Catalyst and system for steam reforming of methane by resistance heating, and preparation of the catalyst

Abstract

The present invention relates to a structured catalyst for catalyzing a steam methane reforming reaction by contacting a hydrocarbon feed gas with the structured catalyst within a given temperature range T. The structured catalyst comprises a macrostructure, the macrostructure comprising a conductive material and loaded with a ceramic coating. The macrostructure is manufactured by 3D printing or extrusion and subsequent sintering, wherein the macrostructure and the ceramic coating are sintered in an oxidizing atmosphere to form a chemical bond between the ceramic coating and the macrostructure. The ceramic coating is loaded with a catalytically active material, the catalytically active material is configured to catalyze the steam methane reforming reaction, and the macrostructure is configured to conduct an electric current to provide an energy flux to the steam methane reforming reaction. The present invention also relates to a method for manufacturing a structured catalyst and a system using the structured catalyst.

Description

Technical Field

[0001] The present invention relates to a structured catalyst for catalyzing a steam methane reforming reaction by resistance heating, a method for making the structured catalyst and a system for performing a steam methane reforming reaction. Background of the Invention

[0003] Carrying out endothermic reactions, such as steam methane reforming, is often challenged by how to efficiently transfer heat to the reaction zone of the catalyst bed within the reactor unit. Conventional convection, conduction and / or radiation heat transfer can be slow and often encounters large resistances in many configurations. This challenge can be illustrated by the tubular reformer in a steam reforming plant, which can actually be regarded as a large heat exchanger in which heat transfer is the rate limiting step. One way to generate heat is by resistive heating. DE102013226126 describes a method for geothermal methane reforming with physical energy recovery, in which methane is reformed into a synthesis gas consisting of carbon monoxide and hydrogen with the aid of carbon dioxide. The starting gases CH4 and CO2 are processed in a fixed bed reactor consisting of conductive and catalytic particles, which are electrically heated to a temperature of about 1000K. The conversion of the reaction gases and the generation of heat for the resulting synthesis gas take place in the fixed bed reactor.

[0004] It is desirable to provide a method of performing an endothermic catalytic chemical reaction and a system for use in the method by resistive heating. It is also desirable to provide a catalyst for catalytic steam methane reforming in which heat is generated by resistive heating and in which the distribution of the current, and thus the heat, is uniform. SUMMARY OF THE INVENTION

[0006] A first aspect of the invention relates to a structured catalyst for catalyzing a steam methane reforming reaction by contacting a hydrocarbon feed gas with the structured catalyst within a given temperature range T, wherein the structured catalyst comprises a macrostructure. The macrostructure comprises a conductive material, and the macrostructure is loaded with a ceramic coating, wherein the macrostructure has been manufactured by extrusion or 3D printing and subsequent sintering. The macrostructure and the ceramic coating are sintered in an oxidizing atmosphere to form a chemical bond between the ceramic coating and the macrostructure, wherein the ceramic coating is loaded with a catalytically active material, which is configured to catalyze the steam methane reforming reaction. The macrostructure is configured to conduct an electric current to provide energy to the chemical reaction.

[0007] When the structured catalyst for catalyzing the steam methane reforming reaction in the system includes a macrostructure containing a catalytically active material, when the macrostructure is subjected to resistive heating (electrical current is passed through the macrostructure), the catalytically active material is heated from the heating of the macrostructure. Thus, the catalytically active material can be any suitable active phase and any suitable element.

[0008] The intimate contact between the catalytically active material and the macrostructure enables efficient heating of the catalytically active phase from heat conduction within the resistively heated macrostructure and the material of the macrostructure loaded with the ceramic coating. Thus, an important feature of the resistive heating process is that the heat is generated within the object itself, rather than by heat conduction from an external heat source. As a result, the structured catalyst can be heated very rapidly.

[0009] The macrostructure is made by extrusion or 3D printing and subsequent sintering. This / these processes give a macrostructure of uniform or nearly uniform shape, which can then be coated with a ceramic coating and impregnated with a catalytically active material. The ceramic coating is applied to those parts of the macrostructure, meaning that these parts are in contact with the gas when the reactor unit containing the structured catalyst is used. For example, the sintering can be carried out in a vacuum or in an atmosphere containing H2. Under given operating conditions, the surface area of ​​the macrostructure, the proportion of the macrostructure coated with the ceramic coating, the type and structure of the ceramic coating and the amount and composition of the catalytically active catalyst material can be adjusted to suit the steam reforming reaction. However, it should be noted that advantageously, substantially all surfaces of the macrostructure are coated with a ceramic coating, and preferably, all or most of the ceramic coating is loaded with catalytically active material. Preferably, only the part of the macrocoating that is connected to the conductor or is arranged to be connected to the conductor is not provided with a ceramic coating. The ceramic coating loaded with catalytically active material reduces or prevents the risk of carbon formation according to the following reaction:

[0010]

[0011] Covering the metal structure with a ceramic coating loaded with catalytically active material ensures that the metal phase of the macrostructure is covered with a coherent oxide layer, which has less potential for carbon formation reactions. In addition, the catalytically active material in the oxide phase will catalyze the steam reforming reaction and bring the reaction gases toward or even close to thermodynamic equilibrium. This increases the partial pressure of hydrogen and reduces the partial pressure of methane, thereby reducing or in many cases eliminating the thermodynamic potential for carbon formation according to the above reaction (A).

[0012] Typically, extruded or 3D printed macrostructures are coherently or cohesively manufactured to provide them with uniform geometric properties. This provides a uniform distribution of current, thereby evenly distributing the charge therein. When extruding or 3D printing macrostructures, the pressure drop from the inlet to the outlet of the reactor unit can be greatly reduced compared to when the catalyst material is in the form of pellets. Throughout the text, the term "coherent" is a synonym for cohesive and therefore refers to materials that are continuously intraconnected or continuously coupled.

[0013] By using a coherently extruded or 3D printed macrostructure with uniform geometrical properties, a uniform distribution of the current and thus a uniform heat flux can be obtained in the macrostructure. In combination with a macrostructure and a ceramic coating sintered in an oxidizing atmosphere to form a chemical bond between the ceramic coating and the macrostructure, particularly high thermal conductivity between the electrically heated macrostructure and the catalytically active material loaded with the ceramic coating is possible, which provides close and almost direct contact between the heat source and the active sites. Therefore, the structured catalyst is compact in terms of gas processing per reactor unit volume, and the reactor unit housing the structured catalyst can also be compact. At the same time, this allows an immediate response to the heating of the process, allowing a rapid start-up. When the macrostructure is extruded or 3D printed, the pressure drop from the inlet to the outlet of the reactor unit can be greatly reduced compared to when the catalyst material is in pellet form.

[0014] The terms "3D print" and "3D print" as used herein refer to a metal additive manufacturing process. Such metal additive manufacturing processes cover 3D printing processes in which materials are connected to structures under computer control to create a three-dimensional object, wherein the structure is solidified, for example by sintering, to provide a macrostructure. Moreover, such metal additive manufacturing processes cover 3D printing processes that do not require subsequent sintering, such as powder bed fusion or direct energy deposition processes. Examples of such powder bed fusion or direct energy deposition processes are laser beam, electron beam or plasma 3D printing processes.

[0015] As used herein, the term "macrostructure" is intended to mean a macrostructural element of any suitable form that provides a high geometric surface area. The material of the macrostructure may be porous, or the macrostructure may be solid. The term "macro" in "macrostructure" refers to a structure that is large enough to be visible to the naked eye without a magnifying device. The size of a macrostructure is typically in the range of tens of centimeters or even meters. Two or more macrostructures may be connected to provide an array of macrostructures having at least one external dimension in the meter range, such as in the range of 0.5 meters, 1 meter, 2 meters, or 5 meters. Such two or more macrostructures may be represented as an "array of macrostructures".

[0016] A non-limiting example of a macrostructure is, for example, a monolith. Two types of macrostructures are particularly suitable for the method of the invention: straight channel elements and cross-corrugated elements. Various geometries of these elements are conceivable.

[0017] The outer dimensions of the macrostructures are usually in the range of centimeters or meters, for example from 50 centimeters to several meters. Advantageously, the dimensions of the macrostructures correspond at least partially to the inner dimensions of the reactor unit containing the structured catalyst. In order to provide a structured catalyst, two or more macrostructures can be connected, which structured catalyst can have at least one outer dimension in the range of meters, for example a length or an area equivalent diameter of 5 m. It is conceivable that the macrostructures may occupy 1 to 10 m 3 Even larger reactor unit volumes. As used herein, the area equivalent diameter of a cross section through a reactor unit is the diameter of a circle equivalent to the area of ​​the cross section.

[0018] The macrostructure comprises a conductive material and is designed to allow current to flow through the macrostructure. Therefore, advantageously, most or all of the material of the macrostructure is conductive. A material with appropriate conductivity should be selected so that the current can heat the macrostructure while flowing through the macrostructure. The material of the macrostructure is, for example, a metallic material. In addition, in order to achieve conductivity throughout the structured catalyst, the macrostructure is advantageously a coherent or continuously internally connected material.

[0019] The catalytic material can be added directly to the metal surface by wash coating. Wash coating of metal surfaces is a well-known process; descriptions are given, for example, in Cybulski, A., and Moulijn, JA, structured catalysts and reactors, Marcel Dekker, Inc, New York, 1998, Chapter 3, and references therein.

[0020] The amount of catalytically active material can be adjusted to the catalytic activity required for a chemical reaction, such as a steam reforming reaction, under given operating conditions. In this way, the pressure drop is low and the amount of catalyst is not more than required, which is particularly advantageous if expensive noble metals are used.

