Microwave reactor

Abstract

A microwave reactor comprising a reaction chamber; microwave source; and a microwave waveguide, wherein the microwave waveguide is configured to direct microwave radiation from the microwave source into the microwave reaction chamber and wherein at least part of the waveguide is disposed in the reaction chamber.

Description

[0001] MICROWAVE REACTOR

[0002] BACKGROUND

[0003] There is an urgent need to reduce combustion of hydrocarbon fuels such as methane and replace these fuels with alternative energy sources. One such alternative energy source is hydrogen which may be used in, for example, an internal combustion engine or a fuel cell.

[0004] Another alternative energy source is lithium-ion batteries, which commonly contain conductive carbon such as carbon black in the battery anode.

[0005] WO2022 / 234302 discloses a microwave reaction process and reactor for forming hydrogen and a carbon product from a hydrocarbon-containing input gas.

[0006] SUMMARY

[0007] The present disclosure provides a microwave reactor comprising a reaction chamber; microwave source; and a microwave waveguide, wherein the microwave waveguide is configured to direct microwave radiation from the microwave source into the microwave reaction chamber and wherein at least part of the waveguide is disposed in the reaction vessel.

[0008] Optionally, the microwave reactor further comprises a microwave source.

[0009] Optionally, the microwave source has an operating frequency in the range of 900-3000 MHz.

[0010] Optionally, the waveguide is disposed in a microwave-transparent waveguide housing.

[0011] Optionally, the microwave-transparent waveguide housing comprises one or more microwave-transparent materials selected from ceramic, quartz or a combination thereof.

[0012] Optionally, the microwave waveguide housing extends through the reaction chamber.

[0013] Optionally, the microwave waveguide housing is disposed parallel to a central axis of the reaction chamber.

[0014] Optionally, the microwave waveguide housing is disposed on the central axis of the reaction chamber. Optionally, the microwave waveguide housing is configured to rotate within the reaction chamber.

[0015] Optionally, one or more fins are disposed on the outer surface of the microwave waveguide housing or on a sleeve surrounding the outer surface of the microwave waveguide housing.

[0016] Optionally, the one or more fins and the microwave waveguide housing or sleeve form a screw.

[0017] Optionally, the microwave reactor comprises a plurality of screws that are rotatable relative to one another.

[0018] Optionally, the microwave waveguide housing is a rectangular or cylindrical waveguide housing.

[0019] Optionally, the reaction chamber is a cylindrical reaction chamber.

[0020] Optionally, the reaction chamber comprises a first end and an opposing second end and wherein the microwave source and microwave waveguide are arranged to direct microwave radiation from at least one of the first and second ends into the reaction chamber.

[0021] Optionally, the microwave waveguide comprises a first waveguide configured to direct microwave radiation from the first end into the reaction chamber and a second waveguide configured to direct microwave radiation from the second end into the reaction chamber.

[0022] Optionally, a microwave barrier is disposed between the first and second waveguides.

[0023] Optionally, the reactor comprises a gas inlet configured to deliver reactant gas into the reaction chamber and a gas outlet configured to draw product gas from the reaction chamber.

[0024] Optionally, the reactor comprises a solid inlet.

[0025] Optionally, the reactor comprises a solid outlet.

[0026] Optionally, the reactor is tilted such that the reaction chamber is not horizontal along its length.

[0027] Optionally, the reactor is tilted such that the solid inlet is vertically higher than the solid outlet. The present disclosure provides a method of forming hydrogen comprising cracking a hydrocarbon in a microwave reactor according to any one of the preceding claims.

[0028] DESCRIPTION OF THE DRAWINGS

[0029] The invention will now be described in more detail with reference to the Figures in which :

[0030] Figure 1 is a block diagram illustrating conversion of an input gas containing a hydrocarbon into hydrogen and carbon using a microwave reactor according to some embodiments;

[0031] Figure 2 is a block diagram illustrating conversion of an input gas containing a hydrocarbon into hydrogen and carbon using a microwave reactor according to some further embodiments;

[0032] Figure 3, which is not drawn to any scale, illustrates a microwave reactor according to an embodiment of the present disclosure.

