An absorbent for efficiently removing SO2 from a mixed gas, a preparation method and application thereof

Abstract

The application discloses an absorbent for efficiently removing SO2 from a mixed gas as well as a preparation method and application thereof, and relates to the field of environmental protection tail gas treatment technology. The absorbent comprises a nitrogen-sulfur co-doped porous carbon substrate, MgO and CeO2 loaded on the porous carbon substrate, and a hydrophobic layer covering the surface of the porous carbon substrate. The porous carbon substrate has a hierarchical pore structure mainly composed of mesopores. The MgO and CeO2 are both nanoscale and are loaded on the surface or in the pores of the porous carbon through stepwise impregnation. The hydrophobic layer is formed by modification of long-chain alkyl compounds. Through the composite loading design of the nitrogen-sulfur co-doped porous carbon substrate and magnesium-cerium oxides, the application realizes the 'adsorption-catalytic oxidation' synergistic mechanism for SO2, so that the desulfurization efficiency is high, and a complex tower system is not needed, and high-efficiency removal can be realized through single-stage adsorption.

Description

Technical Field

[0001] This invention relates to the field of environmental exhaust gas treatment technology, specifically to an absorbent for efficiently removing SO2 from a mixed gas, its preparation method, and its application. Background Technology

[0002] Sulfur dioxide is one of the major air pollutants, produced during industrial production and the combustion of fossil fuels (coal, oil, and natural gas). It combines with water vapor in the air to form sulfurous acid, which, in the presence of PM2.5, is easily oxidized by atmospheric O2 to form sulfur trioxide (SO3) or sulfuric acid (H2SO4), the main components of acid rain (pH < 5.6), causing serious damage to trees, steel structures, and rivers. While posing a threat, sulfur dioxide is also a necessary raw material for the production of sulfuric acid and sulfur. Currently, nearly 90% of sulfur dioxide emissions come from coal combustion. If sulfur dioxide could be recovered from the mixed exhaust gases produced by coal combustion, it would reduce environmental damage while improving economic efficiency.

[0003] Currently, commonly used sulfur dioxide removal technologies include wet, dry, and semi-dry methods. Wet desulfurization typically uses the limestone-gypsum method, which generates a large amount of wastewater, is difficult to treat, and has high equipment maintenance costs. Dry desulfurization typically uses activated carbon / molecular sieve adsorption, which uses the active sites on the surface of the adsorbent to capture sulfur dioxide. However, the capacity of the adsorbent is limited, requiring frequent regeneration, and the number of regeneration cycles is limited. Discarded adsorbent can easily cause secondary pollution. Semi-dry desulfurization often uses spray drying, which has low desulfurization efficiency and limited applicability. The invention patent application CN116603369A discloses a highly efficient sulfur dioxide absorbent with a desulfurization efficiency of up to 99.9%. It produces 99% dry-basis sulfur dioxide as a byproduct during desulfurization, and the desulfurization efficiency is flexibly adjustable. However, the core components of the absorbent provided in this application include organic amine compounds such as N,N'-bis(hydroxyethyl)piperazine and tert-butylaminoethanol. The synthesis of these compounds is complex, resulting in high industrialization costs. The absorbent regeneration process relies on a reboiler (low-pressure steam), leading to high energy consumption and increased operating costs. The desulfurization system includes multi-stage towers (scrubbing tower, absorption tower, regeneration tower), pumps, heat exchangers, etc., resulting in large equipment investment, a large footprint, and high maintenance difficulty. Furthermore, the absorbent has a high pH value (9-12), which accelerates equipment corrosion, leading to high equipment maintenance costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an absorbent for efficiently removing SO2 from a mixed gas, its preparation method and application. The prepared absorbent can achieve efficient removal through single-stage adsorption without the need for a complex tower system, and has a low cost.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An absorbent for efficiently removing SO2 from a mixed gas comprises a nitrogen-sulfur co-doped porous carbon substrate, MgO and CeO2 loaded on the porous carbon substrate, and a hydrophobic layer covering the surface of the porous carbon substrate; wherein the porous carbon substrate has a hierarchical pore structure dominated by mesopores, the MgO and CeO2 are both nanoscale and are loaded onto the surface or pores of the porous carbon through stepwise impregnation, and the hydrophobic layer is formed by modification with a long-chain alkyl compound.

