Reaction initiator

Abstract

A method of forming a reaction initiator comprising contacting a porous particulate carbon material with a solution comprising an ionic metal compound dissolved in a solvent to absorb metal ions of the metal compound into the porous carbon material and calcining the activated carbon comprising the absorbed metal ions.

Description

[0001]REACTION INITIATOR BACKGROUND 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. Another alternative energy source is lithium-ion batteries, which commonly contain conductive carbon such as carbon black in the battery anode. WO2022 / 234302 discloses a microwave reaction process for forming hydrogen and a carbon product from a hydrocarbon-containing input gas. Ellison et al, “Activated carbon supported Ni, Fe, and bimetallic NiFe catalysts for COx- free H2 production by microwave methane pyrolysis” discloses metal-impregnated carbon-based catalysts. SUMMARY The present disclosure provides a method of forming a reaction initiator comprising contacting a porous particulate carbon material with a solution comprising an ionic metal compound dissolved in a solvent to absorb metal ions of the metal compound into the porous carbon material and calcining the activated carbon comprising the absorbed metal ions. Optionally, the porous particulate carbon material has a surface area of at least 400 m2 / g. Optionally, the porous particulate carbon material has a size of at least 0.5 mm. Optionally, the porous carbon material is activated carbon. Optionally, the activated carbon is a biomass-derived activated carbon. The method according to any one of the preceding claims wherein calcining is performed at a temperature of at least 300°C. Optionally, calcining includes microwave heating. Optionally, after absorption of metal ions and prior to calcining, the porous particulate carbon material is dried. Optionally, the dried porous particulate carbon material is contacted with the solution. Optionally, the metal compound is a transition metal compound. Optionally, the metal is iron. Optionally, the solution contains ionic metal compounds of at least two different metals. Optionally, the ionic metal compounds include an iron compound and at least one ionic compound of another transition metal. The present disclosure provides a reaction initiator obtainable by a method as described herein. The present disclosure provides a reaction initiator comprising activated carbon and metal ions absorbed in pores of the activated carbon. The present disclosure provides a a size of at least 0.5 mm. The present disclosure provides a composition comprising a reaction initiator as described herein and a microwave-absorbing material. Optionally, the microwave-absorbing material is silicon carbide. The present disclosure provides a method of converting a hydrocarbon to hydrogen gas and product carbon, the method comprising contacting the heated hydrocarbon with the reaction initiator or composition as described herein. Optionally, the heating is by microwave irradiation. Optionally, the reaction is performed in the presence of a particulate compound having greater hardness than the reaction initiator. Optionally, the reaction initiator is agitated during the reaction. Optionally, the reaction initiator frays during the reaction. Optionally, the conversion is carried out in an apparatus comprising a hydrocarbon gas inlet, a reaction chamber and a product outlet. Optionally, the reaction initiator is removed from the product outlet and returned to the reaction chamber. Optionally, the metal is iron and the product carbon is amorphous carbon. Optionally, the metal includes Ni, Cu or Pt and the product carbon is graphitic carbon. The present disclosure provides a method of forming a reaction initiator comprising mixing a particulate carbon material with a metal compound and calcining the mixture. Optionally, calcining is performed under an inert environment. Optionally, the metal compound is a transition metal compound. Optionally, the metal compound is a metal oxide. The present disclosure provides a reaction initiator obtainable by a method comprising mixing a particulate carbon material with a metal compound and calcining the mixture. The reaction initiator may be used in a method of converting a hydrocarbon to hydrogen gas and product carbon as described anywhere herein. DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the Figures in which: Figure 1, which is not drawn to any scale, illustrates a microwave reaction chamber according to some embodiments; Figure 2, which is not drawn to any scale, illustrates one embodiment of apparatus containing a microwave reaction chamber according to some embodiments; Figure 3, which is not drawn to any scale, illustrates another embodiment of apparatus containing a microwave reaction chamber according to some embodiments; Figure 4 is a graph of methane to hydrogen conversion rate vs time for a microwave reaction using an activated carbon reaction initiator; Figure 5 is a graph of methane to hydrogen conversion rate vs time for a microwave reaction using an iron oxide reaction initiator; Figure 6 is a graph of methane to hydrogen conversion rate vs time for a microwave reaction using a mixed iron oxide and activated carbon reaction initiator; Figure 7 is a graph of methane to hydrogen conversion rate vs time for a microwave reaction using a metal-impregnated activated carbon reaction initiator; Figure 8 is a graph of methane percentage in a gas at the outlet of a microwave reactor for activated carbon with no iron loading and activated carbon with iron loadings of 33% and 77%; and Figure 9 is a graph of methane percentage in a gas at the outlet