Adsorbent for capturing industrial waste gas carbon dioxide as well as preparation method and application thereof

Abstract

The invention discloses an adsorbent for trapping industrial waste gas carbon dioxide as well as a preparation method and application thereof, and relates to the technical field of carbon dioxide trapping. According to the technical scheme, the preparation method comprises the following steps: S1, activating rice straws or wood chips with KOH to prepare porous biochar; s2, performing in-situ growth of a Cu-BTC MOF layer on the surface of the biochar through a hydrothermal method; s3, grafting a polyethyleneimine-polyethylene glycol copolymer on the surface of the charcoal modified by the Cu-BTC MOF layer; and S4, mixing the material obtained in the step S3 with the nano ZnO / carbon quantum dot compound to obtain the adsorbent for capturing industrial waste gas carbon dioxide. According to the prepared adsorbent, the CO2 adsorption capacity is larger than 1.8 mmol / g in the high-humidity (85% RH) environment, and compared with a traditional amino adsorbent, the CO2 adsorption capacity is greatly improved; after 1500 times of circulation, the CO2 adsorption capacity retention rate is greater than 90%, and the high-efficiency and low-consumption carbon capture adsorbent is constructed.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide capture, and particularly relates to an adsorbent for capturing carbon dioxide from industrial waste gas, a preparation method thereof, and an application thereof. Background Art

[0002] The mainstream CO2 capture technologies in the current industrial field are mainly divided into chemical absorption method, physical adsorption method and membrane separation method. However, these technologies all have some key bottlenecks in practical applications, which limit their large-scale popularization and application.

[0003] (1) Chemical absorption method (amine method)

[0004] The chemical absorption method is the most widely used CO2 capture technology at present. It mainly uses amine solvents (such as monoethanolamine MEA, diethanolamine DEA, etc.) to react with CO2 for capture, but this method has the following problems:

[0005] High energy consumption: The main energy consumption of the amine method for capturing CO2 comes from the regeneration process of the solvent. In the regeneration stage, the solvent rich in CO2 needs to be heated to above 110 - 120 °C to desorb CO2 and recycle the solvent. This process usually consumes a large amount of steam, and the energy consumption is as high as 3 - 4 GJ / ton of CO2, accounting for more than 70% of the overall operating cost. Such high energy consumption leads to high capture costs and seriously restricts the economy of this technology.

[0006] Environmental pollution: Amine solvents are volatile, and inevitably some solvent losses will occur during the absorption and regeneration processes. The annual loss rate usually exceeds 15%. These volatile amine substances not only cause economic losses, but also pollute the environment. In addition, toxic by-products such as nitrosamines will be produced during the oxidation of amine solvents, further exacerbating the environmental pollution problem.

[0007] Equipment corrosion: Industrial tail gases such as coal-fired flue gas usually contain a certain amount of acidic gases (such as SO2, NO x etc.), and these acidic gases will react with amine solvents during the wet absorption process, exacerbating the corrosion of equipment such as absorption towers. In actual operation, the corrosion rate of the absorption tower often exceeds 0.5 mm / year, which not only increases the equipment maintenance cost, but also shortens the service life of the equipment, posing a safety hazard.

[0008] (2) Physical adsorption method

[0009] The physical adsorption method uses the surface adsorption of porous solid materials (such as zeolites, activated carbon, etc.) to capture CO2. This method has the following problems:

[0010] Humidity sensitivity: Water vapor in flue gas competes with CO2 for adsorption sites, reducing the CO2 adsorption capacity of the adsorbent. Especially when the ambient relative humidity (%RH) exceeds 70%, the attenuation of the adsorbent's adsorption capacity often exceeds 50%, seriously affecting the capture efficiency.

[0011] Poor cycle stability: During multiple adsorption-desorption cycles of the adsorbent, its microstructure will change to a certain extent, resulting in a decline in adsorption performance. For example, after 500 cycles, the micropore collapse rate of zeolite materials often exceeds 30%, seriously affecting their long-term use performance.

[0012] High regeneration energy consumption: Physical adsorption methods usually use temperature swing adsorption (TSA) or pressure swing adsorption (PSA) for regeneration. Among them, TSA requires heating the adsorbent to 120 - 150 °C to desorb the adsorbed CO2. This process consumes a large amount of thermal energy, and the energy consumption usually exceeds 1.5 MJ / kg CO2, increasing the capture cost.

[0013] (3) Membrane separation method

[0014] The membrane separation method uses the permeation selectivity of the membrane to separate CO2 from other gases. The following problems exist in this method:

[0015] Limited selectivity: The selectivity of currently commercial polymer membrane materials for CO2 / N2 is generally lower than 100, making it difficult to meet the requirements for low-concentration CO2 capture. Especially when dealing with low-concentration CO2 (usually lower than 15%) from emission sources such as coal-fired power plants, the capture efficiency and purity are difficult to meet the requirements.

