Preparation method of calcium hydroxide with high specific surface area

Abstract

The invention relates to the technical field of inorganic material preparation, and particularly discloses a preparation method of calcium hydroxide with high specific surface area, which comprises four stages of raw material pretreatment, hydration reaction, ultrasonic dispersion and drying and crushing, in the initial stage, low-temperature control of 20-30 DEG C is adopted, the initial speed of hydration reaction is reduced at low temperature, a byproduct CaCO generated by local overheating due to violent heat release is avoided, the reaction rate is relieved, Ca (OH) decomposition is prevented at low temperature, the particle nucleation rate is greater than the growth rate at low temperature, and finer and dispersed initial particles are formed; along with consumption of CaO, the medium-stage temperature rises to 30-50 DEG C, weak combination among particles is promoted through temperature rise, a porous network structure is formed, and meanwhile pore collapse caused by high-temperature sintering is avoided; the residual amount of CaO in the later stage is very small, the heat release amount of the reaction is reduced, the temperature is increased to 50-60 DEG C, the reaction kinetics is improved, sufficient hydration of residual CaO is ensured, and residues of unreacted raw materials are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic material preparation, and in particular to a method for preparing calcium hydroxide with increased specific surface area. Background Art

[0002] Calcium hydroxide (Ca(OH)2), an important inorganic chemical raw material, is widely used in flue gas desulfurization, wastewater treatment, soil improvement, and building materials. Its specific surface area is a key parameter affecting its adsorption performance, reactivity, and functional applications. The higher the specific surface area of calcium hydroxide, the greater its reactivity, the smaller the dosage required in desulfurization, adsorption, and other applications, and the higher its efficiency. In order to prepare calcium hydroxide with high specific surface area and high activity, a Chinese invention patent with publication number "CN115340303A" now discloses a calcium hydroxide with high specific surface area and high activity and a preparation method thereof. This method adds a non-ionic surfactant during the lime digestion process to reduce the surface energy of the calcium hydroxide, avoid agglomeration, and improve the dispersion of the calcium hydroxide. The particle size of the calcium hydroxide formed during the digestion process is reduced, the specific surface area is increased, the pore size is enlarged, and the grain size is reduced, thereby making the calcium hydroxide have the characteristics of high specific surface area and high activity. The amount of water added during the digestion process is small, and the calcium hydroxide obtained by lime digestion remains a dry powder with a low water-cement ratio, eliminating the need for a complex drying process. The volume fraction of additives decreases with the reduction in the amount of water, thereby controlling the cost of adding additives and simplifying the preparation process of industrial calcium hydroxide. The increase in the digestion water temperature facilitates lime digestion. If the water temperature is too low, the steam generated in the reaction is insufficient to provide a large amount of heat for quicklime digestion. The operation process is simple, and large-scale production and application are easy to achieve. Since this reaction is carried out at a temperature of 80°C-90°C from beginning to end, if the initial reaction temperature is too high, the reaction will be rapid. In addition, the reaction between CaO and H2O releases heat, which makes the system temperature rise even higher. Moreover, the reaction system is exposed to the air, and the generated Ca(OH)2 easily reacts with CO2 in the air to produce CaCO3. The generation of CaCO3 will reduce the purity of Ca(OH)2 and lead to a decrease in specific surface area. In addition, if the temperature is too high, Ca(OH)2 may partially decompose into CaO, eventually forming a mixture of CaO and Ca(OH)2, which reduces the consistency of the product. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing calcium hydroxide with high specific surface area, so as to solve the problems that in the existing preparation method, the temperature control during the reaction process is too high, which easily leads to the generation of CaCO3 by-products, resulting in a decrease in the specific surface area of the prepared Ca(OH)2; or easily causes the partial decomposition of Ca(OH)2 into CaO, forming a mixture of CaO and Ca(OH)2, and reducing the consistency of the product.

[0004] In order to solve the above problems, the technical solutions provided are as follows: A method for preparing calcium hydroxide with high specific surface area comprises the following steps: S1: Raw material pretreatment: calcium oxide is used as raw material, crushed to a particle size of ≤50 μm by ball mill, and vacuum dried at 150-200 °C for 2-4 hours; S2: Hydration reaction: pre-treated calcium oxide and deionized water are mixed in a mass ratio of 3:8, 0.5-2 wt% of a modifier is added, and the reaction is carried out using segmented temperature control. In the initial stage, the temperature is kept at a low temperature of 20-30°C and stirred for 0.5 hours. In the middle stage, the temperature is kept at 30-50°C and stirred for 0-1 hours. In the later stage, the temperature is gradually raised to 50-60°C and stirred for 0.5 hours to generate calcium hydroxide slurry. S3: Ultrasonic dispersion: transfer the slurry to an ultrasonic processor and ultrasonicate it at a frequency of 20-40 kHz and a power of 100-300 W for 10-30 minutes to destroy particle agglomerates; S4: Drying and crushing, filtering the slurry after ultrasonication; washing the filtered solid with anhydrous ethanol three times, then vacuum drying at 80-100°C to constant weight, and crushing it with air flow to a particle size D50 ≤ 5 μm to obtain calcium hydroxide with a loose porous structure.

