Enhanced microchannel or mesochannel devices and methods of additively manufacturing the same

Abstract

To provide approaches for reducing the number of manufacturing steps, decreasing the number of parts, and / or simplifying the assembly process.SOLUTION: Chemical processors are configured to reduce mass, work in conjunction with solar concentrators, and / or house porous inserts in microchannel or mesochannel devices made by additive manufacturing. Methods of making chemical processors containing porous inserts by additive manufacturing are also disclosed.SELECTED DRAWING: None

Description

Technical Field

[0001] Declaration of Government Support This invention was made with government support under Contract DE-AC0576RL01830 awarded by the U.S. Department of Energy and under Cooperative Research and Development Agreement (CRADA No. 387) operated for the United States Department of Energy by STARS Technology Corporation, Southern California Gas Company, Oregon State University, and Pacific Northwest National Laboratory. The government has certain rights in this invention.

[0002] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 62 / 688,217, filed on June 21, 2018.

[0003] In a broader aspect of the present invention, the disclosure relates to improved chemical processors, preferably microchannel devices or mesochannel devices, and additive manufacturing methods thereof. In a more detailed aspect, the present invention relates to chemical processors associated with solar thermal concentrators.

Background Art

[0004] Additive manufacturing (AM) is a novel method of "printing" devices by locally solidifying powder materials into solids. The flexibility in the design of the structure of this device provides new tools for constructing complex structures, although within certain process limitations. Originally developed for plastics, AM has been adapted for metals. Also, the list of metals that can be "printed" continues to grow and now includes high-temperature alloys such as Inconel and Haynes alloys. Metal additive manufacturing is referred to as selective laser melting (SLM) or direct metal laser sintering (DMLS). The present invention is directed to a type of device, a chemical reactor, and more particularly to a chemical reactor disposed at the focus of a solar thermal concentrator that converts solar heat into chemical energy through an endothermic chemical reaction. Of particular interest is the steam reforming of methane. This chemical reaction reacts water H2O and methane CH4 to generate hydrogen H2, carbon monoxide CO, and carbon dioxide CO2. Alternative endothermic reactions include the reverse water gas shift reaction that converts H2 and CO2 to H2O and CO, and the cracking (dehydrogenation reaction) of alkanes.

[0005] Reactors for exothermic reactions can also be manufactured using AM for reactions such as the water gas shift reaction, ammonia synthesis from H2 and N2, the Sabatier process reaction, methanol synthesis, and combustion reactions, such that a hybrid reactor body capable of accommodating both endothermic and exothermic reactions is possible.

[0006] An important difference between AM and most conventional fabrication processes is the utilization of materials, which differs significantly between "additive" and "subtractive" methods. In the "subtractive" method, a solid piece of material is machined to remove material to provide the structure of the final part. Methods such as machining or processing by photochemical reactions result in a significant portion of the initial material being wasted, in contrast to methods such as extrusion, punching, and stamping that can increase the material utilization rate. The cost of materials for AM parts is proportional to the total mass of the parts.

[0007] Figure 1 shows a comparison of the manufacturing costs estimated at 1000 units per year for the design of a TRL 6 Haynes 230 STARS reactor using conventional "subtractive" machining and DMLS. These costs are obtained from a bottom-up model that is not evaluated as a whole and is derived over time as the cost components change. For this reason, these costs are more useful than actual ones. The lower cost of DMLS is largely due to lower material costs, despite the high cost per pound of DMLS powder. Conventional machining costs are also high for superalloys. Figure 1 shows the motivation for the present invention, which is to reduce the cost of DMLS chemical reactors. The first cost-increasing factor to be addressed is the mass of the reactor. Reducing the mass of the reactor has the advantages of both reducing the cost of the powder (material cost) and shortening the manufacturing time. Shortening the manufacturing time increases the throughput and reduces the cost of the tool per part (the amortized capital cost of the DMLS machine). Together, the material cost and the tool cost account for 63% of the cost of the DMLS produced in Figure 1.

[0008] The second cost-increasing factor is the number of parts and the number of assembly steps associated with inserting a catalyst structure into the reactor. One of our conventional reactor designs consists of three plates that are machined individually and then assembled together in a high-temperature diffusion brazing step after the catalyst foam structure is inserted into the channels. The laser cutting and diffusion brazing steps in Figure 1 further account for 28% of the manufacturing cost. The present invention includes approaches for reducing the number of manufacturing steps, reducing the number of parts, and / or simplifying the assembly process.

[0009] There are other potential benefits of the new reactor design regarding performance and service life. The outer wall of the reactor must be thick enough to withstand the internal pressure, and a thicker wall requires a greater temperature difference across the wall for the same heat flux. For endothermic reactions that receive heat through the reactor wall, such as heat from a solar concentrator, a greater temperature difference means a lower catalyst bed temperature to keep the reactor surface temperature below the metallurgical limits of the reactor. For endothermic reactions such as steam reforming of methane, a higher reaction temperature leads to a higher equilibrium conversion and faster kinetics. Making the reactor wall thinner not only saves on the structural materials and construction time for DMLS, but also allows the catalyst to become hotter and thus more active. This results in cost savings for the catalyst and a reduction in the reactor size. A thicker wall is also disadvantageous for the service life of the reactor. This is because the thermal stress increases due to both the increased temperature difference and the increased structural rigidity. Furthermore, DMLS allows for a more flexible design of 3D structures that can better tolerate thermal expansion, thereby reducing the internal stresses and low-cycle fatigue failure associated with daily or more frequent heating and cooling cycles of the structure during the operation of the solar cell.

