CATALYST AND SYSTEM FOR METHANE STEAM REFORMING BY RESISTANCE HEATING; SAID CATALYST'S PREPARATION

Abstract

The invention relates to a structured catalyst for catalyzing steam methane reforming reaction in a given temperature range T upon bringing a hydrocarbon feed gas into contact with the structured catalyst. The structured catalyst comprises a macroscopic structure, which comprises an electrically conductive material and supports a ceramic coating. The macroscopic structure has been manufactured by 3D printing or extrusion and subsequent sintering, wherein the macroscopic structure and the ceramic coating have been sintered in an oxidizing atmosphere in order to form chemical bonds between the ceramic coating and the macroscopic structure. The ceramic coating supports catalytically active material arranged to catalyze the steam methane reforming reaction, wherein the macroscopic structure is arranged to conduct an electrical current to supply an energy flux to the steam methane reforming reaction. The invention moreover relates to methods of manufacturing the structured catalyst and a system using the structured catalyst.

Claims

1. A structured catalyst for catalyzing steam methane reforming reaction in a given temperature range T upon bringing a hydrocarbon feed gas into contact with said structured catalyst, said structured catalyst comprising a macroscopic structure, said macroscopic structure comprising an electrically conductive material, said macroscopic structure having a resistivity between 10.sup.−5 Ω-m and 10.sup.−7 Ω-m in the given temperature range T, and said macroscopic structure supporting a ceramic coating, wherein the macroscopic structure has been manufactured by extrusion or 3D printing and by subsequent sintering, wherein said macroscopic structure and said ceramic coating have been sintered in an oxidizing atmosphere in order to form chemical bonds between said ceramic coating and said macroscopic structure, wherein said ceramic coating supports catalytically active material, said catalytically active material being arranged to catalyze the steam methane reforming reaction, wherein the macroscopic structure is arranged to conduct an electrical current to supply an energy flux to the steam methane reforming reaction.

2. (canceled)

3. A structured catalyst according to claim 1, wherein the macroscopic structure comprises a plurality of near-parallel or parallel channels.

4-6. (canceled)

7. A structured catalyst according to claim 1, wherein the catalytically active material are sub-micron sized particles.

8. A structured catalyst according to claim 1, wherein the macroscopic structure has at least one electrically insulating part arranged to increase the principal current path within the macroscopic structure, having a length larger than the largest dimension of the macroscopic structure, and. wherein the structured catalyst is configured for use in a system for carrying out a steam methane reforming reaction, in which system the hydrocarbon feed gas enters into the structured catalyst at a first end and a product gas exits the structured catalyst at a second end, said structured catalyst further being configured to have at least two conductors connected to the structured catalyst at a position closer to said first end than to said second end, wherein said structured catalyst is constructed to, during use, direct an electrical current to run from one conductor substantially to said second end along a longitudinal direction of the structured catalyst and return to a second of the at least two conductors along a longitudinal direction of the structured catalyst, wherein the longitudinal direction extends between the first and second ends.

9. A structured catalyst according to claim 1, wherein the resistance and geometry of the material of the macroscopic structure is configured to have a heat generation capacity of 500 to 50000 W/m.sup.2.

10. (canceled)

11. A structured catalyst according to claim 1, wherein the structured catalyst comprises two or more macroscopic structures.

12. A method for manufacturing a structured catalyst according to claim 1, said method comprising the steps of: a) providing a mixture of powdered metallic particles and a binder, b) extruding said mixture to a structure, c) sintering said structure in a non-oxidizing atmosphere at a first temperature T.sub.1, where T.sub.1>1000° C., thereby providing a macroscopic structure, d) providing a ceramic coating onto the macroscopic structure, e) sintering the macroscopic structure and the ceramic coating in an oxidizing atmosphere, at a second temperature T.sub.2, where T.sub.2>800° C., in order to form chemical bonds between said ceramic coating and said macroscopic structure, and f) impregnating the ceramic coating with catalytically active material.

