Directly electrically heated radial flow reactor for endothermic catalytic processes

Abstract

An electrically heated radial flow chemical reactor is described for efficiently providing reaction heat to the endothermic chemical processes of the catalytic type.

Description

[0001] DIRECTLY ELECTRICALLY HEATED RADIAL FLOW REACTOR FOR ENDOTHERMIC CATALYTIC PROCESSES

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a directly electrically heated radial flow chemical reactor to efficiently provide reaction heat to endothermic chemical processes of the catalytic type as an alternative to conventional heating methods.

[0004] BACKGROUND ART

[0005] It is by now ascertained that anthropogenic greenhouse gas emissions into the atmosphere, particularly CO2, are responsible for rapid climate change and damage resulting from extreme natural events; methods are therefore being studied in all sectors of human activity to reduce these emissions as much as possible.

[0006] Chemical plants are considered one of the industrial sectors in which it is most difficult to achieve a drastic reduction in CO2 emissions. A significant share of CO2 emissions in this sector is associated with the need to provide heat to highly endothermic chemical processes.

[0007] For example, methane steam reforming units used in ammonia and methanol synthesis processes account for 1-2% of global CO2 emissions. Half of these emissions are associated with the combustion of natural gas and purge synthesis gas to provide adequate reaction heat to support the production of syngas (a mixture of CO and H2, possibly containing lower amounts of CH4 and CO2).

[0008] Other processes based on endothermic reactions which require high-temperature heat and result in large CO2 emissions include, for example, the reverse water-gas shift reaction, CO2 + H2 — > CO + H2O (also known in the industry as RWGS); ammonia cracking; and aliphatic dehydrogenation reactions (e.g., synthesis of styrene from ethylbenzene).

[0009] In recent years, given the increasing availability of large amounts of electricity from low-carbon renewable sources, many studies have focused on electrically heated reactors; for example, the publication “Plugging in: What electrification can do for industry”, O. Roelofsen et al., McKinsey & Company (2020), claims that it would be already technologically possible to replace up to half of industrial fuel consumption with electricity.

[0010] The use of electric current as a heating source in endothermic reactors is described in several scientific and patent publications.

[0011] A first example of an electrically heated chemical reactor is reported in the article “Electrified methane reforming: A compact approach to greener industrial hydrogen production”, S. T. Wismann et al., Science 364, 756-759 (2019). This reactor consists of a Fe-Cr-Al alloy tube with an external diameter of 6.0 mm and a wall thickness of 0.35 mm; the tube is internally coated with a layer of porous zirconia, impregnated with nickel as a catalyst. The coatings of support structures or surfaces, conventionally made with ceramic materials, are referred to in the sector with the term “washcoa ’, which will also be used in this description. The tube is connected to an electric current generator and, by virtue of the very thin thickness thereof, it acts as an electrical resistor in the circuit. This solution has the limitation of allowing only a small ratio between the quantity of catalyst and the internal volume of the reactor, a ratio that is notoriously low in the case of washcoated solutions of structured catalysts and which decreases as the diameter of the tube constituting the reaction chamber increases, reaching a limited volumetric power density.

[0012] Patent application EP 4043100 Al describes an axial flow system consisting of a tube (pressure shell) and inserts electrically isolated from the tube which are crossed by current, with a configuration similar to that of the Wismann article described above.

[0013] The articles “Electrified methane steam reforming on a washcoated SiSiC foam for low-carbon hydrogen production,” AIChE Journal 69 (2023) el7620

[0014] (https: / / doi.org / 10.1002 / aic.17620) and “Direct electrification of Rh / AhCh washcoated SiSiC foams for methane steam reforming: An experimental and modelling study”, Inti. Journal of Hydrogen Energy, vol. 48 (39) 2023, pp. 14681-14696, both by L. Zheng et al., describe reactors with an axial flow configuration heated by means of an electrically conductive insert connected to an electric generator; such configuration leads to a generated thermal power almost uniformly distributed in the reactor volume.

