Methylcyclohexane dehydrogenation system and method using fuel cell

Abstract

The invention discloses a system and a method for dehydrogenation of methyl cyclohexane by using a fuel cell. The system comprises an electrochemical dehydrogenation power generation unit which takes a solid oxide fuel cell as a reactor and is used for performing an electrochemical dehydrogenation reaction on methylcyclohexane to generate a dehydrogenation product containing toluene and simultaneously generating electric energy; the electrochemical hydrogenation unit takes a proton exchange membrane electrolytic tank as a reactor and is used for carrying out electrochemical hydrogenation reaction on toluene and hydrogen to generate methylcyclohexane; and in the material circulation loop, toluene generated by the electrochemical dehydrogenation power generation unit is at least partially conveyed to the electrochemical hydrogenation unit to serve as a reactant, and methylcyclohexane generated by the electrochemical hydrogenation unit is at least partially conveyed to the electrochemical dehydrogenation power generation unit to serve as a reactant. The electrochemical reaction path is used for replacing traditional thermocatalysis, the reaction efficiency is improved, the energy consumption is reduced, and the system is a green and efficient energy comprehensive utilization system.

Description

TECHNICAL FIELD

[0001] The present application relates to a system and method for methylcyclohexane dehydrogenation using a fuel cell, belonging to the technical field of energy comprehensive utilization. BACKGROUND

[0002] Hydrogen, as a high-efficiency clean secondary energy, has the advantages of high energy density and zero carbon emission of combustion products, and is considered as a key energy carrier to achieve carbon neutralization target, and is widely used in fuel cells, chemical synthesis, metallurgy and energy storage fields. However, the large-scale application of hydrogen still faces technical bottlenecks in the storage and transportation links. Traditional high-pressure gaseous hydrogen storage and low-temperature liquid hydrogen storage have problems such as low safety, high energy consumption and expensive infrastructure cost, which restrict the development of hydrogen energy industry chain.

[0003] Under this background, the liquid organic hydrogen carrier (Liquid Organic Hydrogen Carriers, LOHCs) technology has become an important direction to solve the hydrogen storage and transportation problem because of its high hydrogen storage density, safety and stability at room temperature and pressure, and the use of existing petrochemical facilities for transportation. Methylcyclohexane (Methylcyclohexane, MCH) as a typical LOHC, its hydrogen storage density can reach 6.1wt%, and through the reversible dehydrogenation-hydrogenation reaction (with toluene cycle) to realize hydrogen storage and release, it has chemical stability and recycling, and is considered as a potential hydrogen energy carrier.

[0004] However, the methylcyclohexane dehydrogenation hydrogen production technology still faces key challenges: the existing catalysts generally have low activity, high reaction temperature (>300℃), many by-products and insufficient long-term stability, etc., resulting in low hydrogen production efficiency and rising energy consumption cost. In addition, the strong endothermic characteristics of the dehydrogenation reaction put higher requirements on the reactor design and heat energy management. Therefore, the development of efficient, high selectivity and low cost methylcyclohexane catalytic dehydrogenation technology has urgent technical and commercial value for promoting the large-scale application of hydrogen energy and perfecting the clean energy system.

[0005] Solid oxide fuel cell (SOFC) is a kind of full solid fuel cell which can convert the chemical energy of hydrogen and various hydrocarbon fuel gas (natural gas, propane, coal gas, methanol, etc.) into electric energy at high temperature with high efficiency, and has the advantages of high energy conversion efficiency, low emission, fuel flexibility, etc. It is considered as the most promising technology in the field of energy in the 21st century. It has high selectivity and high conversion efficiency for chemical reaction, produces chemicals and generates electricity at the same time, has high power generation efficiency, and the waste heat of the stack has high value. By using the advantages of SOFC electrochemical reaction, many problems of methylcyclohexane dehydrogenation in traditional process can be solved.