13. A method for manufacturing a structured catalyst according to claim 1, said method comprising the steps of: a) providing a mixture of powdered metallic particles and a binder, b) extruding said mixture to a structure, c) sintering said structure in a non-oxidizing atmosphere at a first temperature T.sub.1, where T.sub.1>1000° C., thereby providing a macroscopic structure, d) providing a ceramic coating onto the macroscopic structure, wherein the ceramic coating supports catalytically active material, and e) sintering the macroscopic structure and the ceramic coating in an oxidizing atmosphere, at a second temperature T.sub.2, where T.sub.2>800° C., in order to form chemical bonds between said ceramic coating and said macroscopic structure.

14. A method for manufacturing a structured catalyst according to claim 1, said method comprising the steps of: a) 3D printing the macroscopic structure with a metal additive manufacturing melting process, b) applying a ceramic coating onto the macroscopic structure, c) sintering the macroscopic structure and the ceramic coating in an oxidizing atmosphere, at a second temperature T.sub.2, where T.sub.2>800° C., and d) impregnating the ceramic coating with catalytically active material, thereby providing the structured catalyst.

15. A method for manufacturing a structured catalyst according to claim 1, said method comprising the steps of: a) 3D printing a metal structure with a binder-based metal additive manufacturing process, b) sintering said metal structure in a non-oxidizing atmosphere at a first temperature T.sub.1, where T.sub.1>1000° C., thereby providing said macroscopic structure, c) applying a ceramic coating onto the macroscopic structure, d) sintering the macroscopic structure and the ceramic coating in an oxidizing atmosphere, at a second temperature T.sub.2, where T.sub.2>800° C., and e) impregnating the ceramic coating with catalytically active material, thereby providing the structured catalyst.

16. A system for carrying out a steam methane reforming reaction in a given temperature range T between about 200° C. and about 1050° C. or a sub-range thereof upon bringing a hydrocarbon feed gas into contact with a structured catalyst according to claim 1, said system comprising: a reactor unit comprising said structured catalyst and at least two conductors electrically connected to said structured catalyst, and an electrical power supply arranged for being connected to said structured catalyst via the at least two conductors in order to allow an electrical current to run through said structured catalyst during operation of said system.

17. (canceled)

18. A system according to claim 16, wherein the connection between the macroscopic structures of said structured catalyst and said at least two conductors is a mechanical connection, a welded connection, a brazed connection, or a combination of said connections.

19. (canceled)

20. A system according to claim 16, wherein the system comprises a control system arranged to control one or more of the following: the electrical current, the voltage, the heat flux, the space velocity, the temperature, or combinations thereof.

21. A system according to claim 16, wherein the hydrocarbon feed gas enters into the structured catalyst at a first end and wherein a product gas exits the structured catalyst at a second end, wherein said at least two conductors are connected to the structured catalyst at a position closer to said first end than to said second end.

22-23. (canceled)

24. A system according to claim 21, wherein said structured catalyst is constructed to direct an electrical current to run from one conductor substantially to said second end of the structured catalyst and return to a second of the at least two conductors.

25. A system according to claim 16, wherein said structured catalyst has at least one electrically insulating part arranged to increase the length of a principal current path between said at least two conductors to a length larger than the largest dimension of the structured catalyst.

26. A system according to claim 16, wherein said structured catalyst has at least one electrically insulating part arranged to direct a current through said structured catalyst in order to ensure that for at least 70% of the length of said structured catalyst, a current density vector of the a principal current path has a non-zero component value parallel to the length of said structured catalyst so that the current is forced from the first end of the structured catalyst towards the second end, and subsequently is forced towards the first end again.

27. A system according to claim 16, wherein said structured catalyst is shaped so as to ensure that during operation of said system a peak current density at a point within the structured catalyst is maximum 1000% of the average current density within the structured catalyst.

28. A structured catalyst according to claim 1, wherein the given temperature range T in which the catalyzing steam methane reforming reaction is to take place during use of the structured catalyst is the range between about 200° C. and about 1050° C. or a sub-range thereof, and wherein the structured catalyst is configured to be heated to temperatures within this temperature range.