[0015] The article “A compact catalytic foam reactor for decomposition of ammonia by the Joule-heating mechanism”, A. Badakhsh et aL, Chemical Engineering Journal, 426 (2021) 130802, describes a reactor consisting of a gas-tight and pressure-tight casing inside which there is an active element formed by a catalyst support in the form of metal foam crossed by current and heated by Joule effect.

[0016] Patent applications WO 2019 / 228798 Al and WO 2022 / 219053 Al describe reactors consisting of a thermally and electrically insulated pressure-tight casing, inside which there are the active elements of the system, which may have different geometries or configurations, but in which, in any case, the crossing of the reactor by the gases involved in the reaction is axial. The text of these documents does not mention the possibility of modulating the volumetric distribution of thermal power.

[0017] Patent application WO 2023 / 062591 Al, assigned to the present Applicant, describes an electrically heated reactor, in which the heating is provided by heating elements in thermal contact with a thermally conductive structure and with the possible contribution of heating from other sources (combustion, thermal jackets, ...); also in this reactor the gas flow occurs in the axial direction. Also in this case, the configuration of the system does not allow to modulate the distribution of thermal power.

[0018] In addition to the specific limitations of each of the configurations described above, a common issue to all these configurations is that they are characterized by a uniform distribution of thermal power in the volume of the reactor when electrically heated; however, this uniform distribution of thermal power is not optimal, and it would be preferable to have a maximum power in the entry area of the reactor.

[0019] Patent application WO 2023 / 013419 Al describes an electrified radial flow reactor, heated by means of a plurality of concentric electrical resistors and covered by a catalyst layer. Each resistor is heated by a specific control system, which allows for a non-uniform heat distribution along the radial coordinate of the reactor. However, the plurality of resistors and control elements leads to complex construction and operation management of the reactor; furthermore, the amount of catalyst is limited to that which may be deposited on the surface of the resistors, therefore much lower than that of a conventional packed-bed reactor. Patent application US 2004 / 0022701 Al describes a system for the abatement of the exhaust gases of internal combustion engines. This system is based on the use of a mixture of perovskites of general formula Ai-xA^Bi-yB^Ch and vanadates of general formula MVO3 or M4V2O7 combined with the application of a plasma to activate reactant gas species and promote the reaction of the species to be abated. Plasma excitation requires voltages in the order of a few kV to tens of kV, and frequencies between 50 and 5000 Hz. The mixture of perovskites and vanadates is in the form of a cylindrical shell (self-supporting, or held in place by the electrodes when in particle form); in the system of this document the gases are forced to pass from the outside of the cylindrical shell towards the central area thereof, thus they cross the structure with a centripetal flow direction.

[0020] It is the object of the present invention to provide a reactor for endothermic catalytic processes which overcomes the limitations of the reactors of the prior art, and in particular which achieves the thermal power distribution preferable for the reactions to be provided, with maximum power dissipation in the entry area of the reactant gases.

[0021] SUMMARY OF THE INVENTION

[0022] These objects are achieved according to the present invention by means of a reactor for carrying out endothermic catalytic reactions, comprising:

[0023] - a pressure-tight casing with a cylindrical side wall and two base walls, defining a chamber;

[0024] - inside and coaxial with said internal chamber, a porous structure with communicating porosities made of a material having an intrinsic electrical resistivity comprised between 1 x 10'6m and 100 (Im, said porous structure having the shape of a cylindrical shell, formed by a single part or by several modules stacked and / or side by side, in which said porous structure has an external diameter which is smaller than the internal diameter of said chamber and a height equal to the height of said chamber, so as to define a cylindrical zone of the reactor corresponding to the internal cavity of the porous structure and an annular zone of the reactor corresponding to the space between the cylindrical wall of the casing and the external surface of the porous structure;