[0007] Furthermore, the molar ratio of nitrogen to sulfur in the porous carbon substrate is 1:0.2-0.5, and the specific surface area of ​​the porous carbon substrate is 800-1200 m². 2 / g, with a pore size distribution of 2-50nm; the particle size of MgO is 20-50nm, the particle size of CeO2 is 5-10nm, and CeO2 is uniformly dispersed on the surface of MgO.

[0008] Furthermore, the preparation method of the above-mentioned absorbent includes the following steps:

[0009] S1, Preparation of nitrogen-sulfur co-doped porous carbon substrate: Carbon source, nitrogen source and sulfur source are mixed in a mass ratio of 4.8-5.8:2.8-3.2:0.8-1.2 and ball-milled to obtain mixed powder; then the mixed powder is heated to 250-350℃ to initially form pores, and then graphitized to 800-850℃ under the assistance of a pulsed electric field and held at that temperature for 2.8-3.5h, and then acid-washed and dried after cooling;

[0010] S2, Magnesium-Cerium Oxide Loading: The porous carbon obtained in step S1 is impregnated in a magnesium salt solution, and after drying and calcination, a carbon-based material loaded with MgO is formed; the carbon-based material loaded with MgO is impregnated in a cerium salt solution, and after drying and calcination, a carbon-based material loaded with magnesium-cerium oxide is formed.

[0011] S3, Surface modification: The material obtained in step S2 is subjected to plasma treatment, then acid washing and activation, and impregnated with stearic acid ethanol solution. After drying, it is subjected to heat treatment to form a hydrophobic layer.

[0012] Furthermore, in step S1, the carbon source is glucose, the nitrogen source is urea, and the sulfur source is thiourea; in step S2, the magnesium salt is magnesium nitrate solution, the cerium salt is cerium nitrate solution, and the pH of the cerium salt solution is 2.8-3.2.

[0013] Furthermore, in step S1, the ball milling speed is 300-350 rpm, the ball-to-material ratio is 8-12:0.8-1.2, and the ball milling time is 1.8-2.2 h.

[0014] Furthermore, in step S1, the temperature is increased to 250-350℃ using a rate gradient of 2℃ / min; and increased to 800-850℃ using a rate gradient of 5℃ / min.

[0015] Furthermore, in step S2, the porous carbon substrate is impregnated in a magnesium nitrate solution with a liquid-to-solid volume ratio of 8-12:0.8-1.2, a magnesium nitrate solution concentration of 0.3-0.6 M, an impregnation time of 28-32 min, and then dried at 55-65℃ for 5.5-6.5 h. Finally, it is calcined at 420-480℃ for 1.8-2.2 h with a gradient temperature increase of 3℃ / min to form a carbon-based material loaded with MgO.

[0016] The carbon-based material loaded with MgO was impregnated in a cerium nitrate solution with a liquid-to-solid volume ratio of 8-12:0.8-1.2 and a concentration of cerium nitrate solution of 0.3-0.6 M. The impregnation was carried out under vacuum for 28-32 min. After impregnation, the temperature was increased to 480-520℃ at a gradient of 2℃ / min and calcined for 2.8-3.2 h to form a carbon-based material loaded with magnesium cerium oxide.

[0017] Further, in step S3, plasma treatment is carried out in an O2 plasma reactor. The plasma treatment conditions are: power 180-220W, pressure 48-52Pa, treatment time 25-35min; acid washing is performed with HNO3 solution with a concentration of 0.08-0.12M, and the acid washing is stirred at 55-65℃ for 1.5-2.5h. After acid washing, the solution is washed with deionized water until neutral and then vacuum dried; the concentration of the stearic acid ethanol solution is 4-6wt%, and the immersion time is 0.8-1.2h; the heat treatment temperature is 280-320℃, and the heat treatment time is 0.8-1.2h.

[0018] The present invention also provides the application of the above-mentioned adsorbent in an industrial flue gas desulfurization system, wherein the adsorbent is placed in a fixed bed or moving bed reactor to perform single-stage adsorption desulfurization on mixed flue gas containing SO2.

