High-dispersion high-specific-surface-area calcium hydroxide and preparation method thereof

Abstract

The invention discloses high-dispersion high-specific-surface-area calcium hydroxide and a preparation method thereof.According to the method, the positive pressure condition in a closed environment is used as physical driving force, and a compound modified digestion solution is forced to overcome resistance and permeate into deep pores of quick lime; and after the reaction is finished, instantaneous pressure relief is performed by utilizing a huge pressure difference between the inside and the outside of a reaction system, so that the overheated liquid water adsorbed between crystal layers is subjected to'flash evaporation ', and volume expansion force is generated to'prop open' particles from the inside, thereby obtaining high-dispersion porous nanoscale powder in situ.

Description

Technical Field

[0001] This application belongs to the field of inorganic chemical engineering, specifically relating to a highly dispersed calcium hydroxide with a high specific surface area and its preparation method. Background Technology

[0002] Calcium hydroxide (Ca(OH)2), as a basic chemical raw material, is widely used in flue gas desulfurization, wastewater treatment, building materials, and fine chemicals. Especially in dry and semi-dry flue gas desulfurization processes, calcium hydroxide acts as a desulfurizing agent, and its specific surface area and pore structure directly determine the contact efficiency and desulfurization performance of the gas-solid reaction. Ordinary industrial-grade calcium hydroxide typically has a specific surface area of ​​around 10-15 m² / g, with small pore volume and low reactivity, resulting in low calcium utilization during desulfurization. This not only increases operating costs but also generates a large amount of difficult-to-treat desulfurization byproducts. Therefore, the preparation of calcium hydroxide with high specific surface area (usually >40 m² / g) and high dispersibility has become a research hotspot in the field of environmental materials.

[0003] Currently, the main industrial processes for producing calcium hydroxide include dry digestion and wet digestion. However, existing production technologies still face the following significant challenges in producing high-quality products: First, there are limitations to traditional atmospheric pressure hydration processes. Traditional quicklime hydration reactions typically occur at atmospheric pressure, with the reaction temperature limited by the boiling point of water. At this temperature, while the hydration reaction of quicklime (CaO) is vigorous, it lacks sufficient driving force to regulate crystal nucleation and growth. The resulting calcium hydroxide crystals tend to stack along specific crystal planes, forming dense, coarse plate-like or blocky particles. Furthermore, the large amount of heat released during the reaction is primarily dissipated directly as water vapor at atmospheric pressure, failing to be effectively utilized to improve the powder structure, resulting in difficulty in significantly increasing the specific surface area of ​​the final product.

[0004] Secondly, there are issues with the modifier's "difficulty in penetration" and "uneven distribution." To suppress crystal growth and increase specific surface area, existing technologies often add modifiers such as organic alcohols and polyhydroxy compounds to the digester water. However, during atmospheric pressure digestion, due to the capillary resistance of the microporous structure of quicklime and the surface tension of the liquid phase, the modifier solution often only wets the outer surface of the quicklime particles. When a hydration reaction occurs on the particle surface to form a calcium hydroxide coating, it further hinders the diffusion of the modifier into the particle interior. This leads to a structural inhomogeneity phenomenon of "surface modification, rough core," where the internally formed crystals remain large and agglomerated, limiting the overall increase in specific surface area.

[0005] Third, the product is prone to agglomeration and post-processing costs are high. Calcium hydroxide powder with a high specific surface area has extremely high surface energy, making it highly susceptible to secondary agglomeration during drying and aging, leading to the loss of effective active sites. To solve the agglomeration problem, some processes have to introduce subsequent mechanical grinding or air jet milling steps, which not only significantly increases equipment investment and energy consumption, but also often damages the original mesoporous structure of the crystals, resulting in pore volume loss.

[0006] In summary, existing technologies lack an industrial-scale preparation method that can overcome liquid-phase mass transfer resistance, achieve deep penetration of the modifier, and effectively utilize reaction heat energy for in-situ anti-agglomeration and pore-forming. Therefore, developing a new process that is simple in terms of equipment, suitable for large-scale industrial production, and capable of stably preparing highly dispersed calcium hydroxide with a high specific surface area is a pressing technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a highly dispersed calcium hydroxide with a high specific surface area and its preparation method. This preparation method utilizes a buffer chamber and a star valve to achieve continuous feeding into a high-pressure vessel; it significantly increases the boiling point of water and the reaction temperature by increasing the pressure of the reaction system, creating a high-temperature and high-pressure reaction environment; after the reaction is completed, it utilizes the "gas explosion" expansion effect generated by instantaneous pressure relief to prepare calcium hydroxide powder with a high specific surface area and high activity.