[0016] Weak anti-pollution ability: Flue gas often contains a certain amount of pollutants such as dust and organic vapors. These pollutants will deposit on the membrane surface or block the membrane pores, resulting in a decrease in membrane flux. In actual operation, the annual attenuation rate of membrane flux often exceeds 20%, seriously affecting the long-term stable operation of the membrane separation system.

[0017] In summary, the existing CO2 capture technologies all have some insurmountable bottlenecks in practical applications. It is urgent to develop new capture technologies or improve existing technologies to meet the increasingly strict carbon emission control requirements. Summary of the invention

[0018] The technical problem to be solved by the present invention is: To overcome the deficiencies of the prior art, provide an adsorbent for capturing carbon dioxide from industrial waste gas, its preparation method and application. In a high-humidity (85% RH) environment, the CO2 adsorption capacity > 1.8 mmol / g, which is greatly improved compared to traditional amine-based adsorbents; after 1500 cycles, the CO2 adsorption capacity retention rate > 90%, constructing an efficient and low-consumption carbon capture adsorbent.

[0019] The technical solution of the present invention is:

[0020] In a first aspect, the present invention provides a method for preparing an adsorbent for capturing carbon dioxide from industrial waste gas, comprising the following steps:

[0021] S1 Preparation of porous biochar by KOH activation of rice straw or sawdust;

[0022] S2 in situ grows a Cu-BTC MOF layer on the biochar surface by a hydrothermal method to form a hydrophobic barrier that selectively blocks the penetration of water molecules;

[0023] S3 grafted polyethyleneimine (PEI)-polyethylene glycol (PEG) copolymer on the surface of biochar modified with Cu-BTC MOF layer to form a humidity-responsive adsorption interface; when RH < 60%, the PEG chain segments shrank, exposing the PEI amine groups to enhance CO2 chemical adsorption; 60-70% RH: PEG began to absorb water and swell, forming local hydrophilic microdomains, but did not fully expand, and some amine groups (-NH2) were still exposed; 70-80% RH: PEG further expanded, covering more amine sites, but still keeping the microporous channels open; CO2 adsorption path: water molecules preferentially occupy macropores / mesopores → CO2 diffuses through micropores to amine sites (the diffusion rate decreases by about 30%); when RH > 80%, PEG absorbs water and swells, forming hydrophilic microdomains to isolate liquid water and maintain amine activity;

[0024] S4: The material obtained in step S3 is mixed with the nano ZnO / carbon quantum dot composite, which can trigger the ZnO / carbon quantum dot composite through the photothermal effect during the adsorbent regeneration stage. 2+ Migrate and repair the surface defects of the adsorbent to obtain an adsorbent for capturing industrial waste gas carbon dioxide.

[0025] Preferably, the specific operation of step S1 is: crushing rice straw or sawdust to 60-100 mesh, mixing with KOH in a mass ratio of 1:(1-4), carbonizing at 500-800° C. for 1-2 h under a nitrogen atmosphere, and acid washing to remove ash to obtain porous biochar.

[0026] Preferably, the specific operation of step S2 is: immersing the biochar in a solution of copper nitrate and trimesic acid, wherein the solvent of the solution is a mixed solvent of ethanol, DMF and H2O in a volume ratio of (0.5-1.5):(0.5-1.5):1, and hydrothermal reaction after ultrasound to form a Cu-BTC MOF layer; the concentration of copper nitrate and trimesic acid in the solution is 0.1-0.5 mol / L; the hydrothermal reaction temperature is 85-120°C, and the time is 6-12h; the thickness of the Cu-BTC MOF layer is 20-30nm, and the pore diameter is 0.7-0.9nm.

[0027] Preferably, the specific operation of step S3 is as follows: spraying a polyethyleneimine-polyethylene glycol copolymer solution on the surface of the biochar modified with the Cu-BTC MOF layer, and drying it under vacuum; wherein, the solvent of the polyethyleneimine-polyethylene glycol copolymer solution is ethanol, the molar ratio of polyethyleneimine to polyethylene glycol is 1:(0.5-2), and the concentration of the polyethyleneimine-polyethylene glycol copolymer solution is 2-3 wt.%; the vacuum drying temperature is 40-60 °C, and the time is 6-12 h.

[0028] Preferably, the specific operation of step S4 is as follows: adding the nano-ZnO / carbon quantum dot composite into the material obtained in step S3 at 2-5 wt.%, and ball-milling and mixing evenly; wherein, the preparation method of the nano-ZnO / carbon quantum dot composite is as follows:

[0029] (1) Preparation of carbon quantum dots: Dissolve the carbon source in water and place it in a high-pressure reaction kettle, carry out hydrothermal reaction at 180-200 °C for 4-8 h, and obtain a carbon quantum dot (CQDs) solution after centrifugal purification;

[0030] (2) Synthesis of nano-ZnO / carbon quantum dot composite: Mix the zinc salt with the carbon quantum dot solution, add a precipitant to adjust the pH to alkaline, transfer it to a high-pressure reaction kettle, carry out hydrothermal reaction at 120-180 °C for 6-12 h, and the ZnO nanoparticles grow in-situ on the surface of the carbon quantum dots to form a nano-ZnO / carbon quantum dot composite;

[0031] (3) Post-treatment: Centrifuge and wash the nano-ZnO / carbon quantum dot composite to neutrality, and freeze-dry to obtain a nano-ZnO / carbon quantum dot composite powder.

