METHOD AND SYSTEM FOR DIRECT THERMAL DECOMPOSITION OF A HYDROCARBON COMPOUND INTO CARBON AND HYDROGEN

Abstract

A method of carrying out direct thermal decomposition of a hydrocarbon compound into carbon and hydrogen comprises: introducing a gaseous feed stream comprising at least one hydrocarbon compound into a reactor; and removing at least hydrogen gas and particulate carbon formed by thermal decomposition from the reactor. The method includes providing in the reactor a layer permeable to the particulate carbon and comprising loose particles other than the particulate carbon in a gas phase and passing the gaseous feed stream through the layer. The loose particles other than the particulate carbon comprise particles comprising a catalyst on a carrier. The method includes removing at least part of the layer from the reactor, separating constituents of the removed part, the constituents including some of the particles comprising a catalyst on a carrier, and returning the separated particles comprising a catalyst on a carrier to the layer.

Claims

1-20. (canceled)

21. A method of carrying out direct thermal decomposition of a hydrocarbon compound into carbon and hydrogen, comprising: introducing a gaseous feed stream comprising at least one hydrocarbon compound into a reactor; and removing at least hydrogen gas and particulate carbon formed by thermal decomposition from the reactor, wherein the method includes: providing in the reactor a layer permeable to the particulate carbon and comprising loose particles other than the particulate carbon in a gas phase, and passing the gaseous feed stream through the layer, wherein the loose particles other than the particulate carbon comprise particles comprising a catalyst on a carrier; and wherein the method includes: (i) removing at least part of the layer from the reactor, (ii) separating constituents of the removed part, the constituents including some of the particles comprising a catalyst on a carrier, and (iii) returning the separated particles comprising a catalyst on a carrier to the layer; wherein: the layer forms a fluidised bed; and the particles comprising a catalyst on a carrier comprise particles of which at least an outer shell is porous and acts as the carrier and which have a hollow core or a porosity decreasing from core to surface.

22. The method according to claim 21, further comprising: introducing a further gas stream into the layer, e.g., an inert gas stream.

23. The method according to claim 22, wherein: the further gas stream comprises nitrogen, and the nitrogen is obtained by reacting with air a gas stream comprising mainly hydrogen, e.g., a gas stream obtained from a product stream from the reactor.

24. The method according to claim 21, further comprising: providing a molten medium in a bubble reactor, and heating the gaseous feed stream by introducing the gaseous feed stream into the molten medium in the bubble reactor.

25. The method according to claim 24, wherein the layer is provided on top of the molten medium in the bubble reactor.

26. The method according to claim 24, wherein the thermal decomposition is effected in at least the molten medium.

27. The method according to claim 21, further comprising: obtaining a gas stream from a product stream from the reactor; and generating electrical power by reacting the gas stream obtained from the product stream with a gas mixture comprising at least one oxidant.

28. The method according to claim 21, wherein: the loose particles other than the particulate carbon are provided from a source; and at least at the source, the particles have a particle size distribution ratio D.sub.90/D.sub.50 of less than 1.6, e.g., less than 1.4 or less than 1.1.

29. The method according to claim 21, wherein the loose particles other than the particulate carbon comprise particles made predominantly of at least one ceramic material.

30. The method according to claim 21, wherein the catalyst comprises at least one transition metal.

31. The method according to according to claim 21, further comprising: obtaining a gas stream from a product stream from the reactor, and separating the hydrogen from at least one other gas present in the gas stream obtained from the product stream.

32. The method according to claim 21, wherein the separation is effected by means of (i) a pressure-swing adsorption, PSA, process, or (ii) a temperature-swing adsorption, TSA, process.

33. The method according to claim 21, wherein: the gaseous feed stream is obtained from natural gas, e.g., Liquefied Natural Gas, LNG, and obtaining the gaseous feed stream comprises separating methane and higher-order hydrocarbons from at least one other constituent of the natural gas by means of (i) a pressure-swing adsorption, PSA, process, or (ii) a temperature-swing adsorption, TSA, process.

34. The method according to claim 32, wherein: the PSA or TSA process comprises introducing the gas stream or natural gas into an adsorption vessel comprising a bed of adsorbent beads; and the beads comprise a hollow core or at least one core comprising at least one inorganic material, which core is porous and non-adsorbent and, on the surface of the core, at least one layer comprising a porous and adsorbent material.

35. The method according to claim 21, wherein separating constituents of the removed part includes separating carbon from the loose particles, e.g., mechanically separating the carbon from the loose particles.

36. The method according to claim 21, wherein: the gaseous feed stream is heated in the fluidised bed to a temperature higher than a temperature at which the gaseous feed stream is introduced into the reactor; and the higher temperature being sufficient to effect the direct thermal decomposition.

37. A system for direct thermal decomposition of a hydrocarbon compound into carbon and hydrogen, comprising: a reactor having at least one outlet for a product stream comprising the hydrogen gas; a conduit for supplying a gaseous feed stream comprising at least one hydrocarbon compound; a device, in communication with the conduit, for introducing the gaseous feed stream into the reactor; and a quantity of loose particles comprising particles comprising a catalyst on a carrier; wherein: the reactor includes an inlet for introducing the loose particles into the reactor to form a layer of the loose particles in a gas phase, the layer being permeable to the particulate carbon; at least part of the layer is removable from the reactor; and the system includes: (i) at least one device for separating constituents of the removed part, and (ii) a device for returning at least some of the particles comprising a catalyst on a carrier that are comprised amongst the constituents to the layer; wherein: the reactor comprises a fluidised bed reactor for providing the layer as a fluidised bed, and the particles comprising a catalyst on a carrier comprise particles of which at least an outer shell is porous and acts as the carrier and which have a hollow core or a porosity decreasing from core to surface.

38. The system according to claim 37, wherein: the reactor comprises a bubble reactor; the system comprises a system for providing a molten medium in the bubble reactor; the device for introducing the gaseous feed stream is arranged to introduce the gaseous feed stream as bubbles in the molten medium in the bubble reactor; and the system is configured to form the layer on the molten medium.