[0006] To achieve the above-mentioned purposes of the present application, the present application provides a system and method for dehydrogenation of methylcyclohexane by using a fuel cell, which can realize mild, efficient and clean hydrogen production from methylcyclohexane. SUMMARY

[0007] The present application aims to provide a system and method for dehydrogenation of methylcyclohexane by using a fuel cell, in particular, The present application relates to simultaneous production of electric energy and heat energy by dehydrogenation of methylcyclohexane using a solid oxide fuel cell: mild and efficient oxidation of methylcyclohexane by means of an electrochemical reaction, control of the reaction temperature, and optional production of toluene, benzene, dioxane and other chemicals; The present application relates to hydrogenation of toluene using a proton exchange membrane electrolytic cell. The present application relates to electrolysis of water to produce hydrogen using a solid oxide electrolytic cell, or co-electrolysis of water / carbon dioxide to produce synthesis gas, and then chemical synthesis of chemicals.

[0008] The present application uses fuel cells and electrolytic cells to construct a new type of "methylcyclohexane-toluene" hydrogen cycle system, which uses a high-temperature solid oxide fuel cell for dehydrogenation of methylcyclohexane, a proton exchange membrane electrolytic cell for hydrogenation of toluene, and a mild, safe and precisely controllable electrochemical environment to replace traditional thermal catalysis with an electrochemical reaction path, thereby improving reaction efficiency and reducing energy consumption. It is a green and efficient energy comprehensive utilization system.

[0009] The present application provides a methylcyclohexane-toluene hydrogen cycle system, which comprises: An electrochemical dehydrogenation power generation unit using a solid oxide fuel cell as a reactor for electrochemical dehydrogenation of methylcyclohexane to produce a dehydrogenation product containing toluene and simultaneously generate electric energy; An electrochemical hydrogenation unit using a proton exchange membrane electrolytic cell as a reactor for electrochemical hydrogenation of toluene and hydrogen to produce methylcyclohexane; And a material circulation loop, wherein the toluene produced by the electrochemical dehydrogenation power generation unit is at least partially delivered to the electrochemical hydrogenation unit as a reactant, and the methylcyclohexane produced by the electrochemical hydrogenation unit is at least partially delivered to the electrochemical dehydrogenation power generation unit as a reactant.

[0010] Preferably, the system further comprises an electrochemical synthesis gas preparation unit using a solid oxide electrolytic cell as a reactor and configured to perform an electrolysis reaction using the electric energy generated by the electrochemical dehydrogenation power generation unit to produce hydrogen; and the hydrogen produced by the electrochemical synthesis gas preparation unit is delivered to the electrochemical hydrogenation unit.

[0011] Preferably, the electrochemical synthesis gas preparation unit is configured to be able to electrolyze water to produce hydrogen, or co-electrolyze water and carbon dioxide to produce synthesis gas containing hydrogen and carbon monoxide.

[0012] The system of the present application further comprises: a thermal energy supply unit configured to provide heat for the system by burning fuel, the fuel being at least partially derived from hydrogen produced by the electrochemical synthesis gas preparation unit or fuel produced by the synthesis gas preparation; and, a carbon cycle loop, carbon dioxide produced by the thermal energy supply unit being delivered to the electrochemical synthesis gas preparation unit for co-electrolysis reaction.

[0013] Based on the system, the present application further provides a hydrogen cycle method, comprising the following steps S1, electrochemical dehydrogenation power generation In the solid oxide fuel cell, methylcyclohexane is subjected to electrochemical dehydrogenation reaction to produce dehydrogenation product containing toluene and generate electric energy; S2, electrochemical hydrogenation step In the proton exchange membrane electrolysis cell, toluene and hydrogen are subjected to electrochemical hydrogenation reaction to produce methylcyclohexane; S3, material cycle step At least part of the toluene produced in the electrochemical dehydrogenation power generation step is used in the electrochemical hydrogenation step, and at least part of the methylcyclohexane produced in the electrochemical hydrogenation step is used in the electrochemical dehydrogenation power generation step.

