Boehmite and preparation method thereof

Abstract

The invention provides boehmite and a preparation method thereof, and the preparation method comprises the following steps: mixing ammonium alum, an alkaline additive and a solvent to obtain a mixed solution, and carrying out hydrothermal treatment on the obtained mixed solution to obtain boehmite. According to the preparation method provided by the invention, the ammonium alum is adopted as a raw material and is mixed with the alkaline additive and the solvent, and then hydrothermal treatment is performed to prepare the boehmite, so that the preparation cost is relatively low, and the boehmite is obtained through one-step reaction, and therefore, the preparation method has the advantage of simple preparation process; in addition, in the preparation method, one or more impurity removal processes do not need to be carried out on the ammonium alum, so that the preparation process is further simplified, and the preparation cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource recovery and relates to boehmite, in particular to boehmite and a preparation method thereof. Background Art

[0002] Boehmite (γ-AlOOH), an important new chemical material, possesses a variety of excellent properties due to its unique crystal structure, including large specific surface area, diverse morphologies, high interfacial free energy, good dispersibility, strong thermal stability, and controllable pore structure. Therefore, boehmite has a wide range of applications in adsorption separation, catalytic supports, composite materials, medicine, optical materials, sensors, and other fields.

[0003] Currently, the main methods for preparing boehmite include sol-gel, template, chemical vapor deposition, water / solvothermal, direct aluminum hydrolysis, and aluminum alkoxide hydrolysis. However, these preparation methods present certain challenges. The sol-gel method requires a long reaction time, has high preparation costs, and is difficult to resolve during post-processing due to agglomeration. Template and chemical vapor deposition methods generally produce boehmite materials with complex morphologies, requiring high requirements for raw materials, auxiliary materials, and equipment, resulting in relatively high overall production costs. The direct aluminum hydrolysis method is difficult to control, the product also exhibits agglomeration, and the aluminum powder presents safety risks. Boehmite prepared by aluminum alkoxide hydrolysis is also prone to agglomeration, and post-processing increases production costs.

[0004] CN106745132A discloses a method for preparing rod-shaped boehmite powder using a gradient heating hydrothermal method. The method comprises the following steps: first, adding the required reaction materials to the inner container of a hydrothermal reactor, sealing the reactor, raising the reaction temperature to a set starting temperature, and maintaining the temperature for a certain period of time; gradually reaching the set maximum reaction temperature using a gradient heating method; maintaining the temperature at the highest temperature for a certain period of time, and then naturally cooling the temperature to room temperature. The precipitated product is centrifuged at a certain speed, and then subjected to post-processing processes such as multiple water washings, anhydrous ethanol washings, and electric forced air drying at a certain temperature and time, thereby achieving regulation of the boehmite powder morphology and successfully preparing rod-shaped boehmite powder.

[0005] CN106830032A discloses a method for preparing hierarchical boehmite powder using a microwave hydrothermal method. The method comprises the following steps: adding reaction materials to the inner container of a microwave hydrothermal reactor, heating the temperature to a set temperature and keeping the temperature for a certain time to make the temperature uniform; evenly dividing the temperature range between the set temperature and the maximum temperature into several temperature intervals, alternately controlling the heating time and the holding time of each temperature interval, gradually reaching the maximum reaction temperature and keeping the temperature, cooling and centrifuging, and then performing post-treatment such as multiple water washing, anhydrous ethanol washing, and vacuum drying at a certain temperature and time to prepare the hierarchical boehmite powder.

[0006] The preparation methods of boehmite disclosed in the prior art all have certain defects, such as high preparation cost and complicated preparation process. Therefore, it is extremely important to develop a new boehmite and its preparation method. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide boehmite and a preparation method thereof. The preparation method provided by the present invention uses ammonium alum as a raw material, mixes it with an alkaline additive and a solvent, and then performs a hydrothermal treatment to prepare boehmite. The preparation method not only has a low preparation cost, but also obtains the boehmite in a one-step reaction, thus having the advantage of a simple preparation process. In addition, the preparation method does not require one or more impurity removal processes for the ammonium alum, thereby further simplifying the preparation process and reducing the preparation cost.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing boehmite, the preparation method comprising:

[0010] A mixed solution is obtained by mixing ammonium alum, an alkaline additive and a solvent, and the mixed solution is subjected to a hydrothermal reaction to obtain boehmite.

