Manganese-lanthanum double-element gradient doped calcium-based desulfurizing agent and preparation method thereof

Abstract

The invention discloses a manganese-lanthanum double-element gradient doped calcium-based desulfurizing agent and a preparation method thereof, and belongs to the technical field of flue gas purification. The method comprises the following steps: preparing a precursor, namely mixing calcium hydroxide, manganous nitrate and lanthanum nitrate, and preparing the precursor by adopting a sol-gel method; gradient doping control: calcining through temperature programming, and forming a gradient doping material by utilizing the diffusion rate difference of Mn < 2 + > and La < 3 + > ions; surface electron structure regulation and control: carrying out heat treatment on the gradient doped material in an inert atmosphere, replacing Ca < 2 + > with Mn < 2 + > to form oxygen vacancy, and improving electron mobility; la < 3 + > forms a La-O-Ca bond on the surface, so that the surface energy is reduced. The preparation method is efficient, the prepared desulfurizing agent has high activity and stability, acid gas in flue gas can be effectively removed, and the problems that an existing material is low in deacidification efficiency in a medium-high-temperature low-water environment and large in medium-low-temperature spraying fly ash amount are solved.

Description

Technical Field

[0001] This invention belongs to the field of flue gas purification technology, specifically relating to a calcium-based desulfurizer with manganese-lanthanum dual-element gradient doping and its preparation method. Background Technology

[0002] Currently, the control of pollutant concentrations in flue gas emissions is becoming increasingly stringent, especially for SO2 and HCl emission concentrations, which have been reduced from 100 mg / Nm³. 3 Reduced to 10~20 mg / Nm 3 The wet process has high investment and operating costs. Many enterprises use the original semi-dry and dry processes, which involve excessive spraying of calcium hydroxide. Ordinary Ca(OH)2 desulfurization has low efficiency, small sulfur capacity, and large amount of desulfurizing agent, resulting in low lime reaction efficiency, generating more secondary pollutants such as fly ash, and making it difficult to meet emission standards.

[0003] To address these issues, researchers have attempted various modification techniques to improve the hardening efficiency of calcium hydroxide. Patent CN117101400B uses a mixture of calcium-based composite raw materials and catalytic oxidation components, calcined together, and combined with organic polymers and phosphorus-containing salts as additives. Through high-temperature activation and synergistic catalysis by rare earth elements, a highly active calcium-based desulfurizer is formed, improving SO2 diffusion channels and enhancing desulfurization efficiency. However, this process is complex and energy-intensive. Patent CN117138547B uses microwave heating to calcine and activate additives such as calcium-based bentonite, forming an activated slurry. CaO powder is then added for digestion, dried, and pulverized to prepare a calcium-based desulfurization powder with high specific surface area and pore volume, enhancing desulfurization effect and reducing environmental pollution. However, its preparation cost is high and the process is complex. CN117263262A discloses a dual-dimensional gradient-doped cathode material and its preparation method. This method effectively reduces interfacial side reactions between primary and secondary spherical particles and the electrolyte by constructing primary and secondary spherical particles for gradient doping, stabilizing the crystal structure and compressive strength of the dual-dimensional gradient-doped cathode material, and improving the overall electrochemical performance of the material. However, in the process of preparing nickel-cobalt-manganese precursors using the co-precipitation method, the crystallinity and uniformity of the precursors still need to be improved.

[0004] Currently, all highly active calcium hydroxide is prepared by high-temperature calcination or digestion of calcium hydroxide precursors, which is a complex, costly, and unstable process. While doping technology is widely used for material modification to improve specific surface area and other properties, it is rarely applied in the preparation of highly active calcium hydroxide. An ideal doping method should effectively solve the problems existing in the current technology and achieve a synergistic improvement in the stability of calcium hydroxide. Therefore, to address the above problems, this invention provides a method for preparing high-efficiency lime directly from ordinary calcium hydroxide using manganese-lanthanum dual-element gradient doping. Summary of the Invention

[0005] Technical problem solved: To address the above-mentioned technical problems, this invention provides a calcium-based desulfurizer with manganese-lanthanum dual-element gradient doping and its preparation method. The preparation method is highly efficient, and the prepared desulfurizer has both high activity and stability, and can effectively remove acidic gases from flue gas. This solves the problems of low acid removal efficiency and large fly ash content in medium- and low-temperature injection environments of existing materials.

