WO2016178849A1

WO2016178849A1 - Membrane-based hydrogen purifiers

Info

Publication number: WO2016178849A1
Application number: PCT/US2016/029232
Authority: WO
Inventors: Vernon Wade Popham; Charles R. Hill
Original assignee: Ballard Fuel Cell Systems Inc.
Priority date: 2015-05-01
Filing date: 2016-04-25
Publication date: 2016-11-10
Also published as: PH12017501903A1; JP6398020B2; JP2018522710A; MY172915A; PH12017501903B1

Abstract

A membrane module for hydrogen separation comprises: a stack of membrane packs (66); a supply manifold; an exhaust manifold; and a feed plate assembly (100) disposed between each membrane pack, the feed plate assembly comprising: a center feed plate (102) comprising a central region, and at least one supply channel (114) and at least one exhaust channel (116) formed through a thickness of the center feed plate on a periphery thereof; and a feed frame (118) interposed between the center feed plate and the adjacent membrane packs, the feed frame formed around a periphery of the center feed plate and forming an open volume between the center feed plate and the adjacent membrane pack; wherein the at least one supply channel fluidly connects the supply manifold with the open volume, and the at least one exhaust channel fluidly connects the exhaust manifold with the open volume.

Description

MEMBRANE-BASED HYDROGEN PURIFIERS

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to hydrogen purifiers and, more specifically, to hydrogen purifiers using hydrogen-selective membranes.

Description of the Related Art

Purified hydrogen gas is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen gas also is an important fuel source for many energy conservation devices. For example, fuel cells use purified hydrogen gas and an oxidant to produce electrical potential. Various processes and devices may be used to produce hydrogen gas. However, many hydrogen-producing processes produce an impure hydrogen gas stream, which may also be referred to as a mixed gas stream that contains hydrogen gas and other gases. Prior to delivering this stream to a fuel cell stack or other hydrogen- consuming device, the mixed gas stream may be purified, such as to remove at least a portion of the other gases.

An exemplary fuel cell system is shown in FIG. 1 and generally indicated at 10. System 10 includes at least one fuel processor 12 and at least one fuel cell stack 22. Fuel processor 12 is adapted to produce a product hydrogen stream 14 containing hydrogen gas from a feed stream 16 containing a feedstock. The fuel cell stack is adapted to produce an electric current from the portion of product hydrogen stream 14 delivered thereto.

Fuel processor 12 produces hydrogen gas through a number of suitable mechanisms. Examples of suitable mechanisms include steam reforming and autothermal reforming, in which reforming catalysts are used to produce hydrogen gas from a feed stream containing a carbon-containing feedstock and water. Other suitable mechanisms for producing hydrogen gas include pyrolysis and catalytic partial oxidation of a carbon-containing feedstock, in which case the feed stream does not contain water. Still another suitable mechanism for producing hydrogen gas is electrolysis, in which case the feedstock is water.

Examples of suitable carbon-containing feedstocks include at least one hydrocarbon or alcohol. Examples of suitable hydrocarbons include methane, propane, natural gas, diesel, kerosene, gasoline and the like. Examples of suitable alcohols include methanol, ethanol, and polyols, such as ethylene glycol and propylene glycol.

Feed stream 16 may be delivered to fuel processor 12 through one or more feed streams. When carbon-containing feedstock 18 is miscible with water, the feedstock is typically delivered with the water component 20 of feed stream 16, such as shown in FIG. 1. When carbon-containing feedstock 18 is immiscible or only slightly miscible with water, these components are typically delivered to fuel processor 12 in separate streams, such as that shown in FIG. 2.

In FIGS. 1 and 2, feed stream 16 is shown being delivered to fuel processor 12 by a feed stream delivery system 17. The delivery system may include one or more pumps that deliver the components of stream 16 from a supply. Additionally, or alternatively, system 17 may include a valve assembly adapted to regulate the flow of the components from a pressurized supply. The supplies may be located external of the fuel cell system, or may be contained within or adjacent the system.