[0008] To achieve the above objectives, the present invention provides a method for preparing highly dispersed calcium hydroxide with a high specific surface area, comprising the following steps: S1. Pressurized Permeation Reaction: The crushed quicklime particles are conveyed to a horizontal positive pressure digester via a buffer feeding mechanism. The heat released during the quicklime reaction, or additional auxiliary heating, is used to establish a positive pressure environment. The reaction system pressure is controlled at 0.2-1.5 MPa, the reaction temperature at 150-200℃, and the pressure is maintained for 15-45 minutes. This step reduces the surface tension of the composite modified digestion liquid and allows it to deeply penetrate into the internal pores of the quicklime particles. This enables the modifier molecules to be uniformly adsorbed on the surface of the calcium hydroxide crystal nuclei formed on both the inner and outer layers, preventing excessive stacking growth of crystals along the C-axis and inducing the formation of plate-like nanocrystals.

[0009] S2. Flash Expansion Discharge: After the digestion reaction is complete, the discharge device of the pressure vessel is opened, and the high-temperature reactants are instantly sprayed out using the pressure difference of the reaction system. During this process, the superheated liquid water undergoes instantaneous flash evaporation. The expansion force generated by the flash evaporation depolymerizes and creates pores in the calcium hydroxide agglomerates, forming a rich mesoporous structure between crystal layers and particles.

[0010] S3. Cooling and Separation: The ejected material undergoes gas-solid separation and preliminary cooling and drying in the primary aging unit, and then passes through the secondary aging unit for aging to obtain highly dispersed calcium hydroxide with a high specific surface area.

[0011] Furthermore, the composite modified digestive fluid is composed of a penetration enhancer, a crystal form blocking agent, and water.

[0012] Penetration aid: selected from one or more of glycerol, polyethylene glycol or sucrose; its addition amount is 1.0%-3.0% of the mass of quicklime; its function is to reduce the surface tension of the digestion liquid and assist water and blocking agent to enter the micropores of quicklime during the pressure holding stage.

[0013] Crystal growth inhibitor: selected from one or more of citric acid, tartaric acid, glutaric acid, malonic acid, or pyrophosphate; its addition amount is 0.5%-1.5% of the mass of quicklime. Its function is to complex with calcium ions, adsorb on specific crystal faces of the crystal nucleus, and inhibit crystal growth.

[0014] Furthermore, the sealed pressure-resistant container is a horizontal digester with a steam jacket; in step S1, the composite modified digestion liquid is sprayed into the sealed pressure-resistant container in an atomized form by a high-pressure pump to ensure that the modifier and the surface of quicklime particles are in full and uniform contact before pressure is established.

[0015] Furthermore, the positive pressure environment is established by prioritizing the use of the heat released from the hydration reaction of quicklime to evaporate water and spontaneously increase pressure; only when the spontaneous pressure increase is insufficient to reach the preset pressure is steam introduced into the steam jacket for auxiliary heating and pressure increase.

[0016] Furthermore, in step S3, the rapid cooling is achieved by introducing cold air into the airflow conveying pipe and directly mixing it with the high-temperature flash-evaporated material. This process rapidly reduces the material temperature to below 100°C within seconds, effectively preventing secondary crystal growth or pore structure collapse caused by excessive residual heat.

[0017] The present invention also provides a highly dispersed calcium hydroxide with a high specific surface area prepared by the above method, characterized in that: the specific surface area is 45-55 m² / g; the pore volume is 0.25-0.45 cm³ / g; the particle size D50 is 1.5-4.0 μm; and the microstructure presents a loosely packed sheet-like nanocrystalline structure.

[0018] The present invention also provides the application of the above-mentioned highly dispersed calcium hydroxide with high specific surface area in dry or semi-dry flue gas desulfurization.

