A method for low-temperature plasma pyrolysis of CO2, a catalyst for pyrolysis, and a method for its preparation.

Abstract

This invention discloses a low-temperature plasma cracking method for CO2, a catalyst for cracking, and its preparation method, belonging to the fields of solid waste resource utilization and low-carbon emission reduction technology. The low-temperature plasma cracking catalyst for CO2 of this invention comprises NiFe2O4 crystals, and the catalyst has a specific surface area of ​​3-5 m² / g. 2 ·g ‑1 The NiFe2O4 crystals have a particle size of 150-200 mesh. The low-temperature plasma pyrolysis method for CO2 of this invention includes: contacting CO2 with the catalyst of this invention under plasma conditions to ionize and degrade CO2, generating CO and O2. This invention prepares a catalyst using electroplating sludge as raw material for CO2 pyrolysis, achieving both resource utilization of electroplating sludge and effective CO2 pyrolysis, while reducing pyrolysis treatment costs.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and low-carbon emission reduction technology, specifically involving a low-temperature plasma cracking method for CO2, a cracking catalyst and its preparation method. Background Technology

[0002] "Carbon neutrality" has become a key term in addressing global climate change. The primary cause of global warming is the excessive emission of greenhouse gases, particularly carbon dioxide, mainly from the burning of fossil fuels. To mitigate or even reverse this trend, countries are committed to achieving carbon neutrality. Pathways to achieving carbon neutrality include improving energy efficiency, developing renewable energy sources, adopting clean technologies, reforestation, and developing carbon capture and storage technologies.

[0003] Among them, CO2 cracking technology is one of the research hotspots for energy conservation and emission reduction. This technology is an advanced technology aimed at breaking down carbon dioxide (CO2) into carbon (C) and oxygen (O2). The core idea behind it is to find an energy-efficient and environmentally friendly way to reduce the concentration of CO2 in the atmosphere, combat global climate change, and provide new possibilities for energy production.

[0004] A search revealed that Chinese utility model patent CN215249587U discloses a carbon dioxide resource utilization system that uses hydrogen and carbon dioxide as reactants to catalytically produce methane, which is then subjected to high-temperature cracking to produce hydrogen and solid carbon fuel, thus realizing the resource utilization of carbon dioxide. Chinese invention patent CN105601074A discloses a novel, highly efficient resource utilization method for the synergistic treatment of electroplating sludge and carbon dioxide. This method uses electroplating sludge as a raw material to prepare biochar, which is then used as a cathode catalyst in a bioelectrochemical system to treat carbon dioxide.

[0005] While both methods effectively treat carbon dioxide, their costs remain high, and their application in industrial settings is challenging. High-temperature pyrolysis of hydrogen, along with the resulting methane, hydrogen, and solid carbon fuels, requires effective separation and purification, increasing manufacturing and operating costs. Furthermore, the preparation of biochar and the establishment of bioelectrochemical systems also incur additional costs. Moreover, although Chinese invention patent CN105601074A achieves the resource utilization of electroplating sludge, this sludge requires high-temperature pyrolysis and must be mixed with HCl, thus posing significant application difficulties and resource consumption issues. Summary of the Invention

[0006] One of the objectives of this invention is to provide a low-temperature plasma cracking method for CO2, a cracking catalyst and its preparation method, which can effectively improve the cracking effect of CO2, facilitate energy conservation and emission reduction, and reduce the cost of CO2 cracking treatment.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] This invention provides a low-temperature plasma cracking catalyst for CO2, which comprises NiFe2O4 crystals and has a specific surface area of ​​3-5 m². 2 ·g -1 The NiFe2O4 crystals have a particle size of 150-200 mesh. By using the catalyst of this invention for low-temperature plasma cracking of CO2, the cracking efficiency of CO2 can be effectively improved.

[0009] Furthermore, the catalyst is obtained by roasting raw materials containing nickel-plating sludge, with an oxygen concentration of 85%-100% in the roasting atmosphere.