39. The system according to claim 37, further comprising a device for introducing a further gas stream, e.g., an inert gas stream, into the layer.

40. The system according to claim 39, wherein: the further gas stream comprises nitrogen; and the system includes a device arranged to obtain the nitrogen by reacting with air a gas stream comprising mainly hydrogen, e.g., a gas stream obtained from a product stream from the reactor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0094] The invention will be explained in further detail with reference to the accompanying drawings, in which:

[0095] FIG. 1 shows a first system for direct thermal decomposition of at least one hydrocarbon compound in a gaseous feed stream into hydrogen and solid particulate carbon; and

[0096] FIG. 2 is a schematic diagram showing a second system for direct thermal decomposition of at least one hydrocarbon compound in a gaseous feed stream into hydrogen and solid particulate carbon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0097] In a first system for direct thermal decomposition (FIG. 1), gas from a gas source 1 is provided as a primary input stream 2. The primary input stream 2 may in particular comprise natural gas. In an embodiment, the primary input stream 2 comprises at least 70 vol.-%, more particularly at least 80 vol.-%, methane.

[0098] The gas source 1 may comprise the gas grid. In another embodiment, the gas source 1 comprises an apparatus for regasification of Liquefied Natural Gas (LNG). In another embodiment, the gas source 1 comprises a fermentation device for producing biogas by anaerobic fermentation from a biodegradable substrate. A suitable substrate comprises algae.

[0099] The primary input stream 2 is treated in an (optional) first gas purifier 3. The first gas purifier 3 may be arranged to reduce the amount of at least one of carbon dioxide, carbon monoxide, carbonyl sulphide, hydrogen sulphide, water vapour, nitrogen, thiols and siloxanes.

[0100] In the illustrated embodiment, the first gas purifier 3 is followed by a first apparatus 4 for carrying out a Pressure-Swing Adsorption (PSA) process. In other embodiments one or the other, or even both of the first gas purifier 3 and the first PSA apparatus 4 may be omitted.

[0101] The first PSA apparatus 4 includes at least one adsorption vessel 5,6. In an embodiment, a bed of adsorbent beads, of which the nature will be described more fully below, is arranged in each vessel 5,6. The first PSA apparatus 4 is arranged to separate methane and other higher-order hydrocarbons from the other constituents of a gas stream 7 provided to the first PSA apparatus 4 as an input gas stream. The result is a gaseous feed stream 8 comprising mainly, e.g., essentially only, gases with the formula C.sub.nH.sub.n+2, where n=1−5. A first pump 9 conveys the gaseous feed stream 8.

[0102] The gaseous feed stream 8 is pre-heated in at least a heat exchanger 10. Further pre-heating may be carried out in an embodiment.

[0103] The gaseous feed stream 8 is then introduced as bubbles in a lower section of a mass of molten medium 11 in a bubble reactor 12. The bubble reactor 12 can comprise a column formed out of quartz.

[0104] The molten medium 11 may comprise a metal or a salt. Metal has relatively good heat transfer properties. The molten medium may in particular be In, Ga, Sn, Bi, Pb or alloys thereof. In an embodiment, the molten metal used as the molten medium 11 has a melting temperature above 500° C.

[0105] Solid particles having a melting point above the melting temperature or melting range of the molten medium 11 may be suspended in the molten medium 11. These solid particles may in particular comprise an active catalyst. Suitable catalysts include Ni, Pt and Pd, in particular Ni. In an alternative embodiment, the molten medium 11 comprises a—or the—catalyst.

[0106] In an embodiment, the molten medium 11 is tin in which a nickel-bismuth catalyst is suspended. In another embodiment, the molten medium 11 is a mixture of 27 wt.-% Ni and 73 wt.-% Bi.

[0107] In the illustrated embodiment, the molten medium 11 is led to the bubble reactor 12 by a bubble lift pump 13 from a furnace 14, e.g., an electric arc furnace. In another embodiment, the gaseous feed stream 8 and the molten medium are pumped into the bubble reactor 12 separately. In such an embodiment, the molten medium 11 may be melted and kept at an appropriate temperature inside the bubble reactor 12, so that the separate furnace 14 can be omitted. In any case, electric heaters (not shown) may be provided in an insulating sleeve surrounding a reactor tube of the bubble reactor 12. One or more gas-fired heaters may be used in addition or instead of electrically powered heating devices to bring the molten medium 11 to or keep the molten medium 11 at the required temperature. The gas for such heaters may be gas from the primary input stream 2, the purified primary input stream 7 or the gaseous feed stream 8, or the gas may comprise gas from a product stream 15 of the bubble reactor 12.

[0108] The temperature of the molten medium 11 may be in the range of 800-1600° C., e.g., 1000-1400° C., specifically 1050-1350° C.

[0109] A separation layer 16 is provided on top of the molten medium 11. The separation layer 16 comprises loose particles other than particulate carbon formed in the molten medium 11. In the illustrated embodiment, these loose particles are fed into the bubble reactor 12 from an external particle source 17, e.g., a container. The feeding need not be continuous and may be carried out only once prior to commencing an operating cycle of the bubble reactor 12. In the illustrated embodiment, feeding whilst the molten medium 11 is present is possible.

[0110] The separation layer 16 forms a fluidised bed. The superficial velocity of the gas flowing through the molten medium 11 and emerging from the molten medium 11 may be less than required or optimal for fluidisation. Rather than increase this velocity, a further gas stream 18 may be introduced with the aid of a pump 19. The further gas stream 18 may comprise an inert gas. In the illustrated embodiment, the further gas stream 18 includes nitrogen.

[0111] The loose particles from the particle source 17 may be spherical. The particles have a diameter of at least 0.1 mm, e.g., at least 1 mm. The diameter may be at most 10 mm, for example.

[0112] In an embodiment, the loose particles from the particle source 17 comprise carrier particles on which a catalyst is provided. The catalyst may in particular be an activated metal. The activated metal may comprise at least one of Ni, Pt and Pd.

