Digestion water for preparing calcium hydroxide with high specific surface area and application thereof

Abstract

This invention discloses a digested water for preparing high specific surface area calcium hydroxide and its application, belonging to the technical field of calcium hydroxide preparation. It consists of a digestion aid and water; the digestion aid includes organic matter and inorganic salts; the organic matter includes sodium p-aminobenzoate and choline chloride; the inorganic salts include calcium chloride and ferric chloride; the mass ratio of ferric chloride, calcium chloride, sodium p-aminobenzoate, choline chloride, and water is 0.8-1.2:4-5:2.5-3.5:1.7-2.3:88-91. The digested water for preparing high specific surface area calcium hydroxide provided by this invention can reduce the water-to-ash ratio of the digested water, reduce the amount of digestion aid, and improve the specific surface area, pore volume, desulfurization capacity, and suspension dispersion stability of calcium hydroxide.

Description

Technical Field

[0001] This invention belongs to the field of calcium hydroxide preparation technology, specifically relating to a digested water for preparing calcium hydroxide with high specific surface area and its application. Background Technology

[0002] Currently, commonly used desulfurizing agents in industry mainly include calcium hydroxide (Ca(OH)2) and sodium bicarbonate (NaHCO3). In the field of flue gas emission treatment for waste incineration, glass melting furnaces, and coal-fired boilers, dry / semi-dry desulfurization has become the mainstream application technology due to its advantages such as simple system, small footprint, and no wastewater discharge. From the reaction mechanism perspective, the reaction between calcium hydroxide and SO2 in flue gas is a gas-solid non-catalytic reaction, which can be started at room temperature. The reaction rate reaches its peak in a medium-low temperature flue gas environment of 80℃-180℃, achieving SO2 fixation by generating insoluble calcium sulfite and calcium sulfate. Sodium bicarbonate, on the other hand, requires thermal decomposition at a high temperature above 150℃ to generate sodium carbonate, and then reacts with SO2 to generate soluble sodium sulfite and sodium sulfate. The reaction start temperature is higher, and it is more sensitive to flue gas temperature fluctuations. Compared with sodium bicarbonate, calcium hydroxide not only has a significant cost advantage, but also has strong stability of desulfurization products and low risk of secondary pollution. Therefore, calcium hydroxide, especially calcium hydroxide with a high specific surface area, has gradually become the main desulfurizing agent in industrial desulfurization.

[0003] The key to increasing the specific surface area of ​​calcium hydroxide lies in controlling grain growth during the quicklime digestion process. Existing technologies mainly achieve this by adding additives to the digestion water. Early technologies often used alcohols as morphology control agents; for example, patent CN117510101A uses methanol, ethanol, and propanol as digestion aids, and patent CN121085563A uses triethanolamine and diethanol monoisopropanol as digestion aids. Research shows that the modification principle of alcohol additives is as follows: alcohols act as surfactants, coating the CaO surface and effectively preventing the aggregation of Ca(OH)2 products by reducing surface tension. Simultaneously, the alcohol solvent reduces the solubility of hydrated products, thereby promoting the precipitation of hydrated products from the CaO aqueous solution, successfully constructing a porous calcium-based desulfurizing agent. This method can increase the specific surface area of ​​calcium hydroxide to a certain extent, but it has the following shortcomings: (1) Alcohol additives mainly inhibit particle growth through surface physical adsorption. Their adsorption on the Ca(OH)2 surface is a reversible process, and the modification effect is limited; (2) After alcohol modification, the polarity of the Ca(OH)2 particle surface is weakened, and the surface transitions from hydrophilic to hydrophobic. In subsequent applications, hydrophobic particles are easily attracted to each other and aggregate due to hydrophobic effects, which intensifies the agglomeration problem; (3) Alcohols are flammable liquids. Their vapors can form explosive mixtures with air, and there is a problem of VOCs volatilization during use, which is not conducive to green and safe production.