[0032] Preferably, in step (1), the carbon source is citric acid or glucose; in step (2), the zinc salt is zinc nitrate, the precipitant is NaOH or ammonia water, and the pH is adjusted to 9.5-10.5.

[0033] In a second aspect, the present invention provides an adsorbent for capturing carbon dioxide from industrial waste gas, which is prepared by the above-mentioned preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas.

[0034] In a third aspect, the present invention provides the application of the above-mentioned adsorbent for capturing carbon dioxide from industrial waste gas. The adsorbent is respectively filled in absorption tower 1, absorption tower 2 and absorption tower 3. First, introduce the industrial waste gas containing carbon dioxide into absorption tower 1. When the adsorbent therein adsorbs carbon dioxide to reach the saturation state, switch the industrial waste gas to absorption tower 2. At the same time, regenerate the adsorbent in absorption tower 1. When the adsorbent in absorption tower 2 reaches the saturation state, switch the industrial waste gas to absorption tower 1 again, and use the regenerated adsorbent to capture and adsorb carbon dioxide in the industrial waste gas again, and so on; absorption tower 3 is used as a standby tower.

[0035] Preferably, the adsorbent regeneration method is as follows: microwave generators and heat exchange tubes are arranged in Absorption Tower 1, Absorption Tower 2 and Absorption Tower 3. The inlet section of the heat exchange tube is arranged on the outer wall of the tower, and the inner wall of the inlet section is coated with CuS@SiO2 nanoparticles to form a photothermal coating. Industrial waste gas is introduced into the inlet section, and the solar energy is converted into heat energy by microwave radiation and the photothermal coating, and the waste heat of the industrial waste gas is used to heat the saturated adsorbent to desorb the adsorbed carbon dioxide.

[0036] Preferably, the desorbed carbon dioxide is used to synthesize methanol together with the H2 produced by electrolyzing water; or the desorbed carbon dioxide is directly hydrogenated to produce formic acid.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention firstly creates an adsorbent with a biochar-MOF-polymer gradient structure, overcoming the problem of adsorbent deactivation in a high-humidity environment. The prepared adsorbent for capturing carbon dioxide from industrial waste gas has a CO2 adsorption capacity >

[0039] 1.8 mmol / g in a high-humidity (85% RH) environment, which is greatly improved compared with traditional amine-based adsorbents; the CO2 / N2 selectivity > 200, and the CO2 adsorption capacity retention rate > 90% after 1500 cycles, constructing an efficient and low-consumption carbon capture adsorbent.

[0040] 2. The regeneration energy consumption of the adsorbent prepared by the present invention < 0.7 MJ / kg CO2, and the energy consumption is greatly reduced compared with the traditional amine method; at the same time, the waste heat of industrial waste gas is utilized during regeneration, and the annual steam cost savings > 300,000 US dollars (calculated based on a scale of 100,000 tons / year).

[0041] 3. The present invention uses a synergistic desorption mechanism to desorb and regenerate the carbon dioxide adsorbed by the adsorbent. By selectively exciting the vibration of CO2 molecules by microwaves, the desorption activation energy is reduced; the local high temperature is provided by the photothermal effect to avoid the energy consumption of overall heating; the preheating of industrial waste gas is utilized to avoid energy waste.

[0042] 4. The carbon dioxide adsorbed by the adsorbent of the present invention can be used to synthesize methanol and formic acid after regeneration, which can offset 35% of the operating cost by the sales income of methanol / formic acid; the comprehensive capture cost ≤ 30 USD / ton CO2; the service life of the adsorbent is extended to 5 years, and the operation and maintenance cost is reduced. Description of the Drawings

[0043] Figure 1 It is a SEM image of the adsorbent for capturing carbon dioxide from industrial waste gas prepared in Example 1 of the present invention.

[0044] Figure 2 It is a schematic structural diagram of the carbon dioxide capture system for industrial waste gas of the present invention.

[0045] In the figure, 1 is the first absorption tower; 2 is the second absorption tower; 3 is the third absorption tower; 4 is the microwave generator; 5 is the carbon dioxide storage tank; 6 is the compressor; 7 is the reactor; 8 is the methanol storage tank. Specific implementation method

[0046] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention.