[0025] - particles of a catalyst in the cavities of the porous structure or a catalytically active material deposited on the walls of the cavities of the porous structure having a resistivity higher than that of the porous structure;

[0026] - a first electrode in contact with the internal surface of the porous structure and such as not to completely cover said internal surface, and a second electrode in contact with the external surface of the porous structure and such as not to completely cover said external surface, said first and second electrodes connected to an electric generator, external to the reactor, sized to heat at least part of the porous structure up to the temperature required by the reaction to be carried out in the reactor;

[0027] - means for electrically insulating said first and second electrodes from the contact with said two base walls of the reactor casing;

[0028] - at least one duct for feeding reactant gases arranged on one of the base walls of the reactor casing in correspondence with said cylindrical zone of the reactor corresponding to the internal cavity of the porous structure; and

[0029] - at least one duct for the outlet of the produced gases arranged on the reactor casing and in correspondence with said annular zone.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] The invention will be described below with reference to the Figures, in which:

[0032] - Figure 1 shows a diagrammatic view in a section along the axis of a possible embodiment of the reactor of the invention;

[0033] - Figure 2 shows a section along a plane perpendicular to the axis of the reactor in a configuration in which a single volume is used to accommodate the catalyzed porous support;

[0034] - Figure 3 shows a diagrammatic view of the reactor of the invention, in a section perpendicular to the axis thereof, in which the relevant radial dimensions of the reactor itself are reported;

[0035] - Figure 4 shows an alternative version of the geometry shown in Figure 2 in which the cylindrical shell-shaped volume is divided into wedges by means of suitable electrical insulators;

[0036] - Figure 5 diagrammatically shows enlargement of a porous structure in which the surfaces of the pores are covered by a ceramic layer on which a catalyst is deposited;

[0037] - Figure 6 diagrammatically shows an enlargement of a porous structure in which catalyst pellets are accommodated.

[0038] DETAILED DESCRIPTION OF THE INVENTION

[0039] The reactor of the invention has a cylindrical geometry with a radial flow, in which the reactant gases are fed by means of a duct to a central cylindrical zone, they radially cross a porous structure which supports the catalyst and are discharged from the reactor by means of a side duct in communication with the peripheral annular zone of the reactor itself.

[0040] This radial flow configuration intrinsically creates a non-uniform power distribution: for geometric reasons related to the side surface of the cylinder increasing as the radius increases, the current density decreases with the radius itself. The heat generation by Joule effect is therefore maximum at the entry and decreases along the radial crossing coordinate, as the reaction proceeds, in accordance with the decrease in energy demand of the system. It is therefore possible to ensure optimal temperature profiles in the catalytic bed, which may be modulated by varying the geometry (ratio between internal diameter and external diameter of the porous structure) given the same power supplied and the same reactor volume.

[0041] In the following description, reference is always made to a single reactor, which may be of various types and take on different configurations, but of course, in the practical implementation of chemical plants, systems consisting of two or more units of the described reactor may be used, generally in parallel with each other, to increase the productivity of the plant.

[0042] In the Figures, an equal number corresponds to an equal element.

[0043] Figures 1 and 2 show two diagrammatic views of the reactor of the invention in a first possible embodiment, respectively in a section along the axis and in a section perpendicular to the axis of the reactor.

[0044] The reactor, 10, has a pressure-tight casing 11 which encloses the active elements of the reactor itself. The casing is formed by joining a cylindrical side wall I la and two base walls, 1 lb and 1 lb’, which define an internal chamber of the casing itself. The walls which constitute the casing 11 have typically a thickness comprised between 1 and 2 cm.

[0045] The cylindrical geometry of the casing, in addition to realizing the advantages of the radial flow conditions of the reagents, avoids the presence of dead corners in the wall where reagents or products may stagnate.

[0046] The size of the reactor may vary within wide limits; typically, the external diameter of the casing may be comprised between 0.1 and 4 m, and the length between 0.2 and 5 m.

