WO2006034100A1

WO2006034100A1 - Membrane steam reformer

Info

Publication number: WO2006034100A1
Application number: PCT/US2005/033289
Authority: WO
Inventors: Scott Lee Wellington; Andreas Nicholas Matzakos; Ivan Petrovich Mardilovich; Yi Hua Ma; Erik Edwin Engwall
Original assignee: Worcester Polytechnic Institute
Priority date: 2004-09-21
Filing date: 2005-09-19
Publication date: 2006-03-30
Also published as: CA2580585A1; JP2008513338A; AU2005286952B2; TW200619136A; NO20071530L; AU2005286952A1; EP1789171A1

Abstract

A hydrogen producing reactor is disclosed. The hydrogen producing reactor has a reaction chamber containing a catalyst bed adapted to produce reaction products con-taining hydrogen from a hydrogen-producing feedstock. The reaction chamber also in-cludes a hydrogen-selective, hydrogen-permeable gas separation module adapted to re-ceive the reaction products from the catalyst bed and to separate a product stream con-taining hydrogen from the reaction products. The gas separation module comprises a porous substrate, an intermediate porous layer located at the porous substrate, and a hy-drogen-selective membrane overlying the intermediate layer. The intermediate porous layer comprises a powder having a Tamman temperature higher than the Tamman tem-perature of the porous substrate. A steam reforming process is also disclosed using the disclosed reactor.

Description

MEMBRANE STEAM REFORMER

Field of the Invention

This invention relates to a reactor suitable for a steam reforming process. The in- vention further relates to a steam reforming process using said steam reforming reactor. Background of the Invention

Purified hydrogen is an important fuel source for many energy conversion de¬ vices. For example, fuel cells use highly purified hydrogen to produce electricity. Chemical processes, such as steam reforming, are usually operated at high temperature and produce hydrogen as well as certain by-products and impurities. Subsequent purifi¬ cation processes are required to remove the undesirable impurities to provide hydrogen sufficiently purified for certain applications, such as a fuel cell.

A majority of the hydrogen-producing chemical processes and subsequent proc¬ esses of hydrogen purification occur in separate apparatus. It is advantageous to have a single, compact and more economical apparatus which combines a hydrogen-production reactor, such as a steam reformer, with a hydrogen separation and purification device which is operable at high temperature.

U.S. 5,997,594, issued December 7, 1999, discloses a steam reformer which con¬ tains a hydrogen purification palladium metal membrane module. The effective life of a typical composite gas separation module having a hydro¬ gen-selective metal membrane bonded to a porous substrate often is limited by diffusion of substrate components into the membrane which decreases the hydrogen permeability of the membrane. The rate of diffusion of the substrate components is greatest when the substrate is at or above its Tamman temperature. A metal lattice at its Tamman tempera- ture is subjected to considerable thermal (atomic) vibration. If there is an interface be¬ tween two metals, such thermal vibration significantly increases the mobility of metal atoms and their consequent diffusion. The Tamman temperature of a material is equal to one-half of its melting point temperature in Kelvin. For example, in the case of a hydro¬ gen-selective palladium membrane on a stainless steel substrate, palladium and stainless steel have melting point temperatures of 1552°C (1825 K) and 1375-1400°C (1648-1673 K), respectively. The corresponding Tamman temperatures are about 64O⁰C (913 K) and 550-560⁰C (823-833 K), respectively. The lower of these Tamman temperatures deter¬ mines the temperature where a significant increase in intermetallic diffusion can occur. Accordingly, at temperatures around 550⁰C considerable thermal vibration and diffusion of stainless steel substrate components into a palladium membrane can be expected in such a composite gas separation module. The alloy created by the diffusion of stainless steel substrate components into a palladium membrane can have reduced hydrogen per¬ meability. Typical hydrogen-selective metal membranes used in hydrogen gas separation modules must be free of defects and/or pinholes that breach the metal layer to prevent the migration of undesired gases through the metal membrane. Thick hydrogen-selective metal membranes, e.g., palladium membranes, generally are very expensive. Porous sub¬ strates used in the fabrication of composite gas separation modules can have broad pore size distributions and/or rough surfaces such that thick gas-selective membranes can be needed to effectively separate gases. Generally, as the thickness of the gas-selective membrane increases, gas flux through the gas separation module decreases. However, in ordinary metal membranes operated at high temperature, intermetallic diffusion between the porous substrate and metal membrane will occur. This diffusion will cause deteriora- tion of the hydrogen flux. Therefore, a need exists for a hydrogen gas separation module which is durable for a high temperature operation by preventing intermetallic diffusion while being thin enough to provide sufficiently high fluxes of hydrogen gas.

Typical reactors operated at high temperatures usually are made of metals which would withstand high temperature for producing hydrogen and high pressure and which are relatively expensive. It would be desirable if lower temperatures could be used so that lower-cost metallurgy can be utilized for the reactor. Therefore, there is a need for providing for the reactors with more uniform heating and having more control over tem¬ peratures at various points to avoid hot spots.

Furthermore, it would be desirable in the art to provide an integrated hydrogen- production and purification reactor design for producing high purity hydrogen having carbon and carbon oxides separated while having minimal production OfNO_x within the integrated reactor. It would also be desirable to provide the modularity needed at bulk- hydrogen production scales so that a producer can match the desired capacity by install¬ ing multiple reactor units of the specific design. This is more cost-effective than either trying to scale up or down the existing large box furnace reactor designs or building sev¬ eral thousand single-tube reactors. It would also be desirable to employ less volume than conventional processes by intensifying the process and using less catalyst and smaller heater space. Furthermore, if the process produced CO₂ in higher concentrations and greater purity than other processes in the art, and the CO₂ could be sequestered for other uses, it would be extremely desirable. Such an integrated system would demonstrate far greater efficiency than any power generating system currently available. Summary of the Invention

In one embodiment, the invention is directed to reactor comprising: a) a reaction chamber comprising a catalyst bed adapted to produce reaction products comprising hydrogen gas from a hydrogen-producing feedstock; and b) at least one hydrogen-selective, hydrogen-permeable gas separation module adapted to receive the reaction products from the catalyst bed and to separate the reaction products into (1) a product stream comprising hydrogen and (2) a byproduct stream, wherein the gas separation module comprises:

(i) a porous substrate;

(ii) an intermediate porous layer overlying the porous substrate, said intermediate porous layer including a powder having a Tamman temperature higher than the Tamman temperature of the porous substrate; and

(iii) a hydrogen-selective membrane, wherein the hydrogen-selective membrane overlies the intermediate porous layer. hi another embodiment, the invention is directed to a steam reforming process for the production of hydrogen, comprising: (a) reacting steam with a hydrogen-producing feedstock at a temperature of from about 200°C to about 700°C and at a pressure of from about 0.1 MPa to about

20 MPa in a steam reforming reaction chamber containing a reforming catalyst to produce a mixture of hydrogen and carbon dioxide with a lesser amount of car- bon monoxide; and

(b) separating hydrogen from said reaction chamber and from said carbon diox¬ ide and carbon monoxide with a hydrogen-selective, hydrogen-permeable gas separation module, where the gas separation module comprises:

(i) a porous substrate; (ii) an intermediate porous layer overlying the porous substrate, said in¬ termediate porous layer including a powder having a Tamman tempera¬ ture higher than the Tamman temperature of the porous substrate; and (iii) a hydrogen-selective membrane, wherein the hydrogen-selective membrane overlies the intermediate porous layer. Brief Description of the Drawings

Figure 1 is a schematic diagram of the novel hydrogen producing reactor with catalyst section, and a hydrogen gas separation tube placed in order from the outside in. Figure 2 is a schematic diagram of one of the configurations of the hydrogen gas separation tubes useful for the present hydrogen-producing reactor and process.

Figure 3 is a cross-section representation of a composite hydrogen gas separation module in the present reactor.

Figure 4 is schematic diagram of a multi-tubular, distributed combustion heated, radial flow, membrane, steam reforming reactor in accordance with the invention. Some of the inlet and outlet streams of the membrane and distributed combustion tubes have been omitted for simplicity.

Figure 5 is a cross-sectional view of the shell of the multi-tubular, distributed combustion heated, radial flow, membrane reactor shown in Figure 4. Figures 6A and 6B are schematic diagrams of a "closed ended" and of an "open ended" distributed combustion ("DC") tubular chamber used to drive the reforming reac¬ tions in the process and apparatus of the present invention.

Figure 7 is a schematic diagram of a multi-tubular, DC heated, axial flow, mem¬ brane steam reforming reactor in accordance with the invention. Figure 8 is a cross section of the shell of the multi-tubular, distributed combus¬ tion heated, axial flow, membrane reactor shown in Figure 7.

Figures 9A & 9B and 9C & 9D are schematic diagrams of two baffle configura¬ tions which can be employed to increase the contact of the reactant gases with the cata¬ lyst in a multi-tubular, distributed combustion-heated, axial flow, membrane reactor in accordance with the invention.

Figures 10, 11, 12, and 13 are top cross section views of the shells of other em¬ bodiments of the multi-tubular, distributed combustion heated, axial flow, membrane, steam reforming reactors of the invention.

Figure 14 is a simplified flow diagram of the distributed combustion membrane steam reformer fuel hybrid power system. Detailed Description of the Invention

The invention relates to a reactor comprising a reaction chamber and a gas sepa¬ ration module. The present invention provides a new apparatus and process for produc ing high purity hydrogen from a hydrogen producing feedstock, said process being ac¬ complished in one reactor, constantly removing pure hydrogen, and optionally using dis¬ tributed combustion as a heat source which provides great improvements in heat ex¬ change efficiency and load-following capabilities to drive the steam reforming reaction. The hydrogen-selective gas separation module has thinner dense gas-selective membrane producing higher rates of gas flux, e.g. hydrogen flux, hydrogen permeation, selectivity as well as durability are maintained or improved. The degree of intermetallic diffusion is also reduced. In another embodiment, the invention is also a zero emission hybrid power system wherein the produced hydrogen is used to power a high-pressure internally or ex- ternally manifold fuel cell, such as a molten carbonate fuel cell. The design can be a membrane steam reforming reactor (MSR) fueled hybrid system makes it possible to capture high concentrations of CO₂ for sequestration or use in other processes. Finally, the design of the system may be scaled down to a mobile, lightweight unit.

Moreover, at bulk-hydrogen production scales, a multi-tubular (multiple distrib- uted combustion tubes and/or multiple hydrogen selective and permeable membrane tubes) containing reactor disclosed herein provides the modularity needed. A producer can match the desired capacity by installing multiple reactor units of the specific design or having multiple distributed combustion tubes and/or multiple hydrogen selective and permeable membrane units in a large steam reformer. This is more cost-effective than either trying to scale up or down the existing large box furnace reactor designs or build¬ ing several thousand single-tube reactors.

The hydrogen-producing reactor of the present invention comprises a) reaction chamber comprising: (i) an inlet adapted to receive a hydrogen-producing feedstock, and (ii) a catalyst bed for producing reaction products comprising hydrogen gas from the hy- drogen-producing feedstock; and b)at least one hydrogen selective, hydrogen permeable composite gas separation module adapted to receive the reaction products from the cata¬ lyst bed and to separate the reaction products into (1) a product stream comprising a ma¬ jor amount of hydrogen and (2) a by-product stream; wherein the composite gas separa¬ tion module comprises: (i)a porous substrate; (ii) an intermediate layer that includes a powder having a Tamnian temperature higher than the Tamman temperature of the po¬ rous metal substrate and wherein the intermediate layer overlies the porous metal sub¬ strate; and (iii) a dense gas-selective membrane, wherein the dense gas-selective mem¬ brane overlies the intermediate layer. In one embodiment, the module is made by apply¬ ing an intermediate layer that includes a powder having a Tamman temperature of the porous metal substrate over a porous metal substrate, followed by applying a dense hy¬ drogen-selective membrane over the intermediate layer.

Non-limiting illustrative example of the hydrogen-producing feedstock include natural gas, methane, ethyl benzene, methanol, ethane, ethanol, propane, butane, light hydrocarbons having 1-4 carbon atoms in each molecule, light petroleum fractions in¬ cluding naphtha, diesel, kerosene, jet fuel or gas oil, and hydrogen, carbon monoxide and mixtures thereof.

In a particular embodiment, the catalyst bed contains baffles in a form selected from the group consisting of (i) washers and disks, and (ii) truncated disks. In a particular embodiment, the reactor is suitable for a dehydrogenation reaction and has a dehydrogenation chamber containing a dehydrogenation catalyst bed with a dehydrogenation catalyst such as an iron-oxdide-containing catalyst. The invention also relates to a process for the dehydrogenation of ethylbenzene comprising the steps of feeding ethylbenzene into the reactor as described above to produce styrene and hydro- gen.

The reactor can be a steam-reforming reactor wherein the reaction chamber is a steam reforming reaction chamber comprising a catalyst bed comprising a steam reform¬ ing catalyst, hi another embodiment, the present invention also relates to a steam reform¬ ing process comprising the steps of reacting a hydrogen-producing feedstock and steam in a reactor as described above. The steam reforming process for the production of hy¬ drogen can comprise the steps of a) reacting steam with a hydrogen-producing feedstock at a temperature of from about 200°C to about 700⁰C and at a pressure of from about 1 bara (absolute) (0.1 MPa (absolute)) to about 200 bara (absolute) (20 Mpa (absolute)) in a steam reforming reaction chamber containing a reforming catalyst to produce a mixture of primarily hydrogen and carbon dioxide, with a lesser amount of carbon monoxide; and b) conducting said reaction in the vicinity of at least one hydrogen-permeable, hydrogen- selective membrane tube, whereby hydrogen formed in said reaction zone permeates through said hydrogen selective membrane tube and is separated from said carbon diox¬ ide and carbon monoxide; wherein the hydrogen selective, hydrogen permeable mem- brane tube is made of a composite gas separation module as described herein. In a par¬ ticular embodiment, the carbon dioxide produced from said steam reforming chamber may have a pressure of from about 0.1 to about 20 MPa, particularly from about 1 to about 5 MPa and the carbon dioxide produced from the steam reforming chamber has a concentration of from about 80% to about 99% molar dry basis, or of from about 90% to about 95% molar dry basis. In a particular embodiment, the carbon dioxide produced from the steam reforming chamber is used at least in part for enhanced recovery of oil in oil wells or enhanced recovery of methane in coal bed methane formations. hi some embodiments, the afore-mentioned hydrogen-producing reactors, includ- ing the steam reformer and dehydrogenation reactor, further comprises at least one heater comprising a distributed combustion chamber in a heat transferring relationship with the catalyst bed. The distributed combustion chamber comprises an inlet and a flow path for an oxidant, an outlet for combustion gas, and a fuel conduit having an inlet for fuel and a plurality of fuel nozzles or openings which provide fluid communication from within the fuel conduit to the flow path of said oxidant. The plurality of fuel nozzles or openings are sized and spaced along the length of said fuel conduit to avoid hot spot formation when the fuel is mixed with said oxidant in said distributed combustion chamber. In one embodiment, the distributed combustion does not form any flame when the fuel is mixed with said oxidant in said distributed combustion chamber and during its heating opera- tion. The distributed combustion heater(s) may also have a preheater capable of preheat¬ ing the oxidant, such as air or oxygen, to a temperature that when said fuel and said oxi¬ dant are mixed in the distributed combustion chamber, the temperature of the resulting mixture of said oxidant and fuel exceeds the autoignition temperature of said mixture, hi some other embodiments, the ratio of the surface area of said distributed combustion chambers to the surface area of said membrane tubes is from about 0.1 to about 20.0, particularly from about 0.2 to about 5.0, more particularly from about 0.5 to about 5.0, and still more particularly from about 0.3 to about 3.0 and even more particularly from about 1.0 to about 3.0. In still some other embodiments, the distributed combustion chamber may have an external tubular dimension such that the length to diameter ratio is higher than 4, or higher than 10

As a particular embodiment, the hydrogen-selective, hydrogen-permeable com¬ posite gas separation module is connected to a section containing a metal hydride precur¬ sor, and the hydrogen formed in the reforming chamber permeates through the mem¬ brane tube to the section containing the metal hydride precursor which reacts with the permeated hydrogen to form hydride. This reaction reduces the effective partial pressure of hydrogen in the permeate stream and drives the equilibrium within the reaction cham¬ ber to produce more hydrogen from the feedstock.