Summary of the Invention

[0010] In a first aspect, the present invention relates to a solar power device comprising a solar heat concentrator having a concave shape and a dome-shaped chemical processor adapted to perform unit operations, the dome-shaped chemical processor being arranged in relation to the solar heat concentrator such that the convex surface of the dome-shaped chemical processor faces the concave surface of the solar heat concentrator, and the convex surface of the chemical processor comprising a tube or tubes for a fluid passage to or from a central area of the dome to an area around the dome. In some preferred embodiments, the device may include one or any combination of the following features. The convex surface of the dome-shaped chemical processor comprises a tube or tubes exposed on the surface of the dome. The convex surface of the dome-shaped chemical processor comprises a tube or tubes containing a methane reforming catalyst or a water gas shift catalyst. The convex surface of the dome-shaped chemical processor comprises a tube or tubes having a plurality of channels providing a radial fluid flow from a source inlet or source manifold near the central region of the dome to the outer edge of the dome and a radial fluid flow from the outer edge to a receiving manifold, the receiving manifold being located near the central region of the dome. The tube or tubes comprise a porous catalyst insert, preferably a methane reforming catalyst. The tube or tubes comprise two portions, a first portion and a second portion, separated by a non-porous heat conducting divider. The first portion comprises a catalyst and the outer side of the device comprises an opening in the divider such that flow from the first portion can pass to the second portion.

[0011] In another aspect, the present invention provides a chemical processor having a channel or channels for a unit process, comprising a first portion providing a radial fluid flow from a source manifold to an outer portion of the device, a second portion providing a radial fluid flow from the outer portion to a receiving manifold, wherein the source manifold and the receiving manifold are located near a central region of the device, and the first and second portions of each channel are separated by a non-porous thermally conductive divider, the first portion being provided with a catalyst, and the outer portion of the device being provided with an opening of the divider near the outer portion of the device, whereby the flow from the first portion can pass to the second portion. The chemical processor can have any of the features described throughout the detailed description and drawings herein.

[0012] In a further aspect, the present invention provides a microchannel or mesochannel device for a unit process, comprising a first plurality of microchannels or mesochannels providing a radial fluid flow from a source manifold to an outer portion of the device, a second plurality of channels providing a radial fluid flow from the outer portion to a receiving manifold, wherein the source manifold and the receiving manifold are located near a central region of the device, and further comprising a catalyst insert or inserts arranged around an outer periphery of the device, the direction of flow in the channels switching from a direction towards the outer portion to a direction away from the outer portion, and a ring arranged around an outer periphery of the device surrounding the catalyst insert or inserts, and a flow path in which the direction of flow in the channels switches from a direction towards the outer portion to a direction away from the outer portion. In some preferred embodiments, the catalyst insert is wedge-shaped. The device can have any of the features described throughout the description and drawings herein.

[0013] In another aspect, the present invention provides a chemical processor having a circular shape, comprising a tube or a plurality of tubes that provide a radial fluid flow from a source inlet or source manifold near the central region of the processor to the outer edge of the processor, wherein the tube or the first plurality of tubes are exposed on the surface of the device, thereby making the surface non-smooth, the tube or the plurality of tubes having a circular, oval, or elliptical cross-section, and the processor being configured for a unit process. The present invention also includes a reverse configuration, in which the source inlet or source manifold and the receiving manifold are disposed near the outer periphery of the device. In some preferred embodiments, the device may include one or any combination of the following features. It comprises a plurality of channels that provide a radial fluid flow from the outer edge to the receiving manifold, the receiving manifold being located near the central region of the device. The tubes and channels have an internal dimension of 1 cm or less. The tube or plurality of tubes, the plurality of channels, or both comprise branched channels that divide into two or more channels as they extend radially. The tube or plurality of tubes, the plurality of channels, or both comprise straight radial channels. The tube or plurality of tubes, the plurality of channels, or both comprise curved channels that extend from the central region to the outer edge. The tube or plurality of tubes comprise a porous insert incorporated within the tube or plurality of tubes. The porous insert comprises a catalytic material, an adsorbent material, or both. The porous insert comprises a porous metal support having a holeless metal film welded to the surface of the porous metal support. The porous insert comprises a metal, a polymer, or a metal oxide. The process has a domed structure. It further comprises a solar heat concentrator disposed to be a focus of the converged solar energy on the exposed surface. The tube or plurality of tubes have a gradient of thermal expansion coefficients, with the thermal expansion coefficient being low on the exposed surface of the tube or plurality of tubes.

[0014] The present invention also includes a method corresponding to performing one or more unit operations, including each use of the device. Preferably, the unit process is selected from the group consisting of exothermic chemical reactions, endothermic chemical reactions (preferably methane reforming), heat exchangers, chemical separation methods, and pyrolysis.

[0015] In a further aspect, the present invention provides a method for manufacturing a microchannel or mesochannel device, including forming a first portion of the channel layer by layer via an additive manufacturing process, embedding a porous insert within the first portion of the channel, covering the porous insert with a protective layer, and forming a second portion of the channel layer by layer over the first portion. In some preferred embodiments, the present invention includes one or more of the following features. The microchannel or mesochannel device is a differential temperature microchannel or mesochannel device. The protective layer comprises a sacrificial material that is removed after the step of forming the second portion of the channel layer by layer over the first portion. (The sacrificial material can be a material that melts at a temperature at least 100 °C (or at least 300 °C) below the melting point of the second portion.) The method includes laser welding the protective layer onto the porous insert. The additive manufacturing process includes directly sintering a metal with a laser. The porous insert comprises a catalyst material, an adsorbent material, or both. The porous insert is a metal, a polymer, or a metal oxide. The porous insert is formed by bonding a protective layer onto a porous metal support, then coating the porous metal support with a metal oxide and a nickel or noble metal to form a methane reforming catalyst, and then calcining before placing the insert within the channel.

[0016] The present invention also includes a method for manufacturing or modifying a chemical processor, including inserting a porous insert (preferably a catalyst) into the device and welding a plug or welding ring to seal the flow path at the outer periphery of the device.

[0017] Aspects of the present invention may also include placing a structure within a fluid channel to improve convective heat transfer and / or to improve the distribution of flow between channels. Generally, any of the aspects of the present invention can be varied according to any feature or combination of features provided in the detailed description of the invention.

[0018] In various embodiments, the advantages of the present invention can include reducing the mass of the device, improving heat transfer, improving durability and lifespan, promoting a more uniform heat profile, or varying and / or controlling the temperature of the reaction differently to achieve efficient operation.