[0113] In a first embodiment, the particles from the particle source 17 may comprise carbon particles with or without an active catalyst provided thereon or a mixture of carbon particles with and particles without an active catalyst provided thereon.

[0114] In a particular example of the first embodiment, the particles from the particle source 17 comprise spherical carbon granules of the type disclosed more fully in WO 2007/131795 A2, the disclosure of which is hereby incorporated by reference. Thus, the particles of the first embodiment may form a granulate comprising at least 50 wt.-% of carbon obtained by pyrolysis of granulated micro-crystalline cellulose and optionally a binder and/or further additives.

[0115] The granules may be porous. The porosity may decrease from core to surface. This increases the mechanical strength and resistance to abrasion. The abrasion rate according to ASTM D4058 may be in the range of 0.2-1.5 wt.-%, for example. The specific surface area may be in the range of 60-1200 m.sup.2/g.

[0116] In a second embodiment, the particles from the particle source 17 comprise ceramic particles with or without an active catalyst provided thereon. The particles may be particles having at least one outer layer and a hollow or a porous core. In a particular example of the second embodiment, the particles from the particle source 17 comprise particles of the type disclosed more fully in EP 2 198 946 A1, WO 2010/072404 A2 and Schmidt, F. et al., “Novel Composite Spherical Granulates with Catalytic Outer Layer and Improved Conversion Efficiency and Selectivity”, Chem. Eng. Technol., 35 (4), Wiley-VCH, 2012, pp. 769-775.

[0117] Thus, the particles of the second embodiment may have at least one of the following properties: [0118] a bulk density in the range of 560-2000 kg.Math.m.sup.−3, e.g., 600-1500 kg.Math.m.sup.−3, more particularly 800-1500 kg.Math.m.sup.−3; [0119] a specific crush strength in the range of 1-7 N.Math.mm.sup.−2; [0120] a diameter in the range of 0.1-5 mm, e.g., 0.25-4 mm, more particularly in the range of 0.5-3 mm; [0121] an overall porosity greater than 40%; [0122] a sphericity of 0.7-1; [0123] a particle size distribution ratio D.sub.90/D.sub.50 of less than 1.6, e.g., less than 1.4, more particularly less than 1.1; [0124] a specific surface area (BET) in the range of 350-800 m.sup.2.Math.g.sup.−1, e.g., in the range of 600-800 m.sup.2.Math.g.sup.−1.

[0125] Where the particles have a hollow, solid or porous core and a porous surface layer, or shell, the ratio of the core diameter to the particle diameter may be in the range of 0.5-0.98, e.g., in the range of 0.6-0.8.

[0126] The porous surface layer, or shell, may comprise at least one zeolite and at least one inorganic binder, e.g., at least one of silica, clay and aluminium oxide.

[0127] Where the core is not hollow but solid or porous, the core may be made of at least one non-adsorbent material. The core may comprise kaolin and/or at least one of attapulgite, bentonite, graphite and a metal.

[0128] The core and surface layer materials may be calcined together.

[0129] Where the core is porous, the core may comprise agglomerated inorganic particles having a mean particle size equal to or smaller than the mean particle size of surrounding agglomerated particles forming the outer layer, or shell.

[0130] The particles of the second embodiment are thus relatively large and strong and can be manufactured with a relatively narrow particle size distribution.

[0131] A third embodiment combines particles of the first and second embodiments.

[0132] The separation layer 16 is effective to separate particulate solid carbon formed primarily in the molten medium 11 from the molten medium 11. This particulate solid carbon will pass through the separation layer 16. The particles of the particulate carbon formed by direct thermal decomposition in the molten medium 11 will be of an order of magnitude smaller than the particles from the particle source 17. The particles will typically have a diameter in the range of 40-100 nm. Even if they form agglomerates, such agglomerates will have a diameter in the range of 15-20.Math.m. The specific surface area based on BET measurements lies within the range of 17-40 m.sup.2/g.

[0133] At least some of the particulate carbon emerging from the separation layer 16 will be entrained with gas in a product stream 15 provided through an outlet of the bubble reactor 12. In the illustrated embodiment, the product stream 15 is conducted in counter-flow through the heat exchanger 10 to a first separator 20 for separating particulate carbon from gas in the product stream 15 to produce a product gas stream 21. The particulate carbon is collected in a first container 22. The first separator 20 may be a cyclone separator, for example.

[0134] In an alternative embodiment, the first separator 20 precedes the heat exchanger 10.

[0135] A further cooling device (not shown) may be provided to cool the product stream 15 or product gas stream 21.

[0136] The first container 22 may comprise bags or a metallic container, e.g., provided with a ceramic porous filter. In another embodiment, the first container 22 may be arranged to hold a suspension of carbon in a liquid. This helps avoid loss of fine carbon powder. The carbon powder is suitable for use in a wide range of applications, e.g., the production of carbon composites, the production of steel, etc.

[0137] In the illustrated embodiment, the product gas stream 21 is provided to a second PSA apparatus 23. The second PSA apparatus 23 may be the only PSA apparatus if the first PSA apparatus 4 is omitted, of course.

[0138] The second PSA apparatus 23 comprises adsorption vessels 24,25 in which a bed of adsorbent beads is arranged.

[0139] The adsorbent beads in each of the first and second PSA apparatus 4,23 may be adsorbent beads as described more fully in WO 2007/131795 A2 or the beads described more fully in EP 2 198 946 A1, WO 2010/072404 A2 and Schmidt, F. et al., “Novel Composite Spherical Granulates with Catalytic Outer Layer and Improved Conversion Efficiency and Selectivity”, Chem. Eng. Technol., 35 (4), Wiley-VCH, 2012, pp. 769-775, as well as above in the context of the particles from the external particle source 17. Thus, the same particles can be used both to form the separation layer 16 and as adsorbents in one or both of the first and second PSA apparatuses 4,23. The beads in the first and second PSA apparatuses 4,23 need not carry a catalyst, however.