[0014] The method of the present application further comprises an electrochemical synthesis gas preparation step: using the electric energy produced in the electrochemical dehydrogenation power generation step to drive the solid oxide electrolysis cell to perform electrolysis reaction to produce hydrogen, and using the produced hydrogen in the electrochemical hydrogenation step; And, the method further comprises a carbon cycle step: collecting carbon dioxide produced in the system, and delivering it into the solid oxide electrolysis cell for co-electrolysis reaction to produce synthesis gas.

[0015] In step S1, the operating temperature of the electrochemical dehydrogenation power generation unit is 418-492℃, and the operating pressure is atmospheric pressure; and by adjusting the operating temperature, the ratio of toluene, benzene and dioxane in the dehydrogenation product can be selectively controlled.

[0016] When the operating temperature is 418-422℃, the dehydrogenation product mainly contains toluene and benzene; when the operating temperature is 488-492℃, the dehydrogenation product contains toluene, benzene and dioxane, and the reaction is as follows: Cathode reaction:

[0017] Anode reaction ①:

[0018] Anode reaction ②:

[0019] Anode reaction ③:

[0020] Reaction ① is the electrode reaction of methylcyclohexane being oxidized to generate toluene, reaction ② is the electrode reaction of methylcyclohexane being oxidized to generate benzene, and reaction ③ is the electrode reaction of methylcyclohexane being oxidized to generate dioxane, the three reactions are simultaneously carried out at 490℃, and the proportion of toluene, benzene and dioxane generated is 12.8:0.6:86.6. At 420℃, reactions ① and ② are the main reactions, and the proportion of toluene and benzene generated is 94:6, by controlling the reaction temperature of the solid oxide fuel cell, toluene, benzene or dioxane chemicals can be selectively prepared.

[0021] In step S2, the operation temperature of the electrochemical hydrogenation unit is 60-80℃, the operation pressure is normal pressure, and the reaction occurring is as follows: Anode reaction:

[0022] Cathode reaction:

[0023] In step S2, the operation temperature of the electrochemical synthesis gas preparation unit is 700-750℃, the operation pressure is normal pressure, and the reaction occurring is as follows: Anode reaction:

[0024] Cathode reaction:

[0025] Or the water and carbon dioxide prepared by the dehydrogenation system are used to generate hydrogen and carbon monoxide through co-electrolysis: Anode reaction: 、 Cathode reaction ①:

[0026] Cathode reaction ②:

[0027] The working principle of the present application is as follows: Air is heated to 490℃ by the burner tail gas and then introduced into the cathode of the solid oxide fuel cell. Methylcyclohexane is heated to 490℃ to form methylcyclohexane steam, which is introduced into the anode of the solid oxide fuel cell. Methylcyclohexane is dehydrogenated into toluene, benzene or dioxane by electrochemical reaction, and the products are water and carbon dioxide. At the same time, high-quality electricity is generated to power the high-temperature electrolysis cell. Toluene, benzene or dioxane is dehydrogenated and then separated by low-temperature crystallization in the post-processing unit. Water and carbon dioxide are heated to 730℃ and then introduced into the cathode of the high-temperature electrolysis cell. Air is heated to 730℃ and then introduced into the anode of the high-temperature electrolysis cell. Hydrogen and carbon monoxide are generated by electrochemical reaction. The synthesis gas is prepared into methane, methanol and other chemicals by the synthesis gas processing unit according to the needs of the user. On the other hand, the hydrogenation system can reduce toluene to methylcyclohexane by a proton exchange membrane electrolysis cell. Toluene is heated to 70℃ and then introduced into the cathode of the proton exchange membrane electrolysis cell. Deionized water is heated to 70℃ and then introduced into the anode of the proton exchange membrane electrolysis cell. Toluene is reduced to methylcyclohexane by electrochemical reaction. The hydrogenation system relying on the proton exchange membrane electrolysis cell and the dehydrogenation system relying on the solid oxide fuel cell are combined to form a new methylcyclohexane-toluene hydrogen storage system.

