Carbon nanotube-based carbon capture and methanation bifunctional material, and preparation method and application thereof

Abstract

The application relates to the field of carbon capture technology and discloses a carbon capture and methanation bifunctional material based on carbon nanotubes as well as a preparation method and application thereof. The method comprises the following steps: (A1) performing primary reduction on multi-walled carbon nanotubes and a nickel salt in the presence of a reducing agent, then mixing the obtained reaction product, hydrazine hydrate and an alkali, and then performing hydrothermal reaction on the obtained mixture to obtain a Ni / CNT composite material; (A2) performing compounding on the Ni / CNT composite material and a calcium-containing compound, and then performing secondary reduction on the compounded product in a hydrogen atmosphere; wherein the compounding mode is physical mixing and / or co-impregnation. The carbon capture and methanation bifunctional material based on carbon nanotubes prepared according to the method can realize carbon dioxide capture and efficient in-situ methanation conversion at a lower temperature at the same time.

Description

Technical Field

[0001] This invention relates to the field of carbon capture technology, specifically to a bifunctional material based on carbon nanotubes for carbon capture and methanation, its preparation method, and its applications. Background Technology

[0002] With the advancement of global carbon neutrality goals, capturing CO2 emitted from industrial processes and converting it into high-value chemicals (such as methane) has become an important research direction. Among these, the integrated CO2 capture and in-situ catalytic conversion technology has received widespread attention in recent years due to its ability to avoid CO2 compression, transportation, and storage, significantly reducing energy consumption and costs. Among numerous integrated processes, calcium cycling (CaL) coupled with methanation is a promising solution. This process utilizes calcium-based materials (CaO) as CO2 adsorbents, capturing CO2 through a carbonation reaction to generate CaCO3. Subsequently, under a hydrogen atmosphere, CaCO3 is reduced to methanation with the aid of a catalyst, simultaneously regenerating CaO and achieving adsorbent recycling. This integrated process avoids the energy-intensive calcination and regeneration steps of traditional calcium cycling, theoretically enabling lower-energy carbon capture and conversion. Currently, Ni / CaO bifunctional materials are a typical material system for realizing the above integrated process. The CaO component is responsible for CO2 capture through a carbonation reaction, while the Ni component is responsible for catalytic hydrogenation methanation. The two reactions described above proceed alternately or synergistically in the same reactor, achieving the coupling of CO2 capture and in-situ conversion. However, this system faces a key bottleneck in industrial applications: the hydromethanation of CaCO3 is kineticly slow, typically requiring high temperatures (>600℃) to achieve a considerable methane yield. Although thermodynamic calculations indicate that the reaction also exhibits good equilibrium conversion at around 400℃, the actual reaction rate is extremely low due to kinetic limitations, making it difficult to achieve efficient operation under mild conditions, which significantly increases process energy consumption.

[0003] The existing technology has the following disadvantages: (1) The reaction temperature is too high: In the existing Ni / CaO bifunctional material integrated CO2 capture and methanation process, the CaCO3 hydrogenation methanation reaction must be maintained above 600℃ to obtain the ideal reaction rate. If the reaction temperature is reduced to the range of 400-500℃, the methanation activity drops sharply and the CO2 conversion rate is usually less than 30%. This temperature limit makes it impossible for the existing technology to operate under milder conditions. (2) The energy consumption is large: Since the high temperature operation above 600℃ must be maintained, the energy consumption of the process increases significantly. This weakens the energy-saving advantage of the calcium cycle coupled methanation process compared with the traditional CO2 capture and independent conversion route. At the same time, the high temperature operation puts higher requirements on the reactor material and thermal management system, increasing the equipment investment cost. (3) The reaction efficiency at medium and low temperatures is low: In the existing Ni / CaO material system, the CaCO3 hydrogenation methanation reaction has a serious kinetic bottleneck in the medium temperature range of 400-500℃. Even though the reaction is thermodynamically feasible within this temperature range, the actual reaction rate is extremely low due to the stable structure of CaCO3 and the difficulty in effectively activating hydrogen species and permeating into the bulk phase to participate in the reaction, making efficient CH4 production impossible. This low reaction efficiency makes it difficult for existing technologies to achieve efficient operation of integrated processes under mild conditions. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem in existing technologies where high temperatures are required to achieve a considerable methane yield during CO2 capture in calcium cycling systems. This invention provides a bifunctional carbon capture and methanation material based on carbon nanotubes, its preparation method, and its applications. The bifunctional carbon capture and methanation material based on carbon nanotubes prepared according to the method described in this invention can achieve carbon dioxide capture while simultaneously realizing efficient in-situ methanation conversion at relatively low temperatures.