[0019] The term As standard patent terminology, "comprising" means "including", and neither of these terms excludes the presence of additional elements or a plurality of elements. In alternative embodiments, the term "comprising" can be replaced with the more restrictive phrases "consisting essentially of" or "consisting of".

[0020] A "microchannel" is a channel that can have at least one inner diameter (dimension from wall to wall, excluding the catalyst) that is less than 1 mm, greater than 1 μm (preferably, 10 μm), and in some embodiments, from 50 μm to 500 μm. Preferably, the microchannel has a length of at least 1 cm, preferably at least 20 cm, and is within these dimensions. In some embodiments, it ranges from 5 cm to 100 cm in length, and in some embodiments, from 10 cm to 60 cm. A microchannel can also be defined by the presence of at least one inlet separate from at least one outlet. A microchannel is not just a channel through a zeolite or a porous material. The length of the microchannel corresponds to the direction of flow through the microchannel. The height and width of the microchannel are substantially perpendicular to the direction of flow through the channel. A mesochannel is defined similarly, except that it has an inner diameter from 1 mm to 1 cm. Usually, the device comprises a plurality of microchannels or mesochannels that share a common header and a common footer. However, some devices have a single header and a single footer. A microchannel device can have a plurality of headers and a plurality of footers. The volume of a channel or manifold depends on the internal space. The walls of the channel are not included in the calculation of the volume.

[0021] The microparticles relate to particles such as catalyst particles that fit within the microchannel or mesochannel. Preferably, the particles (if present) have a size of 2 mm or less (in the maximum dimension), and in some embodiments, 1 mm or less. The size of the particles can be measured by a sieve or a microscope or other suitable techniques. For relatively large particles, sieving is used. The microparticles can be a catalyst, an adsorbent, or an inert material.

[0022] The present invention also includes a method of performing unit operations within the apparatus described herein. "Unit operation" means a chemical reaction, evaporation, compression, chemical separation method, distillation, condensation, mixing, heating, or cooling. "Unit operation" does not simply mean the transfer of fluids, although transfer often occurs along with unit operations. In some preferred embodiments, the unit operation is not merely mixing.

[0023] A channel containing a catalyst is a reaction channel. More generally, a reaction channel is a channel in which a reaction occurs. The walls of the reaction channel are preferably formed of an iron-based alloy such as steel, or a Ni-, Co-, or Fe-based superalloy such as Haynes. The choice of material for the walls of the reaction channel may depend on the reaction for which the reactor is intended. In some embodiments, the walls of the reaction chamber are composed of stainless steel or Inconel® which are durable and have good heat conductivity. Usually, the walls of the reaction channel (usually a tube) are formed of a material that provides the main structural support for the microchannel device.

[0024] The heat exchange fluid may flow through a heat transfer channel (preferably a microchannel or a mesochannel) adjacent to the processing channel (preferably a reaction microchannel or a reaction mesochannel), and can be a gas, or a liquid, or a two-phase material. Also, in a preferred embodiment, the heat exchange fluid is the flow of the product used to recover the heat generated within the reaction channel.

[0025] "Tube" has its conventional meaning of an elongated member having a circular, rectangular with a pair of semi - circles at both ends (which is an example of an ellipse as shown in FIG. 8), or an oval cross - section. There are no corners either inside or outside, and thus no regions where stress concentrates. The wall thickness of the tube is preferably uniform and varies in the range of 10% or less, but may include internal separating walls (barriers) of different thicknesses that divide the interior of the tube into two or more channels. As shown in the illustration, there may be corners between the separating wall and the tube wall, but usually there is no large pressure difference on both sides of the internal separating wall.

[0026] An "exposed" tube has a surface exposed to the atmosphere. This tube is not covered by a plate, and the surface of the exposed tube is curved.

Brief Description of the Drawings

[0027]

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DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention includes devices, manufacturing methods, and processes involving devices formed using additive manufacturing processes. The manufacturing methods may include methods of incorporating a catalyst or other structure into the device as an external object, where they are formed using an additive manufacturing method. Alternatively, a porous or other high surface area structure can be constructed by an AM process during manufacturing and then activated after construction through a coating, impregnation, or removal process. Various structures that can be formed by additive manufacturing suitable as receivers of a parabolic dish type solar thermal concentrator are described.

[0029] There are several articles in the literature that describe devices formed by AM. For example, Gutmann et al., React. Chem. Eng., 2017, 2, 919-927, “Design and 3D printing of a stainless steel reactor for continuous difluoromethylations using fluoroform.”, Stark, AIChE Journal, (2018) 64(4): 1162-1173, “Manufactured Chemistry: Rethinking Unit Operation Design in the Age of Additive Manufacturing.”, Capel et al., Lab Chip, 2013, 13, 4583, “Design and additive manufacture for flow chemistry Article in Lab on a Chip.” Schalansky in US Patent Application No. 2015 / 0137412, entitled “Method of using additive materials for production of fluid flow channels”, describes several AM methods for forming fluid channels. The content of this published patent application is incorporated herein as if fully reproduced below. Several graded metal structures that can be manufactured by AM are described by Khodabakhshi et al. in “Dissimilar metals deposition by directed energy based on powder-fed laser manufacturing,” J. Manufacturing Processes 43 (2019) 83-97. In the present invention, the walls of the tube can be formed with graded properties such as thermal expansion. In a preferred embodiment, the side of the tube facing the solar light source has a lower coefficient of thermal expansion than the side of the tube facing away from the solar light source.The gradient may be continuous from the highest expansion coefficient at the bottom (away from the solar light source) to the lowest expansion coefficient at the top, or may be in 2, 3, or any selected number of regions. In some embodiments, the graded coefficient of thermal expansion may be only on the sides of the tubes that receive heat from the solar concentrator.

[0030] The present invention also includes a device adapted to receive incident solar radiation and use the energy absorbed for an endothermic process, including endothermic chemical reactions, heating of fluids, and separation processes. The general arrangement is a radial flow outward from a central manifold towards the outer edges of the plates and then back through a second set of channels to a second receiving manifold near the center before exiting the device.