[0019] Furthermore, the SO2 concentration in the mixed gas is 500-5000 ppm, the oxygen concentration is 3-8%, and the operating temperature is 100-200℃.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention achieves a synergistic "adsorption-catalytic oxidation" mechanism for SO2 through a composite loading design of a nitrogen-sulfur co-doped porous carbon substrate and magnesium-cerium oxide. Using glucose, urea, and thiourea as precursors, this invention utilizes a multi-level mesoporous structure formed by gradient carbonization (preliminary pore formation at a lower temperature, followed by graphitization). This structure has a large specific surface area and concentrated pore size distribution, providing abundant active sites for SO2 adsorption. The co-doping of nitrogen and sulfur atoms optimizes the electronic structure of the carbon layer, enhancing its chemical adsorption capacity for acidic gases. A pulsed electric field is applied during the graphitization process to orient the carbon layers, improving the efficient mass transfer of the pores. The stepwise impregnation method for loading nano-sized MgO and CeO2 avoids competitive adsorption and improves dispersibility. MgO acts as an alkaline support to enhance the chemical adsorption of SO2, while CeO2... 3+ / Ce 4+ The redox cycle catalyzes the conversion of SO2 to SO3 through oxygen storage capacity, ultimately producing soluble sulfate. This adsorbent achieves a desulfurization efficiency of over 99.9% in simulated flue gas (SO2 concentration 2000ppm), and does not require a complex tower system; high-efficiency removal can be achieved through single-stage adsorption.

[0022] (2) Traditional activated carbon adsorbents experience a sharp drop in desulfurization efficiency under high humidity conditions due to competitive adsorption by water molecules (e.g., a 15% decrease in efficiency at 60% humidity). This invention modifies the surface of the material with a stearic acid-ethanol solution, forming a long-chain alkyl hydrophobic layer that effectively blocks water vapor from occupying adsorption sites while maintaining the unobstructed flow of mesoporous channels. Tests show that under 60% relative humidity, the desulfurization efficiency of the adsorbent decreases by only 2%, significantly better than similar materials. Furthermore, after 100 adsorption-regeneration cycles, the material retains over 90% of its hydrophobic capacity, and the MgO / CeO2 nanoparticles show no agglomeration. This characteristic significantly reduces the frequency of adsorbent replacement, resulting in a substantial long-term cost advantage.

[0023] (3) Existing wet desulfurization technologies (such as the limestone-gypsum method) require the treatment of high-salinity wastewater, while organic amine absorbents are complex to synthesize and easily corrode equipment. This invention employs a fully solid-phase preparation process, using inexpensive and readily available glucose, urea, and thiourea as raw materials. Material functionalization is achieved through gradient carbonization, stepwise impregnation, and plasma treatment, eliminating the need for high-temperature, high-pressure, or complex organic synthesis steps. Acid washing removes metallic impurities, improves the material's structural stability, and avoids secondary heavy metal pollution. The absorbent's pH value is controlled at 7-8, significantly reducing the risk of equipment corrosion compared to traditional alkaline absorbents (pH 9-12), thus reducing equipment maintenance costs and meeting green chemical engineering requirements.

[0024] (4) Traditional adsorption desulfurization requires the treatment of waste adsorbent or low-value by-products (such as gypsum), while the present invention converts SO2 into soluble sulfates (such as magnesium sulfate and cerium sulfate) through a catalytic oxidation mechanism, which can be directly used for fertilizer or catalyst production. Moreover, the purity of the by-products after desulfurization is over 98%, and no additional separation steps are required, which increases the economic benefits of the desulfurization process.

[0025] (5) Existing desulfurization systems typically require multi-stage towers (absorption towers, regeneration towers, etc.), reboilers, and steam-assisted regeneration, resulting in high equipment investment and energy consumption. The absorbent of this invention can be directly applied in fixed-bed or moving-bed reactors, achieving efficient desulfurization through single-stage adsorption. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0027] Example 1

[0028] This embodiment provides an absorbent for efficiently removing sulfur dioxide from a mixed gas, and its preparation method is as follows:

[0029] Step 1: Preparation of porous carbon

[0030] (1) Pretreatment: The carbon source (glucose, purity ≥99%), nitrogen source (urea, analytical grade), and sulfur source (thiourea, analytical grade) were dry-milled in a ball mill for 2 hours to obtain a mixed powder. The mass ratio of glucose, urea, and thiourea was 5:3:1, the ball milling speed was 300 rpm, and the ball-to-material ratio was 10:1.