[0006] Technical solution: A method for preparing a calcium-based desulfurizing agent with manganese-lanthanum dual-element gradient doping, comprising the following steps: Step 1, Precursor preparation: Calcium hydroxide, manganese nitrate and lanthanum nitrate are mixed and the precursor is prepared by sol-gel method; Step 2, Gradient Doping Control: Through programmed temperature rise calcination, using Mn... 2+ and La 3+ Differences in ion diffusion rates create gradient-doped materials; Step 3, Surface electronic structure modulation: The gradient-doped material is heat-treated in an inert atmosphere, Mn 2+ Alternative Ca 2+ Oxygen vacancies are formed at the site, increasing electron mobility; La 3+ La-O-Ca bonds are formed on the surface, reducing the surface energy.

[0007] Preferably, in step 1, the molar ratio of calcium hydroxide, manganese nitrate, and lanthanum nitrate is 98:1:1.

[0008] Preferably, step 1 specifically involves: mixing calcium hydroxide, manganese nitrate, and lanthanum nitrate with water to form a mixed solution, aging it for 4-6 hours, filtering and washing it until neutral, and then drying the washed filter cake at 60-70°C for 4-6 hours to obtain a uniform precursor.

[0009] Furthermore, the pH of the mixed solution is controlled to be 6.5~7.5, and the temperature is controlled to be 60~70℃.

[0010] Preferably, in step 2, the conditions for programmed temperature calcination are: under a nitrogen atmosphere, the temperature is increased to 500~800℃ at a heating rate of 2℃ / min, and held for 2~4 hours.

[0011] Preferably, in step 2, the programmed heating calcination is carried out in a tube furnace, and the material is naturally cooled after calcination to obtain a gradient-doped material.

[0012] Preferably, in step 3, the heat treatment conditions are: temperature controlled at 400~600℃, and heat treatment for 1~2 hours.

[0013] A calcium-based desulfurizer with manganese-lanthanum dual-element gradient doping prepared by the above method.

[0014] Preferably, the X-ray diffraction parameters of the calcium-based desulfurizer are: lattice constant a = 0.514 nm, c = 1.328 nm.

[0015] Preferably, the calcium-based desulfurizing agent has a pore size distribution concentrated in the range of 5-15 nm and a specific surface area of ​​48-52 m². 2 / g.

[0016] Beneficial effects: This invention uses calcium hydroxide to directly prepare highly active calcium hydroxide, which has the following beneficial effects: 1. By mixing calcium hydroxide, manganese nitrate and lanthanum nitrate in a molar ratio of 98:1:1 and preparing a uniform precursor using the sol-gel method, the crystallinity and uniformity of the precursor are effectively improved, solving the problem of insufficient crystallinity and uniformity of the precursor in the prior art. 2. A programmed temperature rise calcination process (500~800℃, heating rate 2℃ / min) is adopted, utilizing Mn 2+ and La 3+ The difference in ion diffusion rate forms a concentration gradient from the inside out (0.2~0.5wt% inside, 1.0~1.5wt% on the surface), realizing the gradient distribution of doping elements, effectively improving the structural stability of the material, and solving the problem of low content of traditional doping elements; 3. Mn 2+ Alternative Ca 2+ Oxygen vacancies are formed at the site, increasing electron mobility (by 25-30%). 3+ The formation of La-O-Ca bonds on the surface reduces the surface energy (by 15-20%), effectively resolving the contradiction between high activity and stability through a dual mechanism of lattice distortion effect and surface charge redistribution. 4. The final product has a specific surface area of ​​48~52m². 2 / g, with a pore size distribution concentrated in 5~15nm, has a good specific surface area and pore structure, which improves the material’s reactivity and electrochemical performance; 5. In flue gas with a moisture content of 5%~15% at 300℃, compared with ordinary calcium hydroxide, the calcium-based desulfurizer prepared by this invention has 1.5~2.5 times higher thermal stability and 50~70% higher selective adsorption capacity for SO2. It significantly improves the stability and selective adsorption performance of the material in medium-high temperature and low water vapor environment, and solves the problems of low acid removal efficiency and large fly ash amount of the material in medium-high temperature and low water environment in the prior art. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments. Example 1