[0047] Example 1

[0048] The preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas in this embodiment includes the following steps:

[0049] S1 Crush rice straw to 80 mesh, mix it with KOH according to a mass ratio of 1:1, carbonize it at 600 °C for 1 h under a nitrogen atmosphere, and remove ash by pickling to obtain porous biochar with a specific surface area of 1920 m 2 / g;

[0050] S2 Immerse the biochar in a solution of 0.1 mol / L copper nitrate and trimesic acid (the solvent is a mixed solvent of ethanol, DMF and H2O with a volume ratio of 0.5:0.5:1), and carry out a hydrothermal reaction at 120 °C for 6 h to in-situ generate a Cu-BTC MOF layer with a thickness of 20 nm and a pore size of 0.82 nm on the surface of the biochar;

[0051] S3 Spray a PEI-PEG copolymer solution on the surface of the biochar modified with the Cu-BTC MOF layer, and vacuum dry it at 60 °C for 6 h to form a humidity-responsive adsorption interface; among them, the solvent of the PEI-PEG copolymer solution is ethanol, the molar ratio of polyethyleneimine to polyethylene glycol is 1:0.5, and the concentration of the PEI-PEG copolymer solution is 2.5 wt.%;

[0052] S4 Add the nano-ZnO / carbon quantum dot composite (particle size 5 nm) to the material obtained in step S3 at 3 wt.%, and mix evenly by ball milling to obtain the adsorbent for capturing carbon dioxide from industrial waste gas; among them, the preparation method of the nano-ZnO / carbon quantum dot composite is as follows:

[0053] (1) Preparation of carbon quantum dots: Dissolve 50 g of glucose in 1000 mL of water, place it in a reaction kettle, carry out a hydrothermal reaction at 190 °C for 5 h, and obtain a carbon quantum dot solution after centrifugal purification;

[0054] (2) Synthesis of nano-ZnO / carbon quantum dot composite: Mix zinc nitrate with the carbon quantum dot solution, where the zinc nitrate is calculated as ZnO, and the mass ratio of ZnO to the carbon quantum dot solution is 5:1; add NaOH to adjust the pH to 10, transfer it to a reaction kettle, and carry out hydrothermal reaction at 150 °C for 8 h. The ZnO nanoparticles grow in-situ on the surface of the carbon quantum dots to form a nano-ZnO / carbon quantum dot composite;

[0055] (3) Post-treatment: Centrifuge and wash the nano-ZnO / carbon quantum dot composite until it is neutral, and then freeze-dry to obtain the nano-ZnO / carbon quantum dot composite powder.

[0056] The SEM image of the adsorbent for capturing carbon dioxide from industrial waste gas prepared in this example is as Figure 1 shown. It can be seen from Figure 1 that the adsorbent prepared in this example consists of biochar, a Cu-BTC MOF layer, and a PEI-PEG copolymer layer from the inside out. The nano-ZnO / carbon quantum dot composite is evenly distributed in the PEI-PEG copolymer layer.

[0057] Example 2

[0058] The preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas in this example includes the following steps:

[0059] S1 Crush rice straw to 100 mesh, mix it with KOH in a mass ratio of 1:4, carbonize it at 800 °C for 1 h under a nitrogen atmosphere, and remove the ash by acid washing to obtain porous biochar with a specific surface area of 1780 m 2 / g;

[0060] S2 Immerse the biochar in a solution of 0.5 mol / L copper nitrate and trimesic acid (the solvent is a mixed solvent of ethanol, DMF, and H2O with a volume ratio of 1.5:1.5:1), and carry out hydrothermal reaction at 85 °C for 12 h to in-situ generate a Cu-BTC MOF layer with a thickness of 30 nm and a pore size of 0.87 nm on the surface of the biochar;

[0061] S3 Spray the PEI-PEG copolymer solution on the surface of the biochar modified with the Cu-BTC MOF layer, and vacuum dry it at 40 °C for 12 h to form a humidity-responsive adsorption interface; among them, the solvent of the PEI-PEG copolymer solution is ethanol, the molar ratio of polyethyleneimine to polyethylene glycol is 1:1, and the concentration of the PEI-PEG copolymer solution is 3 wt.%;

[0062] S4 Add the nano-ZnO / carbon quantum dot composite (particle size 5 nm) to the material obtained in step S3 at 5 wt.%, and mix it evenly by ball milling to obtain the adsorbent for capturing carbon dioxide from industrial waste gas; among them, the preparation method of the nano-ZnO / carbon quantum dot composite is as follows:

[0063] (1) Preparation of carbon quantum dots: Dissolve 50 g of glucose in 1000 mL of water, place it in a reaction kettle, carry out hydrothermal reaction at 200 °C for 4 h, and obtain a carbon quantum dot solution after centrifugation and purification;

[0064] (2) Synthesis of nano-ZnO / carbon quantum dot composite: Mix zinc nitrate with the carbon quantum dot solution, where zinc nitrate is calculated as ZnO, and the mass ratio of ZnO to the carbon quantum dot solution is 5:1; Add NaOH to adjust the pH to 10, transfer it to a reaction kettle, carry out hydrothermal reaction at 180 °C for 6 h, and in-situ growth of ZnO nanoparticles on the surface of carbon quantum dots to form nano-ZnO / carbon quantum dot composite;

[0065] (3) Post-treatment: Centrifuge and wash the nano-ZnO / carbon quantum dot composite to neutrality, and freeze-dry to obtain nano-ZnO / carbon quantum dot composite powder.