[0005] The beneficial effects of the above technical solution are: 1. During the reaction stage of calcium oxide and water, a segmented temperature control method is adopted. In the initial stage, a low temperature of 20-30℃ is adopted. The low temperature reduces the initial rate of the hydration reaction (CaO + H2O → Ca(OH)2), avoids local overheating due to intense heat release, and Ca(OH) reacts with CO2 to produce the by-product CaCO3, which slows down the reaction rate. The low temperature can also prevent the decomposition of Ca(OH)2. At low temperatures, the particle nucleation rate is greater than the growth rate, forming smaller and more dispersed initial particles. As CaO is consumed, the temperature rises to 30-50℃ in the middle stage. Appropriate temperature increase promotes weak bonding between particles and forms a porous network structure, while avoiding pore collapse caused by high-temperature sintering. In the late stage, there is little CaO residue and the reaction heat is reduced. The temperature is raised to 50-60℃ to improve the reaction kinetics, ensure the residual CaO is fully hydrated, and reduce the residue of unreacted raw materials. 2. Segmented temperature control avoids the concentration of reaction exotherm caused by a single high temperature, and prevents local excessive temperature from causing decomposition or sintering. Low temperature promotes isotropic nucleation, and after heating, the crystals preferentially grow along specific crystal planes to form Ca(OH)2 flakes or nanostructures with high specific surface area.

[0006] Preferred solution 1: As a further optimization of the basic solution, the modifier in step S2 is composed of one or more of isopropyl alcohol, trisodium citrate, and n-butanol.

[0007] Preferred solution 2: As a further optimization of preferred solution 1, the modifier is introduced by step-by-step addition, first adding 50% of the modifier in the initial stage of the hydration reaction, and the remaining 50% in the middle stage of the hydration reaction.

[0008] Preferred solution three: As a further optimization of preferred solution two, the hydration reaction in step S2 is carried out in a three-stage digester, which is filled with inert gas for protection.

[0009] Preferred solution four: As a further optimization of preferred solution three, the three-stage digester used in step S2 transfers the excess heat generated by the reaction to step S1 for vacuum drying.

[0010] Preferred solution five: As a further optimization of preferred solution four, the specific surface area of the prepared calcium hydroxide is 35-55 m² / g, and after exposure to an environment with a relative humidity of 80% for 24 hours, the specific surface area retention rate is ≥90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 1 is a process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0012] The following is further described in detail through specific implementation methods: Examples 1-3 are basically as shown in the attached Figure 1 As shown: Example 1 A method for preparing calcium hydroxide with high specific surface area comprises the following steps: S1: Raw material pretreatment: calcium oxide is used as raw material, crushed into particles ≤ 50 μm by ball mill, and dried in a vacuum dryer at 150-200 °C for 2-4 hours; S2: Hydration reaction, the pretreated calcium oxide and deionized water are mixed in a mass ratio of 3:8, and 0.5-2 wt% of the modifier isopropanol is added. The reaction is divided into three stages: initial stage, middle stage and late stage. The modifier is introduced by step-by-step addition, and the three stages are temperature-controlled for reaction. The initial stage is reacted in a primary digester, which maintains a low temperature of 20-30°C and stirs and reacts for 0.5 hour. At the same time, 50% of the modifier is added to the primary digester in the initial stage, and the reaction is transferred to the secondary digester in the middle stage. The secondary digester is heated to 30-50°C and stirred for reaction for 1 hour. The remaining 50% of the modifier is added to the secondary digester. The reaction is transferred to the tertiary digester in the late stage, and the temperature in the tertiary digester is gradually increased to 50-60°C and stirred for reaction for 0.5 hour to generate calcium hydroxide slurry. The primary digester, the secondary digester and the tertiary digester are filled with inert gas protection; the excess heat generated in the primary digester, the secondary digester and the tertiary digester is transferred to the vacuum dryer in step S1 for vacuum drying.

[0013] S3: Ultrasonic dispersion: transfer the slurry to an ultrasonic processor and ultrasonicate it at a frequency of 20-40 kHz and a power of 100-300 W for 10-30 minutes to destroy particle agglomerates; S4: drying and crushing, filtering the slurry after ultrasonication; washing the filtered solid with anhydrous ethanol in a filter residue tank for three times, then drying in a vacuum dryer at 80-100° C. to constant weight, and crushing in a jet mill to a particle size D50 ≤ 5 μm to obtain calcium hydroxide with a loose porous structure.

