Chemical chain reforming of hydrocarbons

Abstract

The invention relates to a method for the thermochemical production of a fuel gas, such as synthesis gas, in a reactor by means of a chemical-looping process comprising a reforming process for hydrocarbons, such as methane, and a carbon dioxide decomposition process, and to a production plant for the method for the thermochemical production of a fuel gas, such as synthesis gas.

Description

Technical Field

[0001] This invention relates to a method for thermochemically producing fuel gases, such as syngas, in a reactor via a chemical looping process, the chemical looping process including, for example, reforming of hydrocarbons such as methane and carbon dioxide decomposition processes, and a thermochemical production apparatus for the method of producing fuel gases. Background Technology

[0002] Syngas is a mixture of hydrogen and carbon monoxide that can be used in a variety of applications. For example, syngas can be used to produce ammonia or methanol, as a combustible fuel, or as a precursor product for the synthesis of liquid fuels via the Fischer-Tropsch process.

[0003] Currently, syngas is mainly produced through steam reforming or partial oxidation of hydrocarbon fuel gases such as natural gas. Chemically chained reforming (CLRM) of methane is a promising but less mature syngas production pathway that utilizes non-stoichiometric metal oxides as oxygen carriers, dividing the methane reforming process into two reaction steps. These two reaction steps are: 1) endothermic reduction of the metal oxide to promote partial oxidation of methane (POM), followed by 2) exothermic re-oxidation of the metal oxide via the decomposition of CO2 and / or H2O, forming additional CO and / or H2, respectively. Equations 1 and 2a / 2b summarize these reactions, using the general formula metal oxide (M... x O y ), where δ represents the non-stoichiometry of oxygen.

[0004]

[0005]

[0006] The decomposition of CO2 and H2O (reactions 2a and 2b, respectively) is thermodynamically and kinetically quite favorable for re-oxidation. Therefore, by using an appropriate proportion of oxidant, the H2 / CO ratio can be controlled at 1:1 to 3:1 without a downstream water-gas shift reactor. The re-oxidation step can also be used to remove carbon deposits formed in the POM step, converting them into additional CO.

[0007] Cerium dioxide (CeO2) is known to be suitable for use as a nonstoichiometric material in CLRMs due to its typically rapid redox kinetics and favorable thermodynamic properties. CeO2 readily undergoes reoxidation under a wide range of conditions and maintains a stable cubic fluorite structure over a broad range of nonstoichiometric conditions, which contributes to achieving high oxygen exchange capacity.

[0008] Although CeO2 is a viable redox feedstock for CLRM at temperatures ≥1000°C, the kinetics of POM slow down below 1000°C, making lower-temperature operation impractical for industrial production purposes. Furthermore, the yield and selectivity of the thermochemical reaction decrease as the number of CLRM cycles increases and the oxidation level at the reactor end approaches stoichiometry.

[0009] Therefore, maintaining acceptable yields and selectivity in syngas production is not easy when using cerium oxide as a catalyst material. As the number of CLRM cycles increases, the ability of cerium oxide to provide good yields and selectivity in the downstream portion of the reactor, mediated by its redox state, decreases.

[0010] Therefore, there is a need to provide a process that maintains sufficient yield and selectivity across multiple CLRM cycles. Summary of the Invention

[0011] This invention provides a method for the thermochemical production of fuel gases, wherein losses in yield and selectivity can be offset, thereby providing a solution that allows the reactor to operate continuously in multiple CLRM cycles.

[0012] The inventors have discovered that by controlling the oxygen nonstoichiometry δ of the metal oxide in the downstream end or downstream portion of the reactor metal oxide element, the loss of yield and selectivity can be substantially mitigated. Therefore, the total selectivity S of carbon monoxide... CO It can be improved from below 0.95 to above 0.95.

[0013] Therefore, a first object of the present invention is to provide a method for producing fuel gas in a thermochemical reactor comprising a metal oxide element in a non-stoichiometric redox state, wherein the fuel gas exits the metal oxide element in a non-stoichiometric redox state at a downstream end of the metal oxide element, the method comprising the following steps:

[0014] - Repeated Chain Reforming Hydrocarbons (CLRH) cycle, wherein the Chain Reforming Hydrocarbons (CLRH) cycle includes

[0015] o Reduction half-cycle, wherein a reducing agent gas stream containing hydrocarbons is reacted with metal oxide M x O y-δox Contact for a predetermined duration to reduce metal oxides in a non-stoichiometric redox state, and

[0016] o Oxidation semi-cycle, wherein an oxidant gas stream containing carbon dioxide, water vapor and / or mixtures thereof is passed through a metal oxide M x O y-δredTo oxidize metal oxides in a non-stoichiometric redox state by contacting them for a predetermined duration.