[0021] In more conventional applications of reformer tubes with pellets, steam reforming reactors are typically designed to maximize heat transfer, and the pellets are simply placed in channels where the process gas flow often results in a large excess of catalytic activity. With respect to conventional steam methane reformers with tubes with catalyst pellets, it is generally believed that the ratio of the reformer tube diameter to the diameter of the catalyst pellets should be greater than 4-5 to ensure good packing of the catalyst pellets. This places restrictions on the geometry of the tubes, since undesirable or excessive pressure drops through the tubes are to be avoided; therefore, the reforming tubes need to have a certain diameter that corresponds to at least 4-5 times the diameter of the catalyst material. Using structured catalysts containing macrostructures, this limitation can be eliminated, thereby providing the possibility of a more compact reformer.

[0022] The structured catalyst of the present invention is arranged to generate heat uniformly over its geometric surface area by resistive heating, so that the temperature distribution of the structured catalyst can be controlled. Thus, it can be ensured that the temperature of the hydrocarbon feed gas does not rise faster than the rate at which the reaction can proceed. Thus, exposure of unconverted hydrocarbons to high temperatures is avoided, so that the formation of carbon from the gas can be thermodynamically avoided.

[0023] In one embodiment, the material of the macrostructure includes iron, chromium, aluminum, cobalt or an alloy thereof. For example, the material of the macrostructure is an alloy comprising iron and chromium, an alloy comprising iron, chromium and aluminum, an alloy comprising iron and cobalt, or an alloy comprising iron, aluminum, nickel and cobalt. "Alnico alloy" is a specific type of alloy that includes iron, aluminum, nickel and cobalt, and may also include copper, titanium and other elements, while FeCrAlloy includes iron, chromium and aluminum. In the tests of the present invention, Kanthal alloy has been shown to be a good choice of material for the macrostructure due to its electrical resistance properties.

[0024] The term "alloy comprising X and Y" refers to an alloy having X and Y as the main components and possibly containing other elements. Due to its properties, iron and its alloys respond very well to resistive heating.

[0025] In one embodiment, the macrostructure comprises a plurality of parallel channels. Thus, the surface area of ​​the macrostructure with catalytically active material that is exposed to the gas is as large as possible.

[0026] Furthermore, when the macrostructure has parallel channels, these parallel channels provide a very low pressure drop across the structured catalyst. In a preferred embodiment, the parallel longitudinal channels are skewed in the longitudinal direction of the macrostructure. In this manner, molecules of hydrocarbon feed gas flowing through the macrostructure will be more likely to tend to hit the active catalytic walls inside the channels, rather than flowing directly through the channels without contacting the walls.

[0027] In one embodiment, the resistivity of the macrostructure is between 10 -5 Ω·m and 10 -7 This resistivity provides a macrostructure with sufficient heat flux for steam methane reforming reactions.

[0028] In one embodiment, the ceramic coating is an oxide comprising aluminum, zirconium, magnesium, cerium, calcium, lanthanum, yttrium, or a combination of at least two of these oxides. The oxide may, for example, be AlZrCeOx. The oxide may additionally comprise silicon and / or titanium.

[0029] In one embodiment, the macrostructure has a plurality of nearly parallel or parallel channels, a plurality of non-parallel channels and / or a plurality of labyrinth channels, wherein the channels have walls defining the channels. Therefore, as long as the surface area of ​​the structured catalyst exposed to the gas is as large as possible, several different forms of macrostructures can be used. In a preferred embodiment, the macrostructure has parallel channels because such parallel channels give the structured catalyst a very small pressure drop. In a preferred embodiment, the parallel longitudinal channels are inclined in the longitudinal direction of the macrostructure. In this way, the gas molecules flowing through the macrostructure will be more likely to tend to hit the wall in the channel, rather than directly flowing through the channel without contacting the wall. The size of the channel should be appropriate, so as to provide enough resistivity for the macrostructure. For example, the channel can be square (as shown in a cross section perpendicular to the channel), and one side of the square is between 1 and 3 mm. However, it is conceivable that the maximum extension of the cross section is about a channel of 4 cm. In addition, the wall thickness should be small enough to provide a relatively large resistance and large enough to provide enough mechanical strength. For example, the wall thickness may be between 0.2 and 2 mm, such as about 0.5 mm, and the thickness of the ceramic coating carried by the wall may be between 10 μm and 500 μm, such as between 50 μm and 200 μm, such as 100 μm. It should be noted that the channel is not necessarily of constant cross-section along the length of the macrostructure. Thus, the channel may have a uniform or varying cross-section along the length of the macrostructure.

[0030] An example of wall dimensions defining the channels and the ceramic coating applied to the wall is a wall thickness between 0.2 and 2 mm, such as about 0.5 mm, and a ceramic coating supported by the wall having a thickness between 50 μm and 200 μm, such as about 100 μm.

[0031] In one embodiment, the catalytically active material comprises nickel, ruthenium, rhodium, cobalt, iridium or a combination of at least two of these elements. Thus, a possible catalytically active material is a combination of nickel and rhodium and another combination of nickel and iridium. Preferably, the macrostructure comprises Fe, Cr, Al, Ni or an alloy thereof. Such alloys may include further elements such as Si, Mn, Y, Zr, C, Co or a combination thereof. For example, the ceramic coating may be an oxide comprising Al, Zr, Mg, Ce and / or Ca. Exemplary coatings are calcium aluminates or magnesium aluminum spinels. Such ceramic coatings may include further elements such as La, Y, Ti, K or a combination thereof. Preferably, the conductor and the macrostructure are made of a material different from the macrostructure. For example, the conductor may be iron, nickel, aluminum, copper, silver or an alloy thereof. The ceramic coating is an electrically insulating material, typically having a thickness of about 100 μm, for example, about 10-500 μm.

[0032] In one embodiment, the catalytically active material is in the form of submicron sized particles. Advantageously, the catalytically active particles are between about 3 nm and about 250 nm in size.

[0033] In one embodiment, the macrostructure has at least one electrically insulating portion that is configured to provide a main current path in the macrostructure and whose length is greater than the maximum dimension of the macrostructure. Such an electrically insulating portion is configured to increase the current path within the macrostructure and thus increase the resistance through the macrostructure. Non-limiting examples of such electrically insulating portions are cuts, slits, or holes in the macrostructure. Such cuts, slits, or holes in the macrostructure can be formed as follows: by post-processing the macrostructure, such as by drilling, cutting, or otherwise removing some of the macrostructure, or can be formed during the process of manufacturing the macrostructure, such as during a 3D printing process or before a sintering process step.

[0034] Optionally, a solid electrically insulating material such as glass may be used that is disposed in a cut or slit in the macrostructure. The solid electrically insulating material within the cut or slit helps to keep the various portions of the macrostructure on the sides of the cut or slit in contact with each other. The cut, slit or hole in the macrostructure may be provided by cutting or drilling into the macrostructure or otherwise removing certain material from the macrostructure. Alternatively, the cut, slit or hole may be formed as follows: if the macrostructure is formed by combining several macrostructures together to form a certain shape, then the cut, slit or hole may be formed so that the cut, slit or hole appears within the macrostructure. Alternatively, if the macrostructure is formed by combining several macrostructures and intermediate ceramic elements together to form a certain shape, the electrically insulating portion may be formed so that the ceramic layer is located between the major surfaces of two or more macrostructures and the macrostructures are combined together only in a confined area.

[0035] The ceramic coating may be a material comprising oxides of aluminum, zirconium, magnesium, cerium, calcium, lanthanum, and / or yttrium.

[0036] As used herein, the term "largest dimension of a macrostructure" is intended to mean the largest internal dimension of a geometric form occupied by the macrostructure. If the macrostructure is box-shaped, the largest dimension will be the diagonal from one corner to the farthest corner, also called the spatial diagonal.

[0037] In one embodiment, the resistance of the material and geometry of the macrostructure are configured to have a resistance of 500 to 50,000 W / m 2 heat generating capacity.

[0038] In one embodiment, the macrostructured material has a porosity in the range of 0 to 60%. As used herein, "porosity" is defined as the volume occupied by voids in the material, i.e., the volume occupied by the walls of the macrostructure relative to the total volume occupied by the walls. Thus, the porosity of the macrostructure does not take into account the voids within the channels of the macrostructure.

[0039] Another aspect of the present invention relates to a structured catalyst comprising two or more macrostructures. The two or more macrostructures are advantageously electrically connected to each other.

[0040] Another aspect of the present invention relates to a method for preparing a structured catalyst according to the present invention. The method comprises the following steps:

[0041] a) mixing powdered metal particles and a binder into a mixture,

[0042] b) extruding the mixture into an extruded structure,

[0043] c) sintering the extruded structure in a non-oxidizing atmosphere at a first temperature T1 to provide a macrostructure, wherein T1>1000° C.,

[0044] d) applying a ceramic coating on the macrostructure,

[0045] e) sintering the macrostructure and the ceramic coating in an oxidizing atmosphere at a second temperature T2, wherein T2>800° C.,

[0046] f) Impregnation of the ceramic coating with a catalytically active material.

[0047] According to another aspect, the present invention relates to a method for producing a structured catalyst according to the present invention. The method comprises the following steps:

[0048] a) mixing powdered metal particles and a binder into a mixture,

[0049] b) extruding the mixture into a structure,

[0050] c) sintering the extruded structure at a first temperature T1 in a non-oxidizing atmosphere, wherein T1>1000° C., thereby providing a macrostructure,

[0051] d) applying a ceramic coating on the macrostructure, wherein the ceramic coating is loaded with a catalytically active material, and

[0052] e) sintering the macrostructure and the ceramic coating in an oxidizing atmosphere at a second temperature T2 to form a chemical bond between the ceramic coating and the macrostructure, wherein T2>800°C.