Fuel cell stack 22 contains at least one, and typically multiple, fuel cells 24 adapted to produce an electric current from the portion of the product hydrogen stream 14 delivered thereto. This electric current may be used to satisfy the energy demands, or applied load, of an associated energy-consuming device 25. Illustrative examples of devices 25 include a motor vehicle, recreational vehicle, boat, tool, light or lighting assemblies, appliances (such as household or other appliances), household, signaling or communication equipment, etc. A fuel cell stack typically includes multiple fuel cells joined together between common end plates 23, which contain fluid delivery/removal conduits (not shown). Examples of suitable fuel cells include proton exchange membrane (PEM) fuel cells and alkaline fuel cells. Fuel cell stack 22 may receive all of product hydrogen stream 14. Some or all of stream 14 may additionally, or alternatively, be delivered, via a suitable conduit, for use in another hydrogen- consuming process, burned for fuel or heat, or stored for later use. As mentioned in the foregoing, one example of a suitable fuel processor 12 is a steam reformer. An example of a suitable steam reformer is shown in FIG. 3 and indicated generally at 30. Reformer 30 includes a reforming, or hydrogen-producing, region 32 that includes a steam reforming catalyst 34. Alternatively, reformer 30 may be an autothermal reformer that includes an autothermal reforming catalyst. In reforming region 32, a reformate stream 36 is produced from the water and carbon- containing feedstock forming feed stream 16. The reformate stream typically contains hydrogen gas and impurities, and therefore is delivered to a purification region, or separation region, 38, where the hydrogen gas is purified. In purification region 38, the hydrogen-containing stream is separated into one or more byproduct streams, which are collectively illustrated at 40, and a hydrogen-rich stream 42 by any suitable pressure- driven separation process. In FIG. 3, hydrogen-rich stream 42 is shown forming product hydrogen stream 14. Purification region 38 includes a membrane module 44 and contains one or more hydrogen-selective membranes 46.

Hydrogen purification using one or more hydrogen-selective membranes is a pressure driven separation process, in which the one or more hydrogen-selective membranes are contained in a pressure vessel. The mixed gas stream contacts the mixed gas surface of the membrane(s), and the product stream is formed from at least a portion of the mixed gas stream that permeates through the membrane(s). The byproduct stream is formed from at least a portion of the mixed gas stream that does not permeate through the membrane(s). The pressure vessel is typically sealed to prevent gases from entering or leaving the pressure vessel except through defined inlet and outlet ports or conduits.

An example of a membrane module configured for use as a hydrogen purifier is schematically illustrated in FIG. 4. As shown, a reformate stream 61 containing hydrogen gas 62 and other gases 63 is delivered to purifier 60, which contains a membrane module 44 constructed according to the present invention. The membrane module contains at least one hydrogen-selective membrane 46, and separates the mixed gas stream into a product stream 64 containing at least substantially hydrogen gas and a byproduct stream 65 containing at least substantially the other gases. Another way to describe the purifier is that the product stream contains at least a substantial portion of the hydrogen gas in the mixed gas stream and that the byproduct stream contains at least a substantial portion of the other gases. Purifier 60 may be integrated with a hydrogen-producing device, such as a fuel processor, to provide a hydrogen- producing device with an integrated hydrogen purifier and/or with a hydrogen- consuming device to provide a hydrogen-consuming device with an integrated hydrogen purifier.

Known membrane modules for use as a hydrogen purifier typically include one or more hydrogen-permeable and hydrogen-selective membranes 46. The hydrogen-permeable membranes may be arranged in pairs around a common permeate support assembly to form a membrane pack, such as that as schematically illustrated in FIG. 5. Examples of suitable materials for hydrogen-selective membranes are palladium and palladium alloys, and especially thin films of such metals and metal alloys. To decrease membrane cost, the palladium (or other precious metal) alloy content as well as the thickness of the membrane is preferably low.