29. A structured catalyst according to claim 8, wherein said structured catalyst has at least three electrically insulating parts arranged to direct current to run from the first conductor through the structured catalyst in a zigzag direction to the second conductor.

30. A structured catalyst according to claim 29, wherein said structured catalyst has three electrically insulating parts arranged to direct current to run from the first conductor through the structured catalyst in a zigzag direction, viz. downwards from the first conductor and around the lower side of the first electrically insulating part, subsequently upwards and around the upper side of the middle electrically insulating part, then downwards again and around the lower side of the third electrically insulating part and finally upwards to the second conductor.

31. A structured catalyst according to claim 1, wherein the structured catalyst has a single vertical slit along the longitudinal axis of the catalyst, which single vertical slit extends from the top of the structured catalyst towards the bottom thereof, along about 90% of the length of the structured catalyst so that the single vertical slit can be seen as parting the structured catalyst into two parts, such as two halves, and wherein each of these two parts has a plurality of horizontal slits, such as five horizontal slits, so that the vertical slit and the horizontal slits function to direct the current in a zig-zag route through the structured catalyst.

32. A system according to claim 24, wherein said at least two conductors are connected to the structured catalyst at said first end, and wherein said structured catalyst has at least one electrically insulating part arranged to increase the length of a principal current path between said at least two conductors.

Description

SHORT DESCRIPTION OF THE FIGURES

[0109] The invention is illustrated by way of the following Figures:

[0110] FIG. 1 shows the structured catalyst according to the invention in a perspective view;

[0111] FIG. 2 shows the structured catalyst of FIG. 1 in a perspective view and with connectors attached;

[0112] FIG. 3 shows an alternative embodiment of the structured catalyst with connectors attached;

[0113] FIG. 4 is a schematic drawing of a cross-section through structured catalyst with electrically insulating parts;

[0114] FIG. 5 is a graph of the approach to equilibrium (ΔT.sub.app,SMR) of the steam methane reforming reaction for different gas flow rates over the structured catalyst;

[0115] FIG. 6a shows an embodiment of a structured catalyst for use in the reactor unit of the system of the invention;

[0116] FIG. 6b shows the current density profile of the structured catalyst shown in FIG. 6a as a function of the electrical effect transferred to the structured catalyst;

[0117] FIGS. 7a and 7b show temperature and conversion profiles as a function of electrical effect transferred to the structured catalyst; and

[0118] FIGS. 8a and 8b show simulation results for temperatures and gas composition along the length of structured catalyst.

DETAILED DESCRIPTION OF THE FIGURES

[0119] FIG. 1 shows the structured catalyst 10 according to the invention in a perspective view. The structured catalyst 10 comprises a macroscopic structure that is coated with a ceramic coating impregnated with catalytically active material. Within the structured catalyst 10 are channels 70 extending along the longitudinal direction (shown by the arrow indicate ‘h’ in FIG. 1) of the macroscopic structure 10; the channels are defined by walls 75. In the embodiment shown in FIG. 1, the walls 75 define an array of square channels 70 when seen from the direction of flow as indicated by the arrow 12. The structured catalyst 10 has a substantially square perimeter when seen from above, defined by the edge lengths e1 and e2.

[0120] The walls 75 of the structured catalyst are of extruded or 3D printed material coated with a ceramic coating, e.g. an oxide, which has been coated onto the macroscopic structure 10. In the Figures, the ceramic coating is not shown. Therefore, during the description of the Figures, a reference to the structured catalyst may be a reference to the macroscopic structure and vice versa, if it is not otherwise indicated. The ceramic coating is impregnated with catalytically active material. Thus, during use in a system for steam methane reforming, 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. In the structured catalyst 10 shown in FIG. 1 a slit 60 has been cut into the structured catalyst 10. This slit 60 can be used to force a current to take a zig-zag route within the macroscopic structure 10 thereby increasing the current path and thus the heat dissipated within the macroscopic structure 10. The slit 60 within the structured catalyst 10 may be provided with embedded insulating material in order to ensure that no current flows in the transverse direction of the slit 60, but the coat alone may also be considered as providing sufficient electrical insulation between the two parts of the macroscopic structure.