In some embodiments, the reactor may contain multiple distributed combustion chambers and/or multiple hydrogen separation tubes, hi some embodiments, the prod- ucts produced are separated by hydrogen-selective, hydrogen-permeable hydrogen sepa¬ ration membrane tube(s) having a ratio of length to diameter of less than about 500, wherein gaps between the membrane tubes are from about ¹A inch (about 0.64 cm) to about 2 inches (about 5.08 cm), and wherein gaps between the membrane and distributed combustion ("DC") tubes are from about % inch (about 0.64 cm) to about 2 inches (about 5.08 cm); or the hydrogen-selective and hydrogen-permeable membrane tube(s) have a ratio of length to diameter of less than about 250, wherein gaps between the membrane tubes are from about ¹A inch (about 1.27 cm) to about 1 inch (about 2.54 cm), and gaps between the membrane and DC tubes are from about ¹A inch (about 1.27 cm) to about 1 inch (about 2.54 cm).

In some embodiments, a sweep gas is used to promote the diffusion of hydrogen through the hydrogen separation module. The sweep gas can be, but is not limited to, steam, carbon dioxide, nitrogen and condensable hydrocarbon.

In some embodiments, the hydrogen-selective membrane is a palladium or an al- loy thereof and the porous substrate is a porous metal substrate or a porous ceramic sub¬ strate. Non-limiting illustrative examples of the palladium alloy include alloy of palla¬ dium with least one of the metals selected from the group consisting of copper, silver, gold, platinum, ruthenium, rhodium, yttrium, cerium and indium. Illustrative non- limiting examples of the porous metal substrate include (i) stainless steel, (ii) an alloy comprising chromium and nickel, (iii) a nickel-based alloy, (iv) an alloy comprising chromium, nickel and molybdenum, (v) porous Hastelloy®, and (vi) porous Inconel.

In one embodiment, the powder used herein comprises a material selected from the group consisting of metal powders, metal oxide powders, ceramic powders, zeolite powders, and combinations thereof. In a particular embodiment, the powder comprises a material selected from the group consisting of tungsten, silver, copper oxide, aluminum oxide and combinations thereof. In one embodiment, the powder has an average particle size ranging from about 0.5 micrometers to about 5 micrometers. In another embodi¬ ment, the powder has a Tamman temperature higher than the Tamman temperature of the dense hydrogen-selective membrane. In one embodiment, the composite gas separation module further comprises a layer of a ceramic bonded to the porous metal substrate and underlying the intermediate layer. In another embodiment, the intermediate layer further includes at least one mate¬ rial having a Tamman temperature less than or about equal to the Tamman temperature of the dense hydrogen-selective membrane. The intermediate layer may further include at least one material selected from the group consisting of silver, gold, copper, cerium and yttrium. In some embodiments, the intermediate layer has an average thickness se¬ lected from the group consisting of : (i) at least about 1 micrometer, (ii) from about 1 to about 10 micrometers, and (iii) from about 1 to about 5 micrometers.

The average pore size of the intermediate porous metal layer may be less than the average pore size of the porous metal substrate. The composite gas separation module may include the following modifications:

(i) a layer of a ceramic bonded to the porous metal substrate and underlying the interme¬ diate layer, (ii) oxidation of the surface of the porous metal substrate prior to applying the intermediate layer, (iii) activation of the porous metal substrate, for example being seeded with nuclei of a hydrogen-selective metal, prior to applying the intermediate layer.

In some embodiments, the intermediate layer is applied by depositing the powder from a slurry, particularly a water-based slurry. hi some embodiments, the hydrogen flux through the module is at least about 4 Nni³/m²-hr, particularly at least about 10 Nm³/m²-hr, and more particularly at least about 28 Nm³/m²-hr at about 35O⁰C and with a hydrogen partial pressure difference of about 1 bara (absolute) (0.1 MPa (absolute)) in the permeate side and 2 bara (absolute) (0.2 MPa (absolute) in the process side. hi one embodiment, the present invention relates to a distributed combustion heated, membrane, dehydrogenation reactor comprising: a) a dehydrogenation chamber containing a catalyst bed, said dehydrogena¬ tion chamber having an inlet for vaporizable hydrocarbon, a flow path for hydrogen and product gases resulting from the dehydrogenation reactions taking place in said dehydrogenation chamber and an outlet for said prod¬ uct gases, b) at least one distributed combustion chamber in a heat transferring rela¬ tionship with said catalyst bed whereby a distributed, controlled heat flux is provided by said distributed combustion chamber to said catalyst bed, said distributed combustion chamber comprising an inlet and a flow path for an oxidant, an outlet for combustion gas and further comprising a fuel conduit having an inlet for fuel and a plurality of fuel nozzles which pro¬ vide fluid communication from within the fuel conduit to the flow path of said oxidant, said plurality of fuel nozzles being sized and spaced along the length of said fuel conduit so that no flame results when said fuel is mixed with said oxidant in said distributed combustion chamber; c) a preheater capable of preheating said oxidant to a temperature that when said fuel and said oxidant are mixed in said distributed combustion cham- ber, the temperature of the resulting mixture of said oxidant and fuel ex¬ ceeds the autoignition temperature of said mixture; and d) at least one hydrogen-selective, hydrogen-permeable, membrane tube in contact with said catalyst bed, said membrane tube having an outlet whereby hydrogen formed in the dehydrogenation chamber permeates into said membrane tube and passes through said outlet. hi the present invention, heat transfer limitations are overcome by the innovative use of distributed combustion (distributed combustion) as the primary heat source. Dis¬ tributed combustion is used to distribute heat throughout the reactor at high heat fluxes without high temperature flames and with low NO_x production. This is achieved by in- jecting small quantities of fuel into a preheated air stream and reaching autoignition con¬ ditions. Fuel quantity is controlled by nozzle size, the temperature rise is very small, and there is much reduced or substantially no hot spots such as flame associated with the combustion (combustion is kinetically limited, rather than mass-transfer limited). Distributed combustion is disclosed in U.S. 5,255,742, U.S. 5,862,858, U.S. 5,899,269, U.S. 6,019,172, and EP 1 021 682 Bl.

An important feature of the distributed combustion is that heat is removed along the length of the combustion chamber so that a temperature is maintained that is signifi¬ cantly below what an adiabatic combustion temperature would be. This almost elimi¬ nates formation OfNO_x, and also significantly reduces metallurgical requirements, thus permitting the use of less expensive materials in construction of equipment.

Generally, distributed combustion involves employing a fuel conduit having an inlet for fuel and a plurality of fuel nozzles or openings which provide fluid communica¬ tion from within the fuel conduit to the flow path of said oxidant. The plurality of fuel nozzles or openings are sized and spaced along the length of said fuel conduit to avoid hot spot formation when the fuel is mixed with said oxidant in said distributed combus¬ tion chamber. It also involves preheating combustion air and fuel gas (e.g., methane, methanol, hydrogen and the like) sufficiently such that when the two streams are com¬ bined the temperature of the mixture exceeds the autoignition temperature of the mixture, but to a temperature less than that which would result in the oxidation upon mixing, be- ing limited by the rate of mixing. Preheating of the combustion air and fuel streams to a temperature between about 815⁰C (about 1500⁰F) and about 126O⁰C (about 2300⁰F) and then mixing the streams in relatively small increments will result in distributed combus¬ tion to avoid hot spots, such as flames. For some fuels such as methanol, preheating to a temperature above about 1000⁰F (517°C) is sufficient. The increments in which the fuel gas is mixed with the combustion gas stream preferably result in about a 20⁰F (11⁰C) to about 200⁰F (111°C) temperature rise in the combustion gas stream due to the combus¬ tion of the fuel.

With most hydrogen-producing, such as steam methane reforming, processes controlling the temperature in the catalyst bed is a problem. The advantages of the dis¬ tributed combustion as a heat source in the present process and apparatus can be summa¬ rized as follows:

• DC helps maintain a more uniform temperature, but simultaneously controls heat flux to match the local heat needed for the material left to be reacted. At the highest heat flux there is as much heat present as can be accommodated by the reaction and as the process progresses less and less heat is required to drive the reaction.

• DC has a lower maximum-temperature combustion gas.

• DC does not have hot spots which might damage the hydrogen-selective, hydrogen- permeable membrane. • DC has a negligible NO_x production.

• DC makes it easier to tailor axial heat flux distribution to minimize entropy produc¬ tion or energy loss and, thus, making it more efficient.

• DC permits a more compact reactor design that is less expensive to build.

• DC permits a modular reactor design, at a wide range of sizes and heat duties. • DC provides a tapered heat flux profile.

Thus, the distributed combustion (DC) used to drive the steam reforming reac¬ tions in the present invention can be described as comprising: a) preheating either a fuel gas or oxidant or both to a temperature that exceeds the autoignition temperature of the mixture of the fuel gas and oxidant when they are mixed; b) passing said fuel gas and oxidant into a heating zone which is in heat trans¬ ferring contact along a substantial portion of the reaction zone, (i.e., the zone in which said reforming reactions take place); and c) mixing the fuel gas and oxidant in said heating zone in a manner that autoig- nition occurs, resulting in combustion without high temperature hot spots such as flames, thereby providing uniform, controllable heat to said reaction zone. In the practice of the invention, some degree of sulfur removal will probably be necessary to protect the palladium material making up the hydrogen-permeable separa¬ tion membrane and the Ni reforming catalyst. Sulfur is a temporary poison to such cata¬ lysts, but the catalyst activity can be regenerated by removing the source of sulfur. The sulfur tolerance of commercial reforming catalysts is dependent upon process conditions. On average, sulfur must be reduced to below 10 ppb to allow the catalyst to function properly.

Feed clean up with ZnO beds or by other means known in the art may be used to remove impurities such as H₂S and other sulfur containing compounds in the feed that could contribute to membrane degradation. For heavier hydrocarbons, like naphtha, some hydrotreating may be necessary to convert organic sulfur to H₂S, as known in the art. Heavy oil, solids carried by liquid water, oxygen, amines, halides, and ammonia are also known poisons for palladium membranes. Carbon monoxide competes with hydro¬ gen for active surface sites, thus reducing the hydrogen permeability by 10% at 3-5 Bar (0.3-0.5 MPa). Thus, the partial pressure needs to stay low for best performance, as is the case in our preferred design.

In another embodiment of the present invention the pure hydrogen generated by the present reactor and process is used in an integrated design to power a fuel cell such as high pressure molten carbonate fuel cell, PEM (proton exchange membrane) fuel cells or SOFC (solid oxide fuel cells) and the like. This embodiment of the present invention has the potential for about 71 % or greater efficiency in the generation of electricity from starting fuel. In addition, due to the unique integration of the system, CO₂ is produced in high concentrations from about 80% to about 95% molar dry basis, and high pressure of from about 0.1 to about 20 MPa, particularly from about 1 to about 5 MPa, and is easier to separate from nitrogen, which makes the system even more efficient. Referring now to Figure 14, a hydrogen-producing feedstock such as vaporizable hydrocarbon and steam 5 are fed into the catalyst section 4 of a DC-membrane reactor of the type described in Figure 1, while preheated air 7 and fuel 14 are fed into the DC heat¬ ing section 2 of the reactor containing fuel tubes 10. A sweep gas (in this case steam) is fed into the DC-membrane reactor at 6. The produced high purity hydrogen stream 12, is directed to the anode compartment of the molten carbonate fuel cell, 20, operating at about 650 ⁰C and 5 Bar (0.5 MPa). The reactor effluent 13 containing the unreacted steam, CO₂ and low quantities of methane, hydrogen and CO, and the flue gas 11 from the DC heater and air, 16 are fed to the cathode compartment of the same fuel cell, 17. The CO₂ reacts with the O₂ to form CO₃ ⁼ anions that transport through the molten car¬ bonate membrane. The CO₃ ^" anions are constantly renewed. The reactions with indi¬ cated transport are described as follows:

CO₂ cathode + 1/2 O₂ cathode + 2e cathode — > CO₃ cathode R- 1

CO₃ cathode — > CO₃ anode R- 2

C0₃ ⁼a_node → CO₂ + 1/2 O₂ anode + 2e^" _anode R. 3

H₂ anode + 1/2 O₂ anode → H₂O_anode "242 kJ/gmθl-H₂ R. 4

Net: H_{2 ano}de + 1/2 O₂ cathode + CO₂ cathode + 2e^" _cathode ^~>

H₂O_anode+ CO₂ anode + 2e^" _anode -242 kJ/gmol-H₂ R. 5

Electricity generated by the fuel cell is shown as electrical output 21. The stream from the anode, 22, now contains the permeated CO₂ and steam but no hydrogen, nitro¬ gen, methane or oxygen, if hydrogen and oxygen are fed in exactly 2:1 stoichiometry. A portion of stream 22 may recycled to the cathode compartment 17 of the fuel cell. The CO₂ recycle stream is shown as 23 on Figure 6. A portion of streams 22 and/or 13 also may be put through a turbine expander to generate electrical or mechanical work 30 and 24, respectively. In the present invention CO₂ is separated from nitrogen essentially for free while electricity is simultaneously generated. Furthermore the CO₂ capture leverage is high. As shown above, each mole of methane is converted to 4 moles of H₂. There¬ fore 4 moles of CO₂ per mole of converted methane are required to transport the oxygen in the fuel cell and are therefore separated from the nitrogen. Thus, this process can also be used to separate CO₂ from an external CO₂ containing stream. The high concentration CO₂ stream, 29, is now a prime candidate for sequestration after the steam is condensed. The CO₂ can be used for oil recovery, or injected into subterranean formations, or con¬ verted to a thermodynamically stable solid. Also, since the present process can be oper- ated to produce high purity hydrogen and nitrogen as well as concentrated C0₂₎ it can be used to facilitate the production of chemicals such as urea, which can be made from these three raw materials. Other chemicals which can be manufactured using the products and by-products of the present process include ammomia and ammonium sulfate. Other uses for the concentrated stream of CO₂ and the high purity hydrogen and nitrogen streams will be apparent to those skilled in the art.

