A method for preparing pseudoboehmite by chlorination

Abstract

This invention belongs to the field of metal compound preparation and relates to a method for preparing pseudoboehmite using a chlorination process. The method includes: mixing hydrochloric acid solution and aluminum salt uniformly to obtain an aluminum-containing acidic solution; adding a surfactant to the aluminum-containing acidic solution to obtain an acidic solution; adding water to a reaction vessel, and then introducing a mixture of the acidic solution and ammonia-containing gas into the reaction vessel for a neutralization reaction; after the neutralization reaction is completed, intermittently introducing a mixture of carbon dioxide and air to cause the pH value of the slurry to decrease stepwise; stopping the reaction after the pH reaches a preset value to obtain a slurry; aging the slurry, filtering to obtain a filter cake, and washing and drying to obtain pseudoboehmite. This invention provides a method for preparing pseudoboehmite using a chlorination process. The pseudoboehmite prepared by this method has a concentrated pore distribution and low bulk density. Furthermore, the method is simple and easy to operate. The alumina obtained after calcination has a large pore volume and pore size, meeting the requirements for preparing a catalyst support with low bulk density and concentrated pore distribution.

Description

Technical Field

[0001] This invention belongs to the field of metal compound preparation, specifically relating to a method for preparing macroporous pseudoboehmite using the aluminum chloride method. Background Technology

[0002] Alumina comes in many types, such as γ-Al₂O₃, η-Al₂O₃, θ-Al₂O₃, δ-Al₂O₃, and α-Al₂O₃. Among them, γ-Al₂O₃, due to its large specific surface area, tunable pore structure, and good thermal stability, can be used as an insulating medium or substrate for semiconductor devices. Therefore, it is often used in the manufacture of fourth-generation semiconductor devices. It also has very wide applications in catalysis, especially in catalytic hydrogenation. The common method for preparing γ-Al₂O₃ is to first prepare boehmite, and then calcine it at a certain temperature to convert it into γ-Al₂O₃. There are generally three industrial methods for preparing boehmite: (1) Neutralization reaction of aluminates and acids, such as carbonization: 2NaAlO2+CO2+3H2O→2Al(OH)3+Na2CO3; (2) Double displacement reactions of aluminum salts and aluminates, such as the aluminum sulfate process: Al2(SO4)3+6NaAlO2+12H2O→8Al(OH)3+3Na2SO4.

[0003] (3) Neutralization reaction of aluminum salts and bases, such as the aluminum chloride process: AlCl3+3NH4OH→Al(OH)3+3NH4Cl; While the carbonization method for preparing boehmite is environmentally friendly and produces boehmite free of corrosive impurities, the resulting boehmite has a diffuse pore distribution and high bulk density, failing to meet the requirements for preparing catalysts with low bulk density and concentrated pore distribution. Boehmite produced by the aluminum sulfate method contains high levels of sulfate, which decomposes into sulfur trioxide during the carrier roasting process, especially at high temperatures, causing significant equipment corrosion. Currently, the aluminum chloride method for producing boehmite results in a poor operating environment and high ammonia nitrogen emissions from the washing process, failing to meet current environmental protection requirements. Therefore, there is an urgent need to develop a greener, milder, and more efficient method for preparing macroporous pseudoboehmite. Summary of the Invention

[0004] To address the shortcomings of existing aluminum chloride methods for producing boehmite, this invention provides a method for preparing boehmite via chlorination. After the neutralization reaction, a mixture of carbon dioxide and air is used to purge the defective boehmite particles, transforming them into ammonium aluminum carbonate [NH4Al(OH)2CO3] particles. The prepared boehmite exhibits a concentrated pore distribution and low bulk density. Furthermore, this method is simple and easy to operate. The alumina obtained after calcination has a large pore volume and pore size, meeting the requirements for preparing a catalyst support with low bulk density and concentrated pore distribution.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for preparing pseudoboehmite by chlorination, comprising: The hydrochloric acid solution and the aluminum salt are mixed evenly to obtain an aluminum-containing acidic solution; A surfactant is added to the aluminum-containing acidic solution to obtain an acidic solution; Water is added to the reaction vessel, and then a mixture of acidic solution and ammonia-containing gas is introduced into the reaction vessel for neutralization. After the neutralization reaction is completed, a mixture of carbon dioxide and air is introduced intermittently to cause the pH value of the slurry to decrease stepwise. Once the pH reaches the preset value, the reaction is stopped and the slurry is obtained. The slurry is aged and filtered to obtain a filter cake, which is then washed and dried to obtain boehmite.

