Calcium-based desulfurizing agent as well as preparation method and application thereof

Abstract

The invention relates to a calcium-based desulfurizer and a preparation method and application thereof, and relates to the technical field of desulfurizers, the calcium-based desulfurizer comprises a calcium-based carrier with a micropore-mesopore-macropore three-level pore structure, and a gamma-aminopropyltriethoxysilane modifier dispersed in pore channels, the molecular imprinting layer is modified by an inactive region on the inner wall of the mesoporous; the preparation method comprises the steps of calcium-based carrier pretreatment, composite pore forming, pre-roasting, hydroxyl strengthening and the like. The efficient mass transfer system is constructed through a three-stage pore structure, the modifier and the molecular imprinting layer synergistically improve the structural stability and the sulfur dioxide adsorption selectivity, the calcium base utilization rate and the desulfurization efficiency are improved, and the industrial flue gas desulfurization requirement is met.

Description

Technical Field

[0001] This invention relates to the field of desulfurizing agent technology, and in particular to a calcium-based desulfurizing agent, its preparation method and application. Background Technology

[0002] With the continuous improvement of global environmental awareness and increasingly stringent environmental regulations, the control of sulfur dioxide emissions from industrial flue gas has become a global focus. Flue gas desulfurization technology is currently the most effective and widely used technology for controlling sulfur dioxide pollution. Based on the morphological characteristics of the desulfurizing agent and desulfurization products, it can be divided into three categories: wet, dry, and semi-dry methods. Among them, dry desulfurization technology, with its advantages of simple process flow, no wastewater discharge, low equipment corrosivity, low system investment cost, small footprint, and dry powder reaction products, is widely used in small and medium-sized boilers, sintering machines, glass kilns, and other scenarios.

[0003] In dry flue gas desulfurization systems, calcium-based desulfurizers, represented by hydrated lime Ca(OH)2, are the most widely used type of desulfurizer due to their abundant reserves of raw materials such as limestone and quicklime, low acquisition costs, good desulfurization activity, and the fact that the sulfur-fixing products such as calcium sulfite and calcium sulfate are insoluble in water, have strong stability, and are easy to transport and recycle in building materials.

[0004] Despite these advantages, conventional calcium-based desulfurizers still face significant technical bottlenecks that severely limit their desulfurization efficiency and industrial application potential: Ordinary Ca(OH)₂ has a low specific surface area, small pore volume, and its pore structure is mostly a disordered stacking morphology. In the initial stage of the desulfurization reaction, solid products such as calcium sulfite and calcium sulfate are deposited and blocked on the particle surface, forming a dense passivation layer. This passivation layer not only blocks mass transfer channels but also covers the active sites on the particle surface, hindering the further diffusion of reactant molecules such as sulfur dioxide, nitrogen, and oxygen into the active sites inside the particles, ultimately leading to a rapid decrease in the reaction rate and insufficient utilization of the desulfurizer.

[0005] To address this issue, Chinese invention patent CN120285763A, published on July 11, 2025, proposes a desulfurizing agent, its preparation method, and its application. This method involves further kneading powdered calcium hydroxide into granular porous calcium hydroxide, and then growing a zinc metal-organic framework in situ on the porous calcium hydroxide framework, grafting amino hydrophilic groups onto it. This approach supplements pore volume and provides additional active sites through the porous structure of the zinc metal-organic framework, while simultaneously regulating the hydrophilicity of the particle surface and improving mechanical strength through amino modification, resulting in a desulfurizing agent with a high specific surface area and good desulfurization effect.

[0006] However, the inventors discovered that the porous structure construction of the above-mentioned technical solution still relies on traditional pore-forming methods such as calcium carbonate decomposition, resulting in poor pore connectivity. This makes the diffusion path of reactant molecules in the pores too long, making it difficult for reaction products to desorb quickly, limiting mass transfer efficiency, and thus affecting the stability of desulfurization efficiency. Summary of the Invention

[0007] To address the problems of disordered pore structure and the formation of passivation layers due to the deposition of reaction products in existing calcium-based desulfurizers, which can lead to blocked mass transfer channels and coverage of active sites, this invention provides a calcium-based desulfurizer, its preparation method, and its application.

[0008] In a first aspect, the present invention provides a calcium-based desulfurizing agent, which adopts the following technical solution: A calcium-based desulfurizing agent, comprising a calcium-based carrier; The calcium-based carrier has a three-level pore structure of micropores-mesopores-macropores, wherein the micropores have a diameter of 0.5–0.8 nm and account for 30–40% of the total pore volume; the mesopores have a diameter of 10–50 nm and account for 50–60% of the total pore volume; and the macropores have a diameter >50 nm and account for 5–10% of the total pore volume. The specific surface area of ​​the carrier is 40-80 m². 2 / g, pore volume ≥0.25cm 3 / g.

[0009] By adopting the above technical solution, micropores provide an extremely high specific surface area, providing sufficient active adsorption sites for sulfur dioxide (SO2) molecules. This allows for the rapid capture of SO2 in flue gas and its enrichment within the pores, creating a high-concentration environment for the subsequent chemical reaction between calcium source and SO2. Mesopores, acting as intermediate channels between micropores and macropores, solve the problems of high mass transfer resistance and easy blockage by reaction products in single microporous structures. They also provide an efficient pathway for the diffusion of SO2 molecules to the active sites in micropores, while reserving space for the initial deposition of reaction products calcium sulfate (CaSO4) and calcium sulfite (CaSO3). Macropores, as macroscopic mass transfer channels, significantly reduce the diffusion resistance of gaseous SO2 within the desulfurizing agent particles. Especially in the later stages of the reaction when the pores are partially occupied by CaSO4 and CaSO3, they can still maintain efficient mass transport, preventing the desulfurization reaction from prematurely terminating due to pore blockage.