[0031] (2) Carbonization: The pretreated mixed powder was gradually heated to 300℃ (2℃ / min) at room temperature. Glucose dehydrated to form an aromatic ring structure, and urea and thiourea partially decomposed to generate gases (NH3, H2S), which initially created pores and formed a porous carbon skeleton. Then, with the assistance of a pulsed electric field (10kHz, 5V / cm), the temperature was gradually increased from 300℃ to 800℃ (5℃ / min), and the carbon skeleton was graphitized. Urea decomposed at high temperature to produce NH3 and CO(NH2)2, and thiourea decomposed at high temperature to produce H2S and NH3. Nitrogen and sulfur atoms were inserted into the carbon layer through substitution or adsorption to form a co-doped structure. The H2S from the decomposition of thiourea reacted with metal impurities to form soluble salts, which could be removed by subsequent acid washing. Finally, the mixture was kept at 800℃ for 3h to stabilize the porous structure and optimize the pore size distribution (mainly mesoporous).

[0032] (3) Post-treatment: After naturally cooling to room temperature under nitrogen protection, the substrate was washed sequentially with 1M HCl (to remove metal impurities) and deionized water until neutral, and then vacuum dried at 80℃ for 12 hours to obtain a nitrogen-sulfur co-doped porous carbon substrate. The molar ratio of nitrogen to sulfur in the porous carbon substrate was 1:0.4, and the specific surface area of ​​the porous carbon substrate was 1200 m².2 / g, with a pore size distribution of 2-50nm.

[0033] Step 2: Loading magnesium cerium oxide

[0034] (1) Prepare 0.5M Mg(NO3)2 solution and 0.3M Ce(NO3)3 solution with deionized water, wherein the pH of Ce(NO3)3 solution is adjusted to 3.0 to prevent cerium salt hydrolysis;

[0035] (2) Impregnation: The porous carbon is immersed in Mg(NO3)2 solution (liquid-solid volume ratio 10:1) and ultrasonically assisted for 30 min (power 200W) to promote infiltration into the pores; after impregnation, it is dried at 60℃ for 6 h, and then calcined at 450℃ for 2 h (heating rate 3℃ / min) to form MgO-carbon material. MgO particles are loaded on the surface or in the pores of the porous carbon. The MgO particles are found to be nanoscale with a size of 20-50 nm.

[0036] (3) Secondary impregnation: The MgO-carbon material is impregnated in Ce(NO3)3 solution with the same liquid-solid ratio (liquid-solid volume ratio 10:1) and vacuum impregnated for 2h to ensure that the solution fully fills the pores; after impregnation, the temperature is gradually increased to 500℃ and calcined for 3h (heating rate 2℃ / min) to form a carbon-based material loaded with magnesium cerium oxide. CeO2 nanoparticles are uniformly dispersed on the MgO surface and the particle size of CeO2 nanoparticles is 5-10nm.

[0037] MgO, as an alkaline support, can enhance the adsorption capacity of materials for acidic gases; cerium's oxygen storage capacity (Ce... 3+ / Ce 4+ The redox cycle promotes catalytic activity and enhances the catalytic oxidation of sulfur dioxide; the supported MgO and CeO2 are both nanoparticles. Their small size exposes more active crystal faces. The step-by-step impregnation process effectively avoids Mg... 2+ With Ce 3+ The competitive adsorption of MgO improves the dispersibility of oxides, while MgO can also provide a high specific surface area to support the dispersion of CeO2.

[0038] Step 3: Modification of carbon-based materials supported on magnesium cerium oxide

[0039] (1) Carbon-based materials loaded with magnesium cerium oxide were placed in an O2 plasma reactor and treated for 30 min at a power of 200 W and a pressure of 50 Pa to activate the lattice oxygen on the CeO2 surface and enhance the CeO2 surface. 3+ / Ce 4+ It improves the redox cycle capacity and optimizes the interaction at the MgO-CeO2 interface to enhance the catalytic oxidation efficiency of SO2.

[0040] (2) The plasma-treated material was immersed in 0.1M HNO3 solution (liquid-solid volume ratio 5:1) and stirred at 60°C for 2 hours to remove unstable impurities on the surface and increase acidic sites (carboxyl and hydroxyl groups), thereby enhancing the chemical adsorption capacity for SO2; then it was washed with deionized water until neutral and dried under vacuum at 80°C for 6 hours.

[0041] (3) The acid-activated material was immersed in a 5 wt% stearic acid ethanol solution (liquid-to-solid volume ratio 8:1), ultrasonically treated for 1 h (power 150 W), dried at 60 °C, and then heat-treated at 300 °C for 1 h under a nitrogen atmosphere. The long-chain alkyl groups of stearic acid can form a hydrophobic layer on the surface of the material, reducing the competition of water vapor for SO2 adsorption, while not blocking the mesoporous structure.