[0006] This invention has found that introducing CO2 after the neutralization reaction of the alkali has two advantages: first, it lowers the pH of the system, dissolving incomplete or defective particles generated during the reaction; second, it introduces carbonate ions to react with dissolved free aluminum ions and free ammonia at a specific pH to generate ammonium aluminum carbonate [NH4Al(OH)2CO3] particles (equation: Al...). 3+ +NH4 + (+CO2+H2O→NH4Al(OH)2CO3), ammonium aluminum carbonate decomposes into ammonia and carbon dioxide upon heating. The release of these gases impacts the alumina, giving it a larger pore volume and a lower bulk density. However, the traditional method of adding liquid acid, due to its strong acidity, causes significant dissolution of the delicate boehmite particles formed, and the free aluminum ions released after dissolution are also lost with the water.

[0007] In a second aspect, the present invention provides a pseudoboehmite prepared by the above-described method.

[0008] A third aspect of the present invention provides the application of the aforementioned pseudoboehmite in the preparation of fourth-generation semiconductor devices and in the field of catalytic hydrogenation.

[0009] The beneficial effects of this invention are as follows: (1) The present invention adopts a mixture of acidic material and ammonia-containing gas flowing into the reactor from the bottom of the reactor in parallel, which overcomes the disadvantages of the traditional aluminum chloride method in producing boehmite, such as environmental impact, low concentration of synthetic raw materials and low production efficiency. (2) The present invention uses dilute hydrochloric acid solution to prepare polyaluminum trichloride solution, which inhibits the easy hydrolysis of aluminum trichloride in water to generate aluminum hydroxide trihydrate [Al(OH)3], resulting in higher crystallinity of the prepared boehmite; (3) In the method of the present invention, since polyaluminum chloride is an inorganic polymer coagulant with coagulation, charge neutralization and bridging effects, it can rapidly coagulate the pseudoboehmite suspended particles and colloids generated during the reaction into larger flocs in the slurry, thereby accelerating the sedimentation process (coagulation effect). It can also neutralize the negatively charged colloidal particles in the water through its positive charge characteristics, making them unstable and easy to coagulate and precipitate (charge neutralization effect). At the same time, the polymer chains form bridges between particles, connecting multiple small particles to form large flocs (bridging effect). This will also cause problems such as uneven solid concentration in the slurry and uneven pseudoboehmite particles generated during the reaction. Therefore, the present invention adds a nonionic surfactant to the acidic solution to reduce the surface tension of the slurry. At the same time, the added surfactant has the properties of penetration and solubilization, making the slurry easy to flow, with uniform solid concentration in the slurry, ensuring that the generated pseudoboehmite particles are uniform, and the slurry has a higher solid content, which also increases the production efficiency. (4) In this invention, a mixture of carbon dioxide and air is used to purge the slurry after the neutralization reaction, gradually reducing the pH value in a stepwise manner. This dissolves the defective boehmite particles generated during the reaction, ensuring that the prepared boehmite particles are intact and uniform. At the same time, the dissolved boehmite particles can generate ammonium aluminum carbonate [NH4Al(OH)2CO3] particles at a specific pH value, giving the prepared boehmite a larger pore volume and a smaller bulk density, and also reducing ammonia nitrogen emissions.

