The present invention relates to reactors that allow chemical reactions to take place in very small space while providing effective mass and heat transport. The reactors can, for example, be used for synthesis reactions, such as synthesis of methanol from hydrogen and carbon monoxide, or the synthesis of hydrogen peroxide from hydrogen and oxygen. Other exemplary reactions include the reforming reaction of hydrocarbon to hydrogen and carbon oxides. The reactors can be suitable for use in conjunction with fuel cells. The invention also relates to methods for making such reactors.
Most fuel cells have to use hydrogen gas as the fuel. However, often hydrocarbon fuels, such as natural gas, gasoline, propane or diesel are more readily available. Therefore, fuel cell technology often utilizes reforming reactions to extract hydrogen gas from hydrocarbons.
There are several ways to reform hydrocarbon fuels to hydrogen, such as steam reforming, partial oxidization reforming and auto-thermal reforming process. These reactions are catalytically take place in a reactor (fuel processor) in elevated temperature (normally in the 200-1000° C. range). In general, fuel processors should meet following criteria: 1) low cost, 2) efficient heat exchange, and 3) suitability for mass fabrication. To decrease the expensive due to catalyst loading, workers seek to increase catalytic efficiency. Fuel reforming reactions involve a significant amount of heat transfer, needed for example to effectively deliver heat to reaction sites (e.g., steam reforming), or to transport heat away from reaction sites (e.g., partial oxidization reforming). Cost effective processes to make reactors that effectively use catalyst and have effective heat transfer properties are needed.
In one embodiment, the invention relates to a stacked reactor comprising: three or more metal layers; two or more catalyst layers sandwiched between the metal layers wherein:
Provided in another embodiment is a method of manufacturing a stacked reactor comprising: providing sheets of shaped material, the shaping having fluid-handling structures adapted to provide channels having depth and width dimensions independently from 10 to 2,000 microns; applying catalyst to the fluid-handling structures; stacking the fluid-handling sheets and alternating metal sheets; and sealing the periphery of the stack by annealing sealant at the periphery to the stacked metal sheets.
Provided in another embodiment is a method of manufacturing a stacked reactor comprising providing sheets of shaped metal, the shaping providing 40% or more surface area than would a flat surface; applying catalyst to shaped surfaces of the metal sheets; stacking the metal sheets; and sealing the periphery of the stack by annealing sealant at the periphery to the stacked metal sheets.
A stacked reactor 250 with alternating feed and drain patterns is illustrated in perspective view
Typically in each fluid-handling layer there is an area in which the ESAR is formed, and an area along the perimeter used to bond the reactor stack together and provide reactant/products input/output channels and/or manifolds. Thin coatings on the structure-forming material ESAR (the coatings used for example to modify the surface properties of the area) can be applied by screen-printing, spraying, painting, and the like. Catalyst materials can be applied on the ESAR by physical processes known in the art such as vacuum deposition, or chemical process, such as sol-gel. Catalyst can be applied either before, or after the reactor stack is assembled. Catalyst can be applied onto or in a porous support such as alumina. Where catalyst is applied to a metal surface, typically a relatively thin interface layer is applied to aid in the bonding of catalyst or bonding of the porous support for catalyst.
When channels are used to form the ESAR, the channels can be a number of shapes. For example, straight channels would be formed using a corrugated layers as illustrated in
By use of relatively narrow channels or other fluid flow pathways, the interaction of reactant (from a fluid such as a gas or liquid) with catalyst is increased, thereby increasing catalytic efficiency. By keeping the channels straight, or smoothly caved, backpressure is minimized. The depth and/or width of the channels or other fluid flow pathways is, for example, 10 to 2,000 microns. The width is the maximum width across the channels horizontally, using the point-of-view illustrated in
The length of the channels or other fluid flow pathways depends on the reactions involved, capacity needs, manufacturing convenience, and the like. Typical lengths can be from 0.5 cm to several meters. For example, the length can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 50 cm or more.
The channels or other fluid flow pathways can be formed by embossing, stamping, rolling, and the likes. The embossing (or other forming process) of the fluid-handling layers 10 could traverse the thickness of the fluid-handling layers, forming channels that, if applied to this embodiment, would contact the metal layers 20 on two sides. The illustrated embodiment in
The thickness of the material used to form fluid-handling layers (in certain embodiments) is, for example, 10 to 2,000 microns. In certain embodiments, the range of the thickness is from one of the following lower endpoints (inclusive) to one of the following upper endpoints (inclusive). The lower endpoints are 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800 and 1,900 microns (μm). The upper endpoints are 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800, 1,900 and 2,000 microns. For example, the thickness can be from 100 to 400 microns.