[0004] To further improve the performance of calcium hydroxide, researchers began to explore multi-component compound formulations. Patent CN112358205A discloses a method for preparing highly active calcium hydroxide, which uses calcium chloride and one or more of diethylene glycol, sucrose, or n-butanol as additives. It employs a high water-to-water ratio process (1:6-8) for digestion, followed by aging, pressure filtration, drying, and pulverization to obtain a product with a specific surface area of ​​15-60 m². 2 / g of calcium hydroxide. This scheme is an improvement over single alcohols, but still has the following shortcomings: (1) The scheme adopts a high water-ash ratio process of 1:6-8, which results in a large amount of water used for digestion and high energy consumption in the subsequent dehydration and drying process; (2) The sucrose in the additive will be partially carbonized during the high-temperature drying process, forming a residual carbon layer on the inner surface of the pores, which will block the reactive sites and affect the desulfurization performance; (3) The pore volume control effect is limited. This scheme can only slightly increase the specific surface area by inhibiting grain growth, and cannot form a uniform pore and microporous structure. The pore volume of the product is usually ≤0.25cm 3 / g, insufficient micropore ratio, limited SO2 adsorption sites, resulting in desulfurization capacity ≤23%, which cannot meet the needs of high-end desulfurization scenarios; (4) poor suspension dispersion stability, the alcohol and sugar added in this scheme have weak dispersion effect, the absolute value of the product's Zeta potential is low, the sedimentation rate is large, and it is easy to agglomerate and settle in actual applications, clogging desulfurization pipelines and nozzles, requiring frequent equipment cleaning, which affects production efficiency.

[0005] Furthermore, the suspension and dispersion stability of existing technologies is generally insufficient. Even at high Zeta potentials, calcium hydroxide suspensions suffer from insufficient particle agglomeration due to the inherent ionic strength of their saturated solutions shielding electrostatic repulsion. High water-to-ash ratio processes directly produce extremely dilute suspensions (solid content of only about 11%-14%), which are then pressed into filter cakes, dried, and pulverized. In subsequent suspension formulations, the solid content of the product typically remains at only 5%-10%. Moreover, during high-temperature drying, particles easily form hard agglomerates through oxygen bridging bonds. These agglomerates are difficult to break down effectively during redispersement with water, resulting in a large number of agglomerated particles rapidly settling in the suspension.

[0006] In summary, the existing technologies for calcium hydroxide digestion preparation still have the following comprehensive problems that have not been effectively solved: (1) Alcohol-based additives have a single mechanism of action and pose safety hazards, resulting in poor product suspension and dispersibility; (2) Compound combination schemes often adopt high water-cement ratio and high energy consumption processes, which have limited improvement on the comprehensive performance of the product, such as pore volume, sulfur capacity, and suspension and dispersion stability; (3) The product has poor suspension and dispersion stability, and is prone to settling and clogging pipes and nozzles in practical applications. Therefore, developing a digested water formulation that can simultaneously improve specific surface area, pore volume, sulfur capacity, and suspension stability, while having low process energy consumption, has important industrial application value. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a digested water for preparing high specific surface area calcium hydroxide and its application, which reduces the water-ash ratio of the digested water, reduces the amount of digestion aids, and improves the specific surface area, pore volume, desulfurization capacity, and suspension dispersion stability of the prepared calcium hydroxide.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing high specific surface area calcium hydroxide digested water uses a mixture of organic matter and inorganic salts as digestion aids dissolved in water; The organic compounds include sodium para-aminobenzoate and choline chloride; The inorganic salts include calcium chloride and ferric chloride; The mass ratio of ferric chloride, calcium chloride, sodium para-aminobenzoate, choline chloride, and water is 0.8-1.2:4-5:2.5-3.5:1.7-2.3:88-91.

[0009] The method for preparing high specific surface area calcium hydroxide digested water is as follows: weigh ferric chloride, calcium chloride, sodium para-aminobenzoate and choline chloride respectively, add them to water, and stir for 28-32 minutes to obtain digested water.

[0010] The digested iron ions undergo hydrolysis in water, resulting in a weakly acidic solution (pH 2.5-4). Under this weakly acidic environment, Fe... 3+ It exists as hydrated iron ions, chloride complexes, and small amounts of organic complexes formed with aminobenzoate. When digested water is mixed with quicklime, the pH of the system rises sharply to alkaline, and Fe... 3+ In-situ hydrolysis generates nano-sized Fe(OH)3 particles. These nanoparticles are uniformly attached to the surface of Ca(OH)2 grains. On the one hand, they effectively inhibit grain growth through physical barrier, thereby increasing the specific surface area of ​​the product. On the other hand, they hinder the close packing between grains and promote the formation of more pores between grains.

[0011] After calcium chloride dissolves in water, Ca 2+ and Cl - Altering the ionic strength of the digester water affects the hydration rate and mass transfer process in the initial stage of quicklime digestion, regulating the formation and growth of Ca(OH)₂ crystal nuclei, which helps to obtain fine and uniform crystals. The added Ca... 2+ The concentration far exceeds the equilibrium concentration of Ca(OH)₂, promoting the rapid formation of Ca(OH)₂ crystal nuclei; at the same time, Ca 2+Adsorbed on the surface of crystal nuclei, the interfacial energy is reduced, decreasing the critical nucleus size and allowing more nuclei to form and grow into fine, uniform grains. As the critical size decreases, more nuclei can form, thus accelerating the formation rate. The accumulation of fine grains creates abundant packing pores, further increasing the pore volume.