[0140] The second PSA apparatus 23 separates hydrogen from other constituent gases of the product gas stream 21. These other gases may be recycled by a pump 26 to be mixed into the gaseous feed stream 8. Alternatively, they may be used for other purposes, e.g., combusted to produce heat or generate electrical power.

[0141] An (optional) compressor pump 27 conveys the hydrogen to an (optional) first hydrogen storage device 28. The first hydrogen storage device 28 may be a tank or pressure vessel, a vessel containing a storage medium such as ammonia or magnesium hydride. Other chemical or physical hydrogen storage systems are conceivable, e.g., Liquid Organic Hydrogen Carrier (LOHC) system for binding and releasing hydrogen through reversible hydrogenation. In an embodiment, the hydrogen is mixed with, e.g., absorbed into, a liquid comprising a hydrocarbon compound or mix of hydrocarbon compounds to produce a fuel, e.g., for use in powering a vehicle. In one embodiment, liquefied gas, e.g., comprising at least liquid propane, is saturated with hydrogen to produce a fuel. The liquefied gas may in particular be bio-propane obtained from glycerol by hydrogenation.

[0142] In the illustrated embodiment, some of the hydrogen is conveyed to a reservoir 29 by a further pump 30, e.g., a reservoir of the type described more fully in EP 3 470 621 A1, hereby incorporated by reference. The reservoir 29 may therefore be a pressure vessel, e.g., a pressure vessel mounted on a skid, for example. In another embodiment, the first hydrogen storage device 28 is the primary, e.g., only, hydrogen storage device. Hydrogen from either the first hydrogen storage device 28 or the reservoir 29 can be supplied as an energy carrier to external users, e.g., via a dedicated hydrogen transport grid or the natural gas grid. There may also be provided a device (not shown) for refuelling vehicles, e.g., cars, buses, lorries, locomotives or ships, with the hydrogen produced by the system or the fuel comprising a mix of hydrogen and one or more hydrocarbon compounds mentioned above. Reference is made to WO 2019/031966 A1 in this respect, the contents of which are hereby incorporated by reference.

[0143] In the illustrated embodiment, a gas stream 31 comprising some of the hydrogen is reacted with air to produce electrical power. In the illustrated embodiment, a turbine 32 coupled to a generator 33, in turn connected to an inverter 34, is used to generate electricity. In other embodiments, a fuel cell may be used or another type of combustion engine than a turbine. The result is a fluid stream 35 comprising mainly nitrogen, but also water vapour. The fluid stream 35 is led to a gas processing system 36 for carrying out at least one of a drying process and a condensation process. The output of the gas processing system will be a gas stream 37 comprising mainly nitrogen, together with a small amount of carbon dioxide and noble gases originating from the atmosphere. The nitrogen gas stream 37 will generally comprise at least 95 vol.-% nitrogen, e.g., at least 99 vol.-% nitrogen.

[0144] In the illustrated embodiment, some of the nitrogen in the nitrogen gas stream 37 is used to pressurise the reservoir 29 using a reservoir pump 38. This may be done in the manner set out more fully in EP 3 470 621 A1, for example. In an alternative embodiment, the reservoir 29 comprises a movable barrier such as a membrane or piston, allowing the nitrogen to regulate the pressure without being mixed with the hydrogen in the reservoir 29.

[0145] In the illustrated embodiment, some of the nitrogen gas stream 37 forms the further gas stream 18. Thus, the separation layer 16 can be maintained as a fluidised bed without introducing oxygen into the bubble reactor 12. It remains the case that the system is used for direct thermal decomposition of at least one hydrocarbon compound into carbon and hydrogen essentially without forming carbon dioxide.

[0146] As mentioned, at least some of the particulate carbon formed in the bubble reactor 12 is carried away in the product stream 15 and recovered in the first separator 20. In the illustrated embodiment, provision is also made for the removal of at least part of the separation layer 16 from the bubble reactor 12, e.g., through the pressure established by the further gas stream 18 or by means of a mechanical device (not shown). The removed part comprises particulate carbon and some of the particles from the particle source 17. A second separator 39 is provided to separate the particulate carbon from these other particles. This is relatively easy due to the difference in particle size and the well-defined particle size of the particles from the particle source 17. The particulate carbon is collected in a second container 40 similar to the first container 22.

[0147] The second separator 39 may comprise an air separator, also known as air sifter, wind sifter or air classifier. In another embodiment, the second separator 39 may comprise a bubbling carbon bed. In particular in the latter embodiment, the second separator may comprise a heat exchanger for pre-heating the gaseous feed stream 8, as indicated by the dashed line in the drawing. Thus, heat may be recovered from the part of the separation layer 16 drawn from the bubble reactor 12 and used to heat the gaseous feed stream 8 prior to the gaseous feed stream 8 being processed in the bubble reactor 12. In this embodiment, the heat exchanger 10 may be omitted, as indicated by the dashed line in the drawing, or the gaseous feed stream 8 may pass through the two heat exchangers in series.

[0148] The particles other than the particulate carbon are returned from the second separator 39 to the separation layer 16 and/or the particle source 17. Re-use is made possible by the relatively high crush strength of these particles and the fact that they can be separated relatively well from the particulate carbon produced in the direct thermal decomposition process.

[0149] In a second direct thermal decomposition system (FIG. 2), gas from a gas source 41 is again provided as a primary input stream 42. The primary input stream 42 may in particular comprise natural gas. In an embodiment, the primary input stream 42 comprises at least 70 vol.-%, more particularly at least 80 vol.-%, methane.

[0150] As in the first system, the gas source 41 may comprise the gas grid, an apparatus for regasification of Liquefied Natural Gas (LNG) or a fermentation device for producing biogas by anaerobic fermentation from a biodegradable substrate such as algae, for example.

[0151] The primary input stream 42 is treated in an (optional) first gas purifier 43. The first gas purifier 43 may be arranged to reduce the amount of at least one of carbon dioxide, carbon monoxide, carbonyl sulphide, hydrogen sulphide, water vapour, nitrogen, thiols and siloxanes.