of a microwave reactor for iron-loaded activated carbon having different particle sizes. DETAILED DESCRIPTION The present invention provides a particulate reaction initiator for promoting conversion of a hydrocarbon to hydrogen and carbon. In some embodiments, the particulate reaction initiator comprises a porous particulate carbon material, comprising a metal disposed in pores thereof. In some embodiments, the particulate reaction initiator is a calcined mixture of a particulate carbon material and a metal compound. Particulate carbon material The starting particulate carbon used to form the reaction initiator may be, without limitation, activated carbon; porous coal; and porous petroleum coke. The starting particulate carbon is suitably porous, particularly in the case where the reaction initiator is formed by absorbing metal ions into pores of the particulate carbon. The starting porous particulate carbon used to form the reaction initiator as described herein may be any porous form of carbon. Preferably, the porous particulate carbon has a surface area of at least 400 m2 / g, optionally at least 600 m2 / g. in the case of activated carbon, the starting activated carbon is preferably derived from biomass. Exemplary biomass from which the activated carbon may be derived include: cellulose, glucose, chitin, chitosan, gelatin and starch- based materials. Exemplary cellulose -based materials include coconut shell, palm kernel shell, lotus stalk, date seeds, leaves, barks, sugarcane bagasse, rice husk and algae. Coal-based activated carbons and petroleum cokes may be used. Preferably, the starting (unloaded) particulate carbon has a diameter of at least 0.2 mm, optionally at least 0.5 mm, optionally 0.2-10 mm or 0.5-10 mm, optionally 1-5 mm. Optionally, no more than 40 weight %, optionally no more than 20 weight % or no more than 10 weight % of the starting porous particulate carbon can pass through a 35 mesh (~500 micron opening). Optionally, no more than 40 weight %, optionally no more than 20 weight % or no more than 10 weight % of the starting porous particulate carbon can pass through a 25 mesh (~700 micron opening). Optionally, none of the starting porous particulate carbon can pass through a 100 mesh (~150 micron opening). Optionally, the particulate carbon is ground prior to use. Grinding may be by any process known to the skilled person that reduces the size of a particulate material, for example a milling process. As will be understood by the skilled person, the particulate carbon typically does not consist solely of carbon; other elements, in particular oxygen, are typically present. The starting particulate carbon, preferably activated carbon, preferably comprises oxygen, more preferably at least 10 weight % oxygen as determined by elemental analysis. Without wishing to be bound by any theory, the presence of oxygen in the particulate carbon facilitates reaction between the metal and carbon during calcining. Reaction initiator formation In some embodiments, formation of the reaction initiator comprises mixing a particulate carbon, optionally a porous particulate carbon, with a metal compound and calcining the mixture. Calcining treatment at a temperature of at least 300˚C, optionally at least 400˚C. Calcining treatment may be continued until no more CO, CO2 or volatile organic compounds are released from the porous carbon material. In some embodiments, formation of the reaction initiator comprises soaking a porous carbon material in a metal ion solution followed by a drying treatment. The starting porous carbon material may be dried, e.g., with heat and / or vacuum treatment, prior to soaking. Drying treatment may increase the availability of pores for absorption of the metal ion solution. The metal ion solution is preferably a transition metal ion solution, more preferably a solution of one or more of an iron, nickel, copper, palladium, or platinum compound. Preferably, the one or more metal ions of the solution include iron ions, more preferably iron (III) ions. The, or each, metal ion of the metal ion solution is preferably present in an amount of at least 0.5 mols / litre, optionally 0.5-5 mols / litre. It will be appreciated that any soluble metal compound may be used for the metal ion solution, for example a metal halide, sulfate or nitrate. The solution is preferably an aqueous solution. Water may be the only solvent of the solution, or one or more further water-miscible solvents may be present. Drying of the porous carbon material, before or after soaking, is preferably at a temperature in the range of 50-200˚C, optionally 50-150˚C. Drying may be carried out under reduced pressure. Preferably, drying is carried out in an inert environment, e.g., under argon or nitrogen gas. Optionally, drying is carried out for at least 1 hour, optionally 1-24 hours. Drying is complete when mass of the dried material does not decrease after1 hour under the drying conditions. The porous carbon material may be subjected to a plurality of soaking and drying treatments. Optionally, the porous carbon material is subjected to soaking and drying treatments until the mass of the treated dried porous carbon material reaches a threshold percentage increase as compared to the starting dried porous carbon material or until the mass of the treated dried porous carbon material stops increasing. Preferably, the mass increase of the treated dried porous carbon material as compared to the starting dried porous carbon material (hereinafter referred to as the “loading” of the porous carbon) is at least 10%, optionally at least 20%, optionally at least 50%. The treated porous carbon material is then calcined. Calcining treatment may