[0031] The structure includes branched tubes. These branched tubes divide into two or more (preferably two) tubes as they extend radially to encourage coverage of all or most of the circular profile. The tubes can be straight or curved along the radius of the circle. The limit of the curved channel structure is a single coiled channel starting from the center and extending outwards towards the outer edge. The return channel can mimic the outward flow channel and allow the fluid to return along the same flow path through adjacent channels. Many alternative structures with various structures for the outward and return flows are expected to promote heat diffusion for a more uniform temperature and improved fluid mixing. The present invention includes a flat structure where the basic flow axis of the channel is in a plane, or a three-dimensional structure with channels curved out of the plane in the "z-axis" direction.

[0032] Some aspects of the present invention also include placing structures within fluid channels to improve convective heat transfer and / or to improve the distribution of flow between channels. Improved heat transfer structures include fins, fins with louvers, pins for increased heat transfer area, and structures for convective mixing of fluids.

[0033] Two-part assembly: Figure 2 shows an embodiment for reducing the assembly to two parts and for eliminating a high-temperature diffusion brazing step that requires a long cycle time in a furnace equipped with a ram press. Gradually heating and cooling the furnace, as well as the time at a temperature that enables bonding of the parts, can take days, leading to a relatively low production capacity. By constructing the reactor-receiver body as a single part using additive manufacturing, substantial material savings are achieved. Figure 2B shows an assembly of two parts of a chemical processor. In a first step, a chemical processor part 35 that includes channels can be formed by AM. Next, a catalyst piece (which may be of other shapes, such as a rectangular or the illustrated pie-shaped piece) 35 is then inserted into an opening around the outer edge as shown in Figure 2B, before closing the reactor by welding a sealing ring 34 in place. In another embodiment, most of the reactor-receiver body is constructed by additive manufacturing as shown in Figure 2B, but the channel openings are in the form of circular holes, such that these channel openings can be individually sealed, for example, with individual wedge-shaped plugs instead of a single welding ring for all channels. The channel ends can be sealed by welding with a welding ring as shown in Figure 2B after insertion of the catalyst. In some preferred embodiments, the welding ring is welded in place by rotary friction welding. In an alternative embodiment, the plug can be welded in place by the welding effect resulting from rotating the wedge-shaped plug, for example, when inserting a wedge-shaped plug into a similarly wedge-shaped hole. The welding ring can be welded in place by conventional welding or friction stir welding, such as in other examples of joining processes, i.e., laser welding or electron beam welding. In the completed device, thermal energy (such as photon collisions) enters the system through the walls 22 of the exposed channels or tubes. Figure 2A is a cross-sectional view showing the exposed wall 22, the catalyst insert 28, the channel plug 24 fixed in place by the joint 26, and the return channel 32. The chemical product flowing out from the catalyst insert 28 flows through the opening 30 into the return channel 32.In an alternative embodiment, a porous insert 28 (such as an absorbent) is used at the location of the catalyst insert 28.

[0034] One significant advantage of this design is the possibility of retrofitting the reactor by removing the ring or individual channel end caps to access and replace the catalyst pieces. This saves replacement costs over time, extends the service life of the reactor hardware, and facilitates recycling of the materials of the catalyst structure. The present invention includes a method of forming a processor, a method of retrofitting a processor, a method of a chemical device, and a method of performing unit operations within a device.

[0035] Cylindrical design: In some embodiments of the present invention, a tubular structure is utilized to take advantage of the inherent strength of a round tube against a flat wall. When a high pressure is applied to one side of a flat wall, a bending force is applied. This force usually has to be resisted by making the wall thicker or by adding supports or reinforcements. On the other hand, as shown in FIG. 3, a tensile stress called hoop stress is basically applied to the wall 82 (see FIG. 8) of a pressurized round tube. As a result, a round tube can have a much thinner wall than a flat wall when formed of the same strength material. Therefore, the AM design composed of a tubular channel instead of a rectangular channel with a flat wall has the potential for significant weight savings due to the thin wall. The inner diameter (or the largest internal dimension) of the tube is preferably in the range of 0.1 mm to 3 cm, preferably in the range of 1 mm to 1.0 cm. For example, a rectangular plate with a width of 0.4 inches (Haynes 230 at 982 °C) with a yield stress of 450 psi requires a thickness of 0.165 inches to withstand a pressure of 10 bar. Alternatively, the wall thickness of a tube with the same yield stress is only 0.065 inches to withstand a pressure of 10 bar. The AM method for branched tubes also enables smaller tubes. Starting with 10 tubes in the central header, the required wall thickness varies from 0.025 inches at the start of the tube length to 0.049 inches at the end of the tube length and continuously increases. Another advantage of AM is the ability to locally vary the wall thickness to optimize the weight. An extruded tube will have a constant diameter and wall thickness. An AM tube can have various diameters and wall thicknesses implemented in a branched tube design.

[0036] The advantages of a tubular geometry are pronounced when the outer wall of the tube is also the outer wall of the reactor and are reduced when the wall of the tube is not the outer wall. The outer wall of the reactor must be thick enough to withstand the internal pressure for reactors heated from the outside and / or endothermic reaction channels, and a thicker wall requires a greater temperature difference across the wall for the same heat flux. A greater temperature difference means a lower catalyst bed temperature to keep the surface temperature of the reactor below the metallurgical limits of the reactor. For endothermic reactions such as steam reforming of methane, a higher reaction temperature leads to a higher equilibrium conversion and faster kinetics. Making the reactor wall thinner not only saves on the materials and build time for the structure with respect to AM, but also allows the catalyst to be at a higher temperature and thus more active, thereby saving on the cost of the catalyst. A thicker wall is also disadvantageous for the service life of the reactor, as the thermal stresses increase due to both the increased temperature difference and the increased structural rigidity. Furthermore, DMLS allows for a more flexible design of 3D structures that can better accommodate thermal expansion, thereby reducing the internal stresses and low-cycle fatigue failure associated with daily or more frequent heating and cooling cycles of the structure during solar operation. These potential advantages of solar operation related to performance and service life are considered.