For low-cost, thin hydrogen-selective membranes, it is important to evenly distribute the reformed gas over the surface of the membrane and reduce the hydrogen diffusion gradient in the direction perpendicular to the surface of the membrane and thereby increase the hydrogen concentration at the surface of the membrane to improve hydrogen separation efficiency. U.S. Patent No. 7,056,369 discloses that in membrane packs having parallel flow, it is important that the reformate gas flow strikes all membrane packs as evenly as possible to achieve good efficiency. In order for the flow to the outside membranes to be the same as to the inside membranes, feed spaces of the same size are provided on the uppermost and lowermost membrane packs of the stack of membrane packs as between two adjacent membrane packs, the uppermost and lowermost feed spaces being delimited by gastight plates which terminate the stack of membrane packs to the top and to the bottom.

A negative hydrogen concentration gradient perpendicular to the membrane surface appears in the feed spaces during continuous diffusion of hydrogen through the membranes, which reduces the efficiency theoretically expected. This effect is countered in '369 by devices for making the gas turbulent, which are preferably plate-shaped components made of porous material which essentially completely fill the respective feed spaces. These components are made porous to the extent that the gain in efficiency due to hydrogen turbulence transversely to the foil is greater than the loss due to the greater flow resistance. However, in this case, the volumetric flow rate of the feed gas will need to be relatively high, which leads to high pressure drop between the inlet and outlet manifolds in the membrane modules, which is undesirable for applications where reformed gas flow rates are low, such that turbulent flow is not possible.

Therefore, while attempts have been made to improve the delivery of hydrogen-rich reformate gas to membrane-based hydrogen separation devices, there still remains a need to improve the efficiency of hydrogen separation in such devices. BRIEF SUMMARY OF THE INVENTION

In brief, a membrane module for hydrogen separation is disclosed, comprising a stack of membrane packs disposed adjacent one another, wherein each membrane pack comprises a pair of hydrogen-selective membranes, a supply manifold for supplying a hydrogen-rich reformate stream to each membrane pack, an exhaust manifold for removing a byproduct stream from each membrane pack, and a feed plate assembly disposed between each membrane pack in the stack. The feed plate assembly comprises a center feed plate comprising a substantially fluid impermeable central region, and at least one supply channel and at least one exhaust channel, wherein the supply channels and the exhaust channels are formed through a thickness of the center feed plate on a periphery thereof. The feed plate assembly further comprises a feed frame interposed between the center feed plate and the adjacent membrane pack, the feed frame being formed around a periphery of the center feed plate and forming an open volume between the substantially fluid impermeable central region of the center feed plate and the adjacent membrane pack. The supply channels in the center feed plate fluidly connect the supply manifold with the open volume formed by the feed frame between the center feed plate and the adjacent membrane pack, and the exhaust channels fluidly connect the exhaust manifold with the open volume.

In one embodiment, the open volume is formed by the thickness of the feed frame between the feed plate and the adjacent membrane pack. In one embodiment, the feed frame overlaps a central portion of the at least one supply channel and the at least one exhaust channel.

In one embodiment, the feed frame comprises a feed plate gasket and an outer feed plate, the feed plate gasket interposed between the central feed plate and the outer feed plate.

In some embodiments, the feed frame is bonded to the central feed plate.

In one embodiment, the feed plate assembly further comprises a supply region and an exhaust region on a periphery thereof, wherein the supply region comprises at least one supply channel, and the exhaust region comprises at least one exhaust channel.

In one embodiment, a thickness of the feed frame is less than a thickness of the center feed plate.

In one embodiment, the supply channels and the exhaust channels have the same geometry.

In one embodiment, the central feed plate comprises more than one supply channel and more than one exhaust channel and the spacing between the supply channels is the same as the spacing between the exhaust channels. In other embodiments, the spacing between the supply channels is different than the spacing between the exhaust channels.

In one embodiment, the total area of the exhaust channels in the central feed plate is larger than the total area of the supply channels.

In one embodiment, the membrane module further comprising a permeate plate assembly for removing a hydrogen-rich permeate stream to a hydrogen manifold, wherein the permeate plate assembly is interposed between the pair of hydrogen-selective membranes in the membrane pack.