[0019] In this application, the water in the reaction system is in a superheated liquid state, and the reaction temperature far exceeds 100°C under normal pressure. The high temperature and high pressure environment increases the reaction rate and promotes the explosive formation of crystal nuclei. The instantaneous generation of a large number of tiny crystal nuclei, combined with the steric hindrance and complexation of organic acids / alcohols in the digestion solution, effectively inhibits excessive crystal growth and aggregation, keeping the product at the nanoscale or submicroscale size. Simultaneously, this application also utilizes the pressure relief process at the end of the reaction. When the high-temperature, high-pressure material is injected into a low-pressure environment, the superheated water adsorbed inside and between the particles undergoes an instantaneous phase transition, resulting in a rapid volume expansion. The generated energy bursts within the particles, effectively tearing and expanding the potentially dense lamellar structure, creating a large number of micropores and mesopores in situ, thereby significantly increasing the specific surface area and pore volume of the product. Beneficial effects of the present invention Compared with the prior art, the present invention has the following significant advantages: The calcium hydroxide powder provided by this invention has a stable specific surface area of ​​45-55 m². 2 / g, pore volume reaches 0.25-0.45cm 3 / g, significantly superior to traditional atmospheric pressure digestion products. Its high specific surface area provides more reactive sites, achieving a desulfurization efficiency of over 98% in dry flue gas desulfurization, with a longer effective action time; The calcium hydroxide powder provided by this invention exhibits extremely high reactivity in dry flue gas desulfurization. Tests show a desulfurization rate greater than 98% and a longer effective working time, with particularly significant advantages under low flue gas humidity conditions.

[0020] The preparation method provided by this invention has no requirements for quicklime raw materials; it can be produced using quicklime with ordinary activity, which greatly reduces production costs. The preparation method provided by this invention employs positive pressure digestion, requiring less water and reagents than traditional dry processes, and generates no wastewater or solid waste. Compared to wet processes, this process offers higher thermal efficiency and reagent utilization, resulting in significant economic benefits. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] Example 1 Raw materials: Second-grade quicklime with an activity of 295 mL and a calcium oxide content of 90%. After crushing, it forms fine particles of 2-4 mm.

[0023] Continuous feeding: The material is conveyed to the raw material silo via belt. The opening and closing degree of the star-shaped discharge valve in the raw material silo is controlled at 87°, and the ash discharge speed is 10.5t / h. The material enters the buffer silo. When the storage capacity of the buffer silo reaches 10t, feeding is stopped and the feed port is closed. The star-shaped discharge valve at the bottom of the buffer silo is opened, and quicklime is continuously added to the horizontal positive pressure digester at a discharge speed of 4.8t / h.

[0024] Positive pressure digestion: Simultaneously, 4.38 t / h of digestion liquid is sprayed into the digester. The digestion liquid is prepared by 1% citric acid + 2% PEG400 + 97% water. The digestion pressure is controlled at 0.6 MPa, and the digestion temperature is 160-180℃. The positive pressure digestion time is 30 min.

[0025] Flash evaporation and post-processing: After the reaction, the bottom valve at the tail of the digester is opened for rapid pressure release and discharge. Calcium hydroxide powder is injected into the primary aging chamber with a high-speed airflow. Gas-solid separation occurs in the primary aging chamber, reducing the material temperature from 177℃ to 81℃ and the moisture content from 12% to 2%. It then flows by gravity to the secondary aging chamber, where the temperature is further reduced to 46℃ and aging continues for 30 minutes. Finally, high specific surface area calcium hydroxide product is obtained through air classification.

[0026] Example 2 Raw materials: Grade A quicklime with an activity of 342 mL and a calcium oxide content of 91%. Crush into 2-4 mm particles.

[0027] Continuous feeding: Control the opening and closing degree of the star valve in the raw material silo to 93°, and the ash discharge speed to 11.6t / h. When the buffer silo storage capacity reaches 10t, switch to discharge mode, open the star valve in the buffer silo (opening degree 72°), and the discharge speed is 6.6t / h.

[0028] Positive pressure digestion: Simultaneously spray 4.2 t / h of digestion liquid, which is prepared by adding 0.6% pyrophosphate, 1.4% glycerol, and 98% water. Control the digestion pressure at 0.8 MPa and the digestion temperature at 170-190℃. Perform positive pressure digestion for 30 minutes.

