than the space between adjacent metal particles12near the first surface20. Alternatively, the porous body10can be said to have a density that decreases in a direction from the first surface20toward the second surface24. The porous body10depicted inFIG. 1thus can be said to have a graded porosity.

As will be set forth more fully below, the porous body10is advantageously configured to provide relatively high hydrogen selectivity at the first surface20due to its relatively low porosity there. The regions of the porous body extending from the first surface20to the second surface24, being relatively more porous than the first surface20, have a relatively lower hydrogen selectivity but correspondingly permit the relatively free flow of gases therethrough. These relatively porous regions of the porous body10can thus be said to provide support to the low-porosity region of the porous body10at the first surface20, which generally is relatively thin and of lower strength, without meaningfully impeding the flow of hydrogen therethrough from the second surface24to the first surface20. As such, the graded porosity feature of the porous body10itself provides both high hydrogen selectivity and high hydrogen flow rates therethrough without the high pressure drop that would be experienced by the hydrogen if the porosity of the porous body10were that of the first surface20throughout the porous body10.

As indicated hereinbefore, the metal particles12can include a quantity of metal fibers. Such fibers advantageously provide good mechanical strength at lower density (as compared with metal powder particles) due to the higher aspect ratio of the fibers (the ratio of the length to the width) as well as due to the multiple joints by which each fiber is connected with other metal particles12.

As is shown inFIG. 1, the metal particles12are all of substantially the same size, and the variation in porosity between the first and second surfaces20and24results from compacting the metal particles12to a greater degree at the first surface20than at the second surface24. In this regard, the porous body10can be manufactured out of several layers of metal particles12, with each layer being compacted to a different degree, or other appropriate methodologies can be employed such as forming each layer out of a slurry of metal particles that are sequentially sprayed, painted, or centrifuged onto a surface, with the layers being sprayed, painted, or centrifuged to different degrees.

The metal coating16is a thin dense adherently bonded layer or foil of a precious metal such as palladium (Pd), palladium alloys, and the like that enhance gas phase chemisorption-dissociation-diffusion of hydrogen therethrough. Such palladium alloys may include palladium—copper (Pd—Cu), palladium—ruthenium (Pd—Ru), and other alloys. As is know in the relevant art, the expression gas phase “chemisorption-dissociation-diffusion” of hydrogen refers to molecular chemisorption and dissociation of hydrogen along the high pressure side of the metal coating16, proton and electron diffusion through the lattice of the metal coating16, and proton and electron reassociation and recombination and desorption of molecular species along the opposite side of the metal coating16. The metal coating16thus can be referred to as a chemisorption-dissociation-diffusion coating. The metal coating16can be applied to the porous body10in any of a variety of fashions such as via electroless plating, electroless plating with osmosis, electroplating, sputtering, electrodeposition, and the like.

In the embodiment depicted inFIG. 1, the metal gas separation membrane4receives the gas stream8against the second surface24and separates hydrogen from the gas stream8to form a permeate stream26of high purity hydrogen gas that flows out of the side of the metal coating16opposite the porous body10. In alternate embodiments (not depicted,) the overall gas flow may be in a reverse direction to that depicted generally inFIG. 1, i.e., the gas stream8may flow directly against the metal coating16such that the permeate stream26would flow out of the second surface24.

By way of example, the metal particles12may be in the form of fibers selected to be of a size in the range of about <1 to 50 microns in diameter and generally less than 10 millimeters in length and are compacted to an appropriate degree to permit the flow of gases therethrough. Hydrogen that passes through the porous body10and reaches the first surface20is then permitted to flow through the metal coating16primarily by chemisorption-dissociation-diffusion.

The metal coating16is preferably configured to be as thin as possible to enhance the flow rate of hydrogen therethrough. The thickness of the metal coating16is thus preferably in approximately the range of 0.1 to 10 microns.

It can thus be seen that the porous body10serves to mechanically support the metal coating16thereon. In this regard, it can be seen that the metal particles12provide numerous points of contact between the porous body10and the metal coating16, which helps the metal coating16to adhere onto the porous body10during operation of the metal gas separation membrane4and during the thermal expansion and contraction of the metal gas separation membrane4during start-up and shut-down operations.