These and other aspects of the invention are evident upon reference in the attached drawings and following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary fuel cell system containing a fuel processor. FIG. 2 is a schematic diagram of another exemplary fuel cell system containing a fuel processor.

FIG. 3 is a schematic diagram of an exemplary fuel processor suitable for use in the fuel cell systems of FIGS. 1 and 2.

FIG. 4 is a schematic diagram of an exemplary hydrogen purifier for a fuel processor.

FIG. 5 is a fragmentary side elevation view of an exemplary membrane pack for use in a hydrogen purifier.

FIG. 6 is an exploded isometric view of a membrane pack including a screen structure having several layers.

FIG. 7 is an exploded isometric view of a membrane pack according to one embodiment.

FIG. 8 is an isometric view of a membrane pack according to one embodiment.

FIG. 9 is an exploded view of a membrane pack according to another embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, certain specific details are set forth in order to provide a thorough understanding of the various embodiments of the invention. However, one skilled in the art will understand that the invention may be practiced without these details. In other instances, well-known structures associated with fuel cells, fuel cell stacks, batteries and fuel cell systems have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the invention.

Unless the context requires otherwise, throughout the specification and claims which follow, the word "comprise" and variations thereof, such as, "comprises" and "comprising" are to be construed in an open, inclusive sense, that is, as "including, but not limited to."

As discussed, a suitable structure for use in the purification region and the purifier of a fuel processor is a membrane module 44 as shown in FIG. 4, which contains one or more hydrogen-permeable and hydrogen-selective membranes 46. The membranes may be formed of any hydrogen-selective material suitable for use in the operating environment and conditions in which the membrane module is operated, such as in a purifier, fuel processor or the like. Examples of suitable materials for membranes 46 are palladium and palladium alloys, and especially thin films of such metals and metal alloys. Palladium alloys have proven particularly effective, especially palladium with 20 wt % to 53 wt % copper. These membranes are typically formed from a thin foil that is approximately 0.001 inches thick. It is within the scope of the present invention, however, that the membranes may be formed from hydrogen-selective metals and metal alloys other than those discussed above and that the membranes may have thicknesses that are larger or smaller than discussed above. For example, the membrane may be made thinner, with commensurate increase in hydrogen flux. Suitable mechanisms for reducing the thickness of the membrane include rolling, sputtering and etching.

As mentioned in the foregoing, the hydrogen-permeable membranes may be arranged in pairs around a common permeate support assembly to form a membrane pack 66, such as that as schematically illustrated in FIG. 5. In such a configuration, the membrane pairs may be referred to as a membrane pack, in that they define a common permeate channel, or harvesting conduit, through which the permeated gas may be collected and removed to form hydrogen-rich reformate stream 42 (or product hydrogen stream 14 or purified hydrogen stream 64, depending on the particular implementation of the membrane module).

It should be understood that the membrane pairs may take a variety of suitable shapes, such as planar packs and tubular packs. Similarly, the membranes may be independently supported, such as with respect to an end plate or around a central passage. For purposes of illustration, the following description and associated illustrations will describe the membrane module as including one or more membrane packs 66. It should be understood that the membranes forming the pack may be two separate membranes, or may be a single membrane folded, rolled or otherwise configured to define two membrane regions, or surfaces, 67 with permeate faces 68 that are oriented toward each other to define a harvesting conduit 69 therebetween from which the permeate gas may be collected and withdrawn.

In some embodiments, a screen structure may be used to support the membranes against high feed pressures, such as that shown in FIG. 6. Screen structure 70 provides support to the hydrogen-selective membranes, and more particularly includes surfaces 71 that against which the permeate sides 68 of the membranes are supported. Screen structure 70 also defines a harvesting conduit through which permeated gas may flow both transverse and parallel to the surface of the membrane through which the gas passes, such as schematically illustrated in FIG. 5 as harvesting conduit 69. The permeate gas, which is at least substantially pure hydrogen gas, may then be harvested or otherwise withdrawn from the membrane module, such as to form streams 42, 64, and/or 14. Because the membranes lie against the screen structure, it is preferable that the screen structure does not obstruct the flow of gas through the hydrogen-selective membrane. The gas that does not pass through the membranes forms one or more byproduct streams.