The stream from the cathode, stream 18, contains all the nitrogen, unreacted oxy¬ gen, a little unpermeated CO₂, and trace amounts of the methane, hydrogen and CO from the MSR effluent. All or part of this stream can be put through a turbine expander (not shown) to generate work (electrical or mechanical), 19. The trace components of stream 18 may be oxidized in a catalytic converter 26, and emitted in the atmosphere as a low CO₂ concentration containing stream 27, containing less than 10% CO₂, preferably less than 1% CO₂. The trace components may also be oxidized inside the fuel cell if the ap¬ propriate catalyst is placed in the cathode compartment. A stream, 28, containing water and steam exits condenser 25 and is recycled to the DC-MSR reactor, and reheated to between about 250 to 500°C .

The zero emission hybrid system of the present invention is extremely efficient. Byproduct compounds are separated, the steam and hydrogen are reheated efficiently, and electricity is produced. Furthermore, water is separated from purified CO₂ which is produced in concentrations large enough to be easily sequestered. Advantages include using waste heat to raise steam and using water collected for recycling to support addi¬ tional steam reforming or other beneficial uses. The system is a totally integrated, ex¬ tremely efficient design having the potential for greater than 71% generation efficiency as mentioned above. The 71% is approximately a 20% fractional improvement over the best results we are aware of in the art, the 60% figure mentioned above that is possible under laboratory conditions. In addition to the great improvement in efficiency, the inte¬ grated design provides a concentrated source of CO₂ for capture and sequestration as well.

Fuel cells which would be suitable for use in the present invention are those that could function in a highly pressurized system. Most fuel cells run at atmospheric condi- tions. For this reason, a high pressure molten carbonate fuel cell is preferred. However, other types of fuel cells, such as PEM fuel cells and SOFC, can also be effectively com¬ bined with the DC-MSR reactor of the present invention. Another very attractive feature is that the DC powered MSR hydrogen generator produces very low NO_x, especially compared with the combined processes known in the art. Due to the use of distributed combustion very little NO_x is generated in this system. Furthermore, other steam reforming reactors used to generate hydrogen known in the art could not feed to the MCFC the flue gas from the furnace as in the present design, be¬ cause they produce high NO_x, which would poison the molten carbonate membrane. hi a particular embodiment of the invention, the aforesaid distributed combustion heated, membrane hydrogen-producing reactor such as a steam reforming reactor con¬ tains multiple distributed combustion chambers (preferably, but not necessarily, in the form of tubes) and multiple hydrogen-selective, hydrogen-permeable membrane tubes disposed in, or otherwise in contact with, the reforming catalyst bed in the reforming chamber. Examples of multi-tubular reactors in accordance with the invention are shown in Figures 4-5, 7-8 and 10-13.

The multi-tubular, distributed combustion heated, membrane hydrogen-producing reactor such as steam reforming reactor in accordance with the invention may be either of the radial flow type as shown in Figures 4 and 5, or may be of the axial flow type as shown in Figures 7-8 and 12-13. In a radial flow reactor the gases generally flow through the reforming catalyst bed radially from outside to inside (or from inside to out¬ side), while in an axial flow reactor the gases generally flow through the reforming cata- lyst bed in the same direction as the axis of the reactor. In the case of a vertical reactor, the flow would be from the top of the reactor to the bottom, or the bottom of the reactor to the top.

The multi-tubular, distributed combustion heated, membrane reactor such as a steam reforming reactor in accordance with the present invention may contain from as few as 2 distributed combustion tubes up to 100 or more, particularly 3 to 19, depending the size of the distributed combustion tubes, the size of the catalyst bed and the level of heat flux desired in the catalyst bed. The size of the distributed combustion tube can vary from about 1 inch (2.5 cm) outer diameter up to about 40 inches (102 cm) or more outer diameter. The number of hydrogen-selective membrane tubes may also vary from as few as 2 up to 400 or more, particularly 3 to 90. The size of the membrane tubes may vary from about 1 inch (2.5 cm) outer diameter up to about 10 inches (25.4 cm) outer diameter or more, hi general, the ratio of distributed combustion tube surface area to membrane tube surface area will be in the range of about 0.1 to about 20.0, particularly from about 0.2 to about 5.0, more particularly from about 0.5 to about 5.0, still more par- ticularly from about 0.3 to about 3.0 and even more particularly from about 1.0 to about 3.0. The term "surface area" when used in reference to the above ratios, means the ex¬ ternal (circumferential) area of the distributed combustion tubes and the membrane tubes. For instance, a 1 inch (2.5 cm) outer diameter tube of 12 inches (30 cm) length would have an external surface area of 37.6 square inches.

Each distributed combustion tube or chamber will have at least one fuel conduit disposed therein. Large distributed combustion chambers generally will have multiple fuel conduits. The distributed combustion chambers or tubes employed in the multi¬ tubular reactors of the invention may be "open ended" or "closed ended" as discussed below in connection with Figures 6 A and 6B.

A sweep gas may be used to promote the diffusion of hydrogen through the hy¬ drogen-selective, hydrogen-permeable membrane, hi case a sweep gas is employed, the membrane tube may contain an inlet and flow path for sweep gas feed and a flow path and outlet for the return of sweep gas and permeated hydrogen. Baffles and/or screens may also be employed in the multi-tubular reactors of the present invention to improve contact of the reactive gases with the catalyst and to im¬ prove flow distribution. The distributed combustion tubes and/or membrane tubes may also be surrounded by cylindrical screens to protect the tubes from direct contact with the catalyst. In one embodiment, the present reactor is an integrated distributed combustion- steam reformer, and the present process or apparatus of is capable of producing high pu¬ rity hydrogen with minimal production of CO, particularly less than about 5 molar%, more particularly less than 3 molar %, and still more particularly less than 2 molar% on a molar dry basis of the total products, and with less than 1000 ppm of CO and particularly less than 10 ppm of CO on a dry basis, more particularly virtually no CO in the hydrogen stream produced. By practice of the present invention it is possible to produce high pu¬ rity hydrogen e.g., hydrogen having a purity on a dry basis of greater than 95%. The present invention can be used to produce hydrogen having purities as high as 97%, 99%, or under optimum conditions 99+%. The effluent (by product) stream from the MSR reactor will typically contain more than 80% CO₂ on a dry basis, e.g., 90% CO₂, 95% CO₂ or 99% CO₂, and less than about 10% CO on a dry basis, e.g., less than about 5% CO, preferably less than 1% CO. Total heat management and turbines may be included in the system to increase the efficiency and produce additional electricity or to do useful work such as compress gases or vapors.

One aspect of the present invention is a distributed combustion heated membrane steam reformer hydrogen generator. In the design of the invention there are disclosed distinct improvements in overall efficiency, particularly size, scalability and heat ex¬ change. The present invention typically employs only one reactor to produce the hydro¬ gen versus typically four reactors used in conventional processes, and part of the heat load is supplied by the water-gas-shift reaction. The design of the invention captures es- sentially all of the heat in the reaction chamber since heat exchange occurs on a molecu¬ lar level, which reduces the overall energy requirements.

Chemical equilibrium and heat transfer limitations are the two factors that govern the production of hydrogen from hydrogen-producing feedstock in conventional reactors. These factors lead to the construction of large reactors fabricated from expensive high temperature tolerant materials. They are enclosed in high temperature furnaces that are needed to supply the high heat fluxes.

In the present invention the two major limitations of chemical equilibrium and heat transfer are overcome by the innovative combination of an in-situ membrane separa¬ tion of hydrogen in combination with a heat source comprising distributed combustion ("DC") that makes it possible to more efficiently use all the energy in the system, as well as provide load following capabilities.

The reformer of the present invention reduces the operating temperature of the steam reforming reactor close to the lower temperature used in a shift reactor. With the temperatures for the steam reforming and shift closer, both operations are combined into one reactor. With both reactions occurring in the same reactor the exothermic heat of reaction of the shift reaction is completely captured to drive the endothermic steam re¬ forming reaction. This reduces the total energy input for the sum of the reactions by 20%. The lower temperature reduces stress and corrosion and allows the reactor to be constructed from much less expensive materials. Combining the operations also reduces the capital and operating cost since only one reactor, instead of two or three, are required. Moreover, the reaction is not kinetics-limited even at the lower temperature, thus, the same or even less catalyst can be used.

The general description for steam reformers, including but not limited to the reac¬ tions, enthalpies, values of equilibrium constants, advantages of integrated distributed combustion-SMR reactor, as well as the advantages of the use of the membrane in the reactor can be found in US 2003/0068269.

The in-situ membrane separation of hydrogen employs a membrane fabricated, particularly from an appropriate metal or metal alloy, on a porous ceramic or porous metal support, as described below, to drive the equilibrium to high conversions. With constant removal of the hydrogen through the membrane, the reactor can be run at much lower than the commercially practiced temperatures of 700-900+°C. A temperature of 500°C is sufficient to drive the kinetics to high conversions when the equilibrium is shifted using the hydrogen separation membrane. At this temperature the selectivity to CO₂ is almost 100%, while higher temperatures favor the formation of CO as a major product.

The term "reforming catalyst" as used herein means any catalyst suitable for cata¬ lyzing a steam reforming reaction, which includes any steam reforming catalyst known to one skilled in the art, as well as any "pre-reforming catalyst" which is suitable for catalyzing steam reforming reactions in addition to being suitable for processing heavier hydrocarbons prior to a steam reforming reaction.

Figure 1 shows a schematic diagram of a hydrogen-producing reactor with cata¬ lyst section, and permeate section. The reactor 1 shown in Figure 1 consists of two con¬ centric sections. The inner concentric section 3 is the permeate section. The annulus, 4, in between is the catalyst section. A hydrogen-producing catalyst, such as a reforming catalyst, is loaded into the annulus section 4 wherein the above-described reactions take place, (section 4 is also variously referred as the catalyst section, the reaction section or the reaction zone). The membrane, 8, is represented on the inside of the small section, 3, (the permeate section) in Figure 1. The feed stream containing hydrogen-producing feedstock, such as a mixture of vaporizable hydrocarbon-containing compounds (e.g. naphtha, methane or methanol) and H₂O with a minimum overall O: C ratio of 2:1 when a steam reforming reaction is car¬ ried out, enters catalyst section 4 at 5. If used, sweep gas for promoting the diffusion of hydrogen through the membrane enters the top of the permeate section 3 at 6. Alterna- tively, sweep gas can be introduced into the permeate section by means of a stinger pipe fitted to bottom of the permeate section, hi case of this alternative, hydrogen in sweep gas would exit the permeate zone at the bottom of the permeate section. Optionally, the stinger pipe to introduce the sweep gas may be connected at the top of the permeate sec- tion in which case the hydrogen and sweep gas would exit at the top of this section. Hy¬ drogen (pure or in sweep gas) exits at 12. Unreacted products and by-products (e.g., CO₂, H₂O, H₂, CH₄, and CO) exit catalyst section 4 at 13. It is also possible to remove the produced hydrogen using a vacuum instead of a sweep gas. The catalyst beds, 4, can be heated by any suitable heating method known to one skilled in the art, such as a by a traditional burner, an electric heating means, a micro¬ wave heating means, etc.

Any hydrogen-producing, particularly vaporizable, feedstock such as an (option¬ ally oxygenated) hydrocarbon-containing compound(s) can be used in the present proc- ess and apparatus, including, but not limited to, methane, methanol, ethane, ethanol, pro¬ pane, butane, light hydrocarbons having 1-4 carbon atoms in each molecule, and light petroleum fractions like naphtha at boiling point range of 120-400⁰F, which is a typical feed for commercial steam reformers. Petroleum fractions heavier than naphtha can also be employed like diesel or kerosene or jet fuel at boiling point range of 177-253⁰C (350- 500⁰F) or gas oil at boiling point range of 228⁰C -405⁰C (450-800⁰F). Hydrogen, carbon monoxide and mixtures thereof, e.g., syn gas, may also be used in the process and appa¬ ratus of the present invention, and are included in the definition of "hydrogen-producing feedstock" or "vaporizable hydrocarbon". Methane was used in the examples to demon¬ strate the process. The catalyst bed can be heated 107 by any suitable means 107, such as electric heating, microwave, conventional combustion, distributed combustion, etc. hi some embodiments, with the distributed combustion-steam reforming process and apparatus of the present invention it is possible to use O: C ratios as low as 2.8, down to 2.6, without coking problems, with the minimum O: C ratio being about 2:1. This results lower energy costs if methane is used as the feed in the present invention, since lower steam to methane ratios can be used thus requiring less energy to vaporize water. Because of the ability to operate at lower O:C ratios, it is also possible to use heavier, less expensive feeds in the distributed combustion-MSR reactor of the present invention than can be used in conventional steam methane reformers. hi another embodiment of the invention, the integrated hydrogen-producing proc- ess and apparatus of the invention can be used to perform water-gas-shift reactions on syngas mixtures (i.e., mixtures of hydrogen and carbon monoxide) produced from con¬ ventional processes like Catalytic Partial Oxidation (CPO), Steam Methane Reforming (SMR) and Autotliermal Reforming (ATR). The integrated distributed combustion- MSR reactor is well suited for this since it produces high purity hydrogen and converts carbon monoxide to carbon dioxide and more hydrogen. Thus, the versatile hydrogen- producing reactor of the invention is capable of replacing the high temperature shift, low temperature shift and methanation reactors and the hydrogen purification section. A mixture of syn gas and vaporizable hydrocarbon can also be used to yield a net reaction which may be either endothermic, thermally neutral or slightly exothermic.

The reactor annulus is packed with steam reforming catalyst and equipped with a perm-selective (i.e., hydrogen selective) membrane that separates hydrogen from the re¬ maining gases as they pass through the catalyst bed. The steam reforming catalyst can be any known in the art. Typically steam reforming catalysts which can be used include, but are not limited to, Group VIII transition metals, particularly nickel. It is often desir¬ able to support the reforming catalysts on a refractory substrate (or support). The sup¬ port is preferably an inert compound. Suitable compounds contain elements of Group III and IV of the Periodic Table, such as, for example the oxides or carbides of Al, Si, Ti, Mg, Ce and Zr. The preferred support composition for the reforming catalyst is alumina. The catalyst used in the examples to demonstrate the present invention was nickel on porous alumina. As the hydrogen is formed in the catalyst bed, it is transported out through the hydrogen-permeable separation membrane filter. Advantages of this tech¬ nology include the capacity to separate essentially pure hydrogen from any poisons that may also be present, including CO and H₂S, and from other fuel diluents. The poisons do not pass through the separation membrane, which is fabricated from one of a variety of hydrogen-permeable and hydrogen-selective materials including ceramics.

The composite gas separation modules described herein include a dense gas- selective membrane such as, for example, a dense hydrogen-selective membrane. The dense hydrogen-selective membrane can include, for example, palladium or an alloy thereof. A "dense gas-selective membrane," as that term is used herein, refers to a com¬ ponent of a composite gas separation module that has one or more layers of a gas- selective material, i.e., a material that is selectively permeable to a gas, and that is not materially breached by regions or points which impair the separation of the gas by allow- ing the passage of an undesired gas. For instance, in one embodiment, the dense gas- selective membrane is not materially breached by regions or points which do not have the desired gas selectivity properties of the gas-selective material. An example of a dense gas-selective membrane is a dense hydrogen-selective membrane that is substan¬ tially free of defects such as open pores, holes, cracks and other physical conditions that impair the gas-selectivity of the composite gas separation module by allowing the pas¬ sage of an undesired gas. In some embodiments, a dense gas-separation membrane can contain one or more non-metallic components, however, the dense gas-separation mem¬ branes described herein can contain at least one metallic component (e.g., a hydrogen- selective metal such as palladium or an alloy thereof).