[0010] Nickel-containing electroplating sludge has a complex composition, containing not only a significant amount of inorganic oxides such as Fe2O3 and NiO, but also organic polymers such as waste filter cloth (carbon fiber polymer filter cloth) generated during electroplating sludge filtration, as well as inorganic flocculants. Therefore, its rational resource utilization not only contributes to resource recycling but also effectively prevents environmental pollution caused by direct accumulation. This invention involves high-temperature calcination of raw materials containing nickel-containing electroplating sludge to form a catalyst with a NiFe2O4 crystal structure as its main component. This catalyst can effectively improve the plasma cracking effect on CO2 while simultaneously enabling the resource utilization of nickel-containing electroplating sludge.

[0011] It should be noted that controlling the oxygen concentration in the calcination atmosphere is crucial for ensuring the plasma cracking effect of CO2. When the oxygen concentration is higher than 85%, highly crystalline NiFe2O4 crystals can be obtained, and the catalyst as a whole has a blocky structure composed of NiFe2O4 particles. This catalyst can effectively improve the plasma cracking effect of CO2. However, when the oxygen concentration decreases, the microstructure of the catalyst changes significantly. At this time, certain carbon rod structures (formed by calcination of organic polymers from electroplating sludge) will exist in the catalyst, and its catalytic effect on CO2 plasma cracking will decrease significantly.

[0012] This invention also provides a method for preparing a low-temperature plasma pyrolysis catalyst for CO2, comprising:

[0013] The raw materials containing nickel-plating sludge are roasted, and the oxygen concentration in the roasting atmosphere is 85%-100%.

[0014] Furthermore, the calcination conditions include a calcination temperature of 800-1100℃ and a calcination time of 4-6 hours. The higher the calcination temperature and the longer the calcination time, the higher the crystallinity of the resulting catalyst. Therefore, considering both the crystallinity of the resulting catalyst and the production cost, the calcination temperature is controlled at 800-1100℃ and the calcination time at 4-6 hours.

[0015] It should be noted that the raw materials containing electroplating sludge mentioned above may contain only electroplating sludge, or other substances may be added as needed; similarly, the roasting temperature mentioned above includes any numerical range within the range mentioned above, such as 800-900℃, 850-950℃, 900-950℃, or 950-1100℃, as well as any specific value within the range of 800-1100℃, such as 800℃, 850℃, 870℃, 890℃, 900℃, 930℃, 970℃, or 1100℃; similarly, the roasting time can also be selected as 4-5h, 4.5-5.5h, 5-6h, 4h, 4.5h, 5h, 5.5h, or 6h, etc.

[0016] Furthermore, the nickel-containing electroplating sludge contains the following components by mass percentage: Fe2O3: 35.34%-37.62%, NiO: 20.6%-23.02%, SO3: 35.26%-38.26%, SiO2: 5.69%-5.82%, and a carbon content of 25.62%-35.23% (the carbon content was determined by industrial analysis combustion method using an infrared carbon-sulfur analyzer; the carbon in the nickel-containing electroplating sludge mainly comes from organic materials such as carbon fiber polymer filter cloth in the electroplating sludge).

[0017] The present invention also provides a low-temperature plasma pyrolysis method for CO2, comprising:

[0018] Under plasma conditions, CO2 is brought into contact with a catalyst to cause CO2 to be ionized and degraded to produce CO and O2;

[0019] The catalyst used is any catalyst of the present invention, or a catalyst prepared by any preparation method of the present invention.

[0020] This invention employs plasma photoelectric decomposition technology to treat CO2, adding NiFe2O4 crystals as a catalyst. The NiFe2O4 crystals provide more active sites, promoting CO2 activation and thus effectively improving the CO2 decomposition efficiency and effect. Furthermore, during the plasma decomposition of CO2, the catalyst can be activated by the plasma, exciting electrons on the surface of the nickel ferrite catalyst, thereby further promoting CO2 decomposition.

[0021] Furthermore, CO2 ionization degradation occurs at room temperature and pressure. By employing the process of this invention, CO2 can be directly cracked at room temperature and pressure. The process is simple to operate and effectively solves the problems of high energy consumption, low energy efficiency, and potential explosion compared to traditional pyrolysis methods for CO2 cracking. Moreover, CO and O2 are extremely difficult to separate under high-temperature conditions, which incurs additional gas separation costs. This invention enables effective separation of CO and O2 under room temperature and water cooling conditions.