[0047] The casing is made of metal materials adapted to ensure pressure tightness and capable of withstanding the temperatures of the reactions carried out in the reactor; the resistance must be mechanical, i.e., the casing shall not deform at operating temperatures, and chemical, i.e., the material with which the casing is made shall not react with reactant gases and products involved in the reaction carried out in the reactor, at the temperatures thereof. The preferred materials for the construction of the casing are stainless steels. Steels useful for the objects of the invention are those with low carbon content (steels with a carbon content of less than 1% by weight, nickel content in the range of 15-25% by weight, chromium content in the range of 20-25% by weight).

[0048] Inside the casing there is a porous structure 12, having the shape of a cylindrical shell, i.e., a tube with thick walls.

[0049] The porous structure 12 is arranged coaxially with respect to the casing and has a length equivalent to that of the chamber; since the two ends of the porous structure come into contact with the two walls 1 lb and 1 lb’, a partition of the internal chamber of the casing is created, which is divided into a cylindrical zone 13 defined by the internal surface of the porous structure 12 and the two walls 11b and 11b’, and an annular zone 14 comprised between the external surface of the porous structure 12, the internal surface of the cylindrical wall I la, and the two walls 1 lb and 1 lb’. The porous structure 12 is in contact with two electrodes. In particular, a first electrode, 15, is in contact with the internal cylindrical surface of the structure 12, facing the central zone 13 of the reactor, while a second electrode, 16, is in contact with the external cylindrical surface of the structure 12, facing the annular zone 14 of the reactor. The two electrodes 15 and 16 are fed by a generator G, by means of suitable electrical connections. The electrical power supplied by the electrodes 15 and 16 allows the porous structure 12 to be electrically heated by Joule effect.

[0050] Figure 3 shows a sectional view of a reactor of the invention, similar to the view in Figure 2 but simplified with respect thereto since the electrodes are not shown. This Figure indicates the relevant radial dimensions of a reactor of the invention, which are the internal radius ri of the reactor, the internal radius n of the porous structure, the external radius n of the porous structure, and the thickness t of the porous structure. The thickness t of the porous structure may vary between 0.02 and 1.5 m, depending on the overall size of the reactor.

[0051] In an alternative embodiment, the porous structure does not constitute a single part which occupies the entire cylindrical shell, but is formed by modules, for example having the same circular crown shape as the structure 12 described above, but a lower height, stacked vertically until reaching the desired height; or alternatively, the modules may be in the form of wedges having the same height as the structure 12 and which, in a top view, are sections of a circular crown; it is also possible to adopt both these embodiments for the modules constituting the complete porous structure, i.e. these have a height which is only a fraction of the height of the overall porous structure and which, in a plan view, have the shape of sections of a circular crown. These configurations, in which the overall porous structure is built in a modular manner, are particularly useful when the porous structure is large in size. Such modules or wedges may be electrically connected in series or in parallel depending on the supply voltage of the system.

[0052] Figure 4 shows, in a diagrammatic sectional view similar to that of Figure 2, an example of a reactor in which the porous structure is formed by modules in the shape of circular crown sections. The reactor, 20, still comprises the external casing I la and the internal chamber thereof is divided by the porous structure into a central cylindrical zone 13 and an external annular zone 14. In this case, however, the porous structure is divided into four modules 22, 22’, 22” and 22’” by four septa 21, 21’, 21” and 21’” made of electrical insulating material. In the case described in the Figure, one of these septa, 21, also interrupts the circular continuity of both the internal and external electrodes, the two septa 21’ and 21’” interrupt the continuity of only the internal electrode, and the sept 21” interrupts the circular continuity of only the external electrode; thereby, the external electrode, which in the reactor 10 is the element 16, is divided into two halves 26 and 26’ in the reactor 20, while the internal electrode, which in reactor 10 is element 15, is divided into three sections 25, 25’ and 25” in the reactor 20. The indications relating to the thickness of the porous structure reported above with reference to Figures 1 and 2 also clearly apply to the embodiment of Figure 4.