[0018] A method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer includes the following steps: Step 1, Precursor Preparation: Step 101: Mix calcium hydroxide, manganese nitrate and lanthanum nitrate in a molar ratio of 98:1:1, wherein the concentration of raw material Ca(OH)2 is 0.1 mol / L, the concentration of Mn(NO3)2 is 0.01 mol / L, and the concentration of La(NO3)3 is 0.001 mol / L; Step 102: Prepare a mixed solution using the sol-gel method, controlling the pH value to be 7.0 and the temperature to be 60℃; Step 103: Aging the mixed solution for 4 hours; Step 104: Filter the aged mixed solution and wash it with deionized water until neutral; Step 105: Dry the washed filter cake at 65°C for 5 hours to obtain a uniform precursor.

[0019] Step 2, Gradient Doping Control: Step 201: Place the uniform precursor in a tube furnace; Step 202: Under a nitrogen atmosphere, heat to 600°C at a heating rate of 2°C / min; Step 203: After holding at the temperature for 3 hours, allow it to cool naturally to room temperature to obtain the gradient-doped material.

[0020] Step 3: Surface electronic structure modulation: Step 301: Heat-treat the gradient-doped material under an inert atmosphere at a temperature controlled at 500℃. Step 302: After keeping warm for 1.5 hours, allow it to cool naturally to room temperature; Step 303: Perform performance tests on the treated material in air with 80% relative humidity.

[0021] The prepared calcium-based desulfurizer has a specific surface area of ​​50 m². 2 The material has a pore size distribution concentrated within 10 nm and a surface dopant content of 1.2 wt%. X-ray diffraction analysis revealed lattice constants a = 0.514 nm and c = 1.328 nm. Under SO2 gas conditions, the material exhibits a 68% increase in selective SO2 adsorption capacity, and thermogravimetric analysis showed a 1.8-fold improvement in its stability at 300℃. Example 2

[0022] A method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer includes the following steps: Step 1, Precursor Preparation: Step 101: Mix Ca(OH)2, Mn(NO3)2 and La(NO3)3 in a molar ratio of 98:1:1, wherein the concentration of Ca(OH)2 is 0.15 mol / L, the concentration of Mn(NO3)2 is 0.015 mol / L, and the concentration of La(NO3)3 is 0.002 mol / L. Step 102: Prepare a mixed solution using the sol-gel method, controlling the pH value to be 6.5 and the temperature to be 70℃; Step 103: Aging the mixed solution for 6 hours; Step 104: Filter the aged mixed solution and wash it with deionized water until neutral; Step 105: Dry the washed filter cake at 70°C for 6 hours to obtain a uniform precursor.

[0023] Step 2, Gradient Doping Control: Step 201: Place the uniform precursor in a tube furnace; Step 202: Under a nitrogen atmosphere, heat to 700°C at a heating rate of 2°C / min; Step 203: After holding at the temperature for 2.5 hours, allow the material to cool naturally to room temperature to obtain the gradient-doped material.

[0024] Step 3: Surface electronic structure modulation: Step 301: Heat-treat the gradient-doped material under an inert atmosphere at a temperature controlled at 550°C. Step 302: After keeping warm for 2 hours, allow it to cool naturally to room temperature; Step 303: Perform performance tests on the treated material in air with 80% relative humidity.

[0025] The specific surface area of ​​the prepared gradient-doped material is 48 m². 2 The material has a pore size distribution concentrated at 8 nm and a surface dopant content of 0.8 wt%. X-ray diffraction analysis revealed a lattice constant of a = 0.514 nm and a lattice constant of c = 1.328 nm. Under SO2 gas conditions, the material exhibits a 62% increase in selective SO2 adsorption capacity, and thermogravimetric analysis showed a 2.1-fold increase in stability at 300℃. Example 3

[0026] A method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer includes the following steps: Step 1, Precursor Preparation: Step 101: Mix Ca(OH)2, Mn(NO3)2 and La(NO3)3 in a molar ratio of 98:1:1, wherein the concentration of Ca(OH)2 is 0.12 mol / L, the concentration of Mn(NO3)2 is 0.02 mol / L, and the concentration of La(NO3)3 is 0.003 mol / L; Step 102: Prepare a mixed solution using the sol-gel method, controlling the pH value to be 7.5 and the temperature to be 65℃; Step 103: Aging the mixed solution for 5 hours; Step 104: Filter the aged mixed solution and wash it with deionized water until neutral; Step 105: Dry the washed filter cake at 60°C for 4 hours to obtain a uniform precursor.