[0066] Example 3

[0067] The preparation method of the adsorbent for capturing carbon dioxide in industrial waste gas in this example includes the following steps:

[0068] S1 Crush rice straw to 60 mesh, mix it with KOH according to a mass ratio of 1:3, carry out carbonization at 500 °C for 2 h under a nitrogen atmosphere, and remove ash by acid washing to obtain porous biochar with a specific surface area of 1920 m 2 / g;

[0069] S2 Immerse the biochar in a solution of 0.2 mol / L copper nitrate and trimesic acid (the solvent is a mixed solvent of ethanol, DMF and H2O with a volume ratio of 1:1:1), carry out hydrothermal reaction at 100 °C for 10 h, and in-situ generate a Cu-BTC MOF layer with a thickness of 23 nm and a pore size of 0.78 nm on the surface of the biochar;

[0070] S3 Spray the PEI-PEG copolymer solution on the surface of the biochar modified with the Cu-BTC MOF layer, and vacuum dry at 50 °C for 8 h to form a humidity-responsive adsorption interface; Among them, the solvent of the PEI-PEG copolymer solution is ethanol, the molar ratio of polyethyleneimine to polyethylene glycol is 1:2, and the concentration of the PEI-PEG copolymer solution is 2 wt.%;

[0071] S4 Add the nano-ZnO / carbon quantum dot composite (particle size 5 nm) to the material obtained in step S3 at 2 wt.%, and ball mill and mix evenly to obtain the adsorbent for capturing carbon dioxide in industrial waste gas; Among them, the preparation method of the nano-ZnO / carbon quantum dot composite is as follows:

[0072] (1) Preparation of carbon quantum dots: Dissolve 50 g of citric acid in 1000 mL of water, place it in a reaction kettle, carry out hydrothermal reaction at 180 °C for 8 h, and obtain a carbon quantum dot solution after centrifugation and purification;

[0073] (2) Synthesis of nano-ZnO / carbon quantum dot composite: Mix zinc nitrate with the carbon quantum dot solution, where the zinc nitrate is calculated as ZnO, and the mass ratio of ZnO to the carbon quantum dot solution is 5:1; add ammonia water to adjust the pH to 10, transfer it to a reaction kettle, and carry out hydrothermal reaction at 120 °C for 12 h. The ZnO nanoparticles grow in-situ on the surface of the carbon quantum dots to form a nano-ZnO / carbon quantum dot composite;

[0074] (3) Post-treatment: Centrifuge and wash the nano-ZnO / carbon quantum dot composite until it is neutral, and then freeze-dry to obtain the nano-ZnO / carbon quantum dot composite powder.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that step S2 is not carried out.

[0077] Comparative Example 2

[0078] The difference from Example 1 is that step S3 is not carried out.

[0079] Comparative Example 3

[0080] The difference from Example 1 is that in step S3, PEI is used to replace PEG in an equimolar amount.

[0081] Comparative Example 4

[0082] The difference from Example 1 is that in step S3, PEG is used to replace PEI in an equimolar amount.

[0083] Comparative Example 5

[0084] The difference from Example 1 is that step S4 is not carried out.

[0085] ] Example 4

[0086] Use the adsorbents prepared in Examples 1-3 and Comparative Examples 1-5 to adsorb carbon dioxide in industrial waste gas. The specific operation is as follows:

[0087] As Figure 2 shown, load them into Absorption Tower 1, Absorption Tower 2, and Absorption Tower 3 respectively. First, introduce the industrial waste gas containing carbon dioxide into Absorption Tower 1. When the adsorbent in it adsorbs carbon dioxide to reach the saturation state, switch the industrial waste gas to Absorption Tower 2. At the same time, regenerate the adsorbent in Absorption Tower 1. When the adsorbent in Absorption Tower 2 reaches the saturation state, switch the industrial waste gas to Absorption Tower 1 again, and use the regenerated adsorbent to capture and adsorb carbon dioxide in the industrial waste gas again, and so on; Absorption Tower 3 is used as a standby tower.

[0088] Use the above adsorption system for capturing carbon dioxide in industrial waste gas to test the capacity and stability of the adsorbents prepared in Examples 1-3. The test method is as follows:

[0089] (1) Static volumetric method (volumetric method / gravimetric method):

[0090] Equipment: High-pressure gas sorption analyzer (such as Micromeritics ASAP 2020), quartz spring microbalance;

[0091] Testing process:

[0092] 1) Pretreatment: The adsorbent sample is degassed at 150 °C under vacuum (≤10 -3 Pa) for 6 h to remove surface adsorbates;

[0093] 2) Isotherm determination: Set the target temperature (such as 25 °C), gradually introduce CO2 gas (purity ≥99.999%), and record the pressure-adsorption amount change data;

[0094] 3) Model fitting: Use the Langmuir or BET equation to calculate the saturated adsorption capacity (mmol / g).

