Bifunctional material, preparation method and application thereof, and carbon dioxide capture and catalytic conversion integrated system

Abstract

The invention relates to the technical field of CO2 capture and CH4 supply, in particular to a bifunctional material, a preparation method and application thereof and a carbon dioxide capture and catalytic conversion integrated system. The invention provides a bifunctional material for coupling calcium cycle carbon dioxide capture and methanation medium-temperature methane preparation. The bifunctional material comprises a porous carrier, and a modified adsorbent and a catalyst which are dispersed and loaded on the porous carrier, the modified adsorbent is calcium oxide of which the surface is coated with a layer of liquid film formed by melting alkali metal nitrate. Calcium carbonate conversion at medium temperature is promoted by doping alkali metal nitrate, a formed molten liquid layer promotes a gas-solid reaction between calcium carbonate and hydrogen, the conversion rate of calcium carbonate and the yield of methane are improved, meanwhile, a large-specific-surface-area porous carrier is used, and the calcium oxide sintering phenomenon caused by nitrate is eliminated; dispersion of calcium oxide and dispersion of a catalyst are promoted, hydrogen dissociation and hydrogen overflow are enhanced, and the carbon dioxide capturing capacity and the calcium carbonate conversion rate of calcium oxide at the medium temperature are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of CO2 capture and CH4 supply, in particular to a dual functional material and a preparation method and application thereof, and a carbon dioxide capture and catalytic conversion integrated system. BACKGROUND

[0002] In recent years, global carbon dioxide (CO2) emissions have risen sharply, exacerbating global climate change. Realizing CO2 resource utilization has become an important way to solve this problem. Methane generated by CO2 methanation reaction can also be used as a natural gas substitute for power generation, heating, transportation and other fields, thereby reducing dependence on traditional fossil fuels and optimizing energy structure.

[0003] The currently commonly used integrated carbon dioxide capture and methanation (ICCM) technology eliminates the gas separation link in the traditional CO2 capture and methanation process, simplifies the overall process flow, and can significantly reduce investment and operating costs. As the most critical CO2 adsorbent in ICCM technology, it is often required to have a wide source and strong CO2 capture and conversion capacity. Calcium oxide, as a low-cost CO2 capture material, has characteristics such as abundant reserves, fast reaction kinetics, and excellent adsorption performance, and is a common adsorbent for ICCM. However, calcium oxide usually needs to be carbonated above 600℃ and decarburized above 900℃, so it is mostly used for high-temperature (above 400℃) CO2 capture process. However, calcium oxide has poor CO2 capture performance at medium temperature (200~400℃), and the CaCO3 conversion rate is low, which limits its further application.

[0004] In order to solve the problem of single calcium oxide, the calcium oxide needs to be modified to obtain a dual functional material (DFMs) that can break through the temperature limit and also has strong capture and catalytic performance at medium temperature, thereby further improving the coupling conversion efficiency of ICCM technology. SUMMARY

[0005] The present application is to overcome the defect that the carbon dioxide capture capacity of calcium oxide at medium temperature is poor, resulting in low conversion rate of calcium carbonate in the prior art, and provides a dual functional material and a preparation method and application thereof, and a carbon dioxide capture and catalytic conversion integrated system to overcome the above-mentioned defects.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions: The application provides a bifunctional material for coupling carbon dioxide capture and methanation of medium-temperature methane production, comprising a porous carrier and a modified adsorbent and catalyst dispersed and loaded on the porous carrier; the modified adsorbent is calcium oxide coated with a liquid film formed by melting of an alkali metal nitrate.

[0007] The application promotes the conversion of calcium carbonate at medium temperature by doping alkali metal nitrate, the formed molten liquid layer promotes the gas-solid reaction of calcium carbonate and hydrogen, improves the conversion rate of calcium carbonate and the yield of methane, and meanwhile, a porous carrier with a large specific surface area is used to eliminate the sintering of calcium oxide caused by nitrate, promote the dispersion of calcium oxide and the dispersion of the catalyst, strengthen hydrogen dissociation and hydrogen overflow, and greatly improve the carbon dioxide capture capacity of calcium oxide and the conversion rate of calcium carbonate at medium temperature.

