A nano-calcium hydroxide, its preparation method and application

Abstract

This invention provides a nano-calcium hydroxide, its preparation method, and its application. The raw materials for preparing the nano-calcium hydroxide, by weight, include: 18-28 parts calcium oxide, 120-150 parts deionized water, 1.5-3.5 parts phosphorylated polyethylene glycol monomethyl ether, 0.8-2.5 parts carboxylated β-cyclodextrin, 2.0-4.5 parts sodium polyaspartate, 0.5-1.8 parts L-lysine, and 0.3-1.0 parts 3-mercaptopropylmethyldimethoxysilane. The nano-calcium hydroxide prepared by this invention uses calcium oxide as the calcium source and is compounded with various functional additives. Through the synergistic effects of coordination, steric hindrance, electrostatic repulsion, and surface modification, it effectively inhibits grain growth and agglomeration, resulting in controllable particle size, good dispersion stability, low system viscosity, and excellent particle uniformity.

Description

Technical Field

[0001] This invention relates to the field of calcium hydroxide preparation technology, specifically to a nano-calcium hydroxide, its preparation method, and its application. Background Technology

[0002] Nano-calcium hydroxide, as a key inorganic nanomaterial in the cutting-edge field of new materials, possesses high specific surface area, high reactivity, good dispersibility, and good biocompatibility. It has applications in areas such as dry flue gas desulfurization, acidic wastewater treatment, reinforcement of stone cultural relics, reinforcement of polymer composite materials, and preparation of lithium battery material precursors. It can provide crucial basic materials for environmental governance, high-end manufacturing, and cultural heritage protection. Current methods for preparing nano-calcium hydroxide mainly include chemical precipitation, calcium oxide digestion, hydrothermal methods, and microemulsion methods. Among these, the aqueous digestion method using calcium oxide as the calcium source is characterized by readily available raw materials, simple process, and environmental friendliness, making it the mainstream technology route for industrial preparation.

[0003] However, existing aqueous digestion preparation processes generally suffer from two major technical defects: First, it is difficult to simultaneously suppress crystal growth and particle agglomeration; calcium hydroxide crystal nuclei tend to grow rapidly in a strongly alkaline aqueous phase, forming agglomerates that are difficult to redisperse, resulting in a wide particle size distribution, low specific surface area, and poor dispersion stability of the product, making it difficult to fully utilize the high reactivity characteristics of nanomaterials; Second, particle surface modification and dispersion control cannot achieve full-process synergy. Traditional dispersants and surface modifiers can only achieve electrostatic stability or steric stabilization individually, making it difficult to achieve synergistic control throughout the entire process of crystal nucleation, growth, and post-treatment. Moreover, the drying process is prone to secondary agglomeration due to capillary forces, ultimately resulting in low reaction efficiency and high raw material consumption of the product under desulfurization and adsorption conditions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a nano-calcium hydroxide, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a nano-calcium hydroxide, the raw materials for which, by weight, are: 18-28 parts calcium oxide, 120-150 parts deionized water, 1.5-3.5 parts phosphorylated polyethylene glycol monomethyl ether, 0.8-2.5 parts carboxylated β-cyclodextrin, 2.0-4.5 parts sodium polyaspartate, 0.5-1.8 parts L-lysine, and 0.3-1.0 parts 3-mercaptopropylmethyldimethoxysilane.

[0006] Using the above technical solution, calcium oxide is used as the calcium source, reacting with deionized water to generate calcium hydroxide; phosphorylated polyethylene glycol monomethyl ether forms coordination with calcium ions through phosphate groups, and the long polyether molecular chains create steric hindrance, inhibiting the growth and agglomeration of calcium hydroxide crystals; carboxylated β-cyclodextrin generates electrostatic repulsion through molecular carboxyl groups and forms weak coordination, assisting in stabilizing calcium hydroxide particles; sodium polyaspartate, as an anionic polyelectrolyte, can reduce the viscosity of the system, increase the electrostatic repulsion between particles, and improve the dispersion performance of the system; L-lysine generates electrostatic repulsion through carboxyl anions, and combines its own molecular structure to play a synergistic dispersion role, limiting the excessive growth of calcium hydroxide crystals; the methoxy group of 3-mercaptopropylmethyldimethoxysilane hydrolyzes in the aqueous phase to generate silanol groups, and the silanol undergoes dehydration condensation bonding with the hydroxyl groups on the surface of calcium hydroxide particles, with the molecular alkyl carbon chains arranged on the particle surface to form a hydrophobic coating structure.

[0007] Preferably, the effective calcium oxide content of the calcium oxide is ≥95%, the magnesium oxide content is ≤1.5%, and the particle size is ≤75μm; the number average molecular weight of the sodium polyaspartate is 3000-4000.

[0008] By employing the above technical solution, the purity of calcium oxide is limited, ensuring the purity of the calcium source and reducing the interference of impurities on the reaction system; the particle size is limited to ≤75μm, which facilitates the uniform dispersion of raw materials in the system and ensures complete digestion. The number-average molecular weight of sodium polyaspartate is limited, which can fully utilize its role as an anionic polyelectrolyte, providing strong electrostatic repulsion to maintain the particle dispersion state, thereby improving the rheological properties of the slurry.

[0009] Preferably, the raw materials for preparing the phosphorylated polyethylene glycol monomethyl ether include, by weight, 90-100 parts of polyethylene glycol monomethyl ether and 12-18 parts of phosphorus pentoxide; The preparation method of the phosphorylated polyethylene glycol monomethyl ether includes the following steps: 1) Add polyethylene glycol monomethyl ether to a reactor equipped with nitrogen protection, mechanical stirring and drying tube, heat to 60-70℃, and dehydrate under vacuum conditions of -0.095~-0.085MPa for 1-2 hours; 2) Cool the system obtained in step 1) to 40-50℃, add phosphorus pentoxide in batches under nitrogen protection, with each batch adding 1 / 5-1 / 4 of the total weight of phosphorus pentoxide, at intervals of 15-30 min, control the reaction temperature ≤55℃, and keep stirring at a speed of 150-250 r / min. 3) After the addition is complete, heat the system to 70-80℃ and continue to stir the reaction at a speed of 150-250r / min for 4-6h. During the reaction, high-purity dry nitrogen is continuously introduced, and the nitrogen flow rate is controlled at 0.5-1.5L / (min·L). 4) After the reaction is complete, cool the system to 30-40℃, and slowly add 5%-10% of deionized water (based on the total weight of polyethylene glycol monomethyl ether and phosphorus pentoxide) over 30-60 minutes for hydrolysis. Stir for 1-2 hours, and then adjust the pH to 6.5-7.0 with 8%-12% sodium hydroxide solution to obtain phosphorylated polyethylene glycol monomethyl ether.