[0010] A suitable specific surface area ensures the density of active sites, avoiding the problem of pores becoming too narrow and easily blocked due to excessive specific surface area; sufficient pore volume provides ample space for the generation and storage of reaction products, effectively alleviating the pore collapse caused by product volume expansion during the reaction process, extending the exposure time of active sites, improving calcium utilization, and further enhancing the desulfurization efficiency of the desulfurizing agent.

[0011] Optionally, it also includes γ-aminopropyltriethoxysilane dispersed and bonded within the pores of the calcium-based support, wherein the γ-aminopropyltriethoxysilane accounts for 1 to 2 wt% of the mass of the calcium-based support.

[0012] By employing the above technical solution, γ-aminopropyltriethoxysilane is used as a modifier. The siloxane group (-Si(OEt)3) in its molecule hydrolyzes in the system to generate silanol groups (-SiOH), which then undergo condensation reactions with the hydroxyl groups (-OH) on the surface of the calcium-based support and the inner walls of the pores to form stable Si-O-Ca covalent bonds. This constructs a three-dimensional cross-linked support network within the pores, effectively suppressing micropore collapse and mesopore shrinkage during high-temperature calcination and maintaining the integrity of the tertiary pore structure. On the other hand, the amino group (-NH2) at the molecule's end, as a basic functional group, can form acid-base interactions with SO2, improving the adsorption selectivity and capacity for SO2. Simultaneously, the amino group can anchor the Ca in the calcium-based support through coordination. 2+ Active sites are reduced during the reaction process to improve their utilization rate.

[0013] In addition, the organic-inorganic hybrid structure of γ-aminopropyltriethoxysilane can moderately regulate the hydrophilicity and hydrophobicity of the carrier surface, reduce the adsorption and condensation of water vapor in the pores of high-humidity flue gas, and alleviate the pore blockage caused by the products CaSO4, CaSO3 and water vapor. Thus, without destroying the original mass transfer pathway, the structural stability and active site utilization of the desulfurizer are improved.

[0014] Optionally, the inactive region of the mesoporous inner wall of the calcium-based support is modified with a molecularly imprinted layer; the thickness of the molecularly imprinted layer is 20-30 nm, the pore size is 0.8-1.2 nm, and the imprinting factor is ≥1.5. The inactive region is the Ca on the carrier surface. 2+ Regions with an active site density of <0.1 mmol / g.

[0015] By employing the above technical solution, the molecular imprinted layer is modified in inactive regions, thus avoiding the imprinted layer from covering the core reaction sites of the calcium-based carrier and ensuring the safety of Ca. 2+ This improves utilization efficiency, reduces the occupation of active sites by non-targeted gases, and ensures the efficient execution of the desulfurization reaction. In addition, the strong bonding of silicon-oxygen bonds in γ-aminopropyltriethoxysilane can enhance the interfacial bonding between the molecular imprint layer and the carrier, preventing the imprint layer from falling off during recycling.

[0016] Secondly, the present invention provides a method for preparing a calcium-based desulfurizing agent, which adopts the following technical solution: A method for preparing a calcium-based desulfurizing agent includes the following steps: Pretreatment of calcium-based carrier: The calcium source is crushed to 200 mesh, soaked in 5wt% hydrochloric acid solution to remove impurities, washed until neutral and dried. Add 3-5wt% of cerium dioxide rare earth additive relative to its mass to the dried calcium source, mix evenly and then ultrasonically disperse for 30 min, and dry at 110℃ for later use. Composite pore-forming and molding: Add composite pore-forming agent and sodium carboxymethyl cellulose at 2 wt% of the mass of the pretreated dried calcium source, mix, roll, and extrude into columnar bodies; the composite pore-forming agent is a mixture of zeolite and diethyl azodicarbonate, the total addition amount is 15-20 wt% of the mass of the pretreated dried calcium source, and the mass ratio of zeolite to diethyl azodicarbonate is 1:(1.2-1.5); Pre-calcination: The formed columnar body is pre-calcined at 600℃ for 2 hours to obtain the intermediate carrier; Surface hydroxyl reinforcement: The intermediate support was immersed in 0.5 mol / L ammonia water for 30 min, washed until neutral, and dried at 110 °C to obtain the calcium-based support.

[0017] By adopting the above technical solution, hydrochloric acid solution can selectively dissolve inert impurities such as iron oxide and silicon dioxide in the calcium source, preventing these impurities from covering the Ca. 2+ Active sites or block subsequently formed pores; the addition of cerium dioxide rare earth additives, on the one hand, reduces SO2 and Ca... 2+ The activation energy of the reaction; on the other hand, the redox properties of cerium dioxide itself can catalyze the oxidation of SO2 to SO4. 2- This accelerates the desulfurization process and enhances the structural stability of the calcium-based carrier in high-temperature desulfurization, preventing the active components from sintering and deactivating. The strong shear force of ultrasonic dispersion breaks down cerium dioxide agglomerates, ensuring that they are tightly bonded to the calcium source matrix.

[0018] Zeolite, as an inorganic pore-forming agent, undergoes a mild reaction with the calcium source during subsequent calcination, directionally generating microporous and mesoporous framework structures, providing sufficient active sites for SO2 adsorption. Diethyl azodicarbonate, as an organic pore-forming agent, rapidly decomposes during the pre-calcination stage, producing gaseous products that expand to form larger interconnected channels, creating macropores. Simultaneously, the macroscopic voids formed by the accumulation of calcium source particles and pore-forming agents are retained as macropores after pre-calcination. Sodium carboxymethyl cellulose binder binds to the calcium source and pore-forming agent particles through intermolecular hydrogen bonds, enhancing the interparticle bonding strength during extrusion molding, thus giving the desulfurizer good mechanical properties.