be by heating the treated porous carbon material to at least 300˚C, optionally at least 400˚C. Calcining treatment may be continued until no more CO, CO2 or volatile organic compounds are released from the porous carbon material. Without wishing to be bound by any theory, the soaking and drying treatment causes metal ions to be loaded into the pores and onto the surface of the porous carbon material and the calcining treatment causes a reaction between the carbon and the metal ion. Again, without wishing to be bound by any theory, the calcining treatment may result in formation of a metal-carbon bond. Preferably, the loaded porous carbon material has a particle size of at least 0.5 mm, optionally 0.5-10 mm, optionally 1-5 mm. Optionally, no more than 40 weight %, optionally no more than 20 weight % or no more than 10 weight % of the starting porous particulate carbon can pass through a 35 mesh (~500 micron opening). Optionally, no more than 40 weight %, optionally no more than 20 weight % or no more than 10 weight % of the starting porous particulate carbon can pass through a 25 mesh (~700 micron opening). Calcining for either a mixture of a particulate carbon and a metal compound or for a porous particulate carbon comprising absorbed metal ions may be performed exclusively by a non-microwave heating method; exclusively by a microwave heating method; or a combination thereof. Without wishing to be bound by any theory, microwaves may enhance the reaction of carbon with metal ions or metal compounds to produce a carbon-metal complex and CO and CO2 as compared to other heating methods. Calcining is preferably performed under an inert (e.g., nitrogen) atmosphere. Non-microwave heating may be by a thermal conduction method, i.e., transfer of heat from an object at higher temperature than the treated porous carbon material. Metal In the case where reaction initiator formation comprises absorbing metal ions from a solution, the metal loaded onto the porous carbon is preferably a transition metal, more preferably one or more of iron, nickel, copper, palladium and platinum. In some embodiments, only one metal is loaded onto the porous carbon. In some embodiments, two or more different metals are loaded onto the porous carbon. Preferably the one or more metals include iron. When the loaded porous carbon is used as a reaction initiator for microwave cracking of a hydrocarbon, the conversion rate of the hydrocarbon into hydrogen and carbon and / or the nature of the carbon product may be affected by the identity of the metal loaded onto the porous carbon. The metal may be selected as described in “Heterogeneous Catalysis” ISBN 90-393-1836-0, published by Utrecht University according to the desired carbon product; for example, iron may be used for formation of amorphous carbon black and iron in combination with nickel or copper may be used in formation of graphitic carbon. Metal compound In the case where reaction initiator formation comprises calcining a mixture of a particulate carbon and a metal compound, the metal compound is preferably a transition metal compound, more preferably a compound of iron, nickel, copper, palladium platinum or mixtures thereof. The metal compound is preferably a metal oxide. In some embodiments, only one metal compound is mixed with the particulate carbon. In some embodiments, two or more different metal compounds are mixed with the porous carbon. Preferably the one or more metal compounds include an iron compound, optionally iron oxide. The metal compound mixed with the particulate carbon may be in solid, preferably particulate, form. The metal compound may be in liquid form. Microwave cracking Microwave cracking may be carried out in any microwave reaction apparatus known to the skilled person. At the start of the reaction, the reaction initiator may be the only solid material in the reactor. 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. During reaction, formation of hydrogen and carbon is catalysed by the reaction initiator, resulting in formation of product carbon on the surface and in the pores of the porous carbon. Product carbon formed in pores may cause the porous carbon particles to break apart (fray), exposing new catalytic sites in the case of porous carbon containing absorbed metal. Fraying of the reaction initiator may be facilitated by agitating the reaction initiator in the reactor with an abrasive particulate material. The abrasive particulate material may be any particulate material which is inert to the reaction conditions and which has a higher hardness, as measured on the Moh scale of hardness, than the reaction initiator. A preferred abrasive particulate material is silicon carbide; it will be appreciated therefore that silicon carbide may provide both microwave absorption and abrasion functionality. Optionally, the reaction initiator: microwave-absorbing material weight ratio is in the range of about 1 : 99 – 99 : 1, preferably 1 : 99 – 10 : 90. The reaction initiator may be agitated by any suitable means, for example passing a gas, which may be the hydrocarbon gas, through a bed comprising or consisting of the reaction initiator; vibration of the reactor; or rotation of the reactor. At the start of the reaction, the reactor may contain one or more other particulate solids such as a microwave absorption material and / or an abrasive material in any arrangement, for example a layered arrangement or a mixed arrangement. Following the reaction, product carbon and the reaction initiator may be separated by any suitable process. Recovered reaction initiator may be returned to the reactor. The carbon product may be, for example, carbon black; graphite; or mixtures thereof. The reaction may be a batch or continuous process. A supply of the reaction initiator may be continuously or continually replenished. By “continually replenished” as used herein means intermittent replenishment. The input gas suitably contains at least 10 % by volume of hydrocarbons, more preferably at least 20% by volume of hydrocarbons. The input gas suitably contains at least 10 % by volume of methane, optionally at least 20% by volume of methane. Hydrocarbons as described herein are preferably selected from C1-4 alkanes and C1-4 alkenes. 