[0005] To achieve the above objectives, the present invention provides a method for preparing a carbon capture and methanation bifunctional material based on carbon nanotubes, the method comprising the following steps: (A1) Multi-walled carbon nanotubes and nickel salts were reduced once in the presence of a reducing agent, and then the resulting reaction product, hydrazine hydrate and alkali were mixed. The resulting mixture was then subjected to a hydrothermal reaction to obtain a Ni / CNT composite material. (A2) The Ni / CNT composite material and the calcium-containing compound are combined, and then the combined product is subjected to a secondary reduction in a hydrogen atmosphere; The composite method is physical mixing and / or co-impregnation.

[0006] Preferably, in step (A1), the mass ratio of the multi-walled carbon nanotubes to the nickel salt is 1:5-15.

[0007] Preferably, the nickel salt is at least one selected from NiSO4·6H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O.

[0008] Preferably, in step (A1), the conditions for the first reduction include: a temperature of 0-5°C and a time of 1-3 hours.

[0009] Preferably, the reducing agent is NaBH4 and / or KBH4.

[0010] Preferably, in step (A1), the mass-to-volume ratio of the multi-walled carbon nanotubes and the hydrazine hydrate is 0.5-3 g: 100 mL.

[0011] Preferably, in step (A1), the conditions for the hydrothermal reaction include: a temperature of 120-180°C and a time of 3-5 hours.

[0012] Preferably, the alkali is at least one of ammonia, urea, and hydrazine hydrate.

[0013] Preferably, in step (A2), the molar ratio of the Ni / CNT composite material (based on Ni component) to the calcium-containing compound (based on Ca component) is 5:90-100.

[0014] Preferably, the calcium-containing compound is at least one selected from calcium oxide, calcium carbonate, and calcium hydroxide.

[0015] Preferably, in step (A2), the conditions for the secondary reduction include: a temperature of 450-550℃ and a time of 0.5-2h.

[0016] Preferably, in step (A2), the specific operation process of the physical mixing includes: mixing the Ni / CNT composite material and the calcium-containing compound by a wet slurry method, and then drying the resulting mixture at 70-90°C.

[0017] Preferably, in step (A2), the specific operation process of co-impregnation includes: mixing the Ni / CNT composite material and the calcium-containing compound in an aqueous solution, stirring at a speed of 100-500 r / min for 1-3 h, and then evaporating the moisture of the resulting mixture at 75-90 °C.

[0018] A second aspect of this invention provides another method for preparing a bifunctional material for carbon capture and methanation, the method comprising the following steps: (B1) A nickel salt and a calcium-containing compound are mixed, and then the resulting mixture is calcined to obtain NiO / CaO powder material; (B2) Multi-walled carbon nanotubes are attached to the NiO / CaO powder material by impregnation, followed by evaporation and then reduction in a hydrogen atmosphere.

[0019] Preferably, in step (B1), the molar ratio of the nickel salt (based on Ni component) to the calcium-containing compound (based on Ca component) is 5:90-100.

[0020] Preferably, the nickel salt is at least one of Ni(NO3)2·6H2O, NiSO4·6H2O, and NiCl2·6H2O.

[0021] Preferably, in step (B1), the calcination conditions include: a temperature of 450-550°C and a time of 0.5-2 hours.

[0022] Preferably, in step (B2), the specific operation process of impregnation includes: dispersing the multi-walled carbon nanotubes and the NiO / CaO powder material in water and stirring.

[0023] Preferably, the stirring conditions include: a rotation speed of 100-500 r / min and a stirring time of 1-3 h.

[0024] Preferably, the mass ratio of the multi-walled carbon nanotubes to the NiO / CaO powder material is 5:90-100.