[0019] Pre-calcination promotes the initial sintering between calcium source particles, forming a stable framework structure and providing support for the preservation of the tertiary porous structure; ammonia significantly increases the density of hydroxyl (-OH) groups on the carrier surface, enhancing the carrier's adsorption capacity for SO2.

[0020] Optionally, after the calcium-based carrier pretreatment step and before the composite pore-forming and molding step, a pore stability modification step is further included, the specific steps of which are as follows: Add 5 wt% γ-aminopropyltriethoxysilane ethanol solution to the pretreated calcium source, stir at 80°C for 2 h, and dry at 110°C.

[0021] By adopting the above technical solution, γ-aminopropyltriethoxysilane is fully hydrolyzed to generate silanol groups (-SiOH), which then undergo a dehydration condensation reaction with the hydroxyl groups (-OH) on the surface of the calcium source to form stable Si-O-Ca covalent bonds. These bonds are uniformly anchored on the surface of the calcium source particles and potential pore sites. An organic-inorganic hybrid protective layer is constructed in advance during the calcium source powder stage, which inhibits excessive sintering and agglomeration between calcium source particles during the subsequent calcination and pore-forming process. This provides a stable framework support for the formation of the tertiary pore structure and reduces the risk of pore collapse and pore size shrinkage at high temperatures.

[0022] Optionally, the surface hydroxylation strengthening step further includes a carrier surface hydroxyl activation step: the product with surface hydroxyl strengthened is introduced into a 30ppm ozone atmosphere and treated at 50°C for 20 minutes.

[0023] By employing the above technical solution, ozone molecules slowly decompose to generate highly reactive hydroxyl radicals and singlet oxygen. These reactive oxygen species can specifically attack the common hydroxyl groups enriched on the surface of the intermediate support after hydroxylation pretreatment. Through electron transfer reactions, some saturated hydroxyl groups are oxidized into more reactive oxygen-containing functional groups, including carboxyl groups (-COOH), phenolic hydroxyl groups (-ArOH), and a small amount of peroxy groups (-OOH). This results in the carboxyl groups generated on the support surface having a stronger proton donor capacity and polarity compared to the original hydroxyl groups. + The amide group forms a hydrogen bond with the lone pair electrons of the nitrogen atom, while the carboxyl group dissociates into -COO. - -NH3 formed by matrix protonation with amide + Electrostatic attraction is generated, which significantly promotes the pre-assembly stability of template molecules and functional monomers.

[0024] Meanwhile, the newly added phenolic hydroxyl and peroxy groups serve as auxiliary active sites, which can form additional dipole-dipole interactions and coordination interactions with the template molecules. This, combined with the specific recognition of the molecular imprinted cavity, creates a synergistic adsorption effect, further enhancing the SO2 adsorption capacity. In addition, the ozone oxidation process can remove trace amounts of organic impurities remaining on the carrier surface, preventing impurities from occupying active sites and ensuring that the molecular imprint modification can uniformly cover the inactive areas of the inner wall of the carrier pores, thereby improving the binding stability of the imprinted layer.

[0025] Optionally, after the surface hydroxyl activation step, a molecular imprint layer functionalization step is further included, the specific steps of which are as follows: Imprinted polymerization: The calcium-based carrier was immersed in the imprinted polymerization reaction solution, pre-assembled in the dark for 4 hours, and then polymerized under 365nm ultraviolet light for 60 minutes at a temperature of 50-60℃. Template elution: The template was ultrasonically washed three times with 0.2 mol / L sodium hydroxide ethanol solution for 30 min each time, and then dried at 110℃. Low-temperature calcination and curing: calcination at 300-350℃ for 4 hours.

[0026] By adopting the above technical solution, in the imprinting polymerization reaction, the pre-assembly enables the SO2 template molecules and acrylamide functional monomers to fully form a stable supramolecular complex through hydrogen bonds and coordination bonds; the polymerization is initiated by heat preservation and ultraviolet light to accelerate the polymerization rate of functional monomers and ethylene glycol dimethacrylate crosslinking agent, forming a crosslinked and dense imprinted cavity that is complementary to the SO2 molecule structure, while avoiding premature desorption of template molecules or decomposition of functional monomers due to high temperature, thus ensuring the integrity of the imprinted layer structure.

[0027] Template molecule elution is performed using an alkaline ethanol solution with ultrasonic washing. The mechanical effect generated by ultrasonic vibration can efficiently remove residual template molecules deep within the pores and inside the imprinted layer. Combined with the dissociation effect of the alkaline environment on the template-monomer complex, it can thoroughly activate the specific recognition sites and prevent residual template from occupying the cavity and affecting the SO2 adsorption capacity. The 300-350℃ range is a low-temperature flexible treatment range, which is lower than the high-temperature calcination temperature commonly used for calcium-based supports, such as 850℃. This protects the hierarchical porous structure and active sites of the calcium-based support and maintains the original mass transfer advantages and reactivity of the support.

[0028] Optionally, in the imprinting polymerization step, the imprinting polymerization reaction solution is prepared as follows: the template molecule, acrylamide, methacrylic acid, ethylene glycol dimethacrylate and composite initiator are dissolved in anhydrous ethanol and ultrasonically dispersed for 10 min to obtain the reaction solution; In the composite initiator, the concentration of benzophenone is 4-6 mg / mL, and the concentration of ammonium persulfate is 2-3 mg / mL; all concentrations are based on the total volume of the reaction solution. The molar ratio of the template molecule, acrylamide, methacrylic acid, and ethylene glycol dimethacrylate is 1:(3-5):(1.3-1.7):(8-12); the template molecule is sulfur dioxide or sodium bisulfite.