[0095] (2) Testing method for stability

[0096] The adsorbent sample is subjected to repeated adsorption / desorption, and then the change in adsorption amount is detected.

[0097] After testing, the capacity and stability test results of the adsorbents prepared in Examples 1-3 and Comparative Examples 1-5 are shown in Table 1:

[0098] Table 1 Capacity and stability test results of the adsorbents prepared in Examples 1-3 and Comparative Examples 1-5

[0099]

[0100]

[0101] As can be seen from Table 1, compared with Example 1, the capacity and stability of the adsorbents prepared in Comparative Examples 1-5 have decreased significantly. This is because in Comparative Example 1, the Cu-BTC MOF layer was not formed, resulting in the loss of its hydrophobic effect, which led to a decrease in adsorption amount and stability. In Comparative Example 2, the PEI-PEG copolymer layer was not formed, thus affecting the adsorption amount and stability of the adsorbent. In Comparative Example 3, PEG was not added during the preparation of the PEI-PEG copolymer layer, causing the adsorbent to be unable to isolate moisture in a high-humidity environment, resulting in a decrease in adsorption amount and stability. In Comparative Example 4, PEI was not added during the preparation of the PEI-PEG copolymer layer, causing the CO2 adsorption capacity of the adsorbent to decrease. In Comparative Example 5, the self-healing effect of the nano-ZnO / carbon quantum dot composite was lacking, resulting in a significant decrease in the stability of the adsorbent.

[0102] Example 5

[0103] After the adsorbent in Absorption Tower 1 reaches saturation in adsorbing carbon dioxide, the industrial waste gas is switched to Absorption Tower 2, and at the same time, the adsorbent in Absorption Tower 1 is regenerated. The method for regenerating the adsorbent is as follows: Figure 2 As shown, microwave generators (frequency of 2.45 GHz, power density of 1.5 W / g, penetration depth up to 30 cm) and heat exchange tubes are provided in Absorption Tower 1, Absorption Tower 2, and Absorption Tower 3. The inlet section of the heat exchange tube is arranged on the outer wall of the tower, and the inner wall of the inlet section is coated with CuS@SiO2 nanoparticles to form a photothermal coating. The thickness of the photothermal coating is 50 nm, which absorbs 808 nm near-infrared light; and industrial waste gas is introduced into the inlet section. Using microwave radiation and the photothermal coating, solar energy and the waste heat of the industrial waste gas are converted into heat energy to heat the saturated adsorbent to 60 °C, so that the adsorbed carbon dioxide is desorbed. The desorption efficiency reaches 98.2%, and the energy consumption is 0.62 MJ / kgCO2.

[0104] Among them, the preparation method of CuS@SiO2 nanoparticles is as follows:

[0105] 1) Preparation of precursor solution: Dissolve 0.1 mol / L copper nitrate (Cu(NO3)2·3H2O) and 0.15 mol / L thiourea (CH4N2S) in a mixed solvent of ethylene glycol (EG) and deionized water (volume ratio 3:1); add 0.5% (w / v) polyvinylpyrrolidone (PVP) as a surfactant and stir for 30 min;

[0106] 2) Solvothermal reaction: Transfer to a high-pressure reaction kettle and react at 180 °C for 12 h;

[0107] 3) Surface modification (enhanced SiO2 coating): Disperse 5 g of CuS generated in step 2) in 50 mL of ethanol, add 0.5 mL of aminopropyltriethoxysilane (APTES), and ultrasonicate for 1 h to modify the surface of CuS with amino groups;

[0108] 4) SiO2 shell coating: Disperse the modified CuS in 100 mL of ethanol, add 5 mL of 28% ammonia water and 2 mL of tetraethyl orthosilicate (TEOS), and stir at room temperature for 12 h;

[0109] 5) Post-treatment: Centrifuge and wash (alternately wash 3 times with ethanol / water), and vacuum dry at 60 °C for 6 h to obtain CuS@SiO2 nanoparticles.

[0110] Comparative Example 6

[0111] The difference from Example 5 lies in that the adsorbent regeneration method is as follows: Electric heating wires are arranged on Absorption Tower 1, Absorption Tower 2, and Absorption Tower 3. The saturated adsorbent is heated to 60 °C by electric heating, so that the adsorbed carbon dioxide is desorbed. The desorption efficiency reaches 96.8%, and the energy consumption is 1.55 MJ / kgCO2.

[0112] By comparing the two adsorbent regeneration methods of Example 5 and Comparative Example 6, it can be seen that the regeneration method of Example 5 can greatly improve the regeneration efficiency and reduce the energy consumption.

