Abstract:
A method is provided for placing high surface area catalyst material ( 320 ) within ceramic micro-reactors. The method comprises forming a first cavity ( 114 ) in a first green sheet ( 112 ) and disposing a high surface area catalyst material ( 320 ) within the first cavity ( 114 ). The first green sheet ( 112 ) is placed adjacent to a second green sheet  118  wherein the first cavity is surrounded by the first and second green sheets. At least one input channel ( 316 ) and one output channel ( 317 ) is provided to the catalyst material before the ceramic micro-reactor is fired.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to ceramic micro-reactors and more particularly to a method of placing catalyst material within the ceramic micro-reactors. 
       BACKGROUND OF THE INVENTION 
       [0002]    intentionally blank 
         [0003]    Fuel reformers have been developed for use in conjunction with various types of systems, e.g., fuel cell devices, but they are typically cumbersome and complex systems consisting of several discrete sections connected together with gas plumbing and hardware to produce hydrogen gas, and are thus not optimal for power source applications with high production volume. Recently fuel reformers have been developed utilizing ceramic monolithic structures in which the miniaturization of the reformer can be achieved. Utilizing multilayer laminated ceramic technology, ceramic components and systems are now being developed for use in microfluidic chemical processing and energy generation systems. Traditionally, multilayer ceramic structures have been used primarily for constructing “3D” circuit boards with a high degree of electronic circuitry or components embedded or integrated into the ceramic. These monolithic ceramic structures formed also have the useful properties of being relatively inert, stable to chemical reactions, and capable of tolerating high temperatures. Additionally, the ceramic materials used to form components or devices, including channeled configurations, are excellent candidates for catalyst supports and so are compatible for use in microreactor devices. An exemplary application being the generation of hydrogen for use in conjunction with fuel cell for power generation. 
         [0004]    During steam reforming, a mixture of hydrocarbon fuel and water is catalytically converted, with the application of heat, to a hydrogen enriched fuel gas for use with fuel cells. Typically, a steam reformer is endothermically operated at an elevated temperature, for example, greater than 200° C., thereby requiring a heat source to ensure the reforming reaction is maintained in its optimal operating temperature. Common means for generating these elevated temperatures has been found using conventional electrical heaters and chemical reactors (combustors) that are physically or thermally linked to the reformation reactor. 
         [0005]    Like most heterogeneous endothermic reactions, steam reformation reaction rates are kinetically limited and thus require high surface area catalysts in order to provide practical rates of hydrogen production. However, since the reaction takes place at elevated temperatures, the overall efficiency of the reformation reaction is, to a large degree, dependent on the heat lost from the reformer to the surroundings while the reaction is taking place. To minimize this heat loss, it is advantageous to construct a reformation reactor with a small volume to minimize the surface area through which heat is lost to the surroundings. So, while the nature of the steam reformation reaction requires high surface area, this must be done in a minimum amount of volume. Thus, the optimal catalyst for this class of reactions is one with very high surface areas contained internally within a very porous structure and the optimal reactor design is one that minimizes external surface area (and thus, system volume) while still maintaining a reasonably low pressure drop. Practically this means that the porous reformation catalyst should occupy as much of the internal reactor volume as possible by minimizing volume for plenums, heat transfer conduits, containment, and, if a wall-coated design, fluid channels down the reactor channel(s) Furthermore, because highly porous catalysts tend to have relatively low thermal conductivity, it is usually optimal for the steam reformation reactor design to minimize thermal transfer lengths between the heat source, such as a combustor, and the bulk of the reformation catalyst (the heat sink during operation). In practice, this often means constructing channels or chambers within the reformation reactor to be on the order of 1 mm or even smaller in at least 1 dimension. Commonly this type of design is often referred to as a “micro-reactor” even though external dimensions of the reactor may be much. 