[0008] Preferably, the porous carrier is carbon nanotubes; and / or, the catalyst is nickel; and / or, the alkali metal nitrate is potassium nitrate.

[0009] The application provides a preparation method of the bifunctional material, comprising: mixing nickel salt, alkali metal nitrate and carbon nanotubes in water, then adding calcium oxide, and then heating, stirring and drying to obtain a slurry; and calcining the slurry to obtain the bifunctional material.

[0010] The application promotes the conversion of calcium carbonate at medium temperature by doping alkali metal nitrate, the formed molten liquid layer promotes the gas-solid reaction of calcium carbonate and hydrogen, improves the conversion rate of calcium carbonate and the yield of methane, and meanwhile, a porous carrier with a large specific surface area is used to eliminate the sintering of calcium oxide caused by nitrate, promote the dispersion of calcium oxide and the dispersion of the catalyst, strengthen hydrogen dissociation and hydrogen overflow, and greatly improve the carbon dioxide capture capacity of calcium oxide and the conversion rate of calcium carbonate at medium temperature.

[0011] However, when the alkali metal molten liquid film is coated, the sintering of calcium oxide is accelerated during the calcination and sintering process, which causes the overall adsorption effect to decrease. Therefore, on this basis, the application utilizes the porous, tubular structure and large specific surface area of carbon nanotubes to disperse and treat calcium oxide to slow down the accelerated sintering, so that the overall adsorption capacity of the bifunctional material is greatly improved, and finally the efficient capture of carbon dioxide at medium temperature is realized.

[0012] Preferably, the alkali metal nitrate is potassium nitrate; and / or, heating and stirring at 70-90 DEG C for at least 1 h; and / or, drying at 100-110 DEG C for at least 12 h; and / or, calcining at 400-500 DEG C for 3-6 h; and / or, calcining at a temperature rising speed of 3-10 DEG C / min; and / or, calcining in an inert atmosphere; And / or, calcination is carried out in an atmosphere of nitrogen and / or argon.

[0013] Preferably, the molar ratio of nickel, alkali metal nitrate, and calcium oxide in the nickel salt is (0.5~1):(2~3):(14~15); and / or, the mass ratio of carbon nanotubes to calcium oxide is 1:(3~6).

[0014] Preferably, the molar ratio of nickel, alkali metal nitrate, and calcium oxide in the nickel salt is (0.8~1):(2~2.5):(14~14.5).

[0015] Preferably, the mass ratio of the carbon nanotubes to calcium oxide is 1:(4~5).

[0016] The present invention also provides the application of bifunctional materials in carbon dioxide capture and methanation at medium temperature to produce methane, wherein the medium temperature range is 350~400℃.

[0017] The present invention also provides a system integrating carbon dioxide capture and catalytic conversion, including a wetting unit and a carbon dioxide capture and conversion unit connected to the wetting unit; air, hydrogen and oxygen introduced from the inlet of the carbon dioxide capture and conversion unit are processed into carbon dioxide and methane by the action of an electrofunctional material disposed inside the carbon dioxide capture and conversion unit, and the carbon dioxide and methane are released from the outlet of the carbon dioxide capture and conversion unit, wherein the electrofunctional material includes a conductive substrate and a bifunctional material, and the conductive substrate is connected to a power source.

[0018] The integrated system provided in this application couples direct air capture of carbon dioxide and methanation via a calcium cycle. During the methanation stage, carbon dioxide capture and conversion are achieved through an electrothermal catalytic reaction on a conductive substrate. Simultaneously, the bifunctional material prepared in this application, due to its excellent carbon dioxide capture capacity at intermediate temperatures, high calcium carbonate conversion rate, and extremely strong cycle stability, can efficiently capture low-concentration carbon dioxide from the air, achieving air purification and energy conversion.