[0017] The method periodically includes increasing the duration of the reduction half-cycle, increasing the flow rate of the reducing agent gas stream, or simultaneously increasing the duration of the reduction half-cycle and the flow rate of the reducing agent gas stream during the hydrocarbon chemical chain reforming (CLRH) cycle.

[0018] Further embodiments of the invention are set forth in the dependent claims.

[0019] Brief description of the attached figures

[0020] Preferred embodiments of the present invention are described below with reference to the accompanying drawings, which are used to illustrate the presently preferred embodiments of the invention and not to limit them. In the drawings,

[0021] Figure 1 The figure shows the δ values ​​of 30 CLRM cycles in a Ni-CeO2 reactor at 800°C when all cycles remain identical (diamond-shaped) and when the cycles are periodically extended (circular) according to the invention. avg The evolution. For each cycle, δ avg The value in the recovery half-cycle (higher δ) avg (value) and oxidation half-cycle (lower δ) avg It oscillates between values, and in every 5th cycle, δ avg The value shifts towards a higher value.

[0022] Figure 2 The carbon monoxide selectivity (Si) in 30 CLRM cycles on a Ni-CeO2 reactor at 800 °C is shown when all cycles remain identical (diamond-shaped) and when the cycles are periodically extended (circular) according to the invention. CO The evolution of selectivity is shown. When the cycle period is extended, the selectivity gradually increases to 0.98 in the three cycles after the period extension, then decreases again to 0.95 in the two cycles, and so on. When the cycle period remains the same, the selectivity tends to stabilize around 0.95.

[0023] Description of preferred implementation scheme

[0024] The first object of the present invention is to provide a method for producing fuel gas in a thermochemical reactor comprising a metal oxide element in a non-stoichiometric redox state, wherein the fuel gas exits the metal oxide element in the non-stoichiometric redox state at a downstream end of the thermochemical reactor, the method comprising the following steps:

[0025] - Repeated Chain Reforming Hydrocarbons (CLRH) cycle, wherein the Chain Reforming Hydrocarbons (CLRH) cycle includes

[0026] o Reduction half-cycle, wherein a reducing agent gas stream containing hydrocarbons is reacted with metal oxide M x O y-δox Contact for a predetermined duration, by changing δ from δ ox Increase to δ red To reduce metal oxides in a non-stoichiometric redox state, and

[0027] o Oxidation semi-cycle, wherein an oxidant gas stream containing carbon dioxide, water vapor and / or mixtures thereof is passed through a metal oxide M x O y-δred Contact for a predetermined duration, by changing δ from δ red Reduce to δ ox To oxidize metal oxides that are in a non-stoichiometric redox state.

[0028] The method periodically includes increasing the duration of the reduction half-cycle, increasing the flow rate of the reducing agent gas stream, or simultaneously increasing the duration of the reduction half-cycle and the flow rate of the reducing agent gas stream during the hydrocarbon chemical chain reforming (CLRH) cycle.

[0029] In the method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, according to the first objective of the present invention, the obtained fuel gas is preferably a mixture of carbon monoxide and hydrogen, also known as syngas.

[0030] Syngas can be used directly as fuel, or further used as feedstock for processes that provide liquid fuels via the Fischer-Tropsch process. When the method of producing fuel gas in a thermochemical reactor is used to directly supply the Fischer-Tropsch process, the preferred range for the CO / H2 ratio is 1.8 to 2.5.

[0031] In the method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state according to the first object of the present invention, the predetermined duration of the reduction half-cycle may be 60 seconds or 120 seconds, and the predetermined duration of the oxidation half-cycle may be 120 seconds or 150 seconds. Therefore, for example, when the predetermined duration of the reduction half-cycle is 60 seconds or 120 seconds, it can be periodically extended to 90 seconds or 150 seconds, respectively. The predetermined durations of the reduction half-cycle and the oxidation half-cycle may be the same or different, and in particular, the predetermined duration of the reduction half-cycle may be longer than the predetermined duration of the oxidation half-cycle. Therefore, for example, the predetermined duration of the reduction half-cycle may be 180 seconds, while the predetermined duration of the oxidation half-cycle may be 150 seconds, i.e., the predetermined duration of the reduction half-cycle is about 20% to 25% longer than the predetermined duration of the oxidation half-cycle.