[0113] Example 6

[0114] The carbon dioxide desorbed in Example 5 is used for methanol synthesis. The specific process is as follows: The desorbed CO2 is temporarily stored in a carbon dioxide storage tank through a compressor. The catalyst Cu-ZnO-Al2O3 / SSZ-13 is loaded into the reactor, and electrolytic hydrogen production H2 is introduced into the reactor through a pipeline. At 220 °C and 5 MPa, H2 and the desorbed CO2 with a molar ratio of 3:1 are introduced into the reactor. The preparation method of the catalyst Cu-ZnO-Al2O3 / SSZ-13 includes the following steps:

[0115] (1) Material pretreatment

[0116] 1) Activation of the SSZ-13 molecular sieve support: The SSZ-13 molecular sieve support (mass ratio of SiO2 to Al2O3 is 20:1) is calcined in a muffle furnace at 550 °C for 4 h;

[0117] 2) Preparation of the metal precursor: A nitrate mixed solution (0.5 mol / L) is prepared according to the molar ratio of Cu:Zn:Al = 6:3:1.

[0118] (2) Ultrasound-assisted impregnation

[0119] The activated SSZ-13 molecular sieve support is immersed in the metal salt solution and ultrasonically treated at 40 kHz for 30 min (power 300 W); Urea is added as a precipitant (molar ratio of metal ions to urea is 1:3);

[0120] (3) Microwave hydrothermal crystallization

[0121] Transfer to a polytetrafluoroethylene reaction kettle, and perform microwave-assisted hydrothermal treatment (180 °C, 2 h, 2.45 GHz) to form a ZnAl-LDH intermediate phase @SSZ-13;

[0122] (4) Temperature-programmed reduction

[0123] The ZnAl-LDH intermediate phase @SSZ-13 is first heated to 350 °C at a rate of 2 °C / min and calcined for 2 h, and a H2 / Ar mixed gas (H2 content is 5 wt.%) is introduced and reduced at 250 °C for 3 h to obtain Cu0 Nanoparticles;

[0124] (5) Surface modification

[0125] Trimethylaluminum was deposited by vapor phase (150 °C, 1 h) to form an Al2O3 protective layer (about 2 nm thick), and finally the catalyst Cu-ZnO-Al2O3 / SSZ-13 was obtained.

[0126] Finally, the methanol synthesized in this example was temporarily stored in a methanol storage tank, and the methanol production rate was 0.48 g / (g catalyst·h); after continuous operation for 1000 h, by detecting the methanol content at the outlet, it was calculated that the catalyst activity decreased by 9%.

[0127] Example 7

[0128] The carbon dioxide desorbed in Example 5 was used for the synthesis of formic acid. The specific process was as follows: 200 g of the catalyst Ru / MOF-808 was loaded into the reactor, the temperature was 100 °C, the pressure was 3 MPa, and the desorbed CO2 was introduced. The preparation method of the catalyst Ru / MOF-808 included the following steps:

[0129] (1) Material pretreatment

[0130] 1) Activation of MOF-808: MOF-808 was vacuum-dried at 120 °C for 12 h to remove the solvent molecules in the pores;

[0131] 2) Treatment of ruthenium precursor: An ethanol solution of 0.1 M RuCl3·xH2O was prepared, and 0.5 equivalent of acetylacetone was added as a stabilizer;

[0132] (2) Ligand exchange and loading

[0133] The activated MOF-808 was immersed in the ruthenium precursor solution (solid-liquid mass ratio 1:50), and refluxed at 80 °C for 6 h under argon protection. Ligand exchange occurred between the -OH of the Zr6O4(OH)4(CO2) 12 cluster and RuCl3;

[0134] (3) UV reduction

[0135] It was transferred to a quartz reactor and irradiated with a 300 W mercury lamp (λ = 365 nm) for 2 h. Methanol vapor was simultaneously introduced as a hole scavenger to form 3 nm Ru nanoclusters;

[0136] (4) Post-treatment optimization

[0137] Supercritical CO2 drying (40 °C, 10 MPa), surface modification with benzoic acid (impregnation with an ethanol solution of 0.1 M benzoic acid), and finally the catalyst Ru / MOF-808 with a Ru loading of 5 wt.% was obtained.

[0138] Finally, the yield of formic acid synthesized in this example > 1 g / (g catalyst·h); after continuous operation for 1000 h, the catalyst activity decreased by 8%.

Claims

1. A method for preparing an adsorbent for capturing carbon dioxide from industrial waste gas, characterized in that It includes the following steps: S1: Porous biochar is prepared by activating rice straw or wood chips with KOH. S2: A Cu-BTC MOF layer is in-situ grown on the surface of the biochar by a hydrothermal method. S3: A polyethyleneimine-polyethylene glycol copolymer is grafted onto the surface of the biochar modified with the Cu-BTC MOF layer. S4: The material obtained in step S3 is mixed with a nano-ZnO / carbon quantum dot composite to obtain an adsorbent for capturing carbon dioxide in industrial waste gas.