[0019] Preferably, the system further includes a detection unit and an information integration unit connected to the detection unit for obtaining carbon dioxide capture and catalytic conversion results; And / or, the system further includes a thermal imaging unit; And / or, the humidification unit is provided with a humidifier and a hygrometer in sequence according to the air intake direction; And / or, the bifunctional material is loaded on the surface of the conductive substrate; And / or, the conductive substrate is graphite felt.

[0020] Graphite felt has a three-dimensional interconnected conductive network structure, short electron migration paths, and low resistivity, which can improve the efficiency of electrochemical reactions.

[0021] Preferably, the detection unit includes a gas chromatography unit and a gas analysis unit.

[0022] Therefore, the present invention has the following beneficial effects: (1) This invention provides a dual-function material that, through the synergistic effect of potassium nitrate doping and carbon nanotube carrier, enables the material to fully utilize the advantages of potassium nitrate in promoting ion transport during both the capture and conversion stages, thereby achieving simultaneous improvement in carbon dioxide capture capacity and calcium carbonate conversion rate at intermediate temperatures.

[0023] (2) The bifunctional material provided by the present invention not only has excellent carbon dioxide capture capacity and calcium carbonate conversion rate at medium temperature, but also has extremely strong stability, maintaining zero decay after 5 cycles and slightly decaying after 20 cycles.

[0024] (3) The present invention utilizes an integrated system constructed with dual-functional materials to efficiently convert low-concentration carbon dioxide into methane through direct air capture technology, significantly reducing the concentration of greenhouse gases in the atmosphere and providing low-cost and highly flexible technical support for the realization of the global carbon neutrality goal.

[0025] (4) The integrated system provided by this invention integrates the direct air capture of carbon dioxide and the methanation process into a single system through electrothermal coupling and material functional integration design. This greatly reduces energy consumption and solves the problems of traditional technologies such as reliance on high-concentration gas sources, complex processes, and large equipment. At the same time, the generated methane serves as a green fuel, providing a sustainable carbon neutrality and technology solution for remote areas or small distributed energy systems, and promoting the green transformation of the energy structure. Attached Figure Description

[0026] Figure 1 The ICCM performance diagrams for different bifunctional materials are shown, where a represents NiCaO, b represents NiCaO-KNO3, c represents NiCaO / CNT, d represents NiCaO-KNO3 / CNT, e represents NiCaO-NaNO3 / CNT, and f represents NiCaO-LiNO3 / CNT. Figure 2 This is a schematic diagram of the integrated system structure; Figure 3 This is a schematic diagram of the integrated system operation; Figure 4 This is a graph showing the gas concentration during the capture phase, collected during the operation of the integrated system. Figure 5 This is a graph showing the gas concentration during the conversion stage, collected during the operation of the integrated system. The codes in the diagram are as follows: wetting unit 100, humidifier 110, hygrometer 120, carbon dioxide capture and conversion unit 200, air inlet 210, air outlet 220, electrical functional material 230, power supply 300, thermal imaging unit 400, detection unit 500, gas chromatography unit 510, gas analysis unit 520, and information integration unit 600. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0028] Dual-functional materials Example 1 0.25 g (0.86 mmol) Ni(NO3)2·6H2O, 0.21 g (2.08 mmol) KNO3, and 0.2 g carbon nanotubes (CNTs) were mixed in 20 mL of deionized water and ultrasonically stirred for 30 min at room temperature. Then, 0.8 g (14.27 mmol) CaO was added to the mixture, and the mixture was heated at 80°C with continuous stirring for 1 h. The resulting slurry was dried overnight at 105°C. The dried solid was calcined in a tube furnace at 450°C under nitrogen atmosphere at a heating rate of 5°C / min for 4 h. The resulting sample was named NiCaO-KNO3 / CNT.

[0029] Comparative Example 1 0.25 g of Ni(NO3)2·6H2O and 0.8 g of CaO were mixed in 20 mL of deionized water and ultrasonically stirred for 30 min at room temperature. Then, the mixture was heated and stirred continuously at 80°C for 1 h. The resulting slurry was dried overnight at 105°C. The dried solid was calcined in a tube furnace at 450°C under nitrogen atmosphere at a heating rate of 5°C / min for 4 h. The resulting sample was named NiCaO.