[0025] Preferably, in step (B2), the reduction conditions include: a temperature of 450-550°C and a time of 0.5-2 hours.

[0026] A third aspect of the present invention provides a carbon capture and methanation bifunctional material based on carbon nanotubes prepared by the method described above.

[0027] The fourth aspect of this invention provides the application of the carbon nanotube-based carbon capture and methanation bifunctional material described above in the carbon dioxide capture process.

[0028] According to the preparation method of the carbon nanotube-based bifunctional material for carbon capture and methanation described in this invention, carbon nanotubes are introduced into the Ni / CaO system to construct a highly efficient hydrogen spillover network, enabling rapid migration of active hydrogen atoms. Simultaneously, CaO serves as the CO2 capture component for carbonation to generate CaCO3, while Ni acts as the catalytic active component for the hydrogenation and methanation of CaCO3. This allows for efficient activation of the CaCO3 hydrogenation and methanation reaction in the mid-temperature range of 400-500℃. Specifically, the carbon nanotube-based bifunctional material for carbon capture and methanation prepared according to the method described in this invention achieves a methane yield of approximately 5 mmol / g at 450℃. Attached Figure Description

[0029] Figure 1 X-ray diffraction patterns of carbon trapping and methanation bifunctional materials based on carbon nanotubes prepared in Examples 1-3 and Comparative Example 1 of this invention; Figure 2 This is a transmission electron microscope image of the carbon capture and methanation bifunctional material based on carbon nanotubes prepared in Example 2 of this invention. Figure 3 The single-cycle methane yield at 450°C is shown for the carbon capture and methanation bifunctional materials based on carbon nanotubes prepared in the comparative example and Examples 1-3 of this invention. Figure 4 This is the reaction effect of cyclic carbon capture and methanation at 450°C in Example 2 of the present invention, where the carbon capture and methanation bifunctional material based on carbon nanotubes was prepared. Detailed Implementation

[0030] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0031] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] In one specific embodiment, the preparation method of the carbon capture and methanation bifunctional material of the present invention includes the following steps: (A1) Multi-walled carbon nanotubes and nickel salts were reduced once in the presence of a reducing agent, and then the resulting reaction product, hydrazine hydrate and alkali were mixed. The resulting mixture was then subjected to a hydrothermal reaction to obtain a Ni / CNT composite material. (A2) The Ni / CNT composite material and the calcium-containing compound are combined, and then the combined product is subjected to a secondary reduction in a hydrogen atmosphere; The composite method is physical mixing and / or co-impregnation.

[0033] In step (A1), the mass ratio of the multi-walled carbon nanotubes to the nickel salt can be 1:5-15, preferably 1:8-12. The nickel salt can be at least one of NiSO4·6H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O. In the most preferred embodiment, the nickel salt is NiSO4·6H2O.

[0034] In step (A1), the conditions for the primary reduction may include a temperature of 0-5°C and a time of 1-3 hours. Preferably, the conditions for the primary reduction include a temperature of 0-2°C and a time of 1.5-2.5 hours. The reducing agent may be NaBH4 and / or KBH4. In the most preferred embodiment, the reducing agent is NaBH4. The primary reduction process may be carried out in an aqueous solution.

[0035] In step (A1), the mass-to-volume ratio of the multi-walled carbon nanotubes and the hydrazine hydrate can be 0.5-3 g: 100 mL, preferably 1-2 g: 100 mL.

[0036] In step (A1), the specific operation process of the first reduction may include: mixing the multi-walled carbon nanotubes (MWCNTs) and water at a mass-to-volume ratio of 2-3 mg:1 mL, followed by ultrasonic treatment for 20-40 min; then adding the nickel salt to the resulting MWCNT suspension and ultrasonicating for another 20-40 min. The resulting mixture is then transferred to an ice-water bath, and a reducing agent is added dropwise for the first reduction. The diameter of the MWCNTs can be 2-50 nm, preferably 10-20 nm. The MWCNTs can be purchased from Hangzhou Lin'an Ruike Carbon Materials Co., Ltd.