[0042] Example 2

[0043] This embodiment provides an absorbent for efficiently removing sulfur dioxide from a mixed gas, and its preparation method is as follows:

[0044] Step 1: Preparation of porous carbon

[0045] (1) Pretreatment: The carbon source (glucose, purity ≥99%), nitrogen source (urea, analytical grade), and sulfur source (thiourea, analytical grade) were dry-milled in a ball mill for 1.8 hours to obtain a mixed powder. The mass ratio of glucose, urea, and thiourea was 4.8:3.0:1, the ball milling speed was 300 rpm, and the ball-to-material ratio was 8:1.2.

[0046] (2) Carbonization: The pretreated mixed powder was gradually heated to 250℃ (2℃ / min) at room temperature. Glucose dehydrated to form an aromatic ring structure, and urea and thiourea partially decomposed to generate gases (NH3, H2S), which initially created pores and formed a porous carbon skeleton. Then, with the assistance of a pulsed electric field (10kHz, 5V / cm), the temperature was gradually increased from 250℃ to 800℃ (5℃ / min), and the carbon skeleton was graphitized. Urea decomposed at high temperature to produce NH3 and CO(NH2)2, and thiourea decomposed at high temperature to produce H2S and NH3. Nitrogen and sulfur atoms were inserted into the carbon layer through substitution or adsorption to form a co-doped structure. The H2S from the decomposition of thiourea reacted with metal impurities to form soluble salts, which could be removed by subsequent acid washing. Finally, the mixture was kept at 750℃ for 2.8h to stabilize the porous structure and optimize the pore size distribution (mainly mesoporous).

[0047] (3) Post-treatment: After naturally cooling to room temperature under nitrogen protection, the substrate was washed sequentially with 0.8M HCl (to remove metal impurities) and deionized water until neutral, and then vacuum dried at 75℃ for 10 hours to obtain a nitrogen-sulfur co-doped porous carbon substrate. Analysis showed that the molar ratio of nitrogen to sulfur in the porous carbon substrate was 1:0.2, and the specific surface area of ​​the porous carbon substrate was 800 m². 2 / g, with a pore size distribution of 2-50nm.

[0048] Step 2: Loading magnesium cerium oxide

[0049] (1) Prepare 0.3M Mg(NO3)2 solution and 0.3M Ce(NO3)3 solution with deionized water, wherein the pH of Ce(NO3)3 solution is adjusted to 2.8 to prevent cerium salt hydrolysis;

[0050] (2) Impregnation: The porous carbon was impregnated in Mg(NO3)2 solution (liquid-solid volume ratio 8:0.8) and ultrasonically assisted for 28 min (power 200W) to promote penetration into the pores. After impregnation, it was dried at 55℃ for 5.5 h and then calcined at 420℃ for 1.8 h (heating rate 3℃ / min) to form MgO-carbon material. MgO particles were loaded on the surface or in the pores of the porous carbon. The MgO particles were found to be nanoscale with a size of 20-50 nm.

[0051] (3) Secondary impregnation: The MgO-carbon material was impregnated in Ce(NO3)3 solution with the same liquid-solid ratio (liquid-solid volume ratio 8:0.8) and vacuum impregnated for 1.8h to ensure that the solution fully fills the pores; after impregnation, the temperature was gradually increased to 480℃ and calcined for 2.8h (heating rate 2℃ / min) to form a carbon-based material loaded with magnesium cerium oxide. CeO2 nanoparticles were uniformly dispersed on the MgO surface and the particle size of CeO2 nanoparticles was 5-10nm.

[0052] MgO, as an alkaline support, can enhance the adsorption capacity of materials for acidic gases; cerium's oxygen storage capacity (Ce... 3+ / Ce 4+ The redox cycle promotes catalytic activity and enhances the catalytic oxidation of sulfur dioxide; the supported MgO and CeO2 are both nanoparticles. Their small size exposes more active crystal faces. The step-by-step impregnation process effectively avoids Mg... 2+ With Ce 3+ The competitive adsorption of MgO improves the dispersibility of oxides, while MgO can also provide a high specific surface area to support the dispersion of CeO2.

[0053] Step 3: Modification of carbon-based materials supported on magnesium cerium oxide

[0054] (1) Carbon-based materials loaded with magnesium cerium oxide were placed in an O2 plasma reactor and treated for 25 min at a power of 180 W and a pressure of 50 Pa to activate the lattice oxygen on the CeO2 surface and enhance the CeO2 surface. 3+ / Ce 4+ It improves the redox cycle capacity and optimizes the interaction at the MgO-CeO2 interface to enhance the catalytic oxidation efficiency of SO2.