         [0006]    Traditional filling of a ceramic-based reactor with high-surface area porous catalyst has been done after the firing (sintering) of the ceramic. Typically this is done by one of three methods: 1) catalyst pellets or particles are sucked, blown, shaken or simply dropped into the reactor (resulting in a packed-bed type reactor); 2) a catalyst paste is vacuumed or pushed into the reactor after which the reactor is heated to dry the paste and/or to burn out pore formers and/or to activate binders (resulting in packed bed or porous fixed bed type reactor); or 3) catalyst slurry is put into the reactor followed by a high velocity gas purge that blows out the slurry from the center areas of the reactor followed by heating to dry the catalyst and/or activate binders (resulting in a wall-coated type reactor). Unfortunately, all of these approaches have draw backs. First and foremost is that post-fire filling of any kind involves one or more manufacturing steps that must be done after the reactor housing is formed and thus it is difficult to have full control over how optimally the catalyst is formed and located. Second, post-fire filled reactor designs often must incorporate compromises that lower overall effectiveness of the reactor in order to accommodate the post-fire filling process, e.g., extra plenums may need to be added or extra inlet/outlet added for filling that must then be capped before operation. The post-fire slurry process has the additional drawback in that the fluid mechanics for blowing out the excess slurry to form a central fluid channel results in a smaller and smaller catalyst volume fraction as the dimensions of the reactor channel are reduced. Put another way, the thickness of the resulting catalyst layer is limited by the flow dynamics of the slurry-coating process, thus possibly limiting the reactor&#39;s catalyst volume fraction below an optimal level. 
         [0007]    Accordingly, it is desirable to provide an improved method of placing catalyst material within ceramic micro-reactors. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0009]      FIG. 1  is a simplified top view of a first portion of a first exemplary embodiment of a micro-reactor; 
           [0010]      FIG. 2  is a simplified side view taken along line  2 - 2  of  FIG. 1 ; 
           [0011]      FIG. 3  is a simplified top view of a second portion of the first exemplary embodiment; 
           [0012]      FIG. 4  is a simplified side view taken along line  4 - 2  of  FIG. 3 ; 
           [0013]      FIG. 5  is a simplified side view of the first exemplary embodiment, including the first and second portion; 
           [0014]      FIG. 6  is a simplified sectional view of a fuel processor including a chemical combustion heater and a reactor for reforming methanol to hydrogen, both of which may be fabricated using the exemplary embodiments, and an integrated fuel cell stack; 
           [0015]      FIG. 7  is a schematic diagram of a fuel cell system including micro-reactors in accordance with the exemplary embodiments integrated with a fuel reformer system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
         [0017]    A process is described herein that allows for integrating a high surface area supported catalyst into a ceramic micro-reactor without significantly changing the processing steps and without additional post-fire processing, thereby allowing for more optimal catalyst placement and loading, lower costs and reduced scrap. This process can form reactor channels with thick high surface area, e.g., non-sintering support, catalyst layers, e.g. greater than 50 micrometer, and high volume fraction of catalyst, e.g., greater than sixty percent within the reactor cavity. 
         [0018]    The process comprises applying high surface area catalyst layers to a green-state ceramic tape, for example, by screen printing or stencil filling techniques. After printing, the ceramic tapes (with metallization, if needed) are laminated together and then fired, thereby forming a single unit. No post-processing is required for catalyst loading. 
         [0019]    An important use of this technology is in portable power applications: specifically, fuel processors (for hydrogen generation). In the fuel processor, the endothermic reformation reaction can effectively utilize a much thicker wall-coated catalyst layer than can be utilized by corresponding heating reaction in the adjacent combustor. For portable applications, total reactor volume is critical (smaller is better) so there is a need for a mass-manufacturable technique for relatively thick wall-coated catalyst layer application that is not limited by the fluid-dynamics inherent in the traditional slurry-coated technique. 
         [0020]    The micro-reactor manufactured in accordance with the exemplary embodiments is anticipated for use in, for example, a fuel processor, an integrated reactor system that includes one or more chemical combustion heater(s), one or more reformation reactors, and possibly additional reactors (such as a water-gas-shift reactor or a preferential oxidizer or methanation reactor) all of which may be fabricated with the exemplary embodiments. The chemical combustion heater is thermally coupled to endothermic reaction zones within the fuel processor. The micro-reactor is formed utilizing multilayer ceramic technology in which thin ceramic layers are assembled then sintered to provide for miniature dimensions in which the encapsulated catalyst(s) are utilized. 
         [0021]    Referring to  FIGS. 1 and 2  and in accordance with a first exemplary embodiment, a first green sheet layer  112  is cut to define opening  114  and channels  116 , and  117  and is then positioned on a second green sheet layer  118  to form a structure  100 . The first green sheet layer  112  may be formed by cutting a green ceramic sheet using a variety of methods including mechanical cutting or punching, laser or other high energy beam drilling, or simply casting or screen printing the green ceramic layer with the holes already formed. Alternatively structure  100  could be made by embossing or ablating a green ceramic layer or by injection molding or casting or some combination there of. Alternatively, structure  100  could be made by a printing or rapid prototyping technique in which a ceramic paste is printed, then cured, and then added to by printing and curing additional layers. This procedure is repeated ( FIGS. 3 and 4 ) for third green sheet layer  312  to define opening  314  and channels  316  and  317  including placement over a fourth green sheet  318  to form a structure  300 . The green sheet layers  112 ,  118 ,  312 ,  318  may comprise any desired thickness, but typically are cut in thicknesses of 50, 125, or 250 micrometers. 