An exemplary screen structure 70 is shown in FIG. 6. Screen structure 70 includes plural screen members 73. In the illustrated embodiment, the screen members include a coarse mesh screen 74 sandwiched between fine mesh screens 76. It should be understood that the terms "fine" and "coarse" are relative terms. In this embodiment, the outer screen members are selected to support membranes 46 without piercing the membranes and without having sufficient apertures, edges or other projections that may pierce, weaken or otherwise damage the membrane under the operation conditions with which the membrane module is used. Because the screen structure needs to provide for flow of the permeated gas generally parallel to the membranes, a relatively coarser inner screen member may be used to provide for enhanced parallel flow conduits. In other words, the finer mesh screens provide better protection for the membranes, while the coarser mesh screen provides better flow generally parallel to the membranes.

The screen members may be of the same or different construction, and that more or less screen members may be used. Generally, any suitable supporting medium that enables permeated gas to flow in the harvesting conduit generally parallel and transverse to the membranes may be used. For example, porous ceramics, porous carbon, porous metal, ceramic foam, carbon foam, and metal foam may be used to form screen structure 70, either alone, or in combination with one or more screen members 73. As another example, fine mesh screens 76 may be formed from expanded metal instead of a woven mesh material. Preferably, screen structure 70 is formed from a corrosion-resistant material that will not impair the operation of the membrane module and devices with which the membrane module is used. Examples of suitable materials for metallic screen members include stainless steels, zirconium and alloys thereof, corrosion-resistant alloys, including Inconel™ alloys, such as 800™, and Hastelloy™ alloys, and alloys of copper and nickel, such as Monel™. Such metallic screen members may optionally include a coating on surface 71, which are typically a metallic oxide or nitride. Examples of suitable coatings include aluminum oxide, or other metal oxides such as chromium oxide, titanium oxide, nickel oxide, tungsten carbide, tungsten nitride, titanium carbide, titanium nitride, and mixtures thereof.

The screen structure and membranes may be incorporated into a membrane pack 66 that includes frame members 88 that are adapted to seal, support and/or interconnect the membrane packs for use in fuel processing systems, gas purification systems, and the like, such as that shown in FIG. 7. With reference to the screen construction of FIG. 7, screen structure 70 fits within a permeate frame or extends at least partially over the surface of the permeate frame to form permeate plate assembly 91. Examples of suitable frame members 88 include supporting frames and/or gaskets. These frames, gaskets or other support structures may also define, at least in part, the fluid manifolds that interconnect the membrane packs in an embodiment of membrane module 44 that contains two or more membrane packs. Examples of suitable gaskets are flexible graphite gaskets, although other materials may be used, such as depending upon the operating conditions in which a particular membrane module is used. Alternatively, each membrane may be fixed to a separate frame that is subsequently attached to the permeate frame rather than adhesively attached to the screen structure (not shown). In another alternative, at least one of the membranes may be attached to the screen structure, such as that described above, to form the permeate plate assembly, thereby eliminating the need for the frame members associated with the membrane.

A feed plate assembly is placed between adjacent membrane packs to deliver the hydrogen-rich reformate stream to the membrane pack for separating hydrogen from the reformate stream, and to remove the resulting hydrogen-depleted stream from the membrane pack. As shown in FIG. 7, feed plate assembly 100 comprises a center feed plate 102 that separates one membrane pack from another membrane pack in a stack. As further shown in FIG. 8, the center feed plate has a substantially fluid impermeable central region 104, as well as a supply region 106 and an exhaust region 108 on the periphery. Supply region 106 fluidly connects supply manifold 110 to central region 104. Similarly, exhaust region 108 fluidly connects exhaust manifold 112 to central region 104. Supply region 106 and exhaust region 108 comprise supply channels 114 and exhaust channels 116, respectively, that are formed though the thickness of the center feed plate.