[0029] Flash evaporation and post-processing: After being sprayed into the primary aging chamber, the material temperature is reduced from 184℃ to 96℃, and the moisture content is reduced from 10% to 1%. Then it enters the secondary aging chamber, where the temperature is reduced to 52℃ and aged for 30 minutes. The product is then obtained by air separation.

[0030] Example 3 Raw materials: Selected high-grade quicklime, with an activity of 380 mL and a calcium oxide content of 93%. Crushed into 2-4 mm particles.

[0031] Continuous feeding: Control the opening degree of the star-shaped discharge valve in the raw material silo to 103°, and the ash discharge rate to 15.8t / h. During the discharge stage of the buffer silo, open the star-shaped discharge valve (opening degree 64°), and the discharge rate is 5.6t / h.

[0032] Positive pressure digestion: Simultaneously spray 3.08 t / h of digestion liquid, which is prepared by 1.4% tartaric acid + 0.8% sucrose + 97.8% water. Control the digestion pressure at 1.0 MPa and the digestion temperature at 180-200℃. Perform positive pressure digestion for 30 minutes.

[0033] Flash evaporation and post-processing: After discharge, the material temperature is reduced from 190℃ to 103℃ and the moisture content is reduced from 8% to 1% in the primary aging chamber. Then it enters the secondary aging chamber, where the temperature is reduced to 54℃ and aged for 30 minutes. The product is obtained by air separation.

[0034] Example 4 Raw materials: Grade A quicklime with an activity of 342 mL and a calcium oxide content of 91%. Crush into 2-4 mm particles.

[0035] Continuous feeding: Control the opening and closing degree of the star-shaped discharge valve in the raw material silo to 95°, and the ash discharge speed to 12t / h. During the discharge stage of the buffer silo, open the star-shaped discharge valve (opening degree 64°), and the discharge speed to 5.6t / h.

[0036] Positive pressure digestion: Simultaneously spray 3.92 t / h of digestion liquid, which is prepared by adding 0.8% glutaric acid, 1.5% diethylene glycol, and 97.7% water. Control the digestion pressure at 0.9 MPa and the digestion temperature at 170-190℃. Perform positive pressure digestion for 30 minutes.

[0037] Flash evaporation and post-processing: After discharge, the material temperature is reduced from 185℃ to 96℃ and the moisture content is reduced from 12% to 2% in the primary aging chamber. Then it enters the secondary aging chamber, where the temperature is reduced to 54℃ and aged for 30 minutes. The product is then obtained by air separation.

[0038] Example 5 Raw materials: Selected high-grade quicklime, with an activity of 380 mL and a calcium oxide content of 93%. Crushed into 2-4 mm particles.

[0039] Continuous feeding: Control the opening degree of the star-shaped discharge valve in the raw material silo to 97°, and the ash discharge rate to 12.1t / h. During the discharge stage of the buffer silo, open the star-shaped discharge valve (opening degree 64°), and the discharge rate is 5.6t / h.

[0040] Positive pressure digestion: Simultaneously spray 3.36 t / h of digestion liquid, which is prepared by 1.2% citric acid + 1% sucrose + 97.8% water. Control the digestion pressure at 0.7 MPa and the digestion temperature at 170-190℃. Perform positive pressure digestion for 30 minutes.

[0041] Flash evaporation and post-processing: After discharge, the material temperature is reduced from 187℃ to 93℃ and the moisture content is reduced from 10% to 1% in the primary aging chamber. Then it enters the secondary aging chamber, where the temperature is reduced to 52℃ and aged for 30 minutes. The product is obtained by air separation.

[0042] The "premium grade," "grade one," and "grade two" quicklime mentioned in this embodiment of the invention are classified according to activity and effective calcium oxide content, referring to industry standards and conventional classification methods in the field. Specific indicators are as follows: Extra-grade quicklime: refers to high-quality quicklime with an activity of ≥360 mL and an effective calcium oxide content of ≥92%. It has an extremely fast reaction rate and is highly exothermic. Grade 1 quicklime: refers to high-quality quicklime with an activity between 320-360 mL and an effective calcium oxide content between 90-92%; Secondary quicklime: refers to ordinary industrial quicklime with an activity between 280-320 mL or an effective calcium oxide content between 88-90%. The process of this invention has good adaptability to the above-mentioned different grades of raw materials.

[0043] To verify the desulfurization effect of the high specific surface area calcium hydroxide prepared in this invention in practical applications, a laboratory simulated flue gas fixed bed reactor was used to evaluate the dry desulfurization process.