[0037] Another new innovation related to the cylindrical embodiment is the insertion of the catalyst structure into the reactor during additive construction. This not only provides additional design flexibility in that the design does not need to accommodate catalyst insertion after the parts are built, but also reduces the number of manufacturing steps. The sequence of steps is: 1) the reactor is partially manufactured by AM (preferably DMLS); 2) construction is stopped, the platen is raised, and powder is suctioned from the catalyst channels; 3) catalyst pieces are inserted into the catalyst channels; and 4) the AM process is restarted to complete the construction. Preferably, the top edge of the catalyst piece is smooth in one plane to accommodate the continuation of the AM build. By the steps of stopping construction, removing powder from the catalyst channels, and inserting the catalyst pieces, the cycle time of construction is increased instead of the post-construction steps that would otherwise be required to insert the catalyst and close the reactor.

[0038] Some embodiments of the novel innovations in the cylindrical design are described below.

[0039] Catalyst Structure: Multiple types of catalyst structures can be incorporated into the devices of the present invention. In some examples, a catalyst structure such as a porous foam or felt is inserted into the channels in one of the concepts described above. A powder or particulate catalyst medium can also be added as a dry medium or slurry. The active catalyst can be embedded in the structure when attaching the reinforcement using various methods including calcination, vapor deposition, and wash coating, or can be added after assembly is complete. Alternatively, a porous catalyst structure can be printed during construction by varying the process parameters. This partially solidifies the powder exiting the sintered high surface area porous medium. Alternatively, it can be added by constructing additional internal structures such as fins or pillars inside the channels that will be coated with the catalyst on the surface area. This also serves as an enlarged area for improving heat transfer.

[0040] The catalytic steam reforming of methane was prepared by first placing the protective layer 1202 on the catalyst insert structure 1204 (a form sheet of FeCrAlY). The protective sheet can be tack welded or laser welded to the porous structure 1204 to form a protected porous structure 1206. The porous structure can be changed to a methane reforming catalyst, for example, by washcoating the structure with a Rh catalyst on MgAl2O4 and then calcining at 500 °C to form a porous catalyst insert 1208. This process is shown in FIG. 12. The catalyst was placed in the channels and the channels were completed by AM. The testing of the device showed excellent methane reforming and hydrogen production without loss of operation after two cycles of use at a temperature of at least 750 °C.

[0041] It has been found that by overheating the cover after the DMLS process resumes, the cover is twisted so that it is not flat, and the cover becomes an obstacle to the powder diffusion bar, which will cause the process to fail. The laser also makes holes through the cover, causing damage to the cover and the insert under the cover, and allowing the powder to enter the cavity.

[0042] The solutions to these problems included using a laser (a DMLS laser in our tests) to tack weld the cover to the built structure. This is done after the structure and cover are inserted and before the powder is spread rearward over the part. Tests showed that the tack welding had to be controlled so that either the cover was held in place or the entire outer edge was stitch welded just enough to effectively seal the outer edge from the powder. Improved results were obtained by forming several passages around the outer edge to allow spot welding and cooling sufficiently before welding again in the same vicinity. Another solution is to vary the laser output and the powder layer thickness after the DMLS build process is resumed. This allows the AM structure to be built and resumed at the top of the insert and cover without damaging these parts.

[0043] When a complete reactor is formed by AM with the catalyst embedded, the catalyst cavities must be protected from the ingress of AM powder through the ends and the "tops". The ends must allow flow so that the catalyst chamber can be closed using a porous wall that allows flow. One of the porous walls is placed at the inlet end towards the central inlet manifold. The powder on its side may exit through the manifold. The second porous wall is located just at the end of the catalyst channels before the opening that leads to the return layer. A significant amount of powder in the outer header and return channels must exit outside the central header of the return channel. A further advantage of the porous walls is that they cause a pressure drop with respect to a good flow distribution within a multi-channel device, thus eliminating the need for orifices or other features to control (usually equalize) the flow through the multiple channels.

[0044] Another way to insert the catalyst structure and prevent substantial intrusion of the AM powder into the catalyst structure may be made possible by using a sacrificial material. By impregnating the catalyst structure with a solid material that can be removed after heating or reacting (to form a fluid), the use of porous walls and the "top" piece is eliminated. For example, a high molecular weight oil (such as paraffin) can fill the voids within the catalyst structure, and then the reactor, after the construction process is complete, is heated so that the molten or gaseous material is removed.

[0045] Tubes of constant radius that branch: Figure 4 shows a first embodiment of a cylindrical design in which a set of tubes extends radially outward from a central manifold. To completely cover the circular area, the tubes branch as this tube extends radially. In this particular embodiment, the diameter of the tube is constant, whereby the thickness of the reactor is constant across the area. The process of splitting the tube is shown in Figure 5. The tube starts with a round cross-section, immediately begins to branch, and as the branching is completed, it gradually unfolds into the cross-section of Figure 8. From this cross-section of Figure 8, as both tubes extend further out, both of these tubes begin to repeat the branching process.

[0046] Mathematically, the tube branches every time the distance from the center of the circle doubles. Figure 6 further shows how the tubes branch periodically.

[0047] In one embodiment of this concept, the inner wall is within the tube and divides the channel into two halves. These are not shown in Figures 4 through 6. The catalyst structure is to be inserted into one of the halves of the channel during the construction of the DMLS before the separation wall is constructed. The opposite side of the tube can be used for heat exchange, such as preheating the incoming reactants or recovering heat from the product stream with respect to the heat of the reaction within the catalyst structure.

[0048] In other embodiments, the catalyst structure is constructed within a tube, such as a sintered porous medium, wall, or pillar, that is coated with the catalyst after the construction of the DMLS is complete.