[0152] In the illustrated second system, the first gas purifier 43 is followed by a first apparatus 44 for carrying out a Pressure-Swing Adsorption (PSA) process. In other embodiments one or the other, or even both of the first gas purifier 43 and the first PSA apparatus 44 may be omitted. A temperature-swing adsorption apparatus may be used instead of the first PSA apparatus 44.

[0153] The first PSA apparatus 44 includes at least one adsorption vessel 45,46. In an embodiment, a bed of adsorbent beads as described above in relation to the first system (FIG. 1) is arranged in each vessel 45,46. The first PSA apparatus 44 is arranged to separate methane and other higher-order hydrocarbons from the other constituents of a gas stream 47 provided to the first PSA apparatus 44 as an input gas stream. The result is a gaseous feed stream 48 comprising mainly, e.g., essentially only, gases with the formula C.sub.nH.sub.n+2, where n=1-5. A first pump 49 conveys the gaseous feed stream 48.

[0154] The gaseous feed stream 48 is pre-heated in a heat exchanger 50. The gaseous feed stream 48 is then pre-heated to a higher temperature in a heating device 51. At this stage, the temperature of the gaseous feed stream 48 may still be below a temperature needed to effect direct thermal decomposition. Alternatively, the temperature may be at a lower end of the temperature range in which direct thermal decomposition takes place, but the gaseous feed stream may reach this temperature only shortly before exiting the heating device 51, so that very little carbon is deposited in the heating device 51. The heating device 51 may be an electric heating device (i.e. one with at least one heating element for effecting Joule heating), a microwave heating device, a plasma heater or a device comprising a molten medium (e.g., molten metal or salt) through which the gaseous feed stream is passed in the form of bubbles.

[0155] The pre-heated gaseous feed stream 48 is then introduced into a continuous fluidised bed reactor 52.

[0156] A layer 53 of loose particles in a gaseous phase forming a fluidised bed is provided in the fluidised bed reactor 52. A further heating device 54 is provided to raise the temperature of the gaseous feed stream 48 to within the range at which direct thermal decomposition takes place, at least within the layer 53 forming the fluidised bed.

[0157] In the illustrated embodiment, a further gas stream 55 is introduced with the aid of a pump 56. The further gas stream 55 may comprise an inert gas. In the illustrated embodiment, the further gas stream 55 includes nitrogen. In the illustrated embodiment, the further gas stream 55 is also pre-heated by the heating device 51. In an alternative embodiment, the further gas stream 55 is heated by a different device and introduced into the fluidised bed reactor 52 separately from the gaseous feed stream 48.

[0158] At least initially, the loose particles are provided from a particle source 57.

[0159] The loose particles from the particle source 57 may be spherical. The particles have a diameter of at least 0.1 mm, e.g., at least 1 mm. The diameter may be at most 10 mm, for example.

[0160] The loose particles from the particle source 57 comprise carrier particles on which a catalyst is provided. The catalyst may in particular be an activated metal. The activated metal may comprise at least one of Ni, Pt and Pd.

[0161] These particles are those of the first and second embodiments of the first system (FIG. 1) as described above. The second embodiment, in which the particles comprise ceramic particles of which at least an outer shell is porous and acts as the carrier for the catalyst, is most suitable.

[0162] The particles of the second embodiment are relatively large and strong and can be manufactured with a relatively narrow particle size distribution.

[0163] The layer 53 forming the fluidised bed is effective to separate particulate solid carbon formed primarily in that layer 53 through the motion of the loose particles. The particles of the particulate carbon formed by direct thermal decomposition will be of an order of magnitude smaller than the particles from the particle source 57. The carbon particles formed in the layer 53 will typically have a diameter in the range of 40-100 nm. Even if they form agglomerates, such agglomerates will have a diameter in the range of 15-20.Math.m. The specific surface area based on BET measurements lies within the range of 17-40 m.sup.2/g.

[0164] At least some of the particulate carbon emerging from the layer 53 forming the fluidised bed will be entrained with gas in a product stream 58 provided through an outlet of the fluidised bed reactor 52. In the illustrated embodiment, the product stream 58 is conducted in counter-flow through the heat exchanger 50 to a first separator 59 for separating particulate carbon from gas in the product stream 58 to produce a product gas stream 60. The particulate carbon is collected in a first container 61. The first separator 59 may be a cyclone separator, for example.

[0165] In an alternative embodiment, the first separator 59 precedes the heat exchanger 50.

[0166] A further cooling device (not shown) may be provided to cool the product stream 58 or product gas stream 60.

[0167] The first container 61 may comprise bags or a metallic container, e.g., provided with a ceramic porous filter. In another embodiment, the first container 61 may be arranged to hold a suspension of carbon in a liquid. This helps avoid loss of fine carbon powder. The carbon powder is suitable for use in a wide range of applications, e.g., the production of carbon composites, the production of steel, etc.

[0168] In the illustrated embodiment, the product gas stream 60 is provided to a second PSA apparatus 62. The second PSA apparatus 62 may be the only PSA apparatus if the first PSA apparatus 44 is omitted, of course.

[0169] The second PSA apparatus 62 comprises adsorption vessels 63,64 in which a bed of adsorbent beads is arranged.

[0170] The adsorbent beads in each of the first and second PSA apparatus 44,62 may be adsorbent beads as described more fully in WO 2007/131795 A2 or the beads described more fully in EP 2 198 946 A1, WO 2010/072404 A2 and Schmidt, F. et al., “Novel Composite Spherical Granulates with Catalytic Outer Layer and Improved Conversion Efficiency and Selectivity”, Chem. Eng. Technol., 35 (4), Wiley-VCH, 2012, pp. 769-775, as well as above in relation to the first system (FIG. 1).

[0171] The second PSA apparatus 62 separates hydrogen from other constituent gases of the product gas stream 60. These other gases may be recycled by a pump 65 to be mixed into the gaseous feed stream 48. Alternatively, they may be used for other purposes, e.g., combusted to produce heat or generate electrical power.