[0014] The calcium hydroxide product prepared in Example 1 was subjected to a BET test, and its specific surface area result was 43.5660 m2 / g, and the product purity was 92.73%.

[0015] Example 2 The difference between Example 2 and Example 1 is that the modifier used is trisodium citrate. The calcium hydroxide product prepared in Example 2 was subjected to a BET test, and its specific surface area result was 35.1517 m2 / g, and the product purity was 93.38%.

[0016] Example 3 The difference between Example 3 and Example 1 is that the modifier used is n-butanol. The calcium hydroxide product prepared in Example 3 was subjected to a BET test, and its specific surface area result was 41.6260 m2 / g, and the product purity was 92.32%.

[0017] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: in the hydration reaction stage, only a primary digester was used, the modifier isopropyl alcohol was added to the primary digester all at once, the temperature of the primary digester was always controlled at 50-60°C, the reaction time was controlled at 2 hours, and the remaining operating steps were the same as those in Example 1. The calcium hydroxide product prepared in Comparative Example 1 was subjected to a BET test, and its specific surface area result was 28.7635 m2 / g, and the product purity was 84.57%.

[0018] From the specific surface area results of the calcium hydroxide prepared in Examples 1-3, it can be seen that when isopropyl alcohol is used as a modifier in Example 1, the specific surface area of the calcium hydroxide prepared is the highest, and the purity of the product is very close to that of Examples 2 and 3, both being above 90%.

[0019] From the specific surface area results of calcium hydroxide prepared in Examples 1-3 and Comparative Example 1, it can be seen that Examples 1-3 use a three-stage digester to divide the hydration reaction into three stages for staged temperature control. Compared with Comparative Example 1 which uses a single high temperature in a single-stage digester, the specific surface area of the prepared calcium hydroxide is much higher than the specific surface area of the calcium hydroxide in Comparative Example 1. Therefore, segmented temperature control can avoid the concentrated reaction exotherm caused by a single high temperature and prevent local excessive temperature from causing decomposition or sintering. The low temperature promotes isotropic nucleation, and after heating, the crystals preferentially grow along specific crystal planes to form Ca(OH)2 flakes or nanostructures with high specific surface area.

[0020] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing calcium hydroxide with high specific surface area, characterized in that: The following steps are involved: S1: Raw material pretreatment: calcium oxide is used as raw material, crushed to a particle size of ≤50 μm by ball mill, and vacuum dried at 150-200 °C for 2-4 hours; S2: Hydration reaction: pre-treated calcium oxide and deionized water are mixed in a mass ratio of 3:8, 0.5-2 wt% of a modifier is added, and the reaction is carried out using segmented temperature control. In the initial stage, the temperature is kept at a low temperature of 20-30°C and stirred for 0.5 hours. In the middle stage, the temperature is kept at 30-50°C and stirred for 0-1 hours. In the later stage, the temperature is gradually raised to 50-60°C and stirred for 0.5 hours to generate calcium hydroxide slurry. S3: Ultrasonic dispersion: transfer the slurry to an ultrasonic processor and ultrasonicate it at a frequency of 20-40 kHz and a power of 100-300 W for 10-30 minutes to destroy particle agglomerates; S4: Drying and crushing, filtering the slurry after ultrasonication; washing the filtered solid with anhydrous ethanol three times, then vacuum drying at 80-100°C to constant weight, and crushing it with air flow to a particle size D50 ≤ 5 μm to obtain calcium hydroxide with a loose porous structure.

2. A method for preparing calcium hydroxide having a high specific surface area according to claim 1, wherein: The modifier in step S2 is composed of one or more of isopropyl alcohol, trisodium citrate, and n-butanol.

3. A method for preparing calcium hydroxide having a high specific surface area according to claim 2, wherein: The modifier is introduced by stepwise addition, firstly adding 50% of the modifier in the initial stage of the hydration reaction, and the remaining 50% in the middle stage of the hydration reaction.

4. A method for preparing calcium hydroxide having a high specific surface area according to claim 3, wherein: The hydration reaction in step S2 is carried out in a three-stage digester, which is filled with inert gas for protection.

5. A method for preparing calcium hydroxide having a high specific surface area according to claim 4, wherein: The three-stage digester used in step S2 transfers the excess heat generated by the reaction to step S1 for vacuum drying.

6. A method for preparing calcium hydroxide having a high specific surface area according to claim 5, wherein: The prepared calcium hydroxide has a specific surface area of 35-55 m² / g, and after being exposed to an environment with a relative humidity of 80% for 24 hours, the specific surface area retention rate is ≥90%.

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