[0037] In step (A1), the conditions for the hydrothermal reaction may include: a temperature of 120-180℃ and a time of 3-5 hours. Preferably, the conditions include: a temperature of 140-160℃ and a time of 3.5-4.5 hours. The hydrothermal reaction can be carried out in a high-pressure reactor. The hydrothermal reaction also includes: centrifuging and washing the resulting reaction product. The centrifugation conditions may include: a rotation speed of 7000-9000 r / min and a time of 7-15 minutes. The reagent used in the washing process can be deionized water. The washing process may be performed once or multiple times, preferably multiple times.

[0038] In step (A1), the alkali can be at least one of ammonia, urea, and hydrazine hydrate. In the most preferred embodiment, the alkali is ammonia.

[0039] In step (A2), the molar ratio of the Ni / CNT composite material (based on Ni content) to the calcium-containing compound (based on Ca content) can be 5:90-100, preferably 5:93-97. The calcium-containing compound can be at least one of calcium oxide, calcium carbonate, and calcium hydroxide. In the most preferred embodiment, the calcium-containing compound is calcium oxide.

[0040] In step (A2), the conditions for the secondary reduction may include: a temperature of 450-550°C and a time of 0.5-2 hours. Preferably, the conditions for the secondary reduction include: a temperature of 470-530°C and a time of 1-1.5 hours. The secondary reduction process can be carried out in an atmosphere furnace.

[0041] In step (A2), preferably, the physical mixing process includes mixing the Ni / CNT composite material and the calcium-containing compound, followed by drying the resulting mixture at 70-90°C. The drying process can be carried out in a vacuum oven.

[0042] In step (A2), the specific operation process of co-impregnation includes: mixing the Ni / CNT composite material and the calcium-containing compound in an aqueous solution, stirring at a speed of 100-500 r / min for 1-3 h, and then evaporating the moisture of the resulting mixture at 75-90 °C.

[0043] In another specific embodiment, the preparation method of the carbon capture and methanation bifunctional material based on carbon nanotubes according to the present invention includes the following steps: (B1) A nickel salt and a calcium-containing compound are mixed, and then the resulting mixture is calcined to obtain NiO / CaO powder material; (B2) Multi-walled carbon nanotubes are attached to the NiO / CaO powder material by impregnation, followed by evaporation and then reduction in a hydrogen atmosphere.

[0044] In step (B1), the molar ratio of the nickel salt (based on Ni content) to the calcium-containing compound (based on Ca content) can be 5:90-100, preferably 5:93-97. The nickel salt can be at least one of Ni(NO3)2·6H2O, NiSO4·6H2O, and NiCl2·6H2O. In the most preferred embodiment, the nickel salt is Ni(NO3)2·6H2O.

[0045] In step (B1), the specific operation process of mixing may include: dissolving the nickel salt and the calcium-containing compound in water, and then evaporating the water at 70-90°C.

[0046] In step (B1), the calcination conditions may include a temperature of 450-550°C and a time of 0.5-2 hours. Preferably, the calcination conditions include a temperature of 480-530°C and a time of 0.5-2 hours. The calcination process can be carried out in an atmosphere furnace.

[0047] In step (B2), the specific impregnation process includes: dispersing the multi-walled carbon nanotubes and the NiO / CaO powder material in water and stirring. The stirring conditions may include: a rotation speed of 100-500 r / min and a stirring time of 1-3 h.

[0048] In step (B2), the mass ratio of the multi-walled carbon nanotubes to the NiO / CaO powder material can be 5:90-100, preferably 5:92-98.

[0049] In step (B2), the reduction conditions may include a temperature of 450-550°C and a time of 0.5-2 hours. Preferably, the reduction conditions include a temperature of 480-530°C and a time of 1-1.5 hours. The reduction process can be carried out in an atmosphere furnace.

[0050] This invention also provides a carbon nanotube-based bifunctional material for carbon capture and methanation prepared by the above method. This carbon nanotube-based bifunctional material can efficiently activate the hydrogenation methanation reaction of CaCO3 in the mid-temperature range of 400-500℃.

[0051] This invention also provides the application of the aforementioned carbon nanotube-based carbon capture and methanation bifunctional material in the carbon dioxide capture process. In practical applications, the CO2 capture capacity and CH4 yield of this carbon nanotube-based carbon capture and methanation bifunctional material can reach 5 mmol / g.