[0033] DETAILED DESCRIPTION

[0034] Referring to Figure 1, a microwave reactor 100 as described herein includes a reaction chamber 102; a microwave waveguide 104 configured to direct microwave radiation from a microwave source into the reaction chamber 102 and disposed in a microwave waveguide housing 106.

[0035] In operation, microwave radiation from a microwave source (not shown) is directed via the microwave waveguide 104 into the reaction chamber 102, causing cracking of hydrocarbon gas in the reaction chamber into hydrogen and solid carbon. The reaction chamber suitably contains a particulate reaction initiator to catalyse the reaction.

[0036] With reference to Figure 2, the microwave reactor preferably further comprises a gas inlet 108 for introduction of hydrogen gas into the reaction chamber; a solid inlet 110 for introduction of a reaction initiator into the reaction chamber; a gas outlet for removal of product hydrogen gas from the reaction chamber; and a solid outlet 114 for removal of product carbon from the reaction chamber. Each inlet and outlet may be opened and closed by any suitable valve arrangement known to the skilled person.

[0037] In some embodiments, the microwave reactor comprises a plurality of gas inlets 108. In some embodiments, a single gas inlet extends along part or all of the length of the reaction chamber. In some embodiments, the reactor comprises at least one gas inlet configured to introduce input gas to an underside of the reaction chamber. By "underside" of the reaction chamber as used herein is meant a lower half of the reaction chamber.

[0038] Preferably, in use a gas inlet of the reactor is covered by solid particulate material in the reaction chamber such that the inlet gas is injected into the solid particulate material.

[0039] In some embodiments, the microwave reactor comprises a plurality of gas outlets 112.

[0040] The microwave reactor may further comprise a frame 116 supporting the microwave reaction chamber 102.

[0041] The microwave reactor may further comprise fins 118 for agitation of solids in the reaction chamber.

[0042] Figure 3 illustrates a reactor according to an embodiment of the present invention.

[0043] In operation, microwave radiation from a microwave source (not shown) is directed via the microwave waveguide 104 into the reaction chamber 102, causing cracking of hydrocarbon gas introduced into the reaction chamber into hydrogen and solid carbon. The reaction may be catalysed by a solid, preferably granular or powdered, reaction initiator which may be introduced via a solid inlet.

[0044] The microwave waveguide 108 is at least partially disposed in the reaction chamber 102. The microwave waveguide 103 disposed in the reaction chamber is disposed in a microwave-transparent waveguide housing 106. The waveguide housing may be, for example, ceramic, quartz or a combination thereof.

[0045] The waveguide housing may have any cross-section. In some embodiments, the waveguide housing has a rectangular cross-section. In some embodiments, the waveguide housing is cylindrical (i.e., the waveguide housing has a circular crosssection).

[0046] The reaction chamber 102 may be of any size or shape. In some embodiments, the reaction chamber is cylindrical. Preferably, an internal width of the reaction chamber (i.e., a diameter in the case of a cylindrical reaction chamber) is in the range of 10-100 cm.

[0047] The reaction chamber may be formed of any suitable material such as a metal or metal alloy, preferably steel, more preferably stainless steel such as Austenitic steel, for example 304, 316 or 321 grade steel. The reaction chamber interior wall may be lined with any suitable material, for example a quartz, glass or ceramic. In the embodiment of Figure 3, the microwave waveguide housing 106 passes through a first end 102A of the reaction chamber 102, extends through the length of the reaction chamber 102 and through an opposing second end 102B of the reaction chamber. Microwave radiation from a microwave source (not shown) may be directed into the reaction chamber via the microwave waveguide through the first end 102A and I or the second end 102B of the reaction chamber. In embodiments where microwave radiation is introduced from both first end 102A and second end 102B, a microwave reflector or a microwave-opaque material may be disposed in the microwave waveguide housing 106 to prevent interference between microwave radiation from the first and second ends.