[0010] (5) The method for preparing boehmite in this invention is simple and easy to operate. The alumina obtained by calcining the boehmite prepared by this method has a large pore volume and a small packing density, which meets the requirements for preparing catalysts with large pore volume and low packing ratio. Detailed Implementation

[0011] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0012] 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. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. 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.

[0013] This invention provides a method for preparing pseudoboehmite by chlorination, comprising: The hydrochloric acid solution and the aluminum salt are mixed evenly to obtain an aluminum-containing acidic solution; A surfactant is added to the aluminum-containing acidic solution to obtain an acidic solution; Water is added to the reaction vessel, and then a mixture of acidic solution and ammonia-containing gas is introduced into the reaction vessel for neutralization. After the neutralization reaction is completed, a mixture of carbon dioxide and air is introduced intermittently to cause the pH value of the slurry to decrease stepwise. Once the pH reaches the preset value, the reaction is stopped and the slurry is obtained. The slurry is aged and filtered to obtain a filter cake, which is then washed and dried to obtain boehmite.

[0014] The type of aluminum-containing acidic solution affects the crystallinity of the prepared boehmite, thus affecting the pore volume and bulk density. Therefore, this invention studies the types of aluminum-containing acidic solutions. Preferably, the aluminum-containing acidic solution is selected from at least one of polyaluminum chloride solution, aluminum chloride solution, and basic aluminum chloride. Using dilute hydrochloric acid solution to prepare the polyaluminum trichloride solution inhibits the easy hydrolysis of aluminum trichloride in water to form aluminum hydroxide trihydrate [Al(OH)3], resulting in a higher crystallinity of the prepared boehmite.

[0015] The Al2O3 content in the aluminum-containing acidic solution also affects the crystallinity of boehmite and the pore volume and bulk density of alumina. Therefore, this invention studies the Al2O3 content in the aluminum-containing acidic solution. Preferably, the concentration of the aluminum-containing acidic solution, calculated as Al2O3, is 60gAl2O3 / L to 120gAl2O3 / L, and more preferably, 70gAl2O3 / L to 110gAl2O3 / L, in order to improve the crystallinity of boehmite, the pore volume of alumina, and reduce the bulk density.

[0016] Studies have found that the concentration of hydrochloric acid affects the stability of polyaluminum trichloride solution and the pore volume and bulk density of alumina. Therefore, this invention studies the concentration of hydrochloric acid. Preferably, the mass concentration of the hydrochloric acid solution is 0.5% to 3.0% to improve the stability of the aluminum-containing acidic solution, which is beneficial to subsequent reactions, and to increase the pore volume and reduce the bulk density of alumina.

[0017] The type of surfactant affects its penetration and solubilization effects. Therefore, this invention studies the types of surfactants. Preferably, the surfactant is a nonionic surfactant or anionic surfactant; more preferably, the surfactant is selected from at least one of fatty alcohol polyoxyethylene ethers, fatty acid polyoxyethylene esters, and alkylphenol and ethylene oxide condensates; even more preferably, the fatty alcohol polyoxyethylene ether is dodecyl isopentenyl diammonium monophosphate. This makes the slurry easy to flow, the solid phase concentration in the slurry uniform, ensures that the generated boehmite particles are uniform, and at the same time, the solid content in the slurry is higher, which also increases the production efficiency.

[0018] The amount of surfactant used also affects the penetration and solubilization effects. Therefore, this invention has studied the amount of surfactant used. Preferably, the amount of surfactant added is 0.5% to 2.5% of the mass of the aluminum-containing acidic solution to obtain better penetration and solubilization effects and improve the performance of boehmite and alumina.

[0019] In this invention, water is introduced into the bottom of the reaction vessel as a solvent for the neutralization reaction. Preferably, the volume of water is 1 / 10 to 1 / 5 of the volume of the reaction vessel to ensure the smooth progress of the reaction and reduce the amount of water used.

[0020] This invention does not impose any special limitation on the type of reaction vessel, as long as it can meet the reaction requirements of this application. Preferably, the reaction vessel is a reaction kettle, which is convenient to purchase and use.