[0029] By adopting the above technical solution, acrylamide and methacrylic acid synergistically enhance the self-assembly stability of template molecules and functional monomers, ensuring that the imprinted cavity formed after subsequent polymerization is consistent with the SO2 molecule structure, thereby improving the imprinting factor and adsorption selectivity. Benzophenone generates free radicals through photolysis under ultraviolet light irradiation, while ammonium persulfate slowly decomposes in the system microenvironment to provide additional free radicals, improving the initiation efficiency of the polymerization reaction. Furthermore, the functional monomers and crosslinking agent ethylene glycol dimethacrylate form an imprinted polymer layer with moderate crosslinking density and uniform structure within the carrier pores, ensuring the integrity of the imprinted cavity. Ultimately, the molecular imprinted layer possesses highly efficient SO2 targeting recognition capability, while maintaining a strong bond between the porous structure and the carrier, significantly improving the adsorption capacity and selectivity of the desulfurizer.

[0030] The molecular imprinting layer uses sulfur dioxide or sodium bisulfite as template molecules to construct a specific recognition cavity that is complementary to the structure of SO2 molecules. Acrylamide achieves rapid adsorption by forming a weak interaction with SO2 through hydrogen bonds, while methacrylic acid enhances the adsorption strength by forming ionic bonds with SO2 through carboxyl groups. The synergistic effect of acrylamide and methacrylic acid significantly improves the binding capacity of the imprinted sites to SO2. Ethylene glycol dimethacrylate forms a dense cross-linked network, giving the molecular imprinting layer a stable three-dimensional structure, allowing SO2 to penetrate rapidly and filtering out interfering gases such as nitrogen and carbon dioxide. Furthermore, it allows the recognized SO2 to diffuse rapidly to the nearby Ca²⁺ active sites to react.

[0031] Optionally, before template elution, the imprinted layer crosslinking strengthening step is further included, in which the polymerized carrier is placed under γ-ray irradiation with an irradiation dose of 5-10 kGy and an irradiation time of 15 min.

[0032] By adopting the above technical solution, chemical reactions are initiated by high-energy gamma rays penetrating the pores of the carrier: the energy can break the CH and CC bonds of the imprinted polymer chains, forming a large number of active free radicals, which promotes the formation of more CC cross-linking bonds through free radical coupling and addition reactions of adjacent polymer chains, thus constructing a denser and more complete three-dimensional cross-linked network on the basis of the original structure.

[0033] First, it significantly improves the crosslinking density and mechanical strength of the imprinted layer, enhancing its resistance to wear and peeling. Second, it suppresses the thermal shrinkage and deformation of the imprinted layer during subsequent high-temperature treatment and desulfurization through a rigid crosslinking network, maintaining efficient targeted recognition capabilities and comprehensively improving the structural stability and adsorption selectivity of the desulfurizer.

[0034] In summary, the present invention has at least one of the following beneficial technical effects: 1. By adopting a three-level pore structure of micropores-mesopores-macropores to form an efficient mass transfer system, micropores provide high-density active sites to enrich SO2, mesopores serve as intermediate diffusion channels to alleviate blockage, and macropores ensure the transport of substances in the later stages of the reaction. The resulting desulfurizer effectively solves the problems of ineffective pore structure and high mass transfer resistance, prolongs the exposure time of active sites, and improves calcium utilization and desulfurization efficiency.

[0035] 2. By constructing a pore support network using γ-aminopropyltriethoxysilane covalent bonds, pore collapse and shrinkage at high temperatures are suppressed. Simultaneously, its amino groups react with SO2 to form an acid-base relationship, anchoring Ca... 2+ Active sites synergistically regulate the hydrophilicity and hydrophobicity of the carrier surface, simultaneously enhancing the structural stability of the desulfurizer without disrupting the mass transfer pathway.

[0036] 3. By using a molecular imprinted layer modified with inactive regions, a SO2-specific recognition cavity is constructed with the synergistic effect of bifunctional monomers. This allows for precise screening of interfering gases such as nitrogen and carbon dioxide, achieving targeted adsorption and rapid diffusion of SO2. This avoids the imprinted layer covering the core active sites and enhances adsorption stability through synergistic effects with modifiers, ensuring the specificity and efficiency of the desulfurization reaction.

[0037] 4. By using composite pore-forming to control the tertiary pore structure parameters, hydroxyl enhancement and ozone activation to improve the binding efficiency of the imprinted layer, and gamma-ray crosslinking and low-temperature calcination to improve structural stability and retention of active sites, the problems of easy destruction of the pore structure and weak binding of the imprinted layer during preparation are solved, ensuring that the desulfurizer maintains stable adsorption selectivity and cycle life in industrial mass production, and is suitable for the continuous operation requirements of industrial flue gas desulfurization. Attached Figure Description

[0038] Figure 1 This is a scanning electron microscope image of the calcium-based desulfurizer in Example 1 of this application, magnified 100,000 times; Figure 2 This is a graph showing the instantaneous desulfurization efficiency changes of the calcium-based desulfurizing agent in Examples 1, 4 and Comparative Example 1 of this application; Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the embodiments.

[0040] Unless otherwise specified, the experimental methods used in the embodiments of this application are conventional methods, and the materials used are commercially available unless otherwise specified.

[0041] Example 1: This example discloses a calcium-based desulfurizing agent and its preparation method.

[0042] A calcium-based desulfurizer includes a calcium-based carrier, wherein the calcium-based carrier is made from a calcium source. In this embodiment, the calcium source is calcite powder with a calcium carbonate content of ≥98.2%. In other embodiments, the calcium source can also be limestone powder with a calcium carbonate content of ≥97.5%.