[0022] Furthermore, the catalyst and filler are uniformly mixed together for the ionization and cracking of CO2. The filler includes, but is not limited to, SiO2 glass microspheres; Al2O3, ZrO2, and BaTiO3 microspheres can also be used as filler materials. These filler materials can generate high electron energy density and electric field strength during discharge; simultaneously, they have a large specific surface area, providing more surface for CO2 molecules to adsorb, thereby increasing the contact opportunities between reactants and the catalyst or active sites, and improving the reaction rate. Moreover, and more importantly, the aforementioned filler materials can act as a support, improving the catalyst's dispersibility and preventing catalyst particle agglomeration, thus increasing the number of effective active sites and further improving cracking efficiency.

[0023] Furthermore, the mass ratio of the catalyst to the packing is 2:(120-130), and the diameter of the packing is 0.4mm-0.6mm.

[0024] Furthermore, the pyrolysis reaction is carried out in a coaxial cylindrical water-cooled single-medium barrier reactor.

[0025] Furthermore, the reactor comprises:

[0026] The external electrode is made of a double-layered quartz tube and serves as the grounding electrode;

[0027] The inner electrode, located inside the double-layered quartz tube, is made of stainless steel and serves as the high-voltage electrode.

[0028] The circulating water cooling unit, encased in the outside of a double-layered quartz tube, is used to control the temperature inside the quartz tube.

[0029] Since increasing the reaction temperature promotes the reverse reaction of carbon dioxide cracking, thus affecting the cracking efficiency, a circulating water cooling unit is installed outside the double-layer quartz tube of the outer electrode to control the reaction temperature. This circulating water cooling unit is made of plexiglass.

[0030] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0031] (1) This invention utilizes low-temperature plasma technology to promote CO2 cracking at room temperature, significantly reducing energy consumption in traditional high-temperature catalytic processes, improving energy utilization efficiency, and reducing the need for high-temperature equipment. Furthermore, this invention uses NiFe2O4 spinel crystals as a catalyst during CO2 plasma cracking, effectively promoting CO2 cracking and improving its cracking efficiency and rate. Simultaneously, the stability and regeneration capacity of the catalyst are crucial for the economic viability and sustainability of practical applications. NiFe2O4 exhibits good stability during CO2 cracking and can maintain its activity during long-term catalytic reactions.

[0032] (2) The present invention uses nickel-containing electroplating sludge as raw material and prepares the NiFe2O4 catalyst by high-temperature calcination, thereby effectively realizing the resource utilization of nickel-containing electroplating sludge, improving the efficiency of environmental governance, reducing the dependence on traditional landfill and high-temperature incineration treatment technologies, reducing environmental pollution and resource waste; at the same time, it significantly reduces the production cost of CO2 cracking catalyst, improves the economic efficiency of the entire CO2 conversion process, and enhances the market competitiveness of the technology.

[0033] (3) The present invention uses plasma-coupled NiFe2O4 catalyst technology to crack CO2. The overall process operation and implementation conditions are simple, and CO2 is converted into useful gases, such as carbon monoxide and other chemical substances. This not only helps to reduce greenhouse gas emissions, but also provides a new source of raw materials for the development of sustainable energy. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the plasma pyrolysis experimental device for CO2 in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the structure of the plasma pyrolysis reactor for CO2 in an embodiment of the present invention;

[0036] Figure 3 The scanning structure of the catalyst prepared in Example 1 is shown.

[0037] Figure 4 The scanning structure of the catalyst prepared in Comparative Example 2 is shown.

[0038] Figure 5 The XRD patterns of the catalysts prepared in Example 1 and Comparative Example 2 are shown below.

[0039] Figure 6 The images show the Raman spectra of the catalysts prepared in Example 1 and Comparative Example 2. Detailed Implementation

[0040] Electroplating sludge solid waste is difficult and expensive to treat, and it can also harm human health. Meanwhile, carbon dioxide greenhouse gas emissions are exacerbating global warming, making the reduction of carbon dioxide concentration a pressing global task. To address these issues, this invention directly roasts electroplating sludge to obtain a NiFe2O4 catalyst. This catalyst is placed in a plasma reactor, and carbon dioxide is introduced. The plasma then cracks the carbon dioxide, achieving rapid carbon dioxide decomposition and simultaneously realizing the resource utilization of waste (including nickel-plating sludge), thus reducing environmental pollution. Furthermore, this invention converts CO2 into carbon monoxide (CO) and oxygen (O2), providing an effective solution for reducing atmospheric CO2 concentration and offering a new pathway for energy conversion and storage. Moreover, this invention can perform CO2 decomposition under low-temperature plasma conditions, effectively reducing reaction energy consumption and equipment requirements.