[0021] The temperature, time, and pH of the neutralization reaction affect the yield and crystallinity of boehmite. Therefore, this invention studies the temperature, time, and pH of the neutralization reaction. Preferably, the temperature of the neutralization reaction is 40℃~70℃ or 45℃~65℃; preferably, the time of the neutralization reaction is 40min~90min or 45min~85min; preferably, the pH of the slurry is controlled to 10.0~13.0 by adjusting the flow rate of the ammonia-containing mixed gas, and more preferably, to 10.5~12.5, in order to improve the yield and crystallinity of boehmite and the pore volume of alumina, and reduce the bulk density.

[0022] This invention employs a method of simultaneously introducing an acidic material and an ammonia-containing mixed gas into the reactor from the bottom, thereby improving the concentration of raw materials and production efficiency. To this end, this invention has studied the flow rate and concentration of the ammonia-containing mixed gas. Preferably, the flow rate of the acidic solution is 20 mL / min to 80 mL / min, more preferably 25 mL / min to 75 mL / min. Preferably, the ammonia-containing mixed gas is a mixture of ammonia and air. The volume percentage of ammonia in the ammonia-containing mixed gas is 10% to 30% to achieve even better production efficiency.

[0023] In this invention, after the neutralization reaction is completed, a mixture of carbon dioxide and air is used to purge the defective boehmite particles into ammonium aluminum carbonate [NH4Al(OH)2CO3] particles. The prepared boehmite has a larger pore volume and a lower bulk density. Preferably, the carbon dioxide-containing gas can be a mixture of carbon dioxide and air; the role of air is to dilute CO2, slow down the reaction, and simultaneously remove the heat generated by the reaction.

[0024] The content and flow rate of carbon dioxide affect the conversion of defective boehmite particles into ammonium aluminum carbonate [NH4Al(OH)2CO3] particles. Therefore, this invention studies the content and flow rate of carbon dioxide. Preferably, the volume percentage of carbon dioxide in the carbon dioxide-containing gas mixture is 30-60%. Preferably, the flow rate of the carbon dioxide and air mixture is 300 mL / min-700 mL / min to effectively increase the proportion of defective boehmite particles converted into ammonium aluminum carbonate [NH4Al(OH)2CO3] particles, resulting in alumina with larger pore volume and lower bulk density.

[0025] The gradient of pH value decrease can also affect the conversion effect of defective boehmite particles. Therefore, this invention studies the specific process of pH value decrease in a stepwise manner. Preferably, the pH value of the slurry in the reactor is controlled to decrease in a stepwise manner. Specifically, after the pH value decreases by 0.5 to 1.0, the mixture of carbon dioxide and air is stopped, and after stabilizing for 5 to 10 minutes, the mixture of carbon dioxide and air is introduced again. The pH value decrease rate and stabilization time can be the same or different. This process is repeated until the pH value of the slurry decreases to the required value, at which point the reaction ends. Preferably, the final pH value of the slurry in the reactor is 7.5 to 10.5 or 8.0 to 10.0 to obtain a better conversion effect, resulting in alumina with larger pore volume and lower bulk density.

[0026] Aging treatment can improve the crystallinity and morphology of boehmite. Therefore, the present invention has studied the conditions for aging treatment. Preferably, the aging conditions are: temperature 50℃~95℃, time 30min~120min; in order to obtain better aging effect, increase the pore volume of alumina and reduce the bulk density.

[0027] Washing with warm water can improve the purity and crystallinity of boehmite. Therefore, this invention has studied the temperature of the washing water. Preferably, deionized water at 50℃ to 80℃ is used to obtain a better washing effect.

[0028] The drying temperature and time affect the moisture content of boehmite. Therefore, this invention studies the drying temperature and time. Preferably, the drying conditions are a temperature of 100-150°C and a time of 6-10 hours to improve drying efficiency.

[0029] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0030] In the following examples, all raw materials are commercially available products.