[0043] A method for preparing a calcium-based desulfurizing agent includes the following steps: 1. Pretreatment of calcium-based carrier Purification: After crushing the calcium source to 200 mesh, put it into the reaction vessel, prepare an acid solution with a concentration of 5 wt% hydrochloric acid, and stir and soak at room temperature for 60 minutes. Washing and drying: After acid leaching, the material is sent to a plate and frame filter press for filtration, washed with industrial water until the pH value of the washing liquid is 7.0±0.1, and the filter cake is sent to a dryer for drying for 4 hours to obtain a dried calcium source. Add rare earth additives: Add 4wt% cerium dioxide rare earth additives to the dried calcium source, mix at 300 rpm for 30 min, and then ultrasonically disperse at 50 kW power and 40 kHz frequency for 30 min. After dispersion, the material is sent back to the dryer and dried at 110℃ for 3 h to obtain the pretreated calcium source.

[0044] 2. Composite pore formation and molding Preparation of pore-forming agent: Zeolite and diethyl azodicarbonate were mixed at a mass ratio of 1:1.35 at 200 rpm for 20 min until homogeneous to obtain a composite pore-forming agent; Mixing and compaction: The pretreated calcium source, the composite pore-forming agent with an addition amount of 18 wt% of the pretreated dry calcium source, and the sodium carboxymethyl cellulose with an addition amount of 2 wt% of the pretreated dry calcium source are added to the mixer and mixed at 150 rpm for 40 min. The mixed material is then fed into the compaction mill and compacted 3 times for 5 min each time. The moisture content of the compacted material is controlled at 9±1 wt%. Extrusion molding: The crushed material is fed into an extrusion granulator and extruded into a columnar body of Φ3mm×8mm. It is then air-dried for 30 minutes under hot air temperature of 60℃.

[0045] 3. Pre-calcination: The formed columnar body is pre-calcined at 600℃ for 2 hours, then cooled naturally to room temperature in the cooling section to obtain the intermediate carrier.

[0046] 4. Surface hydroxyl reinforcement: The intermediate carrier was immersed in 0.5 mol / L ammonia water for 30 min. After immersion, it was filtered by a plate and frame filter press, washed with water until the pH value was 7.0±0.1, and dried at 110℃ for 3 h to obtain the hydroxyl-reinforced carrier.

[0047] The scanning electron microscope image of the micropore-mesopore-macropore three-level pore structure is shown below. Figure 1As shown, the obtained calcium-based desulfurizer has a three-level pore structure of micropores, mesopores, and macropores.

[0048] The testing mainly examines the structure of the tertiary pores, pore stability, and desulfurization efficiency.

[0049] The structure of the tertiary pores: to verify the specific surface area, pore size distribution and total pore volume of the tertiary pores of the calcium-based support.

[0050] The specific testing method is as follows: According to GB / T19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method", take 1.0g of desulfurizing agent sample, crush it to 100 mesh, put it into a sample tube, and degas it under vacuum at 110℃ for 4h; under liquid nitrogen -196℃ conditions, introduce high-purity nitrogen gas with a purity ≥99.999% and perform adsorption-desorption isotherm test, with a pressure range of 0.01-1.0P / P0.

[0051] Pore ​​stability (%): Used to evaluate the stability of the formed tertiary pore structure, ensuring that the desulfurizer does not collapse or degrade in performance under industrial conditions.

[0052] The specific testing method is as follows: According to GB / T30077-2013 "Evaluation Method for Surface Modification Effect of Nanopowder Materials", the desulfurizer sample is placed in a fixed-bed reactor, and simulated industrial flue gas is introduced with SO2 concentration of 1500ppm, oxygen of 8%, carbon dioxide of 12%, nitrogen balance, humidity of 15%, 120℃, and gas space velocity of 2000h⁻¹. -1 Under the condition of continuous operation for 100 hours, the total pore volume is tested and the pore volume retention rate is calculated. The pore volume retention rate is calculated as follows: (total pore volume after test / total pore volume before test) × 100%.

[0053] Desulfurization efficiency: Verify the desulfurizing agent's ability to remove SO2 from industrial flue gas and ensure that the desulfurization efficiency meets the requirements of industrial applications. It is evaluated by saturated sulfur capacity (g / g). The higher the saturated sulfur capacity value, the higher the desulfurization efficiency per gram of desulfurizing agent.

[0054] The specific testing method is as follows: Based on the industry standard DL / T986-2016 "Performance Acceptance Test Specification for Flue Gas Desulfurization Devices in Thermal Power Plants", a desulfurizing agent sample is loaded into a fixed-bed reactor, and simulated industrial flue gas is introduced with an SO2 concentration of 1500 ppm, oxygen of 8%, carbon dioxide of 12%, nitrogen balance, humidity of 15%, at 120℃ and a gas hourly space velocity of 1500 h⁻¹. -1 Simulated flue gas was continuously introduced, and the saturated sulfur capacity was measured. The saturated sulfur capacity S = (C_in × V × M_S) / (22.4 × m × 10⁻⁶) 6 ), where C_in is the SO2 concentration at the inlet, V is the cumulative gas volume (L), M_S is the molar mass of sulfur (32 g / mol), and m is the sample mass (g).

[0055] Example 2: This example discloses a calcium-based desulfurizing agent and its preparation method.

[0056] In this embodiment, a calcium-based desulfurizing agent, in addition to a calcium-based carrier, also includes γ-aminopropyltriethoxysilane dispersed and bonded within the pores of the calcium-based carrier, wherein the γ-aminopropyltriethoxysilane accounts for 1.5 wt% of the mass of the calcium-based carrier; the purpose of its addition is to improve the pore stability of the calcium-based carrier.

[0057] Therefore, a method for preparing a calcium-based desulfurizing agent includes the following steps: 1. Pretreatment of calcium-based carrier: Same as in Example 1.