[0028] Currently, there is no related technology report on methylcyclohexane dehydrogenation using fuel cells. The present application has the following advantages: (1) The present application uses solid oxide fuel cells to dehydrogenate methylcyclohexane while generating electricity and heat: has the following advantages: ① reduces energy consumption: SOFC technology couples the endothermic dehydrogenation reaction with the exothermic power generation reaction, the heat of the power generation reaction directly supplies the dehydrogenation reaction, the reaction heat is used to maintain the system temperature, greatly reduces the energy consumption, compared with the traditional catalytic dehydrogenation, saves a lot of energy consumption; ② reaction condition optimization: the reaction temperature range of the present application is 420℃-490℃, which can prevent the high-temperature cracking of methylcyclohexane and prevent the carbon deposition of the electrode catalyst, the operating pressure of the present application is atmospheric pressure, which can simplify the safety design of the system; ③ high-value products: hydrogen produced by anode dehydrogenation is directly oxidized in SOFC to generate electricity, and through tail gas treatment, recyclable toluene and other chemicals can be separated, realizing energy and chemical co-production; ④ environmental protection and carbon emission reduction benefit: SOFC dehydrogenation power generation process produces a small amount of carbon dioxide, combined with the high-temperature electrolysis system, can realize near-zero carbon emission in the whole life cycle, at the same time, the toluene byproduct can be recycled for hydrogen storage carrier regeneration, forming a "hydrogen storage-dehydrogenation-power generation" closed loop. The present application realizes efficient energy conversion by relying on electrochemical reaction through the integrated design of "hydrogen storage-dehydrogenation-power generation", breaks through the high energy consumption limitation of traditional process, realizes the selectivity of products by controlling the reaction temperature, at the same time, produces high-value chemicals and zero-carbon electricity, provides a new path of efficient, energy-saving and environmentally friendly for hydrogen energy storage and transportation system.

[0029] (2) The present application uses proton exchange membrane electrolysis cell to carry out toluene hydrogenation, and uses "low temperature electrochemical activation + precise control" to replace traditional high pressure thermal catalysis, which has the following advantages: ① Mild reaction conditions: the proton exchange membrane electrolysis cell works at low temperature of 60-80 DEG C, which is much lower than the high temperature of 140-200 DEG C required by traditional thermal catalytic hydrogenation, which significantly reduces energy consumption and operation risk. ② Integrated design: the proton exchange membrane electrolysis cell can directly use the active hydrogen generated by electrolysis of water for toluene hydrogenation, skipping the hydrogen molecule generation step, realizing "hydrogen production-hydrogen storage" one step completion, and simplifying the system. ③ Precise control: the hydrogenation rate can be controlled in real time by adjusting the current density, avoiding side reactions, and being easier to control than the thermal catalytic process. ④ High safety: normal pressure operation avoids the high pressure hydrogen risk in the traditional process. ⑤ Environmental benefits: driven by green electricity generated by the dehydrogenation system, the whole process is close to zero carbon emission. ⑥ High product purity: the output of the cathode chamber does not contain unreacted hydrogen, and high purity methylcyclohexane can be obtained by simple distillation.

[0030] (3) The present application uses solid oxide electrolysis cell, which can simultaneously treat water and carbon dioxide generated by the dehydrogenation system, and the product is flexible and adjustable, and the required reactants can be obtained by the system, and high value products are generated, realizing near zero carbon emission of the system and greatly improving the energy utilization efficiency of the system. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of the methylcyclohexane dehydrogenation system using fuel cell of the present application. DETAILED DESCRIPTION

[0032] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0033] The materials, reagents and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0034] The present application relates to the field of hydrogen energy storage and electrochemical conversion technology, in particular to a methylcyclohexane dehydrogenation system and method using fuel cell.

[0035] Methylcyclohexane-toluene organic liquid hydrogen storage system (LOHC) is a promising hydrogen storage and transportation scheme. However, the traditional thermal catalytic dehydrogenation process has problems such as high reaction temperature, high energy consumption, easy carbon deposition and deactivation of catalyst, poor product selectivity, etc.; and the traditional hydrogenation process needs to be carried out at high temperature and high pressure, which has safety risk and high energy consumption problem. These bottlenecks restrict the large-scale commercial application of the technology.