[0052] The following examples further illustrate the carbon nanotube-based carbon capture and methanation bifunctional material, its preparation method, and its applications according to the present invention. The examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0053] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0054] Example 1 (A1) Take 50 mg of multi-walled carbon nanotubes (average diameter 10 nm, purchased from Hangzhou Lin'an Ruike Carbon Materials Co., Ltd., the same below), add 20 mL of deionized water, and sonicate for 30 min. Add 0.524 g of NiSO4·6H2O to the obtained carbon nanotube suspension, sonicate for 30 min, and then transfer the resulting mixture to a three-necked flask and immerse it in an ice-water bath. Add 10 mL of pre-cooled 2 wt% NaBH4 aqueous solution dropwise, and carry out a reduction at 0 °C for 2 h. Transfer the resulting reaction solution to a high-pressure reactor, add 10 mL of ammonia and 4 mL of hydrazine hydrate, and hydrothermally react at 150 °C for 4 h. After the reaction is completed, collect the product by centrifugation at 8000 r / min for 10 min, wash three times with deionized water, and dry at 100 °C for 12 h to obtain the Ni / CNT composite material.

[0055] (A2) Take the Ni / CNT composite material obtained in step (1) and add a measured amount of CaO powder (molar ratio Ni:Ca=5:95) and stir evenly. Dry at 80℃ for 12h. Reduce the dried powder at 500℃ in a pure hydrogen atmosphere for 1h to obtain carbon capture and methanation bifunctional material A1 based on carbon nanotubes.

[0056] Example 2 (A1) Take 50 mg of multi-walled carbon nanotubes and add them to 20 mL of deionized water. Disperse the mixture by sonication for 30 min. Add 0.524 g of NiSO4·6H2O to the resulting carbon nanotube suspension and sonicate for 30 min. Then, transfer the resulting mixture to a three-necked flask and immerse it in an ice-water bath. Add 10 mL of pre-cooled 2 wt% NaBH4 aqueous solution dropwise and perform a reduction at 0 °C for 2 h. Transfer the resulting reaction solution to a high-pressure reactor and add 10 mL of ammonia and 4 mL of hydrazine hydrate. Perform a hydrothermal reaction at 150 °C for 4 h. After the reaction is complete, collect the product by centrifugation at 8000 r / min for 10 min. Wash the product three times with deionized water and finally disperse it in 20 mL of water for later use to obtain a dispersion of Ni / CNT composite material.

[0057] (A2) Take the dispersion of Ni / CNT composite material obtained in step (1), add a measured amount of CaO powder (molar ratio Ni:Ca=5:95) and stir evenly. Stir and impregnate for 2 hours, evaporate the water at 80°C, and reduce the dried solid in a pure hydrogen atmosphere at 500°C for 1 hour to obtain carbon capture and methanation bifunctional material A2 based on carbon nanotubes.

[0058] Example 3 (B1) Dissolve measured amounts of Ni(NO3)2·6H2O and CaO in water at a molar ratio of Ni:Ca=5:95, evaporate the water at 80°C, and calcine in air at 500°C to obtain NiO / CaO powder material.

[0059] (B2) Disperse the NiO / CaO powder material obtained in step (B1) in water, add multi-walled carbon nanotubes, the mass ratio of multi-walled carbon nanotubes to NiO / CaO powder material is 5:95, stir and impregnate for 2 hours, evaporate the water at 80°C, and reduce in a pure hydrogen atmosphere at 500°C for 1 hour to obtain carbon capture and methanation bifunctional material A3 based on carbon nanotubes.

[0060] Example 4 The carbon capture and methanation bifunctional material was prepared according to Example 1, except that in step (A1), the mass of NiSO4·6H2O was adjusted to 0.235g, resulting in carbon nanotube-based carbon capture and methanation bifunctional material A4.

[0061] Example 5 The carbon capture and methanation bifunctional material was prepared according to Example 1, except that in step (A1), NiSO4·6H2O was replaced with Ni(NO3)2·6H2O to obtain carbon nanotube-based carbon capture and methanation bifunctional material A5.

[0062] Example 6 The carbon capture and methanation bifunctional material was prepared according to Example 1, except that in step (A1), NaBH4 was replaced with KBH4 to obtain carbon nanotube-based carbon capture and methanation bifunctional material A6.