[0121] The channels 70 in the structured catalyst 10 are open in both ends. In use of the structured catalyst in a reactor unit, a hydrocarbon feed gas flows through the unit, in the direction shown by arrows 11 and 12 in FIG. 1, and gets heated via contact with the walls 75 of the channels 70 and by heat radiation, conduction and convection. The heat drives the desired steam methane reforming process. The walls 75 of the channels 70 may e.g. have a thickness of 0.5 mm, and the ceramic coating coated onto the walls may e.g. have a thickness of 0.1 mm. Even though the arrows 11 and 12 indicates that the flow of the hydrocarbon feed gas is down-flow, the opposite flow direction, viz. an up-flow, is also conceivable.

[0122] FIG. 2 shows the structured catalyst 10 of FIG. 1 in a perspective view and with connectors 7 attached. The connectors 7 each connects a part of the structured catalyst 10 to a conductor 40. The conductors 40 are both connected to a power supply (not shown). Each of the connectors 7 are connected to an upper part of the structured catalyst. When the conductors 40 are connected to a power supply, an electrical current runs to the corresponding connector 7 via the conductor and runs through the structured catalyst 10. The slit 60 hinders the current flow in a transverse direction (horizontal direction of FIG. 2) throughout its lengths along the height h of the structured catalyst 10. Therefore, the current runs in a direction downwards as seen in FIG. 2 in the part of the structured catalyst 10 along the slit 60, subsequently it runs transversely to the longitudinal direction below the slit 60 as seen in FIG. 2 and finally the current runs upwards in the longitudinal direction of the structured catalyst 10 to the other connector 7. The connectors 7 in FIG. 2 are mechanically fastened to the structured catalyst by means such as screws and bolts. However, additional or alternative fastening means are conceivable. In an embodiment, the electrical power supply generates a voltage of 3V and a current of 400 A. In another embodiment the electrical power supply generates a voltage of 1 V and a current of 200 A.

[0123] The connectors 7 are e.g. made in materials like iron, aluminum, nickel, cupper or alloys thereof.

[0124] As mentioned, the structured catalyst 10 is coated with a ceramic coating supporting the catalytically active material. However, the parts of the structured catalyst 10 which are connected to the connectors 7 should not be coated with a ceramic coating. Instead, the macroscopic support of the structured catalyst 10 should be exposed or connected directly to the connectors 7 in order to obtain a good electrical connection between the macroscopic structure and the connector. Processing by e.g. polishing of the interface between the macroscopic structure and the connector may advantageously be done during assembly.

[0125] When the connectors 7 and thus the conductors 40 are connected to the same end of the structured catalyst 10, viz. the upper end as seen in FIG. 2, the gas entering into a reactor unit housing the structured catalyst 10 would be able to cool the connectors 7 and the conductors 40. For instance, the hydrocarbon gas entering into such a reactor unit could have a temperature of 400° C. or 500° C. and would thus keep the connectors 7 and conductors 40 from reaching temperatures much higher than this temperature.

[0126] FIG. 3 shows an alternative embodiment of the structured catalyst 10′ with connectors 7′ attached.

[0127] The structured catalyst 10′ shown in FIG. 3 has a square or rectangular cross section, like the structured catalyst 10 shown in FIGS. 1 and 2; however, the structured catalyst 10′ of FIG. 3 does not have any slit cut through it. In the upper and lower ends of the macroscopic structure 10′ are positioned a conductor 40. The material of the conductor 40 is e.g. nickel. Alternatively, other appropriate metals could be used as electrical current distributors, or alloys such as FeCrAlloy. Connectors 7′ in the form of electrical conducting bars are used for guiding the current across the structured catalyst 10, i.e. the macroscopic structure. The connectors 7′ are fastened to the conductors 40 and to the structured catalyst 10′ by use of mechanical fastening means; however, alternative or additional fastening means are also conceivable.