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. By “input gas” as used herein is meant a gas entering a microwave reaction chamber. 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. 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. Optionally, pressure of gas in the microwave reaction chamber is 0.1-10 atmospheres, preferably 0.5-3 atmospheres or 0.5-2 atmospheres. Optionally, the microwave frequency is in the range of 0.5 – 20 GHz. 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 1-100kW. It will be understood that the microwave power required will depend in part on the size of the reactor. Figure 1 is a schematic view of a microwave reactor 60. A tube 120, which is transparent to microwave energy, is positioned in microwave chamber 122. A waveguide 124 having slots 126 is provided to direct microwave radiation into the chamber. In the embodiment of Figure 1, the waveguide is attached to an external wall of the microwave chamber 126 however the skilled person will be aware of other configurations. In some embodiments, the waveguide 124 may pass through the microwave chamber; for example, the wave guide may be attached to an internal wall of the microwave chamber. The internal walls of the microwave chamber are suitably selected for reflection of microwaves. The position of the waveguide relative to the internal walls may be selected for reflection of microwaves towards the tube 120. The width and spacing of the slots may be optimized for the microwave wavelength used. A source of microwave energy 128 is configured to direct microwave energy into the waveguide 124. In one embodiment, tube 120 is quartz glass. Figure 1 illustrates a microwave reactor in which the carbon and / or metal or metal compound, optional microwave absorbing material and input gas within the microwave reaction chamber are contained within a tube which is transparent to microwave energy, however other embodiments will be apparent to the skilled person. The microwave reaction chamber of Figure 1 has a half-oval cross-section however it will be understood that any suitable shape, e.g., a rectangle, may be used. Figure 1 illustrates a microwave reactor having a single waveguide directing radiation into the microwave reaction chamber. In other embodiments, a plurality of such waveguides is provided. In the embodiment of Figure 1 input gas passes through the microwave chamber 122 in tube 120 containing the carbon and / or metal or metal compound and, if present, the microwave absorption material. The input gas may enter from inlet 136 and flow through the tube where it comes into contact with the reaction initiator and, if present, the microwave absorption material and exit the reaction chamber at outlet 138. Figure 1 illustrates an arrangement in which the tube 120 is substantially vertical. According to this embodiment, gas may flow upwards through the tube 120. In other arrangements, the tube 120 may be closer to the horizontal than the vertical. The microwave reaction chamber may be insulated to prevent heat loss, e.g., due to an endothermic hydrocarbon cracking reaction. Figure 2 illustrates apparatus 100 according to an embodiment of the present disclosure containing a microwave reaction chamber 122, for example as described with reference to Figure 1. The microwave reaction chamber has a gas inlet and a gas outlet. The tube 120, as shown in Figure 1, may extend between some or all of the distance between an inlet 136 and an outlet 138 of the microwave reaction chamber. The gas inlet and gas outlet may be opposing ends of the tube 120, as described with reference to Figure 1. The apparatus may comprise a feed hopper for introduction of metal or metal compound into the microwave reaction chamber and, optionally, a microwave-absorbing material, for example carbon black or silicon carbide. The feed hopper may be connected to a solid inlet of the tube 120. The microwave reaction chamber may contain a moving bed. Any moving bed arrangement known to the skilled person may be used. In some embodiments, the microwave reaction chamber 122 of apparatus such as illustrated in Figure 2 may contain a screw, forming a pipe and screw arrangement to move the solid contents in the microwave reaction chamber 122 through the microwave chamber. In some embodiments, the moving bed may be a vibrating bed. Solid product exiting the microwave reaction chamber may be collected in a collector 142. The tube 120 may contain a solid outlet for removal of solid product exiting the microwave chamber. The solid product may be collected in a collector. The carbon product may be separated using any method known to the skilled person. Suitably, no components of the reaction bed are separated from one another within the microwave chamber. In some embodiments, the moving bed may be inclined relative to the horizontal, for example as illustrated in Figure 3. The moving bed allows for continuous or batch reactions to be carried out. Figures 2 and 3 illustrate apparatus having a plurality of microwave energy sources 128. It will be appreciated that the number of microwave energy sources may be selected according to the desired