[0030] Comparative Example 2 0.25 g Ni(NO3)2·6H2O and 0.21 g KNO3 were mixed in 20 mL of deionized water and ultrasonically stirred for 30 min at room temperature. Then, 0.8 g CaO was added to the mixture, and the mixture was heated at 80°C with continuous stirring for 1 h. The resulting slurry was dried overnight at 105°C. The dried solid was calcined in a tube furnace at 450°C under nitrogen atmosphere at a heating rate of 5°C / min for 4 h. The resulting sample was named NiCaO-KNO3.

[0031] Comparative Example 3 0.25 g Ni(NO3)2·6H2O and 0.2 g CNTs were mixed in 20 mL of deionized water and ultrasonically stirred for 30 min at room temperature. Then, 0.8 g CaO was added to the mixture, and the mixture was heated at 80°C with continuous stirring for 1 h. The resulting slurry was dried overnight at 105°C. The dried solid was calcined in a tube furnace at 450°C under nitrogen atmosphere at a heating rate of 5°C / min for 4 h. The resulting sample was named NiCaO / CNT.

[0032] Comparative Example 4 This comparative example is basically the same as Example 1, except that KNO3 is replaced with equimolar amounts of LiNO3.

[0033] Comparative Example 5 This comparative example is basically the same as Example 1, except that KNO3 is replaced with an equimolar amount of NaNO3.

[0034] The materials obtained in Example 1 and Comparative Examples 1-5 were subjected to CO2 capture and methanation experiments to investigate the performance of each catalyst. The reaction process and conditions were as follows: (1) Heating stage: Under N2 conditions, the temperature is increased from room temperature to 400℃ at a rate of 5℃ / min; (2) Pre-reduction stage: pure H2, reaction time 120 min; (3) Purge with N2 for 5 min; (4) CO2 capture stage: 15% CO2, nitrogen as the equilibrium gas, reaction time 60 min; (5) Purge with N2 for 5 min; (6) Methanation conversion stage: pure H2, reaction time 120 min; (7) Purge with N2 for 5 min.

[0035] The reaction temperature throughout the process was 400℃, and the flow rate was 100 mL / min. The test results are shown in Table 1.

[0036] Table 1. Medium-temperature CO2 capture and methanation performance of different catalysts

[0037] As shown in Table 1, the CO2 capture and in-situ methanation tests conducted at 400°C indicate that NiCaO exhibits the worst performance, while NiCaO-KNO3 / CNT demonstrates the best overall performance: a CO2 capture capacity of 11.60 mmol / g. DFMs The yield of CH4 was 11.00 mmol / g. DFMs It also exhibits 100% CH4 selectivity and 94.82% CO2 conversion rate. From Figure 1 a~ Figure 1 The d-axis provides information on the specific gas concentration curves during the reaction process. The methanation process exhibits a typical rapid reaction phase (reaction of surface CaCO3 with H2) and a slow diffusion phase (reaction of H2 with deep CaCO3), indicating that the synergistic effect of KNO3 and CNTs is crucial for performance improvement.

[0038] Comparing the data from Example 1 and Comparative Examples 1-3, it can be seen that while introducing CNTs alone (NiCaO / CNT) can increase CO2 capture (attributed to improved CaO dispersion), the CaCO3 conversion rate remains low due to the lack of KNO3's promoting effect. Conversely, while introducing KNO3 alone (NiCaO-KNO3) can improve methanation performance to a limited extent, the overall performance is poor due to the sintering effect. The results confirm that only synergistic modification of KNO3 and CNTs can achieve simultaneous optimization of CO2 capture and conversion performance.

[0039] The effects of other alkali metal nitrates (sodium nitrate, lithium nitrate) on performance were also investigated, comparing the data results of Example 1 and Comparative Examples 4-5 (Table 1 and 2). Figure 1 e Figure 1 f), potassium nitrate exhibits the best performance, while LiNO3 causes the most severe sintering of calcium oxide, thus affecting performance.