[0048] In other embodiments, the microwave waveguide 108 and housing 106 containing the microwave waveguide may extend only part way into the reaction chamber 102.

[0049] The microwave waveguide may be any form of waveguide capable of guiding microwave radiation into the reaction chamber. In some embodiments, the microwave waveguide 108 comprises a plurality of microwave-transparent apertures in the region of the waveguide contained within the reaction chamber, thus providing a "leaky" waveguide within the reaction chamber. The apertures may take any suitable form, for example parallel slots.

[0050] The reactor may contain a single waveguide. The reactor may contain two or more waveguides.

[0051] The, or each, waveguide may be tunable. Waveguides may be manually or automatically tuned using any waveguide tuning means known to the skilled person.

[0052] Each waveguide may optionally have a tuning system which adjusts the microwave distribution. Tuning can be made at the start of the reactor operation and I or during reactor operation. Preferably, tuning is adjusted, optionally continually adjusted, to maintain reflected power below 50%, ideally below 10%. Optionally, the microwave power of the microwave source or sources (which is a combined microwave power in the case of multiple microwave sources) is at least 1 kW, optionally 1 kW - 1MW, optionally 1- lOOkW. It will be understood that the microwave power required will depend in part on the size of the reactor.

[0053] Any form of seal known to the skilled person may be provided to form a gas-tight seal between the microwave waveguide housing 106 and the reaction chamber 102, for example a rubber seal around the microwave waveguide housing 106. The microwave waveguide 108 of Figure 1 is disposed along a central axis of the reaction chamber 102. In other embodiments, the microwave waveguide 108 may have an axis that is parallel to but offset from a central axis of the reaction chamber or not parallel to the reaction chamber.

[0054] The microwave waveguide 108 of Figure 1 is linear. In other embodiments, the microwave waveguide may have a curved, e.g. spiral, shape.

[0055] The microwave reactor of Figure 1 comprises a frame 116 configured to support the reaction chamber and the microwave waveguide housing 106. The frame 116 of Figure 1 is further configured to rotate the microwave waveguide housing 106 relative to the reaction chamber 102. A plurality of fins 118 are disposed on an outer surface of the microwave waveguide housing 106 or on a sleeve around the microwave waveguide housing. The fins 118 may extend some or all of the distance between the outer surface of the microwave waveguide housing and the inner surface of the reaction chamber 102. In operation, the microwave waveguide housing 106 or sleeve and fins 118 may be rotated within the reaction chamber to agitate or otherwise move solids within the reaction chamber.

[0056] The plurality of fins 118 may, with the microwave waveguide housing 106 or sleeve, form a screw configured to move solids in the reaction chamber towards an end of the reaction chamber. In other embodiments, a single continuous fin may be arranged to form a screw thread with the microwave waveguide housing 106 or sleeve. According to these embodiments, a solid inlet is disposed at an "upstream" position of the reactor and a solid outlet is disposed at a "downstream" position of the reactor; in the embodiment of Figure 1, the screw is configured to move solids away from end 102A and towards end 102B of the reaction chamber 102.

[0057] The reactor may comprise only one screw configured to move particulate solid disposed in the reactor.

[0058] The reactor may comprise two or more independently operable screws configured to move particulate solid disposed in the reactor. Optionally, a single first fin or a plurality of first fins disposed on a first surface form a first screw and a single second fin or a plurality of second fins disposed on a second surface form a second screw wherein the first and second screws can be rotated relative to one another, and preferably independently of one another.

[0059] The first and second fins may have different dimensions, forming first and second screw threads of different dimensions. In other embodiments, the microwave waveguide housing 106 may be stationary and the reaction chamber 102 may rotate around the microwave waveguide housing 106.

[0060] In some embodiments, the reactor is horizontal in use.