[0055] (2) The plasma-treated material was immersed in 0.1M HNO3 solution (liquid-solid volume ratio 5:1) and stirred at 55°C for 1.5h to remove unstable impurities on the surface and increase acidic sites (carboxyl and hydroxyl groups), thereby enhancing the chemical adsorption capacity for SO2; then it was washed with deionized water until neutral and dried under vacuum at 75°C for 5h.

[0056] (3) The acid-activated material was immersed in a 4 wt% stearic acid ethanol solution (liquid-to-solid volume ratio 8:1), ultrasonically treated for 0.8 h (power 120 W), dried at 55 °C, and then heat-treated at 280 °C for 0.8 h under a nitrogen atmosphere. The long-chain alkyl groups of stearic acid can form a hydrophobic layer on the surface of the material, reducing the competition of water vapor for SO2 adsorption, while not blocking the mesoporous structure.

[0057] Example 3

[0058] Step 1: Preparation of porous carbon

[0059] (1) Pretreatment: The carbon source (glucose, purity ≥99%), nitrogen source (urea, analytical grade), and sulfur source (thiourea, analytical grade) were dry-milled in a ball mill for 2.2 hours to obtain a mixed powder. The mass ratio of glucose, urea, and thiourea was 5:3:1, the ball milling speed was 350 rpm, and the ball-to-material ratio was 10:1.

[0060] (2) Carbonization: The pretreated mixed powder was gradually heated to 350℃ (2℃ / min) at room temperature. Glucose dehydrated to form an aromatic ring structure, and urea and thiourea partially decomposed to generate gases (NH3, H2S), which initially created pores and formed a porous carbon skeleton. Then, with the assistance of a pulsed electric field (10kHz, 5V / cm), the temperature was gradually increased from 300℃ to 850℃ (5℃ / min), and the carbon skeleton was graphitized. Urea decomposed at high temperature to produce NH3 and CO(NH2)2, and thiourea decomposed at high temperature to produce H2S and NH3. Nitrogen and sulfur atoms were inserted into the carbon layer through substitution or adsorption to form a co-doped structure. The H2S from the decomposition of thiourea reacted with metal impurities to form soluble salts, which could be removed by subsequent acid washing. Finally, the mixture was kept at 850℃ for 3.5h to stabilize the porous structure and optimize the pore size distribution (mainly mesoporous).

[0061] (3) Post-treatment: After naturally cooling to room temperature under nitrogen protection, the substrate was washed sequentially with 1.2M HCl (to remove metal impurities) and deionized water until neutral, and then vacuum dried at 85℃ for 15 h to obtain a nitrogen-sulfur co-doped porous carbon substrate. Analysis showed that the molar ratio of nitrogen to sulfur in the porous carbon substrate was 1:0.5, and the specific surface area of ​​the porous carbon substrate was 1200 m². 2 / g, with a pore size distribution of 2-50nm.

[0062] Step 2: Loading magnesium cerium oxide

[0063] (1) Prepare 0.6M Mg(NO3)2 solution and 0.6M Ce(NO3)3 solution with deionized water, wherein the pH of Ce(NO3)3 solution is adjusted to 3.2 to prevent cerium salt hydrolysis;

[0064] (2) Impregnation: The porous carbon was immersed in Mg(NO3)2 solution (liquid-solid volume ratio 10:1) and ultrasonically assisted for 32 min (power 200W) to promote infiltration into the pores; after impregnation, it was dried at 65℃ for 6.5 h and then calcined at 480℃ for 2.2 h (heating rate 3℃ / min) to form MgO-carbon material. MgO particles were loaded on the surface or in the pores of the porous carbon. The MgO particles were found to be nanoscale with a size of 20-50 nm.

[0065] (3) Secondary impregnation: The MgO-carbon material was impregnated in Ce(NO3)3 solution with the same liquid-to-solid ratio (liquid-to-solid volume ratio 10:1) and vacuum impregnated for 2.2 h to ensure that the solution fully fills the pores; after impregnation, the temperature was gradually increased to 520℃ and calcined for 3.2 h (heating rate 2℃ / min) to form a carbon-based material loaded with magnesium cerium oxide. CeO2 nanoparticles were uniformly dispersed on the MgO surface and the particle size of CeO2 nanoparticles was 5-10 nm.