[0040] Integrated System Preparation of electrofunctional materials: 1.5 g Ni(NO3)2·6H2O, 1 g KNO3, and 1 g CNTs were mixed in 30 mL of deionized water and ultrasonically stirred for 30 min at room temperature. Then, 3.3 g CaO was added to the mixture, and the mixture was heated and stirred continuously at 80 °C for 1 h. A graphite felt (100 mm × 12 mm × 3 mm) was then immersed in the slurry for 1 h, and subsequently dried at 105 °C for 2 h. The dried graphite felt was then calcined in a tube furnace at 450 °C under a nitrogen atmosphere at a heating rate of 5 °C / min for 4 h. The resulting sample was named NiCaO-KNO3 / CNT.

[0041] The load was determined by weighing. The mass of the graphite felt before soaking and after pre-reduction was measured, and the difference between the two masses was the actual load.

[0042] Integrated system: such as Figure 2 As shown, the prepared electrofunctional material 230 is placed inside the carbon dioxide capture and conversion unit 200, and its two ends are connected to a power source using conductive wires to prepare for subsequent electrothermal catalysis. To ensure complete air intake and easy air exhaust, an air inlet 210 and an air outlet 220 are vertically arranged on both sides of the carbon dioxide capture and conversion unit 200. Air, H2, and N2 entering the system are humidified by the humidification unit 100 and then enter the carbon dioxide capture and conversion unit 200 through the air inlet 210. Under electrothermal catalysis, the electrofunctional material 230 captures CO2 from the air and converts it into CH4. The generated CO2 and CH4 enter the detection unit 500 through the air outlet of the carbon dioxide capture and conversion unit 200. If thermal imaging is required during the electrothermal catalysis process, it is tested using the thermal imaging unit 400. The detection unit 500 is divided into a gas chromatography unit 510 and a gas analysis unit 520, which respectively use a gas chromatograph to measure CO2 and a gas analyzer to measure CH4; that is, CO2 and CH4 are directly measured after exiting the gas outlet 220 and connected to the gas chromatograph and gas analyzer. After the detection is completed, the data is collected and analyzed by the information integration unit 600 (computer), such as... Figures 4-5 The result.

[0043] like Figure 3 As shown in the flowchart, the integrated system completes the capture, conversion, collection, analysis, and processing of CO2 in the air. In the CO2 capture stage, air is introduced into the humidifier 110 (water bath device) at room temperature, and then the humidified air is introduced into the quartz tube (of the CO2 capture and conversion unit 200). The bifunctional material coated on the graphite felt inside the tube begins to capture CO2. When the adsorption layer is saturated, the air supply is stopped, and N2 is introduced for purging. After the remaining air is exhausted, the connecting wires at both ends of the graphite felt are energized in an H2 atmosphere. The graphite felt rapidly heats up to 400℃ (thermal response time <300s), undergoing a methanation reaction. CaCO3 is directly hydrogenated to convert CO2 into CH4. After one conversion process is completed, the energizer is stopped, and H2 is introduced, followed by air for the next round of CO2 capture. By periodically switching the energizer on and off and changing the introduced gas, CO2 in the air can be continuously captured and converted into CH4, achieving continuous reuse of CO2. The simulation experiment was conducted according to this procedure and the following parameters. The test results are shown in Table 2. Figures 4-5 : (1) Pre-reduction stage: pure H2, flow rate of 100 mL / min, power of 67 W to heat to 400℃, reaction time of 120 min; (2) Collection stage: simulated air (400 ppm CO2), flow rate of 200 mL / min, room temperature, reaction time 36 h; (3) Purge with N2 for 5 min; (4) Methanation conversion stage: pure H2, flow rate of 100 mL / min, power of 67 W to heat to 400℃, reaction time of 180 min, temperature is recorded in real time by infrared thermal imager during the reaction; (5) Purge with N2 for 5 min.