[0011] Waste glass powder, generated during the production and processing of lithium-containing glass, is rich in valuable elements such as lithium, silicon, and aluminum. In the recovery process for these valuable elements, aluminum is primarily recovered as ammonium alum (NH₄Al(SO₄)₂·12H₂O).

[0012] Ammonium alum is extremely versatile and can be used for industrial water purifiers, sizing agents in the paper industry, leavening agents in the food industry, raw materials for polyaluminium and aluminium compounds, etc. However, as an aluminium product from waste glass powder, ammonium alum still contains a small amount of foreign elements that are difficult to remove after purification. In the process of preparing high-purity aluminium compounds as raw materials using ammonium alum as raw material, raw material purity affects the quality of the prepared product to a great extent, so generally pure raw materials are adopted to prepare the product, or one or more impurity removal processes are added after using impure raw materials, which not only causes complicated processes but also improves preparation cost. Therefore, if the ammonium alum with a small amount of foreign elements that are difficult to remove can be directly used to prepare chemical materials, the utilization of aluminium element in ammonium alum can be greatly realized, and the preparation cost of this chemical materials can be greatly reduced.

[0013] The preparation method provided by the present invention uses ammonium alum as a raw material, mixes it with an alkaline additive and a solvent, and then performs a hydrothermal treatment to prepare boehmite. The method not only has a low preparation cost, but also obtains the boehmite in a one-step reaction, thus having the advantage of a simple preparation process. In addition, the ammonium alum used in the preparation method is an aluminum-extracted product of waste glass powder, which has a low cost, and does not require one or more impurity removal processes for the ammonium alum, thereby further simplifying the preparation process and reducing the preparation cost.

[0014] Preferably, the concentration of ammonium alum in the mixed solution is 0.3 to 1.5 mol / L, for example, it can be 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] In the present invention, when the concentration of ammonium alum is 0.3-1.5 mol / L, the prepared boehmite has better performance. This is because when the concentration of ammonium alum is 0.3-1.5 mol / L, the hydrolysis rate of aluminum ions and the generation of crystal nuclei reach a dynamic balance; not only is the coarsening of the boehmite grains ultimately obtained, which is caused by a slow crystal nucleation rate due to an excessively low concentration of ammonium alum, avoided, but also the agglomeration of boehmite particles caused by an excessively high concentration of ammonium alum is avoided; ammonium alum with a suitable concentration can form small-sized nanoparticles through uniform nucleation to increase the specific surface area, and can also form a uniform plate-like morphology through directional growth of a layered structure, thereby reducing pore blockage caused by disordered accumulation; in addition, ammonium alum with a suitable concentration can also inhibit the encapsulation effect of impurity ions, making it easier to remove impurities in the aluminum salt through washing, thereby improving the purity of the boehmite.

[0016] Preferably, the alkaline additive includes any one of urea, sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonia water or sodium hydroxide, or a combination of at least two thereof.

[0017] In the present invention, since the alkaline additive can slowly release hydroxide in the hydrothermal reaction, thereby controlling the formation of boehmite, excessive alkalinity will promote the formation of aluminum hydroxide. Therefore, using any one of urea, sodium bicarbonate, sodium carbonate or ammonium bicarbonate, or a combination of at least two thereof as the alkaline additive is conducive to the formation of boehmite.

[0018] Preferably, the alkaline additive includes any one of urea, sodium bicarbonate, sodium carbonate or ammonium bicarbonate, or a combination of at least two thereof, preferably urea.

[0019] In the present invention, when urea is used as the alkaline additive, firstly, the alkaline additive can slowly release hydroxide in the hydrothermal reaction, thereby controlling the formation of boehmite. Excessive alkalinity will promote the formation of aluminum hydroxide, and the rate at which urea releases hydroxide is relatively slow, which is conducive to the formation of boehmite by the hydrothermal reaction. Secondly, since urea does not contain impurity elements such as Na, a weakly alkaline environment is created while improving the purity of the boehmite finally prepared.