[0172] An (optional) compressor pump 66 conveys the hydrogen to an (optional) first hydrogen storage device 67. The first hydrogen storage device 67 may be constituted or used in the same manner as the first hydrogen storage device 28 of the first system (FIG. 1).

[0173] In the illustrated embodiment of the second system (FIG. 2), some of the hydrogen is conveyed to a reservoir 68 by a further pump 69, e.g., a reservoir of the type described more fully in EP 3 470 621 A1, hereby incorporated by reference. The reservoir 68 may therefore be a pressure vessel, e.g., a pressure vessel mounted on a skid, for example. In another embodiment, the first hydrogen storage device 67 is the primary, e.g., only, hydrogen storage device. Hydrogen from either the first hydrogen storage device 67 or the reservoir 68 can be supplied as an energy carrier to external users, e.g., via a dedicated hydrogen transport grid or the natural gas grid. There may also be provided a device (not shown) for refuelling vehicles, e.g., cars, buses, lorries, locomotives or ships with the hydrogen produced by the system or the fuel comprising a mix of hydrogen and one or more hydrocarbon compounds mentioned above. Again, reference is made to WO 2019/031966 A1 in this respect, the contents of which are hereby incorporated by reference.

[0174] In the illustrated embodiment, a gas stream 70 comprising some of the hydrogen is reacted with air to produce electrical power. In the illustrated embodiment, a turbine 71 coupled to a generator 72, in turn connected to an inverter 73, is used to generate electricity. In other embodiments, a fuel cell may be used or another type of combustion engine than a turbine. The result is a fluid stream 74 comprising mainly nitrogen, but also water vapour. The fluid stream 74 is led to a gas processing system 75 for carrying out at least one of a drying process and a condensation process. The output of the gas processing system will be a gas stream 76 comprising mainly nitrogen, together with a small amount of carbon dioxide and noble gases originating from the atmosphere. The nitrogen gas stream 76 will generally comprise at least 95 vol.-% nitrogen, e.g., at least 99 vol.-% nitrogen.

[0175] In the illustrated embodiment, some of the nitrogen in the nitrogen gas stream 76 is used to pressurise the reservoir 68 using a reservoir pump 77. This may be done in the manner set out more fully in EP 3 470 621 A1, for example. In an alternative embodiment, the reservoir 68 comprises a movable barrier such as a membrane or piston, allowing the nitrogen to regulate the pressure without being mixed with the hydrogen in the reservoir 68.

[0176] In the illustrated embodiment, some of the nitrogen gas stream 76 forms the further gas stream 55. Thus, the layer 53 can be maintained as a fluidised bed without introducing oxygen into the fluidised bed reactor 52. It remains the case that the system is used for direct thermal decomposition of at least one hydrocarbon compound into carbon and hydrogen essentially without forming carbon dioxide.

[0177] As mentioned, at least some of the particulate carbon formed in the fluidised bed reactor 52 is carried away in the product stream 58 and recovered in the first separator 59. In the second system, as in the first system (FIG. 1), provision is also made for the removal of at least part of the layer 53 forming the fluidised bed from the fluidised bed reactor 52, e.g., through the pressure established by the further gas stream 55 or by means of a mechanical device (not shown) or gravity. The removed part comprises particulate carbon and some of the carrier particles carrying the catalyst. A second separator 78 is provided to separate the particulate carbon from these other particles. The second separator 78 may be an elutriation device or air sifter, or a cascade impactor, for example. The second separator 78 may comprise a mechanical device, e.g., arranged to separate carbon formed on the particles comprising a catalyst on a carrier mechanically, for example through friction.

[0178] In an alternative embodiment, separation may be achieved chemically.

[0179] In another embodiment, the second separator 78 may comprise a bubbling carbon bed.

[0180] The particulate carbon is collected in a second container 79 similar to the first container 61.

[0181] The particles other than the particulate carbon are returned in a particle stream 80 from the second separator 78 to the layer 53 forming the fluidised bed through a separate port into the fluidised bed reactor 52 and/or to the particle source 57. The particle stream 80 may be returned mechanically or carried in a stream of compressed gas, for example. This may include gas from the further gas stream 55. Re-use is made possible by the relatively high crush strength of these particles and the fact that they can be separated relatively well from the particulate carbon produced in the direct thermal decomposition process.

[0182] The invention is not limited to the embodiments described above, which may be varied within the scope of the accompanying claims. For example, in the first direct thermal decomposition system, the separation layer 16 may be higher than the height of the column of molten medium 11 in the bubble reactor 12. The molten medium 11 may comprise no catalyst, either as a constituent component or suspended therein. Instead of circulating the molten medium 11 a heat exchange medium may be circulated between a heating device and the bubble reactor 12. The particulate carbon may be formed mainly in the molten medium 11, mainly in the separation layer 16 or in approximately equal proportions in both.

[0183] A membrane separation device may be used instead of the second PSA apparatuses 23,62. In particular, but not only, in that case, the product stream 15,58 or product gas stream 15,60 may be pressurised by a solid-state electrochemical compressor (not shown). Suitable examples are disclosed in WO 2020/106155 A1 or WO 2020/106153 A1. Such a compressor may also or alternatively be used to implement any one of the pumps 9,26,27,30,38; 49,65,66,69,77.

[0184] In both systems, energy used to drive the thermal decomposition reaction may be supplied at least in part from a source of renewable energy, e.g., wind energy or solar energy, potentially allowing a negative-emission effect to be achieved.

[0185] The general introduction and the description of the first direct thermal decomposition system relate, according to an independent aspect, to a:

[0186] 1. Method of carrying out direct thermal decomposition of a hydrocarbon compound into carbon and hydrogen, comprising: [0187] providing a molten medium 11 in a bubble reactor 12; [0188] introducing a gaseous feed stream 8 comprising at least one hydrocarbon compound into the molten medium 11 in the bubble reactor 12; and [0189] removing at least hydrogen gas and particulate carbon formed by thermal decomposition from the reactor 12 at a level above the molten medium 11, [0190] wherein the method includes providing on top of the molten medium 11 a layer 16 permeable to the particulate carbon and comprising loose particles other than the particulate carbon in a gas phase.