[0044] Table 2 CO2 capture and methanation performance

[0045] As can be seen from the data in Table 2, NiCaO-KNO3 / CNT exhibits excellent overall performance: CO2 capture capacity reaches 13.50 mmol / g. DFMs The yield of CH4 was 10.87 mmol / g. DFMs It also exhibits 100% CH4 selectivity and 80.5% CO2 conversion. From Figure 4 , Figure 5 The specific gas concentration curves of the reaction process can be obtained. These results demonstrate that the integrated system of the present invention has a long-lasting CO2 capture capability, can stably and completely adsorb CO2 for up to 10 hours, and is suitable for long-term continuous operation.

[0046] This invention demonstrates significant technological advantages in the field of CO2 resource recovery through highly efficient adsorption-catalysis synergistic design. The developed NiCaO-KNO3 / CNT exhibits extremely high selectivity for methane, with side reactions completely suppressed. Furthermore, the integrated system achieves stable temperature control with minimal temperature fluctuations, proving its excellent thermal stability.

Claims

1. A bifunctional material coupling calcium cycle carbon dioxide capture and methanation mesophilic methane production, characterized in that, The porous carrier and the modified adsorbent and catalyst dispersedly loaded on the porous carrier; the modified adsorbent is calcium oxide coated with a liquid film of molten alkali metal nitrate.

2. The bifunctional material of claim 1, wherein, The porous carrier is carbon nanotube; and / or, the catalyst is nickel; and / or, the alkali metal nitrate is potassium nitrate.

3. The method of producing a bifunctional material according to claim 1 or 2, wherein The method comprises: mixing nickel salt, alkali metal nitrate and carbon nanotube in water, adding calcium oxide, and then heating, stirring and drying to obtain a slurry; calcining the slurry to obtain the bifunctional material.

4. The production method according to claim 3, wherein The alkali metal nitrate is potassium nitrate; and / or, heating and stirring at 70-90℃ for at least 1 h; and / or, drying at 100-110℃ for at least 12 h; and / or, calcining at 400-500℃ for 3-6 h; and / or, calcining at a temperature increasing rate of 3-10℃ / min; and / or, calcining in an inert atmosphere; and / or, calcining in an atmosphere of nitrogen and / or argon.

5. The production method according to claim 3 or 4, characterized by, The molar ratio of nickel in the nickel salt, alkali metal nitrate and calcium oxide is (0.5-1):(2-3):(14-15); and / or, the mass ratio of carbon nanotube to calcium oxide is 1:(3-6).

6. Use of the bifunctional material according to claim 1 or 2 or the bifunctional material produced according to any one of claims 3 to 5 for carbon dioxide capture and methanation at moderate temperatures, characterized in that, The temperature range of the medium temperature is 350-400℃.

7. A system for integrated carbon dioxide capture and catalytic conversion, characterized by, The system comprises a wetting unit and a carbon dioxide capture and conversion unit in communication with the wetting unit; air, hydrogen and oxygen introduced from the inlet of the carbon dioxide capture and conversion unit are treated into carbon dioxide and methane by the action of an electric functional material arranged inside the carbon dioxide capture and conversion unit, and the carbon dioxide and methane are released from the outlet of the carbon dioxide capture and conversion unit, the electric functional material comprising an electrically conductive substrate and the bifunctional material of claim 1 or 2 or the bifunctional material prepared by the method of any one of claims 3-5, and the electrically conductive substrate is connected to a power source.

8. The system of claim 7, wherein, The system further comprises a detection unit and an information integration unit connected to the detection unit for obtaining the carbon dioxide capture and catalytic conversion results. and / or, the system further comprises a thermal imaging unit; and / or, the wetting unit is sequentially provided with a humidifier and a hygrometer in the direction of air inlet; and / or, the bifunctional material is loaded on the surface of the electrically conductive substrate; and / or, the electrically conductive substrate is graphite felt.

9. The system of claim 8, wherein, The detection unit comprises a gas chromatography unit and a gas analysis unit.

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