[0128] Connectors 7″ at the lower end of the structured catalyst 10′ may be made of a different material compared to the connectors 7′ at the upper end of the structured catalyst 10′ as seen in FIG. 3. For example, the connectors 7′ may be of cupper, whilst the connectors 7″ may be of nickel. Since nickel has a lower conductivity than cupper, the connectors 7″ are larger than the connectors 7′.

[0129] The embodiment shown in FIG. 3 is suitable for temperatures below 800° C., such as 600-700° C.

[0130] FIG. 4 is a schematic drawing of a cross-section through a structured catalyst 10″ of the invention, with electrically insulating parts 60′. The electrically insulating parts are shown as hatched parts in FIG. 4. In the embodiment shown in FIG. 4, three pieces of electrically insulating parts 60′ intersects the structured catalyst 10″ in most of the longitudinal direction thereof. Conductors 7 are connected to the upper side of the structured catalyst 10″ as seen in FIG. 4. During use of the structured catalyst 10″, the conductors 7 are connected to a power supply and a hydrocarbon feed gas is brought into contact with the structured catalyst 10″. Thus, current runs from the first conductor through the structured catalyst 10″ in a zigzag direction, viz. downwards from the first conductor and around the lower side of the first electrically insulating part 60′, subsequently upwards and around the upper side of the middle electrically insulating part 60′, then downwards again and around the lower side of the third electrically insulating part 60′ and finally upwards to the second conductor 7. It should be noted that any appropriate number of electrically insulating parts 60′ is conceivable. The electrically insulating parts 60′ are solid, electrically insulating material, e.g. glass, and they are provided in cuts or slits in the macroscopic structure. The electrically insulating parts 60′ ensures that the parts of the macroscopic structure on the sides electrically insulating parts 60′ are kept from each other. It should be noted, that in this embodiment, as in all the embodiments of the invention, the direction of flow of gas may be the same as the direction of the current through the structured catalyst, or it may be different.

[0131] In the embodiment of FIG. 4, the direction of flow of gas is e.g. from the upper side of the structured catalyst 10″ towards the bottom of the structured catalyst 10″; thus, the flow of current only the same as the direction of the flow of gas as some parts of the structured catalyst 10″, whilst the direction of the current is transverse to the direction of the flow of gas at some parts and opposite (upwards) in some parts.

[0132] FIG. 5 is a graph of the approach to equilibrium (ΔT.sub.app,SMR) of the steam methane reforming reaction for different gas flow rates over the structured catalyst.

[0133] FIG. 5 shows that for a given gas flow rate over the structured catalyst, the approach to equilibrium at the entry into a reactor unit housing the structured catalyst, the approach to equilibrium is in the range 160-175° C. When the hydrocarbon gas flows over the structured catalyst, the approach to equilibrium is reduced. FIG. 5 shows the approach to equilibrium (ΔT.sub.app,SMR for gas flow rates from 10000 Nm.sup.3/h to 200000 Nm.sup.3/h. For the lowest gas flow rate, 10000 Nm.sup.3/h, the approach to equilibrium becomes less than 10° C. at about 13% of the reactor length. Here, the reactor length is seen as the current path length along the structured catalyst, so that the total reactor length of the structured catalyst 10 shown in FIG. 1 is about 2 h. For higher gas flow rates, the approach to equilibrium is higher the higher the gas flow rate, so that for a gas flow rate of 200000 Nm.sup.3/h, the approach to equilibrium reaches a minimum value just below 80° C.

[0134] A general trend in all the curves in the FIG. 5 is that the approach to equilibrium is continuously decreasing from the entry into the structured catalyst until a pseudo equilibrium is reached, where the heat added and the heat consumed roughly equal each other. The approach to equilibrium from this stage is substantially constant or has a slightly increasing development due to the overall increasing temperature of the reactor unit. For e.g. the flow rate 150000 Nm.sup.3/h, the approach to equilibrium goes below 60° C. at about 80% of the reactor length, but subsequently increases to about 60° C.