In its simplest form, the metal gas separation membrane could comprise solely a porous body being manufactured out of metal particles and having a constant density and porosity throughout, with the porous body serving as the transmission member that separates hydrogen from a gas stream. In addition, the porous body may be of a graded density to reduce the pressure drop across the porous body10and/or can additionally include the metal coating16to further increase hydrogen selectivity.

A second embodiment of a metal gas separation membrane104is indicated generally in FIG.2. The metal gas separation membrane104includes a transmission member106having a porous body110in which the graded porosity thereof is achieved by providing metal particles112that vary in size from relatively finer metal particles112A at the first surface120to relatively coarser metal particles112B at the second surface124.

By way of example, the relatively finer metal particles112A may be in the form of fibers of a size in the range of about 25 to 100 nanometers in diameter and <1 to 5 millimeters in length, and the relatively coarser particles112B may be in the form of fibers of a size in the range of about <1 to 50 microns in diameter and <10 millimeters in length.

A third embodiment of a metal gas separation membrane1004in accordance with the present invention is indicated generally in FIG.3. The metal gas separation membrane1004is similar to the metal gas separation membranes set forth above and includes a porous body1010having a first surface1020and a second surface1024opposite one another, a layer of ceramic particles1028disposed on the first surface1020, and a chemisorption-dissociation-diffusion coating1016disposed on the layer of ceramic particles1028. The porous body1010is of a graded porosity that results from the use of metal particles of varying sizes that range from relatively finer metal particles1012A disposed at the first surface1020to relatively coarser metal particles1012B disposed at the second surface1024.

The metal gas separation membrane1004may be of a hollow, generally cylindrical configuration, although other configurations such as those set forth above, may be employed without departing from the concept of the present invention. In such a hollow cylindrical configuration, the outer diameter of the metal gas separation membrane1004may be in the range of about 5 to 15 millimeters, and preferably in the range of about 5 to 8 millimeters, although the outer diameter may be larger or smaller than that set forth herein. The wall thickness of the porous body1010may be in the range of about 0.1 millimeters (100 microns) to 5 millimeters, and preferably in the range of about 0.5 millimeters (500 microns) to 2 millimeters, and such wall thickness is generally defined as the distance between the first surface1020and the second surface1024.

The layer of ceramic particles1028may be of a thickness less than 50 microns and preferably in the range of about than 10 microns to 12 microns, and the pore size thereof may be less than about 5 nanometers. The ceramic particles1028may be of a size in the range of about 25 to 100 nanometers and may include materials such as Al2O3, TiO2, Al2O3—TiO2, and ZrO2although other materials may be employed.

The chemisorption-dissociation-diffusion coating1016may be of a thickness of approximately less than 10 microns and may be made up of particles sized in the range of about less than 0.01 microns to 0.02 microns. The chemisorption-dissociation-diffusion coating1016is made of known proton conducting media such as palladium (Pd) and alloys thereof such as palladium—copper (Pd—Cu) and palladium—ruthenium (Pd—Ru), although other known proton conducting media including those set forth above may be employed without departing from the concept of the present invention.

The porous body1010may be made up of known materials such as FeAl, Haynes® 160 (available from Haynes International of Kokomo, Ind. 46904, USA), RA-333® or RA85H® (available from Rolled Alloys, Temperance, Mich. 48182, USA), 602CA, and Fecralloy, although other materials including those set forth above may be employed. The size range of the finer and coarser metal particles1012A and1012B may be the same as that set forth above or may be of other sizes depending upon the specific needs of the particular application.

A fourth embodiment of a metal gas separation membrane1104in accordance with the present invention is indicated generally in FIG.4. The metal gas separation membrane1104is similar to the metal gas separation1004but includes a porous body1110having a catalytic enhancement in the form of particles of catalytic material that range in size from relatively finer particles of catalytic material1118A disposed at the first surface1120to relatively coarser particles of catalytic material1118B disposed at the second surface1124in a fashion similar to the relatively finer and coarser metal particles1112A and1112B. The particles of catalytic material1118A and1118B are particles of precious metal such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), nickel (Ni), iridium (Ir), and alloys thereof and are depicted inFIG. 4as being shaded. The particles of catalytic material1118A and1118B promote the water gas shift reaction, the ammonia decomposition reaction, and the like in a known fashion to increase the concentration or availability of hydrogen. Alternately, fine catalytic particles of uniform size can be dispersed throughout the porous body1110and/or a layer of ceramic particles1128disposed against the first surface1120, and may coat or be adhered to the metal and/or the ceramic particles. The metal gas separation membrane1104additionally includes a support member1144disposed against the chemisorption-dissociation-diffusion coating1116. It is understood that the metal gas separation membranes4,104, and1004can be catalytically enhanced in any of the fashions set forth above and/or can include the support member1144.