The term "support," as used herein, includes a substrate, a surface treated sub¬ strate, a substrate upon which a material (e.g., a gas-selective material) has been depos¬ ited, a substrate with an overlying intermediate layer, or a subsequently plated substrate upon which a dense gas-selective membrane has been or will be formed. Serving as a support structure, the substrate can enhance the durability and strength of the composite gas separation module.

"Gas-selective material," as used herein, refers to those materials which, when formed into dense gas-selective membranes, allow the passage of a select gas, or select gases, through the dense gas-selective membrane. Suitable gas-selective materials in- elude metals, ceramics (e.g., perovskite and perovskite-like materials) and zeolites (e.g., MFI and Zeolites A, X, etc.). In one embodiment, the gas-selective material is a hydro¬ gen-selective metal such as palladium or an alloy thereof. Examples of suitable palla¬ dium alloys include palladium alloyed with at least one of the metals selected from the group consisting of copper, silver, gold, platinum, ruthenium, rhodium, yttrium, cerium and indium. For example, palladium/silver and palladium/copper alloys can be used to form dense hydrogen-selective membranes, hi one embodiment, the gas-selective mate¬ rial is a ceramic such as oxygen gas-selective perovskite.

The side of the support upon which the dense gas-selective membrane is formed is referred to herein as the "outside" or "membrane-side" and the opposite side of the support is called the "inside" or "substrate-side" surface. However, it should be noted that the dense gas-selective membrane can be formed on the exterior surface and/or the interior surface of the substrate. For example, the dense gas-selective membrane can be formed on either or both surfaces of a planar substrate or can be formed on the exterior and/or interior surfaces of a substrate tube. Preferably, the dense gas-selective mem- brane is formed on only one surface of the substrate, for example, on either the exterior or the interior surface of a substrate tube.

In one embodiment, the gas-selective material can include a combination of sub¬ stances, for example, a combination of a hydrogen-selective metal and a zeolite, hi one embodiment, the zeolite used in a combination of substances is gas-selective. In an al- ternative embodiment, the zeolite used in a combination of substances is not gas- selective, for example, the zeolite used in a combination of substances is not hydrogen- selective.

Specific embodiments of the invention, including the composite gas separation modules, methods for fabricating the composite gas separation modules, and the method for selectively separating hydrogen gas from a hydrogen gas-containing gaseous stream follow. Details of optional components of the composite gas separation modules and method steps employed in various embodiments of methods for fabrication of the com¬ posite gas separation modules are described thereafter under separate subheadings. Figure 2 illustrates a cylindrical composite gas separation module 110 as one em¬ bodiment of the invention. Composite gas separation module 110 includes porous sub¬ strate 112, intermediate layer 114, and dense gas-selective membrane 116. As illus¬ trated, intermediate layer 114 and dense gas-selective membrane 116 overlie the outside surface of cylindrical porous substrate 112. hi alternative embodiments not illustrated, intermediate layer 114 and dense gas-selective membrane 116 can overlie the interior surface of cylindrical porous substrate 112 (with the dense gas-selective membrane form¬ ing the innermost of the three cylindrical layers) or can overlie both the interior and the exterior surfaces of porous substrate 112. hi a preferred embodiment, intermediate layer 114 and dense gas-selective membrane 116 overlie only either the interior or the exterior surface of porous substrate 112. The composite gas separation module can take any of a variety of forms including a cylindrical tube, as illustrated in Figure 2, or a planar sur¬ face, hi one embodiment, porous metal substrate 112 also includes a layer of ceramic bonded thereto.

The composite gas separation module used herein includes a porous metal sub- strate. The porous metal substrate can be formed from any of a variety of components known to those of ordinary skill in the art. Examples of suitable substrate components include, but are not limited to, iron, nickel, palladium, platinum, titanium, chromium, porous silver, porous copper, aluminum, and alloys thereof, e.g., steel, stainless steel, porous stainless steel, HASTELLOY^® alloys (e.g., HASTELLO Y^® C-22^®) (trademarks of Haynes International, Inc., Kokomo, IN) and INCONEL^® alloys (e.g., INCONEL^® alloy 625) (INCONEL is a trademark of Huntington Alloys Corp., Huntington WV). hi one embodiment, the porous metal substrate is an alloy containing chromium and nickel (e.g., INCONEL^® alloy 625). hi an additional embodiment, the alloy contains chro¬ mium, nickel and molybdenum such as, for example, HASTELLOY^® C-22^® or IN- CONEL^® alloy 625. The porous metal substrate can be porous stainless steel. Cylinders of porous stainless steel that are suitable for use as substrates are available from Mott Metallurgical Corporation (Farmington, CT) and from Pall Corporation (East Hills, NY), for example. The substrate can also be metal mesh, sintered metal powder, refractory metals, metal oxides, ceramics, porous refractory solids, honeycomb alumina, aluminate, silica, porous plates, zirconia, cordierite, mullite, magnesia, silica matrix, silica alumina, porous Vycar, carbon, glasses, and the like.

One of ordinary skill in the art can select substrate thickness, porosity, and pore size distribution using techniques known in the art. Desired substrate thickness, porosity and pore size distribution can be selected based on, among other factors, the operating conditions of the final composite gas separation module such as operating pressure. Substrates having generally higher porosities and generally smaller pore sizes are par¬ ticularly suited for producing composite gas separation modules. In some embodiments, the substrate can have a porosity in a range of about 5 to about 75% or about 15 to about 50%. While the pore size distribution of a substrate can vary, the substrate can have pore diameters that range from about 0.1 micrometers or less to about 15 micrometers or more. Generally, smaller pore sizes are preferred. However, in some embodiments, sub¬ strates having larger pores are used and a powder layer having a generally smaller pore size is formed over the substrate (e.g., a graded support is formed). In some embodiments, the mean or median pore size of the substrate can be about

0.1 to about 15 micrometers, e.g., from about 0.1 to about 1, 3, 5, 7 or about 10 microme¬ ters. For example, the substrate can be an about 0.1 micrometer grade substrate to an about 0.5 micrometer grade substrate, e.g., 0.1 micrometer, 0.2 micrometer, and 0.5 mi¬ crometer grades of stainless steel substrates can be used. In one embodiment, the sub- strate is 0.1 micrometer grade HASTELLO Y^® alloy.

The composite gas separation module also includes an intermediate layer, wherein the intermediate layer overlies the porous metal substrate. In one embodiment, for example, the intermediate layer has a top side and a bottom side and the intermediate layer is directly adjacent to the porous metal substrate on the bottom side and is directly adjacent to the dense hydrogen-selective membrane on the top side.

The intermediate layer can include a powder having a Tamman temperature higher than the Tamman temperature of the porous metal substrate. The intermediate layer can include a powder having a Tamman temperature higher than the Tamman tem¬ perature of the dense hydrogen-selective membrane. For example, in one embodiment, the intermediate layer includes a powder having a Tamman temperature higher than both the Tamman temperature of the porous metal substrate and the Tamman temperature of the dense hydrogen-selective membrane. Powder of the intermediate layer is typically substantially unsintered. For example, the powder having a Tamman temperature higher than the Tamman temperature of the porous metal substrate is substantially unsintered.

In another embodiment, the present invention includes a composite gas separation module having a porous metal substrate; an intermediate powder layer; and a dense gas- selective membrane, wherein the dense gas-selective membrane overlies the intermediate powder layer. The intermediate powder layer includes a powder that is typically sub- stantially unsintered.

In some embodiments, the powder can have a melting point temperature higher than the melting point temperature of the porous metal substrate. The intermediate layer can include a powder having a melting point temperature higher than the melting point temperature of the dense hydrogen-selective membrane. For example, in one embodi- ment, the intermediate layer includes a powder having a melting point temperature higher than both the melting point temperature of the porous metal substrate and the melting point temperature of the dense hydrogen-selective membrane.

The powder can include metal powders, metal oxide powders, ceramic powders, zeolite powders, and combinations thereof, among others. The powder can include a blend or a layering of different powders including powders of differing compositions and/or particle sizes. For example, in one embodiment, the powder includes tungsten powder and silver powder. The powder particles can have various morphologies and shapes. For example, the powder particles can be ordered or amorphous. In one em¬ bodiment, the powder includes spherical or mostly spherical particles. The powder of the intermediate layer can include materials such as, for example, tungsten, silver, copper oxide, aluminum oxide, zirconia, titania, silicon carbide, chro¬ mium oxide, and combinations thereof. In various embodiments, the powder can include tungsten powder, e.g., particle sizes of about 1 to about 5 micrometers or particle sizes less than 1 micrometer; silver powder, e.g., spherical particles of sizes of about 0.5 to about 1 micrometer or particles of sizes of about 0.6 to about 2 micrometers; copper ox¬ ide powder, e.g., copper (II) oxide powder particles of less than 5 micrometers or of about 0.01 micrometer; aluminum oxide (Al₂O₃) powder, e.g., aluminum oxide powder particles of about 0.01 to about 5 micrometers; other ceramic powder; zeolite powder; and combinations thereof. The powder of the intermediate layer can have a particle size that assists in pre¬ venting undesired intermetallic diffusion between the porous metal substrate and a dense gas-selective membrane, hi one embodiment, the powder can have an average particle size of at least about 0.01 micrometer such as at least about 0.1, 0.5, 1, or at least about 5 micrometers. In some embodiments, the powder can have an average particle size of less than 5 micrometers such as less than 1, 0.5, 0.1, or less than 0.01 micrometers. In one embodiment, the powder has an average particle size of about 0.5 to about 5 micrometers such as, for example, about 1 to about 5 micrometers or about 0.6 to about 2 microme¬ ters. In one embodiment, the intermediate layer is at least about 1, 2, 3, 4, or at least about 5 micrometers thick. For example, the intermediate layer can be about 1 to about 10, such as about 1 to about 5 or about 5 to about 10 micrometers thick, hi one embodi¬ ment, the intermediate layer is not significantly less porous to helium gas flux than the porous substrate. The intermediate layer can have an average pore size that is less than the average pore size of the porous metal substrate, hi one embodiment, the largest

(maximum) pore of the intermediate layer is smaller than the largest pore of the porous metal substrate. Maximum Pore Size can be measured by a typical "Bubble Point" test such as per ISO standard 4003 or per ASTM E-128

The intermediate layer can protect against intermetallic diffusion between the po- rous metal substrate and the dense gas-selective membrane. In some embodiments, in¬ termetallic diffusion can occur between the porous metal substrate and the intermediate layer, but this diffusion does not substantially impair the performance of the dense gas- selective membrane, hi one aspect of the present invention, the intermediate layer can include at least one metal that enhances the gas permeability of the dense gas-selective membrane upon intermetallic diffusion of the metal into the membrane. For example, the intermediate layer can further include at least one material having a Tamman tem¬ perature less than or about equal to the Tamman temperature of the dense hydrogen- selective membrane. In one embodiment, the intermediate layer further includes at least one material selected from the group consisting of silver, gold, copper, cerium and yt- trium.

In some embodiments, intermetallic diffusion of some species between the inter¬ mediate layer and the dense gas-selective membrane enhances the permeability of the membrane. Without wishing to be held to any particular theory, intermetallic diffusion of species at concentrations that enhance membrane permeance between the intermediate layer and the dense gas-selective membrane is not thought to be harmful to the gas selec¬ tivity of the membrane. For example, the formation of a palladium alloy via diffusion of intermediate layer atoms into a dense hydrogen-selective membrane can enhance the hy¬ drogen permeability of a dense hydrogen-selective membrane that includes palladium or alloy thereof. In some embodiments, the intermediate layer includes palladium, silver, gold, copper, cerium and/or yttrium, the dense gas-selective membrane includes palla¬ dium, and intermetallic diffusion of one or more of these metals from the intermediate layer into the dense gas-selective membrane improves the selective gas permeation through the membrane. Preferably, in one embodiment, the intermediate layer does not contain a concentration of a material which causes a substantial reduction in the per¬ formance of the dense gas-selective membrane upon diffusion of that material into the membrane. hi some embodiments, the intermediate layer of the present invention can im¬ prove adhesion of the dense gas-selective membrane to the porous metal substrate. For example, during a gas separation operation, the composite gas separation modules de¬ scribed herein can avoid membrane blistering, delamination and/or cracking even when operating at high temperatures and/or for extended periods of time. Without wishing to be held to any particular theory, the improvement in adhesion can result from inter- diffusion of the metal particles of the intermediate layer and/or intermetallic diffusion between the intermediate layer and the porous metal substrate on one side and the dense gas-selective membrane on the other side. For example, inter-diffusion can occur with some components when the composite gas separation module is heated to operational temperatures (e.g., about 35O⁰C to about 600⁰C).

The composite gas separation module can further include a substrate surface treatment underlying the intermediate layer, as described infra. For example, a layer of a ceramic can be bonded to the porous metal substrate and underlie the intermediate layer. The ceramic can include oxides, nitrides, and/or carbides, for example, iron oxide, iron nitride, iron carbide and/or aluminum oxide.

The composite gas separation module can also further comprise a layer of a metal selected from the group consisting of palladium, gold and platinum, wherein the layer of metal overlies the porous metal substrate and/or a substrate surface treatment and under¬ lies the intermediate layer.

The composite gas separation module includes a dense gas-selective membrane, wherein the dense gas-selective membrane overlies the intermediate layer, hi one em- bodiment, the dense gas-selective membrane is selectively permeable to hydrogen, e.g., the dense gas-selective membrane is a dense hydrogen-selective membrane and can in¬ clude one or more hydrogen-selective metals or alloys thereof. "Hydrogen-selective metals" include, but are not limited to, niobium (Nb), tantalum (Ta), vanadium (V), pal- ladium (Pd), platinum (Pt), zirconium (Zr) and hydrogen-selective alloys thereof. Palla¬ dium and alloys of palladium are preferred. For example, palladium can be alloyed with at least one of the metals selected from the group consisting of copper, silver, gold, plati¬ num, ruthenium, rhodium, yttrium, cerium and indium.

Where the gas separation module is to be used at temperatures below about 300°C, the dense gas-selective membrane can be formed of a palladium alloy such as, for example, an alloy of about 75 to about 77 weight percent palladium and about 25 to about 23 weight percent silver. An alloy is typically preferred at low temperatures be¬ cause pure palladium can undergo a phase change in the presence of hydrogen at or be¬ low about 300°C and this phase change can lead to embrittlement and cracking of the membrane after repeated cycling in the presence of hydrogen.