[0012] The carboxyl group of sodium p-aminobenzoate and Ca 2+ Coordination: The -NH2 group in the molecule enhances its anchoring effect on a specific crystal plane through hydrogen bonding, introducing a negative charge to the Ca(OH)2 surface. Its molecules adsorb on the Ca(OH)2 crystal surface, inhibiting the directional growth of grains through steric hindrance, making the grain morphology irregular and increasing the porosity between grains.

[0013] Choline chloride cations neutralize the surface negative charge through electrostatic attraction, forming an organic composite interface layer with p-aminobenzoate ions, thus adjusting the zeta potential. At the same time, choline chloride, as a quaternary ammonium salt cationic surfactant, reduces the surface tension of the digested water, improves the wettability of quicklime particles, and makes the digestion reaction more uniform.

[0014] Application of the digested water from the above formula in the preparation of calcium hydroxide with high specific surface area: Weigh out 0.8-1.2 parts of ferric chloride, 4-5 parts of calcium chloride, 2.5-3.5 parts of sodium para-aminobenzoate, and 1.7-2.3 parts of choline chloride according to their respective weights. Add them to 88-91 parts of water and stir for 28-32 minutes to obtain digested water. Heat the digested water to 30-50℃, mix it with crushed quicklime, and add the heated digested water at a uniform rate over 3-5 minutes while stirring at 200-400 rpm. Control the digestion reaction for 14-16 minutes, and then dry it at 95-100℃ to constant weight to obtain the finished calcium hydroxide. The mass-to-volume ratio of quicklime to slaked water is 48-52g:38-42ml; The particle size of the crushed quicklime is ≤180μm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses a four-component compound of ferric chloride, calcium chloride, sodium para-aminobenzoate, and choline chloride as a digestion aid, leveraging the synergistic effect of inorganic salts and organic matter. The components achieve synergistic regulation throughout the entire lifecycle, including nucleation, growth, and dispersion. Ferric chloride exists as a soluble complex, which is released in situ during digestion according to pH, generating nano-sized Fe(OH)3 that uniformly adheres to the surface of Ca(OH)2 crystals, inhibiting crystal growth and hindering compact packing. Calcium chloride regulates ionic strength, reduces the interfacial energy of the crystal nucleus, promotes the formation of fine and uniform crystal nuclei, and the accumulation of fine crystals forms abundant packing pores. Sodium para-aminobenzoate selectively adsorbs crystal faces, inhibits directional growth, makes the crystal morphology irregular, and increases intercrystalline porosity. Choline chloride and sodium para-aminobenzoate form an organic composite interfacial layer, regulating the zeta potential and improving wettability. The synergistic effect of the four components makes the crystals finer and the packing looser, significantly increasing the pore volume and producing a significant synergistic effect.

[0016] (2) The calcium hydroxide prepared by this invention has high specific surface area, high pore volume, and high desulfurization capacity. The specific surface area of ​​the product, as determined by nitrogen adsorption, reaches 50.95-53.16 m². 2 / g, pore volume reaches 0.30-0.34 cm³ 3 / g; In simulated flue gas desulfurization tests, the sulfur capacity reached 24.82-26.51%; Meanwhile, the product exhibits excellent suspension and dispersion stability in water, with an absolute value of Zeta potential greater than 48.2-51.8 mV and a settling rate of 0.021-0.025 mm / min, meeting the requirements for suspension stability indicators. Attached Figure Description

[0017] Figure 1 The isothermal adsorption-desorption curves of calcium hydroxide prepared in Example 2 are shown. Figure 2 This is the differential distribution curve of the mesopore size of the calcium hydroxide prepared in Example 2 under BJH adsorption. Detailed Implementation

[0018] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0019] Example 1 Weigh out 0.8g of ferric chloride, 4g of calcium chloride, 2.5g of sodium para-aminobenzoate, and 1.7g of choline chloride, add them to 91g of water, and stir for 28 minutes to obtain digested water. Then heat the digested water to 30℃. Weigh out 48g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 38ml of the above digested water to the digester, stir, and control the digestion time to 14 minutes. Then dry at 95℃ to constant weight to obtain the finished calcium hydroxide product.