[0063] Example 7 The carbon capture and methanation bifunctional material was prepared according to Example 1, except that in step (A1), ammonia was replaced with urea to obtain carbon nanotube-based carbon capture and methanation bifunctional material A7.

[0064] Example 8 The carbon capture and methanation bifunctional material was prepared according to Example 1, except that in step (A2), calcium oxide was replaced with calcium carbonate to obtain carbon nanotube-based carbon capture and methanation bifunctional material A8.

[0065] Example 9 The carbon capture and methanation bifunctional material was prepared according to Example 3, except that in step (B1), Ni(NO3)2·6H2O was replaced with NiCl2·6H2O to obtain carbon nanotube-based carbon capture and methanation bifunctional material A9.

[0066] Example 10 The carbon capture and methanation bifunctional material was prepared according to Example 3, except that in step (B2), the mass ratio of multi-walled carbon nanotubes and NiO / CaO powder was adjusted to 5:80 to obtain carbon capture and methanation bifunctional material A10 based on carbon nanotubes.

[0067] Comparative Example 1 A carbon capture and methanation bifunctional material based on carbon nanotubes was prepared according to Example 1, except that multi-walled carbon nanotubes were not added in step (A1), resulting in carbon capture and methanation bifunctional material D1 based on carbon nanotubes.

[0068] Comparative Example 2 A carbon nanotube-based bifunctional material for carbon capture and methanation was prepared according to Example 1, except that ammonia was not added in step (A1), resulting in carbon nanotube-based bifunctional material D2.

[0069] Comparative Example 3 A carbon capture and methanation bifunctional material based on carbon nanotubes was prepared according to Example 3, except that multi-walled carbon nanotubes were not added in step (B2), resulting in carbon capture and methanation bifunctional material D3 based on carbon nanotubes.

[0070] Test case The structure and performance parameters of the carbon capture and methanation bifunctional materials based on carbon nanotubes prepared in the above embodiments and comparative examples were characterized and tested according to the following methods: (1) X-ray diffraction: The carbon trapping and methanation bifunctional materials A1-A3 and D1 based on carbon nanotubes were characterized by X-ray diffraction. Figure 1 X-ray diffraction patterns of carbon trapping and methanation bifunctional materials A1-A3 and D1 based on carbon nanotubes are shown.

[0071] (2) Transmission electron microscopy: The structure of carbon trapping and methanation bifunctional material A2 based on carbon nanotubes was characterized by transmission electron microscopy. Figure 2 Transmission electron microscopy image of A2, a carbon-based bifunctional material for trapping and methanation of carbon nanotubes.

[0072] (3) Carbon capture and methanation performance: 0.1 g of the test material was weighed and placed in a fixed-bed quartz reaction tube. Reduction was performed for 1 h at 500 °C under a pure hydrogen atmosphere (100 mL / min), followed by cooling to 450 °C. First, a 10% CO2 / N2 mixture (100 mL / min) was introduced for CO2 capture for 30 min, then N2 was introduced for purging for 5 min, and finally pure H2 (100 mL / min) was introduced for hydrogenation methanation for 60 min. The concentrations of CO2, CH4, CO, and H2 in the outlet gas were monitored in real time by an online gas analyzer. The CO2 capture amount (mmol / g) and CH4 yield (mmol / g) were calculated by concentration-time integration. The above cycle was repeated 10 times to evaluate the cyclic stability of the material. Figure 3 A comparison chart showing the performance advantages of carbon capture and methanation bifunctional materials A1-A3 based on carbon nanotubes is presented. Figure 4 The stability of the carbon nanotube-based bifunctional material for carbon capture and methanation prepared in Example 2 during cyclic carbon capture and methanation at 450 °C is shown.

[0073] The performance parameters of the carbon capture and methanation bifunctional materials based on carbon nanotubes in the above embodiments and comparative examples are shown in Table 1 below.

[0074] Table 1

[0075] The results from the examples and comparative examples show that the carbon nanotube-based carbon capture and methanation bifunctional material prepared according to the method described in this invention has significantly higher CO2 capture capacity and CH4 yield.