dimensions and operating conditions of the apparatus. An input gas, e.g., natural gas, may be heated by a pre-heater before entering the microwave reaction chamber. The pressure of gas in the apparatus may be set to any desired pressure, which may be above or below 1 atmosphere, for example by use of a gas compressor 146. In some embodiments, for example as illustrated in Figure 2, a feedstock gas and an input gas are the same, i.e., the feedstock gas is delivered to a microwave reaction chamber without any treatment to change its composition. In some embodiments, a feedstock gas is treated to change its composition to an input gas composition, for example to remove oxygen-containing gases, particularly water. Hydrogen contained in product gas exiting the microwave reaction chamber may be separated by a hydrogen separator 148 into hydrogen gas, and any unreacted input gas which may be recycled back to the microwave reaction chamber. In the embodiment of Figure 1, product gas separated from hydrogen is recycled to the microwave chamber. In some other embodiments, not shown, for example where a metal oxide produces carbon monoxide and carbon dioxide, carbon monoxide may be separated from the product gas by a carbon monoxide separator. Remaining product gas may be recycled to the microwave reactor and carbon monoxide may be delivered to the fuel for the preheater 144 for combustion to provide heating of the preheater. Fine particles entrained within the product gas, e.g., fine carbon black, may be separated using a particle filter 150 and collected in a particle collector 152. It will be understood by the skilled person that the components of the apparatus of Figures 2 and 3 may be arranged in any suitable order. The moving bed reactor may enable continuous production of carbon product, which may be removed from an outlet of the reaction chamber. The removed carbon product may or may not be separated from the metal or metal compound. Unseparated carbon product may be subsequently separated by any method known to the skilled person. A portion of the separated or unseparated carbon product may be recycled back into the reactor. In other embodiments, the microwave reaction chamber may have a fluidised bed or fixed bed. 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. 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. Examples Example 1 - Reaction initiator formation Coconut-derived activated carbon having a surface area of 1,000 m2 / g and particle size of 3-5 mm was dried with hot nitrogen gas at 100°C for about 24 hours to remove absorbed water. The dried activated carbon was soaked in ferric nitrate nonahydrate solution for 24 hours and then dried under hot inert (nitrogen) gas at 100°C for about 24 hours. The soaking and drying steps were repeated until at least a 20% weight increase of the dried activated carbon was achieved. The loaded activated carbon was calcined under an inert gas at 500˚C either by thermal treatment or by microwave irradiation in a mixture with silicon carbide. Example 2 - Microwave cracking comparison of loaded and unloaded activated carbon A microwave reactor as illustrated in Figure 1 was packed with a reaction initiator and, optionally, silicon carbide. Microwave cracking of methane was carried out as set out in Table 1. Table 1 Iron- Activated Iron Oxide Carbon + Iron impregnated Carbon Alone Alone Oxide mixed activated carbon Reactor Diameter 0.6 3 3 3 Inlet Gas CH4CH4CH4CH4Inlet Gas Flow Rate (cfh) 0.5 0.5 2 1.2 Inlet Temp (F) 400 400 400 600 1000g Carbon powder + Reaction Initiator (g) 50 1100g 100g Fe ~1,500g SiC NA 1500g 200g ~1000g Microwave Power 2-2.5kW 3-4.5 kw 2-3 kw 4 kw Figure 4 5 6 7 With reference to Figures 4-7, a mixture of activated carbon and iron oxide stabilised at a conversion rate of above 80% after about 100 minutes. Without wishing to be bound by any theory, an iron-carbon complex is formed during microwave treatment. The iron-impregnated activated carbon maintained a methane to hydrogen conversion rate at above 80% for a period of over 250 minutes, and above 90% for nearly 200 minutes, significantly outperforming granulated activated carbon (GAC) alone iron oxide alone or a mixture of activated carbon and iron oxide. It was observed that the particle size of the iron-impregnated activated carbon reaction initiator removed from the reactor after the reaction was smaller than the initiator before reaction. Without wishing to be bound by any theory, the iron- impregnated activated carbon frays during the reaction, thereby exposing new reaction sites and enabling maintenance of a high conversion rate over a prolonged period of time. Example 3 – Effect of metal loading level Microwave cracking of methane was carried out using iron-impregnated activated carbon as described in Example 2 with iron loadings of 33% and 77%. For comparison, activated carbon with no iron loading was also used. The activated carbon used in these experiments all had a similar size. Pure CH4 was flowed into the microwave reactor at 1L / min and the outlet concentration of CH4 and H2 was measured. With reference to Figure 8, a higher iron loading gave lower measured CH4 at the outlet, indicating greater conversion of CH4 at higher loadings. Example 4 – Effect of particle size Cracking was carried out as described in Example 2 using the following iron-impregnated particulate activated carbons: (i) Diameter 0.40-1.70 mm, 83% iron loading (ii) Diameter 0.25-0.65 mm, 77% iron loading With reference to Figure 9, the particles with smaller diameter gave lower measured CH4 at the outlet, despite the slightly lower loading of iron, indicating greater conversion of CH4 at lower particle size.