The metal gas separation membrane1104may be employed in an environment in which a gas stream flows against or along the second surface1124and into the porous body1110where it catalytically interacts with the particles of catalytic material1118A and1118B. Hydrogen gas then flows through the layer of ceramic particles1128and passes through the chemisorption-dissociation-diffusion coating1116in a fashion set forth above.

The support member1144retains the chemisorption-dissociation-diffusion coating1116and the layer of ceramic particles1128disposed on the porous body1110when gas flows through the porous body1110prior to contacting the chemisorption-dissociation-diffusion coating1116. In this regard, the support member1144helps to resist the chemisorption-dissociation-diffusion coating1116and the layer of ceramic particles1128from being blown away from or becoming otherwise dislodged from the porous body1110as a result of the substantial pressure drop in going from the second surface1124to the outermost portions of the chemisorption-dissociation-diffusion coating1116. The support member1144may be in the form of a metal mesh, a screen, a densified perforated sleeve, as well as other appropriate configurations.

A first embodiment of a gas separation module1258in accordance with the present invention is indicated generally in FIG.5. The gas separation module1258includes a housing1260within which are disposed a plurality of metal gas separation membranes1204in accordance with the present invention. While the metal gas separation membranes1204employed in the gas separation module1258may be the metal gas separation membranes1004, it is understood that any of the metal gas separation membranes set forth herein may be employed in the gas separation module1258without departing from the concept of the present invention.

In general terms, the gas separation module1258can be stated as being structured to receive a feed gas stream1208and to separate it into a permeate gas stream1226and a retentate gas stream1261. While the permeate gas stream1226may be high purity hydrogen gas, it is understood that the gas separation module1258potentially could be configured such that the permeate gas stream1226is another gas such as oxygen.

The housing1260is a generally hollow member formed with a core1262, within which are disposed a first mounting member1264and a second mounting member1266. The first and second mounting members1264and1266are in the form of first and second tube sheets.

Each metal gas separation membrane1204is an elongated substantially cylindrical member having a first end1268and an opposite second end1270and being formed with an elongated void1274formed therein and extending substantially throughout the longitudinal extent of the metal gas separation membrane1204. Each metal gas separation membrane1204includes a first surface1220and a second surface1224, with the second surface1224being defined by the void1274. For purposes of clarity, the metal gas separation membranes1204shown inFIG. 5do not depict a layer of ceramic particles, a chemisorption-dissociation-diffusion coating, or a support member, although it is understood that one or more of these features may be incorporated therein.

In accordance with the present invention, the metal gas separation membranes1204are supported on the first and second mounting members1264and1266. More specifically, the metal gas separation membranes1204are fixedly attached to the first and second mounting members1264and1266such as by welding or other appropriate attachment methodology.

By configuring the porous bodies of the metal gas separation membranes1204to be formed of metal instead of ceramic or other metallic oxide, the metal gas separation membranes1204can be welded to the metallic first and second mounting members1264and1266. Such welded attachment is particularly advantageous because it overcomes the problems inherent in attempting to seal a joint between a ceramic member and a metallic member such as occurred with previously known ceramic support structures in previously known gas separation membranes. Additionally, the metal gas separation membranes1204are less susceptible to thermal shock than ceramic members, and furthermore are not subject to configurational deformation problems that can plague ceramic members during firing operations.

As can be seen inFIG. 5, the first ends1268of the metal gas separation membranes1204are abuttingly and sealingly mounted to the first mounting member1264, whereby the first ends1268are closed. In contrast thereto, the second ends1270are mounted adjacent holes1276formed in the second mounting member1266, whereby the second ends1270are open. The first mounting member1264is formed with a plurality of perforations1278in the regions thereof that are not used for sealing the first ends1268of the metal gas separation membranes1204.

The metal gas separation membranes1204each include a generally defined interior1277and a generally defined exterior1279. The interior1277of each metal gas separation membrane1204is defined by the void1274. The exterior1279is opposite the interior1277and is defined as being the regions that are disposed radially outwardly beyond the outermost components of the metal gas separation membranes1204, whether the outermost components be the porous body, a layer of ceramic particles, a chemisorption-dissociation-diffusion coating, or a support member.