[0031] Example 1 (1) Prepare a 1.5% hydrochloric acid solution, add polyaluminum chloride and stir to dissolve, then adjust to an aluminum-containing acidic solution with a concentration of 80gAl2O3 / L (calculated as Al2O3); (2) Add 0.7% of the nonionic surfactant fatty alcohol polyoxyethylene ether, equivalent to the mass of the aluminum-containing acidic solution, to the aluminum-containing acidic solution to obtain an acidic solution; (3) Add 800 mL of deionized water to the 5.0 L reactor, start the stirring and heating device, and when the temperature of the deionized water in the reactor reaches 48 °C, simultaneously introduce acidic solution and a mixture of ammonia gas (15% ammonia by volume, the remainder being air) from the bottom of the reactor to carry out the neutralization reaction. Control the flow rate of the acidic solution to 65 mL / min, and control the pH value of the slurry to be stable at 11.5 by adjusting the flow rate of the mixed gas, and keep the temperature constant. The reaction ends after 50 min. (4) A mixture of carbon dioxide and air with a volume percentage of 40% carbon dioxide was introduced into the reactor from the bottom at a flow rate of 650 mL / min. When the pH value of the slurry in the reactor dropped to 10.7, the mixture of carbon dioxide and air was stopped and stabilized for 7 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 9.8, the mixture of carbon dioxide and air was stopped and stabilized for 7 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 9.0, the mixture of carbon dioxide and air was stopped and stabilized for 7 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 8.5, the mixture of carbon dioxide and air was stopped and the reaction ended. (5) The slurry was heated to 90℃ and kept at a constant temperature for aging for 90 minutes. After aging, it was washed with deionized water at 75℃. The filter cake was dried at 120℃ for 8 hours to obtain pseudoboehmite S-1. The content of aluminum hydroxide trihydrate [Al(OH)3] was not detected by analysis.

[0032] The obtained pseudoboehmite S-1 was calcined at 600℃ for 3 hours to obtain alumina s-1, and the analytical results are shown in Table 1.

[0033] Example 2 The rest is the same as in Example 1, except that the concentration of the aluminum-containing acidic solution was adjusted to 105gAl2O3 / L, and the volume percentage of ammonia in the mixture of ammonia and air was adjusted to 25%, resulting in pseudoboehmite S-2. Analysis showed that no aluminum hydroxide trihydrate [Al(OH)3] content was detected.

[0034] The obtained pseudoboehmite S-2 was then calcined at 600℃ for 3 hours to obtain alumina s-2. The analysis results are shown in Table 1.

[0035] Example 3 The process was the same as in Example 1, except that the nonionic surfactant added to the aluminum-containing acidic solution was replaced with fatty acid polyoxyethylene ester; the amount added was 2.3% of the mass of the acidic solution, resulting in pseudoboehmite S-3, and analysis showed that no aluminum hydroxide trihydrate [Al(OH)3] content was detected.

[0036] The obtained pseudoboehmite S-3 was then calcined at 600℃ for 3 hours to obtain alumina S-3. The analytical results are shown in Table 1.

[0037] Example 4 The process was the same as in Example 1, except that the volume percentage of carbon dioxide introduced into the reactor from the bottom was changed to a mixture of carbon dioxide and air (55%), and the flow rate of the mixture was changed to 450 mL / min. This yielded boehmite S-4, and analysis showed no detection of aluminum hydroxide trihydrate [Al(OH)3].

[0038] The obtained pseudoboehmite S-4 was then calcined at 600℃ for 3 hours to obtain alumina S-4. The analysis results are shown in Table 1.

