A chemically chained carbon dioxide methanation method, a circulating medium, and its preparation method

Abstract

This invention discloses a chemically chained carbon dioxide methanation method, encompassing CO2 methanation and circulating medium regeneration steps. CO2 and some hydrogen gas are contacted with a circulating medium in a reduced state. The methanation active centers on the circulating medium catalyze the CO2 methanation to produce methane and water. The water rapidly reacts with the reduced circulating medium to generate hydrogen gas, and oxygen is stored in an oxygen carrier. This invention also discloses a circulating medium for chemically chained carbon dioxide methanation. After participating in methanation, excess hydrogen gas is introduced to fully convert it to a reduced state. Ru-doped Ni is selected as the main active component, and cerium oxide and iron oxide are used as oxygen carriers. The oxygen carrier and catalytic active component are composited using co-precipitation and impregnation methods. This invention also discloses a method for preparing the circulating medium for chemically chained carbon dioxide methanation.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide methanation technology, and more particularly to a chemical chain carbon dioxide methanation method, a recycling medium, and a method for preparing the same. Background Technology

[0002] With the over-exploitation of fossil fuels and the increasing deterioration of the natural environment, energy is shifting towards the utilization of distributed renewable energy. To address global climate change and the energy crisis, achieving a low-carbon transformation has become the main theme of the world's power industry development. In the current low-carbon context, the integration of methane as a natural gas energy source has emerged as an option for achieving low-carbon dispatch in new power systems.

[0003] Carbon dioxide (CO2) is a stable substance with a standard enthalpy of formation (ΔfGm) of 394.38 kJ / mol. As a weak oxidizing agent, CO2 can be reduced with sufficient energy input. The methanation of carbon dioxide is an important pathway for the resource utilization of carbon dioxide, producing methane while reducing carbon dioxide emissions, which can then be directly used in existing natural gas energy networks.

[0004] For example, Chinese patent document CN114917916A discloses a high oxygen storage capacity and high stability oxygen carrier and its preparation method, which discloses Ni / CeO2 and La 0.8 Sr 0.2 FeO3 composite oxygen carriers are used for methane reforming to produce hydrogen; for example, Chinese patent document CN111087026B discloses a chemically chained methane partial oxidation oxygen carrier, its preparation method, and its application, which discloses LaMn 1-x- y Fe x Co y O3 oxygen carriers are used in the partial oxidation of methane. While these technical solutions disclose designs for different oxygen carriers, they only consider the oxygen-carrying capacity of the carrier and not the catalytic activity of the methanation reaction. The technical solutions provided in the aforementioned literature are not suitable for large-scale industrial production. Due to the high pressure and rapid reaction characteristics of CO2 methanation, high requirements are placed on the stability of the catalyst and its high-temperature thermal effect. Summary of the Invention

[0005] The technical problem to be solved by this invention is to resolve the contradiction between reaction stability and reaction conversion rate in the large-scale industrial production of carbon dioxide chemical chain methanation. The purpose of this invention is to provide a technical solution that can be applied to industrial production scenarios, and improves methane conversion rate while ensuring reaction rate under the condition of promoting high temperature thermal effect through circulating medium.

[0006] The technical solution adopted in this invention is: a chemical chain carbon dioxide methanation method, the steps of which include: S1: catalytic CO2 methanation step in a reduced state circulating medium; S2: regeneration step in a reduced state circulating medium.

[0007] With the participation of the circulating medium, the combination of methanation and regeneration of the circulating medium in a reduced state can be applied to high-conversion scenarios in industrial production, thereby improving the utilization rate of carbon dioxide resources.

[0008] In this scheme, the specific steps described in step S1 are as follows: CO2 and some hydrogen are contacted with a circulating medium in a reduced state, the active component of the circulating medium catalyzes the methanation of CO2 to obtain methane and water, the water rapidly reacts with the reduced circulating medium to generate hydrogen, and oxygen is stored in an oxygen carrier.