The fluid-handling layers can have structures such as channels formed on both sides, as illustrated in
As illustrated by the layer shown in
By “maze” of channels is meant a structure that (i) provides 40% or more surface area than would provided by hypothetical flat surfaces sandwiching the ESAR region of the fluid handling layer and (ii) provides that the majority of fluid flowing through the fluid handling layer must take a nonlinear or non-smoothly curving path. In certain embodiments, the internal surfaces of the ESAR provide 40% or more, or 45% or more, or 50% or more, or 60% or more, or 100% or more, or 200% or more, or 400% or more, or 1000% or more, surface area than would provided by hypothetical flat surfaces sandwiching the ESAR region of the fluid handling layer.
Where the ESAR is formed by shaped metal layers coated with ceramic interface, the depth is the average separation from ceramic interface surface to ceramic interface surface, and width is not a descriptive parameter.
In certain embodiments, enhanced contact between a fluid in the reactor and the sides of the channels are obtained, for example, (i) with smaller channels having the depths and widths recited above or (ii) by use of a sinusoidal-like flow pathway.
Useful materials for forming channels (and manifolds and seals) include, for example, rubber, plastic, ceramic (including glass), and the like. The material can favorably have a coefficient of expansion similar to that of the metal layers. One useful such material is the ceramic green tape available for tape cast processes. The channels can be formed by embossing, stamping and rolling processes, and the like. The green tape can be laminated (such as after channel forming) to the metal plates using Low-Temperature Co-fired Ceramic-on-Metal technology (LTCC-M), such as described in U.S. Pat. No. 5,581,876, U.S. Pat. No. 5,725,808, U.S. Pat. No. 5,747,931 or U.S. Pat. No. 6,140,795.
It should be recognized that by forming the fluid-handling layers of sub-layers and annealing the sub-layers into a fluid-handling layer, more complex structures for the ESAR can be obtained. Such more complicated structures can be used, for example, to improve the flow field.
In certain embodiments the fluid accessible regions of the ESARs can have good thermal connection with one or both of the sandwiching metal layers. For example, the metal layers may be insulated from these fluid accessible regions by less thermally conductive material that is, for example, 10 microns or less thick, 5 microns or less thick, 4 microns or less thick, 3 microns or less thick or 2 microns or less thick. Porous support for catalyst is not included in the measurement of such thickness.
One process for assembling a reactor of the invention is:
In one embodiment illustrated in
Sealant 612 confines reactants in the channel-area. The top row of channels 611, between the top two metal layers 620, are shaded. At the ends of the channels, the shaping of the metal layer can flatten or otherwise be appropriately shaped, creating a manifold for applying the reactants to the corresponding row of channels. Sealant 612 can be used to shape the plumbing of the manifolds, as described above.
In a given row of channels, sealing between the channels is typically not crucial. If needed, such internal sealing can be achieved, for example, by applying a thin layer of sealant to the metal layers, uniformly or at contact regions, and thereby providing internal sealant that seals as the sealant 612 is being sealed.
In another embodiment, reactor 750 (
In another embodiment, reactor 850 (
The metal plates can be, for example, from 5 to 1,000 microns thick. In certain embodiments, the range of the plate thickness is from one of the following lower endpoints (inclusive) to one of the following upper endpoints (inclusive). The lower endpoints are 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800 and 900 microns (μm). The upper endpoints are 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900 and 1,000 microns. For example, the thickness can be from 10 to 100 microns.
Useful metals for the metal plates include, for example, stainless steel, titanium, Kovar, other alloys and the like, with the metal selected for stability in the reactor environment. The metal plates can also be coated (or cladded) with a second metal or ceramic for better thermal conductivity or chemical stability. The metal can in many instances be stainless steel.