Claims

CLAIMS 1. A method of forming a reaction initiator comprising contacting a porous particulate carbon material with a solution comprising an ionic metal compound dissolved in a solvent to absorb metal ions of the metal compound into the porous carbon material and calcining the activated carbon comprising the absorbed metal ions.

2. The method according to claim 1 wherein the porous particulate carbon material has a surface area of at least 400 m2 / g.

3. The method according to claim 1 or 2 wherein the porous particulate carbon material has a size of at least 0.5 mm.

4. The method according to any one of the preceding claims wherein the porous carbon material is activated carbon.

5. The method according to claim 4 wherein the activated carbon is a biomass-derived activated carbon. The method according to any one of the preceding claims wherein calcining is performed at a temperature of at least 300°C.

6. The method according to any one of the preceding claims wherein calcining includes microwave heating.

7. The method according to any one of the preceding claims wherein, after absorption of metal ions and prior to calcining, the porous particulate carbon material is dried.

8. The method according to claim 7 wherein the dried porous particulate carbon material is contacted with the solution.

9. The method according to any one of the preceding claims wherein the metal compound is a transition metal compound.

10. The method according to claim 9 wherein the metal is iron.

11. The method according to any one of the preceding claims wherein the solution contains ionic metal compounds of at least two different metals.

12. The method according to claim 11 wherein the ionic metal compounds include an iron compound and at least one ionic compound of another transition metal.

13. A reaction initiator obtainable by a method according to any one of the preceding claims.

14. A reaction initiator comprising activated carbon and metal ions absorbed in pores of the activated carbon.

15. The reaction initiator according to claim 13 or 14 having a size of at least 0.5 mm.

16. A composition comprising a reaction initiator according to any one of claims 13-15 and a microwave-absorbing material.

17. The composition according to claim 16 wherein the microwave-absorbing material is silicon carbide.

18. A method of converting a hydrocarbon to hydrogen gas and product carbon, the method comprising contacting the heated hydrocarbon with the reaction initiator or composition according to any one of claims 13-17.

19. The method according to claim 18 wherein the heating is by microwave irradiation.

20. The method according to claim 18 or 19 wherein the reaction is performed in the presence of a particulate compound having greater hardness than the reaction initiator.

21. The method according to any one of claims 18-20 wherein the reaction initiator is agitated during the reaction.

22. The method according to any one of claims 18-21 wherein the reaction initiator frays during the reaction.

23. The method according to any one of claims 18-22 wherein the conversion is carried out in an apparatus comprising a hydrocarbon gas inlet, a reaction chamber and a product outlet.

24. The method according to claim 23 wherein the reaction initiator is removed from the product outlet and returned to the reaction chamber.

25. The method according to any of claims 18-24 wherein the metal is iron and the product carbon is amorphous carbon.

26. The method according to any of claims 18-24 wherein the metal includes Ni, Cu or Pt and the product carbon is graphitic carbon.

27. A method of forming a reaction initiator comprising mixing a particulate carbon material with a metal compound and calcining the mixture.

28. The method according to claim 27 wherein calcining is performed under an inert environment.

29. The method according to claim 27 or 28 wherein the metal compound is a transition metal compound.

30. The method according to any one of claims 27-29 wherein the metal compound is a metal oxide.

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