2. The preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 1, characterized in that, The specific operation of step S1 is as follows: Rice straw or wood chips are crushed to 60-100 meshes, mixed with KOH according to a mass ratio of 1:(1-4), carbonized at 500-800 °C for 1-2 h under a nitrogen atmosphere, and the ash is removed by pickling to obtain porous biochar.

3. The preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 1, characterized in that, The specific operation of step S2 is as follows: The biochar is impregnated in a solution of copper nitrate and trimesic acid. The solvent of the solution is a mixed solvent of ethanol, DMF and H2O with a volume ratio of (0.5-1.5):(0.5-1.5):

1. After ultrasonic treatment, a hydrothermal reaction is carried out to form a Cu-BTC MOF layer; the concentrations of copper nitrate and trimesic acid in the solution are 0.1-0.5 mol / L; the hydrothermal reaction temperature is 85-120 °C and the time is 6-12 h; the thickness of the Cu-BTC MOF layer is 20-30 nm and the pore diameter is 0.7-0.9 nm.

4. The preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 1, characterized in that, The specific operation of step S3 is as follows: A polyethyleneimine-polyethylene glycol copolymer solution is sprayed on the surface of the biochar modified with the Cu-BTC MOF layer and dried in vacuum; among them, the solvent of the polyethyleneimine-polyethylene glycol copolymer solution is ethanol, the molar ratio of polyethyleneimine to polyethylene glycol is 1:(0.5-2), and the concentration of the polyethyleneimine-polyethylene glycol copolymer solution is 2-3 wt.%; the vacuum drying temperature is 40-60 °C and the time is 6-12 h.

5. The preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 1, characterized in that, The specific operation of step S4 is as follows: The nano-ZnO / carbon quantum dot composite is added to the material obtained in step S3 at 2-5 wt.%, and ball-milled and mixed evenly; among them, the preparation method of the nano-ZnO / carbon quantum dot composite is as follows: (1) Preparation of carbon quantum dots: The carbon source is dissolved in water and placed in a reaction kettle, and a hydrothermal reaction is carried out at 180-200 °C for 4-8 h. After centrifugal purification, a carbon quantum dot solution is obtained. (2) Synthesis of nano-ZnO / carbon quantum dot composite: The zinc salt and the carbon quantum dot solution are mixed, a precipitating agent is added to adjust the pH to alkaline, transferred to a reaction kettle, and a hydrothermal reaction is carried out at 120-180 °C for 6-12 h. Nano-ZnO particles grow in-situ on the surface of the carbon quantum dots to form a nano-ZnO / carbon quantum dot composite. (3) Post-treatment: The nano-ZnO / carbon quantum dot composite is centrifuged and washed to neutrality, and freeze-dried to obtain a nano-ZnO / carbon quantum dot composite powder.

6. The preparation method of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 5, characterized in that, In step (1), the carbon source is citric acid or glucose; in step (2), the zinc salt is zinc nitrate, the precipitating agent is NaOH or ammonia water, and the pH is adjusted to 9.5-10.

5.

7. An adsorbent for capturing carbon dioxide from industrial waste gas, characterized in that, It is prepared by the preparation method of the adsorbent for capturing carbon dioxide in industrial waste gas as described in any one of claims 1-7.

8. Use of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 7, characterized in that, They are respectively loaded into Absorption Tower 1, Absorption Tower 2 and Absorption Tower 3. First, industrial waste gas containing carbon dioxide is introduced into Absorption Tower 1. When the adsorbent therein adsorbs carbon dioxide to reach the saturation state, the industrial waste gas is switched to Absorption Tower 2. At the same time, the adsorbent in Absorption Tower 1 is regenerated. When the adsorbent in Absorption Tower 2 reaches the saturation state, the industrial waste gas is switched to Absorption Tower 1 again, and the regenerated adsorbent is used to capture and adsorb carbon dioxide in the industrial waste gas again, and so on; Absorption Tower 3 serves as a standby tower.

9. Use of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 8, characterized in that, The adsorbent regeneration method is as follows: Microwave generators and heat exchange tubes are provided in Absorption Tower 1, Absorption Tower 2 and Absorption Tower 3. The inlet section of the heat exchange tube is arranged on the outer wall of the tower, and the inner wall of the inlet section is coated with CuS@SiO2 nanoparticles to form a photothermal coating. Industrial waste gas is introduced into the inlet section, and the solar energy is converted into heat energy by microwave radiation and the photothermal coating, as well as the waste heat of the industrial waste gas, to heat the adsorbent in the saturation state, so that the adsorbed carbon dioxide is desorbed.

10. Use of the adsorbent for capturing carbon dioxide from industrial waste gas according to claim 9, characterized in that, The desorbed carbon dioxide is used to synthesize methanol together with the H2 produced by electrolyzing water; or the desorbed carbon dioxide is directly hydrogenated to formic acid.

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