[0053] In the case of the reactor of Figures 1 and 2, the overall electric current through the porous structure 12 remains constant along the radial coordinate; the current density in the system is therefore a function of 1 / r and, if a uniform electrical resistivity is taken on for the porous structure, the specific thermal power generated varies along the radius as 1 / r2. Thereby, the dissipated thermal power (and therefore the heating of the reactant system) is maximum in the entry area of the reactant gases in the porous structure 12, and decreases along the radial coordinate towards the outside; this heat distribution is the optimal one for obtaining the reactions expected in the reactor, and is not obtained with the axial flow reactors of the prior art.

[0054] In the case shown in Figure 4, the modules constituting the overall porous structure are electrically connected in series: assuming, for example, that section 25 of the internal electrode is the point with the highest potential, the current flows, in sequence, in module 22, in electrode 26, in module 22’, in electrode 25’, in module 22”, in electrode 26’, in module 22’” and finally in electrode 25”, which is the point with the lowest potential. Such configuration maintains the advantages associated with radial power distribution but allows the overall circuit resistance to be modulated. While the resistance of the configuration in Figure 2 is given by the properties of the material and by the chosen geometry, with the modular system in Figure 4, the number of sections into which the overall porous structure is divided introduces a further degree of freedom in the design of the reactor. In this configuration, assuming that the volume of the septa 21-21”’ is negligible, the resistance is equal to R / n2, n being the number of modules into which the volume of the overall porous structure is divided and R being the resistance of the system consisting of a single porous structure.

[0055] To ensure a homogeneous heating of the porous structures, the electrodes, 15 and 16 in the case of the structure in Figure 1 and 2, or 25, 25’, 25”, 26 and 26’ in the case of the structure in Figure 4, are distributed uniformly on the internal and external cylindrical surfaces of the structure itself, but in such a way as to leave part of said surfaces free for the passage of the reactant gases from the zone 13 towards the porous structure, and from the latter towards the zone 14. This condition may be obtained for example with electrodes in the form of a mesh or net or of a perforated metal sheet, preferably with an orderly distribution of the holes.

[0056] The electrodes may be made of steel, copper, aluminum. The fundamental feature of these elements is the low electrical resistivity, which in fact allows for an electrical isopotential over the entire surface and the ability to transport high current densities without overheating. Ideally, the resistivity of the electrode must be at least 2-3 orders of magnitude lower than that of the one or more porous structures described above.

[0057] In the case where the catalytic material is deposited on the surfaces of the cavities of the porous structure, the electrodes only have the function of providing electrical contact with the structure itself, and the contact surface between the electrodes and the porous structure is preferably the minimum possible which allows for an effective heating thereof, leaving as much as possible of surface of the structure free for the passage of gas.

[0058] In the case of catalytic material in the form of pellets, the electrodes also have the function of retaining the pellets inside the structure itself, and therefore, in addition to the dimensional features imposed by the requirement for effective heating of the structure, they must also have openings smaller than the pellets. Since the electrodes are present over the entire extension of the internal and external cylindrical surfaces of the porous structure, they also come into contact with the upper and lower walls of the reactor chamber. To avoid short circuits due to contact between the ends of the electrodes and the metal base walls 1 lb and 1 lb’ of the reactor casing, in the internal part of the chamber in correspondence with said base walls there are two electrical insulating elements 17a and 17b, made for example with technical ceramics, alumina, mullite or similar materials.

[0059] In all the configurations described above, and also in other possible ones which derive from combinations of the modalities described above, the passage from zone 13 to zone 14 is therefore possible only through the porosities of the porous structure (12 or 22-22’” in the examples in Figures 1, 2 and 4); the reactant gases entering the reactor in the central cylindrical zone 13 are then forced to cross the porous structure where they come in contact with the catalyst, giving rise to the desired reaction; the reaction products then exit the external cylindrical surface of the porous structure towards the annular zone 14, and are released from the reactor. The flow of gases in the reactor, and in particular in the porous structure, is therefore of the radial type from the inside towards the outside.