[0061] In some embodiments, the reactor is tilted in use such that a solid product inlet is vertically higher than a solid product outlet.

[0062] Product hydrogen and carbon may be removed via gas and solid outlets, respectively. Optionally, the reaction initiator and any other solids removed from the solid outlet are separated from product carbon and returned to the solid inlet.

[0063] Optionally, any unreacted hydrocarbon present in the product hydrogen removed via the gas outlet is separated from the product hydrogen and returned to the gas inlet.

[0064] The waveguide housing may be purged with a gas having a higher ionization potential than oxygen, for example nitrogen, prior to operation of the reactor. The high ionization potential of the purge gas may prevent or reduce formation of plasma in the waveguide housing during operation of the reactor as compared to a waveguide housing containing air.

[0065] Solids

[0066] The, or each, solid introduced into the reaction chamber is suitably in particulate form, e.g., in the form of a power or granules. Preferably, a reaction initiator is provided in the reaction chamber. The reaction initiator may be a metal compound, more preferably a transition metal compound, for example an iron, nickel, copper, palladium, or platinum compound or combinations thereof. Two or more different metal compounds may be provided in the reaction chamber. The, or each, metal compound may be a metal oxide.

[0067] Preferably, the reaction chamber further comprises a particulate microwave-absorbing material, for example silicon carbide. The microwave-absorbing particles may be of the same size as the reaction initiator. The microwave-absorbing particles may be of a different size from the reaction initiator to facilitate separation of the reaction initiator and the microwave-absorbing particles.

[0068] Optionally, the reaction initiator is loaded onto a carrier, for example a porous carbon.

[0069] At the start of the reaction, the reaction initiator may be the only solid material in the reaction chamber. Preferably, the reaction chamber further contains a particulate microwave-absorbing material. Suitably, the microwave-absorbing material is a solid material which increases rapidly in temperature upon exposure to microwave radiation, and which does not react with the input hydrocarbon gas to form hydrogen. In this way, heat may be transferred from the microwave-absorbing material to the hydrocarbon. A preferred microwave-absorbing compound is silicon carbide.

[0070] Input gas

[0071] The input gas contains one or more hydrocarbons. The input gas suitably contains at least 10 % by volume of hydrocarbons, more preferably at least 20% by volume of hydrocarbons.

[0072] The input gas suitably contains at least 10 % by volume of methane, optionally at least 20% by volume of methane.

[0073] Hydrocarbons as described herein are preferably selected from Ci-4 alkanes and Ci-4 alkenes.

[0074] Preferably, the input gas contains less than 10 % by volume of water, preferably less than 1 % by volume of water. Optionally, the input gas is free from water.

[0075] Input gas may be heated by a pre-heater before entering the microwave reaction chamber. Optionally, input gas is pre-heated to a temperature of no more than 1000°C, optionally no more than 900°C, optionally in the range of 200 - 900°C, optionally in the range of 400-600°C, most preferably about 500°C.

[0076] Preferably, gas in the microwave reaction chamber is below a plasma-forming temperature of the gas. Optionally, the temperature of gas within the microwave reaction temperature is below 900°C, optionally in the range of 200-900°C, optionally 400-600°C, optionally about 500°C. Gas temperature may be measured by an optical method such as Infrared Optical Pyrometer, e.g., in a headspace of the reactor.

[0077] Optionally, pressure of gas in the microwave reaction chamber is 0.1-10 atmospheres, preferably 0.5-3 atmospheres or 0.5-2 atmospheres.

[0078] Optionally, the microwave frequency is in the range of 0.5 - 20 GHz, optionally 900-3000 MHz.

[0079] Preferably the reactor diameter is over twice the bed depth penetration for the microwave frequency which is given by the following formula: where f is the microwave frequency 8' refers to the relative permittivity, p' refers to the relative permeability and tan6 refers to the loss tangent.

[0080] For 2450 MHz microwave, the preferred diameter is 20-60cm. For 915 MHz microwave, the preferred diameter is 50-150cm.