[0049] Branching, increasing radius tubes: Another embodiment of the tubular design is a tube with an increasing radius. Instead of gradually branching as the tube extends radially outward, the tube remains as is, its diameter increases, and then it divides into two tubes of half the diameter at a position at some radius from the center. Each of the two tubes increases in diameter as it extends radially until these two tubes also divide into two tubes. The minimum amount of wall material is used when the stress in the inner wall is kept constant at the allowable stress for that material. For the tube, the maximum stress is the following hoop stress in the assumed relationship for a thin wall. JPEG2025108498000001.jpg1737

[0050] Here, p is the design pressure, r is the radius of the tube, and t is the thickness of the tube wall. To maintain a constant wall stress while increasing the diameter of the tube, it is necessary to increase the wall thickness. Integrating Equation 1 over the length l of the tube increasing from diameter D1 to D2 gives the minimum wall volume for a given allowable stress σ. JPEG2025108498000002.jpg1461

[0051] The parameters incorporated into the branched tube structure are the radius of the central hole, the number of the first tubes extending from the central hole, and the length of the first segment. Figure 7 shows the mass of the tube wall with respect to the number of tubes extending from the central hole for a 1 / 2-inch central hole and a 1 / 2-inch first length. The mass of the TRL6 reactor built on the DOE EERE Solar project was 4.58 kg. There is room to significantly reduce the mass of the reactor and the cost after the additively manufactured reactor. However, other design considerations are the total amount of catalyst and the heat transfer from the reactor wall to the catalyst. The TRL6 reactor has a catalyst structure of 243.25 cm3. If only half of the tube volume contains the catalyst, the amount of that catalyst volume will not fit inside the tubes of this reactor as shown in Figure 7. Furthermore, the diameter of the tube becomes larger than 0.5 inches if the array starts with less than 10 tubes. This is considerably larger than the 5 mm (1 / 5 inch) thickness of the catalyst of TRL6. As a result, the increase in the heat transfer distance is a problem. Both problems of catalyst volume and heat transfer distance are overcome by changing the cross-section of the tube from circular to the capsule shape shown in Figure 8. The wall dividing the capsule-shaped tubes is twice the thickness of the round wall to maintain the same maximum wall stress. The height of the straight wall becomes a parameter that can be varied to provide sufficient internal volume to accommodate the desired catalyst volume. Figure 9 shows the wall mass for a reactor with capsule-shaped branched tubes of a constant internal volume of 487.5 cm3. The calculation of the wall mass shows the possibility of saving the wall mass to 2 / 3 from the 4.58 kg TRL6 reactor. The mass saving reduces the number of tubes extending from the central hole by more than about 30. When the first tube is 20, the maximum catalyst thickness in the direction of the incident sunlight is 6 - 7 mm. This is close to the 5 mm catalyst thickness of TRL6. The round "hills" on the outer surface and the thin wall are more than compensating for the nominally thicker catalyst.For 20 tubes extending from a 1 / 2-inch central hole with a length of the first tube of 1 / 4 inch, the mass of the tube wall is 1.83 kg, the minimum diameter is 0.101 inch, the maximum diameter is 0.202 inch, the height of the inner wall is 0.333 inch, and the thickness of the catalyst is 6.8 mm.

[0052] An alternative approach is to maintain a constant reactor thickness by varying the height of the separation wall as the diameter changes. This may be easier to manufacture since the catalyst thickness is uniform.

[0053] Helical tubes: The structures shown in FIGS. 4 to 6 have straight tubes extending radially from a central hole. In other embodiments, the tubes are curved and helical from the center towards the outer edge. See FIG. 10. The helical structure is pre-adapted to the solar reactor-receiver to accommodate the non-uniform incident solar flux on the surface of the reactor. At the limit, a single coiled helical tube as in FIG. 11 covers the entire area receiving the incident solar flux. The coil shape can also be formed in a capsule-shaped cross-section as shown in FIG. 8, except that adjacent channels show adjacent coils of the same tube instead of separate tubes as described above. Similar reactor mass savings are expected by having thin walls as described for other structures. The difficulty with a single coiled tube or capsule-shaped tube is that a fairly long channel length increases the pressure drop. This can be alleviated by having two or more coils coiling outwards from the center towards the outer edge. In yet another embodiment, the coil can branch at one or more points of the helix. Thus, there are numerous combinations of structures from straight branched tubes to curved branched tubes to single coiled tubes. The choice of structure depends on performance, pressure drop, manufacturing cost, and the reliability and lifespan of the reactor.

[0054] Return channels: The design of a reactor with radial fluid channels typically has a process fluid that flows outward from a central manifold (hole) to an outer peripheral manifold and then radially back to a second central manifold before exiting the reactor. Embodiments include options for placing the same or different catalysts in both the outward-flow channels and the return channels, only in the outward-flow channels, or only in the return channels. FIG. 8 shows the inner wall 86 of a tube or capsule tube for dividing the outward-flow channels and the return channels with catalyst 88 placed anywhere. FIG. 8 shows symmetric channels that equally divide the volume between the outward-flow channel 88 and the return channel 84. Other embodiments have walls that are shifted downward or upward to increase the volume of the outward channels or the return channels, respectively. Still other embodiments have an asymmetric structure where one profile is for the outward-flow channels and a different profile is for the return channels. For example, the return channels can have a different pitch. For example, by doubling the pitch, two return channels are provided for each outward-flow channel to improve heat transfer in the return channels.

[0055] Figures 4 through 6, and 8, show return channels that follow the same path as the outward flow channels, such as the split tube shown in FIG. 8. In other embodiments, the design of the structure of the return channels can be decoupled from the outward flow channels. One example is the counter spiral structure of the previously used IDR, Solar Thermochemical Reactor with Reaction and Thermal Recuperation Channels Arranged in Counter Spirals. Crossing the return flow channels and thermally contacting them with multiple outward flow channels has the advantage of heat diffusion and more uniform temperature within the reactor. Various methods are envisioned for constructing two fluid channel structures for the mechanical support of a pressurized reactor. The outer manifold can be designed to simply return the fluid within a given outward flow channel through an adjacent return channel when the structure is symmetric. Alternatively, the manifold can return the fluid through the return channel of another outward flow channel. One reason is to provide heat transfer and diffusion between areas of the reactor. Other embodiments will have an open manifold, allowing the mixing of fluids from multiple outward flow channels before entering the return channels. The outer manifold can mix the fluid from two or more outward flow channels across the entire outward flow channels.