[0036] The present application aims to overcome the defects of the prior art, and provides a green, efficient and precisely controllable methylcyclohexane dehydrogenation system and method. The core is to abandon the traditional thermal catalytic path and build an integrated system driven by electrochemical reaction to realize the synergy and cycle of "hydrogen storage-dehydrogenation-power generation-chemical synthesis".

[0037] The technical solution of the present application mainly includes: using a solid oxide fuel cell as a reactor to electrochemically dehydrogenate methylcyclohexane at medium temperature (420-490°C) and normal pressure to generate high-value chemicals such as toluene, benzene or dioxane, and simultaneously directly generate electric energy, realizing efficient conversion of chemical energy to electric energy, internal utilization of reaction heat, and greatly reducing energy consumption. A proton exchange membrane electrolytic cell is used as a reactor to electrochemically hydrogenate the dehydrogenation product toluene at low temperature (60-80°C) and normal pressure to regenerate methylcyclohexane, realizing mild, safe and precise control of the hydrogenation process. Further, using a solid oxide electrolytic cell, using green electricity generated by the fuel cell, water generated by the dehydrogenation process, or co-electrolyzing water and carbon dioxide generated by the system, hydrogen or synthesis gas is generated, thereby realizing the cycle of hydrogen resources and internal utilization of carbon elements. The above system, through ingenious material and energy integration, constitutes a complete, nearly zero-carbon emission hydrogen cycle and comprehensive utilization system.

[0038] The present application has the following advantages: High energy efficiency: coupling the endothermic dehydrogenation reaction with the exothermic power generation reaction, realizing energy cascade utilization, and the system energy consumption is significantly lower than that of the traditional process.

[0039] Mild reaction conditions: the dehydrogenation and hydrogenation processes are carried out at normal pressure, and the operation safety is high; the hydrogenation temperature is much lower than that of the traditional thermal catalytic method.

[0040] Strong controllability of products: by accurately controlling the operating temperature of the fuel cell, the selectivity of the dehydrogenation products (toluene, benzene, dioxane) can be controlled.

[0041] Green and environmentally friendly: the carbon elements in the system can be recycled, and the whole life cycle is nearly zero carbon emission with green electricity driving.

[0042] Integrated co-production: the system simultaneously produces zero-carbon electricity and high-value chemicals, realizing the co-production of energy and chemical products, and achieving significant economic benefits.

[0043] The present application provides a new technical path for large-scale, safe and economic hydrogen storage and efficient conversion.

[0044] For example, Figure 1As shown, the system for methylcyclohexane dehydrogenation provided by the present application using fuel cells mainly comprises: an electrochemical hydrogenation unit (a proton exchange membrane electrolysis cell, PEMEC), an electrochemical dehydrogenation power generation unit (a solid oxide fuel cell, SOFC), an electrochemical synthesis gas preparation unit (a solid oxide electrolysis cell, SOEC), a chemical separation and synthesis unit, and a heat management unit.

[0045] The working principle and material circulation path of the system of the present application are as follows: Dehydrogenation and power generation process: methylcyclohexane (MCH) in the storage tank is vaporized and preheated to the reaction temperature, and then is transported to the anode of the SOFC. Air is preheated and introduced into the cathode of the SOFC. In the SOFC, MCH undergoes an electrochemical oxidation dehydrogenation reaction in the anode to generate chemicals such as toluene (TOL) and release electrons; oxygen is reduced by obtaining electrons in the cathode. The electrons flow from the anode to the cathode through an external circuit, thereby generating direct current power. This process simultaneously produces water (H2O) and carbon dioxide (CO2).

[0046] Product separation and chemical synthesis: the anode tail gas (containing TOL, unreacted MCH, H2O, CO2, and a small amount of by-products) discharged from the SOFC enters the chemical separation and synthesis unit. First, high-purity target chemicals such as TOL, benzene, or dioxane are separated by condensation, rectification, crystallization, and other operations. The separated H2O and CO2 are collected.