[0081] Hydrogen and carbon produced by a process as described herein may be used in a wide variety of applications known to the skilled person. Applications for hydrogen include, without limitation, as a fuel for an internal combustion engine or a hydrogen fuel cell. Applications for carbon black include, without limitation, in rubber, in dyes or as a component of a lithium-ion battery anode.

[0082] A reactor as described herein may be installed in a location where hydrogen fuel is required, for example a filling station for vehicles. Optionally, hydrogen produced according to a process described herein may be transferred directly to a storage tank on the same site.

Claims

CLAIMS1. A microwave reactor comprising a reaction chamber; microwave source; and a microwave waveguide, wherein the microwave waveguide is configured to direct microwave radiation from the microwave source into the microwave reaction chamber and wherein at least part of the waveguide is disposed in the reaction chamber.

2. The microwave reactor according to claim 1 further comprising a microwave source.

3. The microwave reactor according to claim 2 wherein the microwave source has an operating frequency in the range of 900-3000 MHz.

4. The microwave reactor according to any one of the preceding claims wherein the waveguide is disposed in a microwave-transparent waveguide housing.

5. The microwave reactor according to claim 4 wherein the microwave-transparent waveguide housing comprises one or more microwave-transparent materials selected from ceramic, quartz or a combination thereof.

6. The microwave reactor according to any one of the preceding claims wherein the microwave waveguide housing extends through the reaction chamber.

7. The microwave reactor according to claim 6 wherein the microwave waveguide housing is disposed parallel to a central axis of the reaction chamber.

8. The microwave reactor according to claim 7 wherein the microwave waveguide housing is disposed on the central axis of the reaction chamber.

9. The microwave reactor according to any one of the preceding claims wherein the microwave waveguide housing is configured to rotate within the reaction chamber.

10. The microwave reactor according to claim 9 wherein one or more fins are disposed on the outer surface of the microwave waveguide housing or on a sleeve surrounding the outer surface of the microwave waveguide housing.

11. The microwave reactor according to claim 10 wherein the one or more fins and the microwave waveguide housing or sleeve form a screw.

12. The microwave reactor according to claim 11 wherein the microwave reactor comprises a plurality of screws that are rotatable relative to one another.

13. The microwave reactor according to any one of the preceding claims wherein the microwave waveguide housing is a rectangular or cylindrical waveguide housing.

14. The microwave reactor according to any one of the preceding claims wherein the reaction chamber is a cylindrical reaction chamber.

15. The microwave reactor according to any one of the preceding claims wherein the reaction chamber comprises a first end and an opposing second end and wherein the microwave source and microwave waveguide are arranged to direct microwave radiation from at least one of the first and second ends into the reaction chamber.

16. The microwave reactor according to claim 15 wherein the microwave waveguide comprises a first waveguide configured to direct microwave radiation from the first end into the reaction chamber and a second waveguide configured to direct microwave radiation from the second end into the reaction chamber.

17. The microwave reactor according to claim 16 wherein a microwave barrier is disposed between the first and second waveguides.

18. The microwave reactor according to any one of the preceding claims wherein the waveguide is tunable.

19. The microwave reactor according to any one of the preceding claims wherein the reactor comprises a gas inlet configured to deliver reactant gas into the reaction chamber and a gas outlet configured to draw product gas from the reaction chamber.

20. The microwave reactor according to any one of the preceding claims wherein the reactor comprises a solid inlet.

21. The microwave reactor according to any one of the preceding claims wherein the reactor comprises a solid outlet.

22. The microwave reactor according to any of the preceding claims where in the reactor is tilted such that the reaction chamber is not horizontal along its length.

23. The microwave reactor according to claims 19-21 wherein the reactor is tilted such that the solid inlet is vertically higher than the solid outlet.

24. A method of forming hydrogen comprising cracking a hydrocarbon in a microwave reactor according to any one of the preceding claims.

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