In one embodiment, the dense gas-separation membrane can include one or more non-metallic components, hi another embodiment, the dense gas-separation membrane can include one or more components that are not gas-selective materials, e.g., compo¬ nents that are not hydrogen-selective materials. In one embodiment, the thickness of the dense gas-selective membrane is less than about 3 times the diameter of the largest pore of the porous substrate. For example, the thickness of the dense gas-selective membrane can be less than about 2.5, 2, or less than about 1.5 times the diameter of the largest pore of the porous substrate. While the thickness of the dense gas-selective membrane can depend, among other factors, on the size of the largest pores in the porous substrate, in some embodiments the dense gas- selective membrane is less than about 25, 20, 15, 12 or less than about 10 microns in thickness. For example, in one embodiment, the thickness of the dense gas-selective membrane is less than about 14 microns such as about 3 to 14 microns. In one particular embodiment, the dense gas-selective membrane is of substantially uniform thickness. In a particularly suitable fabrication method, any contaminants are initially cleaned from the substrate, for example, by treating the substrate with an alkaline solu¬ tion such as by soaking the substrate in an approximately 60°C ultrasonic bath for about half an hour. Cleaning is typically followed by rinsing such as, for example, wherein the substrate is sequentially rinsed in tap water, deionized water and isopropanol. Prepara- tion of the porous substrate can also include surface treatment; formation of an additional intermetallic diffusion barrier such as by oxidizing the substrate, described infra; surface activation, described infra; and/or deposition of a metal such as palladium, gold or plati¬ num, described infra, prior to applying the intermediate layer over the porous metal sub- strate.

The intermediate layer is generally applied over the porous metal substrate prior to application of a dense gas-selective membrane. In one embodiment, the intermediate layer is first applied over the porous metal substrate and includes a powder having a Tamman temperature higher than the Tamman temperature of the porous metal substrate and then a dense gas-selective membrane (e.g., a hydrogen selective membrane) is ap¬ plied over the intermediate layer.

The intermediate layer can be applied using any of a number of techniques for applying a powder to a porous surface. For example, the intermediate layer can be ap¬ plied using powder particles transported to the support by a gas (e.g. , a gas stream), hi other embodiments, the powder particles are pressed and/or rubbed onto the support, hi one embodiment, the intermediate layer is applied by depositing the powder from a slurry or suspension. For example, in one embodiment, the intermediate layer can be applied by depositing the powder from a liquid-based, e.g., water-based, slurry or sus¬ pension, hi some embodiments, the intermediate layer can be applied by depositing sev- eral powders of varying compositions and/or particle size, e.g., from a slurry or suspen¬ sion containing several different materials. For example, in one embodiment, a water- based slurry is prepared by mixing water with tungsten particles, silver particles, copper oxide particles, aluminum oxide particles, ceramic particles, zeolite particles, and/or a combination thereof. The slurry can contain, e.g., about 0.1 to about 30 g/L powder particles. For ex¬ ample, the slurry can contain about 0.1 to about 20, about 1 to about 15, about 5 to about 15, about 8 to about 12, or about 10 g/L powder particles having a Tamman temperature higher than the Tamman temperature of the porous metal substrate. For example, in one embodiment, the slurry can contain about 0.1 to about 20 g/L tungsten powder. hi some embodiments, an additive that prevents or slows agglomeration and/or sedimentation of powder particles is added to the slurry or suspension, hi one embodi¬ ment, a polymer such as poly(ethylene glycol) (PEG) is added to the slurry or suspen¬ sion. For example, in one embodiment, a slurry can contain about 1 to about 25, about 5 to about 15, or about 10 grams/liter polymer such as PEG. hi one specific embodiment, the slurry can contain about 5 to about 15 grams metal particles, such as tungsten powder particles, and about 5 to about 15 grams polymer such as PEG. In some embodiments, an additive can enhance the mechanical properties of the filter cake during handling, e.g., by acting as a binder. The intermediate layer can applied by depositing the powder from a slurry or sus¬ pension by filtering the slurry through a porous support. For example, in one embodi¬ ment, the powder is deposited on a porous support as a filter cake after a slurry is filtered through the porous support. In some embodiments, a vacuum is applied to one side of a porous support and a slurry is applied to the opposite side of the porous support. Thus, a filter cake can accumulate on the side of the support to which the slurry is applied and filtrate can be collected on the side of the support to which the vacuum is applied. In one embodiment, a vacuum is applied to the tube side of a tubular support and a slurry is ap¬ plied to the membrane side of the tubular support.

In some embodiments, the intermediate layer is applied using a liquid-based com- position such as a water-based slurry. Following deposition of a powder, the liquid- wetted powder can be dried, hi other embodiments, the powder can be kept wet as sub¬ sequent application of a dense hydrogen-selective membrane is made over the intermedi¬ ate layer. For example, in some embodiments, the filter cake applied by a slurry or sus¬ pension is dried prior to a subsequent surface activation step. In other embodiments, the filter cake applied by a slurry or suspension is kept wet prior to a subsequent surface ac¬ tivation step.

In one embodiment, the present invention can include the step of depositing a hy¬ drogen-selective metal on the intermediate layer, thereby forming a coated substrate and abrading the surface of the coated substrate, thereby forming a polished substrate, prior to formation of the dense gas-selective membrane (e.g., a dense hydrogen-selective membrane) over the intermediate layer.

Following application of the intermediate layer, a dense gas-selective membrane is applied over the intermediate layer. For example, a dense gas-selective membrane can be applied by depositing a gas-selective metal, e.g., a hydrogen-selective metal, over the intermediate layer. Without wishing to be held to any particular theory, it is believed that by depositing a layer of metal (e.g., a hydrogen-selective metal) on the intermediate layer, the intermediate layer can be mechanically stabilized.

In one embodiment, palladium or an alloy thereof is deposited, e.g., electrolessly plated, over the intermediate layer, thereby forming a dense gas-selective membrane. Application of the dense gas-selective membrane can include surface activating the in¬ termediate layer prior to depositing dense gas-selective membrane components. In some embodiments, a vacuum is applied to one side of a porous support and an activation composition is applied to the opposite side of the porous support. In one embodiment, a vacuum is applied to the tube side of a tubular support and an activation composition is applied to the membrane side of the tubular support.

Components of the dense gas-selective membrane, e.g., a hydrogen-selective metal or an alloy thereof, can be deposited over the intermediate layer using any of the techniques known in the art for depositing such materials on a support. For example, a component of the dense gas-selective membrane can be deposited on the support using electroless plating, thermal deposition, chemical vapor deposition, electroplating, spray deposition, sputter coating, e-beam evaporation, ion beam evaporation or spray pyroly- sis. In some embodiments, a vacuum is applied to one side of a porous support and an plating composition, such as an electroless plating solution, is applied to the opposite side of the porous support. In one embodiment, a vacuum is applied to the tube side of a tubular support and a plating composition is applied to the membrane side of the tubular support.

An alloy of a gas-selective metal can be deposited over the intermediate layer as a component of the dense gas-selective membrane. In one embodiment, a palladium/silver alloy is formed by first depositing palladium onto the support by electroless deposition and then depositing silver, also by electroless deposition, onto the support. An alloy membrane layer can then be formed by heating the silver and palladium layers, for ex¬ ample, to about 500°C to about 1000°C in an inert or hydrogen atmosphere, hi one em¬ bodiment, metal components can be co-deposited onto the support to form a layer of a finely divided mixture of small regions of the pure metal components. In another em¬ bodiment, a technique such as sputtering or chemical vapor deposition is used to simul¬ taneously deposit two or more metals to form an alloy layer on the support. hi one embodiment, a small quantity of the metal, sufficient to cover the pore walls of the substrate, for example less than about 10, 7, 5, 3 or 1 percent of the ultimate thickness of the dense gaseous membrane, is deposited on the porous substrate without a significant reduction of the substrate porosity. Typically, the deposition of palladium, gold and/or platinum on the porous substrate is made by surface activating and plating on the side of the substrate opposite to the side on which a gas-selective membrane will be formed. For example, in one embodiment, a deposit of palladium, gold and/or platinum is formed from the inside of a substrate tube (e.g., using an electroless plating solution) and a dense gas-selective membrane is subsequently formed on the outside of the sub¬ strate tube. The gas separation modules can also be fabricated by selectively surface acti¬ vating a support proximate to a defect and preferentially depositing a material on the se- lectively surface activated portion of the support. The method is discussed in "Method for Curing Defects in the Fabrication of a Composite Gas Separation Module," U.S. Ap¬ plication Serial No. 10/804,848 filed March 19, 2004. hi one embodiment, the invention includes removing residual metal chlorides, for example, by treatment with an aqueous phosphoric acid solution, e.g., 10% phosphoric acid solution. For example, the treatment can include application of 10% phosphoric acid solution at room temperature for a time sufficient to convert residual metal chlorides to metal phosphates, e.g., about 30 minutes, followed by appropriate rinsing and drying, e.g., rinsing with deionized water for about 30 minutes and drying at about 120⁰C for at least about 2 hours. hi some embodiments, the composite gas separation modules are made by one or more of the following steps :(i)substrate surface treatments by oxidizing the surface of the substrate or by forming a nitride layer, (ii) surface activation of the support, e.g. with aqueous stannous chloride and palladium chloride prior to deposition of metal mem¬ brane, or (iii) metal deposition over the support or the intermediate layer, which steps as well as methods suitable for fabricating the hydrogen gas separation module are de¬ scribed in U.S. Patent No. 6,152,987; U.S. Patent Application No.10/804,848, 10/804,846; U.S. Patent Application No. 10/804,847, entitled "Method for Fabricating Composite Gas Separation Modules," filed on March 19, 2004; and U.S. Patent Applica¬ tion No. 10/896,743, filed on July 21, 2004. The following illustrative embodiments will serve to illustrate the invention dis¬ closed herein. The examples are intended only as a means of illustration and should not be construed as limiting the scope of the invention in any way. Those skilled in the art will recognize many variations that may be made without departing from the spirit of the disclosed invention. ILLUSTRATIVE EMBODIMENT 1

Figure 4 shows a schematic diagram of a multi-tubular, DC heated, radial flow, membrane, steam reforming reactor in accordance with the present invention, hi the reac¬ tor shown in Figure 4, a vaporizable hydrocarbon and steam enter the reactor at inlet 69 and flow through the reforming catalyst bed 70 (which is in the form of an annulus) con- taining multiple membrane tubes 71 (made by a process as described in Illustrative Em¬ bodiment 11 or Illustrative Embodiment 12) and multiple DC tubes 72 surrounded by the catalyst bed. In this embodiment the feed gases and reaction gases flow through the cata¬ lyst bed radially from outside to inside. The multiple hydrogen-selective, hydrogen- permeable, membrane tubes 71 are disposed axially in concentric rows in the reforming catalyst bed and serve to remove hydrogen, which is produced by the reforming reac¬ tions. The multiple DC tubes (i.e., chambers) 72 are also disposed axially in concentric rows in the reforming catalyst bed (for example, in a ratio of 1 :2 or other number of DC tubes to the number of membrane tubes). The multiple DC tubes are in contact with the reforming catalyst bed and provide a controlled, distributed heat flux to the catalyst bed sufficient to drive the reforming reactions. While the membrane tubes and the DC tubes are shown to be in concentric rows in Figure 4, other geometric arrangements of these tubes can be suitably employed, and are within the scope of the present invention.

The DC tubes 72 generally comprise a fuel conduit disposed within a larger tube with an inlet and flow path for a preheated oxidant (e.g., preheated air) and an outlet for combustion (flue) gas. The DC tubes may be closed ended with a fuel conduit, oxidant inlet and flow path, and flue gas outlet arranged as shown in Figure 6A, or may open ended with the fuel conduit, oxidant inlet and flow path arranged as shown in Figure 6B. High purity hydrogen is removed from the multi-tubular, radial flow, reactor shown in Figure 8 via outlets 73, with the aid of vacuum. Optionally, a sweep gas may be used to promote the diffusion of hydrogen through the membrane of the membrane tubes 71. If a sweep gas is employed, the membrane tubes 71 may contain an outer sweep gas feed tube and an inner return tube for sweep gas and hydrogen as discussed in Figure 12. By-product gases, including unpermeated hydrogen, if not further used inter- nally for heat production, e.g., combustion or heat exchange, exit the multi-tubular, ra¬ dial flow, reactor via outlet 74. A hollow tube or cylinder 75 may optionally be used for flow distribution. ILLUSTRATIVE EMBODIMENT 2

Figure 5 is a top cross-section view of the shell of the multi-tubular, DC heated, radial flow, membrane, steam reforming reactor of Figure 4. The cross sectional view of the reactor shows multiple membrane tubes 71 (made by a process as described in Illus¬ trative Embodiment 11 or Illustrative Embodiment 12) and multiple DC tubes 72 dis¬ persed in catalyst bed 70 with optional hollow tube or cylinder 75 being in the center of the reactor. In the example shown, the membrane tubes 71 have outside diameters (OD) of about one inch (2.5 cm) while DC tubes have an OD of approximately two inches (5.1 cm), al¬ though other sizes of these tubes can be suitably employed. If a sweep gas is employed, the membrane tubes 71 may contain an outer sweep gas feed tube and an inner return tube for sweep gas and hydrogen as shown in Figures 8 and 13. A larger shell containing more tubes duplicating this pattern can also be used. ILLUSTRATIVE EMBODIMENT 3

Figures 6 A and 6B are schematic diagrams showing an example of a "closed ended" and of an "open ended" distributed combustion tubular chamber which are used to drive the reforming reactions in various embodiments of the present invention. Refer¬ ring to Fig. 6A, an oxidant (in this case preheated air) enters the DC tube at inlet 76 and mixes with fuel which enters the DC tube at inlet 77 and passes into fuel conduit 78 through nozzles 79 spaced along the length of the fuel conduit, whereupon it mixes with the air which has been preheated to a temperature such that the temperature of the result- ing mixture of fuel and air is above the autoignition temperature of the mixture. The re¬ action of the fuel passing through the nozzles and mixing with the flowing preheated air at a temperature above the autoignition temperature of the mixture, results in distributed combustion which releases controlled heat along the length of the DC tube as shown, with no flames or hot spots. The combustion gases, (i.e., flue gas) exit the DC tube at outlet 80.

In the "open ended" DC tubular chamber shown in Fig. 6B, preheated air enters the DC tube at inlet 76 and the fuel at inlet 77, and the fuel passes through conduit 78 and nozzles 79, similar to "closed end" DC tube in Fig. 6 A. However, in the case of the "open ended" DC tube, the flue gas exits the DC tube at open end 81, instead of outlet 80 as shown in Fig.6A.

ILLUSTRATIVE EMBODIMENT 4

Figure 7 is a schematic drawing of a multi-tubular, DC heated, axial flow, mem¬ brane, steam reforming reactor in accordance with the present invention. In the reactor shown in Figure 7, a vaporizable hydrocarbon and steam enter the reactor at inlet 69 and flow through the reforming catalyst bed 70 containing multiple hydrogen- selective membrane tubes 71 (made by a process as described in Illustrative Embodiment 11 or Illustrative Embodiment 12) and multiple DC tubes 72. In this embodiment the feed gases and reaction gases flow through the catalyst bed axially from the top of the catalyst bed to the bottom. The multiple hydrogen-selective membrane tubes 71 are disposed axially in the reforming catalyst bed and serve to remove hydrogen which is produced by the reforming reactions. In the embodiment shown the membrane tubes are closed at the top and a sweep gas (e.g. steam) is employed, which enters the reactor at inlet 85 into the bottom of the membrane tubes where it flows upward in the outer part of the membrane tube, counter-current to the hydrocarbon and steam feed. A stinger pipe fitted to the bot¬ tom of the permeate section may be used to distribute the sweep gas in the membrane tube. The permeated hydrogen and sweep gas flow downward in a return tube located in the center of the membrane tube and exit the reactor via outlet 86. The pressure drop in the permeate pipe section is significant when the length of the pipe relative to the diame- ter exceeds a given limit. Actually, the volumetric amount of hydrogen crossing the membrane is proportional to the membrane area, D*D*L and the multiplier is the veloc¬ ity, which is fixed as a function relating to Sievert's law, the description of which can be found in US2003/0068269. The same hydrogen amount has to flow across the pipe cross section which is equal to π*D²/4. The ratio of hydrogen velocities through the pipe and through the membrane respectively is proportional to (π *D*L)/(π *D²/4) or to L/D.