[0041] like Figure 1 The diagram illustrates one example of the CO2 plasma pyrolysis experimental system used in this invention (the actual experimental system and reactor structure are not limited to this). It includes a plasma reactor, a gas supply unit, and a detection unit. The reaction gas (high-purity CO2) is directly supplied from a gas cylinder, and the gas flow rate is controlled by a mass flow meter. The gas enters through the reactor inlet, reacts fully throughout the discharge region, and is then discharged through the outlet as exhaust gas. A CTP-2000K high-frequency AC power supply is used, and the power output voltage is detected by a high-voltage probe connected between the power supply and the high-voltage electrode. The discharge current is measured by a low-voltage probe, which measures the voltage across a 50-ohm external resistor between the reactor and the grounding electrode. Alternatively, to determine the amount of charge accumulated during the discharge process and thus calculate the output power, this external resistor can be replaced with a capacitor for measurement. The types and concentrations of gases before and after the reaction are detected by a gas analysis mass spectrometer (HPR-20R&D).

[0042] like Figure 2 The image shows one example of a plasma reactor, employing a coaxial cylindrical water-cooled single-medium barrier reactor, specifically including:

[0043] The external electrode is made of a double-layered quartz tube and serves as the grounding electrode;

[0044] The inner electrode, located inside the double-layer quartz tube, is made of stainless steel and serves as the high-voltage electrode; specifically, a stainless steel tube is installed inside the double-layer quartz tube, and the stainless steel electrode is placed inside the stainless steel tube.

[0045] The circulating water cooling unit, encased in the outside of a double-layered quartz tube, is used to control the temperature inside the quartz tube.

[0046] The reactor's gas inlet and outlet, as well as water inlet and outlet, are all connected to silicone hoses. The single-sided discharge gap (with the catalyst placed within the discharge gap) is 2 mm, and the effective discharge width is 50 mm. Since increased reaction temperature promotes the reverse reaction of carbon dioxide cracking, thus affecting the cracking efficiency, a circulating water cooling unit, made of plexiglass, is installed outside the double-layered quartz tube of the external electrode to control the reaction temperature.

[0047] To further understand the content of this invention, it will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0048] Example 1

[0049] The CO2 plasma pyrolysis method of this embodiment is operated as follows: 80 mg of catalyst is filled into the plasma reactor; water cooling is turned on (the water cooling temperature is fixed at 20°C), and high-purity carbon dioxide is introduced at a gas flow rate of 30 ml / min. When the air in the reactor is exhausted and the reactor is filled with a high-purity carbon dioxide atmosphere, the plasma generator is turned on to start ionization, and the ionization input power is 100 W.

[0050] The catalyst preparation process in this embodiment is as follows: nickel-containing electroplating sludge is dried, crushed, and placed in a crucible, then placed in a muffle furnace, heated to 1000°C at a rate of 5°C / min, and calcined for 4 hours in a gas atmosphere with an oxygen concentration of 100%. After calcination, the sample is allowed to cool to room temperature.

[0051] In this embodiment, the nickel-containing electroplating sludge is the nickel-containing electroplating sludge generated during the production process of Baosteel Zhanjiang Iron & Steel Co., Ltd., which contains the following components by mass percentage: Fe2O3: 37.62%, NiO: 21.3%, SO3: 35.26%, SiO2: 5.82%, and carbon content of 30.05%.

[0052] The structural morphology and XRD pattern of the catalyst prepared in this embodiment are as follows: Figure 3 , Figure 5 As shown in the attached figures, the main phase of the catalyst in this embodiment is NiFe2O4, and the NiFe2O4 has a high degree of crystallinity. The microstructure of the catalyst is a blocky structure composed of NiFe2O4 particles, and the specific surface area of ​​the catalyst is 3.65 m². 2 ·g -1 The size of NiFe2O4 crystals is 150-200 mesh.