[0060] To ensure this condition, the porous structure has communicating porosities, which means that there are no completely closed pores in the material and that there is a free path which connects any pair of pores of the structure. The porosity of this structure is comprised between 70 and 97%, preferably between 80 and 90%; this value is the ratio between the total volume of the pores and the geometric volume of the structure calculated taking into account the external dimensions thereof. The total volume of the pores may be measured with gravimetric measurements by comparing the density of the catalytic support and the density of the source material.

[0061] The size of the pores are comprised between 0.2 and 5 mm. Pores of this size may be obtained for example with foaming methods, extrusion in the case of honeycomb structures produced by extrusion / turning or according to the various techniques, such as selective melting, powder thread deposition or chemical binder deposition, which are defined as “additive manufacturing” or 3D printing.

[0062] In the case of foams, the cavities have irregular polyhedral shapes, in which the material of the structure is present only on the edges of these polyhedral shapes while the faces are open, putting each cavity in communication with the adjacent ones. The cavities in this case have a variable size and a disordered distribution in the structure.

[0063] With additive manufacturing techniques, on the other hand, Periodic Open Cellular Structure (POCS) are produced in which the cavities typically have a constant shape and size and an ordered and periodic distribution in the structure; POCS structures, as well as the methods for the production thereof, are described for example in patent EP 3436674 Bl, in patent KR 102149821 Bl and in patent application DE 102016009272 Al.

[0064] The material used to make the porous structure must have an intrinsic electrical resistivity comprised between 1 x 10'6(Im and 100 (Im, preferably between 1 x 10'4and 1 (Im, to ensure the possibility of obtaining the power densities required for the catalytic process with voltage drops of 1-1000 V between the two electrodes. The choice of material depends on the reaction which is intended to be carried out with the reactor, since the temperature at which the reaction must be carried out and any chemical incompatibilities with the reacting system and the products thereof depend on this. Useful materials for making the porous structure are silicon carbide, silicon carbide bonded by silicon (SiSiC) and silicon dinitride.

[0065] The porous structure may have the pore surfaces covered with catalytic material; this configuration generally requires that a catalyst layer be firstly deposited on the pore surfaces by means of the well-known washcoating technique. This possibility is diagrammatically shown in Figure 5, taking as an example a porous structure in the form of a foam; the Figure shows in the upper part a micrograph of a ceramic foam, and in the lower part an enlarged reproduction of the edge 50 of a cavity of the porous structure highlighted in the round section in the Figure; the edge 50 consists of a support 51 formed by one of the materials mentioned above, covered by a layer 52 of catalytic material.

[0066] Alternatively, the porous structure may simply accommodate catalyst pellets in the porosities thereof. The pellets are loaded by pouring them from above inside the porosities, possibly aiding the entry of the pellets into the pores by making the porous structure or the reactor casing vibrate. This possibility is diagrammatically shown in Figure 6, considering as an example in this case a porous structure of the POCS type. The Figure shows the structure, 61, in whose cavities there are pellets 62 covered with catalytic material or entirely made of catalytic material.

[0067] Only as an example, Figures 5 and 6 show the cases in which the catalyst in the form of a coating of the washcoat type is present on a porous structure in the form of a foam, and the catalyst pellets are accommodated in a POCS structure, but of course it is also possible to realize the reactor by depositing the catalyst by washcoating on a POCS structure, or by inserting pellets in a porous foam structure.