[0053] This method of making a structured catalyst differs from previous methods of making a structured catalyst in that in step d), the ceramic coating provided to the macrostructure already contains the catalytically active material. Thus, the catalytically active material can be mixed into the material of the ceramic coating before the macrostructure is provided with the ceramic coating. Otherwise, the catalytically active material is provided by impregnating the macrostructure, immersing the macrostructure in a slurry containing the catalytically active material or loading the catalytically active material onto the macrostructure in another way.

[0054] An exemplary sintering temperature of step c) may be about 1050°C.

[0055] The non-oxidizing atmosphere used in step c) is a reducing atmosphere or an inert atmosphere. The term "reducing atmosphere" is intended to mean an atmosphere that contains more reducing gas molecules than oxidizing gas molecules, for example more H2 than O2 and / or more H2 than H2O.

[0056] According to another aspect, the present invention relates to a method for producing a structured catalyst according to the present invention. The method comprises the following steps:

[0057] a) 3D printing macrostructures using metal additive manufacturing melt processes,

[0058] b) applying a ceramic coating on the macrostructure,

[0059] c) sintering the macrostructure and the ceramic coating in an oxidizing atmosphere at a second temperature T2, wherein T2>800° C., and

[0060] d) impregnating the ceramic coating with a catalytically active material, thereby providing a structured catalyst.

[0061] According to yet another aspect, the present invention relates to another method for producing a structured catalyst according to the present invention. The method comprises the following steps:

[0062] a) 3D printing of metal structures via binder-based metal additive manufacturing processes,

[0063] b) sintering the metal structure in a non-oxidizing atmosphere at a first temperature T1, wherein T1>1000° C., thereby providing a macrostructure,

[0064] c) applying a ceramic coating on the macrostructure,

[0065] d) Sintering the macrostructure and the ceramic coating at a second temperature T2 in an oxidizing atmosphere, wherein T2>800°C.

[0066] e) impregnating the ceramic coating with a catalytically active material, thereby providing a structured catalyst.

[0067] The latter method of making structured catalysts differs from the former method of making structured catalysts in that when the metal structure is 3D printed with binder-based metal additive manufacturing, the structure is first created and then sintered in a separate step. When the metal structure is 3D printed via a metal additive manufacturing step, the structure is also sintered, but this is usually done together with the creation of the 3D structure. For example, layers of metal material are deposited, sintered, and these two steps are repeated until the 3D structure is created.

[0068] Sintering, extrusion and 3D printing all provide macrostructures of uniform and coherent shape, onto which catalytically active materials can then be coated. Typically, the catalytically active materials are coated on those portions of the macrostructure that will come into contact with the gas when the structured catalyst is in use.

[0069] When the extruded or 3D-printed structure and the ceramic coating are sintered in an oxidative atmosphere to form a chemical bond between the ceramic coating and the macrostructure, it is possible to obtain particularly high heat conduction between the macrostructure and the ceramic coating loaded with the catalytically active material. As a result, the structured catalyst is compact in terms of heat transfer to the active sites, and the reactor unit housing the structured catalyst can be compact and limited only by the chemical reaction rate.

[0070] Binders or adhesives are any material or substance that holds or draws other materials together by adhesion or cohesion to form a mechanically, chemically coherent whole. Binders can be, but are not limited to, photopolymers, thermoplastics, or cellulose ethers. Examples of binders are: methylcellulose, polyoxymethylene, polyethylene oxide, polyvinyl alcohol, sodium carboxymethylcellulose (cellulose gum), alginates, ethyl cellulose, and asphalt.

[0071] Another aspect of the present invention relates to a system for performing a steam methane reforming reaction by contacting a hydrocarbon feed gas with a structured catalyst according to the present invention within a given temperature range T. The system comprises a reactor unit comprising a structured catalyst and at least two conductors electrically connected to the structured catalyst; and a power supply configured to connect the structured catalyst to the at least two conductors to allow an electric current to pass through the structured catalyst during operation of the reactor unit.

[0072] Typically, in operation, gas flows through the reactor unit in an upward or downward direction so that the gas flows through the channels in the structured catalyst along its length. When the catalyst material comprises an array or a plurality of macrostructures, the individual macrostructures may be placed side by side, stacked one on top of the other, or in a combination thereof.

[0073] A technical advantage of the system is that the energy consumption required for heating is low compared to the prior art, since no excess flue gas heating is produced and the like does not occur. Another advantage is that the system can be compact due to the efficient heat transfer between the macrostructure and the catalytically active material. Heating processes known to date are ineffective and inefficient. Another advantage is that the system of the invention is easy to implement, since relatively few components are required for the system. The conductors of the reactor unit each include at least one contact point for making electrical contact between the conductor and an electrical wire or an electrical connector, so that the electrical wire or electrical connector can connect the power supply and the reactor unit.

[0074] Another advantage of the system of the invention is that the flow through the structured catalyst can be upward flow when the structured catalyst is a structured catalyst. In the case of pellets, this is more difficult due to the risk of fluidization. Therefore, a lot of piping can be avoided, reducing equipment costs.

[0075] The system generally comprises further elements known to the person skilled in the art, such as means for ensuring a gas-tight reactor unit.

[0076] In an embodiment of the system, the conductor and the macrostructure are made of different materials.

[0077] In one embodiment, the connection between the macrostructure of the structured catalyst and the at least two conductors is a mechanical connection, a welding connection, a soldering connection or a combination of these connections. The mechanical connection is, for example, a press fit connection or a threaded connection.

[0078] In one embodiment, the conductor is preferably made of one of the following elements: iron, nickel, aluminum, copper, chromium; or an alloy of these elements. For example, the conductor is copper, an alloy of copper, nickel, an alloy of nickel, or an FeCrAlloy type alloy. The conductor may be completely or partially the same material as the macrostructure. Alternatively, the conductor may be a different material.

[0079] In one embodiment, a hydrocarbon feed gas enters a structured catalyst at a first end, and a product gas leaves the structured catalyst at a second end, wherein at least two conductors are connected to the structured catalyst at a position close to the first end rather than the second end. The term "first end of the structured catalyst" refers to the end of the structured catalyst where the feed gas enters the structured catalyst, and the term "second end of the structured catalyst" refers to the end of the structured catalyst where the gas leaves the structured catalyst. In addition, it should be noted that the term "at least two conductors are connected to the structured catalyst at a position close to the first end of the structured catalyst rather than the second end of the structured catalyst on the structured catalyst" means that two / all of the at least two conductors are close to the first end of the structured catalyst rather than the second end. Preferably, at least two conductors are connected to the first end of the structured catalyst or within a quarter of the length of the macrostructure closest to the first end.

[0080] When the pressure housing includes an inlet for feeding process gas and an outlet for discharging product gas, wherein the inlet is positioned so that the feed gas enters the structured catalyst at a first end of the structured catalyst and the product gas leaves the structured catalyst at a second end of the structured catalyst, and when the at least two conductors are connected to the structured catalyst at a location on the structured catalyst closer to the inlet than to the outlet, the at least two conductors can be placed in a relatively cooler portion of the reactor unit of the system. The temperature of the first end of the structured catalyst is lower than the temperature of the second end of the structured catalyst because:

[0081] - the feed gas directed through the inlet may cool the at least two conductors before being further heated by the structured catalyst along the path of the gas through the structured catalyst;

[0082] - Due to the heat provided to the structured catalyst by the electricity, the inlet feed gas entering the first end of the structured catalyst will be at a lower temperature than the product gas leaving the second end of the structured catalyst.

[0083] - The endothermic nature of the steam reforming reaction absorbs heat,

[0084] - The structured catalyst is configured to conduct an electrical current from one conductor substantially to a second end of the structured catalyst and then back to a second of the at least two conductors.

[0085] Thus, the temperature profile of the structured catalyst will correspond to a substantially continuously increasing temperature along the path of the feed gas through the structured catalyst. This corresponds to a greatly increased conversion of methane in the feed gas to hydrogen and carbon monoxide.

[0086] Thus, current is introduced into and withdrawn from the macrostructure via an electrode located in a relatively cool first end of the macrostructure. Advantageously, the temperature of all conductive elements other than the macrostructure is kept low to protect the connection between the conductor and the structured catalyst. When the temperature of the conductor and other conductive elements other than the macrostructure is relatively low, there are fewer restrictions on the materials suitable for the conductor and other conductive elements other than the macrostructure. As the temperature of the conductive element increases, its resistivity increases; therefore, it is desirable to avoid unnecessary heating of all other components within the system reactor unit other than the macrostructure.

[0087] It should be noted that the term "conductive elements other than macrostructures" is intended to include conductive elements that are arranged to connect a power source to the structured catalyst as well as potential connections between macrostructures or structured catalysts.

[0088] The combination of a substantially continuous increase in the temperature profile of the structured catalyst along the path of the feed gas through the structured catalyst and a controllable heat flux from the structured catalyst enables control of the reaction front of the chemical reaction.