[0020] Example 2 Weigh out 1g of ferric chloride, 4.5g of calcium chloride, 3g of sodium para-aminobenzoate, and 2g of choline chloride, and add them to 89.5g of water. Stir for 30 minutes to obtain digested water, then heat the digested water to 40℃. Weigh out 50g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 40ml of the digested water to the digester, stir, and control the digestion time to 15 minutes. Then dry at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0021] Example 3 Weigh out 1.2g of ferric chloride, 5g of calcium chloride, 3.5g of sodium para-aminobenzoate, and 2.3g of choline chloride, add them to 88g of water, and stir for 32 minutes to obtain digested water. Then heat the digested water to 50℃. Weigh out 52g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 42ml of the above digested water to the digester, stir, and control the digestion time to 16 minutes. Then dry at 100℃ to constant weight to obtain the finished calcium hydroxide product.

[0022] Comparative Example 1 Weigh out 0g of ferric chloride, 4.5g of calcium chloride, 3g of sodium para-aminobenzoate, and 2g of choline chloride, and add them to 89.5g of water. Stir for 30 minutes to obtain digested water, then heat the digested water to 40℃. Weigh out 50g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 40ml of the digested water to the digester, stir, and control the digestion time to 15 minutes. Then dry at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0023] Comparative Example 2 Weigh out 1g of ferric chloride, 0g of calcium chloride, 3g of sodium para-aminobenzoate, and 2g of choline chloride, and add them to 89.5g of water. Stir for 30 minutes to obtain digested water, then heat the digested water to 40℃. Weigh out 50g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 40ml of the above digested water to the digester, stir, and control the digestion time to 15 minutes. Then dry at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0024] Comparative Example 3 Weigh out 1g of ferric chloride, 4.5g of calcium chloride, 0g of sodium para-aminobenzoate, and 2g of choline chloride, and add them to 89.5g of water. Stir for 30 minutes to obtain digested water, then heat the digested water to 40℃. Weigh out 50g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 40ml of the digested water to the digester, stir, and control the digestion time to 15 minutes. Then dry at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0025] Comparative Example 4 Weigh out 1g of ferric chloride, 4.5g of calcium chloride, 3g of sodium para-aminobenzoate, and 0g of choline chloride, and add them to 89.5g of water. Stir for 30 minutes to obtain digested water, then heat the digested water to 40℃. Weigh out 50g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 40ml of the digested water to the digester, stir, and control the digestion time to 15 minutes. Then dry at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0026] Comparative Example 5 Weigh out 0g of ferric chloride, 0g of calcium chloride, 3g of sodium para-aminobenzoate, and 2g of choline chloride, and add them to 89.5g of water. Stir for 30 minutes to obtain digested water, then heat the digested water to 40℃. Weigh out 50g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 40ml of the above digested water to the digester, stir, and control the digestion time to 15 minutes. Then dry at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0027] Comparative Example 6 Weigh out 1g of ferric chloride, 4.5g of calcium chloride, 0g of sodium para-aminobenzoate, and 0g of choline chloride, and add them to 89.5g of water. Stir for 30 minutes to obtain digested water, then heat the digested water to 40℃. Weigh out 50g of pulverized quicklime (particle size ≤180μm) and place it in a digester. Then add 40ml of the above digested water to the digester, stir, and control the digestion time to 15 minutes. Then dry at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0028] Comparative Example 7 Water was used directly as the digestion water, and the digestion water was heated to 40℃. 50g of crushed quicklime with a particle size ≤180μm was weighed and placed in a digester; then 40ml of the above digestion water was added to the digester, stirred, and the digestion time was controlled at 15min. Then it was dried at 98℃ to constant weight to obtain the finished calcium hydroxide product.

[0029] Detection Example 1 The specific surface area, pore volume, sulfur capacity, and suspension stability of the calcium hydroxide prepared in Examples 1-3 and Comparative Examples 1-7 were tested; the test results are shown in Table 1 and... Figure 1-2 As shown.

[0030] Specific surface area and pore volume were tested using nitrogen adsorption.

[0031] Desulfurization test: Weigh 1 gram of composite desulfurizing agent, denoted as m0, and place it in a quartz tube with an inner diameter of 16 mm. Weigh the entire tube together, denoted as m1. Place the quartz tube vertically into a furnace and set the temperature to 200℃. Introduce sulfur dioxide gas at a flow rate of 40 ml / min. After 3 minutes, close the sulfur dioxide valve, remove the quartz tube, and weigh it, denoted as m2. The sulfur capacity is calculated using the formula: Sulfur capacity = (m2 - m1) / m0.