[0135] FIG. 6a shows an embodiment of a structured catalyst 10″ for use in the reactor unit of the system of the invention. FIG. 6a shows the structured catalyst 10″ in a perspective view. It can be seen that the structured catalyst 10″ has a single vertical slit 60 along the longitudinal axis of the catalyst 10″ as shown in FIG. 6a. The single vertical slit 60 extends from the top of the structured catalyst 10″ towards the bottom thereof, along about 90% of the length of the structured catalyst. The single vertical slit 60 can be seen as parting the structured catalyst 10″ into two halves. Each of these two halves has five horizontal slits 65. The vertical slit 60 and the horizontal slits 65 function to direct the current in a zig-zag route through the structured catalyst.

[0136] FIG. 6b shows the current density of the structured catalyst 10″ shown in FIG. 6a as a function of the electrical effect transferred to the structured catalyst 10″. FIG. 6b is the result of a multiphysics computational fluid dynamics simulations in Comsol software of the current distribution of the structure in FIG. 6a. In FIG. 6b the structured catalyst 10″ is seen from the side. Two electrodes (not shown in FIG. 6b) are connected to the upper end on the left side of the structured catalyst 10″. As illustrated by the intensity of the current density, as depicted on the scale in the right part of FIG. 6b, when a power source is connected to the structured catalyst 10″, a current runs from the upper end thereof in zig-zag form, due to the horizontal slits, to the bottom of the structure catalyst 10″, to the back thereof, viz. into the paper as seen in FIG. 6b, and subsequently upwards in zig-zag form towards the second electrode. The temperature of the structured catalyst 10″ depends upon the current density throughout the structured catalyst 10″. It can be seen in FIG. 6b, that the current density is highest at the end points of horizontal slits 65 into the structured catalyst 10″. These points are the points where the current path turns direction, i.e. where the current through the structured catalyst 10″ is forced or directed in another direction. Moreover, it can be deduced that the current density vector of the principal current path has a non-zero component value parallel to the length of said structured catalyst for more than 80% of the structure. In conclusion, it is clear from FIG. 6b that the principal current path can be controlled in the structured catalyst. This feature gives control of the temperature profile inside the structured catalyst.

[0137] It should be noted, that even though the structured catalysts shown in the figures are shown as having channels with a square cross section, as seen perpendicular to the z-axis, any appropriate shape of the cross sections of the channels is conceivable. Thus, the channels of the structured catalyst could alternatively be e.g. triangular, hexagonal, octagonal, or circular, where triangular, square, and hexagonal shapes are preferred.

[0138] FIGS. 7a and 7b shows temperature and conversion profiles as a function of electrical effect transferred to the structured catalyst. FIG. 7a is the result of a laboratory test of bench scale system having a length of 12 cm and a volume 108 cm.sup.3 of the structured catalyst as defined by the outer walls/sides thereof and configuration as depicted in FIG. 1 where Cu conductors has been welded to the first 2 cm of the monolith on opposing sides in the first end. The pressure of the pressure shell was 3.5 bar, the temperature of the feed gas inlet into the reactor unit of the system was about 200° C. The composition of the feed gas was 31.8% CH.sub.4, 2.4% H.sub.2, 65.8% H.sub.2O and the total gas flow was 102.2 NI/h. It should be noted, that the energy balance is substantially better in a larger scale than in the small scale experimental conditions behind the graphs of FIG. 7a, due to high energy loss in this relative small scale. However, it is clear from FIG. 7a that with increasing power, both the conversion of methane and the temperature increases. The temperature reaches above 900° C. and the methane conversion reaches above 98%.

[0139] FIG. 7b shows a similar experiment as described above, but with a pressure of 21 bar. Again, it is clear from FIG. 7b that with increasing power, both the conversion of methane and the temperature increases. The temperature reaches above 1060° C. and the methane conversion reaches above 95%.