[0089] In one embodiment, the system includes a control system, which is configured to control one or more of the following: electric current, voltage, heat flux, space velocity or a combination thereof. Thus, the energy flux from the structured catalyst and the heat of reaction of the steam methane reaction can be controlled, so that the structured catalyst provides enough heat to achieve rapid heating in a limited equilibrium method. Therefore, the heat flux of the structured catalyst can be controlled and directly matched with the heat of reaction, thereby matching the kinetic properties of its catalytically active material. The term "energy matches the heat of reaction" refers to that the heat flux provided by the macrostructure is sufficient to achieve rapid heating within the limit of approaching reaction equilibrium (i.e., within a temperature range of about ± 30 ° of the methane reforming reaction equilibrium temperature). This means that more heat can be provided by the resistance heating of the macrostructure until the chemical reaction can no longer use more energy / heat. Therefore, the heat flux of the macrostructure can be adapted to the required heat of reaction for the steam methane reforming reaction.

[0090] In one embodiment, the height of the structured catalyst or reactor unit is less than 5 meters. The height of the structured catalyst can even be less than 5 meters, for example less than 2 meters, or even 1 meter. The overall size of the structured catalyst in the reactor unit can provide a relatively high and thin reactor unit or a smaller and wider reactor unit. In general, since the structured catalyst has an effective heat transfer directly to the catalytically active material, a compact reactor unit is feasible. It should also be noted that the size of the structured catalyst can be relatively freely selected, so that the shape of the structured catalyst can be almost cubic, or can be wider than its height. The volume of the reactor unit is closely related to the volume of the structured catalyst. The structured catalyst has, for example, an external dimension of 2 meters by 1 meter by 1 meter, corresponding to a volume of 2 cubic meters. Many other suitable sizes are possible; however, the volume of the structured catalyst is typically about several cubic meters, typically less than 10 or 15 cubic meters. The gas space velocity evaluated by the gas flow rate relative to the geometric surface area of ​​the structured catalyst is typically 0.6 to 60Nm 3 / m 2 / h, e.g. 3 to 17 Nm 3 / m 2 / h, or 9 to 14Nm 3 / m 2 / h. Given the occupied volume of the structured catalyst, the space velocity is 700Nm 3 / m 3 / h to 70000Nm 3 / m 3 / h, for example 3500Nm 3 / m 3 / h to 20000Nm 3 / m 3 / h, or 11000Nm 3 / m 3 / h to 16000Nm 3 / m 3 / h. Relative to the volume of active catalyst, i.e. the volume of ceramic coating, the space velocity is given as 6000 Nm 3 / m 3 / h and 1200000Nm 3 / m 3 / h. Operating within these ranges of space velocity can achieve the desired conversion. It should be noted that the space velocity of the gas is intended to represent the space velocity of the gas entering the reactor system, i.e., the feed gas and the cooling gas.

[0091] When the reactor unit is compact, the number of external piping to the reactor unit can be reduced compared to conventional steam methane reformers, thereby reducing the amount of material and thereby the cost of such piping. This is in contrast to conventional steam methane reformers, which typically have multiple tubes within the combustion furnace, the tubes having an inner diameter of about 10 cm and a length of about 13 meters. Furthermore, advantageously, the amount of synthesis gas produced in a single reactor unit pressure shell of the system is greatly increased compared to the amount of synthesis gas produced by a single tube in known tubular steam reformers. In a standard tubular steam reformer, the amount of synthesis gas produced in a single tube of the tubular steam reformer is up to 500 Nm 3 / h. In contrast, the reactor units of the system of the present invention are configured to generate up to or greater than 2000 Nm 3 / h, for example, in a single reactor unit or pressure housing, even up to or exceeding 10000 Nm 3 / h. This can be done in the absence of O2 in the feed gas and with the methane content of the produced syngas below 10%. When a single reactor unit or pressure shell is equipped with a reactor that can produce up to 10000 Nm 3 / h of synthesis gas, it is no longer necessary to provide a plurality of pressure shells or a device for distributing the feed gas to a plurality of such individual pressure shells.

[0092] As used in this paragraph, the volume of a structured catalyst is calculated as the volume of a box or other suitable figure having similar external dimensions to the catalyst. This volume is different from the internal volume of the structured catalyst because its internal volume is calculated as the volume within the channels or walls of the structured catalyst. As used herein, the term "structured catalyst" covers such a situation where a single extruded or 3D printed structured catalyst having a ceramic coating and a catalytically active material, in the form of an extruded or 3D printed macrostructure, is contained in a reactor unit; and such a situation where the structured catalyst comprises two or more macrostructures contained in a reactor unit; such two or more extruded or 3D printed macrostructures are loaded with a ceramic coating, which in turn is loaded with a catalytically active material.

[0093] In one embodiment, the conductor surrounds the macrostructure. Typically, the conductor has a shape similar to the macrostructure. This ensures good electrical connection and good current distribution through the macrostructure. For example, in the case where the macrostructure has a circular outer shape, extending a full circle or 360 degrees of mechanical angle, the conductor can be a closed loop. There is an opening in the middle of the ring to allow hydrocarbon feed gas to enter the macrostructure. Therefore, in one embodiment, the inner diameter of the opening of the ring substantially corresponds to the diameter of the macrostructure.

[0094] In one embodiment, the macrostructure is a longitudinal structure that includes a conductor at each end of the longitudinal structure. The conductor is preferably shaped as a current distributor to ensure that the current is evenly distributed throughout the macrostructure. The conductor acting as a distributor is physically and electrically in contact with the longitudinal structure. In the case where the macrostructure includes multiple parallel conductors, the conductor is physically and electrically in contact with the end of one or more channels.

[0095] As shown, the gas flow through the structured catalyst is axial or coaxial with the length or z-axis of the structured catalyst. Although the drawings show the z-axis of the structured catalyst as vertical, it should be noted that the reactor can be positioned in any suitable manner so that the structured catalyst and the gas flow through it can be, for example, horizontal, upside down compared to the drawings, or at a 45° angle to the horizontal.

[0096] The conductor has a connection point for connecting an electric wire to the conductor so that the conductor can be connected to a power source. It has been shown that the location of the connection point of the two conductors of the system may affect the current distribution within the macrostructure. For example, in the case where the macrostructure is a longitudinal structure with an annular conductor at each of its two ends, it is advantageous to rotate the connection points of the two conductors 180 degrees relative to each other. In order to increase the path of the current in the structured catalyst, other measures can be taken. An example may be to provide two conductors at one end of the structured catalyst and to provide insulation concentrated and axially inside the macrostructure, except at the opposite end to the end of the conductor; thereby forcing the current to flow from the first conductor throughout the length of the structured catalyst and flow back to the other conductor throughout the length of the catalyst.

[0097] In one embodiment, the structured catalyst is heated to a temperature within a given temperature range T. The given temperature range T is a range between about 200°C and about 1050°C or a sub-range thereof. Thus, the outlet temperature of the gas leaving the reactor unit may be up to about 1050°C.

[0098] In one embodiment of the reactor system, the structured catalyst is configured to guide the current from one conductor to flow substantially to the second end of the structured catalyst and back to the second of the at least two conductors. In an embodiment of the system, the structured catalyst has an electrically insulating portion that is configured to increase the length of the main current path between the at least two conductors to a length greater than the maximum dimension of the structured catalyst. Such an electrically insulating portion is configured to increase the current path, thereby increasing the resistance through the structured catalyst. Therefore, the current path through the structured catalyst can be longer than the maximum dimension of the structured catalyst, for example, 50%, 100%, 200%, 1000% or even 10000%. As described above, this helps to ensure that the temperature profile of the structured catalyst corresponds to a substantially continuously rising temperature along the path of the feed gas through the structured catalyst.

[0099] Moreover, such an electrically insulating portion is configured to direct current from a conductor (which is closer to the first end of the structured catalyst than the second end) to the second end of the structured catalyst and back to a second conductor, which is closer to the first end of the structured catalyst than the second end. Preferably, the current is configured to run from the first end of the structured catalyst to the second end and back to the first end. As shown in the figure, the first end of the structured catalyst is its top end. Figure 1-4 The arrow indicated as "z" in 6a represents the z-axis along the length of the structured catalyst. The z coordinate of the current density vector accompanying the main current path in the structured catalyst along most of the length of the current path will have a positive or negative value. The main current path refers to the path of electrons through the macrostructure of the structured catalyst with the highest current density. The main current path can also be understood as the path with the minimum electrical length through the macrostructure of the structured catalyst. The current is governed by Ohm's law in the conductive structure. Geometrically, the main current path can be quantified as the maximum current density vector in the plane perpendicular to the gas flow direction of the coherent surface of the macrostructure. As shown in the figure, at the bottom of the structured catalyst, the current will turn, and the z coordinate of the accompanying current density vector here will be zero.

[0100] In one embodiment of the system, the electrically insulating portion of the structured catalyst is configured to direct the current through the structured catalyst to ensure that for at least 70% of the length of the structured catalyst, the current density vector of the main current path has a non-zero component value parallel to the length of the structured catalyst. Thus, for at least 70% of the length of the structured catalyst, the current density vector will have a positive or negative component value parallel to the length of the structured catalyst. Thus, for at least 70%, such as 90% or 95%, of the length of the structured catalyst, i.e., along the z-axis (e.g., Figure 1-5Or 6a), the current density vector of the main current path will have a positive or negative value on the z-axis. This means that the current is forced from the first end of the structured catalyst to the second end, and then forced to the first end. The gas temperature entering the first end of the structured catalyst and the endothermic steam reforming reaction occurring on the structured catalyst absorb the heat from the structured catalyst. Therefore, the first end of the structured catalyst remains colder than the second end, and by ensuring that the current density vector of the main current path has a non-zero component value parallel to the length of the structured catalyst, this is carried out with a substantially continuously increasing temperature distribution, providing a controllable reaction front. In one embodiment, the current density vector has a non-zero component value parallel to the length of the structured catalyst, accounting for 70% of the length of the structured catalyst, preferably 80%, more preferably 90%, and even more preferably 95%. It should be noted that the term "length of the structured catalyst" refers to the size of the structured catalyst in the gas flow direction in the reactor unit accommodating the structured catalyst. In the structured catalyst as shown in the figure, the length is longitudinal, i.e., its longest dimension. In some drawings, this is represented by arrow z.