[0191] Because the loose particles of the layer are from an external source, they can be tailored to achieve good separation between the molten medium and the particulate carbon formed by thermal decomposition, as well as good separation from the particulate carbon. The particulate carbon, having a controlled size generally much lower than the particle size of the loose particles from the external source, will pass through the layer. The particulate carbon can then easily be separated from the particles from the external source, if not already entrained by the product gas. The particulate carbon emerging from the layer is separated from the molten medium relatively effectively by the layer of loose particles. Such separation can be carried out only in the layer or in a separator separate from the bubble reactor to which part of the layer is led. By using particles other than the particulate carbon, the particle properties and the superficial velocity of the gas can be set independently. The superficial velocity can be optimised for conversion of the hydrocarbon compound into carbon and hydrogen, in particular to achieve a minimum conversion yield. The loose particles can be selected for best possible separation given the superficial velocity.

[0192] The gases in the gaseous feed stream will generally comprise or consist essentially of gases with the formula C.sub.nH.sub.n+2, where n=1−5. Direct thermal decomposition, also known as pyrolysis, is an endothermic reaction in which essentially no CO.sub.2 is produced. The process is thus environmentally friendlier than Steam Methane Reforming (SMR), for example, as well as being simpler and requiring less energy. Conversion yields of over 90% can be achieved, which is sufficient for many applications to avoid having to purify the product gas stream.

[0193] The particulate carbon formed in the method is mainly in the form of graphite. The carbon will usually be in the form of powder comprising flakes having a largest diameter in the range of 40-100 nm. Even if the powder forms clusters or agglomerates, these will have a diameter in the range of 15-20.Math.m. The particles other than the particulate carbon may have a diameter an order of magnitude larger than that of the particulate carbon. For example, the particles other than the particulate carbon may have a diameter, or a mean diameter D.sub.50, of at least 0.1 mm, e.g., at least 0.2 mm, for example at least 1 mm.

[0194] The method yields a product stream from the bubble reactor, wherein the product stream consists of a stream of gas comprising at least the hydrogen, as well as of entrained solid matter. At least 90%, e.g., at least 95%, more particularly at least 99% by mass of the entrained solid matter is formed by solid carbon. The remainder comprises essentially impurities. Examples of such impurities include the material of the molten medium, any catalyst present in the bubble reactor and minerals already present in the feed stream (e.g., where the feed stream comprises biogas).

[0195] Embodiments are defined in the following clauses:

[0196] 2. Method according to clause 1, [0197] wherein the layer 16 forms a fluidised bed.

[0198] 3. Method according to clause 2, comprising [0199] i.introducing a further gas stream 18 into the layer 16, e.g., an inert gas stream.

[0200] 4. Method according to clause 3, [0201] wherein the further gas stream 18 comprises nitrogen, and [0202] wherein the nitrogen is obtained by reacting with air a gas stream 31 comprising mainly hydrogen, e.g., a gas stream 31 obtained from a product stream 15 from the bubble reactor 12.

[0203] 5. Method according to any one of the preceding clauses, [0204] wherein the thermal decomposition is effected in at least the molten medium 11.

[0205] 6. Method according to any one of the preceding clauses, including [0206] obtaining a gas stream 31 from a product stream 15 from the bubble reactor 12 and [0207] generating electrical power by reacting the gas stream 31 obtained from the product stream 15 with a gas mixture comprising at least one oxidant.

[0208] 7. Method according to any one of the preceding clauses, [0209] wherein the loose particles other than the particulate carbon comprise spherical particles.

[0210] 8. Method according to any one of the preceding clauses, [0211] wherein the loose particles other than the particulate carbon are provided from a source, and [0212] wherein, at least at source, the particles have a particle size distribution ratio D.sub.90/D.sub.50 of less than 1.6, e.g., less than 1.4 or less than 1.1.

[0213] 9. Method according to any one of the preceding clauses, [0214] wherein the loose particles other than the particulate carbon comprise particles comprising a catalyst on a carrier.

[0215] 10. Method according to any one of the preceding clauses, [0216] wherein the loose particles other than the particulate carbon comprise particles made predominantly of at least one ceramic material.

[0217] 11. Method according to any one of the preceding clauses, [0218] wherein the loose particles other than the particulate carbon comprise particles of which at least an outer shell is porous.

[0219] 12. Method according to any one of the preceding clauses, [0220] wherein the loose particles other than the particulate carbon comprise particles having a hollow core.

[0221] 13. Method according to any one of the preceding clauses, comprising [0222] removing at least part of the layer 16 from the bubble reactor 12, and [0223] separating constituents of the removed part, e.g., in an air separator.

[0224] 14. Method according to any one of the preceding clauses, comprising [0225] obtaining a gas stream 21 from a product stream 15 from the bubble reactor 12, and [0226] separating the hydrogen from at least one other gas present in the gas stream 21 obtained from the product stream 15.

[0227] 15. Method according to clause 14, [0228] wherein the separation is effected by means of a pressure-swing adsorption, PSA, process or a temperature-swing adsorption, TSA, process.

[0229] 16. Method according to any one of the preceding clauses, [0230] wherein the gaseous feed stream 8 is obtained from natural gas, e.g., Liquefied Natural Gas, LNG, and [0231] wherein obtaining the gaseous feed stream 8 comprises separating methane and higher-order hydrocarbons from at least one other constituent of the natural gas by means of a pressure-swing adsorption, PSA, process or a temperature-swing adsorption, TSA, process.

[0232] 17. Method according to at least one of clauses 15 and 16, [0233] wherein the PSA or TSA process comprises introducing the gas stream 21 or natural gas into an adsorption vessel 5,6,24,25 comprising a bed of adsorbent beads, [0234] wherein the beads comprise a hollow core or at least one core comprising at least one inorganic material, which core is porous and non-adsorbent and, on the surface of the core, at least one layer comprising a porous and adsorbent material.