[0140] FIGS. 8a and 8b show simulation results for temperatures and gas composition along the length of structured catalyst. A single channel of a structured catalyst is simulated. The length of the structured catalyst of this simulation, and thus of the single channel, is 10 cm. The conditions within the pressure shell/structured catalyst/channel is: [0141] Pressure: 29 barg [0142] T inlet: 466° C. [0143] Total flow: 30 NI/h [0144] Composition of the feed gas inlet into the reactor/channel: 31.8% methane, 8.8% hydrogen, 2.3% carbon dioxide, and 57.1% steam.

[0145] In FIG. 8a, the temperature of the wall of the channel is indicated by Tw and the temperature in the center of the channel is indicated by Tc. Tw and Tc are read from the scale to the right of the graphs. The methane conversion is indicated by Cc and is read from the scale to the left of the graphs.

[0146] From FIG. 8a it is seen that the temperature of the wall of a channel in the structured catalyst increases continuously along almost all of the length of the structured catalyst. The temperature is about 480° C. at the first end of the structured catalyst (z=0 cm) and about 1020° C. at the second end of the structured catalyst (z=10 cm). The increase of temperature is steepest the first 10% of the structured catalyst, and only in the last few percent of the length of the structured catalyst, the temperature does not change much. Thus, when the current turns around at the second end of the structured catalyst, from going downwards to upwards in the FIG. 1a, the temperature of the walls of the channels of the structured catalyst does not change substantially for increasing z-values. However, FIG. 8a also shows that the temperature in the center of the channel keeps on increasing along the whole length of the structured catalyst. It should be noted, though, that the temperature in the center of the channel remains substantially constant for the first 5-7% of the length of the structured catalyst. This is due to the fact that the gas inlet into the structured catalyst cools the structured catalyst in the vicinity of the first end thereof and due to thermal energy transport delay from the wall to the center of the channel.

[0147] In FIG. 8a, the conversion of methane in the center of the channel of the structured catalyst is also shown. It can be seen that the conversion is close to zero for the first 10-12% of the length of the channel, and that the conversion subsequently increases monotonously and reaches a value of about 85%. As noted above, small scale reactors and simulations thereof provide for less than optimal numbers, and that considerably higher conversion is achievable in a real scale system. However, the simulation provides information on the tendencies of the conversion rate and temperature throughout the structured catalyst.

[0148] FIG. 8b shows the partial pressures of the principle active gasses within the channel of the structured catalyst of FIG. 8a. From FIG. 8b, it is clear that the partial pressures of steam and methane diminish considerably along the length of the channel of the structured catalyst, whilst the partial pressures of hydrogen and carbon monoxide increase considerably. Moreover, the partial pressure of carbon dioxide increases slightly along the length of the structured catalyst, but decreases towards the highest temperatures where the reverse water gas shift reaction is thermodynamically favored.

Example 1

[0149] As noted above, a general advantage of carrying out steam reforming of hydrocarbons using resistance heating as compared to the present side fired reformers or top fired reformers, is that such fired reformers are limited in the hot part by the heat transfer rate to the catalytic zone. By use of resistance heating, this heat transfer limitation can be circumvented since the structured catalyst itself is heated directly by the electrical current running in the macroscopic structure.

[0150] The steam reforming reaction generate i.a. hydrogen and/or synthesis gas from a hydrocarbon gas. Synthesis gas is a gas mixture comprising hydrogen, carbon monoxide, and often also carbon dioxide. Today, the decentralized market for hydrogen is often dependent on expensive distribution and storage of hydrogen. As an alternative to this, resistance heated reforming could be envisioned as a small scale hydrogen production technology potentially with fast startup for ad hoc hydrogen production and a heating system based on electricity instead of a fired hot box.

[0151] The structured catalyst for the steam reforming reaction, CH.sub.4+H.sub.2OCO+3H.sub.2, at a temperature within the temperature range from about 700° C. to about 950° C. or even 1050° C. is for example a macroscopic structure of FeCrAlloy alloy coated with a ZrAlMgO.sub.x based coat and impregnating with Ni as active phase.

[0152] Hydrogen production can be facilitated at 860° C. and 5 bar with a steam to hydrocarbon carbon ratio of 2 using this structured catalyst for the reaction. The heat for the reaction is supplied by a current running in the macroscopic structure.