[0010] Using the above technical solution, polyethylene glycol monomethyl ether and phosphorus pentoxide are combined in a specific ratio to provide sufficient raw materials for the phosphorylation reaction and ensure the orderly progress of the reaction. During the preparation process, vacuum dehydration can remove trace amounts of moisture from the polyethylene glycol monomethyl ether, nitrogen protection can reduce the interference of external impurities and oxygen on the reaction, and adding phosphorus pentoxide in batches and controlling the reaction temperature can make the reaction proceed smoothly and avoid excessively violent local reactions. Subsequent heating reaction, hydrolysis and pH adjustment steps can promote the full phosphorylation reaction of polyethylene glycol monomethyl ether, and finally obtain phosphorylated polyethylene glycol monomethyl ether that meets the requirements. This product can participate in the stable preparation of nano-calcium hydroxide through the coordination of its phosphate groups with calcium ions.

[0011] Preferably, the raw materials for preparing the carboxylated β-cyclodextrin, by weight, include: 90-100 parts of β-cyclodextrin, 250-300 parts of N,N-dimethylformamide, 40-60 parts of succinic anhydride, 8-12 parts of anhydrous pyridine, and 30-40 parts of deionized water.

[0012] Using the above technical solution, β-cyclodextrin provides the basic framework for the carboxylation reaction; N,N-dimethylformamide can dissolve β-cyclodextrin, providing a homogeneous liquid environment for the reaction of raw materials; succinic anhydride, as a carboxylating agent, can introduce carboxyl groups into the β-cyclodextrin molecule; and anhydrous pyridine can promote the reaction between β-cyclodextrin and succinic anhydride, ensuring the sufficiency of the carboxylation reaction.

[0013] Preferably, the method for preparing the carboxylated β-cyclodextrin includes the following steps: (1) Dissolve β-cyclodextrin in a mixture of N,N-dimethylformamide and deionized water, heat to 60-70℃, and stir at 150-250r / min until completely dissolved; (2) Under nitrogen protection, add succinic anhydride to the solution obtained in step (1), and then add anhydrous pyridine dropwise at a constant rate over 30-60 min. Heat to 80-90℃ and stir the reaction at a speed of 150-250 r / min for 10-15 h. (3) After the reaction is completed, cool to room temperature, slowly pour the reaction solution into anhydrous ethanol at 0-5℃ with a volume of 4-5 times that of the reaction solution to precipitate, filter, wash the precipitate with anhydrous ethanol 3-5 times, then dissolve the washed solid in 300-400 parts by weight of deionized water, adjust the pH to 2.0-3.0 with 8%-12% hydrochloric acid, and then centrifuge at 3000-5000r / min for 10-20min to collect the precipitate; (4) The precipitate collected in step (3) is redispersed in deionized water and then transferred to a dialysis bag with a molecular weight cutoff of 1000-1200 Da. Dialyze with deionized water for 24-28 hours, changing the water every 6-8 hours. The solid obtained after dialysis is freeze-dried at -55~-45℃ and vacuum degree of 20-30 Pa for 24-28 hours to obtain carboxylated β-cyclodextrin.

[0014] Using the above technical solution, β-cyclodextrin is dissolved in a mixture of N,N-dimethylformamide and deionized water and stirred to provide a homogeneous environment for the carboxylation reaction of β-cyclodextrin and succinic anhydride. After adding succinic anhydride and anhydrous pyridine, the mixture is heated and stirred to promote the carboxylation reaction of β-cyclodextrin. After the reaction, the reaction solution is poured into anhydrous ethanol to precipitate the precipitate, which is then washed to achieve preliminary separation of the reaction products. The washed solid is dissolved in deionized water, the pH is adjusted, and centrifuged to remove unreacted succinic acid. After redissolving the precipitate, small molecule impurities are removed by dialysis, and then the product is freeze-dried to obtain carboxylated β-cyclodextrin. Each step works synergistically to ensure the sufficiency of the carboxylation reaction and the purity of the product.

[0015] Preferably, the raw materials for preparation, by weight, include: 20-25 parts calcium oxide, 130-140 parts deionized water, 2-3 parts phosphorylated polyethylene glycol monomethyl ether, 1-2 parts carboxylated β-cyclodextrin, 2.5-3.5 parts sodium polyaspartate, 0.8-1.5 parts L-lysine, and 0.4-0.8 parts 3-mercaptopropylmethyldimethoxysilane.

[0016] This invention also provides a method for preparing nano-calcium hydroxide, comprising the following steps: S1. Add deionized water to the reaction vessel, start stirring, and add phosphorylated polyethylene glycol monomethyl ether, carboxylated β-cyclodextrin, sodium polyaspartate and L-lysine in sequence. Stir at 150-250 r / min at 25-35℃ for 15-25 min to dissolve and obtain functional base liquid. S2. Add calcium oxide to the functional base liquid obtained in step S1, and stir at 150-250 r / min for 10-20 min at 25-35℃. S3. Heat the system obtained in step S2 to 50-65℃ and stir at 150-300 r / min for 2.5-4.5 h to digest the reaction. When foam is generated in the reaction system, add 0.10-0.15 parts by weight of polyether modified silicone oil as a defoamer at one time. If no foam is generated, no defoamer needs to be added. S4. Cool the system obtained in step S3 to 30-35℃, add 3-mercaptopropylmethyldimethoxysilane dropwise at a uniform rate over 30-60 min, and then continue stirring the reaction at a speed of 150-300 r / min for 1.5-2.5 h. S5. Adjust the pH of the system obtained in step S4 to 8.5-9.5 with dilute hydrochloric acid with a mass fraction of 8%-12%. Then stir at 55-60℃ and 150-250r / min for 30-60min. After that, centrifuge the slurry after reaction, discard the supernatant, wash and dry the precipitate, and then crush and depolymerize it using an air jet mill. After crushing, classify it through a 200-400 mesh sieve, and take the sieve-underfill material as nano calcium hydroxide powder.

[0017] Using the above technical solution, phosphorylated polyethylene glycol monomethyl ether, carboxylated β-cyclodextrin, sodium polyaspartate, and L-lysine are dissolved to form a functional base liquid. This base liquid can be adsorbed onto the surface of newly formed calcium hydroxide crystal nuclei through coordination and steric hindrance effects in subsequent reactions, inhibiting crystal growth and agglomeration. After calcium oxide is added to the base liquid and dispersed by stirring, it can fully contact water to undergo a digestion reaction to generate calcium hydroxide. Polyether-modified silicone oil can reduce foam generated during the reaction and ensure stable reaction. 3-mercaptopropylmethyldimethoxysilane can react with the hydroxyl groups on the surface of calcium hydroxide by slow dropwise addition, achieving surface modification. Operations such as pH adjustment, heat preservation and stirring, centrifugation, washing, drying, air jet milling and deagglomeration, and sieve classification can remove impurities and make the product uniformly dispersed, ultimately obtaining nano-calcium hydroxide powder.

[0018] Preferably, in step S5, the centrifugation speed is 10000-11000 r / min and the centrifugation time is 15-25 min; the precipitate is washed with deionized water 2-3 times and then washed with anhydrous ethanol 1-2 times, and after each washing, it is centrifuged at 7500-8500 r / min for 10-15 min.