[0047] Electrolysis and synthesis gas preparation: the electric energy generated by the SOFC is used by the SOEC. The separated H2O (or a mixture of H2O and CO2) is preheated and introduced into the cathode of the SOEC, and air is introduced into the anode of the SOEC. In the SOEC, hydrogen (H2) is generated by water electrolysis or syngas (Syngas) is generated by co-electrolysis of H2O / CO2 using electric energy.

[0048] Hydrogenation process: part of the TOL separated in step 2 and H2 generated by the SOEC in step 3 are transported to the PEMEC. In the PEMEC, TOL is hydrogenated by electrochemical reaction in the cathode to regenerate MCH. The generated MCH can be returned to the storage tank, completing the circulation of the "MCH-TOL" hydrogen carrier.

[0049] Heat management and carbon cycle: the heat required by the system is provided by the heat management unit (such as a burner). The fuel of the burner can be derived from H2, syngas generated by the SOEC, or methanol / methane synthesized from syngas. The CO2 in the flue gas generated by combustion can be captured and transported to the cathode of the SOEC to participate in the co-electrolysis reaction, thereby realizing the recycling of carbon elements in the system and significantly reducing carbon emissions.

[0050] Preferred embodiment: The SOFC preferably operates at a temperature of 420°C to 490°C and at atmospheric pressure. Within this temperature range, the selectivity of the dehydrogenation products can be controlled by precisely controlling the reaction temperature. For example, when the reaction temperature is controlled at about 420°C, the product is mainly toluene with a small amount of benzene; when the reaction temperature is controlled at about 490°C, a considerable proportion of dioxane is generated in the product.

[0051] The PEMEC preferably operates at a temperature of 60°C to 80°C and at atmospheric pressure. This low temperature and atmospheric pressure greatly improves the safety of operation and the hydrogenation rate can be controlled in real time and accurately by adjusting the current density.

[0052] The SOEC preferably operates at a temperature of 700°C to 750°C and at atmospheric pressure. This high temperature is beneficial to reduce the overpotential of the electrolysis reaction and improve the energy conversion efficiency.

[0053] The application will be described in detail below through a non-limiting example.

[0054] After the air is preheated to 490°C by the burner exhaust, it is introduced into the cathode of the SOFC. At the same time, the liquid methylcyclohexane (MCH) is vaporized and preheated to 490°C, and then introduced into the anode of the SOFC in the form of steam.

[0055] An electrochemical reaction occurs inside the SOFC, and MCH is converted by dehydrogenation. The reaction temperature is controlled at 490°C, and at this temperature, the anode outlet gas is analyzed to be a mixture of toluene, benzene and dioxane in a ratio of about 12.8:0.6:86.6. This reaction simultaneously generates electrical energy and thermal energy. The anode exhaust gas (containing chemicals, water vapor, carbon dioxide) after the reaction enters the subsequent processing unit.

[0056] The anode exhaust gas first passes through a condensation and rectification system (dehydrogenation post-processing unit). Through a low-temperature crystallization separation device, high-purity toluene, benzene and dioxane products are extracted respectively.

[0057] The separated water (H2O) and carbon dioxide (CO2) are mixed and heated to 730°C, and then introduced into the cathode of the SOEC. The air is heated to 730°C and introduced into the anode of the SOEC. The electricity required for the operation of the SOEC is provided by the aforementioned SOFC. In the cathode of the SOEC, H2O and CO2 undergo a co-electrolysis reaction to generate synthesis gas (H2 and CO). The generated synthesis gas enters the synthesis gas processing unit and is synthesized into methanol in a catalytic reactor.

[0058] A portion of the separated high purity toluene is heated to 70°C and fed to the cathode of a proton exchange membrane electrolysis cell (PEMEC). At the same time, deionized water is heated to 70°C and fed to the anode of the PEMEC. In the PEMEC, an electric current is passed, and the toluene is electrochemically reduced at the cathode to reform methylcyclohexane (MCH). The MCH produced can be returned to the storage tank for use in the next dehydrogenation cycle, thus creating a complete, electrochemically based "methylcyclohexane-toluene" hydrogen cycle storage and transport system.