[0053] Example 2

[0054] The CO2 plasma pyrolysis method in this embodiment is basically the same as that in Embodiment 1. The main difference is that in this embodiment, 80 mg of catalyst and 5 g of glass microspheres (0.4 mm-0.6 mm in diameter) are mixed evenly and then placed together in a plasma reactor for carbon dioxide pyrolysis.

[0055] Comparative Example 1

[0056] The plasma pyrolysis process parameters for CO2 in this comparative example are the same as in Example 1. The main difference is that no catalyst or filler is added in this comparative example.

[0057] Comparative Example 2

[0058] The plasma pyrolysis process parameters for CO2 in this comparative example are the same as those in Example 1. The main difference is that the oxygen concentration in the calcination atmosphere is controlled to be 20% when preparing the catalyst in this comparative example.

[0059] like Figure 4 , Figure 5 As shown, the main phase of the catalyst prepared in this comparative example is still NiFe2O4, but its microstructure includes a carbon rod structure (combined with...). Figure 6 Its Raman spectrum shows obvious D and G bands, and the intensity ratio of the two is ID / IG is 1.05, which proves that the catalyst contains a high degree of graphitization structure, as well as NiFe2O4 crystals distributed on the surface of the carbon rod.

[0060] Comparative Example 3

[0061] The plasma pyrolysis process parameters for CO2 in this comparative example are the same as those in Example 2. The main difference is that the oxygen concentration in the calcination atmosphere is controlled to be 20% when preparing the catalyst in this comparative example.

[0062] The exhaust gas was collected during the ionization process, and the concentrations of carbon dioxide, carbon monoxide, and oxygen in the exhaust gas of Examples 1, 2, and Comparative Examples 1-3 were detected online in real time using a gas analysis mass spectrometer (HPR-20R&D) to determine the CO2 cracking effect. The detection results are shown in Tables 1-5. According to the data in the tables, by controlling the oxygen concentration in the catalyst preparation process to be in a high concentration range (greater than 85%), the plasma catalytic cracking effect of the catalyst on carbon dioxide can be effectively guaranteed, and the composite addition of the catalyst and glass microspheres can further improve the catalytic effect.

[0063] Table 1 Gas conversion concentration in Example 1

[0064] Time / min <![CDATA[O2 / %]]> CO / % <![CDATA[CO2 / %]]> 5 4.73 9.9 85.36 10 4.8 10.05 85.15 15 4.83 10.13 85.03

[0065] Table 2 Gas Conversion Concentration in Example 2

[0066] Time / min <![CDATA[O2 / %]]> CO / % <![CDATA[CO2 / %]]> 5 5.14 11 83.85 510 5.16 11.1 83.74 1015 5.17 11.14 83.67

[0067] Table 3 Comparative Example 1 Gas Conversion Concentration

[0068] Time / min <![CDATA[O2 / %]]> CO / % <![CDATA[CO2 / %]]> 5 2.26 4.53 93.21 10 2.31 4.6 93.09 15 2.34 4.64 93.03

[0069] Table 4 Gas Conversion Concentration (Comparative Example 2)

[0070]

[0071]

[0072] Table 5 Gas Conversion Concentration in Comparative Example 3

[0073] Time / min <![CDATA[O2 / %]]> CO / % <![CDATA[CO2 / %]]> 5 3.46 9.52 87.02 10 3.49 9.58 86.93 15 3.51 9.61 86.88

[0074] Example 3

[0075] The CO2 plasma pyrolysis method in this embodiment is basically the same as that in Embodiment 1, with the main difference being: in this embodiment, the calcination temperature is controlled at 1100℃, the calcination time is 5h, the oxygen concentration in the calcination atmosphere is 90%, and the particle size of the nickel-plating sludge particles is 400 mesh. The nickel-plating sludge in this embodiment contains the following components by mass percentage: Fe2O3: 35.97%, NiO: 23.02%, SO3: 35.32%, SiO2: 5.69%, and a carbon content of 35.23%. Simultaneously, the carbon dioxide inlet flow rate in the reactor is controlled at 35ml / min, the ionization input power is 110W, and the catalyst addition amount is 90mg.