[0101] The power source is used to supply power to the macrostructure. For example, the current can be direct current, alternating current or pulsed current. By the method of the present invention, the structured catalyst is heated by resistive heating. This provides the heat required for the steam methane reforming reaction. When the hydrocarbon feed gas contacts the structured catalyst, heating of the hydrocarbon feed gas is provided by conduction, typically by adsorption on the surface of the structured catalyst, and by convection before the hydrocarbon feed gas contacts the surface of the structured catalyst. The catalytic chemical reaction of the hydrocarbon feed gas in the reactor unit produces a product gas, which is discharged from the reactor unit and can be used for further processing.

[0102] In one embodiment, the energy delivered to the macrostructure is 1 to 50 kW / m 2. These figures are exemplary only and depend on the size of the structured catalyst. However, the current, voltage and frequency available in the industry are generally sufficient to heat the structured catalyst. If alternating current is used, the suitable frequency should be in the range of 50-60Hz. The voltage between at least two electrodes can be any suitable voltage set to provide the desired heat flux. If the voltage is too low, the heat flux may become too low, and if the voltage is too high, the risk of arcing will increase. Exemplary values ​​are, for example, a voltage between 50 and 4000V, for example, between 100 and 1000V. Such values ​​will make the compactness of the macrostructure and the compactness of the reactor unit of the system possible. In addition, the current flowing between the electrodes through the macrostructure can be any suitable current, which together with the selected voltage will provide the required heat flux. The current can be, for example, between 100 and 2000A, for example, between 200 and 1500A.

[0103] In one embodiment, the given temperature range T is a range between about 200°C and about 1050°C. In a preferred embodiment, the given temperature range T is a range between about 400°C and about 1050°C. This temperature range is intended to represent the maximum temperature experienced by the hydrocarbon feed gas and / or product gas within the reactor unit containing the structured catalyst, and therefore this temperature range is also intended to cover the temperature of the product gas leaving the reactor unit. Typically, the outlet temperature of the product gas is in the range of 600°C to about 1050°C. In one embodiment, the design pressure of the reactor unit is between about 1 bar and about 50 bar, or even higher.

[0104] In one embodiment, the structured catalyst is shaped to ensure that during operation of the system, the peak current density at a point within the structured catalyst is at most 1000% of the average current density within the structured catalyst, preferably at most 500% of the average current density within the structured catalyst, more preferably at most 300% of the average current density within the structured catalyst, and most preferably at most 150% of the average current density within the structured catalyst. Thus, hot spots that may be harmful to the structured catalyst are avoided. The shaping of the structured catalyst to avoid the peak current density within the structured catalyst exceeding 1000% of the average current density can, for example, be by providing slits and / or cuts in the structured catalyst, as described above and shown in conjunction with the accompanying drawings. It should be noted that even though the current distribution throughout the structured catalyst may be somewhat uneven, such as Figure 6b As shown, however, due to the thermal conductivity of the conductive material of the macrostructure, the temperature within the structured catalyst wall is also relatively uniform. Therefore, due to the thermal conductivity of the macrostructure, if the current density in some parts of the macrostructure is slightly lower, it is not detrimental to the operation of the system.

[0105] When the steam reforming reaction is carried out at a relatively low pressure (e.g. 5 bar) When the steam reforming of hydrocarbons is carried out, the maximum temperature required should be between about 800°C and about 900°C. In more general terms, steam reforming of hydrocarbons can be described as: The maximum temperature required is usually between about 750°C and about 1050°C, while the pressure will be between 1 and 50 bar. For higher hydrocarbons with n ≥ 2, the maximum temperature required is usually between about 400°C and about 1050°C. Reverse Water Gas Shift Reaction Typically a high maximum temperature is required to push the equilibrium towards CO, so at a pressure of 1 to 50 bar, the temperature should be between about 600° C. and about 1050° C. Therefore, preferred temperature subranges for a given temperature range T are the range between about 750° C. and about 1050° C., the range between about 800° C. and about 950° C., or the range between about 600° C. and about 1050° C. However, other subranges of about 400° C. and about 1050° C. are conceivable depending on the reactions carried out in the reactor unit.

[0106] Examples of hydrocarbon gases are natural gas, city gas, methane or a mixture of methane and higher hydrocarbons. According to one embodiment, the inlet temperature of the hydrocarbon feed gas entering the reactor unit is about 200°C to about 600°C, and the outlet temperature of the product gas leaving the reactor unit is about 700°C to about 1050°C.

[0107] To control the reaction temperature, the heat added / removed from the reactor unit needs to be balanced with the heat consumed / generated by the chemical reaction. The addition / removal of heat needs to be balanced with the reaction rate, and in particular the approach to equilibrium as defined by β, where β is the ratio between the reaction quotient and the reaction equilibrium constant, where values ​​approaching 1 indicate that the reaction mixture is close to equilibrium and values ​​approaching 0 mean that the reaction mixture is far from equilibrium. In general, it is desirable to have the highest possible reaction rate, which is achieved at a low β, as long as the temperature can be adequately controlled by balancing the added energy in parallel.

[0108] For the steam methane reforming reaction, which is endothermic, heat needs to be added to the reaction to ensure that the reaction continues. Otherwise, the reaction will reach equilibrium, the β value will approach 1, and the reaction will slow down. However, on the other hand, if the temperature increases faster than the reaction rate, it is undesirable because exposing the unconverted hydrocarbons to high temperatures will result in the formation of thermodynamic carbon from the actual gas. A good way to follow this behavior is to use an approach to equilibrium. The approach to equilibrium for the steam reforming reaction is found by a preliminary calculation of the reaction quotient (Q) for a given gas as follows:

[0109]

[0110] Here j is the mole fraction of compound j and P is the total pressure (bar). This is used to determine the equilibrium temperature (T eq ), at which temperature a given reaction quotient is equal to the equilibrium constant:

[0111] Q=K SMR (T eq )

[0112] Where K SMR is the thermodynamic equilibrium constant of the steam methane reforming reaction. Then the approximate equilibrium (ΔT app，SMR ) is defined as:

[0113] ΔT app，SMR =TT eq

[0114] where T is the bulk temperature of the gas surrounding the catalyst material used.

[0115] In order to ensure the good performance of steam reforming catalyst, it is hoped that the catalyst can be app，SMR Classically, large industrial reformers have been designed to obtain a near equilibrium of 5-20°C at the reactor outlet.

[0116] Using the present invention, the heat flux can be controlled and matched directly to the kinetic properties of the catalyst material since they are somewhat unrelated.

[0117] BRIEF DESCRIPTION OF THE DRAWINGS

[0118] The present invention is illustrated by the following drawings:

[0119] Figure 1 The structured catalyst according to the invention is shown in a perspective view.

[0120] Figure 2 Shows a perspective view Figure 1 a structured catalyst in which a connector is attached;

[0121] Figure 3 An alternative embodiment of a structured catalyst with a connector attached is shown.

[0122] Figure 4 is a schematic cross-sectional view of a structured catalyst with an electrically insulating portion.

[0123] Figure 5 The steam methane reforming reaction approaches equilibrium at different gas flow rates on the structured catalyst (AT app，SMR )’s picture.

[0124] Figure 6a An embodiment of a structured catalyst for use in a reactor unit of the system of the present invention is shown.

[0125] Figure 6b Shows Figure 6a The current density distribution of the structured catalyst shown varies with the electrical effect delivered to the structured catalyst;

[0126] Figure 7a and 7b shows the temperature and conversion curves as a function of the electrical effect imparted to the structured catalyst; and

[0127] Figure 8a and 8b Simulation results for temperature and gas composition along the length of the structured catalyst are shown. DETAILED DESCRIPTION OF THE INVENTION

[0129] Figure 1 A structured catalyst 10 according to the present invention is shown in perspective view. The structured catalyst 10 comprises a macrostructure coated with a ceramic coating impregnated with a catalytically active material. Within the structured catalyst 10 are longitudinal directions ( Figure 1 The passage 70 is defined by a wall 75. Figure 1 In the embodiment shown, the walls 75 define an array of square channels 70 when viewed in the direction of flow as indicated by arrow 12. When viewed from above, the structured catalyst 10 has a substantially square perimeter defined by edge lengths el and e2.

[0130] The walls 75 of the structured catalyst are an extruded or 3D printed material coated with a ceramic coating, such as an oxide, which has been applied to the macrostructure 10. The ceramic coating is not shown in the figure. Therefore, during the description of the figures, if not otherwise indicated, references to the structured catalyst may be references to the macrostructure and vice versa. The ceramic coating is impregnated with a catalytically active material. Thus, when used in a steam methane reforming system, a hydrocarbon feed gas flows through the channels 70 and interacts with the heated surface of the structured catalyst and with the catalytically active material supported by the ceramic coating. Figure 1 In the structured catalyst 10 shown, slits 60 have been cut into the structured catalyst 10. The slits 60 can be used to force the current to take a zigzag route within the macrostructure 10, thereby increasing the current path and thus dissipating heat within the macrostructure 10. To ensure that no current flows in a transverse direction of the slits 60, the slits 60 in the structured catalyst 10 can be provided with embedded insulating material, but it is believed that a coating alone can also provide sufficient electrical insulation between the two components of the macrostructure.