[0059] The above description is merely that of a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions easily conceived by those skilled in the art within the technical scope disclosed by the present application shall be encompassed within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A methylcyclohexane-toluene hydrogen cycle system, comprising: An electrochemical dehydrogenation power generation unit uses a solid oxide fuel cell as a reactor to electrochemically dehydrogenate methylcyclohexane to produce dehydrogenation products containing toluene, while simultaneously generating electricity. The electrochemical hydrogenation unit uses a proton exchange membrane electrolyzer as a reactor to electrochemically hydrogenate toluene and hydrogen to produce methylcyclohexane. In addition, in the material recycling loop, toluene generated by the electrochemical dehydrogenation power generation unit is at least partially transported to the electrochemical hydrogenation unit as a reactant, and methylcyclohexane generated by the electrochemical hydrogenation unit is at least partially transported to the electrochemical dehydrogenation power generation unit as a reactant.

2. The system according to claim 1, characterized in that: The system also includes an electrochemical syngas preparation unit, which uses a solid oxide electrolysis cell as a reactor and is configured to use the electrical energy generated by the electrochemical dehydrogenation power generation unit to perform an electrolysis reaction to produce hydrogen; the hydrogen produced by the electrochemical syngas preparation unit is transported to the electrochemical hydrogenation unit.

3. The system according to claim 2, characterized in that: The electrochemical synthesis gas preparation unit is configured to electrolyze water to produce hydrogen, or to co-electrolyze water and carbon dioxide to produce synthesis gas containing hydrogen and carbon monoxide.

4. The system according to claim 3, characterized in that: The system also includes: A heat supply unit configured to provide heat to the system by burning fuel, said fuel being at least partially derived from hydrogen produced by the electrochemical syngas preparation unit or fuel prepared from said syngas; and, In the carbon cycle loop, the carbon dioxide generated by the heat supply unit is transported to the electrochemical synthesis gas preparation unit for co-electrolysis reaction.

5. A method for hydrogen cycling using the system of any one of claims 1-4, comprising the following steps: S1, Electrochemical Dehydrogenation Power Generation In a solid oxide fuel cell, methylcyclohexane undergoes an electrochemical dehydrogenation reaction to generate dehydrogenation products containing toluene and produce electrical energy. S2, Electrochemical hydrogenation step In a proton exchange membrane electrolyzer, toluene and hydrogen undergo an electrochemical hydrogenation reaction to produce methylcyclohexane; S3, Material Circulation Steps At least a portion of the toluene produced in the electrochemical dehydrogenation power generation step is used in the electrochemical hydrogenation step, and at least a portion of the methylcyclohexane produced in the electrochemical hydrogenation step is used in the electrochemical dehydrogenation power generation step.

6. The method according to claim 5, characterized in that: The method further includes an electrochemical synthesis gas preparation step: using the electrical energy generated in the electrochemical dehydrogenation power generation step to drive a solid oxide electrolytic cell to perform an electrolysis reaction to generate hydrogen, and using the generated hydrogen in the electrochemical hydrogenation step; Furthermore, the method also includes a carbon recycling step: collecting the carbon dioxide generated in the system and passing it into the solid oxide electrolytic cell for co-electrolysis to produce syngas.

7. The method according to claim 5 or 6, characterized in that: In step S1, the operating temperature of the electrochemical dehydrogenation power generation unit is 418℃-492℃, and the operating pressure is atmospheric pressure; and by adjusting the operating temperature, the proportions of toluene, benzene, and dioxane in the dehydrogenation products can be selectively controlled.

8. The method according to claim 7, characterized in that: When the operating temperature is 418-422℃, the dehydrogenation products are mainly toluene and benzene; when the operating temperature is 488-492℃, the dehydrogenation products include toluene, benzene and dioxane.

9. The method according to any one of claims 5-7, characterized in that: In step S2, the operating temperature of the electrochemical hydrogenation unit is 60℃-80℃, and the operating pressure is atmospheric pressure.

10. The method according to any one of claims 6-8, characterized in that: In step S2, the operating temperature of the electrochemical synthesis gas preparation unit is 700℃-750℃, and the operating pressure is atmospheric pressure.

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