         [0022]    A catalyst material  320  is dispensed within the openings  114  and  314 , preferably by an ink jet process to a desired thickness; however, other processes such as screen printing or stencil filling techniques could be used. 
         [0023]    Referring to  FIG. 4 , another green sheet layer  412  is cut to define the opening  414 . The structure  300  is flipped ( FIGS. 5 and 6 ) and laminated on one side of the green sheet layer  412  and the structure  100  is laminated on an opposed side of the green sheet layer  412 , wherein the first and third green sheet layers  112 ,  312  are aligned to one another so the catalyst material  320  within openings  114  and  314  are aligned with one end of opening  414 , and channels  116  and  316  are aligned with the other end of the opening  414 . Since the catalyst material  320  was printed only within the openings  114 ,  314 , a gap  502  is defined by the opening  414  not occupied by the catalyst material  118 ,  318 . Channels  116 ,  316  and channels  117 ,  317  provide an inlet and an outlet, respectively, to the gap  502 , and therefore to the catalyst material  420 . 
         [0024]    Catalyst layers  320  formed using this process are typically between 50 and 1000 micrometers thick, however one of the significant advantages of this technique is that it allows construction of catalyst layers of any desired thickness. Furthermore, this pre-fired (green state) catalyst filling technique allows for the precise placement of the catalyst to ensure optimal reactor performance and does not require any additional inlets or outlets or flow channels that are sometimes required with post-fire catalyst filling techniques. 
         [0025]    Referring now to  FIG. 7 , illustrated is a fuel processor  740  according to the present invention, including a plurality of microfluidic channels as well as a reformation reactor, and a chemical combustion heater, either of which could be fabricated according to any of the previously disclosed embodiments of the present invention. Fuel processor system  740  is comprised of a three-dimensional multilayer ceramic structure  742 . Ceramic structure  742  is formed utilizing multilayer laminate ceramic technology. Structure  742  is typically formed in component parts which are then sintered in such a way as to provide for a monolithic housing. Ceramic structure  742  has defined therein a fuel processor, generally referenced  744 . Fuel processor  744  includes a reformation-reaction zone, or fuel reformer  746 , a vaporization chamber, or vaporization zone  748 , and an integrated chemical combustion heater,  750 . It should be understood that the high surface area catalyst(s) within the fuel reformer  746  and/or the chemical combustion heater  750  could be formed according to any of the previously disclosed embodiments herein. In addition, included as a part of fuel processor  744 , is a waste heat recovery zone  752 , and a fuel cell stack  754 . 
         [0026]    Ceramic structure  742  further includes at least one fuel inlet ceramic cavity  756  in fluidic communication with fuel vaporizer  748  and a liquid fuel source. At least one fuel input inlet  758  is formed to provide for fluidic communication between a fuel source  760 , and combustion heater  750 . It should be understood that anticipated by this disclosure is a single fuel tank that is in fluidic communication with both fuel vaporizer  748  and chemical combustion heater  750 . 
         [0027]    During operation of the fuel processor  740 , fuel  757  enters fuel vaporizer  748  through a ceramic cavity  756  and is vaporized with the vaporous fuel exiting vaporizer  748  through output  762  which is in fluidic communication with fuel reformer  746 . Fuel inlet  758  provides for the input of fuel to chemical combustion heater  750 . An air inlet  764  provides for the input of air to chemical combustion heater  750  and to waste heat recovery zone  752 . Chemical combustion heater  750  allows for complete air oxidation of fuel input  758  and subsequent dissipation of heat through structure  742  and more specifically, to fuel reformer  746  and fuel vaporizer  748 . 