[0009] In this scheme, step S1 is further described as follows: an excess of hydrogen gas is introduced into the circulating medium after methanation with CO2 to fully convert the partially oxidized circulating medium into a reduced circulating medium.

[0010] Furthermore, the methanation temperature is 400–600°C, and the regeneration temperature is 600–900°C.

[0011] The present invention also employs the following technical solution: a circulating medium for the chemical chain carbon dioxide methanation, wherein the oxidation and reduction states of the circulating medium are reversible, and the general chemical formula is Ru. z -Ni y / Ce 1-x Fe x O 2-δ This indicates that 0.2≤x≤0.5, 0.1≤y≤0.4, and 0.001≤z≤0.01.

[0012] By making the circulating medium reversible, high conversion rates can be achieved in industrial production scenarios, while reducing production costs.

[0013] In this scheme, Ru and Ni are used as catalytically active components, and cerium oxide (CeO2) and iron oxide (Fe2O3) are used as oxygen carriers. The oxygen carriers and catalytically active components are synthesized by precipitation and impregnation methods.

[0014] Furthermore, Ru and Ni were directly loaded onto the precipitated cerium hydroxide and iron hydroxide composite, and an oxidized circulating medium was obtained by high-temperature calcination. The calcination atmosphere was air, the calcination temperature was 500–700℃, and the calcination time was 1–4 h.

[0015] The present invention also employs the following technical solution: a method for preparing a circulating medium for chemically chained carbon dioxide methanation, comprising the following steps: T1: precipitating cerium and iron ions in an aqueous solution with ammonia to obtain a composite hydroxide; T2: impregnating Ru and Ni onto the hydroxide and drying it; T3: calcining the particles at 500°C and grinding them to obtain an oxidized circulating medium.

[0016] By using a reversible preparation method for the circulating medium, the circulating medium can be recycled, thereby reducing production costs in industrial production scenarios and achieving high carbon dioxide conversion rates.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] The chemical chain carbon dioxide methanation method proposed in this invention can rapidly remove water, a product of the methanation process, and obtain hydrogen gas. This significantly promotes the shift of the CO2 methanation equilibrium under high-temperature methanation conditions, breaking the equilibrium limitation of the high-temperature methanation reaction, and simultaneously improving the methanation reaction rate and conversion rate. This methanation method can simultaneously achieve the removal of water, a product of the methanation process, and the high-temperature methanation reaction, with rapid conversion.

[0019] The circulating medium proposed in this invention has both circulating redox capability and methanation activity. It utilizes the highly methanogenic metals Ru and Ni to achieve efficient conversion of carbon dioxide and hydrogen, and utilizes the more metallic Fe to achieve hydrogen production by reacting with H2O under CO2, H2 and H2O atmospheres. The oxygen transfer and Fe redox are improved by using CeO2 and Fe2O3 composite oxygen carriers.

[0020] The circulating medium produced by the preparation method proposed in this invention can achieve chemical chain CO2 methanation under strong reducing (H2) and weak reducing (CO2+CH4+H2+H2O) atmospheres through cyclic oxidation-reduction, which is suitable for large-scale industrial production. Attached Figure Description

[0021] Figure 1 This is a flowchart of the chemical chain methanation reaction of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below through embodiments.

[0023] According to the methanation reaction equation:

[0024]

[0025] This reaction is a reversible, strongly exothermic process. As the temperature increases, the equilibrium CO2 conversion rate decreases significantly, and the product H2O greatly limits the methanation process. Furthermore, every 1% conversion of CO2 generates an adiabatic temperature rise of approximately 60°C. High CO2 conversion rates can be achieved through the design of highly efficient catalysts to realize low-temperature methanation. However, due to the strongly exothermic nature of methanation, complex reactors are required to effectively remove heat and maintain a low reaction temperature, preventing a decrease in the equilibrium conversion rate due to temperature increases. Simultaneously, low-temperature reactions tend to result in a lower reaction rate. Therefore, resolving the contradiction between reaction equilibrium and reaction temperature in the methanation process is crucial.