Center feed plate 102 does not include flow channels or the like in its central region 104. Instead, a feed frame 118 is formed on the periphery of each side of the central feed plate to create an open volume between central region 104 and its adjacent membrane pack that is formed by the thickness of feed frame 118. In some embodiments feed frame 118 is bonded to the center feed plate 102, for example by brazing, while in other embodiments feed frame 118 may comprise an outer feed plate 120 and a feed plate gasket 122 interposed between the outer feed plate 120 and the center feed plate 102 as further described in relation to Figure 9. As shown in Figure 8, feed frame 118 overlaps a central portion of channels 1 14, 116 (i.e., should not overlap channels 114, 116 at their ends) so that the reformate stream provided from supply manifold 110 flows through channels 114 in the supply region (and underneath feed frame 118), and then into the open volume formed by the thickness of feed frame 118. In a likewise manner, the byproduct stream flows from the open volume through channels 116 in the exhaust region (and underneath feed frame 118), and then to exhaust manifold 112. Therefore, the width of feed frame 118 in the area that overlaps a central portion of channels 114, 116 of center feed plate 102 is necessarily smaller than the span of channels 114, 116 so that supply and exhaust manifolds 110, 112 are fluidly connected to the open volume.

For parallel flow designs of membrane modules, the total mass flow of the reformate stream is divided between the membrane packs, which results in low gas velocities to each of the membrane pack and low pressure drops, typically less than 5 psi between the supply and exhaust regions. As a result, the flow velocity of the reformate stream will be in the laminar flow region and the hydrogen concentration at the surface of the membrane is governed by diffusion. For thin membranes, the hydrogen flux through the membrane is relatively high and, thus, it is desirable to have a high hydrogen concentration at the surface of the membrane (i.e., low hydrogen concentration gradient in the direction perpendicular to the membrane surface) so that hydrogen flux through the membrane is maximized, which increases efficiency of the hydrogen separation device.

One skilled in the art will appreciate that to maximize hydrogen concentration at the surface of the membrane on the feed side of the membrane, particularly with laminar flow of the reformate stream over the surface of the membrane, it is preferable to reduce the gas volume on the feed zone. In previous designs, the gas volume in the feed zone is linked to the size of the feed channels (and the thickness of the feed plates/gaskets that situate between membrane packs in prior art designs) that fluidly connect the inlet and outlet manifolds to the feed zone. However, in the present design, the size of the channels in the supply and exhaust regions of the center plate are decoupled from the gas volume, thereby allowing large, low pressure drop feed channels to provide the reformate stream to the feed zone while allowing low gas volumes in the feed zone, which is preferable to reduce the hydrogen diffusion gradient of the reformate in the direction perpendicular to the surface of the membrane. In particular, it is desirable to reduce the effective height of the gas volume in the active area of the membrane pack, which is linked to the thickness of the feed frame in the present design and no longer limited by the size of the channels in the supply and exhaust regions. Therefore in some embodiments, the thickness of the feed frame is less than the thickness of the center feed plate. In another embodiment, feed frame 118 may comprise of two or more separate parts. For example, feed frame 118 may comprise an outer feed plate 120 and a feed plate gasket 122 interposed between outer feed plate 120 and center feed plate 102, as shown in FIG. 9. The thickness of outer feed plate 120 and feed plate gasket 122 forms the open volume. The thickness of outer feed plate 120 may be about 0.5 mm or less and the thickness of feed plate gasket 122 may be about 0.5 mm or less. For example, the outer feed plate and the feed plate gasket may be about 0.25 mm or less, and may be the same or different thicknesses. One skilled in the art will be able to select a suitable thickness of the plate and gasket based on the desired effective height of the gas volume in the active area and the functional limitations of each part. Again, outer feed plate 120 and feed plate gasket 122 overlap a central portion of channels 114, 116 so that inlet and outlet manifolds 110, 112 are fluidly connected to the open volume.