[0019] Using the above technical solution, in step S5, centrifugation at a specific speed and time can effectively separate the precipitate from the supernatant, separating the nano-calcium hydroxide precipitate from the soluble impurities in the system; washing with deionized water can remove water-soluble impurities attached to the precipitate surface, and washing with anhydrous ethanol can remove residual moisture and some organic impurities on the precipitate surface; centrifugation after each washing can separate the impurities that fall off during the washing process from the precipitate, ensuring the purity of the precipitate and laying the foundation for subsequent drying, pulverization, and deagglomeration to obtain qualified nano-calcium hydroxide powder.

[0020] Preferably, in step S5, the drying conditions are: vacuum degree of -0.095~-0.085MPa, temperature of 60-75℃, and time of 12-20h; the pulverizing pressure of the air jet mill for pulverizing and depolymerizing is 0.6-0.8MPa, and the classifying speed is 4000-5000r / min.

[0021] Using the above technical solution, in step S5, the drying conditions of specific vacuum degree, temperature and time can effectively remove moisture and residual solvent from the nano calcium hydroxide precipitate, ensuring that the product is fully dried; the airflow pulverization and deagglomeration with specific pulverization pressure and staged speed can break up the agglomerates that may be formed during the drying process, so that the product is evenly dispersed.

[0022] This application also discloses the application of nano-calcium hydroxide in dry flue gas desulfurization, wherein the nano-calcium hydroxide is any of the aforementioned nano-calcium hydroxide.

[0023] Using the above technical solution, the nano-calcium hydroxide has a high specific surface area, good dispersibility and chemical reactivity; when applied to dry flue gas desulfurization, it can be uniformly dispersed in the flue and fully react with sulfur dioxide, which is beneficial to improving the flue gas desulfurization effect.

[0024] The beneficial effects of this invention are as follows: Calcium oxide, as a calcium source, reacts with deionized water to form calcium hydroxide. Phosphorylated polyethylene glycol monomethyl ether coordinates with calcium ions through its phosphate groups, and the long polyether molecular chains create steric hindrance, inhibiting calcium hydroxide crystal growth and particle agglomeration. Carboxylated β-cyclodextrin generates electrostatic repulsion through its carboxyl groups and forms weak coordination, helping to stabilize calcium hydroxide particles. Sodium polyaspartate, as an anionic polyelectrolyte, reduces system viscosity, increases electrostatic repulsion between particles, and improves system dispersion performance. L-lysine generates electrostatic repulsion through its carboxyl anions, and its molecular structure plays a synergistic dispersing role, limiting excessive growth of calcium hydroxide crystals. The methoxy group of 3-mercaptopropylmethyldimethoxysilane hydrolyzes in the aqueous phase to generate silanol groups. The silanol undergoes dehydration condensation bonding with the hydroxyl groups on the surface of calcium hydroxide particles, and the alkyl carbon chains of the molecules are arranged on the particle surface to form a hydrophobic coating structure. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The specific information on the raw materials used in the embodiments of the present invention is shown in Table 1.

[0027] Table 1

[0028] Example 1: This embodiment provides a nano-calcium hydroxide, which, by weight, comprises the following raw materials: 18 parts calcium oxide, 120 parts deionized water, 1.5 parts phosphorylated polyethylene glycol monomethyl ether, 0.8 parts carboxylated β-cyclodextrin, 2 parts sodium polyaspartate, 0.5 parts L-lysine, and 0.3 parts 3-mercaptopropylmethyldimethoxysilane. The effective calcium oxide content of the calcium oxide is ≥95%, the magnesium oxide content is ≤1.5%, and the particle size is ≤75μm; the number average molecular weight of the sodium polyaspartate is 3000.

[0029] The raw materials for preparing phosphorylated polyethylene glycol monomethyl ether, by weight, include: 90 parts polyethylene glycol monomethyl ether and 12 parts phosphorus pentoxide; the preparation method of phosphorylated polyethylene glycol monomethyl ether includes the following steps: 1) Add polyethylene glycol monomethyl ether to a reactor equipped with nitrogen protection, mechanical stirring and drying tube, heat to 60°C, and dehydrate under vacuum at -0.095MPa for 1 hour; 2) Cool the system obtained in step 1) to 40°C, add phosphorus pentoxide in batches under nitrogen protection, with each batch adding 1 / 5 of the total weight of phosphorus pentoxide, at 15-minute intervals, controlling the reaction temperature to ≤55°C, and stirring at 150 r / min. 3) After the addition is complete, heat the system to 70°C and continue to stir the reaction at 150 r / min for 4 h. During the reaction, high-purity dry nitrogen is continuously introduced, and the nitrogen flow rate is controlled at 0.5 L / (min·L). 4) After the reaction is complete, the system is cooled to 30°C, and deionized water accounting for 5% of the total weight of polyethylene glycol monomethyl ether and phosphorus pentoxide is slowly added within 30 min for hydrolysis. The mixture is stirred for 1 h, and then the pH is adjusted to 6.5 with 8% sodium hydroxide solution to obtain phosphorylated polyethylene glycol monomethyl ether.

[0030] The raw materials for preparing carboxylated β-cyclodextrin, by weight, include: 90 parts β-cyclodextrin, 250 parts N,N-dimethylformamide, 40 parts succinic anhydride, 8 parts anhydrous pyridine, and 30 parts deionized water.

[0031] The preparation method of carboxylated β-cyclodextrin includes the following steps: (1) Dissolve β-cyclodextrin in a mixture of N,N-dimethylformamide and deionized water, heat to 60°C, and stir at 150 r / min until completely dissolved; (2) Under nitrogen protection, succinic anhydride was added to the solution obtained in step (1), followed by anhydrous pyridine being added dropwise at a uniform rate over 30 min. The temperature was raised to 80 °C, and the reaction was stirred at a speed of 150 r / min for 10 h. (3) After the reaction is completed, cool to room temperature, slowly pour the reaction solution into anhydrous ethanol at 0℃ with a volume of 4 times that of the reaction solution to precipitate, filter, wash the precipitate with anhydrous ethanol 3 times, then dissolve the washed solid in 300 parts by weight of deionized water, adjust the pH to 2.0 with 8% hydrochloric acid, and then centrifuge at 3000 r / min for 10 min to collect the precipitate. (4) The precipitate collected in step (3) was redispersed in deionized water and then transferred to a dialysis bag with a molecular weight cutoff of 1000 Da. The dialysis was performed with deionized water for 24 hours, and the water was changed every 6 hours. The solid obtained after dialysis was freeze-dried at -55°C and 20 Pa vacuum for 24 hours to obtain carboxylated β-cyclodextrin.