[0056] Improved heat exchange: Heat transfer of the flux of incident sunlight from the surface of the reactor, through the outer wall and the catalyst structure, to support endothermic heterogeneous reactions and other processes is important with respect to the performance of the reactor. An important aspect of the present invention is to make the outer wall thin to reduce the heat transfer resistance through the outer wall. Heat transfer in the open return channels can also be important. For example, by transferring heat from the hot fluid in the return channels to the catalyst structure in the outward flow channels, the conversion of solar energy to chemical energy can be improved and the overall energy efficiency of the system can be improved. Various techniques for improving heat transfer in either the outward flow channels or the return channels are anticipated. Structures with a large area, such as straight fins, louvered fins, pins or other structures, can be formed during the manufacture of the reactor and extend from the separating wall, which is the main heat transfer surface between the outward flow channels and the return channels, into the fluid channels or the catalyst structure. Such structures with an extended area can also be formed during the manufacture of the reactor, extend from the wall receiving the flux of sunlight to the catalyst structure, and improve heat transfer. The structure can also improve heat transfer by mixing the fluid, such as by a static mixer structure.

[0057] Non-smooth structure: The reactor structures shown in FIGS. 2 through 6 are planar, meaning that the major axes of the channels all lie within a two-dimensional plane. The flexibility of additive manufacturing allows for 3-D structures in which the fluid channels curve out of the main plane of the reactor, so-called Z-direction curvature. The advantages of 3-D structures include a larger outer surface area for receiving incident solar energy, thereby reducing the average local heat flux into the reactor. Another advantage is reducing the thermal stresses associated with the thermal expansion of the structure. One embodiment of a 3-D structure is a dome-shaped or hemispherical structure. An example of this type of structure is shown in FIG. 10. This convex structure allows the hottest outer surface receiving incident sunlight to expand more than the cooler underside, thereby reducing the stress within the structure. A hemisphere with a circular cross-section is just one of a number of possible 3-D structures. Other structures include parabolic and S-shaped. The alternative shapes create opportunities to locally adjust the angle of incidence of the flux on the outer surface of the reactor, better match the characteristics of paired solar thermal concentrators, and mitigate hot spots due to optical imperfections.

[0058] Pressure drop structures: A uniform flow distribution between channels is desired for a constant residence time and exposure to the catalyst, as well as for heat transfer. To create a pressure drop that aids in uniformly distributing the flow, features are often added at the inlet or outlet (or anywhere within the flow path). The features can include orifices or other flow restrictors, extended flow path lengths such as serpentine small channels, or porous walls. These features can be added during the additive manufacturing fabrication process.

[0059] Other processes: The main use of the present invention is a solar thermochemical reactor that uses the radiation of incident sunlight to provide heat for a heterogeneous catalyst for the endothermic steam reforming reaction of methane. Other endothermic processes are envisioned, including other endothermic chemical reactions such as the dry reforming of methane with CO2 or the reverse water gas shift reaction. Examples of reactor designs, including differential temperature reactors for endothermic and exothermic reactions, and corresponding reactions that can be manufactured using the techniques described herein, are described in U.S. Patent No. 7,297,324. This document is incorporated herein as if fully reproduced below. Differential temperature reactors achieve improved chemical conversion compared to adiabatic reactors for reactions with limited equilibrium that exhibit substantial temperature dependence. Differential temperature microchannel or mesochannel reactors include adding heat (for endothermic reactions) or removing heat (for exothermic reactions) by, for example, using adjacent channels through which a heat exchange fluid flows or in which another reaction occurs. Preferably, the heat exchange function achieves a temperature profile along the length of the reaction channel that promotes greater chemical conversion.

[0060] Aspects of the present invention can also be used in solar receivers. In a solar receiver, solar energy is converted into sensible or latent heat in a heat transfer fluid. Other examples are sorption processes for heat pumps or chemical separation processes. For example, a solar heat pump transfers heat from a lower temperature to a higher temperature using an absorption (liquid solvent) or adsorption (solid solvent) heat pump cycle. An example is to exchange the catalyst of the above-described invention with a solid adsorbent that adsorbs a refrigerant at low temperature and pressure and desorbs it at high temperature and pressure using solar energy. Applications include building heating, ventilation, and air conditioning (HVAC), as well as refrigeration. Similarly, the adsorbent can be used for chemical separation processes in a temperature swing adsorption (TSA) process, or a thermally enhanced pressure swing adsorption (PSA) process. One application would be to capture carbon dioxide from the air, power plant effluents, or other potential sources.

[0061] Catalytic chemical reactions are very well known, and the appropriate conditions and catalysts are very well known and need not be described herein. As modified catalysts, or as Sabatier catalysts (usually Ni or Ru / Al2O3), ammonia synthesis (usually Ru, or iron oxide, or Co-Mo-N), or reverse water gas shift reaction (common catalysts include oxides of iron, chromium, and optionally magnesium) it is sufficient to identify the catalyst.

[0062] In some preferred embodiments, the present invention converts methane or other alkanes or mixtures of hydrocarbons to hydrogen by steam reforming or dry reforming. The steam reforming process requires hydrocarbons (or a plurality of hydrocarbons) and steam (H2O). The mixture of reactants may include other components such as CO, or non-reactive diluents such as nitrogen or other inert gases. In some preferred processes, the reactant stream consists essentially of hydrocarbons and steam. In some preferred embodiments, the steam to carbon ratio in the reactant stream is from 3 to 1 to 1 to 1, and in some embodiments, 1.5 to 1 or less. Hydrocarbons include alkanes, alkenes, alcohols, aromatic compounds, and combinations thereof. The hydrocarbon can be natural gas. Preferred alkanes are C1 to C such as methane, ethane, propane, butane, and isooctane 10is an alkane. The steam reforming catalyst preferably contains one or more of ruthenium, rhodium, iridium, nickel, palladium, platinum, and combinations thereof as catalytically active materials. Rhodium is particularly preferred. In some preferred embodiments, the catalyst (including all support materials) contains 0.5 wt% to 10 wt% Rh, more preferably 1 wt% to 3 wt% Rh. The catalyst may also include an alumina support with respect to the catalytically active material. The "alumina support" contains aluminum atoms attached to oxygen atoms and may have additional elements. Preferably, the alumina support contains one or more stabilizing elements that improve the stability of the catalyst under hydrothermal conditions. Examples of stabilizing elements are Mg, Ba, La, and Y, and combinations thereof. Preferably, the catalytically active material (such as Rh) is present in the form of small particles on the surface of the alumina support. The steam reforming reaction is preferably carried out at a temperature higher than 400 °C, more preferably from 500 °C to 1000 °C, even more preferably from 650 °C to 900 °C. The reaction can be carried out at a wide range of pressures, from below atmospheric pressure to very high pressures. In some embodiments, the process is carried out at a pressure of 10 atm to 30 atm, more preferably 12 atm to 25 atm. The partial pressure of H2O is preferably at least 0.2 atm, in some embodiments at least 2 atm, and in some embodiments in the range of 5 atm to 20 atm.