The center feed plate and outer feed frames may be made of any suitable material, such as stainless steels and other metallic alloys. In specific embodiments, 300 series stainless steels may be used. In embodiments where the feed frame comprises an outer feed plate and a feed plate gasket, the outer feed plate may also be made of stainless steels and other metallic alloys while the feed plate gasket may be made of compressible graphite. Feed frame 118 may be optionally attached to one or both of the adjacent membrane packs by any suitable method depending on the material or materials used for feed frame 1 18, such as adhesive bonding, diffusion bonding, welding, brazing, and the like.

The size and geometry of channels 114, 116 that are formed through the thickness of center feed plate 102 at supply region 106 and exhaust region 108 can be determined by one skilled in the art, so long as channels 114, 116 extend beyond the overlapping feed frame so that the supply manifold is fluidly connected to the open volume and membrane pack. For example, the quantity and dimensions of channels 114, 116 will be a balance of the desired Reynolds Number or flow area and the length and width of channels 114, 116 that must be bridged by the outer feed frame, and must be able to support the gasket load across the gap formed by channels 114, 116. There will be a practical limit for the stamping or other process to cut channels 114, 116. For example, there may be 10 to 20 channels that range from about 1 mm to about 4 mm in width, and about 10 to 20 mm in length, at each of the supply and exhaust regions. The limit for some processes will be where the width of channels 114, 116 equals the thickness of center feed plate 102. One skilled in the art will appreciate that channels 114, 116 may not need to be the same dimensions in the same regions (i.e., each of supply channels 114 do not need to have the same dimensions in the supply region and each of exhaust channels 116 do not need to have the same dimensions in the exhaust region.) The thickness of the center feed plate may be about 0.5 mm to about 3 mm. One skilled in the art will appreciate that the thickness of the center feed plate will be determined by the desired stiffness, strength, and mass of the plate, as well as the flow parameters of the reformate stream. The size and geometry of supply channels 114 and exhaust channels 116 of the center feed plate may be the same or may be different. An asymmetrical design of the exhaust channels may be conceived to improve the flow distribution, gas mixing and reducing the hydrogen concentration gradients in central region 104. For example, in some embodiments, the total area of the exhaust channels 116 is larger than the total area of the supply channels 114. In addition, the spacing between the supply channels 114 may be the same or may be different than the spacing between the exhaust channels 116. One advantage of having the same size and geometries is that the center feed plate is symmetrical, so manufacturing is easier and cheaper. However by having exhaust channels with a different geometry than the supply channels and by having the spacing between the exhaust channels different than the spacing between the supply channels it is possible to better stir the reformate in the central region 104 for reducing the concentration gradient of the reformate stream above the membrane which helps improve the hydrogen recovery process. By increasing the exhaust channel area compared to the supply channel area it is possible to reduce the pressure drop within the membrane pack and therefore reduce the number of membrane packs in the membrane module. The number and total area of supply channels 114 and exhaust channels 116 can be selected to control the pressure drop across the membrane pack and to decrease the concentration gradient of the reformate stream above the membrane. The membrane module discussed herein may include one or more membrane packs 66, typically along with suitable supply and exhaust manifolds through which the mixed gas stream, such as reformate stream 36 or mixed gas stream 61, is delivered to the membrane module and from which the hydrogen-rich and byproduct streams are removed. When the membrane module includes a plurality of membrane packs, the module may include fluid manifolds interconnecting the packs, such as to deliver or supply a mixed gas stream thereto, to withdraw or remove purified hydrogen gas therefrom, and/or to withdraw or remove the gas that does not pass through the membranes from the membrane module. When the membrane module includes a plurality of membrane packs, the permeate stream, byproduct stream, or both, from a first membrane pack may optionally be sent to another membrane pack for further purification.

It should be understood that the geometry of the frame members, gaskets, membranes and screen members shown in the figures are provided as illustrative examples, and it should be understood that these components may be of any suitable shape. Similarly, the configuration and orientation of the passages through the gaskets and plates may vary, depending upon the particular application with which the membrane module will be used.