[0032] This embodiment also provides a method for preparing nano-calcium hydroxide, including the following steps: S1. Add deionized water to the reaction vessel, start stirring, and add phosphorylated polyethylene glycol monomethyl ether, carboxylated β-cyclodextrin, sodium polyaspartate and L-lysine in sequence. Stir at 150 r / min at 25°C for 15 min to dissolve and obtain functional base liquid. S2. Add calcium oxide to the functional base liquid obtained in step S1 and stir at 150 r / min for 10 min at 25°C. S3. Heat the system obtained in step S2 to 50°C and stir at 150 r / min for 2.5 h to digest the reaction. When foam is generated in the reaction system, add 0.1 parts by weight of polyether modified silicone oil as a defoamer at once; if no foam is generated, no defoamer needs to be added. S4. Cool the system obtained in step S3 to 30°C, add 3-mercaptopropylmethyldimethoxysilane dropwise at a uniform rate over 30 min, and then continue stirring the reaction at a speed of 150 r / min for 1.5 h. S5. Adjust the pH of the system obtained in step S4 to 8.5 with 8% dilute hydrochloric acid. Then stir at 150 r / min for 30 min at 55℃. Centrifuge the slurry after reaction at 10000 r / min for 15 min and discard the supernatant. Wash the precipitate twice with deionized water and once with anhydrous ethanol. After each washing, centrifuge at 7500 r / min for 10 min. Place the washed product in a vacuum drying oven and dry it at -0.095 MPa and 60℃ for 12 h. After drying, pulverize and depolymerize it using an air jet mill at a pressure of 0.6 MPa and a classification speed of 4000 r / min. After pulverization, classify it through a 200-mesh sieve and take the sieve-underfill material as nano-calcium hydroxide powder.

[0033] This embodiment also discloses the application of nano-calcium hydroxide in dry flue gas desulfurization, wherein the nano-calcium hydroxide is any of the aforementioned nano-calcium hydroxide.

[0034] Operating conditions: Flue gas volume 150,000 Nm³ 3 / h, initial sulfur dioxide concentration 1200 mg / Nm 3 The flue gas temperature was 125±2℃.

[0035] Material balance: sulfur dioxide mass flow rate = 150000 × 1200 × 10 -6 =180kg / h Sulfur dioxide molar flow rate ≈ 180000 / 64.06 ≈ 2810 mol / h Considering the gas-solid contact efficiency of dry desulfurization and actual industrial operating experience, the calcium-sulfur molar ratio is controlled at 2.2:1. The required molar amount of calcium hydroxide is approximately 2810 × 2.2 mol / h. The required mass of calcium hydroxide is approximately 6182 × 74.09 ≈ 458 kg / h. Operating parameters and results: The nano-calcium hydroxide powder prepared in Example 1 was injected into the preheater outlet flue at a rate of 458 kg / h using a pneumatic conveying device. The powder specific surface area reached 122 m² / h. 2 / g, the nanoparticles disperse rapidly in the flue and react fully with sulfur dioxide. Continuous operation monitoring results show that the outlet sulfur dioxide concentration is consistently below 18 mg / Nm³. 3 The desulfurization efficiency has consistently remained above 99%.

[0036] Example 2: This embodiment provides a nano-calcium hydroxide, which, by weight, comprises the following raw materials: 28 parts calcium oxide, 150 parts deionized water, 3.5 parts phosphorylated polyethylene glycol monomethyl ether, 2.5 parts carboxylated β-cyclodextrin, 4.5 parts sodium polyaspartate, 1.8 parts L-lysine, and 1 part 3-mercaptopropylmethyldimethoxysilane. The effective calcium oxide content of the calcium oxide is ≥95%, the magnesium oxide content is ≤1.5%, and the particle size is ≤75μm; the number average molecular weight of the sodium polyaspartate is 4000.

[0037] The raw materials for preparing phosphorylated polyethylene glycol monomethyl ether, by weight, include: 100 parts polyethylene glycol monomethyl ether and 18 parts phosphorus pentoxide; the preparation method of phosphorylated polyethylene glycol monomethyl ether includes the following steps: 1) Add polyethylene glycol monomethyl ether to a reactor equipped with nitrogen protection, mechanical stirring and drying tube, heat to 70°C, and vacuum dehydrate for 2 hours under a vacuum of -0.085 MPa; 2) Cool the system obtained in step 1) to 50°C, add phosphorus pentoxide in batches under nitrogen protection, with each batch adding 1 / 4 of the total weight of phosphorus pentoxide at 30-minute intervals, controlling the reaction temperature to ≤55°C, and stirring at 250 r / min. 3) After the addition is complete, heat the system to 80°C and continue to stir the reaction at 250 r / min for 6 h. During the reaction, high-purity dry nitrogen is continuously introduced, and the nitrogen flow rate is controlled at 1.5 L / (min·L). 4) After the reaction is complete, the system is cooled to 40°C, and deionized water accounting for 10% of the total weight of polyethylene glycol monomethyl ether and phosphorus pentoxide is slowly added over 60 min for hydrolysis. The mixture is stirred for 2 h, and then the pH is adjusted to 7.0 with a 12% sodium hydroxide solution to obtain phosphorylated polyethylene glycol monomethyl ether.

[0038] The raw materials for preparing carboxylated β-cyclodextrin, by weight, include: 100 parts β-cyclodextrin, 300 parts N,N-dimethylformamide, 60 parts succinic anhydride, 12 parts anhydrous pyridine, and 40 parts deionized water.

[0039] The preparation method of carboxylated β-cyclodextrin includes the following steps: (1) Dissolve β-cyclodextrin in a mixture of N,N-dimethylformamide and deionized water, heat to 70°C, and stir at 250 r / min until completely dissolved; (2) Under nitrogen protection, succinic anhydride was added to the solution obtained in step (1), and then anhydrous pyridine was added dropwise at a uniform rate over 60 min. The temperature was raised to 90°C and the reaction was stirred at a speed of 250 r / min for 15 h. (3) After the reaction is completed, cool to room temperature, slowly pour the reaction solution into anhydrous ethanol at 5°C with a volume of 5 times that of the reaction solution to precipitate, filter, wash the precipitate with anhydrous ethanol 5 times, then dissolve the washed solid in 400 parts by weight of deionized water, adjust the pH to 3.0 with 12% hydrochloric acid, and then centrifuge at 5000 r / min for 20 min to collect the precipitate; (4) The precipitate collected in step (3) was redispersed in deionized water and then transferred to a dialysis bag with a molecular weight cutoff of 1200 Da. Dialysis was performed with deionized water for 28 hours, with the water changed every 8 hours. The solid obtained after dialysis was freeze-dried at -45°C and 30 Pa for 28 hours to obtain carboxylated β-cyclodextrin.