Sealant/bonding material can favorably have a coefficient of expansion similar to that of the metal layers. Materials include plastic, ceramic (including glass ceramic), metal, and the like. For the method of manufacturing wherein the catalyst is applied prior to sealing, the sealing method should be one that utilizes a temperature (and time of temperature treatment) that is tolerated by the catalyst. One method, well suited for use with glass ceramic, is LTCC-M. Other methods include, for example, welding, hot pressing. The sealing is favorably at a temperature from 200° C. to 1,000° C. (e.g., from 50° C. to 1000° C. above the anticipated operating temperature of the highest temperature reaction for which the reactor is designed). In certain embodiments, the range of temperature for sealing is from one of the following lower endpoints (inclusive) to one of the following upper endpoints (inclusive). The lower endpoints are 200, 250, 300, 400, 500, 600, 700, 800 and 900° C. The upper endpoints are 250, 300, 400, 500, 600, 700, 800, 900 and 1,000° C.
In embodiments that corrugated metal, the separation gap between the metal plates (at the non-shaped boundaries) is, for example, 10 to 1,000 microns. In certain embodiments, the range of the thickness is from one of the following lower endpoints (inclusive) to one of the following upper endpoints (inclusive). The lower endpoints are 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800 and 900 microns (μm). The upper endpoints are 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900 and 1,000 microns. For example, the separation gap can be from 50 to 200 microns.
Catalysts can be selected based on the anticipated chemistry. Catalysts can be, for example, a precious metal, such as Pt, Pd, Ru, Rh, a non-precious metal, such as Ni, Co, Mn, Ti, Cr, V, or the alloys or compounds of the foregoing. Generally, a more controlled amount of catalyst will be applied to the channels if the application is done prior to enclosing the channels in the device. Coating methods include wash coating, Sol-gel, vacuum deposition, and the like. Coating methods such as wash coating can be applied after the device is put together.
A process for assembling a corrugated metal-containing reactor of the invention is:
CH4+H2O+Heat→H2+CO Eq. 1
The reforming gas is fed into the fuel cell to generate electricity. Then the depleted fuel is mixed with air and catalytically combusted in the exothermic reaction layers of the reactor.
H2+O2→H2O+Heat Eq. 2
and CO+O2→CO2+Heat Eq. 3
The heat generated from these exothermic reactions (Eq. 2, 3) transport through metal plates between adjacent layers to support the endothermic reaction (Eq. 1) in the adjacent layers.
Another design to incorporate a reactor into a fuel cell system is shown in
CH4+O2→H2+CO+Heat Eq. 4
The POX (mixture of H2 and CO) is then mixed with steam and fed into endothermic reaction layers of the reactor to catalyze an endothermic shift reaction to obtain clean H2 (without CO).
CO+H2O+Heat→H2+CO2 Eq. 5
The clean H2 is fed into fuel cell (such as a proton exchange membrane fuel cell, where clean H2 is needed) to generate electricity. The heat generated in POX reaction (Eq. 4) transports through metal plates to adjacent shift reaction (Eq. 5) layers.
In another embodiment, reactor 350 has integrated heat exchange layers. As shown in
In some embodiments, reactor is built with a preliminary heat exchanger such as a fluid pre-heater. As shown in
In other embodiments, heating elements are incorporated to provide heat (or additional heat). For example, heating elements 442 can be incorporated between two fluid-handling sub-layers 410A and 410B, as illustrated in
Where a number in a given figure for a given embodiment is not individually described, that number corresponds to element(s) identified by the same last two digits for another embodiment. Hence, element 420 is a metal layer as in the first illustrated embodiment (for metal layer 20).
Definitions
The following terms shall have, for the purposes of this application, the respective meanings set forth below.
Not Significantly Degrade the Catalyst
A temperature, in conjunction with the time of its application, does not significantly degrade a catalyst if 80% of catalytic capacity remains.
Temperature
The temperature of a sealing operation is the temperature of an oven in which the sealing operation occurs. The individual structures of the device may or may not achieve this temperature during the sealing operation.
Publications and references, including but not limited to patents and patent applications, cited in this specification are herein incorporated by reference in their entirety in the entire portion cited as if each individual publication or reference were specifically and individually indicated to be incorporated by reference herein as being fully set forth. Any patent application to which this application claims priority is also incorporated by reference herein in the manner described above for publications and references.
While this invention has been described with an emphasis upon preferred embodiments, it will be obvious to those of ordinary skill in the art that variations in the preferred devices and methods may be used and that it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the claims that follow.