It should also be understood that the hydrogen purity of the product stream, the hydrogen content of the byproduct stream, the percentage of hydrogen from the mixed gas stream that forms the byproduct stream, and similar compositions of the product and byproduct streams may be selectively varied depending upon the construction of the membrane module and/or the operating conditions within which the membrane module is used. For example, the compositions of the product and byproduct streams may vary at least partially in response to at least the following factors: the temperature of the membrane module, the pressure difference between the feed gas and the permeate gas in the membrane module, the composition of the hydrogen-selective membrane, degradation of the hydrogen-selective membrane, the thickness of the hydrogen-selective membrane, the composition of the mixed gas stream, the number of hydrogen-selective membranes used in the membrane module, and the number of sequential membranes through which the mixed gas, product and/or byproduct streams may pass.

The present invention is applicable in any device in which a stream containing hydrogen gas is purified to produce a purified hydrogen stream. The invention is similarly applicable to fuel processing systems in which hydrogen gas is produced from a feed stream and subsequently purified, such as for delivery to a fuel cell stack or other hydrogen-consuming device.

While the present membrane modules have been described for use in PEM fuel cell systems, it is anticipated that they would be useful in other fuel cell systems having an operating temperature below about 450°C. They are particularly suited for acid electrolyte fuel cells, including phosphoric acid, PEM and liquid feed fuel cells.

All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference in their entirety.

While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. It is therefore contemplated by the appended claims to cover such modifications that incorporate those features coming within the scope of the invention.

This application also claims the benefit of U.S. Provisional Patent Application No. 62/155,653, filed May 1, 2015, and is incorporated herein by reference in its entirety.

Claims

CLAIMS What is claimed is:

1. A membrane module for hydrogen separation, comprising:

a stack of membrane packs disposed adjacent one another, wherein each membrane pack comprises a pair of hydrogen-selective membranes;

a supply manifold for supplying a hydrogen-rich reformate stream to each membrane pack;

an exhaust manifold for removing a byproduct stream from each membrane pack; and

a feed plate assembly disposed between each membrane pack in the stack, the feed plate assembly comprising:

a center feed plate comprising a substantially fluid impermeable central region, and at least one supply channel and at least one exhaust channel, wherein the at least one supply channel and the at least one exhaust channel are formed through a thickness of the center feed plate on a periphery thereof; and

a feed frame interposed between the center feed plate and the adjacent membrane pack, the feed frame being formed around a periphery of the center feed plate and forming an open volume between the substantially fluid impermeable central region of the center feed plate and the adjacent membrane pack;

wherein the at least one supply channel fluidly connects the supply manifold with the open volume, and the at least one exhaust channel fluidly connects the exhaust manifold with the open volume.

2. The membrane module of claim 1, wherein the open volume is formed by a thickness of the feed frame between the center feed plate and the adjacent membrane pack.

3. The membrane module of claim 1, wherein the feed frame overlaps a central portion of the at least one supply channel and the at least one exhaust channel.

4. The membrane module of claim 1, wherein the feed frame comprises a feed plate gasket and an outer feed plate, the feed plate gasket interposed between the central feed plate and the outer feed plate.

5. The membrane module of claim 1 wherein the feed frame is bonded to the central feed plate.

6. The membrane module of claim 1, wherein the feed plate assembly further comprises a supply region and an exhaust region on a periphery thereof, wherein the supply region comprises the at least one supply channel, and the exhaust region comprises at least one exhaust channel.

7. The membrane module of claim 1, wherein a thickness of the feed frame is less than a thickness of the center feed plate.

8. The membrane module of claim 1, wherein the at least one supply channel and the at least one exhaust channel have the same geometry.

9. The membrane module of claim 1 wherein the central feed plate comprises more than one supply channel and more than one exhaust channel and the spacing between the supply channels is the same as the spacing between the exhaust channels.

10. The membrane module of claim 1 wherein the total area of the at least one exhaust channel is larger than the total area of the at least one supply channel.

11. The membrane module of claim 1, further comprising a permeate plate assembly for removing a hydrogen-rich permeate stream to a hydrogen manifold, wherein the permeate plate assembly is interposed between the pair of hydrogen- selective membranes in the membrane pack.