[0076] Example 4

[0077] The CO2 plasma pyrolysis method in this embodiment is basically the same as that in Embodiment 1, with the main differences being: the roasting temperature in this embodiment is 800℃, the roasting time is 6h, the oxygen concentration in the roasting atmosphere is 85%, and the particle size of the nickel-containing electroplating sludge is 300 mesh. The nickel-containing electroplating sludge in this embodiment contains the following components by mass percentage: Fe2O3: 35.34%, NiO: 20.6%, SO3: 38.26%, SiO2: 5.8%, and a carbon content of 25.62%. Simultaneously, the carbon dioxide inlet flow rate in the reactor is controlled at 40ml / min, the ionization input power is 120W, and the catalyst addition amount is 100mg.

[0078] Example 5

[0079] The CO2 plasma pyrolysis method in this embodiment is basically the same as that in Embodiment 2, with the main difference being: the roasting temperature in this embodiment is 850℃, the roasting time is 6h, and the nickel-containing electroplating sludge in this embodiment contains the following components by mass percentage: Fe2O3: 35.34%, NiO: 20.6%, SO3: 38.26%, SiO2: 5.8%, and the carbon content is 25.62%. Simultaneously, the carbon dioxide inlet flow rate in the reactor is controlled at 40ml / min, the ionization input power is 120W, the catalyst addition is 100mg, and the glass microsphere addition is 4g.

[0080] In summary, this invention proposes a technology for cracking carbon dioxide using a catalyst prepared from electroplating sludge under low-temperature plasma conditions. This technology not only realizes the transformation of electroplating sludge into a valuable resource and the cracking of carbon dioxide, but also achieves rapid cracking and conversion at room temperature. The carbon monoxide and oxygen generated by this technology have important roles and applications in various fields such as industrial production, energy conversion, environmental protection, and life support.

Claims

1. A low-temperature plasma cracking catalyst for CO2, characterized in that, The catalyst contains NiFe2O4 crystals and has a specific surface area of ​​3-5 m². 2 ·g -1 The particle size of NiFe2O4 crystals is 150-200 mesh; the catalyst is obtained by roasting raw materials containing nickel electroplating sludge, and the oxygen concentration in the roasting atmosphere is 85%-100%.

2. A method for preparing a low-temperature plasma cracking catalyst for CO2, characterized in that, include: The raw materials containing nickel-plating sludge are roasted, and the oxygen concentration in the roasting atmosphere is 85%-100%.

3. The method for preparing the low-temperature plasma cracking catalyst for CO2 according to claim 2, characterized in that, The roasting conditions include: a roasting temperature of 800-1100℃ and a roasting time of 4-6 hours.

4. A method for low-temperature plasma pyrolysis of CO2, characterized in that, include: Under plasma conditions, CO2 is brought into contact with a catalyst to cause CO2 to be ionized and degraded to produce CO and O2; The catalyst is the catalyst described in claim 1, or the catalyst prepared by the preparation method of claim 2 or 3.

5. The low-temperature plasma pyrolysis method for CO2 according to claim 4, characterized in that, CO2 ionization degradation occurs at room temperature and pressure.

6. The low-temperature plasma pyrolysis method for CO2 according to claim 4 or 5, characterized in that, The catalyst and filler are mixed uniformly for the ionization and cracking of CO2. The filler includes, but is not limited to, SiO2 glass microspheres, Al2O3, ZrO2 or BaTiO3 microspheres.

7. The low-temperature plasma pyrolysis method for CO2 according to claim 6, characterized in that, The mass ratio of the catalyst to the packing is 2:(120-130), and the diameter of the packing is 0.4mm-0.6mm.

8. The low-temperature plasma pyrolysis method for CO2 according to claim 6, characterized in that, The pyrolysis reaction is carried out in a coaxial cylindrical water-cooled single-medium barrier reactor.

9. The low-temperature plasma pyrolysis method for CO2 according to claim 8, characterized in that, The reactor includes: The external electrode is made of a double-layered quartz tube and serves as the grounding electrode; The inner electrode, located inside the double-layered quartz tube, is made of stainless steel and serves as the high-voltage electrode. The circulating water cooling unit, encased in the outside of a double-layered quartz tube, is used to control the temperature inside the quartz tube.

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