[0131] Both ends of the channel 70 in the structured catalyst 10 are open. When the structured catalyst is used in a reactor unit, the hydrocarbon feed gas flows along the channel 70. Figure 1 The direction indicated by the arrows 11 and 12 in the middle flows through the unit and is heated by contact with the wall 75 of the channel 70 and by thermal radiation, conduction and convection. The heat drives the desired steam methane reforming process. The wall 75 of the channel 70 may, for example, have a thickness of 0.5 mm, and a ceramic coating having a thickness of 0.1 mm may be applied to the wall, for example. Even though the arrows 11 and 12 indicate that the hydrocarbon feed gas flow is downward, the opposite flow direction, i.e. upward flow, is also conceivable.

[0132] Figure 2 Shown in perspective Figure 1 The structured catalyst 10 is provided with a connector 7 attached thereto. The connectors 7 each connect a portion of the structured catalyst 10 to a conductor 40. The conductors 40 are each connected to a power source (not shown). Each connector 7 is connected to the upper portion of the structured catalyst. When the conductor 40 is connected to the power source, current flows through the conductor to the corresponding connector 7 and passes through the structured catalyst 10. The slits 60 impede the flow of current in the lateral direction ( Figure 2 Therefore, if Figure 2 As shown, the current flows downward along the slit 60 along the portion of the structured catalyst 10, and then it flows transversely to the longitudinal direction below the slit 60, as shown in FIG. Figure 2 As shown in FIG. 1 a , finally, the current flows upward along the longitudinal direction of the structured catalyst 10 to another connector 7 . Figure 2 The connector 7 in is mechanically fixed to the structured catalyst by means such as screws and bolts. However, additional or alternative fixing means are contemplated. In one embodiment, the power supply generates a voltage of 3V and a current of 400A. In another embodiment, the power supply generates a voltage of 1V and a current of 200A.

[0133] The connector 7 is made of, for example, a material such as iron, aluminum, nickel, copper, or an alloy thereof.

[0134] As described above, the structured catalyst 10 is coated with a ceramic coating loaded with a catalytically active material. However, the portion of the structured catalyst 10 connected to the connector 7 should not be coated with a ceramic coating. Instead, the macroscopic support of the structured catalyst 10 should be exposed or directly connected to the connector 7 to obtain a good electrical connection between the macrostructure and the connector. This process can be advantageously performed during assembly, for example, by polishing the interface between the macrostructure and the connector.

[0135] When the connector 7 and the conductor 40 are connected to the same end of the structured catalyst 10, that is, Figure 2At the upper end shown, the gas entering the reactor unit containing the structured catalyst 10 will be able to cool the connector 7 and the conductor 40. For example, the hydrocarbon gas entering such a reactor unit may have a temperature of 400°C or 500°C, and thus the connector 7 and the conductor 40 will not reach a temperature much higher than this.

[0136] Figure 3 An alternative embodiment of a structured catalyst 10' is shown with a connector 7'.

[0137] Figure 3 The structured catalyst 10' shown has a square or rectangular cross-section, similar to Figure 1 and 2 The structured catalyst 10 shown; however, Figure 3 The structured catalyst 10' does not have any slit cuts passing through it. Conductors 40 are placed at the upper and lower ends of the macrostructure 10'. The material of the conductor 40 is, for example, nickel. Alternatively, other suitable metals, or alloys such as FeCrAlloy, can be used as current distributors. The connector 7' in the form of a conductive rod is used to guide the current through the structured catalyst 10, i.e. the macrostructure. The connector 7' is fixed to the conductor 40 and the structured catalyst 10' by using a mechanical fixing device; however, alternative or additional fastening methods are also conceivable.

[0138] like Figure 3 As shown, connector 7" at the lower end of structured catalyst 10' may be made of a different material than connector 7' at the upper end of structured catalyst 10'. For example, connector 7' may be copper, while connector 7' may be nickel. Because nickel has a lower electrical conductivity than copper, connector 7" is larger than connector 7'.

[0139] Figure 3 The embodiment shown is suitable for temperatures below 800°C, for example 600-700°C.

[0140] Figure 4 is a schematic diagram of a cross section through a structured catalyst 10" of the present invention and an electrically insulating portion 60'. The electrically insulating portion is Figure 4 In the Figure 4 In the embodiment shown, three electrically insulating portions 60' intersect the structured catalyst 10" in most of its longitudinal direction. The conductor 7 is connected to the upper side of the structured catalyst 10", as shown in FIG. Figure 4As shown. During use of the structured catalyst 10", the conductor 7 is connected to a power source, and a hydrocarbon feed gas is brought into contact with the structured catalyst 10". Thus, the current flows from the first conductor through the structured catalyst 10" in a zigzag direction, i.e., from the first conductor downwardly and around the lower side of the first electrically insulating portion 60', then upwardly and around the upper side of the middle electrically insulating portion 60', then downwardly again and around the lower side of the third electrically insulating portion 60', and finally upwardly to the second conductor 7. It should be noted that any suitable number of electrically insulating portions 60' is conceivable. The electrically insulating portions 60' are solid electrically insulating materials, such as glass, which are provided in the form of cuts or slits in the macrostructure. The electrically insulating portions 60' ensure that the macrostructure portions are insulated from each other on the sides of the electrically insulating portions 60'. It should be noted that in this embodiment, as in all embodiments of the present invention, the flow direction of the gas may be the same as the direction of the current passing through the structured catalyst, or may be different. In Figure 4 In the embodiment of the present invention, the flow direction of the gas is, for example, from the upper side of the structured catalyst 10" to the bottom of the structured catalyst 10"; therefore, the flow of the current is only in the same direction as the gas flow, just like some parts of the structured catalyst 10", while the direction of the current is perpendicular to the direction of the gas flow in some parts and opposite (upward) in some parts.

[0141] Figure 5 The steam methane reforming reaction approaches equilibrium (ΔT app，SMR )’s picture.

[0142] Figure 5 It is shown that for a given gas flow rate over the structured catalyst, the approach to equilibrium upon entering the reactor unit containing the structured catalyst is 160-175° C. The approach to equilibrium decreases as the hydrocarbon gas flows over the structured catalyst. Figure 5 Shown from 10000Nm 3 / h to 200000Nm 3 / h gas flow rate approaches equilibrium (ΔT app，SMR ). For the minimum gas flow rate of 10000Nm 3 / h, the approach to equilibrium becomes below 10 °C at about 13% of the reactor length. Here, the reactor length is regarded as the length of the current path along the structured catalyst, so Figure 1 The total reactor length of the structured catalyst 10 shown in FIG. 1 is about 2 h. For higher gas flow rates, the higher the gas flow rate, the higher the approach to equilibrium, thus, for 200000 Nm 3 / h gas flow rate, the approach to equilibrium only reaches a minimum value below 80℃.

[0143] Figure 5 The general trend of all the curves in is that the approach to equilibrium decreases from the time of entry into the structured catalyst until pseudo-equilibrium is reached, where the heat added and the heat consumed are approximately equal. The approach to equilibrium from this stage is essentially constant or slightly increasing due to the overall temperature increase of the reactor unit. For example, if the flow rate is 150000Nm 3 / h, the approach to equilibrium is below 60°C at about 80% of the reactor length, but then rises to about 60°C.

[0144] Figure 6a An embodiment of a structured catalyst 10" for use in a reactor unit of the system of the present invention is shown. Figure 6a The structured catalyst 10" is shown in perspective view. As can be seen, the structured catalyst 10" has a single vertical slit 60 along the longitudinal axis of the catalyst 10". Figure 6a As shown. A single vertical slit 60 extends from the top of the structured catalyst 10" to the bottom thereof, along approximately 90% of the length of the structured catalyst. The single vertical slit 60 can be viewed as dividing the structured catalyst 10" into two halves. Each of the two halves has five horizontal slits 65. The function of the vertical slits 60 and the horizontal slits 65 is to allow the current to pass through the structured catalyst in a zigzag route.

[0145] Figure 6b Shows Figure 6a The relationship between the current density of the structured catalyst 10" and the electrical effect delivered to the structured catalyst 10" shown in FIG. Figure 6b In Comsol software Figure 6a Results of a multiphysics computational fluid dynamics simulation of the current distribution in the structure. Figure 6b The structured catalyst 10 is seen from the side. The two electrodes ( Figure 6b (not shown) is connected to the upper end of the left side of the structured catalyst 10". Figure 6b The scale bar on the right shows the intensity of the current density. When the power source is connected to the structured catalyst 10", the current extends from the upper end of the structured catalyst 10" to the bottom of the structured catalyst 10" and then to the back of the structured catalyst 10" in a zigzag manner due to the horizontal slits, and then enters the paper. Figure 6b As shown, it then zigzags upward toward the second electrode. The temperature of the structured catalyst 10" depends on the current density passing through the entire structured catalyst 10". Figure 6bIt can be seen from the graph that the current density is highest at the endpoints of the horizontal slits 65 entering the structured catalyst 10". These points are the points where the current path turns, that is, the current through the structured catalyst 10" is forced or directed in another direction. In addition, it can be inferred that for more than 80% of the structures, the current density vector of the main current path has a non-zero component value parallel to the length of the structured catalyst. In summary, from Figure 6b It can be clearly seen that the main current path can be controlled in the structured catalyst. This feature can control the temperature profile inside the structured catalyst.

[0146] It should be noted that even though the structured catalyst shown in the figures is shown as having channels with a square cross-section viewed perpendicular to the z-axis, any suitable shape of the cross-section of the channel is contemplated. Thus, the channels of the structured catalyst may alternatively be, for example, triangular, hexagonal, octagonal or circular, with triangular, square and hexagonal being preferred.