[0026] A chemical loop reaction is a series of reactions that utilize a reversible circulating medium to decompose the main reaction into a series of reactions occurring at different times or locations, enabling in-situ separation of products. Chemical loop reactions are used in processes such as combustion and reforming for hydrogen production, achieving industrialization. In methanation, a reversible circulating medium reacts with the water produced during methanation, generating some hydrogen while fixing oxygen in the circulating medium as hydroxyl groups. This causes water to leave the reaction system, significantly shifting the equilibrium towards methane formation. The chemical loop methanation process allows for rapid reactions at high temperatures and high equilibrium conversion rates.

[0027] In this invention, methane steam reforming and CO2 methanation are two reciprocal reactions. The catalytic performance considered in the design of the oxygen carrier is similar, with CeO2 being the main active component. The actual conversion process of chemical chain methanation differs significantly from that of methane steam reforming. Chemical chain methanation requires a circulating medium with good CO2 adsorption and hydrogen dissociation capabilities; simultaneously, the circulating medium needs to achieve redox reactions under reducing atmospheres of varying degrees of reduction, rather than simply circulating between reducing and oxidizing atmospheres.

[0028] Ni is an active component, but its activity is generally lower than that of noble metals such as Ru and Pt. This invention uses Ru to modify Ni, thereby improving the catalyst activity and making it economical. CeO2, Al2O3, TiO2, SiO2, ZrO2, etc. are available catalyst supports. CeO2 has good stability and is abundant. This invention uses CeO2 combined with different active components to obtain methanation catalysts with significantly different activities and stability.

[0029] The circulating medium used in this invention selects Ru-doped Ni as the main active component, and uses cerium oxide (CeO2) and iron oxide (Fe2O3) as oxygen carriers. The oxygen carriers and catalytic active components are combined by co-precipitation and impregnation methods.

[0030] Example 1.

[0031] A method for preparing a circulating medium for chemically chained carbon dioxide methanation mainly includes the following steps:

[0032] Step 1: Preparation of raw material solution. Cerium nitrate or cerium chloride is dissolved in water with ferric nitrate / ferric chloride in different molar ratios to form a solution with a total cation concentration of 1 mol / L.

[0033] Step 2: Ion precipitation. Concentrated ammonia solution is added dropwise to the raw material solution, maintaining the pH at 10. When the pH rises to 11, the addition is stopped. The precipitate is allowed to age for 12 hours, then filtered and washed to obtain the hydroxide precipitate.

[0034] Step 3: Loading the active component. Ruthenium chloride and nickel nitrate were dissolved in water according to the doping ratio to obtain a 5 mol / L aqueous solution. The hydroxide precipitate was then dispersed in the aqueous solution, fully dispersed, allowed to stand, and then dried.

[0035] Step 4: High-temperature calcination. The dried solid is calcined in air at a rate of 3℃ / min to 500℃ for 4 hours, then naturally cooled to room temperature and thoroughly ground to obtain the oxidized circulating medium.

[0036] Example 2.

[0037] A chemically looped carbon dioxide methanation method involves contacting CO2 and a portion of hydrogen with a recycle medium in a reduced state. The active component of the recycle medium catalyzes the methanation of CO2 to produce methane and water. The water rapidly reacts with the reduced recycle medium to generate hydrogen, while oxygen is stored in an oxygen carrier. Excess hydrogen is then introduced into the recycle medium after CO2 methanation to fully convert the partially oxidized recycle medium into a reduced recycle medium.

[0038] According to the preparation method described in Example 1, the circulating medium Ru was obtained. 0.005 -Ni 0.15 / Ce 0.5 Fe 0.5 O 2-δ .