[0039] Example 5 (1) Prepare a 2.0% hydrochloric acid solution, add polyaluminum chloride and stir to dissolve, then adjust to an aluminum-containing acidic solution with a concentration of 95gAl2O3 / L (calculated as Al2O3); (2) Add 1.2% of the nonionic surfactant fatty alcohol polyoxyethylene ether, equivalent to the mass of the aluminum-containing acidic solution, to the aluminum-containing acidic solution to obtain an acidic solution; (3) Add 600 mL of deionized water to the 5.0 L reactor, start the stirring and heating device, and when the temperature of the deionized water in the reactor reaches 62 °C, simultaneously introduce acidic solution and a mixture of ammonia gas (23% ammonia by volume, the remainder being air) from the bottom of the reactor to carry out the neutralization reaction. Control the flow rate of the acidic solution to 45 mL / min, and control the pH value of the slurry to be stable at 12.2 by adjusting the flow rate of the mixed gas, and keep the temperature constant. The reaction ends after 75 min. (4) A mixture of carbon dioxide and air with a volume percentage of 55% carbon dioxide was introduced into the reactor from the bottom at a flow rate of 400 mL / min. When the pH value of the slurry in the reactor dropped to 11.6, the mixture of carbon dioxide and air was stopped and stabilized for 6 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 10.7, the mixture of carbon dioxide and air was stopped and stabilized for 9 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 10.0, the mixture of carbon dioxide and air was stopped and stabilized for 6 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 9.4, the mixture of carbon dioxide and air was stopped and the reaction ended. (5) The slurry was heated to 85℃ and kept at a constant temperature for aging for 110 minutes. After aging, it was washed with deionized water at 70℃. The filter cake was dried at 150℃ for 6 hours to obtain pseudoboehmite S-5. The content of aluminum hydroxide trihydrate [Al(OH)3] was not detected by analysis.

[0040] The obtained pseudoboehmite S-5 was calcined at 600℃ for 3 hours to obtain alumina s-5, and the analytical results are shown in Table 1.

[0041] Comparative Example 1 (without hydrochloric acid solution) (1) Add polyaluminum chloride to deionized water, stir to dissolve, and then prepare an aluminum-containing acidic solution with a concentration of 80gAl2O3 / L (calculated as Al2O3); (2) Add 800 mL of deionized water to a 5.0 L reactor, start the stirring and heating device, and when the temperature of the deionized water in the reactor reaches 48 °C, simultaneously introduce a mixture of aluminum-containing acidic solution and ammonia-containing gas (15% ammonia by volume, the remainder being air) from the bottom of the reactor to carry out a neutralization reaction. Control the flow rate of the aluminum-containing acidic solution to 65 mL / min, and control the pH value of the slurry to be stable at 11.5 by adjusting the flow rate of the mixed gas, and keep the temperature constant. The reaction ends after 50 min. (3) A mixture of carbon dioxide and air with a volume percentage of 40% was introduced into the reactor from the bottom at a flow rate of 650 mL / min. When the pH value of the slurry in the reactor dropped to 10.7, the mixture of carbon dioxide and air was stopped and stabilized for 7 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 9.8, the mixture of carbon dioxide and air was stopped and stabilized for 7 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 9.0, the mixture of carbon dioxide and air was stopped and stabilized for 7 min. The mixture of carbon dioxide and air was then introduced again. When the pH value of the slurry dropped to 8.5, the mixture of carbon dioxide and air was stopped and the reaction ended. (4) The slurry was heated to 90℃ and kept at a constant temperature for aging for 90 minutes. After aging, it was washed with deionized water at 75℃. The filter cake was dried at 120℃ for 8 hours to obtain pseudoboehmite F-1. The content of aluminum hydroxide trihydrate [Al(OH)3] was found to be 5.5%.

[0042] The obtained pseudoboehmite F-1 was calcined at 600℃ for 3 hours to obtain alumina f-1, and the analytical results are shown in Table 1.