[0066] MgO, as an alkaline support, can enhance the adsorption capacity of materials for acidic gases; cerium's oxygen storage capacity (Ce... 3+ / Ce 4+ The redox cycle promotes catalytic activity and enhances the catalytic oxidation of sulfur dioxide; the supported MgO and CeO2 are both nanoparticles. Their small size exposes more active crystal faces. The step-by-step impregnation process effectively avoids Mg... 2+ With Ce 3+ The competitive adsorption of MgO improves the dispersibility of oxides, while MgO can also provide a high specific surface area to support the dispersion of CeO2.

[0067] Step 3: Modification of carbon-based materials supported on magnesium cerium oxide

[0068] (1) Carbon-based materials loaded with magnesium cerium oxide were placed in an O2 plasma reactor and treated for 35 min at a power of 220 W and a pressure of 52 Pa to activate the lattice oxygen on the CeO2 surface and enhance the CeO2 surface. 3+ / Ce 4+ It improves the redox cycle capacity and optimizes the interaction at the MgO-CeO2 interface to enhance the catalytic oxidation efficiency of SO2.

[0069] (2) The plasma-treated material was immersed in 0.1M HNO3 solution (liquid-solid volume ratio 5:1) and stirred at 65°C for 2.5h to remove unstable impurities on the surface and increase acidic sites (carboxyl and hydroxyl groups), thereby enhancing the chemical adsorption capacity for SO2; then it was washed with deionized water until neutral and dried under vacuum at 85°C for 8h.

[0070] (3) The acid-activated material was immersed in a 6wt% stearic acid ethanol solution (liquid-to-solid volume ratio 10:1.2), ultrasonically treated for 1.2 h (power 160W), dried at 65℃, and then heat-treated at 320℃ for 1.2 h under a nitrogen atmosphere. The long-chain alkyl groups of stearic acid can form a hydrophobic layer on the surface of the material, reducing the competition of water vapor for SO2 adsorption, while not blocking the mesoporous structure.

[0071] The performance of the adsorbents prepared in Examples 1, 2, and 3 was tested as follows:

[0072] Comparative Example 1: Traditional activated carbon adsorbent;

[0073] Comparative Example 2: Limestone-Gypsum Method (Wet Method);

[0074] Comparative Example 3: Organic amine absorbent provided in invention patent application CN116603369A.

[0075] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-3. The simulation conditions for all examples and comparative examples were consistent, and the simulation experimental conditions are as follows:

[0076] (1) Simulated flue gas: SO2 2000ppm, O2 5%, N2 balance, temperature 150℃, gas flow rate 1L / min, adsorbent dosage 10g;

[0077] (2) Regeneration conditions: 300℃ air regeneration for 1 hour / cycle;

[0078] (3) Corrosion test: Carbon steel test pieces were immersed in 10% absorbent slurry (50℃, 30 days).

[0079]

[0080] The absorbents prepared in this invention (Examples 1, 2, and 3) show an efficiency decrease of only 2% at 60% humidity, significantly better than activated carbon (15% decrease) and organic amines (5% decrease). The limestone-gypsum method, requiring spraying water, is not directly affected by humidity, but generates wastewater requiring additional treatment. The absorbents prepared in this invention produce high-purity sulfate (magnesium sulfate / cerium sulfate) as a byproduct during use, with a purity of 98%, which can be directly used in fertilizer or catalyst production, demonstrating significant economic advantages. In contrast, the gypsum byproduct of the limestone-gypsum method has low purity and limited market value. Testing shows that the sulfur dioxide absorbent provided by this invention has a near-neutral pH (7-8), resulting in a low corrosion rate and significantly extending equipment lifespan. Limestone-gypsum and organic amines, on the other hand, have higher pH values ​​and higher corrosion rates, requiring maintenance or replacement after a period of use, which can increase equipment costs to some extent.