[0147] Figure 7a and 7b The temperature and conversion curves are shown as a function of the electrical effect delivered to the structured catalyst. Figure 7a is the experimental test result of a laboratory scale system with a length of 12 cm and a volume of 108 cm 3 The structured catalyst is composed of Figure 1 The outer wall / side and construction shown in the figure are defined, where on the opposite side of the first end, a copper conductor is welded to the first 2 cm of the monolith. The pressure of the pressure shell is 3.5 bar, and the feed gas temperature entering the system reactor unit is about 200°C. The composition of the feed gas is 31.8% CH4, 2.4% H2, 65.8% H2O, and the total gas flow rate is 102.2 Nl / h. It should be noted that due to the high energy losses at relatively small scales, the energy balance is better than that at larger scales. Figure 7a The conditions of the small-scale experiments shown in the graph are much better. Figure 7a It can be clearly seen that with the increase of power, the conversion rate of methane and the temperature both increase. When the temperature reaches above 900°C, the methane conversion rate reaches above 98%.

[0148] Figure 7b shows a similar experiment to that above, but at 21 bar. Again, from Figure 7b It can be clearly seen that with the increase of power, the conversion rate of methane and the temperature both increase. When the temperature reaches above 1060°C, the methane conversion rate reaches above 95%.

[0149] Figure 8a and 8bSimulation results showing temperature and gas composition along the length of the structured catalyst. A single channel of the structured catalyst is simulated. The length of the structured catalyst for this simulation is 10 cm, so the length of the single channel is 10 cm. The conditions within the pressure housing / structured catalyst / channel are:

[0150] Pressure: 29 bar

[0151] Import: 466℃

[0152] Total flow rate: 30Nl / h

[0153] • Feed gas composition entering the reactor / channel: 31.8% methane, 8.8% hydrogen, 2.3% carbon dioxide and 57.1% steam.

[0154] exist Figure 8a In the graph, the temperature of the channel wall is represented by Tw and the temperature of the channel center is represented by Tc. Tw and Tc are read from the scale on the right side of the graph. The methane conversion is represented by Cc and is read from the scale on the left side of the graph.

[0155] from Figure 8a As can be seen in Figure 1, the temperature of the channel walls in the structured catalyst increases continuously along almost all of the length of the structured catalyst. The temperature at the first end of the structured catalyst (z = 0 cm) is about 480 ° C, and the temperature at the second end of the structured catalyst (z = 10 cm) is about 1020 ° C. The temperature increase is steepest in the first 10% of the structured catalyst, and only in the last few percent of the length of the structured catalyst does the temperature change little. Therefore, when the current is turned around at the second end of the structured catalyst (from Figure 1 a), the temperature of the structured catalyst channel wall does not change substantially with increasing z values. However, Figure 8a It is also shown that the temperature in the center of the channel continues to increase along the entire length of the structured catalyst. However, it should be noted that the temperature in the center of the channel remains essentially constant for the first 5-7% of the length of the structured catalyst. This is due to the fact that the gas entering the structured catalyst cools the structured catalyst near its first end and due to the delay in the transfer of thermal energy from the wall to the center of the channel.

[0156] exist Figure 8a In Figure 1, the methane conversion in the center of the structured catalyst channel is also shown. It can be seen that for the first 10-12% of the channel length, the conversion is close to zero and that the conversion then increases monotonically and reaches a value of about 85%. As mentioned above, the small-scale reactor and its simulation provide less than optimal numbers, and significantly higher conversions can be achieved in a real-scale system. However, the simulation provides information about the conversion and temperature trends throughout the structured catalyst.

[0157] Figure 8b Shows Figure 8a The partial pressure of the main active gas in the channels of the structured catalyst. Figure 8b It can be clearly seen that the partial pressures of steam and methane decrease greatly along the length of the structured catalyst channels, while the partial pressures of hydrogen and carbon monoxide increase significantly. In addition, the partial pressure of carbon dioxide increases slightly along the length of the structured catalyst, but decreases towards the highest temperature, where the reverse water-gas shift reaction is thermodynamically favored.

[0158] Embodiment 1:

[0159] As discussed above, a general advantage of using resistive heating for steam reforming of hydrocarbons over current side-fired or top-fired reformers is that such fired reformers are limited in the hot section by the rate of heat transfer to the catalytic zone. By using resistive heating, this heat transfer limitation can be avoided because the structured catalyst itself is heated directly by the electric current running through the macrostructure.

[0160] Steam reforming reactions produce, for example, hydrogen and / or syngas from hydrocarbons. Syngas is a gas mixture containing hydrogen, carbon monoxide, and often also carbon dioxide. Today, decentralized markets for hydrogen often rely on expensive distribution and storage of hydrogen. As an alternative, resistive heated reforming can be envisioned as a small-scale hydrogen production technology that may have the potential for rapid startup for dedicated hydrogen production, as well as an electrical-based heating system rather than a combustion hot box.

[0161] For steam reforming reactions at temperatures ranging from about 700°C to about 950°C or even 1050°C The structured catalyst is a macrostructure of an alloy such as FeCrAlloy, which is coated with a ZrAlMgO-based x coating and impregnated with Ni as the active phase.

[0162] The structured catalyst was used to perform a reaction that promoted hydrogen production at 860°C and 5 bar with a steam to hydrocarbon carbon ratio of 2. The heat for the reaction was provided by an electric current running through the macrostructure.

[0163] Reforming of higher hydrocarbons:

[0164] Steam reforming of higher hydrocarbons is also possible: wherein n≥2. The reaction may be carried out at a temperature of about 400°C to about 950°C.

[0165] Suitable structured catalysts are, for example, coated with ZrAlMgO-based x Macrostructure of FeCrAlloy alloy coated and impregnated with Ni as active phase.

[0166] Embodiment 2:

[0167] An example of calculation for the process of the present invention is given in Table 1 below. A hydrocarbon feed gas, including, for example, hydrocarbon gas, hydrogen and steam, is fed to the structured catalyst of the present invention. The feed stream is pressurized to 28 kg / cm 2 ·g pressure, temperature is 500 ℃. The structured catalyst is in the form of a macrostructure with a square cross-section, the size of which is 0.4 times 0.4 times 0.35 meters. The structured catalyst has 10,000 channels, square cross-section, and a side length or edge length of 0.32 centimeters. The structured catalyst has slits parallel to its longitudinal direction, forming clusters of 5 times 5 channels. Except for the ends, these clusters are respectively insulated from adjacent clusters so that the current path through the macrostructure is a zigzag path. A current of 200A and a voltage of about 500V are applied to the structured catalyst of the present invention to heat the macrostructure, thereby heating the gas passing through the macrostructure, which corresponds to a power of 99kW deposited in the macrostructure.

[0168] During the time when the feed gas passes through the structured catalyst, the feed gas is heated by the structured catalyst and undergoes steam methane reforming to obtain a product gas having an outlet temperature of 963°C.

[0169] Table 1

[0170]

[0171] Example 3

[0172] Example 6 relates to a reactor unit comprising a structured catalyst in the form of a macrostructure having a total of 78,540 channels, each having a total wall length of 0.00628 m in cross section and a length of 2 m, giving a total surface area of ​​the catalyst surface of 987 m 2 For a reactor unit with this macrostructure, simulations were performed with varying gas flow rates across the macrostructure, with the gas composition in all calculations being 8.8% H2, 56.8% H2O, 0.2% N2, 0.1% CO, 2.3% CO2, and 31.8% CH4. In each simulation, kinetic models of steam methane reforming and water gas shift were established, and the surface flux (Q) of energy from the electrically heated macrostructure was varied, thereby adjusting the outlet temperature of the product gas from the reactor unit housing the macrostructure to 920°C. Figure 5 The figure shows the approach to equilibrium along the length of the reactor at varying total gas flow rates. 3 / h), the temperature at the outlet of the reactor unit approaches equilibrium below 5 °C, which means that the hydrocarbon conversion rate is 77%, while at a high flow rate (150000 Nm 3 / h), the approach to equilibrium is above 60°C, which corresponds to a conversion of only 64% of the hydrocarbons, and thus a low efficiency in the use of hydrocarbons. Therefore, the tight control of the heat flux in the present invention allows a tight control of the approach to equilibrium along the length of the reactor unit.

Claims

1. A reactor unit comprising a structured catalyst (10, 10', 10") and at least two conductors (40) electrically connected to the structured catalyst (10, 10', 10"), The structured catalyst (10, 10', 10") is used to catalyze a steam methane reforming reaction by contacting a hydrocarbon feed gas with the structured catalyst (10, 10', 10") within a given temperature range T; the structured catalyst (10, 10', 10") comprises a macrostructure, the macrostructure comprising a conductive material and having 10 -5 Ω·m to 10 -7 Ω·m resistivity, the macrostructure is loaded with a ceramic coating; wherein the macrostructure is manufactured by extrusion or 3D printing and subsequent sintering, wherein the macrostructure and the ceramic coating are sintered in an oxidizing atmosphere to form a chemical bond between the ceramic coating and the macrostructure; wherein the ceramic coating is loaded with a catalytically active material, the catalytically active material being configured to catalyze a steam methane reforming reaction; wherein the macrostructure is configured to conduct an electric current to provide an energy flux to the steam methane reforming reaction by resistive heating; wherein the at least two conductors (40) are shaped as current distributors to ensure that the supplied current is evenly distributed throughout the macrostructure during use; wherein the structured catalyst (10, 10', 10") is configured to be used in a system for performing a steam methane reforming reaction, in which the hydrocarbon feed gas enters the structured catalyst (10, 10', 10") at a first end and the product gas leaves the structured catalyst (10, 10', 10") at a second end; the at least two conductors are connected to the structured catalyst (10, 10', 10") at a position closer to the first end than to the second end; and Wherein during use, the structured catalyst (10, 10', 10") is configured to direct current from one conductor (40) to flow substantially along the longitudinal direction of the structured catalyst (10, 10', 10") to the second end and return along the longitudinal direction of the structured catalyst (10, 10', 10") to the second of at least two conductors (40); wherein the longitudinal direction extends between the first end and the second end.