[0043] Comparative Example 2 (pH value decreased without a stepwise decrease) (1) Prepare a 1.5% hydrochloric acid solution, add polyaluminum chloride and stir to dissolve, then adjust to an aluminum-containing acidic solution with a concentration of 80gAl2O3 / L (calculated as Al2O3); (2) Add 0.7% of the nonionic surfactant fatty alcohol polyoxyethylene ether, equivalent to the mass of the aluminum-containing acidic solution, to the aluminum-containing acidic solution to obtain an acidic solution; (3) Add 800 mL of deionized water to the 5.0 L reactor, start the stirring and heating device, and when the temperature of the deionized water in the reactor reaches 48 °C, simultaneously introduce a mixture of aluminum-containing acidic solution and ammonia-containing gas (15% ammonia by volume, the remainder being air) from the bottom of the reactor to carry out the neutralization reaction. Control the flow rate of the acidic solution to 65 mL / min, and control the pH value of the slurry to be stable at 11.5 by adjusting the flow rate of the mixed gas, and keep the temperature constant. The reaction ends after 50 min. (4) A mixture of carbon dioxide and air with a volume percentage of 40% was introduced into the reactor from the bottom at a flow rate of 650 mL / min. When the pH value of the slurry in the reactor dropped to 8.5, the introduction of the mixture of carbon dioxide and air was stopped, and the reaction ended. (5) The slurry was heated to 90℃ and kept at a constant temperature for aging for 90 minutes. After aging, it was washed with deionized water at 75℃. The filter cake was dried at 120℃ for 8 hours to obtain pseudoboehmite F-2. The content of aluminum hydroxide trihydrate [Al(OH)3] was not detected by analysis.

[0044] The obtained pseudoboehmite F-2 was calcined at 600℃ for 3 hours to obtain alumina f-2, and the analytical results are shown in Table 1.

[0045] Comparative Example 3 (a mixture of gas containing carbon dioxide and air without the introduction of carbon dioxide) (1) Prepare a 1.5% hydrochloric acid solution, add polyaluminum chloride and stir to dissolve, then adjust to an aluminum-containing acidic solution with a concentration of 80gAl2O3 / L (calculated as Al2O3); (2) Add 0.7% of the nonionic surfactant fatty alcohol polyoxyethylene ether, equivalent to the mass of the aluminum-containing acidic solution, to the aluminum-containing acidic solution to obtain an acidic solution; (3) Add 800 mL of deionized water to the 5.0 L reactor, start the stirring and heating device, and when the temperature of the deionized water in the reactor reaches 48 °C, simultaneously introduce acidic solution and a mixture of ammonia and air with a volume percentage of 15% ammonia gas from the bottom of the reactor for neutralization reaction. Control the flow rate of the acidic solution to 65 mL / min, and control the pH value of the slurry to be stable at 8.5 by adjusting the flow rate of the mixed gas, and keep the temperature constant. The reaction ends after 50 min. (4) The slurry was heated to 90℃ and kept at a constant temperature for aging for 90 minutes. After aging, it was washed with deionized water at 75℃. The filter cake was dried at 120℃ for 8 hours to obtain pseudoboehmite F-3. The content of aluminum hydroxide trihydrate [Al(OH)3] was not detected by analysis.

[0046] The obtained pseudoboehmite F-3 was calcined at 600℃ for 3 hours to obtain alumina f-3, and the analytical results are shown in Table 1.

[0047] Table 1. Analytical results of the pseudoboehmite prepared in this invention after calcination.

[0048] As can be seen from the comparison between Example 1 and Comparative Example 1, the alumina prepared by using dilute hydrochloric acid to prepare an aluminum-containing acidic solution has a larger pore volume and a smaller packing density compared with water.

[0049] As can be seen from the comparison between Example 1 and Comparative Example 2, in the stage of introducing a mixed gas of carbon dioxide and air, the method of stepwise decrease of pH value can better improve the pore volume of alumina and reduce the bulk density.

[0050] As can be seen from the comparison between Example 1 and Comparative Example 3, the introduction of carbon dioxide to transform defective boehmite particles can significantly increase the pore volume of alumina and reduce the bulk density.