[0081] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an absorbent for efficient removal of SO2 from a mixed gas, characterized by, Comprise the following steps: S1, preparation of nitrogen and sulfur co-doped porous carbon substrate: the carbon source, nitrogen source and sulfur source are mixed and ball milled according to the mass ratio of 4.8-5.8:2.8-3.2:0.8-1.2 to obtain a mixed powder; then the mixed powder is gradually heated to 250-350℃ for preliminary pore forming, and then gradually heated to 800-850℃ for graphitization under the assistance of pulse electric field and kept for 2.8-3.5 h, and after cooling, it is acid washed and dried; S2, loading magnesium cerium oxide: the porous carbon obtained in step S1 is immersed in a magnesium salt solution, dried and calcined to form a carbon-based material loaded with MgO; the carbon-based material loaded with MgO is immersed in a cerium salt solution, dried and calcined to form a carbon-based material loaded with magnesium cerium oxide; S3, surface modification: the material obtained in step S2 is treated by plasma, then activated by acid washing and immersed in a stearic acid ethanol solution, and after drying, it is heat treated to form a hydrophobic layer; The absorbent prepared by the above preparation method comprises a nitrogen and sulfur co-doped porous carbon substrate, MgO and CeO2 loaded on the porous carbon substrate, and a hydrophobic layer covering the surface of the porous carbon substrate; wherein the porous carbon substrate has a hierarchical pore structure dominated by mesopores, and the MgO and CeO2 are both nanoscale and loaded on the surface or in the pores of the porous carbon by stepwise immersion.

2. The method for preparing an absorbent according to claim 1, characterized by, The molar ratio of nitrogen to sulfur in the porous carbon substrate is 1:0.2-0.5, the specific surface area of the porous carbon substrate is 800-1200 m² / g, and the pore size distribution is 2-50 nm; the particle size of the MgO is 20-50 nm, and the particle size of the CeO2 is 5-10 nm, and the CeO2 is uniformly dispersed on the surface of the MgO.

3. The method of claim 2, wherein the absorbent is prepared by a method comprising: In step S1, the carbon source is glucose, the nitrogen source is urea, and the sulfur source is thiourea; in step S2, the magnesium salt is a magnesium nitrate solution, and the cerium salt is a cerium nitrate solution, and the pH of the cerium salt solution is 2.8-3.

2.

4. The method for preparing an absorbent according to claim 3, characterized by, In step S1, the rotation speed during ball milling is 300-350 rpm, and the ball-to-material ratio is 8-12: 0.8-1.2, and the ball milling time is 1.8-2.2 h.

5. The method of claim 4, wherein the absorbent is prepared by the steps of: In step S1, the temperature is gradually increased to 250-350℃ at a rate of 2℃ / min, and then gradually increased to 800-850℃ at a rate of 5℃ / min.

6. The method of claim 5, wherein the absorbent is prepared by In step S2, the porous carbon substrate is immersed in a magnesium nitrate solution, and the liquid-to-solid volume ratio is 8-12: 0.8-1.2, the concentration of the magnesium nitrate solution is 0.3-0.6 M, the immersion time is 28-32 min, and after immersion, it is dried at 55-65℃ for 5.5-6.5 h, then gradually heated to 420-480℃ at a rate of 3℃ / min for calcination for 1.8-2.2 h to form a carbon-based material loaded with MgO; The carbon-based material loaded with MgO is immersed in a cerium nitrate solution, and the liquid-to-solid volume ratio is 8-12: 0.8-1.2, the concentration of the cerium nitrate solution is 0.3-0.6 M, vacuum immersion is performed for 28-32 min, and after immersion, it is gradually heated to 480-520℃ at a rate of 2℃ / min for calcination for 2.8-3.2 h to form a carbon-based material loaded with magnesium cerium oxide.

7. The method for preparing the absorbent according to claim 6, characterized in that, In step S3, plasma treatment is carried out in an O2 plasma reactor under the following conditions: power 180-220 W, pressure 48-52 Pa, and treatment time 25-35 min; acid washing is performed with a 0.08-0.12 M HNO3 solution, and the acid washing is carried out with stirring at 55-65℃ for 1.5-2.5 h; after acid washing, the solution is washed with deionized water until neutral and then vacuum dried; the concentration of the stearic acid ethanol solution is 4-6 wt%, and the solution is impregnated for 0.8-1.2 h; the heat treatment temperature is 280-320℃, and the heat treatment time is 0.8-1.2 h.

8. The use of the absorbent prepared by the preparation method according to any one of claims 1-7 in an industrial flue gas desulfurization system, characterized in that, The absorbent is placed in a fixed-bed or moving-bed reactor to perform single-stage adsorption desulfurization on mixed flue gas containing SO2.

9. Use of an absorbent according to claim 8, characterised in that, The mixed gas has an SO2 concentration of 500-5000 ppm, an oxygen concentration of 3-8%, and an operating temperature of 100-200℃.

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