[0040] This embodiment also provides a method for preparing nano-calcium hydroxide, including the following steps: S1. Add deionized water to the reaction vessel, start stirring, and add phosphorylated polyethylene glycol monomethyl ether, carboxylated β-cyclodextrin, sodium polyaspartate and L-lysine in sequence. Stir at 250 r / min at 35℃ for 25 min to dissolve and obtain functional base liquid. S2. Add calcium oxide to the functional base liquid obtained in step S1 and stir at 250 r / min for 20 min at 35℃. S3. Heat the system obtained in step S2 to 65°C and stir at 300 r / min for 4.5 h to digest the reaction. When foam is generated in the reaction system, add 0.15 parts by weight of polyether modified silicone oil as a defoamer at one time; if no foam is generated, no defoamer needs to be added. S4. Cool the system obtained in step S3 to 35°C, add 3-mercaptopropylmethyldimethoxysilane dropwise at a uniform rate over 60 min, and then continue stirring the reaction at 300 r / min for 2.5 h. S5. Adjust the pH of the system obtained in step S4 to 9.5 with 12% dilute hydrochloric acid. Then stir at 250 r / min for 60 min at 60℃. Centrifuge the slurry after reaction at 11000 r / min for 25 min and discard the supernatant. Wash the precipitate three times with deionized water and twice with anhydrous ethanol. After each washing, centrifuge at 8500 r / min for 15 min. Place the washed product in a vacuum drying oven and dry it at -0.085 MPa and 75℃ for 20 h. After drying, pulverize and depolymerize it using an air jet mill at a pressure of 0.8 MPa and a classification speed of 5000 r / min. After pulverization, classify it through a 400-mesh sieve and take the sieve-underfill material as nano-calcium hydroxide powder.

[0041] This embodiment also discloses the application of nano-calcium hydroxide in dry flue gas desulfurization, and the specific application method is the same as in Embodiment 1.

[0042] Example 3: This embodiment provides a nano-calcium hydroxide, which, by weight, comprises the following raw materials: 23 parts calcium oxide, 135 parts deionized water, 2.5 parts phosphorylated polyethylene glycol monomethyl ether, 1.6 parts carboxylated β-cyclodextrin, 3.2 parts sodium polyaspartate, 1.2 parts L-lysine, and 0.7 parts 3-mercaptopropylmethyldimethoxysilane. The effective calcium oxide content of the calcium oxide is ≥95%, the magnesium oxide content is ≤1.5%, and the particle size is ≤75μm; the number average molecular weight of the sodium polyaspartate is 3500.

[0043] The raw materials for preparing phosphorylated polyethylene glycol monomethyl ether, by weight, include: 95 parts polyethylene glycol monomethyl ether and 15 parts phosphorus pentoxide; the preparation method of phosphorylated polyethylene glycol monomethyl ether includes the following steps: 1) Add polyethylene glycol monomethyl ether to a reactor equipped with nitrogen protection, mechanical stirring and drying tube, heat to 65℃, and dehydrate under vacuum at -0.09MPa for 1.5h; 2) Cool the system obtained in step 1) to 45°C, add phosphorus pentoxide in batches under nitrogen protection, with each batch adding 1 / 4 of the total weight of phosphorus pentoxide at 22 min intervals, control the reaction temperature to ≤55°C, and keep stirring at 200 r / min. 3) After the addition is complete, heat the system to 75°C and continue to stir the reaction at 200 r / min for 5 h. During the reaction, high-purity dry nitrogen is continuously introduced, and the nitrogen flow rate is controlled at 1.0 L / (min·L). 4) After the reaction is complete, the system is cooled to 35°C, and deionized water accounting for 8% of the total weight of polyethylene glycol monomethyl ether and phosphorus pentoxide is slowly added over 45 min for hydrolysis. The mixture is stirred for 1.5 h, and then the pH is adjusted to 6.8 with a 10% sodium hydroxide solution to obtain phosphorylated polyethylene glycol monomethyl ether.

[0044] The raw materials for preparing carboxylated β-cyclodextrin, by weight, include: 95 parts β-cyclodextrin, 275 parts N,N-dimethylformamide, 50 parts succinic anhydride, 10 parts anhydrous pyridine, and 35 parts deionized water.

[0045] The preparation method of carboxylated β-cyclodextrin includes the following steps: (1) Dissolve β-cyclodextrin in a mixture of N,N-dimethylformamide and deionized water, heat to 65°C, and stir at 200 r / min until completely dissolved; (2) Under nitrogen protection, succinic anhydride was added to the solution obtained in step (1), and then anhydrous pyridine was added dropwise at a constant rate over 45 min. The temperature was raised to 85°C and the reaction was stirred at a speed of 200 r / min for 12 h. (3) After the reaction is completed, cool to room temperature, slowly pour the reaction solution into anhydrous ethanol at 3°C ​​with a volume of 5 times that of the reaction solution to precipitate, filter, wash the precipitate with anhydrous ethanol 4 times, then dissolve the washed solid in 350 parts by weight of deionized water, adjust the pH to 2.5 with 10% hydrochloric acid, and then centrifuge at 4000 r / min for 15 min to collect the precipitate; (4) The precipitate collected in step (3) was redispersed in deionized water and then transferred to a dialysis bag with a molecular weight cutoff of 1100 Da. The dialysis was performed with deionized water for 26 h, and the water was changed every 7 h. The solid obtained after dialysis was freeze-dried at -50 °C and 25 Pa vacuum for 26 h to obtain carboxylated β-cyclodextrin.

[0046] This embodiment also provides a method for preparing nano-calcium hydroxide, including the following steps: S1. Add deionized water to the reaction vessel, start stirring, and add phosphorylated polyethylene glycol monomethyl ether, carboxylated β-cyclodextrin, sodium polyaspartate and L-lysine in sequence. Stir at 200 r / min at 30℃ for 20 min to dissolve and obtain functional base liquid. S2. Add calcium oxide to the functional substrate obtained in step S1 and stir at 200 r / min for 15 min at 30°C. S3. Heat the system obtained in step S2 to 58°C and stir at 220 r / min for 3.5 h to digest the reaction. When foam is generated in the reaction system, add 0.12 parts by weight of polyether modified silicone oil as a defoamer at once; if no foam is generated, no defoamer needs to be added. S4. Cool the system obtained in step S3 to 32°C, add 3-mercaptopropylmethyldimethoxysilane dropwise at a uniform rate over 45 min, and then continue stirring the reaction at a speed of 220 r / min for 2 h. S5. Adjust the pH of the system obtained in step S4 to 9.0 with 10% dilute hydrochloric acid. Then stir at 200 r / min for 45 min at 58℃. Centrifuge the slurry after reaction at 10500 r / min for 20 min and discard the supernatant. Wash the precipitate three times with deionized water and twice with anhydrous ethanol. After each washing, centrifuge at 8000 r / min for 12 min. Place the washed product in a vacuum drying oven and dry it at -0.09 MPa and 68℃ for 16 h. After drying, pulverize and depolymerize it using an air jet mill at a pressure of 0.7 MPa and a classification speed of 4500 r / min. After pulverization, classify it through a 300-mesh sieve and take the sieve-underfill material as nano-calcium hydroxide powder.

[0047] This embodiment also discloses the application of nano-calcium hydroxide in dry flue gas desulfurization, and the specific application method is the same as in Embodiment 1.