[0032] In a method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, according to the first object of the invention, the thermochemical reactor comprises metal oxide elements as catalytically active materials, enabling the thermochemical production of fuel gas from feed gas. For example, the metal oxide elements can have various shapes and forms. As an example, the metal oxide elements can be in the form of monolithic units or a packed bed of individual metal oxide subunits. As another example, the metal oxide elements can be formed from multiple subunits, which can be identical, for example, metal oxide elements formed from multiple identical tubular or annular subunits. Generally, the metal oxide is preferably provided in a form that ensures a high surface area to volume ratio to increase the contact surface between the metal oxide and the feed gas. For example, the metal oxide is preferably a metal oxide foam, such as an open-cell metal oxide foam.

[0033] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor comprising a metal oxide element in a non-stoichiometric redox state, the metal oxide element is an elongated metal oxide element. During operation of the thermochemical reactor, a feed gas, whether an oxidant or a reductant gas, flows through the elongated metal oxide element along its longitudinal axis by entering at its upstream end. During its passage through the elongated metal oxide element, the feed gas is converted into carbon monoxide and hydrogen, i.e., syngas, which exits at its downstream end. A preferred example of an elongated metal oxide element is a tubular packed bed metal oxide element.

[0034] In the method for producing fuel gas in a thermochemical reactor comprising a metal oxide element in a non-stoichiometric redox state, according to the first objective of the present invention, the metal oxide M of the metal oxide element x O y-δ It is in a non-stoichiometric redox state. The non-stoichiometric redox state is quantified by δ, where δ represents a non-zero positive real number, and x and y represent natural integers, provided that y is greater than δ.

[0035] In a particular embodiment of a method for producing fuel gas in a thermochemical reactor comprising or composed of metal oxide elements in a non-stoichiometric redox state, δ is increased at the downstream end portion of the metal oxide elements during a periodically extended reduction half-cycle to enhance selectivity, particularly for carbon monoxide. Specifically, δ is increased to a value of at least 0.05, preferably at least 0.1 and up to 0.25, and more preferably up to 0.5.

[0036] In a particular embodiment of a method for producing fuel gas in a thermochemical reactor comprising or composed of Ni-CeO2 elements in a non-stoichiometric redox state, δ is increased at the downstream end of the Ni-CeO2 elements during a periodically extended reduction half-cycle to enhance selectivity, particularly for carbon monoxide. Specifically, during the periodically extended reduction half-cycle, δ is increased to a value of at least 0.05, preferably at least 0.1 and up to 0.25, and more preferably up to 0.5.

[0037] The inventors have discovered that better yield and selectivity can be achieved by controlling the oxygen nonstoichiometry δ of the metal oxide in the downstream end or downstream portion of the metal oxide element. For example, when the metal oxide is cerium oxide (CeO) 2-δ ) or nickel-cerium earth (Ni-CeO) 2-δ When δ is maintained at a value of at least 0.05, preferably at least 0.1 and up to 0.25, and preferably up to 0.5, at the downstream end or downstream portion of the metal oxide element, the total selectivity of carbon monoxide can be improved. CO .

[0038] While δ may not be directly measurable, it can be determined by identifying the composition of the gas exiting the downstream end or downstream portion of the metal oxide element. For example, mass spectrometry or infrared spectroscopy can be used to analyze the composition and / or flow rate of the gas exiting the downstream end or downstream portion of the metal oxide element. In particular, hydrogen, carbon dioxide, and methane can be determined qualitatively and quantitatively, allowing for the calculation of selectivity, such as the selectivity for carbon monoxide (S0). CO This allows for the calculation of δ of the metal oxide at the downstream end or downstream portion of the metal oxide element.

[0039] In the method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, according to the first object of the present invention, a hydrocarbon chemical chain reforming (CLRH) cycle is repeated during reactor operation. The hydrocarbon chemical chain reforming (CLRH) cycle comprises a reduction half-cycle and an oxidation half-cycle, which are induced by alternately supplying the reactor with a reducing agent gas or an oxidizing agent gas as feed gas.

