Patent Application
20090036303
The present invention generally relates to ceramic micro-reactors and more particularly to a method of placing catalyst material within the ceramic micro-reactors.
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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.
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.
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.
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's catalyst volume fraction below an optimal level.
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.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
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.
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.
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.
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.
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.
Referring to
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.
Referring to
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.
Referring now to
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.
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.
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.
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
Finally, it is anticipated by this disclosure that although illustrated in
Illustrated in
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.