[0058] 2. Channel stability modification: Prepare a 5 wt% γ-aminopropyltriethoxysilane ethanol solution and stir at 80 rpm until dissolved; add the pretreated calcium source and the γ-aminopropyltriethoxysilane ethanol solution to the reaction vessel at a solid-liquid ratio of 1:0.32 (g / mL), stir magnetically at 80℃ and 60 rpm for 2 h; dry at 110℃ for 4 h to obtain the modified calcium source; 3. Composite pore formation and molding: Same as in Example 1; 4. Pre-calcination: Same as in Example 1; 5. Surface hydroxyl reinforcement: Same as in Example 1.

[0059] Everything else is the same as in Example 1.

[0060] Example 3: This example discloses a calcium-based desulfurizing agent and its preparation method.

[0061] In this embodiment, a method for preparing a calcium-based desulfurizing agent includes the following steps: Following the surface hydroxyl strengthening step, the process also includes a carrier surface hydroxyl activation step: The hydroxyl-enhanced carrier was placed in a constant-temperature reactor, purged with 30 ppm ozone, and kept at 50°C for 20 minutes. It was then allowed to cool naturally to room temperature to obtain the activated carrier.

[0062] Everything else is exactly the same as in Example 2.

[0063] Example 4: This example discloses a calcium-based desulfurizing agent and its preparation method.

[0064] In this embodiment, a calcium-based desulfurizing agent is provided, wherein the inactive region of the mesoporous inner wall of the calcium-based carrier is modified with a molecularly imprinted layer; the thickness of the molecularly imprinted layer is 25±5nm, the pore size is 1.0±0.2nm, and the imprinting factor is 2.0. The surface of the calcium-based support includes active and inactive regions, with the active region being the calcium on the support surface. 2+The region with an active site density ≥ 0.1 mmol / g, and the inactive region being the Ca on the support surface. 2+ Regions with an active site density of <0.1 mmol / g.

[0065] Therefore, a method for preparing a calcium-based desulfurizer further includes a molecularly imprinted layer functionalization step after the hydroxyl activation step on the carrier surface, specifically: Preparation of the imprinted polymerization reaction solution: The monomers and composite initiator were dissolved in anhydrous ethanol according to the template molecule: acrylamide: methacrylic acid: ethylene glycol dimethacrylate = 1:4:1.5:10 (molar ratio), and ultrasonically dispersed for 10 min to obtain the reaction solution. The concentration of benzophenone in the total reaction solution was 5 mg / mL, and the concentration of ammonium persulfate in the total reaction solution was 2.5 mg / mL. In this embodiment, the template molecule was sulfur dioxide; in other embodiments, sodium bisulfite can also be used as the template molecule. Imprinted polymerization: The activated carrier was immersed in the above reaction solution at a solid-liquid ratio of 1:2 (g / mL), pre-assembled in the dark for 4 hours, and then polymerized under 365nm ultraviolet light at 55℃ for 60 minutes in a constant temperature ultraviolet reactor. Template elution: The template was ultrasonically washed three times with 0.2 mol / L sodium hydroxide ethanol solution for 30 min each time, and then dried at 110℃ for 3 h. Low-temperature calcination and curing: After washing, the carrier is sent into a muffle furnace and calcined at 320°C for 4 hours, and then naturally cooled to room temperature.

[0066] Everything else is exactly the same as in Example 3.

[0067] Example 5: This example discloses a calcium-based desulfurizing agent and its preparation method.

[0068] In this embodiment, a method for preparing a calcium-based desulfurizing agent includes the following steps: Preparation of reaction solution: Same as in Example 4; Imprinted polymerization: The activated carrier was immersed in the above reaction solution at a solid-liquid ratio of 1:2 (g / mL), pre-assembled in the dark for 4 hours, and then polymerized under 365nm ultraviolet light at 55℃ for 60 minutes in a constant temperature ultraviolet reactor. Imprinted layer crosslinking reinforcement: The polymerized carrier was placed under γ-ray irradiation with an irradiation dose of 8 kGy and an irradiation time of 15 min; Template elution: The template was ultrasonically washed three times with 0.2 mol / L sodium hydroxide ethanol solution for 30 min each time, and then dried at 110℃ for 3 h. Low-temperature calcination and curing: After washing, the carrier is sent into a muffle furnace and calcined at 320°C for 4 hours, and then naturally cooled to room temperature.

[0069] Everything else is exactly the same as in Example 4.

[0070] The key performance indicators of the calcium-based desulfurizers described in Examples 1-5 and the calcium-based desulfurizers prepared by the same method were tested, and the results are shown in Table 1. Table 1:

[0071] Data from Example 1 shows that the composite pore-forming agent zeolite, acting as a rigid template, constructs a microporous-mesoporous framework. Diethyl azodicarbonate, through decomposition, generates gas to expand macropores, achieving a balanced ratio of specific surface area, total pore volume, and micropores, mesopores, and macropores, thus providing a basic channel for SO2 diffusion and reaction. The surface hydroxyl reinforcement step enhances the Ca... 2+ The degree of exposure of active sites, coupled with the promotion of reactivity by cerium dioxide rare earth additives, resulted in a saturated sulfur capacity of 0.16 g / g, slightly higher than the upper limit of conventional calcium-based desulfurizers (0.15 g / g), demonstrating the feasibility of the process.

[0072] Comparing Example 1 and Example 2, it can be seen that in Example 2, when γ-aminopropyltriethoxysilane is dispersed and bonded within the pores of the calcium-based support, the microporous-mesoporous-macroporous tertiary pore structure constructed by the composite pore-forming agent is not destroyed. Therefore, the specific surface area, total pore volume, and tertiary pore ratio only fluctuate slightly, maintaining the basic channels for SO2 transport and reaction. Simultaneously, the silicon-oxygen bonds strengthen the pore wall structure through chemical bonding, effectively inhibiting the erosion and collapse of the pores by the acidic simulated flue gas during detection, resulting in a significant increase in pore volume retention. Furthermore, the improved pore stability reduces the amount of calcium deposits during the desulfurization process. 2+ The loss of active sites increases the contact efficiency between active sites and SO2, thereby promoting the increase of saturated sulfur capacity.