[0040] In the reduction semi-cycle, a reducing agent gas stream containing hydrocarbons is reacted with a metal oxide M. x O y-δox Contact for a predetermined duration is used to reduce metal oxides in a non-stoichiometric redox state. During the reduction half-cycle, hydrocarbons in the reducing agent gas are oxidized to carbon monoxide, and the metal oxides are reduced in their non-stoichiometric redox state, δ from δ ox To δ red Increase.

[0041] In an oxidation half-cycle, metal oxides in a non-stoichiometric redox state are oxidized by contacting a stream of oxidant gas containing carbon dioxide, water vapor, and / or mixtures thereof with the gas for a predetermined duration. During the oxidation half-cycle, the carbon dioxide and / or water vapor of the oxidant gas are reduced to carbon monoxide and / or hydrogen, and the metal oxides are oxidized in their non-stoichiometric redox state, δ from δ red To δ ox reduce.

[0042] In the method for producing fuel gas in a thermochemical reactor comprising a metal oxide element in a non-stoichiometric redox state, according to the first object of the invention, the δ at the downstream end or downstream portion of the metal oxide element is maintained in the range of 0.05 to 0.5 by periodically increasing the duration of the reduction half-cycle, increasing the flow rate of the reducing agent gas stream, or simultaneously increasing the duration of the reduction half-cycle and the flow rate of the reducing agent gas stream during a hydrocarbon chemical chain reforming (CLRH) cycle. When the thermochemical reactor is repeatedly operated on multiple identical hydrocarbon chemical chain reforming (CLRH) cycles, the selectivity of the thermochemical reactor, and therefore δ, exhibits a drift towards lower selectivity or a lower δ value. To counteract this loss of selectivity in the thermochemical reactor, the reduction half-cycle can be periodically extended to re-establish a higher δ value at the downstream end of the metal oxide element, or the flow rate of the reducing agent gas can be increased to re-establish a higher δ value at the downstream end of the metal oxide element, or both measures can be used simultaneously.

[0043] After a higher δ value of at least 0.05, preferably at least 0.1, is re-established in the downstream end portion, the thermochemical reactor can be run again for a certain number of repeated hydrocarbon chemical chain reforming (CLRH) cycles until the δ value in the downstream end portion drops below the threshold, i.e., below 0.1 or below 0.05.

[0044] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the metal oxide is La-Sr-Mn based perovskite, cerium oxide, and preferably nickel-cerium oxide.

[0045] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, the metal oxide is Ni. 0 -Cerium-rich earth, preferably with Ni content based on Ni 0 The amount of Ni-cerium clay is 1 to 10% by weight, more preferably 4% to 8% by weight. Ni-cerium clay is obtained by depositing metallic Ni on the surface of CeO2 particles via a wet impregnation method, particularly on CeO2 particles with a diameter of approximately 500 µm to 1400 µm. It should be noted that depositing metallic Ni on the surface of CeO2 particles via the wet impregnation method results in discrete Ni particles on the CeO2 particle surface. 0 These particles, which may have nanoscale diameters up to 10 micrometers, produce a material different from Ni-doped CeO2, in which Ni is incorporated into the metal oxide lattice.

[0046] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, the thermochemical reactor is operated at a temperature below 1000°C, preferably between 650°C and 950°C, and more preferably between 700°C and 800°C. While the thermochemical reactor can operate at temperatures below 650°C, the kinetics of thermochemical production are significantly slowed down, making it impractical for fuel production.

[0047] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, the periodicity is every N hydrocarbon chemical chain reforming (CLRH) cycles, where N is a non-zero integer, preferably at least 2, more preferably 2 to 25, and even more preferably 2 to 15. It is understood that the periodicity will depend on parameters such as feed gas and metal oxides, but the principle remains the same: after a certain number of repeated hydrocarbon chemical chain reforming (CLRH) cycles, a higher δ value of at least 0.05 or at least 0.1 is re-established.

[0048] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the periodicity is every 4 to 10 chain chemical reforming (CLRH) cycles, preferably every 4, 5, or 6 CLRH cycles. It is understood that the periodicity will depend on parameters such as the feed gas and the metal oxides, but the principle remains the same: after a certain number of repeated CLRH cycles, a higher δ value needs to be re-established.