2. The reactor unit according to claim 1, wherein the given temperature range T for the catalytic steam methane reforming reaction during the use of the structured catalyst (10, 10', 10") is a temperature interval of 200°C to 1050°C; and the structured catalyst (10, 10', 10") is configured to be heated to a temperature within the temperature interval.

3. A reactor unit according to claim 1 or 2, wherein the macrostructure comprises a plurality of nearly parallel or parallel channels (70).

4. A reactor unit according to claim 1 or 2, wherein the catalytically active material is in the form of submicron sized particles.

5. The reactor unit according to claim 1 or 2, wherein the macrostructure has at least one electrically insulating portion (60') which is arranged to increase the main current path within the macrostructure and has a length greater than the maximum dimension of the macrostructure.

6. The reactor unit according to claim 5, wherein the structured catalyst (10, 10', 10") has at least three electrically insulating portions, and the at least three electrically insulating portions are configured to guide current from a first conductor (40) to flow through the structured catalyst (10, 10', 10") to a second conductor (40) in a zigzag direction.

7. The reactor unit according to claim 6, wherein the structured catalyst (10, 10', 10") has at least three electrically insulating parts, and the at least three electrically insulating parts are configured to guide the current from the first conductor (40) to flow through the structured catalyst (10, 10', 10") in a zigzag direction, that is, to guide the current from the first conductor (40) downward and around the lower side of the first electrically insulating part (60'), then upward and around the upper side of the middle electrically insulating part (60'), then downward again and around the lower side of the third electrically insulating part (60'), and finally upward to the second conductor (40).

8. A reactor unit according to claim 1 or 2, wherein the structured catalyst (10, 10', 10") has a single vertical slit (60) along the longitudinal direction of the structured catalyst (10, 10', 10"), the single vertical slit (60) extending from the top of the structured catalyst (10, 10', 10") to the bottom thereof, along about 90% of the length of the structured catalyst (10, 10', 10"), so that the single vertical slit (60) divides the structured catalyst (10, 10', 10") into two halves; wherein each of the two halves has a horizontal slit (65), so that the vertical slit (60) and the horizontal slit (65) play a role in causing an electric current to pass through the structured catalyst (10, 10', 10") in a zigzag route.

9. The reactor unit of claim 1 or 2, wherein the resistance of the material and geometry of the macrostructure are configured to have a resistance of 500 to 50,000 W / m 2 heat generating capacity.

10. The reactor unit according to claim 1 or 2, wherein the structured catalyst (10, 10', 10") comprises two or more electrically connected macrostructures, wherein the individual macrostructures are placed side by side, on top of each other or a combination thereof.

11. A method for manufacturing a reactor unit according to any one of claims 1 to 10, the method comprising the following steps: a) providing a mixture of powdered metal particles and a binder, b) extruding the mixture into a structure, c) sintering the structure in a non-oxidizing atmosphere at a first temperature T1 to provide a macrostructure, wherein T1>1000° C., d) providing a ceramic coating on the macrostructure, e) sintering the macrostructure and the ceramic coating in an oxidizing atmosphere at a second temperature T2 to form a chemical bond between the ceramic coating and the macrostructure, wherein T2>800° C., f) impregnating the ceramic coating with a catalytically active material; and The method further comprises the step of connecting at least two conductors (40) to the structured catalyst (10, 10', 10") at a location closer to the first end than to the second end.

12. A method for manufacturing a reactor unit according to any one of claims 1 to 10, the method comprising the following steps: a) providing a mixture of powdered metal particles and a binder, b) extruding the mixture into a structure, c) sintering the structure in a non-oxidizing atmosphere at a first temperature T1 to provide a macrostructure, wherein T1>1000° C., d) providing a ceramic coating on the macrostructure, wherein the ceramic coating is loaded with a catalytically active material, and e) sintering the macrostructure and the ceramic coating in an oxidizing atmosphere at a second temperature T2 to form a chemical bond between the ceramic coating and the macrostructure, wherein T2>800° C.; and The method further comprises the step of connecting at least two conductors (40) to the structured catalyst (10, 10', 10") at a location closer to the first end than to the second end.

13. A method of manufacturing a reactor unit according to any one of claims 1 to 10, the method comprising the following steps: a) 3D printing of macrostructures by metal additive manufacturing fusion processes, b) applying a ceramic coating on the macrostructure, c) sintering the macrostructure and the ceramic coating in an oxidizing atmosphere at a second temperature T2, wherein T2>800° C., and d) impregnating the ceramic coating with a catalytically active material, thereby providing the structured catalyst (10, 10', 10"); and The method further comprises the step of connecting at least two conductors (40) to the structured catalyst (10, 10', 10") at a location closer to the first end than to the second end.

14. A method of manufacturing a reactor unit according to any one of claims 1 to 10, the method comprising the steps of: a) 3D printing of metal structures via binder-based metal additive manufacturing processes, b) sintering the metal structure in a non-oxidizing atmosphere at a first temperature T1, thereby providing the macrostructure, wherein T1>1000° C., c) applying a ceramic coating on the macrostructure, d) sintering the macrostructure and the ceramic coating in an oxidizing atmosphere at a second temperature T2, wherein T2>800° C., e) impregnating the ceramic coating with a catalytically active material, thereby providing the structured catalyst (10, 10', 10"); and The method further comprises the step of connecting at least two conductors (40) to the structured catalyst (10, 10', 10") at a location closer to the first end than to the second end.

15. A system for carrying out a steam methane reforming reaction by contacting a hydrocarbon feed gas with a structured catalyst (10, 10', 10") in a reactor unit according to any one of claims 1 to 10 within a given temperature range T, wherein the given temperature range T is an interval between 200°C and 1050°C; the system comprising: - a reactor unit comprising the structured catalyst (10, 10', 10") and at least two conductors (40) electrically connected to the structured catalyst (10, 10', 10"), and - an electrical power supply arranged to be connected to the structured catalyst (10, 10', 10") via at least two conductors (40) to allow electric current to pass through the structured catalyst (10, 10', 10") during operation of the reactor unit; and a pressure housing comprising an inlet for process gas to enter the structured catalyst (10, 10', 10") and an outlet for product gas to exit the structured catalyst (10, 10', 10"); wherein the hydrocarbon feed gas enters the structured catalyst (10, 10', 10") at a first end and the product gas leaves the structured catalyst (10, 10', 10") at a second end, and the at least two conductors are connected to the structured catalyst (10, 10', 10") at a position closer to the first end than to the second end.

16. The system according to claim 15, wherein the at least two conductors (40) surround the structured catalyst (10, 10', 10").

17. The system according to claim 15 or 16, wherein the at least two conductors (40) establish an electrical connection of the conductors to the structured catalyst (10, 10', 10") via a connector (7).

18. The system of claim 17, wherein the connector is made of a material selected from iron, aluminum, copper, nickel, or alloys thereof.

19. The system of claim 17, wherein the connector is in the form of a conductive rod.

20. The system according to claim 15 or 16, wherein the connection between the macrostructure of the structured catalyst (10, 10', 10") and the at least two conductors (40) is a mechanical connection, a welded connection, or a combination thereof.

21. The system of claim 15 or 16, wherein the system comprises a control system configured to control one or more of: current, voltage, heat flux, and space velocity.

22. The system of claim 15, wherein the structured catalyst (10, 10', 10") is configured to direct current from one conductor (40) substantially to a second end of the structured catalyst (10, 10', 10") and back to a second of at least two conductors (40).

23. The system of claim 15 or 16, wherein the structured catalyst (10, 10', 10") has at least one electrically insulating portion (60') configured to increase the length of a main current path between the at least two conductors (40) to a length greater than a maximum dimension of the structured catalyst (10, 10', 10").

24. The system of claim 23, wherein the at least two conductors (40) are connected to the structured catalyst (10, 10', 10") at the first end, and wherein the structured catalyst (10, 10', 10") has at least one electrically insulating portion (60'), the at least one electrically insulating portion (60') being configured to increase a main current path between the at least two conductors (40).

25. A system according to claim 15 or 16, wherein the structured catalyst (10, 10', 10") has at least one electrically insulating portion (60'), the electrically insulating portion (60') being configured to direct current through the structured catalyst (10, 10', 10") to ensure that for at least 70% of the length of the structured catalyst (10, 10', 10"), the current density vector of the main current path has a non-zero component value parallel to the length of the structured catalyst (10, 10', 10"), so that current is forced from the first end of the structured catalyst (10, 10', 10") to the second end and then to the first end.

26. A system according to claim 15 or 16, wherein the structured catalyst (10, 10', 10") is shaped to ensure that during operation of the system, the peak current density at a point within the structured catalyst (10, 10', 10") is at most 1000% of the average current density within the structured catalyst (10, 10', 10").

27. The system of claim 15 or 16, wherein the at least two conductors (40) have a shape similar to the macrostructure.

28. The system of claim 20, wherein the welded connection between the macrostructure of the structured catalyst (10, 10', 10") and the at least two conductors (40) is a brazed connection.

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