The first and second mounting members1264and1266define an inlet manifold1282therebetween that is disposed to the exterior1279of all of the metal gas separation membranes1204. Stated otherwise, the inlet manifold1282is the portion of the core1262between the first and second mounting members1264and1266that is not occupied by the metal gas separation membranes1204. Similarly, the second mounting member1266defines a permeate gas manifold1284extending from the side of the second mounting member1266opposite the inlet manifold1282. Still similarly, the first mounting member1264defines a retentate manifold1286extending from the side of the first mounting member1264opposite the inlet manifold1282. The permeate gas manifold1284and the retentate manifold1286are disposed within the core1262.

The housing1260is additionally formed with a feed gas inlet1288, a retentate gas outlet1290, and a permeate gas outlet1292. The permeate gas outlet1292is in fluid communication with the permeate gas manifold1284. The retentate gas outlet1290is in fluid communication with the retentate manifold1286. The feed gas inlet1288is in fluid communication with the inlet manifold1282. Inasmuch as the first mounting member1264is formed with the perforations1278, the feed gas inlet1288is additionally in fluid communication with the retentate manifold1286and the retentate gas outlet1290through the perforations1278.

The gas separation module1258additionally includes a catalytic enhancement1294. In the embodiment depicted inFIG. 5, the catalytic enhancement1294is disposed within the inlet manifold1282of the housing1260, which is generally to the exterior1279of the metal gas separation membranes1204. The catalytic enhancement1294is in the form of catalytic materials1296that are disposed on or are otherwise supported by a scaffold apparatus1298. The catalytic materials1296may include any of the catalytic materials set forth herein.

The scaffold apparatus1298may be in the form of metal fibers, chemical vapor infiltration silicon carbide (CVI-SiC) reticulated foam, and the like. In this regard, if the scaffold apparatus1298is in the form of metal fibers, the catalytic materials1296may be plated onto the metal fibers, may be distributed throughout the fibers, or may themselves comprise the metal fibers that form the scaffold apparatus1298. It is understood, however, that the catalytic enhancement1294within the inlet manifold1282may be of other configurations than that specifically set forth herein without departing from the concept of the present invention.

In operation, the feed gas stream1208flows through the feed gas inlet1288and into the inlet manifold1282where it flows into contact with the catalytic enhancement1294. The catalytic enhancement1294promotes the water gas shift reaction, the ammonia decomposition reaction, and the like to increase the concentration or the availability of hydrogen within the feed gas stream1208. The catalytic enhancement1294is advantageously configured to be highly porous and thus permit the free flow of the feed gas stream1208therethrough. Depending upon the specific makeup of the feed gas stream1208or the specific needs of the particular application, the gas separation module1258may be configured to not include the catalytic enhancement1294.

The feed gas stream1208including gaseous hydrogen thereafter flows into contact with the metal gas separation membranes1204. Hydrogen gas flows through the metal gas separation membranes1204from the exterior1279thereof to the interior1277thereof and along the voids1274to form the permeate gas stream1226which then flows into the permeate gas manifold1284and out of the permeate gas outlet1292. The feed gas stream1208from which the hydrogen has been substantially removed flows through the perforations1278and into the retentate manifold1286where it forms the retentate gas stream1261that flows out of the retentate manifold1286.

The perforations1278formed in the first mounting member1264help to retain the catalytic enhancement1294within the inlet manifold1282and additionally assist in maintaining the substantial pressure drop between the feed gas stream1208and the retentate gas stream1261that helps to drive the separation of the permeate gas stream1226from the feed gas stream1208. Since the metal gas separation membranes1204and the first and second mounting members1264and1266are all manufactured substantially out of metal, the metal gas separation membranes1204can be welded to the first and second mounting members1264and1266. Such sealing attachment additionally makes the gas separation module1258well suited to the elevated temperatures and pressures typically encountered in separating the permeate gas stream1226from the feed gas stream1208.