[0073] Comparing Example 3 with Example 2, it can be seen that the total pore volume, specific surface area, micropore ratio, pore volume retention rate, and saturated sulfur capacity are all improved in Example 3. The overall distribution of the tertiary pores is basically stable, indicating that ozone activation did not destroy the stable silicon-oxygen bond structure formed by γ-aminopropyltriethoxysilane on the inner wall of the pores in Example 2. Therefore, the pore stability and the distribution of the tertiary pores did not fluctuate significantly. At the same time, the oxidation effect of ozone can convert some inert hydroxyl groups on the carrier surface into more active hydroxyl groups, which not only increases the exposure of surface active sites but also enhances the Ca2+ content. 2+ The reactivity of the active sites promotes the contact and reaction between SO2 and the calcium-based support.

[0074] Comparing Example 4 with Example 3, it can be seen that in Example 4, after the hydroxyl groups on the carrier surface were activated, a molecularly imprinted layer was added for functionalization. The specific surface area, total pore volume, and micropore ratio all increased slightly, while the mesopore ratio decreased slightly. This is because the molecularly imprinted layer modifies the inactive regions of the mesopore inner wall, neither blocking the pores nor hindering the increase of surface adsorption sites through the three-dimensional network structure of the imprinted polymer. Simultaneously, the binding of the imprinted layer with the hydroxyl groups on the carrier surface slightly optimized the pore structure regularity. The slightly improved pore volume retention rate indicates that the molecularly imprinted layer has a slight coating effect on the mesopore inner wall, reducing the erosion of the pores by flue gas scouring. The increased saturated sulfur capacity indicates that the molecularly imprinted layer can specifically recognize and capture SO2 molecules, enriching them in Ca2+. 2+ Near the active site, mass transfer resistance is significantly reduced, promoting SO2 and Ca... 2+ The full reaction further illustrates the role of molecular imprinting technology in improving the specific adsorption and reaction efficiency of desulfurizing agents.

[0075] Comparing Example 5 with Example 4, it can be seen that Example 5 added a γ-ray crosslinking enhancement step after molecular imprinting polymerization, resulting in an increase in specific surface area, total pore volume, and micropore ratio. Essentially, γ-rays induce crosslinking reactions in the imprinted polymer molecular chains, forming a denser and more regular three-dimensional network structure. The crosslinking of chain segments optimizes the surface roughness of the imprinted layer, indirectly increasing the adsorption sites. The improved pore volume retention rate is due to the significantly enhanced bonding force between the crosslinked molecular imprinted layer and the inner wall of the carrier mesopores, which can effectively resist the erosion of acidic components and airflow scouring in simulated flue gas, reducing pore damage caused by imprinted layer detachment. The improved saturated sulfur capacity is due to the stable crosslinked structure making the specific recognition sites of the imprinted layer less prone to deformation, resulting in more stable enrichment and mass transfer efficiency of SO2 molecules.

[0076] Comparative Example 1: This comparative example discloses a calcium-based desulfurizing agent and its preparation method.

[0077] In this comparative example, a single pore-forming agent was used instead of a composite pore-forming agent. The single pore-forming agent used was zeolite, and the remaining preparation steps and raw material steps were the same as in Example 1.

[0078] Comparative Example 2: This comparative example discloses a calcium-based desulfurizing agent and its preparation method.

[0079] In this comparative example, a single pore-forming agent is still used instead of a composite pore-forming agent. The single pore-forming agent used is diethyl azodicarbonate, and the remaining preparation steps and raw material steps are the same as in Example 1.

[0080] Key performance indicators of the calcium-based desulfurizers described in Comparative Examples 1-2 and those prepared by the same method were tested. The test results are shown in Table 2. Table 2:

[0081] By comparing Comparative Example 1 with Example 1, it can be seen that Comparative Example 1 relies solely on zeolite for pore formation, lacking the macropore expansion and pore connectivity optimization brought about by gas pore formation. This results in a low proportion of micropores, an excessively high proportion of mesopores, and a disordered distribution of macropores. The specific surface area and total pore volume are both low. At the same time, the single-pore structure is prone to collapse after aging of simulated industrial flue gas, resulting in low pore volume retention rate and low saturated sulfur capacity. Ultimately, SO2 is difficult to fully diffuse to the internal active sites and react.

[0082] In addition, the instantaneous desulfurization rate was tested in Examples 1, 4, and Comparative Example 1. The specific testing method is as follows: According to the industry standard DL / T986-2016 "Performance Acceptance Test Specification for Flue Gas Desulfurization Devices in Thermal Power Plants", a desulfurizing agent sample was loaded into a fixed-bed reactor, and simulated industrial flue gas was introduced with an SO2 concentration of 1500 ppm, oxygen of 8%, carbon dioxide of 12%, nitrogen balance, humidity of 15%, temperature of 120°C, and gas space velocity of 1500 h⁻¹. -1 Simulated flue gas was continuously introduced, and the SO2 concentration at the inlet and outlet was recorded every 10 minutes. The instantaneous desulfurization efficiency was calculated as: (C_in-C_out) / C_in×100%, where C_in is the inlet SO2 concentration and C_out is the outlet SO2 concentration.

[0083] See the data changes for each group. Figure 2 As can be seen, Example 4 has the highest instantaneous desulfurization rate, followed by Example 1, while Comparative Example 1 has the lowest instantaneous desulfurization rate.