[0235] The general introduction and the description of the first direct thermal decomposition system also relate, according to an independent aspect, to a:

[0236] 18. System for direct thermal decomposition of a hydrocarbon compound into carbon and hydrogen, e.g., by means of a method according to any one of the preceding clauses, comprising: [0237] a bubble reactor 12 having at least one outlet for a product stream 15 comprising the hydrogen gas, [0238] a system for providing a molten medium 11 in the bubble reactor 12; [0239] a conduit for supplying a gaseous feed stream 8 comprising at least one hydrocarbon compound; [0240] a device 13, in communication with the conduit, for introducing the gaseous feed stream 8 as bubbles into the molten medium 11 in the bubble reactor 12; and [0241] a quantity of loose particles comprising particles comprising a catalyst on a carrier, [0242] wherein the bubble reactor 12 includes an inlet for introducing the loose particles other than particulate carbon formed in the molten medium 11 into the bubble reactor 12 to form a layer 16 of the loose particles in a gas phase on the molten medium 11, the layer 16 being permeable to the particulate carbon.

[0243] Embodiments of the system are defined in the following clauses:

[0244] 19. System according to clause 18, [0245] wherein the system for providing a molten medium 11 in the bubble reactor 12 is arranged to maintain the molten medium 11 at a temperature sufficient to achieve thermal decomposition of the hydrocarbon compound in the molten medium 11.

[0246] 20. System according to clause 18 or 19, further comprising a device 19 for introducing a further gas stream 18 e.g., an inert gas stream, into the layer 16.

[0247] 21. System according to clause 20, [0248] wherein the further gas stream 18 comprises nitrogen, and [0249] wherein the system includes a device 32,36 arranged to obtain the nitrogen by reacting with air a gas stream 31 comprising mainly hydrogen, e.g., a gas stream 31 obtained from a product stream 15 from the bubble reactor 12.

[0250] 22. System according to any one of clauses 18-21, further including a system 32,33,34 for generating electrical power by reacting a gas stream 31 obtained from a product stream 15 from the bubble reactor 12 with a gas mixture comprising at least one oxidant.

[0251] 23. System according to any one of clauses 18-22, [0252] wherein at least part of the layer 16 is removable from the bubble reactor 12, and [0253] the system includes at least one device 39 for separating constituents of the removed part, e.g., an air separator.

[0254] 24. System according to any one of clauses 18-23, further comprising an apparatus 23 for separating the hydrogen from at least one other gas in a gas stream 21 obtained from a product stream 15 from the bubble reactor 12, e.g., a pressure-swing adsorption, PSA, apparatus or a temperature-swing adsorption, TSA, apparatus.

[0255] 25. System according to any one of clauses 18-24, further including at least one pressure-swing adsorption, PSA, apparatus 4 or temperature-swing adsorption, TSA, apparatus for obtaining the gaseous feed stream 8 by separating methane and higher-order hydrocarbons from at least one other constituent of natural gas, e.g., Liquefied Natural Gas, LNG.

[0256] 26. System according to at least one of clauses 24 and 25, [0257] wherein the PSA apparatus 4,23 or TSA apparatus comprises at least one adsorption vessel 5,6,24,25 comprising a bed of composite adsorbent beads, and [0258] wherein the beads comprise at least one core comprising at least one inorganic material, which core is porous and non-adsorbent and, on the surface of the core, at least one layer comprising a porous and adsorbent material.

LIST OF REFERENCE NUMERALS

[0259] 1—gas source [0260] 2—primary input stream [0261] 3—first gas purifier [0262] 4—first PSA apparatus [0263] 5—adsorption vessel [0264] 6—adsorption vessel [0265] 7—purified primary input stream [0266] 8—gaseous feed stream [0267] 9—first pump [0268] 10—heat exchanger [0269] 11—molten medium [0270] 12—bubble reactor [0271] 13—bubble lift pump [0272] 14—furnace [0273] 15—product stream [0274] 16—separation layer [0275] 17—particle source [0276] 18—further gas stream [0277] 19—further gas stream pump [0278] 20—first separator [0279] 21—product gas stream [0280] 22—container [0281] 23—second PSA apparatus [0282] 24—adsorption vessel [0283] 25—adsorption vessel [0284] 26—gas recycling pump [0285] 27—compressor pump [0286] 28—first hydrogen storage device [0287] 29—reservoir [0288] 30—further pump [0289] 31—hydrogen gas stream [0290] 32—turbine [0291] 33—generator [0292] 34—inverter [0293] 35—fluid stream [0294] 36—gas processing system [0295] 37—nitrogen gas stream [0296] 38—reservoir pump [0297] 39—second separator [0298] 40—second container [0299] 41—gas source [0300] 42—primary input stream [0301] 43—first gas purifier [0302] 44—first PSA apparatus [0303] 45—adsorption vessel [0304] 46—adsorption vessel [0305] 47—purified primary input stream [0306] 48—gaseous feed stream [0307] 49—first pump [0308] 50—heat exchanger [0309] 51—heating device [0310] 52—fluidised bed reactor [0311] 53—particle layer [0312] 54—reactor heating device [0313] 55—further gas stream [0314] 56—further gas stream pump [0315] 57—particle source [0316] 58—product stream [0317] 59—first separator [0318] 60—product gas stream [0319] 61—container [0320] 62—second PSA apparatus [0321] 63—adsorption vessel [0322] 64—adsorption vessel [0323] 65—gas recycling pump [0324] 66—compressor pump [0325] 67—first hydrogen storage device [0326] 68—reservoir [0327] 69—further pump [0328] 70—hydrogen gas stream [0329] 71—turbine [0330] 72—generator [0331] 73—inverter [0332] 74—fluid stream [0333] 75—gas processing system [0334] 76—nitrogen gas stream [0335] 77—reservoir pump [0336] 78—second separator [0337] 79—second container [0338] 80—particle stream