[0027] Step 2, Gradient Doping Control: Step 201: Place the uniform precursor in a tube furnace; Step 202: Under a nitrogen atmosphere, heat to 800°C at a heating rate of 2°C / min; Step 203: After holding at the temperature for 2 hours, allow the material to cool naturally to room temperature to obtain the gradient-doped material.

[0028] Step 3: Surface electronic structure modulation: Step 301: Heat-treat the gradient-doped material under an inert atmosphere at a temperature controlled at 600℃. Step 302: After keeping warm for 1 hour, allow it to cool naturally to room temperature; Step 303: Perform performance tests on the treated material in air with 80% relative humidity.

[0029] The specific surface area of ​​the prepared gradient-doped material is 52 m². 2 The material has a pore size distribution concentrated at 12 nm and a surface dopant content of 1.5 wt%. X-ray diffraction analysis revealed a lattice constant of a = 0.514 nm and c = 1.328 nm. Under SO2 gas conditions, the material exhibits a 70% increase in selective SO2 adsorption capacity, and thermogravimetric analysis showed a 2.5-fold improvement in its stability at 300℃.

Claims

1. A method for preparing a calcium-based desulfurizing agent with manganese-lanthanum dual-element gradient doping, characterized in that, The steps include the following: Step 1, Precursor preparation: Calcium hydroxide, manganese nitrate and lanthanum nitrate are mixed and the precursor is prepared by sol-gel method; Step 2, Gradient Doping Control: Through programmed temperature rise calcination, using Mn... 2+ and La 3+ Differences in ion diffusion rates create gradient-doped materials; Step 3, Surface electronic structure modulation: The gradient-doped material is heat-treated in an inert atmosphere, Mn 2+ Alternative Ca 2+ Oxygen vacancies are formed at the site, increasing electron mobility; La 3+ La-O-Ca bonds are formed on the surface, reducing the surface energy.

2. The method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 1, characterized in that, In step 1, the molar ratio of calcium hydroxide, manganese nitrate, and lanthanum nitrate is 98:1:

1.

3. The method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 1, characterized in that, Step 1 specifically involves: mixing calcium hydroxide, manganese nitrate, and lanthanum nitrate with water to form a mixed solution, aging it for 4-6 hours, filtering and washing it until neutral, and then drying the washed filter cake at 60-70°C for 4-6 hours to obtain a uniform precursor.

4. The method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 3, characterized in that, The pH of the mixed solution is controlled at 6.5~7.5, and the temperature is controlled at 60~70℃.

5. The method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 1, characterized in that, In step 2, the conditions for programmed temperature calcination are as follows: under a nitrogen atmosphere, the temperature is increased to 500~800℃ at a heating rate of 2℃ / min, and held for 2~4 hours.

6. The method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 1, characterized in that, In step 2, the programmed heating calcination is carried out in a tube furnace, and the material is naturally cooled after calcination to obtain a gradient-doped material.

7. The method for preparing a manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 1, characterized in that, In step 3, the heat treatment conditions are: temperature controlled at 400~600℃, and heat treatment for 1~2 hours.

8. A calcium-based desulfurizer with manganese-lanthanum dual-element gradient doping prepared by the method of claim 1.

9. The manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 8, characterized in that, The X-ray diffraction parameters of the calcium-based desulfurizer are: lattice constant a = 0.514 nm, c = 1.328 nm.

10. The manganese-lanthanum dual-element gradient-doped calcium-based desulfurizer according to claim 8, characterized in that, The calcium-based desulfurizing agent has a pore size distribution concentrated in the range of 5-15 nm and a specific surface area of ​​48-52 m². 2 / g.