[0048] Comparative Example 1: A nano-calcium hydroxide, its preparation method and application, differs from Example 3 only in that phosphorylated polyethylene glycol monomethyl ether is not added.

[0049] Comparative Example 2: A nano-calcium hydroxide, its preparation method and application, differs from Example 3 only in that: no carboxylated β-cyclodextrin is added.

[0050] Comparative Example 3: A nano-calcium hydroxide, its preparation method and application, differs from Example 3 only in that sodium polyaspartate is not added.

[0051] Comparative Example 4: A nano-calcium hydroxide, its preparation method and application, differs from Example 3 only in that L-lysine is not added.

[0052] Comparative Example 5: A nano-calcium hydroxide, its preparation method, and its application are disclosed. The only difference between this and Example 3 is that an equal weight of unmodified polyethylene glycol monomethyl ether is used instead of phosphorylated polyethylene glycol monomethyl ether.

[0053] Comparative Example 6: A nano-calcium hydroxide, its preparation method and application, differs from Example 3 only in that: an equal weight of unmodified β-cyclodextrin is used instead of carboxylated β-cyclodextrin.

[0054] Comparative Example 7: A nano-calcium hydroxide, its preparation method and application, differs from Example 3 only in that: sodium polyaspartate is replaced with an equal weight of hexadecyltrimethylammonium bromide.

[0055] Comparative Example 8: A nano-calcium hydroxide, its preparation method and application, differs from Example 3 only in that 3-mercaptopropylmethyldimethoxysilane is not added.

[0056] The nano-calcium hydroxide obtained in Examples 1-3 and Comparative Examples 1-8 were tested for the following properties: 1. Measurement of average particle size and particle size distribution (PDI): The measurements were performed using a Zetasizer Nano ZS90 nanoparticle size potentiometer. The sample was prepared as a 0.5 mg / mL aqueous dispersion, ultrasonically dispersed for 15 min (ultrasonic power 200 W), and a suitable amount of dispersion was placed in a cuvette. After equilibration at 25℃ for 2 min, the sample was measured. Nitrogen gas was used for protection throughout the ultrasonic dispersion and testing process to prevent the reaction of carbon dioxide in the air with calcium hydroxide to form calcium carbonate impurities. Each sample was measured in triplicate, and the average value was taken.

[0057] 2. Specific surface area determination: According to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption-BET Method", a NOVA4200e specific surface area analyzer was used, and the nitrogen adsorption-desorption method was employed for determination. Before testing, the sample was degassed under vacuum at 80℃ for 4 hours, and multi-point BET tests were conducted with a relative pressure (P / P0) range of 0.05-0.30.

[0058] 3. Determination of dispersion stability: Accurately weigh 1.0 g of nano-calcium hydroxide powder and add it to 100 mL of deionized water. Disperse ultrasonically for 15 min (ultrasonic power 200 W). After standing for 24 h, use a pipette to draw 20 mL of the supernatant from 1 cm below the liquid surface and place it in a pre-weighed weighing bottle. Dry the bottle at 105 °C until constant weight and calculate the solid content of the supernatant. The dispersion stability retention rate (R) is calculated using the following formula: R=(m 24 / m0)×100% In the formula, m0 is the initial theoretical solid content (converted value, i.e., the theoretical solid content of 20 mL corresponding to 1.0 g / 100 mL = 10 mg / mL is 200 mg), m 24 The solid content (mg) was determined by drying 20 mL of the supernatant after standing for 24 hours.

[0059] 4. Contact angle measurement: Sample discs were prepared using a compression method: 0.5 g of nano-calcium hydroxide powder was weighed and placed into a mold with a diameter of 20 mm. The mold was then pressed at 15 MPa for 1 min to obtain a smooth cylindrical disc. The static contact angle was measured using an optical contact angle meter with deionized water as the test solution, employing the seated drop method. Measurements were taken at five different locations on each sample disc, and the average value was recorded.

[0060] 5. Desulfurization efficiency measurement: Simulated flue gas desulfurization tests were conducted in a fixed-bed reactor. Simulated flue gas conditions: sulfur dioxide concentration 800 mg / Nm³. 3 The oxygen concentration was 6%, the carbon dioxide concentration was 15%, and nitrogen was used as the balance gas. The total gas flow rate was 1 L / min, and the reaction temperature was 150℃. Accurately weigh 0.5 g of nano-calcium hydroxide sample and spread it evenly on the reactor sieve plate. Simulated flue gas was introduced and reacted for 30 min. The inlet and outlet sulfur dioxide concentrations were measured using a flue gas analyzer. The desulfurization efficiency (η) was calculated using the following formula: η = [(C_in - C_out) / C_in] × 100% In the formula, C_in is the inlet sulfur dioxide concentration (mg / Nm³). 3 C_out represents the outlet sulfur dioxide concentration (mg / Nm³). 3 ).

[0061] The results are shown in Tables 2 and 3.

[0062] Table 2 Basic Physicochemical Properties

[0063] Table 3 Application Performance

[0064] Using Example 3 as the control group, the performance differences and causes of Comparative Examples 1-8 are analyzed as follows: Comparative Example 1: Without the addition of phosphorylated polyethylene glycol monomethyl ether, the average particle size increased significantly from 17.5 nm to 68.3 nm (an increase of approximately 290.3%), the PDI increased from 0.095 to 0.415 (an increase of approximately 336.8%), and the specific surface area increased from 122 m² / g. 2 / g decreased to 72m 2 / g (a decrease of approximately 41.0%), dispersion stability decreased from 95% to 58% (a decrease of approximately 38.9%), desulfurization efficiency decreased from 99.3% to 90.1% (a decrease of approximately 9.3%), and contact angle decreased from 112° to 98° (a decrease of approximately 12.5%). The phosphate groups in phosphorylated polyethylene glycol monomethyl ether can form strong coordination anchors with calcium ions, firmly anchoring the polyether chains to the crystal nucleus surface, providing steric hindrance and inhibiting one-dimensional crystal growth. Without this component, the crystal nucleus surface loses its strong coordination modification, the polyether chains cannot be effectively anchored, the steric hindrance effect is significantly weakened, leading to rapid growth and severe agglomeration of nano-calcium hydroxide crystals, a significant decrease in specific surface area and dispersion stability, and a corresponding reduction in desulfurization activity.

[0065] Comparative Example 2: Without the addition of carboxylated β-cyclodextrin, the average particle size increased from 17.5 nm to 56.5 nm (an increase of approximately 222.9%), the PDI increased from 0.095 to 0.352 (an increase of approximately 270.5%), and the specific surface area increased from 122 m² / g. 2 / g decreased to 86m 2 / g (a decrease of approximately 29.5%), dispersion stability decreased from 95% to 65% (a decrease of approximately 31.6%), desulfurization efficiency decreased from 99.3% to 92.4% (a decrease of approximately 6.9%), and contact angle decreased from 112° to 100° (a decrease of approximately 10.7%). Carboxylated β-cyclodextrin utilizes its macrocyclic multi-carboxyl structure to stabilize particles through multi-point weak coordination and electrostatic repulsion, and can chelate calcium ions to slow down the diffusion rate and delay Ostwald ripening; after its deletion, the inhibitory effect of the system on calcium ion diffusion is weakened, the grain growth and ripening process is accelerated, resulting in increased particle size, wider particle size distribution and decreased specific surface area.