[0153] Reforming of Higher Hydrocarbons:

[0154] Steam reforming of higher hydrocarbons may also take place: C.sub.nH.sub.m+(n/2)H.sub.2OnCO+(m/2+n/2)H.sub.2, where n≥2. This reaction may take place at a temperature within the range from about 400° C. to about 950° C.

[0155] A suitable structured catalyst is for example a macroscopic structure of FeCrAlloy alloy coated with a ZrAlMgO.sub.x based coat and impregnating with nickel as active phase.

Example 2

[0156] An example calculation of the process of the invention is given in Table 1 below. A hydrocarbon feed gas comprising i.a. a hydrocarbon gas, hydrogen and steam is fed to the structured catalyst of the invention. The feed stream is pressurized to a pressure of 28 kg/cm.sup.2.Math.g and has a temperature of 500° C. The structured catalyst is in the form of 1 macroscopic structure having a square cross section, which has a size of 0.4 times 0.4 times 0.35 meter. The structured catalyst has 10000 channels with a square cross section having a side or edge length of 0.32 cm. The structured catalyst has slits parallel to the longitudinal direction thereof, so that clusters of 5 times 5 channels are formed. The clusters are individually insulated from the neighboring cluster, except from the ends, so that the current path through the macroscopic structure is a zig-zag formed path. A current of 200 A and a voltage of ca. 500 V are applied to the structured catalyst of the invention in order to heat the macroscopic structure and thus the gas passing over the macroscopic structure, corresponding to a power deposited in the macroscopic structure of 99 kW.

[0157] During the passage of the feed gas through the structured catalyst, the feed gas is heated by the structured catalyst and undergoes steam methane reforming to a product gas having an exit temperature of 963° C.

TABLE-US-00001 TABLE 1 Structured catalyst size: Edge size (e1 = e2) [m] 0.4 Height h [m] 0.35 Total volume [L] 55.4 Feed gas Product gas T [° C.] 500 963 P [kg/cm.sup.2 g] 27.97 27.47 CO.sub.2 [Nm.sup.3/h] 1.7 7.3 N.sub.2 [Nm.sup.3/h] 0.3 0.3 CH.sub.4 [Nm.sup.3/h] 26.3 1.6 H.sub.2 [Nm.sup.3/h] 5.9 85.4 CO [Nm.sup.3/h] 0 19.1 H.sub.2O [Nm.sup.3/h] 80.5 50.2 Total flow [Nm.sup.3/h] 114.7 163.9 Power [kW] 99

Example 3

[0158] Example 6 relates to a reactor unit comprising a structured catalyst in the form of a macroscopic structure having in total 78540 channels with a total wall length of one channel in the cross section of 0.00628 m each and a length of 2 m, giving a total surface area of 987 m.sup.2 of catalyst surface. For a reactor unit with this macroscopic structure, a simulation with varying gas flow over the macroscopic structure was made where the gas composition in all calculations was 8.8% H.sub.2, 56.8% H.sub.2O, 0.2% N.sub.2, 0.1% CO, 2.3% CO.sub.2, and 31.8% CH.sub.4. In each simulation a kinetic model for steam methane reforming and water gas shift was used and a variation in the surface flux (Q) of energy from the electrically heated macroscopic structure was made to adjust the exit temperature of the product gas from the reactor unit housing the macroscopic structure to 920° C. FIG. 5 shows the approach to equilibrium along the reactor length at varying total gas flow rates. The Figure shows that at low feed flows (10000 Nm.sup.3/h), the approach to the equilibrium at the outlet of the reactor unit is below 5° C., which translate into a hydrocarbon conversion of 77%, while at the high flows (150000 Nm.sup.3/h) the approach to equilibrium is above 60° C., which correspond to a hydrocarbon conversion of only 64%, and the hydrocarbons therefore are used less efficiently. The close control of the heat flux in the current invention therefore allows for controlling the approach to equilibrium closely along the length of the reactor unit.