Pressure drop increases with gas velocity. If this ratio exceeds a limit, then the velocity in the permeate pipe exceeds a limit too, since the velocity through the membrane is fixed. Then the pressure drop in the permeate pipe becomes high and it reduces the hy¬ drogen flux by creating back pressure in the permeate section. In such a case, the reactor design has to accommodate either a higher membrane diameter, or a reduced length.

There are also multiple DC tubes (i.e., chambers) 72 disposed axially in the re¬ forming catalyst bed. In the embodiment shown the DC tubes are "closed ended" tubes with preheated air entering at inlet 76, fuel entering at 77 and combustion gas (i.e., flue ^' gas) exiting the reactor at outlet 80. The multiple DC tubes are in heat transferring con- tact with the reforming catalyst bed 70 and provide a controlled, distributed heat flux to the catalyst bed sufficient to drive the reforming reactions. While the membrane tubes and the DC tubes are shown to be in a particular geometric pattern in Figure 11, it is un¬ derstood that other geometric arrangements of these tubes may be used and are within the scope of the invention. While "closed ended" DC tubes are employed in the particu- lar reactor shown in Figure 7, "open ended" DC tubes may be suitably employed as well. Also, the DC tubes and/or the membrane tubes may be surrounded by cylindrical screens (not shown) to protect them from getting in direct contact with the catalyst, and allow insertion of these tubes even after the catalyst is loaded into the reactor. The DC chamber must be free of obstructions and have a tubular dimension for the external or exterior tube of the DC chamber such that the length to diameter ratio is higher than a given limit, preferably more than 4. This ratio ensures that the air velocity in the chamber becomes higher than the flame velocity of the fuel and that turbulence is induced to improve heat transfer. In such a condition, no flames are created or stabilized. Any obstructions (like baffles) would create stagnation points where flames would form and stabilize.

High purity hydrogen, which diffuses through the membrane into the membrane tubes, is removed from the reactor via outlet(s) 86 together with the sweep gas (in this case steam). While outlet 86 is shown in Figure 7 to be located on the side of the reactor, this outlet may optionally be located at the bottom of the reactor thereby avoiding a bot¬ tom side exit manifold. A further option involves the use of a vacuum instead of a sweep gas to facilitate diffusion of the hydrogen through the membrane into the membrane tubes. Vacuum can be induced either mechanically with a pump or chemically with a metal hydride precursor which reacts away the hydrogen to form metal hydride. The hy¬ dride is on-line for a given period of time and when it is saturated, a parallel compart¬ ment can be put on-line, while the original compartment is isolated and heated to desorb and produce the hydrogen. This is advantageous in cases where the hydrogen needs to be stored and/or shipped to a customer or in cases where the cost of electrical energy for running a pump is higher than using waste energy to desorb the hydrogen from the hy¬ dride. Detailed economics will dictate the right choice.

In another embodiment of the reactor in Figure 7, the sweep gas inlet 85 and the hydrogen, sweep gas outlet 86 and their associated plenums, may be placed on the top of the reactor allowing easy access to the bottom of the reactor, hi a further embodiment of the reactor of Figure 11, the preheated air inlet 76, the fuel inlet 77 and the flue gas outlet 80 and their associated plenums may be placed on the bottom of the reactor allowing easy access to the top of the reactor.

By-product gases, including carbon dioxide, steam, and minor amounts of carbon monoxide and unpermeated hydrogen, if not further used internally for heat production, e.g., combustion or heat exchange, exit the multi-tubular, axial flow, reactor via outlet 74. The reactor shown in Fig. 11 may be equipped with baffles and/or screens such as the baffles shown in Figures 13A and 13B or 13C and 13D. ILLUSTRATIVE EMBODIMENT 5

Figure 8 is a top cross-section view of the shell of the multi-tubular, DC heated, axial flow, membrane reactor shown in Figure 7. In the embodiment shown multiple membrane tubes 71 (made by a process as described in Illustrative Embodiment 11 or Illustrative Embodiment 12) and multiple DC tubes 72 are dispersed in reforming cata¬ lyst bed 70. The multiple DC tubes employed in this embodiment are "closed ended" DC tubes as discussed above in connection with Figure 7. The membrane tubes are equipped with an outer sweep gas feed tube and an inner hydrogen, sweep gas return tube as discussed in connection with Figure 7. A typical reactor of the type shown in this Figure 8 may comprise, for example, 19 DC tubes of 5.5" (14 cm) outer diameter and 90 membrane tubes of 2" (5.1 cm) outer diameter enclosed in a shell of 3.5 ft (1.1 m) di¬ ameter containing catalyst in the void spaces. Other shell sizes and numbers of tubes can be suitably employed depending on the capacity needed. The design parameter which is of utmost importance is the optimum gap between the membrane and the DC tubes. If a high gap is assumed, then heat transfer limitations occur since the flow of enthalpy from DC to the reforming reaction is slow. The membranes may not operate isothermally and cold spots may develop, thus reducing the reactor efficiency. If a small gap is assumed, then there may be problems with insufficient catalyst penetration in the gap, overheating of the membrane, or even touching of the hot DC tube with the membrane in conditions where the tubes are not perfectly straight. A narrow gap limitation will make reactor fab¬ rication more expensive, since clearances are hard to achieve. Thus, an intermediate gap is more preferable. As a particular non-limiting example, the gap between the membrane and the DC tubes is from about ¹A inch (about 0.6 cm) to about 2 inches (about 5.1 cm), particularly from about ¹A inch (about 1.3 cm) to about 1 inch (about 2.5 cm). The gap between the membrane tubes may be from about ¹A inch (0.6 cm) to about 2 inches (5.1 cm), particularly from about ¹A inch (1.3 cm) to about 1 inch (2.5 cm) and this has to be also optimized. The hydrogen-permeable membrane tube has a ratio of length to diame¬ ter of less than about 500. ILLUSTRATIVE EMBODIMENT 6 Figures 9 A and 9B and 9C and 9D show two different configurations of baffles which may be employed in the multi-tubular, DC heated, axial flow, membrane steam reforming reactors of the invention to increase contact of the reactant gases with the cata¬ lyst in the catalyst beds. The baffle configuration shown in Figures 9A and 9B comprise a washer shaped baffle 87 and a disk shaped baffle 88 arranged in an alternating pattern. This baffle arrangement causes the feed and reactant gases to flow through the hole in the washer shaped baffle and be deflected by disk shaped baffle thereby enhancing the contact of the reactant gases with the catalyst (not shown) which is packed in the area between the baffles. The baffle arrangement shown in Figures 9C and 9D comprises truncated disks

89 which are placed in an alternating pattern (truncated left and truncated right) in the reactor thereby causing the feed and reactant gases to "zigzag" as they flow through the catalyst (not shown) which is packed in the area between the baffles.

The baffles in Figures 9A&B and 9C&D will have openings (not shown) to allow the DC tubes and membrane tubes to pass through them. Screens positioned in vertical alignment (not shown) may also be used to support the baffles and in some cases hold the catalyst away from the shell wall or from the center of the shell for better gas flow distribution. ILLUSTRATIVE EMBODIMENT 7 Figure 13 is a top cross-section view of the shell of a multi-tubular reactor in ac¬ cordance with one embodiment of the invention in which four membrane tubes 71 (made by a process as described in Illustrative Embodiment 11 or Illustrative Embodiment 12) are dispersed in the reforming catalyst bed 70 which is packed into reactor tube 82, while the DC chamber is in the form of an annulus surrounding the reforming catalyst bed. The tubular DC chamber (which is defined by outer wall 83 and the wall of the reactor tube 82) contains multiple fuel conduits 78 having nozzles (not shown) through which fuel flows and mixes with preheated air flowing in the DC chamber whereupon combus¬ tion occurs. If a sweep gas is employed, the membrane tubes 71 may contain an outer sweep gas feed tube and an inner return tube for sweep gas and hydrogen as shown in Figure 13. In one embodiment of the invention, the membrane tubes have an outer di¬ ameter of 2 inches (5.1 cm), while the outer DC tube has an inner diameter of approxi¬ mately 8.6 inches (21.8 cm). However, other sizes can be suitably employed. ILLUSTRATIVE EMBODIMENT 8

Figure 10 is a top cross-section view of the shell of another embodiment of the multi-tubular, axial flow, reactor of the invention in which multiple reactor tubes 82 packed with reforming catalyst are employed. In this example each of the six reactor tubes 82 contains a catalyst bed 70 and a membrane tube 71 (made by a process as de¬ scribed in Illustrative Embodiment 11 or Illustrative Embodiment 12) containing an outer sweep gas feed tube and an inner hydrogen, sweep gas return tube. Heat is provided to the reforming catalyst beds by the tubular DC chamber defined by outer wall 83 and in¬ ner wall 84. The DC chamber contains multiple fuel conduits 78 dispersed at various intervals in the DC chamber. A hollow tube or cylinder defined by inner wall 84 may optionally be used for flow distribution. ILLUSTRATIVE EMBODIMENT 9

Figure 12 is a top cross-section view of the shell of further embodiment of the multi-tubular, axial flow, reactor of the invention in which four membrane tubes are dis¬ persed in each of six reactor tubes 82 containing catalyst beds 70. Heat is provided to the catalyst beds by DC chamber defined by outer wall 83 and inner wall 84. The DC chamber contains multiple fuel conduits 78 having nozzles 79 (not shown). If a sweep gas is employed, the membrane tubes 71 (made by a process as described in Illustrative Embodiment 11 or Illustrative Embodiment 12) may contain an outer sweep gas feed tube and an inner return tube for sweep gas and hydrogen as discussed above in connec¬ tion with Figures 8 and 13. The hollow cylinder or tube defined by inner wall 84 may optionally be used for flow distribution. ILLUSTRATIVE EMBODIMENT IQ

Figure 12 is a top cross-section view of the shell of a further embodiment of the multi-tubular, axial flow, reactor of the invention in which six membrane tubes 71 (made by a process as described in Illustrative Embodiment 11 or Illustrative Embodiment 12) are dispersed in each of the six reactor tubes 82 packed with reforming catalyst. Heat is provided to the reforming catalyst beds by the DC chamber defined by outer wall 83 and inner wall 84. The DC chamber contains multiple fuel conduits 78. Additional heat may be provided to the catalyst beds by employing an DC tube 72 in the center of each of the reactor tubes 82 as shown in Figure 12. The hollow tube or cylinder defined by inner wall 84 may optionally be used for flow distribution.

If a sweep gas is employed, the membrane tubes 71 may contain an outer sweep gas feed tube and an inner return tube for sweep gas and hydrogen as discussed in Figure 12. ILLUSTRATIVE EMBODIMENT 11 This embodiment describes the fabrication of a composite structure which can be used for making the hydrogen-permeable and hydrogen-selective membrane tubes for the reactors of Illustrative Embodiments 1-10. It has a dense hydrogen-selective membrane, an intermediate layer that includes a tungsten powder, and a nominal 0.1 media grade porous 316L stainless steel ("PSS") support. A 6 inch (15.2 cm) long, 1 inch (2.5 cm) outside diameter section of PSS tube, welded to sections of 1 inch (2.5 cm) outer diameter dense, non-porous 316L stainless steel tube on each end, was obtained from Mott Metallurgical Corporation. Contami¬ nants were removed by cleaning the tube in an ultrasonic bath with alkaline solution at 60°C for one half hour. The tube was then sequentially rinsed using tap water, deionized water and isopropanol. The tube was oxidized in static air at 400°C for 12 hours wherein the rates of heating and cooling were 3°C per minute.

A thin layer of tungsten powder was then applied to the outer surface of the PSS support by the following room temperature filtration operation. First, a slurry of the tungsten powder was prepared. The slurry included 1 liter (L) deinoized water (DI) wa¬ ter, 10 grams (g) poly(ethylene glycol) (PEG) (average molecular weight (MW) 3,400) (Sigma- Aldrich, St. Louis, MO, Cat. No. 20,244-4) and 20 g tungsten powder having a particle size of about 1 to 5 micrometers. (Alfa Aesar, Ward Hill, MA, tungsten powder (average particle size (APS) 1 to 5 microns), Stock No. 10400, Lot No. E03M02.) The exterior of the support was exposed to the slurry in a closed plastic cell while a vacuum was applied to the inside of the support tube. A vacuum pump was used to reduce the absolute pressure to about 0 kilopascals (kPa) on the inside of the support tube. The closed plastic cell containing the slurry and the support was shaken throughout filtration of the slurry through the support. Some of the liquid from the slurry was thereby drawn through the porous support and a filter cake of tungsten powder formed on the outside of the support. Filtration of the slurry using this technique was performed for one hour. The support and filter cake were dried in an oven at 12O⁰C overnight. This procedure failed to produce a uniform filter cake coverage of the support. The filter cake was removed using a brush after drying. A new filter cake was then applied to the support by a variation of the procedure described above. A fresh slurry was made with the same composition as described su¬ pra. The exterior of the support was immersed into an open cylinder with constantly stirring slurry for about 90 seconds while a vacuum was applied to the inside of the sup¬ port tube (absolute pressure of about 0 kPa). The support was removed from the slurry and dried under vacuum at room temperature about one hour and then it was dried with¬ out vacuum in oven at 12O⁰C overnight. Tungsten powder thickness was estimated as 17.3 micrometers. The tungsten powder layer was uniform and it appeared strong enough to continue with subsequent activation and plating. Ail attempt was then made to surface activate the support using aqueous stannous chloride (SnCl₂) and palladium chloride (PdCl₂) as described supra. However, a sub¬ stantial quantity of the tungsten powder fell off the support into the activation solutions. The support was rinsed in DI water and dried at 12O⁰C overnight. The remaining tung- sten powder was removed from the dried surface of the support using an artist's brush and the support was immersed in DI water in an ultrasonic bath for 15 min and then dried at 12O⁰C overnight.