[0044] 1. Experimental Apparatus and Conditions: A quantitative (1.0 g) sample of calcium hydroxide powder prepared in the example was evenly spread in a constant-temperature fixed-bed reaction tube. Simulated industrial flue gas was prepared, with an initial sulfur dioxide (SO2) concentration set at 1500 mg / Nm³. 3 (Simulating typical coal-fired flue gas concentration), the carrier gas is nitrogen, and the gas flow rate is controlled at 500 mL / min.

[0045] 2. Experimental Procedure: The reaction system was heated and maintained at 160℃ (simulating the typical operating temperature of dry desulfurization). Simulated flue gas was introduced, and the SO2 concentration at the reactor outlet was continuously monitored using a flue gas analyzer until breakthrough occurred.

[0046] 3. Result Calculation: Select the outlet concentration data 30 minutes before the reaction, and calculate the average desulfurization rate according to the formula: Desulfurization efficiency = (Inlet concentration - Outlet concentration) / Inlet concentration × 100%.

[0047] The performance test results are shown in Table 1 below: Table 1

[0048] Tests showed that the calcium hydroxide products prepared in the above examples all achieved a desulfurization rate of greater than 98% in dry desulfurization experiments.

Claims

1. A method for preparing highly dispersed calcium hydroxide with high specific surface area, characterized in that, Includes the following steps: S1. The crushed quicklime particles are conveyed to the horizontal positive pressure digester through a buffer feeding mechanism, and a composite modified digestion liquid is sprayed in to carry out the digestion reaction. S2. After the reaction is complete, open the discharge device at the tail of the horizontal positive pressure digester to spray the material into the first-stage aging tank to depolymerize and create pores in the calcium hydroxide particles. S3. After depolymerization and pore formation, gas-solid separation and preliminary drying are carried out in the first-stage aging unit, and then the product enters the second-stage aging unit for aging and sorting to obtain high specific surface area calcium hydroxide powder.

2. The preparation method according to claim 1, characterized in that, The composite modified digestive fluid is composed of a osmosis aid, a crystal form blocking agent, and water; and / or, The penetration enhancer is selected from one or more of glycerol, polyethylene glycol, or sucrose; the crystal form blocking agent is selected from one or more of citric acid, tartaric acid, glutaric acid, malonic acid, or pyrophosphate.

3. The preparation method according to claim 2, characterized in that, In step S1, the buffer feeding mechanism includes a raw material bin, a buffer bin, and a star-shaped discharge valve installed at the inlet and outlet of the buffer bin.

4. The preparation method according to claim 1, characterized in that, In step S1, the activity of the quicklime is 280-360 mL, and the particle size after crushing is 2-5 mm; the stirring rate in the sealed pressure-resistant container is controlled at 50-150 rpm.

5. The preparation method according to claim 1, characterized in that, In step S1, the heat released by the hydration reaction of quicklime is preferentially used to evaporate the water and spontaneously increase the pressure; when the spontaneous pressure increase is insufficient to reach the preset pressure, steam is introduced into the jacket of the sealed pressure-resistant container for auxiliary heating and pressure increase.

6. The preparation method according to claim 1, characterized in that, In step S1, the pressure of the digestion reaction is 0.2-1.5 MPa, and the reaction temperature is 150-200℃.

7. The preparation method according to claim 1, characterized in that, In step S2, the discharge device is a pneumatic ball valve or a quick-opening valve; the material is sprayed from the sealed pressure-resistant container into the primary settling chamber.

8. The preparation method according to claim 1, characterized in that, In step S3, the material is mixed with the introduced cold air during the pneumatic conveying process; then it enters the secondary aging device for aging for 20-40 minutes at an aging temperature of 40-60℃.

9. A highly dispersed calcium hydroxide with a high specific surface area prepared by the method according to any one of claims 1-8, characterized in that: The specific surface area of ​​the calcium hydroxide is 45-55 m². 2 / g; pore volume is 0.25-0.45cm³ 3 / g; particle size D50 is 1.5-4.0μm; microstructure presents as a loosely packed sheet-like nanocrystal structure.

10. The application of the highly dispersed, high specific surface area calcium hydroxide as described in claim 9 in dry or semi-dry flue gas desulfurization.

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