[0039] The catalyst performance in this embodiment was tested using a fixed-bed tubular reactor. The H2, CH4, CO2, and Ar carrier gas used in the test were all supplied by cylinder gas with a purity greater than 99.99%. The specific evaluation methods and index calculation methods are as follows:

[0040] 50g of circulating medium was loaded into a stainless steel reaction tube with an inner diameter of 30mm and a wall thickness of 1.5mm. A certain amount of high-temperature resistant quartz wool was placed at both ends of the catalyst bed to disperse the fluid and stabilize the catalyst position. A thermocouple was inserted into the catalyst bed to accurately control the catalyst testing temperature. Finally, the airtightness of the device was tested with soapy water. After the airtightness was deemed satisfactory, the catalyst was reduced for 2 hours at 600℃ under a pure H2 flow (200mL / min), and then cooled to 400℃. The gas was then quickly switched to a mixture of CO2, H2, and CH4 in a volume ratio of 1:2:1, with a total flow rate of 100mL / min. The products were determined using an online gas chromatograph equipped with a thermal conductivity detector (TCD).

[0041] The main performance evaluation indicators for catalysts include: CO2 conversion rate. CH4 selectivity CO selectivity (S) CO The following formulas are used to calculate the values ​​of each:

[0042]

[0043]

[0044]

[0045] In the formula, F in and F out , , represent the total flow rates of the raw material and product gases, respectively, and x and y represent the volume fractions of the corresponding components in the raw material and product gases, determined by gas chromatography using a standard curve.

[0046] A CO2 conversion rate of 94% (equilibrium conversion rate of 81%) and a CH4 selectivity of 99% were achieved at 400℃.

[0047] Example 3.

[0048] According to the method for preparing the circulating medium of the present invention, the circulating medium Ru is obtained. 0.01 -Ni 0.1 / Ce 0.8 Fe 0.2 O 2-δ .

[0049] The methanation method described in Example 2 was used to test the chemical chain methanation activity. A CO2 conversion of 92% was obtained at 400°C, with an equilibrium conversion of 81% and a CH4 selectivity of 99%.

[0050] Example 4.

[0051] According to the method for preparing the circulating medium of the present invention, the circulating medium Ru is obtained. 0.001 -Ni 0.1 / Ce0.5 Fe 0.5 O 2-δ .

[0052] The methanation method described in Example 2 was used to test the chemical chain methanation activity. A CO2 conversion of 89% was obtained at 400°C, with an equilibrium conversion of 81% and a CH4 selectivity of 99%.

[0053] Example 5.

[0054] According to the method for preparing the circulating medium described in this invention, the circulating medium Ru is obtained. 0.005 -Ni 0.15 / Ce 0.8 Fe 0.2 O 2-δ .

[0055] The methanation method described in Example 2 was used to test the chemical chain methanation activity. A CO2 conversion of 93% (equilibrium conversion 65%) and a CH4 selectivity of 98% were obtained at 600°C.

[0056] As can be seen from the above embodiments, the circulating medium prepared by the present invention, using the methanation method of the present invention, can simultaneously achieve the removal of water from the methanation product and the high-temperature methanation reaction, resulting in a high conversion rate under high-temperature conditions.

Claims

1. A method for the preparation of a circulating medium for chemical looping carbon dioxide methanation, c h a r a c t e r i s e d b y, Comprising the following steps: Step 1: Preparation of raw solution, cerium nitrate or cerium chloride and ferric nitrate or ferric chloride are dissolved in water to form a solution with a total cation concentration of 1 mol / L; Step 2: Ion precipitation, concentrated ammonia is added dropwise to the raw solution to maintain a pH of 10, and when the pH rises to 11, the dropwise addition is stopped; the precipitate is aged for 12 h, filtered and washed to obtain a hydroxide precipitate; Step 3: Loading active components, dissolve ruthenium chloride and nickel nitrate according to the doping ratio to obtain a 5 mol / L aqueous solution, then disperse the hydroxide precipitate in the aqueous solution, disperse thoroughly, and dry after standing; Step 4: High-temperature calcination, dry the solid in an air atmosphere at a rate of 3 ℃ / min to 500 ℃ for 4 h, then naturally cool to room temperature, and grind thoroughly to obtain an oxidized state of the circulating medium; The circulating medium is Ru 0.005 -Ni 0.15 / Ce 0.5 Fe 0.5 O 2-δ .