By applying the relatively higher ambient pressure of the feed gas stream1208to the exterior1279of the metal gas separation membranes1204, such relatively higher ambient pressure would have a tendency to seat a chemisorption-dissociation-diffusion coating and/or a layer of ceramic particles disposed at the first surface1220of the metal gas separation membrane1204against the first surface1220. Additionally, the catalytic enhancement1294disposed within the inlet manifold1282increases the extent to which hydrogen can be generated and removed from the feed gas stream1208.

Alternatively, if the metal gas separation membrane1204is configured to include a ceramic layer and/or chemisorption-dissociation-diffusion coating applied to the second surface1224instead of to the first surface1220, the metal gas separation membrane1204would preferably include a support member within the interior1277and disposed against the ceramic layer or the chemisorption-dissociation-diffusion coating to resist the ceramic layer and/or the chemisorption-dissociation-diffusion coating from being blown off the second surface1224by the relatively higher ambient pressure applied to the first surface1220. In such a configuration, the gas separation module1258may be configured to include a catalytic enhancement incorporated into the metal gas separation membranes1204themselves in a fashion similar to the metal gas separation membrane1104. Such a catalytic enhancement incorporated into the metal gas separation membranes1204may take the place of the catalytic enhancement1294, such that the gas separation module1258may be configured to not include the catalytic enhancement1294.

A second embodiment of a gas separation module1358in accordance with the present invention is indicated generally in FIG.6. The gas separation module1358includes a housing1360and a plurality of metal gas separation membranes1304substantially disposed internally therein. The gas separation module1358is similar to the gas separation module1258in that the housing1360is formed with a core1362within which are disposed a first mounting member1364and a second mounting member1366in the form of tube sheets that support the metal gas separation membranes1304. The gas separation module1358is different, however, in the way that the feed gas stream1308interacts with the metal gas separation membranes1304to form the permeate gas stream1326and the retentate gas stream1361.

As can be seen inFIG. 6, the metal gas separation membranes1304each include a first end1368and a second end1370, except that the second end1370is defined as the free end of a tube extension1372that extends from a porous body1310of the metal gas separation membranes1304and is connected with the second mounting member1366. The tube extension1372has a relatively narrower hollow inner cavity than the void1374extending through the porous body1310of each metal gas separation membrane1304. The metal gas separation membranes1304each include the porous body1310which has a first surface1320and a second surface1324opposite one another. The interior1377of each metal gas separation membrane1304is defined by the second surface1324and the void1374thereof, and the exterior1379is opposite thereto.

The first and second ends1368and1370of the metal gas separation membranes1304are open and the feed gas stream1308flows through the void1374. In this regard, it can be seen that the first mounting member1364is formed with a plurality of openings1380to which the first ends1368are attached, such as via welding as set forth above. Similarly, the second mounting member1366is formed with a plurality of holes1376to which the second ends1370of the metal gas separation membranes1304are attached, such as via welding. As such, the first and second mounting members1364and1366define a permeate gas manifold therebetween that is flow communication with a permeate gas outlet1392formed in the housing1316. The first mounting member1364defines an inlet manifold1382that is opposite the permeate gas manifold1384and that is in flow communication with a feed gas inlet1388formed in the housing1360. Additionally, the second mounting member1366defines a retentate manifold1386that is opposite the permeate gas manifold1384and that is in flow communication with a retentate gas outlet1390formed in the housing1360. Inasmuch as the metal gas separation membranes1304are sealingly attached to the first and second mounting members1364and1366, the permeate gas manifold1384is configured to be free of leaks between it and either of inlet and retentate manifolds1382and1386.

The gas separation module1358additionally includes a catalytic enhancement1394that is in the form of catalytic materials1396mounted on or otherwise disposed on a scaffold apparatus1398that is disposed within the voids1374of each of the metal gas separation membranes1304. The relatively narrowed tube extension1372helps to retain the catalytic enhancement disposed within the porous body1310, although it is understood that such function could be provided by a screen, a mesh, or other such structure.

The metal gas separation membranes1304may themselves include a catalytic enhancement in the form of particles of catalytic material1318(depicted as dots inFIG. 6) formed therewith. The catalytic materials1396and the particles of catalytic material1318can be made from any of the catalytic materials set forth herein. The catalytic enhancement1394depicted inFIG. 6thus includes both the catalytic materials1396disposed on the scaffold apparatus1398as well as the particles of catalytic material1318.