A new filter cake was then applied to the support by a variation of the procedure described above. A new slurry was made that contained 1 L DI water, 1O g poly(ethylene glycol) (PEG), and 1O g of the APS 1 to 5 micrometer tungsten powder described above. The exterior of the support was then exposed to the slurry for about 90 seconds while a vacuum from an water aspirator (absolute pressure of about 51 kPa) was applied to the inside of the support tube. The support and resulting filter cake were then immediately activated without drying using the following procedure. The support and filter cake were surface activated by sequentially immersing the exterior of the support in aqueous baths Of SnCl₂ and PdCl₂ while a vacuum from an wa¬ ter aspirator (absolute pressure of about 51 kPa) was applied to the inside of the support tube. The exterior of the tube was immersed in 500 mL of aqueous SnCl₂ (1 g/L) at 2O⁰C for about 5 minutes and was subsequently rinsed with deionized water. The exte- rior of the tube was then immersed in 500 mL of aqueous PdCl₂ (0.1 g/L) at 20°C for about 5 minutes followed by rinsing first with 0.01 molar hydrochloric acid and then with deionized water. During surface activation with vacuum, it was necessary to add small amounts of the activation solutions to replenish the liquid drawn through the sup¬ port by the vacuum. The above-described surface activation cycle was performed a total of two times. The support was then dried for 1 hour at room temperature while the above-described vacuum was applied to the interior of the tube. The support was then dried overnight in an oven (with no vacuum applied) at 12O⁰C. This procedure produced a uniform dried tungsten filter cake {e.g., an intermediate layer) with a thickness of about 3.4 micrometers, determined gravimetrically based on the weight of the dried tungsten powder and trace PEG with no correction for the porosity of the filter cake.

Following surface activation, a porous palladium/silver layer was applied over the intermediate layer of tungsten powder by electro less plating while a vacuum from an water aspirator (absolute pressure of about 51 kPa) was applied to the inside of the sup- port. Thin layers of palladium (Pd) and silver (Ag) were sequentially deposited using electroless plating as described below.

Palladium layers were deposited on the tube by electroless plating according to the following procedure. The tube was immersed in a plating solution at room tempera- ture. The plating solution was composed of 4 grams Pd(NH₃)₄Cl₂ ' H₂O/liter, 198 millili¬ ters NH₄OH (28 weight percent)/liter, 40.1 grams Na₂EDTA/liter, and 6 milliliters aque¬ ous H₂NNH₂ (1 M)/liter. The plating solution and tube were placed in a water bath at 60°C. During plating, the level of plating solution was kept constant by adding a small quantity of plating solution for loss of solution to the vacuum. After the palladium in the plating solution was depleted, the tube was removed and rinsed with deionized water at 60°C with 4 to 5 rinses.

Silver layers were deposited on the tube by electroless plating according to the following procedure. The tube was immersed in a plating solution at room temperature. One liter of the plating solution contained 0.519 grams AgNO₃, 198 milliliters of concen- trated aqueous NH₄OH (28 weight percent), 40.1 grams Na₂EDTA, and 6 milliliters IM aqueous H₂NNH₂, and the balance was DI water. The plating solution and tube were placed in a water bath at 6O⁰C. During plating, the level of plating solution was kept constant by adding a small quantity of plating solution for loss of solution to the vacuum. After the silver in the plating solution was depleted, the tube was removed and rinsed with deionized water at 60⁰C with 4 to 5 rinses.

Each metallic layer was applied by contacting the tube with a plating solution for 90 minutes and was followed by rinsing the tube with deionized water, but not with in¬ termediate activation, drying or sintering. The specific layers, an estimate of the layer thicknesses, and the order of their application were Pd (about 4.5 micrometers), Ag (about 0.9 micrometers), Pd (about 4.5 micrometers), Ag (about 0.9 micrometers) and Pd (about 4.5 micrometers) (a total of five layers). (Thickness estimates were based on time of contact with the plating solutions. The average rate of metal deposition was deter¬ mined for a test piece of a similar support and the identical plating solution and activa¬ tion procedure. The test pieces were activated, then plated for 90 minutes and then rinsed, dried and weighed. From that it was possible to estimate the thickness which was deposited over 90 minutes.) The deposition rate under a vacuum (absolute pressure range of about 51 to about 67 kPa) increased three times as compared to experiments in which deposition was performed without vacuum applied. After applying the above- described palladium and silver layers, the membrane was dried at 12O⁰C in air overnight. Helium flux was measured across the membrane thus formed. These measurements in¬ dicated that the membrane was not gas tight at this point. The total thickness of the po¬ rous palladium/silver layer after these steps was 16.4 micrometers (determined gravimet- rically). The membrane was slightly sanded with 2,400 grit sandpaper (Waterproof SiIi- con Carbide, P=2400, Struers, Inc., Westlake, OH). The final thickness of the porous palladium/silver layer after sanding was 12.8 micromteers (determined gravimetrically). Then, the membrane was surface activated using three surface activation cycles, described supra but under a light aspirator vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support. Palladium was then deposited on the exterior of the tube by electroless plating according to the above-described proce¬ dure, with an aspirator vacuum (absolute pressure range of about 78 to about 84 kPa) ap¬ plied to the inside of the support, three times for 90 minutes each time (a total of 4.5 hours of plating). Between each of the 90 minute platings, the membrane was rinsed with DI water (at 6O⁰C) not less than three times. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120°C. A total 9.4 micrometers of pal¬ ladium, gravimetrically determined, was applied to the support. The membrane was slightly sanded with 2,400 grit sandpaper (Waterproof Silicon Carbide, Struers, Inc.). The thickness of the palladium layer after these steps was 6.4 micromters (determined gravimetrically). The thickness is determined by weighing sample before and after and determine Pd mass, volume and then calculate the thickness based on plated area.

Then, the membrane was surface activated using three surface activation cycles, described supra, with an aspirator vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support. Palladium was then deposited on the exte¬ rior of the tube by electroless plating according to the above-described procedure, with an aspirator vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support, four times for 90 minutes each time (a total of 6 hours of plating). Between each of the 90 minute platings, the membrane was rinsed with DI water (at 6O⁰C) not less than three times. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120⁰C. The thickness of the palladium layer after these steps was 16.2 micrometers (determined gravimetrically).

Then, the membrane was surface activated using two surface activation cycles, described supra under no vacuum. Palladium was then deposited on the exterior of the tube by electroless plating according to the above-described procedure without vacuum 5 times for 1.5, 1.5, 1.5, 2, and 2 hours, respectively, for a total of 8.5 hours of plating. Be- tween each of the platings, the membrane was rinsed with DI water (at 60°C) not less than three times. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120°C. The thickness of the palladium layer after these steps was 22.6 micrometers (determined gravimetrically). Then, the membrane was surface activated using two surface activation cycles, described supra under no vacuum. Palladium was then deposited on the exterior of the tube by electroless plating according to the above-described procedure without vacuum 3 times for 1.5, 1.5, and 2 hours, respectively, for a total of 5 hours of plating. Between each of the platings, the membrane was rinsed with DI water (at 6O⁰C) not less than three times. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120⁰C. The thickness of the palladium layer after these steps was 27.6 mi¬ crometers (determined gravimetrically).

Then, the membrane was surface activated using two surface activation cycles, described supra under no vacuum. Palladium was then deposited on the exterior of the tube by electroless plating according to the above-described procedure without vacuum 3 times for 1.5, 2, and 2 hours, respectively, for a total of 5.5 hours of plating. Between each of the platings, the membrane was rinsed with DI water (at 6O⁰C) not less than three times. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120⁰C. Thus, a final total of 33.6 micrometers of palladium, gravimetrically determined, had been applied to the support.

Helium leak and hydrogen permeance of this membrane were observed at 500⁰C for over 800 hours. A maximum hydrogen permeance of 13.6 (m³/m²-h-atm°^'5)sτp was obtained and no decline in hydrogen permeance was observed over the entire test period. During this test, the membrane was periodically switched from hydrogen gas to helium gas to measure the leak (a pressure difference of 1 atmosphere (atm) was applied). This was done a total of 8 times. The helium leak at 500⁰C increased from 0.4 to 3.7 standard cubic centimeters per minute (seem) during the first 4 cycles (approximately 450 hours at 500⁰C) then remained at a relatively stable value between 3.7 and 4.0 seem for all meas¬ urements thereafter. The time required to reach a plateau in the helium leak corre- sponded to the time required to reach the maximum stable hydrogen permeance. ILLUSTRATIVE EMBODIMENT 12

This embodiment describes the fabrication of a composite structure which can be used for making the hydrogen-permeable and hydrogen-selective membrane tubes for the reactors of Illustrative Embodiments 1-10. It has a dense hydrogen-selective membrane, an intermediate layer that includes an aluminum oxide (Al₂O₃) powder, and a nominal 0.1 media grade porous HASTELLOY^® C-22^® support. (HASTELLOY^® C-22^® is a nickel-chromium-molybdenum-iron-tungsten alloy.)

A 6 inch (15.2 cm) long, 1 inch (2.5 cm) outer diameter section of porous HASTELLOY^® C-22^® tube, welded to sections of 1 inch (2.5 cm) outer diameter dense, non-porous 316L stainless steel tube on each end, was obtained from Mott Metallurgical Corporation. Contaminants were removed by cleaning the tube in an ultrasonic bath with alkaline solution at 6O⁰C for one half hour. The tube was then sequentially rinsed using tap water, deionized water and isopropanol. The tube was oxidized in static air at 700⁰C for 12 hours. The rate of heating and cooling was 3⁰C per minute.

A thin layer OfAl₂O₃ powder was then applied to the outer surface of the support by the following room temperature filtration operation. First, a slurry of the Al₂O₃ pow¬ der was prepared. One liter of the slurry included 5 g Al₂O₃ powder having a particle size of about 1 micrometer (CAS 1344-28-1, Alfa Aesar, Ward Hill, MA) with the bal- ance DI water.

The exterior of the support was exposed to the slurry for 105 seconds while a wa¬ ter aspirator vacuum (absolute pressure of about 23 kPa) was applied to the inside of the support tube. Some of the liquid was thereby drawn through the porous support and a filter cake OfAl₂O₃ powder formed on the outside of the support. The slurry was con- tinuously stirred as filtration occurred.

The support and resulting filter cake were then immediately activated without drying using the following procedure. The support and filter cake were surface activated by sequentially immersing the exterior of the support in aqueous baths of SnCl₂ and PdCl₂ while a water aspirator vacuum (absolute pressure of about 23 kPa) was applied to the inside of the support tube. The exterior of the tube was immersed in 500 mL of aqueous SnCl₂ (1 g/L) at 20°C for about 5 minutes and was subsequently rinsed with de- ionized water. The exterior of the tube was then immersed in 500 mL of aqueous PdCl₂ (0.1 g/L) at 20°C for about 5 minutes followed by rinsing first with 0.01 molar hydro¬ chloric acid and then with deionized water. The above-described surface activation cycle was performed one time. The activated wet filter cake and support were then plated with palladium from the outside, as described in Example 1 using one palladium plating solu¬ tion for 60 minutes (a total of 1 hour) while a water aspirator vacuum was applied to the inside of the support (absolute pressure range of about 78 to about 84 kPa). The result¬ ing palladium layer remained porous. After the palladium plating, the membrane was dried and it was determined that the thickness of the palladium stabilized Al₂O₃ filter cake (impregnated with palladium) was 2 micrometers. The above steps Of Al₂O₃ slurry filtration, surface activation and electroless palladium plating were then repeated with several modifications described infra. First, a new water slurry containing a mixture OfAl₂O₃ powders with different particle sizes was prepared. A one liter Al₂O₃ water slurry was prepared containing 0.81 g Al₂O₃ powder with 1 micrometer particles, 0.2 g Al₂O₃ powder with 0.2 microme¬ ter particles, and 0.12 g Al₂O₃ powder with 0.01 to 0.02 micrometer particles. (All Al₂O₃ powders were obtained from Alfa Aesar.) The slurry was applied to the support using the following non-stop procedure with a vacuum (absolute pressure of about 67 kPa) ap¬ plied to the inside of the support. The support was immersed in the slurry for 5 sec and immediately surface activated one time, as described supra, then again immersed in the slurry for 30 sec and immediately surface activated one time, and finally again immersed in the slurry for 45 sec and immediately surface activated. Then palladium was plated, as described supra, one time for 45 min while a vacuum was applied to the inside of the support (absolute pressure range of about 78 to about 84 kPa). This process resulted in the deposition of an additional 3.8 micrometers OfAl₂O₃ filter cake impregnated with palladium.

Then, a porous Pd/Ag/Pd/Ag/Pd layer with a total thickness of 5.75 micrometers was applied over the support by electroless plating as described in Example 1 but with¬ out vacuum (neither surface activation nor palladium plating in this case used vacuum). The resulting membrane was slightly sanded with 2,400 grit sandpaper (Waterproof Sili¬ con Carbide, Struers, hie).

The support was surface activated by repeating the surface activation cycle, de- scribed supra, three times with an aspirator vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support. Palladium was then deposited on the exterior of the tube by electroless plating according to the procedure described in Ex¬ ample 1, with an aspirator vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support, three times for 2, 1.5, and 2 hours, respectively, each time for a total of 5.5 hours. Between each of the 1.5 or 2 hour platings, the membrane was rinsed with DI water (at 60°C) not less than three times. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120°C. 5.35 micrometers of palladium, gravimetrically determined, was applied to the support using this proce¬ dure. The resulting membrane had a hydrogen permeance of 27.6 (m³/m²-h-atm^{0 5})sτp at 500⁰C. This hydrogen permeance was stable for 78 hours. At the end of the hydrogen permeance experiment, the helium leak at 500⁰C with a pressure difference of 1 atm was 0.8 seem. This corresponds to an ideal hydrogen/helium separation factor of 2750. ILLUSTRATIVE EMBODIMENT 13

This embodiment describes the fabrication of a composite structure which can be used for making the hydrogen-permeable and hydrogen-selective membrane tubes for the reactors of Illustrative Embodiments 1-10. It has a dense hydrogen-selective membrane, an intermediate layer that includes a tungsten powder and silver powder, and a nominal 0.1 media grade porous HASTELLO Y^® C-22^® support.

A 6 inch (15.2 cm) long, 1 inch (2.5 cm) outer diameter section of porous HASTELLO Y^® C-22^® tube, welded to sections of 1 inch (2.5 cm) outer diameter dense, non-porous 316L stainless steel tube on each end, was obtained from Mott Metallurgical Corporation. Contaminants were removed by cleaning the tube in an ultrasonic bath with alkaline solution at 60°C for one half hour. The tube was then sequentially rinsed using tap water, deionized water and isopropanol. The tube was oxidized in static air at 700°C for 12 hours. The rate of heating and cooling was 3°C per minute.

A thin layer of tungsten and silver was then applied to the outer surface of the support by the following room temperature filtration operation. First, a slurry of the tungsten and silver was prepared. The one-liter water slurry included: 5 g PEG, average MW 3,400 (Sigma-Aldrich, Cat. No. 20,244-4); 0.98 g tungsten powder, less than 1 mi¬ crometer particles (Alfa Aesar, Stock No. 44210, LotNo. H29M20); 1.48 g tungsten powder, 1 to 5 micrometer particles (Alfa Aesar, Stock No. 10400, Lot No. E03M02); and 1.7 g silver powder, 0.6 to 2 micrometer particles (Alfa Aesar, Stock No. 41298, Lot No. F27K20).

The exterior of the support was exposed to the slurry for 15 seconds while a wa¬ ter aspirator vacuum (absolute pressure of about 67 kPa) was applied to the inside of the support tube. Some of the liquid was thereby drawn through the porous support and a filter cake of tungsten and silver powder formed on the outside of the support. The slurry was continuously stirred as filtration occurred.