[0066] Comparative Example 3: Without the addition of sodium polyaspartate, the average particle size increased from 17.5 nm to 42.1 nm (an increase of approximately 140.6%), the PDI increased from 0.095 to 0.268 (an increase of approximately 182.1%), and the specific surface area increased from 122 m² / g. 2 / g decreased to 95m 2 / g (a decrease of approximately 22.1%), dispersion stability decreased from 95% to 72% (a decrease of approximately 24.2%), and contact angle decreased from 112° to 104° (a decrease of approximately 7.1%). Sodium polyaspartate, as an anionic polyelectrolyte, can provide strong electrostatic repulsion on the particle surface and reduce the viscosity of the system; without it, the electrostatic repulsion between particles weakens, the viscosity of the system increases, leading to decreased dispersibility, and nanoparticles are prone to soft agglomeration, resulting in increased particle size and reduced dispersion stability.

[0067] Comparative Example 4: Without the addition of L-lysine, the average particle size increased from 17.5 nm to 35.8 nm (an increase of approximately 104.6%), the PDI increased from 0.095 to 0.225 (an increase of approximately 136.8%), and the specific surface area increased from 122 m² / g.2 / g decreased to 102m 2 / g (a decrease of approximately 16.4%), dispersion stability decreased from 95% to 78% (a decrease of approximately 17.9%), and contact angle decreased from 112° to 106° (a decrease of approximately 5.4%). Under strongly alkaline conditions of pH 12.2-12.6, the carboxyl anion of L-lysine can provide electrostatic repulsion, and its molecular structure also contributes a certain degree of steric hindrance; after its loss, the surface charge density of the particles decreases, the electrostatic stabilizing effect is insufficient, the grain growth inhibition effect is weakened, resulting in a significant increase in particle size and PDI.

[0068] Comparative Example 5: Replacing phosphorylated polyethylene glycol monomethyl ether with an equal weight of unmodified polyethylene glycol monomethyl ether increased the average particle size from 17.5 nm to 49.2 nm (an increase of approximately 181.1%), the PDI from 0.095 to 0.302 (an increase of approximately 217.9%), and the specific surface area from 122 m² / g. 2 / g decreased to 89m 2 / g (a decrease of approximately 27.0%), dispersion stability decreased from 95% to 68% (a decrease of approximately 28.4%), desulfurization efficiency decreased from 99.3% to 92.9% (a decrease of approximately 6.4%), and contact angle decreased from 112° to 102° (a decrease of approximately 8.9%). Unmodified polyethylene glycol monomethyl ether lacks phosphate groups and cannot form strong coordination anchors with calcium ions. It is difficult to firmly adsorb onto specific crystal faces and exert steric hindrance effects, thus it cannot effectively inhibit grain growth and agglomeration, and its performance is significantly inferior to that of Example 3.

[0069] Comparative Example 6: Replacing carboxylated β-cyclodextrin with an equal weight of unmodified β-cyclodextrin increased the average particle size from 17.5 nm to 45.6 nm (an increase of approximately 160.6%), the PDI from 0.095 to 0.285 (an increase of approximately 200.0%), and the specific surface area from 122 m² / g. 2 / g decreased to 92m 2 / g (a decrease of approximately 24.6%), dispersion stability decreased from 95% to 70% (a decrease of approximately 26.3%), desulfurization efficiency decreased from 99.3% to 93.2% (a decrease of approximately 6.1%), and contact angle decreased from 112° to 103° (a decrease of approximately 8.0%). Unmodified β-cyclodextrin lacks carboxyl groups, thus failing to provide multi-point weak coordination, strong electrostatic repulsion, and chelation of calcium ions. Furthermore, the hydrophobic stabilizing effect of its cavity structure is also difficult to fully utilize due to the lack of surface carboxyl groups, resulting in a significant decrease in grain growth control ability.

[0070] Comparative Example 7: Replacing sodium polyaspartate with an equal weight of cetyltrimethylammonium bromide significantly increased the average particle size from 17.5 nm to 71.2 nm (an increase of approximately 306.9%), the PDI from 0.095 to 0.408 (an increase of approximately 329.5%), and the specific surface area from 122 m² / g. 2 / g decreased to 74m 2 / g (a decrease of approximately 39.3%), dispersion stability decreased from 95% to 55% (a decrease of approximately 42.1%), desulfurization efficiency decreased from 99.3% to 89.5% (a decrease of approximately 9.9%), and contact angle decreased from 112° to 96° (a decrease of approximately 14.3%). Hexadecyltrimethylammonium bromide is a cationic surfactant. In the strongly alkaline system of this invention, the surface of nano-calcium hydroxide particles carries a negative charge. After the two are mixed, a charge neutralization effect occurs, the electrostatic repulsion between particles disappears, and electrostatic adsorption occurs, inducing a large amount of particle aggregation. This, in turn, significantly increases the particle size, correspondingly decreases the dispersion stability, and significantly reduces the desulfurization efficiency, thus demonstrating the suitability and necessity of anionic sodium polyaspartate in the system of this invention.

[0071] Comparative Example 8: Without the addition of 3-mercaptopropylmethyldimethoxysilane, the average particle size increased from 17.5 nm to 36.2 nm (an increase of approximately 106.9%), the PDI increased from 0.095 to 0.188 (an increase of approximately 97.9%), and the specific surface area increased from 122 m² / g. 2 / g decreased to 95m 2 / g (a decrease of approximately 22.1%), dispersion stability decreased from 95% to 84% (a decrease of approximately 11.6%), desulfurization efficiency decreased from 99.3% to 94.8% (a decrease of approximately 4.5%), and contact angle decreased significantly from 112° to 58° (a decrease of approximately 48.2%). 3-Mercaptopropylmethyldimethoxysilane was hydrolyzed and condensed to graft hydrophobic organic groups onto the surface of nano-calcium hydroxide particles, constructing an organic coating layer. Without this silane modifier, the particle surface retained a large number of hydrophilic hydroxyl groups, exhibiting strong hydrophilicity. The aqueous phase easily settled and stratified, resulting in a significant decrease in dispersion stability. Irreversible hard agglomerates were easily formed during the drying process, and airflow pulverization could only partially deagglomerate them. The lack of a hydrophobic organic coating layer on the particle surface altered the configuration of the gas-solid contact interface with flue gas sulfur dioxide, reducing the utilization rate of effective reactive sites and causing a decrease in desulfurization efficiency. Simultaneously, the surface hydrophilicity caused water to spread on the powder surface, resulting in a significant decrease in the water contact angle.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nano-calcium hydroxide, characterized in that, The raw materials for its preparation, by weight, include: 18-28 parts calcium oxide, 120-150 parts deionized water, 1.5-3.5 parts phosphorylated polyethylene glycol monomethyl ether, 0.8-2.5 parts carboxylated β-cyclodextrin, 2.0-4.5 parts sodium polyaspartate, 0.5-1.8 parts L-lysine, and 0.3-1.0 parts 3-mercaptopropylmethyldimethoxysilane.