[0051] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing pseudoboehmite by chlorination, characterized in that, include: The hydrochloric acid solution and the aluminum salt are mixed evenly to obtain an aluminum-containing acidic solution; A surfactant is added to the aluminum-containing acidic solution to obtain an acidic solution; Water is added to the reaction vessel, and then a mixture of acidic solution and ammonia-containing gas is introduced into the reaction vessel for neutralization. After the neutralization reaction is completed, a mixture of carbon dioxide and air is introduced intermittently to cause the pH value of the slurry to decrease stepwise. Once the pH reaches the preset value, the reaction is stopped and the slurry is obtained. The slurry is aged and filtered to obtain a filter cake, which is then washed and dried to obtain boehmite.

2. The method for preparing pseudoboehmite by chlorination as described in claim 1, characterized in that, The aluminum-containing acidic solution is selected from at least one of polyaluminum chloride solution, aluminum chloride solution, and basic aluminum chloride.

3. The method for preparing pseudoboehmite by chlorination as described in claim 1, characterized in that, The concentration of the aluminum-containing acidic solution, calculated as Al2O3, is 60gAl2O3 / L to 120gAl2O3 / L, or 70gAl2O3 / L to 110gAl2O3 / L. Alternatively, the mass concentration of the hydrochloric acid solution is 0.5% to 3.0%.

4. The method for preparing pseudoboehmite by chlorination as described in claim 1, characterized in that, The surfactant is a nonionic surfactant or anionic surfactant; Alternatively, the surfactant is selected from at least one of fatty alcohol polyoxyethylene ethers, fatty acid polyoxyethylene esters, and alkylphenol-ethylene oxide condensates; Alternatively, the fatty alcohol polyoxyethylene ether is dodecyl isopentenol diammonium monophosphate salt; Alternatively, the amount of surfactant added is 0.5% to 2.5% of the mass of the aluminum-containing acidic solution.

5. The method for preparing pseudoboehmite by chlorination as described in claim 1, characterized in that, The volume of the water is 1 / 10 to 1 / 5 of the volume of the reaction vessel; Alternatively, the reaction vessel may be a reaction kettle.

6. The method for preparing pseudoboehmite by chloride process as described in claim 1, characterized in that, The neutralization reaction is carried out at a temperature of 40℃~70℃ or 45℃~65℃. Alternatively, the neutralization reaction may take 40 to 90 minutes or 45 to 85 minutes. Alternatively, the pH of the slurry can be controlled at 10.0–13.0 or 10.5–12.5; Alternatively, the flow rate of the acidic solution is 20 mL / min to 80 mL / min or 25 mL / min to 75 mL / min; Alternatively, the ammonia-containing gas mixture is a mixture of ammonia and air; the volume percentage of ammonia in the ammonia-containing gas mixture is 10-30%.

7. The method for preparing pseudoboehmite by chlorination as described in claim 1, characterized in that, The carbon dioxide-containing gas can be a mixture of carbon dioxide and air; Alternatively, the volume percentage of carbon dioxide in the carbon dioxide-containing gas mixture is 30% to 60%. Alternatively, the flow rate of the mixture of carbon dioxide and air is 300 mL / min to 700 mL / min.

8. The method for preparing pseudoboehmite by chloride process as described in claim 1, characterized in that, The pH value of the slurry in the reactor is controlled to decrease in a stepwise manner. Specifically, the mixture of carbon dioxide and air is stopped after the pH value decreases by 0.5 to 1.

0. After stabilizing for 5 to 10 minutes, the mixture of carbon dioxide and air is introduced again. The pH value decrease rate and stabilization time can be the same or different. This process is repeated until the pH value of the slurry decreases to the required value, at which point the reaction ends. The final pH value of the slurry in the reactor is 7.5–10.5 or 8.0–10.0; Alternatively, the aging conditions are: temperature 50℃~95℃, time 30min~120min; Alternatively, deionized water at 50℃~80℃ can be used for washing; Alternatively, the drying conditions are a temperature of 100–150℃ and a time of 6–10 hours.

9. The pseudoboehmite prepared by the method according to any one of claims 1-8.

10. The application of the boehmite according to claim 9 in the preparation of fourth-generation semiconductor devices and in the field of catalytic hydrogenation.

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