The support and resulting filter cake were then immediately surface activated without drying one time, as described in Example 2, with a vacuum (absolute pressure of about 67 kPa) applied to the inside of the support. The surface activated support (without drying) was again immersed in the same slurry for 30 seconds and immediately surface activated one time and then again im¬ mersed in the slurry for 45 seconds and immediately surface activated one time. All these steps were applied as a non-stop procedure with a vacuum (absolute pressure of about 67 kPa) applied to the inside of the support and without intermediate drying steps. During these operations, a portion of the silver powder was observed to float on the sur¬ face of the slurry. During application of the slurry, the support was moved up and down continuously to insure uniform contact of the support surface with the floating silver powder. This process resulted in the deposition of a tungsten powder filter cake with traces of silver powder.

The wet support was palladium plated one time (using one plating solution) for 30 minutes with a vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support. Without wishing to be held to any particular theory, the electroless plating of palladium using vacuum is thought to have resulted in the deposi- tion of palladium in the voids within the filter cake. Therefore, this filter cake is thought to have been stabilized by the electroless deposition of palladium, which is thought to have bound at least some of the adjacent powder particles together. The total thickness of the filter cake and plated palladium at this stage was 3.5 micrometers. (It was esti¬ mated that 3.5 micrometers contained about 2.5 micrometers of tungsten/silver and about 1 micrometer of palladium impregnated therein).

Then, using the method described in Example 2, a porous Pd/Ag/Pd/Ag/Pd layer with a total thickness of 3.5 micrometers was applied over the support by electroless plating without vacuum and with plating times of about half (45 min palladium plating; 45 minutes silver plating; 45 minutes palladium plating; 45 minutes silver plating; 45 minutes palladium plating (both activation and plating were performed without vac¬ uum)). After the plating and rinsing with DI water, the membrane was dried for 2 hours at 12O⁰C. Then, the support was slightly sanded with 2,400 grit sandpaper (Waterproof Silicon Carbide, Struers, hie).

The support was surface activated by repeating the surface activation cycle, de- scribed in Example 2, three times with a vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support. Palladium was then deposited on the exterior of the tube by electroless plating according to the procedure described in Exam¬ ple 1 three times for 90, 90, and 60 minutes each time, respectively, for a total of 4 hours. Between each of the 60 or 90 minute platings, the membrane was rinsed with DI water (at 60°C) not less than three times. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120°C. 6.0 micrometers of palladium, gravimetri- cally determined, was applied to the support. The support was again surface activated twice with a vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support and then palladium was plated under the same vacuum three times for 50 minutes, 100 minutes, and 60 minutes, respectively. After the last plating and rinsing with DI water, the membrane was dried for 2 hours at 120⁰C. The resulting membrane had a thickness of 10.2 micrometers of palladium (gravimetrically deter¬ mined). The membrane was activated three times without vacuum and plated with palla¬ dium for one hour without vacuum and the thickness of the membrane became 11.2 mi¬ crometers. The wet membrane was finished by immediately electroplating a 0.6 mi¬ crometer layer of gold over the support followed by electroless plating of a 1.3 microme¬ ter palladium layer without any surface activation. The resulting membrane had a final hydrogen permeance of 41.7 (m³/m²-h- atm^α5)sτp at 500⁰C after 250 hours. ILLUSTRATIVE EMBODIMENT 14

A 6 inch (15.2 cm) long, 1 inch (2.5 cm) outer diameter section of porous HASTELLOY^® C-22^® tube, welded to sections of 1 inch (2.5 cm) outer diameter dense, non-porous 316L stainless steel tube on each end, was obtained from Mott Metallurgical Corporation. Contaminants were removed by cleaning the tube in an ultrasonic bath with alkaline solution at 60°C for one half hour. The tube was then sequentially rinsed using tap water, deionized water and isopropanol. The tube was oxidized in static air at 700°C for 12 hours. The rate of heating and cooling was 3°C per minute. A filter cake of tungsten and silver was then applied to the outer surface of the support tube by the following room temperature filtration operation. First, a slurry of the tungsten and silver was prepared. The one-liter water slurry included: 5 g PEG, average MW 3,400 (Sigma- Aldrich, Cat. No. 20,244-4); 4.6 g/L tungsten powder, less than 1 mi¬ crometer particles (Alfa Aesar, Stock No. 44210, Lot No. H29M20); and 0.4 g/L silver powder, 0.6 to 2.0 micrometer particles (Alfa Aesar, Stock No. 41298, Lot No. F27K20). The dry ingredients were added to water and stirred overnight to form the slurry.

The dry clean support was wetted with DI water by immersing the outside of the support in the water while pulling a light vacuum on the inside. Then, the exterior of the wetted support was exposed to the slurry for about 3 minutes while a water aspirator vac¬ uum (absolute pressure range of about 34 to about 51 kPa) was applied to the inside of the support tube. The support was raised and lowered in and out of the slurry repeatedly during exposure to the slurry and with the vacuum continuously applied to the inside of the support. Some of the liquid was drawn through the porous support and a filter cake of tungsten and silver powder formed on the outside of the support. The slurry was con¬ tinuously stirred as filtration occurred. After 3 minutes of exposure to the slurry, the support was exposed to DI water for about 5 minutes while the vacuum continued to be applied to the inside of the support tube.

The support and resulting filter cake were then immediately surface activated without drying one time, as described in Example 2, with a vacuum (absolute pressure range of about 34 to about 51 kPa) applied to the inside of the support. Following sur¬ face activation, the support and filter cake were dried in room temperature air with the vacuum applied to the inside of the support for 2 minutes. The surface activated support and filter cake were then dried overnight at 12O⁰C with no vacuum applied. At this point, the thickness of the dry filter cake was estimated to be about 3.5 micrometers (gravimetrically determined).

Then, a porous Pd/Ag/Pd/Ag/Pd layer with a total thickness of about 12 mi¬ crometers was applied over the support by electroless plating (with no intermediate dry¬ ing steps) as described in Example 1 while a vacuum (absolute pressure range of about 78 to about 84 IcPa) was applied to the inside of the support tube. The plating solutions were at atmospheric pressure. The metallic layers were applied by contacting the support with a plating solution for 1.5 hours (palladium), 45 min. (silver), 45 min. (palladium), 45 min. (silver), and then 45 min. (palladium). Following the final layer of palladium, the support was dried overnight at 12O⁰C. The surface of the Pd/Ag/Pd/Ag/Pd layer was lightly brushed, reducing the thick¬ ness of the layer to about 10.8 micrometers. The exterior of the support was then surface activated once, as described supra, while applying a vacuum (absolute pressure of about 67 kPa) to the inside of the support. Then, the exterior of the support was immediately plated with palladium according to the electroless plating procedure described in Exam- pie 1 two times for 2 hours each time while a vacuum (absolute pressure range of about 78 to about 84 kPa) was applied to the inside of the support tube for a total of 4 hours. Between each of the 2 hour platings, the membrane was rinsed with DI water (at 60°C) not less than three times. There was no intermediate surface activation or drying of these palladium layers between the two platings. After the last plating and rinsing with DI wa¬ ter, the membrane was dried for 2 hours at 120⁰C. 4.3 micrometers of palladium, gra- vimetrically determined, had been applied to the support.

The support and resulting filter cake were then immediately surface activated without drying 3 times, as described in Example 1 with no vacuum applied to the inside of the support. Then, the exterior of the support was plated with palladium three times for 1.5 hours each time (with no vacuum applied to the inside of the support tube) for a total of 4.5 hours. Between each of the 1.5 hour platings, the membrane was rinsed with DI water (at 6O⁰C) not less than three times. There was no intermediate surface activa¬ tion or drying of these palladium layers between the three platings. After the last plating and rinsing with DI water, the membrane was dried overnight at 120⁰C. After drying, it was gravimetrically determined that about 5.9 micrometers of additional palladium had been applied for a total thickness of 10.2 micrometers of palladium on top of the Pd/Ag/Pd/Ag/Pd layer.

The support and resulting filter cake were then again surface activated without drying 3 times, as described in Example 1 with no vacuum applied to the inside of the support. Then, the exterior of the support was plated with palladium three times for 1.5 hours each time (with no vacuum applied to the inside of the support tube) for a total of 4.5 hours. Between each of the 1.5 hour platings, the membrane was rinsed with DI wa¬ ter (at 6O⁰C) not less than three times. There was no intermediate surface activation or drying of these palladium layers between the three platings. After the last plating and rinsing with DI water, the membrane was dried overnight at 120⁰C. After drying, it was gravimetrically determined that about 4.7 micrometers of additional palladium had been applied for a total thickness of 14.9 micrometers of palladium on top of the Pd/Ag/Pd/Ag/Pd layer. The surface of the membrane was then lightly sanded using 2400 grit sandpaper.

The thickness of the palladium layer covering the Pd/Ag/Pd/Ag/Pd layer was then gra¬ vimetrically determined to be 11.7 micrometers.

The support and resulting filter cake were then again surface activated without drying 3 times, as described in Example 1 with no vacuum applied to the inside of the support tube. Then, the exterior of the support was plated with palladium three times for 1.5, 1.5 and 1 hour, respectively, each time (with a vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support) for a total of 4 hours. Be¬ tween each of the 1.5 or 1 hour platings, the membrane was rinsed with DI water (at 60°C) not less than three times. There was no intermediate surface activation or drying of these palladium layers between the three platings. After the last plating and rinsing with DI water, the membrane was dried overnight at 120°C.

The support and resulting filter cake were once again surface activated without drying 3 times, as described in Example 1 with no vacuum applied to the inside of the support tube. Then, the exterior of the support was plated with palladium three times for 1.5, 2 and 1.5 hours, respectively, each time (with a vacuum (absolute pressure range of about 78 to about 84 kPa) applied to the inside of the support) for a total of 5 hours. Be¬ tween each of the 1.5 or 2 hour platings, the membrane was rinsed with DI water (at 60°C) not less than three times. There was no intermediate surface activation or drying of these palladium layers between the three platings. After the last plating and rinsing with DI water, the membrane was dried overnight at 120°C. It was gravimetrically de¬ termined that a total thickness of 21.3 micrometers of palladium had been applied top of the Pd/Ag/Pd/Ag/Pd layer.

The resulting membrane had a hydrogen permeance of 21.8 [m³/m²-hr-atrn°^'5]sτp after 96 hours of testing at 500⁰C.

The ranges and limitations provided in the instant specification and claims are those, which are believed to particularly point out and distinctly claim the instant inven¬ tion. It is, however, understood that other ranges and limitations that perform substan¬ tially the same function in substantially the same manner to obtain the same or substan- tially the same result are intended to be within the scope of the instant inventions defined by the instant specification and claim.

Claims

C L A I M S

1. A reactor comprising: a) a reaction chamber comprising: a catalyst bed adapted to produce reaction products comprising hydrogen gas from a hydrogen-producing feedstock; and b) at least one hydrogen-selective, hydrogen-permeable gas separation module adapted to receive the reaction products from the catalyst bed and to separate the reaction products into (1) a product stream comprising hydrogen and (2) a byproduct stream, wherein the gas separation module comprises:

(i) a porous substrate; (ii) an intermediate porous layer overlying the porous substrate, said intermediate porous layer including a powder having a Tamman temperature higher than the Tamman temperature of the porous substrate; and (iii) a hydrogen-selective membrane, wherein the hydrogen-selective membrane overlies the intermediate porous layer.

2. A steam reforming process for the production of hydrogen, comprising:

(a) reacting steam with a hydrogen-producing feedstock at a temperature of from about 200°C to about 700°C and at a pressure of from about 0.1 MPa to about 20 MPa in a steam reforming reaction chamber containing a reforming catalyst to produce a mixture of hydrogen and carbon dioxide with a lesser amount of carbon monoxide; and

(b) separating hydrogen from said reaction chamber and from said carbon dioxide and carbon monoxide with a hydrogen-selective, hydrogen-permeable gas separa¬ tion module, where the gas separation module comprises: (i) a porous substrate;

(ii) an intermediate porous layer overlying the porous substrate, said intermediate porous layer including a powder having a Tamman temperature higher than the Tamman temperature of the porous substrate; and (iii) a hydrogen-selective membrane, wherein the hydrogen-selective membrane overlies the intermediate porous layer.

3. The reactor or process of claims 1 or 2 further comprising at least one distributed combustion chamber in a heat transferring relationship with said catalyst bed.

4. The reactor or process of any of claims 1- 3 wherein the gas separation module is a tube.

5. The reactor or process of any of claims 1 - 4 wherein a metal hydride precursor is separated from said reaction chamber by said gas separation module, where said metal hydride precursor is located to react with hydrogen permeating said gas separation mod¬ ule to form a metal hydride.

6. The reactor or process of any of claims 1 - 5 wherein the hydrogen-selective mem¬ brane is formed of palladium or an alloy thereof with at least one metal selected from the group consisting of copper, silver, gold, platinum, ruthenium, rhodium, yttrium, cerium, and indium; and the porous substrate is a porous ceramic substrate or a porous metal sub¬ strate selected from the group consisting of stainless steel, and alloy comprising chro¬ mium and nickel, a nickel based alloy, and an alloy comprising chromium, nickel, and molybdenum.

7. The reactor or process of any of claims 1 - 6 wherein the powder of the intermediate porous layer comprises a material selected from the group consisting of metal powders, metal oxide powders, ceramic powders, zeolite powders, and combinations thereof.

8. The reactor or process of any of claims 1 - 7 wherein the powder of the intermediate porous layer comprises a material selected from the group consisting of tungsten, silver, copper oxide, aluminum oxide, and combinations thereof.

9. The reactor or process of any of claims 1 - 8 wherein the powder of the intermediate porous layer has a Tamman temperature higher than the Tamman temperature of the hy¬ drogen-selective membrane.

10. The reactor or process of any of claims 1 - 9 wherein the intermediate porous layer further comprises at least one material having a Tamman temperature less than or equal to the Tamman temperature of the hydrogen-selective membrane.

11. The reactor or process of any of claims 1 - 10 wherein the powder of the intermedi- ate porous layer has an average particle size of from about 0.5 to about 5 micrometers.

12. The reactor or process of any of claims 1 - 11 wherein the intermediate porous layer has an average thickness of from about 1 to about 10 micrometers.

13. The reactor or process of any of claims 1 - 12 wherein the average pore size of the intermediate porous layer is less than the average pore size of the porous substrate.

14. The reactor or process of any of claims 1 - 13 wherein the gas separation module further comprises a layer of ceramic over the porous substrate and underlying the inter¬ mediate porous layer.

15. The reactor or process of any of claims 1 - 14 wherein the porous substrate of the gas separation module is oxidized.

16. The reactor or process of any of claims 1 - 15 wherein the surface of the porous sub¬ strate underlying the intermediate porous layer is seeded with nuclei of a hydrogen- selective material.

17. The reactor of claim 1 wherein the reactor is a steam reforming reactor and the cata¬ lyst bed is steam reforming catalyst bed.

18. The reactor of claim 1 wherein the reactor is a dehydrogenation reactor and the cata¬ lyst bed is a dehydrogenation catalyst bed.

19. An integrated steam reforming reactor-hydrogen fuel cell comprising the reactor of claim 1 wherein the product stream containing hydrogen is delivered from the reactor to an anode compartment of a hydrogen fuel cell and the byproduct stream from the reactor is delivered to a cathode compartment of the hydrogen fuel cell.