2. A method for the preparation of a circulating medium for chemical looping carbon dioxide methanation, c h a r a c t e r i s e d b y, Comprising the following steps: Step 1: Preparation of raw solution, cerium nitrate or cerium chloride and ferric nitrate or ferric chloride are dissolved in water to form a solution with a total cation concentration of 1 mol / L; Step 2: Ion precipitation, concentrated ammonia is added dropwise to the raw solution to maintain a pH of 10, and when the pH rises to 11, the dropwise addition is stopped; the precipitate is aged for 12 h, filtered and washed to obtain a hydroxide precipitate; Step 3: Loading active components, dissolve ruthenium chloride and nickel nitrate according to the doping ratio to obtain a 5 mol / L aqueous solution, then disperse the hydroxide precipitate in the aqueous solution, disperse thoroughly, and dry after standing; Step 4: High-temperature calcination, dry the solid in an air atmosphere at a rate of 3 ℃ / min to 500 ℃ for 4 h, then naturally cool to room temperature, and grind thoroughly to obtain an oxidized state of the circulating medium; The circulating medium is Ru 0.01 -Ni 0.1 / Ce 0.8 Fe 0.2 O 2-δ .

3. A method for the preparation of a circulating medium for chemical looping carbon dioxide methanation, c h a r a c t e r i s e d b y, Comprising the following steps: Step 1: Preparation of raw solution, cerium nitrate or cerium chloride and ferric nitrate or ferric chloride are dissolved in water to form a solution with a total cation concentration of 1 mol / L; Step 2: Ion precipitation, concentrated ammonia is added dropwise to the raw solution to maintain a pH of 10, and when the pH rises to 11, the dropwise addition is stopped; the precipitate is aged for 12 h, filtered and washed to obtain a hydroxide precipitate; Step 3: Loading active components, dissolve ruthenium chloride and nickel nitrate according to the doping ratio to obtain a 5 mol / L aqueous solution, then disperse the hydroxide precipitate in the aqueous solution, disperse thoroughly, and dry after standing; Step 4: High-temperature calcination, dry the solid in an air atmosphere at a rate of 3 ℃ / min to 500 ℃ for 4 h, then naturally cool to room temperature, and grind thoroughly to obtain an oxidized state of the circulating medium; The circulating medium is Ru 0.001 -Ni 0.1 / Ce 0.5 Fe 0.5 O 2-δ .

4. A method for the preparation of a circulating medium for chemical looping carbon dioxide methanation, c h a r a c t e r i s e d b y, Comprising the following steps: Step 1: Preparation of raw solution, cerium nitrate or cerium chloride and ferric nitrate or ferric chloride are dissolved in water to form a solution with a total cation concentration of 1 mol / L; Step 2: Ion precipitation, concentrated ammonia is added dropwise to the raw solution to maintain a pH of 10, and when the pH rises to 11, the dropwise addition is stopped; the precipitate is aged for 12 h, filtered and washed to obtain a hydroxide precipitate; Step 3: Loading active components, dissolve ruthenium chloride and nickel nitrate according to the doping ratio to obtain a 5 mol / L aqueous solution, then disperse the hydroxide precipitate in the aqueous solution, disperse thoroughly, and dry after standing; Step 4: High-temperature calcination, dry the solid in an air atmosphere at a rate of 3 ℃ / min to 500 ℃ for 4 h, then naturally cool to room temperature, and grind thoroughly to obtain an oxidized state of the circulating medium; Step 4: High temperature calcination, the dry solid was calcined in air atmosphere at 3 ℃ / min to 500 ℃ for 4 h, then naturally cooled to room temperature, fully ground, to obtain the oxidized state of the circulation medium; The circulating medium is Ru 0.005 -Ni 0.15 / Ce 0.8 Fe 0.2 O 2-δ .