[0049] Typically, the duration or mass flow rate of the reducing agent gas is determined by measuring the composition of the gas exiting the downstream side of the reactor, and particularly by measuring the amount of carbon monoxide exiting at the downstream end of the reactor. Therefore, the appropriate periodicity and extent of the reduction half-cycle can be determined for a given metal oxide and given reaction conditions. Generally, adjusting the reduction half-cycle is appropriate when the carbon monoxide selectivity drops below 0.95, because in this case, δ will have dropped below 0.1, or even below 0.05.

[0050] In a particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, when the duration of the reduction half-cycle is increased without changing the flow rate of the reducing agent gas stream, the increase is at least 25%, preferably 50%, more preferably 60%, and most preferably up to 100%.

[0051] In a particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, when the flow rate of the reduction half-cycle is increased by at least 25%, preferably by 50%, more preferably by 60%, and most preferably by up to 100%, without changing the duration of the reducing agent gas flow.

[0052] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the reducing agent gas comprises or consists of hydrocarbon gases selected from methane, ethane, propane, butane, and mixtures thereof.

[0053] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the reducing gas comprises methane in combination with ethane, propane, butane, and mixtures thereof, more preferably comprising at least 50% by weight of methane, and even more preferably comprising at least 75% by weight of methane in combination with ethane, propane, butane, and mixtures thereof.

[0054] In one specific embodiment of the method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the reducing gas is methane. In another specific embodiment of the method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the reducing gas comprises less than 5% by weight, preferably less than 3% by weight, of a non-hydrocarbon gas, particularly an inert gas. The inert gas may be, for example, nitrogen, and rare gases such as argon or helium.

[0055] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the oxidant gas comprises or consists of carbon dioxide or a mixture of carbon dioxide and water vapor.

[0056] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, the oxidant gas comprises more than 75% by weight, preferably more than 95% by weight, of carbon dioxide and / or water vapor, particularly carbon dioxide, water vapor, or a mixture of carbon dioxide and water vapor. Furthermore, the oxidant gas comprises less than 5% by weight, preferably less than 3% by weight, of an inert gas. The inert gas may be, for example, nitrogen, a rare gas such as argon, or helium.

[0057] In one particular embodiment of a method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, the duration of the reduction half-cycle is increased by at least 15, 20, 30, or 60 seconds without altering the duration of the reducing agent gas flow.

[0058] Experimental data

[0059] Experimental setup:

[0060] The production of fuel gas takes place in a horizontal thermochemical tubular reactor, which is made of alumina tubes with a diameter of 4 mm and contains a 1-gram metal oxide element made of Ni-CeO2, wherein Ni is deposited on the surface of cerium oxide. 0 The particle weight is approximately 5% by weight. This redox raw material is synthesized by depositing metallic Ni on the surface of CeO2 particles with a diameter of 500µm to 1400µm using an equal-volume impregnation method.

[0061] The gas flow rate in the reactor is regulated by three mass flow controllers (MKS GE50A), and the operating temperature is set and maintained using a Carbolite furnace (Carbolite STF 16 / 180). All gas flow rate and temperature inputs are controlled via a custom LabVIEW program. Downstream gas analysis includes a mass spectrometer (HPR-20 QIC, Hiden Analytical) for measuring the flow rates of H2 and CO2, and an infrared analyzer (Siemens Ultramat 23) for quantifying the flow rates of CH4 and CO.

[0062] Each CLRM cycle consists of four steps: 1) partial oxidation of methane, equilibrated with φCH4=10vol% Ar (gas), called the reduction step; 2) purging in Ar (gas) for 10 minutes; 3) equilibration oxidation with φCO2=5vol% Ar (gas), called the oxidation step; and then 4) purging again in Ar (gas) for 10 minutes.

[0063] The reactor was run for 30 CLRM cycles at 800°C. The total flow rate for each step was set to 100 sccm, corresponding to a gas velocity of 0.135 m / s.

[0064] The reaction time of the method according to the present invention is: t red,1 =120 seconds, t red =60 seconds, and t ox =150 seconds. In every 5th CLRM cycle, the reaction time t red Increase by 50%, that is, from 60 seconds to 90 seconds.

[0065] The reaction time for the constant cycle method is: t red,1 =120 seconds, t red =60 seconds, and t ox =150 seconds.

[0066] The final t of the two experiments ox All were set to 15 minutes to ensure complete oxidation of Ni-CeO2.