2. The nano-calcium hydroxide according to claim 1, characterized in that, The effective calcium oxide content of the calcium oxide is ≥95%, the magnesium oxide content is ≤1.5%, and the particle size is ≤75μm; the number average molecular weight of the polyaspartic acid sodium is 3000-4000.

3. The nano-calcium hydroxide according to claim 1, characterized in that, The raw materials for preparing the phosphorylated polyethylene glycol monomethyl ether, by weight, include: 90-100 parts of polyethylene glycol monomethyl ether and 12-18 parts of phosphorus pentoxide. The preparation method of the phosphorylated polyethylene glycol monomethyl ether includes the following steps: 1) Add polyethylene glycol monomethyl ether to a reactor equipped with nitrogen protection, mechanical stirring and drying tube, heat to 60-70℃, and dehydrate under vacuum conditions of -0.095~-0.085MPa for 1-2 hours; 2) Cool the system obtained in step 1) to 40-50℃, add phosphorus pentoxide in batches under nitrogen protection, with each batch adding 1 / 5-1 / 4 of the total weight of phosphorus pentoxide, at intervals of 15-30 min, control the reaction temperature ≤55℃, and keep stirring at a speed of 150-250 r / min. 3) After the addition is complete, heat the system to 70-80℃ and continue to stir the reaction at a speed of 150-250r / min for 4-6h. During the reaction, high-purity dry nitrogen is continuously introduced, and the nitrogen flow rate is controlled at 0.5-1.5L / (min·L). 4) After the reaction is complete, cool the system to 30-40℃, and slowly add 5%-10% of deionized water (based on the total weight of polyethylene glycol monomethyl ether and phosphorus pentoxide) over 30-60 minutes for hydrolysis. Stir for 1-2 hours, and then adjust the pH to 6.5-7.0 with 8%-12% sodium hydroxide solution to obtain phosphorylated polyethylene glycol monomethyl ether.

4. The nano-calcium hydroxide according to claim 1, characterized in that, The raw materials for preparing the carboxylated β-cyclodextrin, by weight, include: 90-100 parts of β-cyclodextrin, 250-300 parts of N,N-dimethylformamide, 40-60 parts of succinic anhydride, 8-12 parts of anhydrous pyridine, and 30-40 parts of deionized water.

5. The nano-calcium hydroxide according to claim 4, characterized in that, The preparation method of the carboxylated β-cyclodextrin includes the following steps: (1) Dissolve β-cyclodextrin in a mixture of N,N-dimethylformamide and deionized water, heat to 60-70℃, and stir at 150-250r / min until completely dissolved; (2) Under nitrogen protection, add succinic anhydride to the solution obtained in step (1), and then add anhydrous pyridine dropwise at a constant rate over 30-60 min. Heat to 80-90℃ and stir the reaction at a speed of 150-250 r / min for 10-15 h. (3) After the reaction is completed, cool to room temperature, slowly pour the reaction solution into anhydrous ethanol at 0-5℃ with a volume of 4-5 times that of the reaction solution to precipitate, filter, wash the precipitate with anhydrous ethanol 3-5 times, then dissolve the washed solid in 300-400 parts by weight of deionized water, adjust the pH to 2.0-3.0 with 8%-12% hydrochloric acid, and then centrifuge at 3000-5000r / min for 10-20min to collect the precipitate; (4) The precipitate collected in step (3) is redispersed in deionized water and then transferred to a dialysis bag with a molecular weight cutoff of 1000-1200 Da. Dialyze with deionized water for 24-28 hours, changing the water every 6-8 hours. The solid obtained after dialysis is freeze-dried at -55~-45℃ and vacuum degree of 20-30 Pa for 24-28 hours to obtain carboxylated β-cyclodextrin.

6. The nano-calcium hydroxide according to any one of claims 1-5, characterized in that, The raw materials for its preparation, by weight, include: 20-25 parts calcium oxide, 130-140 parts deionized water, 2-3 parts phosphorylated polyethylene glycol monomethyl ether, 1-2 parts carboxylated β-cyclodextrin, 2.5-3.5 parts sodium polyaspartate, 0.8-1.5 parts L-lysine, and 0.4-0.8 parts 3-mercaptopropylmethyldimethoxysilane.

7. A method for preparing nano-calcium hydroxide according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Add deionized water to the reaction vessel, start stirring, and add phosphorylated polyethylene glycol monomethyl ether, carboxylated β-cyclodextrin, sodium polyaspartate and L-lysine in sequence. Stir at 150-250 r / min at 25-35℃ for 15-25 min to dissolve and obtain functional base liquid. S2. Add calcium oxide to the functional base liquid obtained in step S1, and stir at 150-250 r / min for 10-20 min at 25-35℃. S3. Heat the system obtained in step S2 to 50-65℃ and stir at 150-300 r / min to digest the reaction for 2.5-4.5 h. S4. Cool the system obtained in step S3 to 30-35℃, add 3-mercaptopropylmethyldimethoxysilane dropwise at a uniform rate over 30-60 min, and then continue stirring the reaction at a speed of 150-300 r / min for 1.5-2.5 h. S5. Adjust the pH of the system obtained in step S4 to 8.5-9.5 with dilute hydrochloric acid with a mass fraction of 8%-12%. Then stir at 55-60℃ and 150-250r / min for 30-60min. After that, centrifuge the slurry after reaction, discard the supernatant, wash and dry the precipitate, and then crush and depolymerize it using an air jet mill. After crushing, classify it through a 200-400 mesh sieve, and take the sieve-underfill material as nano calcium hydroxide powder.

8. The method for preparing nano-calcium hydroxide according to claim 7, characterized in that, In step S5, the centrifugation speed is 10000-11000 r / min and the centrifugation time is 15-25 min; the precipitate is washed with deionized water 2-3 times and then washed with anhydrous ethanol 1-2 times. After each washing, the precipitate is centrifuged at 7500-8500 r / min for 10-15 min.

9. The method for preparing nano-calcium hydroxide according to claim 7, characterized in that, In step S5, the drying conditions are: vacuum degree of -0.095~-0.085MPa, temperature of 60-75℃, and time of 12-20h; the pulverizing pressure of the air jet mill for pulverizing and depolymerizing is 0.6-0.8MPa, and the classifying speed is 4000-5000r / min.

10. An application of nano-calcium hydroxide in dry flue gas desulfurization, characterized in that, The nano-calcium hydroxide is the nano-calcium hydroxide described in any one of claims 1-5.

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