[0076] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a carbon capture and methanation bifunctional material based on carbon nanotubes, characterized in that, The method includes the following steps: (A1) Multi-walled carbon nanotubes and nickel salts were reduced once in the presence of a reducing agent, and then the resulting reaction product, hydrazine hydrate and alkali were mixed. The resulting mixture was then subjected to a hydrothermal reaction to obtain a Ni / CNT composite material. (A2) The Ni / CNT composite material and the calcium-containing compound are combined, and then the combined product is subjected to a secondary reduction in a hydrogen atmosphere; The composite method is physical mixing and / or co-impregnation.

2. The method according to claim 1, characterized in that, In step (A1), the mass ratio of the multi-walled carbon nanotubes to the nickel salt is 1:5-15; Preferably, the nickel salt is at least one selected from NiSO4·6H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O.

3. The method according to claim 1 or 2, characterized in that, In step (A1), the conditions for the first reduction include: a temperature of 0-5℃ and a time of 1-3h; Preferably, the reducing agent is at least one of NaBH4 and / or KBH4.

4. The method according to any one of claims 1-3, characterized in that, In step (A1), the mass-volume ratio of the multi-walled carbon nanotubes and the hydrazine hydrate is 0.5-3 g: 100 mL.

5. The method according to any one of claims 1-4, characterized in that, In step (A1), the conditions for the hydrothermal reaction include: a temperature of 120-180℃ and a time of 3-5 hours; Preferably, the alkali is at least one of ammonia, urea, and hydrazine hydrate.

6. The method according to claim 1, characterized in that, In step (A2), the molar ratio of the Ni / CNT composite material (based on Ni component) to the calcium-containing compound (based on Ca component) is 5:90-100. Preferably, the calcium-containing compound is at least one selected from calcium oxide, calcium carbonate, and calcium hydroxide.

7. The method according to claim 1 or 6, characterized in that, In step (A2), the conditions for the secondary reduction include: a temperature of 450-550℃ and a time of 0.5-2h.

8. The method according to claim 1, 6, or 7, characterized in that, In step (A2), the specific operation process of the physical mixing includes: mixing the Ni / CNT composite material and the calcium-containing compound, and then drying the resulting mixture at 70-90°C.

9. The method according to claim 1, characterized in that, In step (A2), the specific operation process of co-impregnation includes: mixing the Ni / CNT composite material and the calcium-containing compound by wet slurry mixing, stirring at a speed of 100-500 r / min for 1-3 h, and then evaporating the moisture of the resulting mixture at 75-90 °C.

10. A method for preparing a bifunctional material based on carbon nanotubes for carbon capture and methanation, characterized in that, The method includes the following steps: (B1) A nickel salt and a calcium-containing compound are mixed, and then the resulting mixture is calcined to obtain NiO / CaO powder material; (B2) Multi-walled carbon nanotubes are attached to the NiO / CaO powder material by impregnation, followed by evaporation and then reduction in a hydrogen atmosphere.

11. The method according to claim 10, characterized in that, In step (B1), the molar ratio of the nickel salt (based on Ni component) to the calcium-containing compound (based on Ca component) is 5:90-100. Preferably, the nickel salt is at least one of Ni(NO3)2·6H2O, NiSO4·6H2O, and NiCl2·6H2O.

12. The method according to claim 10 or 11, characterized in that, In step (B1), the calcination conditions include a temperature of 450-550℃ and a time of 0.5-2h.

13. The method according to claim 10, characterized in that, In step (B2), the specific impregnation process includes: dispersing the multi-walled carbon nanotubes and the NiO / CaO powder material in water and stirring; Preferably, the stirring conditions include: a rotation speed of 100-500 r / min and a stirring time of 1-3 h; Preferably, the mass ratio of the multi-walled carbon nanotubes to the NiO / CaO powder material is 5:90-100.

14. The method according to claim 10 or 13, characterized in that, In step (B2), the reduction conditions include a temperature of 450-550℃ and a time of 0.5-2h.

15. A carbon nanotube-based carbon capture and methanation bifunctional material prepared by the method according to any one of claims 1-14.

16. The application of the carbon nanotube-based carbon capture and methanation bifunctional material as described in claim 15 in the carbon dioxide capture process.

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