[0067] The method for producing fuel gas in a thermochemical reactor containing metal oxide elements in a non-stoichiometric redox state, according to the present invention, and the method for producing syngas by maintaining the same cycle, are also described.

[0068] exist Figure 1 and Figure 2 The results of these two methods over 30 CLRM cycles at 800℃ were compared. It can be seen that... Figure 2In this invention, the method of periodically increasing the duration of the reduction step (green, circle every 5th cycle) achieves higher selectivity S in subsequent cycles than the method of keeping the duration of the reduction step constant (black, diamond). CO In particular, it is evident that the selectivity S of the periodic method decreases after extending the reduction step during the 10th, 15th, 20th, and 25th CLRM cycles. CO The selectivity S was increased to approximately 0.95, higher than that observed in the constant method. CO .

[0069] Explanation of reference numerals in the attached figures

[0070] none.

Claims

1. A method for producing fuel gas in a thermochemical reactor comprising a metal oxide element in a non-stoichiometric redox state, wherein the fuel gas exits the metal oxide element in a non-stoichiometric redox state at a downstream end of the metal oxide element, the method comprising the steps of: - Repeated chain reaction (CLRH) cycles, wherein the chain reaction (CLRH) cycle includes: o Reduction semi-cycle, wherein a reducing agent gas stream containing hydrocarbons is reacted with a metal oxide M x O y-δox Contact for a predetermined duration to reduce metal oxide M x O y ;as well as o Oxidation semi-cycle, wherein an oxidant gas stream containing carbon dioxide, water vapor and / or mixtures thereof is passed through a metal oxide M x O y-δred Contact for a predetermined duration to oxidize metal oxide M x O y , The method periodically includes, during a hydrocarbon chemical chain reforming (CLRH) cycle, increasing the predetermined duration of the reduction half-cycle, increasing the flow rate of the reducing agent gas stream, or simultaneously increasing the duration of the reduction half-cycle and the flow rate of the reducing agent gas stream.

2. The method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state according to claim 1, wherein the metal oxide is cerium oxide (CeO2), and preferably Ni. 0 -CeO2.

3. A method for producing fuel gas in a thermochemical reactor comprising a metal oxide element in a non-stoichiometric redox state, according to any one of the preceding claims, wherein the metal oxide is Ni. 0 -CeO2, preferably having a Ni-based composition. 0 - The Ni content is 1% to 10% by weight of cerium oxide, more preferably 4% to 8% by weight.

4. A method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state according to any one of the preceding claims, wherein the periodicity is every 4 to 10 hydrocarbon chemical chain reforming (CLRH) cycles, preferably every 4, 5 or 6 hydrocarbon chemical chain reforming (CLRH) cycles.

5. A method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, according to any one of the preceding claims, wherein, Without changing the flow rate of the reducing agent gas stream, the duration of the reduction half-cycle is increased by at least 25%, preferably by 50%, more preferably by 60%, and most preferably by up to 100%.

6. A method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, according to any one of the preceding claims, wherein, Without changing the predetermined duration of the reducing agent gas flow, the flow rate of the reduction half-cycle is increased by at least 25%, preferably by 50%, more preferably by 60%, and most preferably by up to 100%.

7. A method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state according to any one of the preceding claims, wherein the reducing agent gas comprises or consists of a hydrocarbon gas selected from methane, ethane, propane, butane and mixtures thereof, and more preferably comprises at least 50% by weight of methane, and / or less than 5% by weight, preferably less than 3% by weight of non-hydrocarbon gas.

8. A method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state, according to any one of the preceding claims, wherein, Without changing the duration of the reducing agent gas flow, the duration of the reduction half-cycle is increased by at least 15, 20, 30, or 60 seconds.

9. A method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state according to any one of the preceding claims, wherein the thermochemical reactor is operated at a temperature below 1000°C, preferably 650°C to 950°C, more preferably 700°C to 800°C.

10. A method for producing fuel gas in a thermochemical reactor comprising metal oxide elements in a non-stoichiometric redox state according to any one of the preceding claims, wherein a predetermined duration of the oxidation half-cycle is longer than a predetermined duration of the reduction half-cycle, and preferably wherein the predetermined duration of the oxidation half-cycle is at least 20%, or about 20% to 25%, longer than the predetermined duration of the reduction half-cycle.

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