[0084] By comparing Comparative Example 2 with Example 1, it can be seen that in Comparative Example 2, the pore-forming effect of diethyl azodicarbonate alone can only form macropores through gas escape, lacking micropore-mesopore support. This results in a small specific surface area and low total pore volume, further leading to insufficient SO2 adsorption sites. The macropore-dominated structure is prone to collapse after aging of simulated industrial flue gas, making it difficult for SO2 to adsorb onto the calcium-based support. 2+ The active sites are in full contact, which leads to incomplete desulfurization reaction and low saturated sulfur capacity.

[0085] As can be seen from Table 1, the desulfurization effect of the desulfurizing agents prepared in Examples 1-5 is significantly higher than that in Comparative Examples 1-2, indicating that the desulfurizing agents prepared in this invention can be used in industrial flue gas desulfurization scenarios and have significant practical significance.

[0086] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A calcium-based desulfurizing agent, characterized in that, Including calcium-based carriers; The calcium-based carrier has a three-level pore structure of micropores-mesopores-macropores, wherein the micropores have a diameter of 0.5–0.8 nm and account for 30–40% of the total pore volume; the mesopores have a diameter of 10–50 nm and account for 50–60% of the total pore volume; and the macropores have a diameter >50 nm and account for 5–10% of the total pore volume. The specific surface area of ​​the carrier is 40-80 m². 2 / g, pore volume ≥0.25cm 3 / g.

2. The calcium-based desulfurizer according to claim 1, characterized in that, It also includes γ-aminopropyltriethoxysilane dispersed and bonded within the pores of the calcium-based carrier, wherein the γ-aminopropyltriethoxysilane accounts for 1 to 2 wt% of the mass of the calcium-based carrier.

3. A calcium-based desulfurizing agent according to claim 1 or 2, characterized in that, The inactive region of the mesoporous inner wall of the calcium-based support is modified with a molecularly imprinted layer; the thickness of the molecularly imprinted layer is 20-30 nm, the pore size is 0.8-1.2 nm, and the imprinting factor is ≥1.

5. The inactive region is the Ca on the carrier surface. 2+ Regions with an active site density of <0.1 mmol / g.

4. A method for preparing a calcium-based desulfurizing agent according to any one of claims 1-3, characterized in that, Includes the following steps: Pretreatment of calcium-based carrier: The calcium source is crushed to 200 mesh, soaked in 5wt% hydrochloric acid solution to remove impurities, washed until neutral and dried. Add 3-5wt% of cerium dioxide rare earth additive relative to its mass to the dried calcium source, mix evenly and then ultrasonically disperse for 30 min, and dry at 110℃ for later use. Composite pore-forming and molding: Add composite pore-forming agent and sodium carboxymethyl cellulose at 2 wt% of the mass of the pretreated dried calcium source, mix, roll, and extrude into columnar bodies; the composite pore-forming agent is a mixture of zeolite and diethyl azodicarbonate, the total addition amount is 15-20 wt% of the mass of the pretreated dried calcium source, and the mass ratio of zeolite to diethyl azodicarbonate is 1:(1.2-1.5); Pre-calcination: The formed columnar body is pre-calcined at 600℃ for 2 hours to obtain the intermediate carrier; Surface hydroxyl reinforcement: The intermediate carrier was immersed in 0.5 mol / L ammonia water for 30 min, washed until neutral, and dried at 110 °C.

5. The method for preparing a calcium-based desulfurizing agent according to claim 4, characterized in that, After the calcium-based carrier pretreatment step and before the composite pore-forming and molding step, a pore stability modification step is also included, the specific steps of which are as follows: Add 5 wt% γ-aminopropyltriethoxysilane ethanol solution to the pretreated calcium source, stir at 80°C for 2 h, and dry at 110°C.

6. The method for preparing a calcium-based desulfurizing agent according to claim 5, characterized in that, The surface hydroxylation strengthening step is followed by a carrier surface hydroxyl activation step: the product with surface hydroxyl strengthening is introduced into a 30ppm ozone atmosphere and treated at 50°C for 20 minutes.

7. The method for preparing a calcium-based desulfurizing agent according to claim 6, characterized in that, Following the surface hydroxyl activation step, a molecular imprint layer functionalization step is also included, the specific steps of which are as follows: Imprinted polymerization: The calcium-based carrier was immersed in the imprinted polymerization reaction solution, pre-assembled in the dark for 4 hours, and then polymerized under 365nm ultraviolet light for 60 minutes at a temperature of 50-60℃. Template elution: The template was ultrasonically washed three times with 0.2 mol / L sodium hydroxide ethanol solution for 30 min each time, and then dried at 110℃. Low-temperature calcination and curing: calcination at 300-350℃ for 4 hours.

8. The method for preparing a calcium-based desulfurizing agent according to claim 7, characterized in that, In the imprinting polymerization step, the imprinting polymerization reaction solution is prepared as follows: the template molecule, acrylamide, methacrylic acid, ethylene glycol dimethacrylate and composite initiator are dissolved in anhydrous ethanol and ultrasonically dispersed for 10 min to obtain the reaction solution; In the composite initiator, the concentration of benzophenone is 4-6 mg / mL, and the concentration of ammonium persulfate is 2-3 mg / mL; all concentrations are based on the total volume of the reaction solution. The molar ratio of the template molecule, acrylamide, methacrylic acid, and ethylene glycol dimethacrylate is 1:(3-5):(1.3-1.7):(8-12); the template molecule is sulfur dioxide or sodium bisulfite.

9. The method for preparing a calcium-based desulfurizing agent according to claim 7, characterized in that, Before template elution, the imprinted layer crosslinking strengthening step is also included, in which the polymerized carrier is placed under γ-ray irradiation with an irradiation dose of 5-10 kGy and an irradiation time of 15 min.

10. The application of a calcium-based desulfurizer according to any one of claims 1-3, or a calcium-based desulfurizer obtained by the preparation method according to any one of claims 4-9, in an industrial flue gas sulfur dioxide removal process.

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