In operation, the feed gas stream1308flows through the feed gas inlet1388and into the inlet manifold1382, after which it flows through the first ends1368of the metal gas separation membranes1304and into the voids1374thereof. The feed gas stream1308then interacts with the catalytic enhancement1394which increases the concentration and availability of hydrogen gas by promoting the water gas shift reaction, the ammonia decomposition reaction, and the like. Hydrogen gas flows through the second surface1324of each metal gas separation membrane1304in a direction toward the first surface1320. Thereafter, hydrogen gas flows into the permeate gas manifold1384to form the permeate gas stream1326which flows out of the permeate gas outlet1392. The portion of the feed gas stream1308from which the hydrogen has been substantially removed continues to flow through the tube extension1372and into the retentate manifold1386where it forms the retentate gas stream1361that flows out of the retentate gas outlet1390.

If the metal gas separation membranes1304are configured to include the chemisorption-dissociation-diffusion coating16,1016, or1116applied to the second surface1324of each metal gas separation membrane1304, the support member1144(not shown inFIG. 6) disposed against the chemisorption-dissociation-diffusion coating16,1016, or1116would provide a separation mechanism to facilitate insertion of the catalytic enhancement1394and to avoid damage to the chemisorption-dissociation-diffusion coating16,1016, or1116. Should the chemisorption-dissociation-diffusion coating16,1016, or1116be applied to the first surface1320of each metal gas separation membrane1304, a support member1144(not shown inFIG. 6) disposed against the chemisorption-dissociation-diffusion coating16,1016, or1116would advantageously resist the relatively higher ambient pressure applied to the second surface1324and retain the chemisorption-dissociation-diffusion coating and/or the layer of ceramic particles on the porous body to maintain the integrity of the metal gas separation membranes1304and to ensure the continued high purity of the permeate gas stream1326.

A third embodiment of a gas separation module1458in accordance with the present invention is indicated generally in FIG.7. The gas separation module1458is similar to the gas separation module1358in that it includes a housing1460within which are disposed a plurality of metal separation membranes1404that have a flow pattern similar to that of the gas separation module1358. The gas separation module1458is different, however, in that the catalytic enhancement1494thereof is limited to the particles of catalytic material1418(depicted as dots inFIG. 7) formed integrally with the metal gas separation membranes1404and does not include catalytic materials disposed on a scaffold apparatus within the voids1474of the metal gas separation membranes1404. Additionally, the metal gas separation membranes1404do not include the relatively narrowed tube extensions1372.

The feed gas stream1408flows into the voids1474of the metal gas separation membranes1404and catalytically interacts with the particles of catalytic material1418to increase the concentration and availability of hydrogen by promoting the water gas shift reaction, the ammonia decomposition reaction, and the like. The hydrogen in the feed gas stream1408, meaning both the hydrogen initially present therein as well as that which was catalytically formed by the particles of catalytic material1418, passes through the metal gas separation membranes1404via Knudsen Diffusion and chemisorption-dissociation-diffusion (if appropriate) to form the permeate gas stream1426. The gas from which the hydrogen has been removed continues to flow along the voids1474to form the retentate gas stream1461. The gas separation module1458is thus catalytically enhanced by specifically configuring the metal gas separation membranes1404thereof to provide such a feature. The chemisorption-dissociation-diffusion coating (not shown) would be disposed on a first surface1420of each metal gas separation membrane1404, and an overlying support member (not shown) would enhance the structural integrity of each such chemisorption-dissociation-diffusion coating.

As indicated above, the metal gas separation membrane in its simplest form includes a porous body of metal particles having a constant porosity throughout. In addition thereto, the porosity of the porous body may vary from a first surface to a second opposite surface. Still alternatively, or in addition thereto, the porous body may include a layer of palladium, palladium-alloy, and the like which enhances gas phase chemisorption-dissociation-diffusion of hydrogen therethrough. Still alternatively, or in addition thereto, the porous body may include a coating in the form of a plurality of ceramic particles thereon that further reduce the porosity of the porous body. Still alternatively, or in addition thereto, the metal gas separation membrane may include a catalytic enhancement of various configurations. Still alternatively, or in addition thereto, the metal gas separation membrane may be mounted on a support structure to assist the metal gas separation membrane to withstand the operating pressures and temperatures of a particular application.

While a number of particular embodiments of the present invention have been described herein, it is understood that various changes, additions, modifications, and adaptations may be made without departing from the scope of the present invention, as set forth in the following claims.