[0068] The catalytic material which is accommodated within the pores of the structure depends on the chemical reaction to be carried out in the reactor. Examples of conventional endothermic reactions which may be carried out in a reactor of the invention, with the characteristic catalysts thereof, are given below:

[0069] A) natural gas / biogas steam reforming: for example using catalysts based on Ni or Rh on dispersing ceramic supports such as alumina, magnesium / aluminates;

[0070] B) ammonia cracking: for example using catalysts based on Fe, Ru, Ni on alumina, titania, SiCh;

[0071] C) dehydrogenation of alkanes: for example using catalysts based on Pt, Sn on dispersing ceramic supports;

[0072] D) reverse water-gas shift reaction (RWGS): for example using catalysts based on Ni, Fe, Pt, Cu on dispersing ceramic supports such as alumina.

[0073] Finally, the reactor comprises at least one duct for feeding reactant gases and at least one exhaust duct for produced gases; the feeding and exhaust ducts conventionally have a section which is a fraction of about 10-15% compared to the overall section of the reactor.

[0074] A possible arrangement of the two feeding and exhaust ducts is shown in Figure 1. In this example, the feeding duct, 18, is arranged on one of the base walls of the reactor casing (in Figure 1, wall 1 lb is exemplified) in correspondence with the cylindrical zone 13, while the exhaust duct, 19, is arranged on the reactor casing and in correspondence with the annular zone 14 of the reactor, in particular on the wall 1 la of the casing 11 and in the vicinity of the wall 1 lb’; the exhaust duct may also be present on the wall 1 lb’. This configuration, in which the feeding duct is arranged on a base of the cylindrical casing, and the exhaust duct is arranged on the opposite base or in proximity thereto, is defined in the industry as “centrifugal geometry Z”. The reactor of the invention may also take on an alternative configuration (not shown in the Figures), in which the exhaust duct is arranged on the same base on which the feeding duct is, or in proximity thereto; this possible alternative geometry is known in the industry as “centrifugal Greek pi geometry.”

[0075] In each of these possible configurations, the feeding duct is arranged in correspondence with the cylindrical zone 13, and the exhaust duct is arranged on the reactor casing and in correspondence with the annular zone 14 of the reactor.

[0076] To increase the thermal efficiency of the reactor, it is also possible to add thereto a layer of thermal insulation adhering to the internal part of the cylindrical wall I la of the casing, or externally to the casing, or in both arrangements.

Claims

CLAIMS1. Reactor (10; 20) for carrying out endothermic catalytic reactions, comprising:- a pressure-tight casing (11) with a cylindrical side wall (I la) and two base walls (1 lb, 1 lb’), defining a chamber;- inside and coaxial with said internal chamber, a porous structure (12) with communicating porosities made of a material having an intrinsic electrical resistivity comprised between 1 x 10'6Qm and 100 (Im, said porous structure having the shape of a cylindrical shell, formed by a single part or by several modules stacked and / or side by side, and wherein said porous structure has an external diameter which is smaller than the internal diameter of said chamber and a height equal to the height of said chamber, so as to define a cylindrical zone (13) of the reactor corresponding to the internal cavity of the porous structure and an annular zone (14) of the reactor corresponding to the space between the cylindrical wall (1 la) of the casing and the external surface of the structure;- particles of a catalyst (62) in the cavities of the porous structure or a catalytically active material (52) deposited on the walls of the cavities of the porous structure;- a first electrode (15) in contact with the internal surface of the porous structure and such as not to completely cover said internal surface, and a second electrode (16) in contact with the external surface of the porous structure and such as not to completely cover said external surface, said first and second electrodes connected to an electric generator (G), external to the reactor, sized to heat at least part of the porous structure up to the temperature required by the reaction to be carried out in the reactor;- means (17a, 17b) for electrically insulating said first and second electrodes from contact with said two base walls of the reactor casing;- at least one duct (18) for feeding reactant gases arranged on one of the base walls of the reactor casing in correspondence with said cylindrical zone (13) of the reactorcorresponding to the internal cavity of the porous structure; and at least one duct (19) for the outlet of the produced gases arranged on the reactor casing and in correspondence with said annular zone.