         [0028]    Fuel  757  entering fuel vaporizer  748  is vaporized and the resultant vaporous methanol and water enters the reaction zone, or more specifically fuel reformer,  746  where it is converted to hydrogen enriched gas. There is provided a hydrogen enriched gas outlet channel  766  from fuel reformer  746  that is in fluidic communication with an inlet to fuel cell stack  754 , and more particularly to a fuel cell anode  755 . Fuel cell anode  755  provides for depletion of hydrogen from the hydrogen enriched gas mixture. This hydrogen depleted hydrogen enriched gas mixture exits fuel cell stack  754 , and more particularly anode  755  through a fluidic communication  768  and is input to an inlet of chemical combustion heater  750 . Chemical combustion heater  750  also oxidizes portions of this gas mixture to generate heat and provides for any uncombusted materials present, such as remaining hydrogen and carbon monoxide, to undergo air oxidation to water and carbon dioxide, and these as well nitrogen from air, are then vented through an outlet  772  away from structure  742  into the atmosphere. 
         [0029]    Efficient thermal insulators  774  and  776  are positioned around fuel processor  744 , under fuel vaporizer zone  748 , and above fuel cell stack  754  to keep outer temperatures low for packaging and also to keep heat generated within the device localized to the fuel processor  744 . As illustrated in  FIG. 7 , in this particular example, high temperature fuel cell stack  754  is integrated with fuel processor  744 . This particular fuel cell design allows for the operation of the fuel cell stack at a temperature ranging from 140-230° C., with a preferred temperature of 170° C. Fuel vaporizer zone  748  operates at a temperature ranging from 120-230° C., with a preferred temperature of 180° C. and fuel reformer  746  operates at a temperature ranging from 180-300° C., with a preferred temperature of 250° C. Additionally, in this particular embodiment of fuel processor system  740 , included is a top cap  778 . 
         [0030]    Finally, it is anticipated by this disclosure that although illustrated in  FIG. 7  is the integration of fuel cell stack  754  with processor  744 , a design in which a fuel cell is not integrated with fuel processor  744  is additionally anticipated. Further information on a reformed hydrogen fuel system device of this type can be found in U.S. patent application Ser. No. 09/649,528, entitled “HYDROGEN GENERATOR UTILIZING CERAMIC TECHNOLOGY”, filed Aug. 28, 2000, assigned to the same assignee. When fuel cell stack  754  is integrated with fuel reformer  746 , advantage can be taken of the heat of the substrate to operate high temperature fuel cell stack  754 . For high power applications, it is convenient to design a separate fuel cell stack  754  and a fuel processor unit  744  and couple them to supply the hydrogen enriched fuel for the fuel cell. In such instances, when a fuel cell stack is not integrated with the fuel processor, and the fuel processor is designed as a stand alone device, external connection can be made to connect the stand alone fuel processor to a traditional fuel cell stack for higher power applications. 
         [0031]    Illustrated in  FIG. 8  in a simplified block diagram  880 , is the fuel processor system  740  of  FIG. 7 , including a multilayer ceramic structure, a fuel processor, a fuel cell stack, insulators, and fuels, similar to previously described multilayer ceramic structure  742  having a fuel processor  744 , fuel cell stack  754 , insulators  774  and  776 , and fuels  754  and  760  of device  740 . As illustrated, a fuel cartridge, generally including an optional pump mechanism  882  supplies water and methanol into a steam reformer  884 , generally similar to fuel reformer  746  of  FIG. 7  and a chemical combustion heater  886 , generally similar to chemical combustion heater  750  of  FIG. 7 . An air supply  888  provides for the supplying of air to heater  886  and a fuel cell stack  892 . Heater  886  is monitored by a temperature sensor, including control circuitry,  890  thereby providing for steam reformer  884  to operate at a temperature of approximately 230° C. Operation of steam reformer  884  at this temperature allows for the reforming of input fuel  882  into a reformed gas mixture, generally referred to as the hydrogen enriched gas. More particularly, in the presence of a catalyst, such as copper oxide, zinc oxide, or copper zinc oxide, the fuel solution  882  is reformed into hydrogen, carbon dioxide, and some carbon monoxide. Steam reformer  884  operates in conjunction with an optional carbon monoxide cleanup (not shown), that in the presence of a preferential oxidation catalyst and air (or 0 2 ), reforms a large percentage of the present carbon monoxide into carbon dioxide. This reformed gas mixture supplies fuel through a fuel output to fuel cell  892 , generally similar to fuel cell stack  754  of  FIG. 7 . Fuel cell  892  generates electricity  894  and is illustrated in this particular example as providing energy to a DC-DC converter  896 , thereby supplying power to a cell phone  898  and/or battery  800 , for example. 
         [0032]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.