5. A method of chemical looping carbon dioxide methanation, c h a r a c t e r i s e d in that, It was carried out by a fixed bed tubular reactor, H2, CH4, CO2 and Ar used as carrier gas for chromatography were provided by cylinder gas with purity greater than 99.99%, 50 g of the circulation medium was loaded into a reaction tube with an inner diameter of 30 mm and a wall thickness of 1.5 mm, made of stainless steel, a certain amount of high-temperature quartz wool was plugged into the upper and lower ends of the circulation medium layer to disperse the fluid and stabilize the position of the circulation medium, and a thermocouple was inserted into the position of the circulation medium bed layer to control the test temperature of the circulation medium, finally the air tightness was detected by soap water detection device; after the air tightness was qualified, the circulation medium was reduced at 600 ℃ under the flow of pure H2 200 mL / min for 2 h, then cooled to 400 ℃; the gas was quickly switched to a mixed gas of CO2, H2 and CH4 with a volume ratio of 1:2:1, and the total flow rate was 100 mL / min; the product was determined by an online gas chromatograph with a thermal conductivity detector TCD; The circulating medium is Ru 0.005 -Ni 0.15 / Ce 0.5 Fe 0.5 O 2-δ .

6. A method of chemical looping carbon dioxide methanation, c h a r a c t e r i s e d in that, It was carried out by a fixed bed tubular reactor, H2, CH4, CO2 and Ar used as carrier gas for chromatography were provided by cylinder gas with purity greater than 99.99%, 50 g of the circulation medium was loaded into a reaction tube with an inner diameter of 30 mm and a wall thickness of 1.5 mm, made of stainless steel, a certain amount of high-temperature quartz wool was plugged into the upper and lower ends of the circulation medium layer to disperse the fluid and stabilize the position of the circulation medium, and a thermocouple was inserted into the position of the circulation medium bed layer to control the test temperature of the circulation medium, finally the air tightness was detected by soap water detection device; after the air tightness was qualified, the circulation medium was reduced at 600 ℃ under the flow of pure H2 200 mL / min for 2 h, then cooled to 400 ℃; the gas was quickly switched to a mixed gas of CO2, H2 and CH4 with a volume ratio of 1:2:1, and the total flow rate was 100 mL / min; the product was determined by an online gas chromatograph with a thermal conductivity detector TCD; The circulating medium is Ru 0.01 -Ni 0.1 / Ce 0.8 Fe 0.2 O 2-δ .

7. A method of chemical looping carbon dioxide methanation, c h a r a c t e r i s e d in that, It was carried out by a fixed bed tubular reactor, H2, CH4, CO2 and Ar used as carrier gas for chromatography were provided by cylinder gas with purity greater than 99.99%, 50 g of the circulation medium was loaded into a reaction tube with an inner diameter of 30 mm and a wall thickness of 1.5 mm, made of stainless steel, a certain amount of high-temperature quartz wool was plugged into the upper and lower ends of the circulation medium layer to disperse the fluid and stabilize the position of the circulation medium, and a thermocouple was inserted into the position of the circulation medium bed layer to control the test temperature of the circulation medium, finally the air tightness was detected by soap water detection device; after the air tightness was qualified, the circulation medium was reduced at 600 ℃ under the flow of pure H2 200 mL / min for 2 h, then cooled to 400 ℃; the gas was quickly switched to a mixed gas of CO2, H2 and CH4 with a volume ratio of 1:2:1, and the total flow rate was 100 mL / min; the product was determined by an online gas chromatograph with a thermal conductivity detector TCD; The circulating medium is Ru 0.001 -Ni 0.1 / Ce 0.5 Fe 0.5 O 2-δ .

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