[0063] In some preferred configurations, the catalyst (for steam reforming or other chemical reactions) includes a large-pore substrate thereunder. Examples of preferred large-pore substrates include commercially available metallic foam materials, more preferably metallic felts. Prior to depositing any coating, the large-pore substrate has a porosity of at least 5%, more preferably from 30% to 99%, even more preferably from 70% to 98%. In some preferred embodiments, the large-pore substrate has an average pore size by volume measurement, as measured by BET, of 0.1 μm or greater, more preferably between 1 μm and 500 μm. Preferred forms of the porous substrate are foam materials or felts, which are preferably formed of a thermally stable electrically conductive material, preferably a metal such as stainless steel or FeCrAlY alloy. These porous substrates can be made thin, such as between 0.1 cm and 1 cm. The foam material is a continuous structure with continuous walls having pores defined throughout the structure. Alternatively, the catalyst may take any conventional form, such as powder or pellets.

[0064] Catalysts having large pores preferably have a pore volume that is from 5% to 98%, more preferably from 30% to 95%, of the total volume of the porous material. Preferably, at least 20% (more preferably at least 50%) of the pore volume of the material is composed of pores with a size (diameter) in the range from 0.1 micron to 300 microns, more preferably from 0.3 micron to 200 microns, and even more preferably from 1 micron to 100 microns. The pore volume and the pore size distribution are measured by mercury porosimetry (assuming a cylindrical pore geometry) and nitrogen adsorption. As is known, mercury porosimetry and nitrogen adsorption are complementary techniques, with mercury porosimetry being more accurate for the measurement of large pore sizes (greater than 30 nm) and nitrogen adsorption being more accurate for small pores (less than 50 nm). A pore size in the range of about 0.1 micron to 300 microns allows molecules to diffuse molecularly through the material, mostly under gas-phase catalyst conditions. The catalyst insert preferably has a height of 1 cm or less, and in some embodiments, the height and width are from 0.1 cm to 1.0 cm. In some embodiments, the porous insert occupies at least 60%, and in some embodiments, at least 90%, of the cross-sectional area of the microchannel. In an alternative preferred embodiment, the catalyst is a coating (washcoat) of the material within the reaction channel or channels.

Claims

**Claim 1** A microchannel or mesochannel device, comprising: a first plurality of microchannels or mesochannels that provide a radial fluid flow from a source manifold to an outer edge of the device; and a second plurality of channels that provide a radial fluid flow from the outer edge to a receiving manifold, wherein the source manifold and the receiving manifold are located near a central region of the device, and the device is configured for a unit process, the microchannel or mesochannel device, further comprising a catalyst insert or a plurality of catalyst inserts disposed around the outer edge of the device, wherein the direction of the flow in the channels switches from a direction towards the outer edge to a direction away from the outer edge, and further comprising a ring disposed around the outer periphery of the device surrounding the catalyst insert or the plurality of catalyst inserts, and a flow path in which the direction of the flow in the channels switches from a direction towards the outer edge to a direction away from the outer edge. The microchannel or mesochannel device. **Claim 2** The microchannel or mesochannel device according to claim 1, wherein the catalyst insert is wedge-shaped. **Claim 3** The microchannel or mesochannel device according to claim 1, wherein the first plurality of microchannels or mesochannels, the second plurality of channels, or both have an internal dimension of 1 cm or less. **Claim 4** The microchannel or mesochannel device according to claim 1, wherein the first plurality of microchannels or mesochannels, the second plurality of channels, or both comprise straight radial channels. **Claim 5** The microchannel or mesochannel device according to claim 1, wherein the first plurality of microchannels or mesochannels, the second plurality of channels, or both comprise curved channels extending from the central region to the outer edge. **Claim 6** The microchannel or mesochannel device according to claim 1, further comprising a solar thermal concentrator disposed to focus concentrated solar energy. **Claim 7** The microchannel or mesochannel device according to claim 1, wherein the catalyst insert or inserts are disposed inside both the first plurality of microchannels or mesochannels and the second plurality of channels.

8. The microchannel or mesochannel device according to claim 1, wherein the catalyst insert or inserts comprise a catalyst for steam reforming or reverse water gas shift reaction.

9. A method for manufacturing a microchannel or mesochannel device, the method comprising: forming a first portion of the channel layer by layer through an additive manufacturing process; embedding a porous catalyst structure into the pores of the first portion of the channel together with a solid material, wherein the solid material is removable by heating or reaction; forming a second portion of the channel layer by layer by powder additive manufacturing on the first portion, wherein the solid material protects the catalyst structure from substantial intrusion by powder additive manufacturing; and removing the solid material by converting it to a fluid through heating or reaction.

10. The method according to claim 9, wherein the solid material comprises a high molecular weight oil.

11. A chemical processor having a circular shape, comprising a tube or tubes that provide a radial fluid flow from a source inlet or source manifold near the central region of the processor to the outer edge of the processor, wherein the tube or tubes are exposed on the exposed surface of the chemical processor, whereby the surface is not smooth, the tube or tubes having a circular, oval, or elliptical cross-section, and the processor being configured for a unit process, wherein the tube or tubes comprise branched channels that divide into two or more channels as they extend radially; the chemical processor.

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