[0032] Suspension stability: Take the finished calcium hydroxide, dilute it with deionized water to a solid content of 0.1 wt%, adjust the pH to 10.5, and measure the Zeta potential after constant temperature equilibrium at 25℃; use the gravity sedimentation method, take the finished calcium hydroxide, dilute it with deionized water to a solid content of 10 wt%, and detect the sedimentation rate.

[0033] Table 1: Comparison of formulations and specific surface areas of each embodiment and comparative example

[0034] Figure 1 The isothermal adsorption-desorption curves are used to detect the specific surface area of ​​calcium hydroxide obtained in Example 2. Figure 2 The BJH adsorption mesopore size differential distribution curve of calcium hydroxide prepared in Example 2 shows that the pore size is mainly concentrated in the mesopore range (2-50nm), and the concentrated distribution indicates that a stacked pore structure that is beneficial to improving pore volume is formed between the grains.

[0035] In Comparative Example 1, FeCl3 was missing. FeCl3 forms a soluble complex in weakly acidic digested water, which hydrolyzes in situ upon contact with alkali to generate nano-Fe(OH)3 that pins the surface of the grains. After its absence, the pinning effect disappears, and the specific surface area and sulfur capacity decrease, but other components can still maintain some properties. Comparative Example 2 lacks CaCl2, and CaCl2 provides Ca... 2+ and Cl - Regulate ionic strength and reduce Fe 3+ Hydrolysis rate; Ca 2+ Adsorption on the crystal nucleus surface lowers the interfacial energy, promoting the formation of more fine crystal nuclei. After deletion, the crystal nuclei coarsen, and the specific surface area decreases significantly (37.54), which is the most severe among all single deletions.

[0036] Comparative Example 3 lacks sodium p-aminobenzoate, which is related to Fe.3+ Chelation enables pH-responsive release, selectively adsorbs Ca(OH)2 crystal faces to inhibit growth, and introduces a negative charge. After its loss, the Zeta potential drops sharply to 24.3 mV (below the stability threshold), resulting in severe particle aggregation and a sedimentation rate as high as 0.163.

[0037] Comparative Example 4 showed the absence of choline chloride, which formed an organic composite interfacial layer with sodium p-aminobenzoate, regulating the Zeta potential to the optimal range (40-60 mV) and reducing surface tension to improve wetting. After the absence of choline chloride, the Zeta potential decreased to 32.4 mV, the sedimentation rate deteriorated to 0.106, and both the specific surface area and pore volume decreased.

[0038] Comparative Example 5 lacked inorganic salts (FeCl3 and CaCl2), retaining only sodium p-aminobenzoate and choline chloride. Specific surface area, pore volume, and sulfur capacity decreased significantly (lower than Comparative Example 2) because inorganic salts are indispensable for crystal nucleation and pinning effects; however, organic matter still provided some dispersion stability, with an absolute Zeta potential (39.5 mV) higher than Comparative Examples 3 and 4, and a sedimentation rate (0.078 mm / min) better than Comparative Example 2.

[0039] Comparative Example 6 lacked organic matter, retaining only FeCl3 and CaCl2. Specific surface area (43.5 m²) 2 The concentration of inorganic salts ( / g) was higher than that of Comparative Example 2 (lacking CaCl2) but lower than that of Comparative Example 1 (lacking FeCl3), indicating that inorganic salts have a certain degree of control over morphology, but lack the adsorption and dispersion stabilization effect of organic matter on crystal faces, resulting in a lower absolute value of Zeta potential (30.2 mV) and a faster sedimentation rate (0.137 mm / min).

[0040] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high specific surface area calcium hydroxide digested water, characterized in that, Composed of digestive aids and water; The digestive aids include organic matter and inorganic salts; The organic compounds include sodium para-aminobenzoate and choline chloride; The inorganic salts include calcium chloride and ferric chloride.

2. The method for preparing high specific surface area calcium hydroxide digested water according to claim 1, characterized in that, The mass ratio of ferric chloride, calcium chloride, sodium para-aminobenzoate, choline chloride, and water is 0.8-1.2:4-5:2.5-3.5:1.7-2.3:88-91.

3. The application of the digested water according to any one of claims 1-2 in the preparation of calcium hydroxide with high specific surface area, characterized in that, Heat the digested water to 30-50℃, mix it with crushed quicklime, and add the heated digested water at a uniform rate over 3-5 minutes while stirring at 200-400 rpm. Control the digestion reaction for 14-16 minutes, and then dry it at 95-100℃ to constant weight to obtain the finished calcium hydroxide. The mass-to-volume ratio of quicklime to digested water is 48-52g:38-42ml.

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