2. Reactor according to claim 1, wherein the external diameter of the casing is comprised between 0.1 and 4 m, the length of the reactor is comprised between 0.2 and 5 m, the thickness t of the porous structure (12) is comprised between 0.02 and 1.5 m, and the walls of the casing have a thickness comprised between 1 and 2 cm.

3. Reactor according to any one of claims 1 or 2, wherein the casing is made of a stainless steel, preferably a steel with a carbon content lower than 1% by weight, nickel content in the range of 15-25% by weight, and chromium content in the range of 20-25% by weight.

4. Reactor according to any one of the preceding claims, wherein the porous structure (12) is formed by modules having the same circular crown shape as the overall porous structure but lower in height, stacked vertically until reaching the desired height, or is formed by modules in the form of wedges having the same height as the overall porous structure and in the shape of circular crown sections in a top view, or by modules having a height lower than that of the overall porous structure and in the shape of circular crown sections in a top view.

5. Reactor (20) according to claim 4, wherein the overall porous structure is divided by four septa (21, 21’, 21”, 21’”) made of electrical insulating material into four modules in the shape of circular crown sections in a top view (22, 22’, 22”, 22’”), and wherein one of said septa (21) interrupts the circular continuity of both the internal electrode and the external electrode, two of said septa (21’, 21’”) interrupt the continuity of only the internal electrode (15), and one of said septa (21”) interrupts the circular continuityof only the external electrode (16).

6. Reactor according to any one of the preceding claims, wherein the electrodes (15, 16;25, 25’, 25”, 26, 26’) are made with a material selected from steel, copper and aluminum, they are uniformly distributed on the internal and external cylindrical surfaces of the overall porous structure, and they are in the form of a mesh or net or a perforated metal sheet, to leave part of said surfaces free for the passage of the reactant gases from the cylindrical zone (13) towards the porous structure, and from the porous structure towards the annular zone (14).

7. Reactor according to any one of the preceding claims wherein, when the catalytic material is in the form of pellets, the electrodes have openings smaller than those of said pellets to retain the pellets inside the porous structure.

8. Reactor according to any one of the preceding claims, wherein the porosity of the porous structure is comprised between 70 and 97% and the size of the pores is comprised between 0.2 and 5 mm.

9. Reactor according to any one of the preceding claims, wherein the porous structure, made of a single part or formed by stacked and / or side by side modules, is produced with a ceramic foaming method, by extrusion in the case of honeycomb structures, or with additive manufacturing or 3D printing techniques chosen from selective melting, powder thread deposition and chemical binder deposition.

10. Reactor according to claim 9, wherein when the porous structure, made of a single part or formed by stacked and / or side by side modules, is produced with additive manufacturing techniques, this has a structure of the “POCS” type in which the cavities have essentially constant shape and size and an ordered and periodic distribution.

11. Reactor according to any one of the preceding claims, wherein the material with which the porous structure (12) is made of has an intrinsic electrical resistivity comprised between 1 x 10'4Qm and 1 Qm.

12. Reactor according to any one of the preceding claims, wherein the material with which the porous structure is made of is selected from silicon carbide, silicon carbide bonded by silicon (SiSiC) and silicon dinitride.

13. Reactor according to any one of the preceding claims, wherein the ducts (18) for feeding reactant gases and the exhaust ducts (19) for the produced gases have a section comprised between 10 and 15% with respect to the overall section of the reactor.

14. Reactor according to any one of the preceding claims, wherein the duct for feeding reactant gases is arranged on one of the base walls of the reactor casing, while the exhaust duct for the produced gases is arranged on the reactor casing on the base wall of the casing opposite to that on which said feeding duct is arranged, or on the same base wall of said feeding duct, or on the cylindrical side wall (1 la) of the casing in the vicinity of one of said two base walls.

15. Reactor according to any one of the preceding claims, further comprising a thermal insulation layer adhering to the internal part of the cylindrical wall (1 la) of the casing, or externally to said casing, or in both arrangements.

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