[0020] Preferably, the molar ratio of ammonium alum to the alkaline additive in the mixture is 1:(0.5-2), for example, it can be 1:0.5, 1:0.8, 1:1.0, 1:1.2, 1:1.5, 1:1.8 or 1:2.0, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0021] In the present invention, when the molar ratio of ammonium alum to urea is 1:(0.5-2), the prepared boehmite has better performance. This is because when the molar ratio of ammonium alum to urea is 1:(0.5-2), it can ensure that ammonium alum can release enough hydroxide to form boehmite at an appropriate speed, and can also avoid the excessively fast generation rate of hydroxide, which leads to the generation of aluminum hydroxide.

[0022] Preferably, the amount of ammonium alum mixed in the mixture is 0.04 to 0.16 mol, for example, 0.04 mol, 0.06 mol, 0.08 mol, 0.10 mol, 0.12 mol, 0.14 mol or 0.16 mol, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0023] Preferably, the amount of urea mixed in the mixture is 0.04 to 0.16 mol, for example, 0.04 mol, 0.06 mol, 0.08 mol, 0.10 mol, 0.12 mol, 0.14 mol or 0.16 mol, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0024] Preferably, a dispersant is also mixed into the mixing.

[0025] Preferably, the dispersant comprises anhydrous ethanol, and the solvent comprises water.

[0026] Preferably, the volume ratio of the dispersant to the solvent in the mixture is (0.1-0.6):1, for example, it can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1 or 0.6:1, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0027] Preferably, the total volume of the dispersant and the solvent mixed in the mixing is 100 to 150 mL, for example, 100 mL, 110 mL, 120 mL, 130 mL, 140 mL or 150 mL, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0028] Preferably, the temperature of the hydrothermal treatment is 150-220° C., and the time is 6-12 hours.

[0029] The temperature of the hydrothermal treatment in the present invention is 150-220°C, for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C or 220°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable; the time is 6-12h, for example, it can be 6h, 7h, 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0030] In the present invention, the temperature of the hydrothermal treatment affects the properties of the prepared boehmite; when the temperature of the hydrothermal treatment is 150-220°C, the prepared boehmite has better properties. This is because this temperature range can not only promote the uniform hydrolysis of ammonium alum and the nucleation of boehmite, but also generate a large number of fine crystal nuclei, thereby inhibiting excessive particle growth and agglomeration.

[0031] The hydrothermal treatment time in the present invention is 6 to 12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0032] Preferably, the preparation method further comprises filtering, water washing, alcohol washing and drying in sequence after the hydrothermal treatment.

[0033] Preferably, the liquid-to-solid ratio during the water washing process is 3 to 5 mL / g, and the number of water washings is 1 to 2 times.

[0034] The liquid-to-solid ratio in the water washing process of the present invention is 3 to 5 mL / g, for example, 3 mL / g, 3.5 mL / g, 4 mL / g, 4.5 mL / g or 5 mL / g, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; the number of water washings is 1 to 2 times, for example, 1 time or 2 times, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0035] Preferably, the liquid-to-solid ratio during the alcohol washing process is 3-5 mL / g, the number of alcohol washings is 1-2 times, and the reagent used in the alcohol washing includes anhydrous ethanol.

[0036] The liquid-to-solid ratio in the alcohol washing process of the present invention is 3 to 5 mL / g, for example, 3 mL / g, 3.5 mL / g, 4 mL / g, 4.5 mL / g or 5 mL / g, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; the number of water washings is 1 to 2 times, for example, 1 time or 2 times, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0037] Preferably, the drying temperature is 50-80° C. and the drying time is 6-12 hours.

[0038] The drying temperature in the present invention is 50-80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0039] The drying time in the present invention is 6 to 12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0040] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises:

[0041] (1) After mixing ammonium alum, urea, anhydrous ethanol and water, a mixed solution is obtained, wherein the concentration of ammonium alum in the mixed solution is 0.3-1.5 mol / L, the molar ratio of ammonium alum to urea is 1:(0.5-2), the volume ratio of anhydrous ethanol to water is (0.1-0.6):1, and the total volume of anhydrous ethanol and water is 100-150 mL

[0042] (2) subjecting the mixed solution obtained in step (1) to hydrothermal treatment at 150-220° C. for 6-12 hours, filtering, washing with water 1-2 times, and washing with alcohol 1-2 times, and drying at 50-80° C. for 6-12 hours to obtain boehmite;

[0043] The liquid-to-solid ratio in the water washing process is 3-5 mL / g, and the liquid-to-solid ratio in the alcohol washing process is 3-5 mL / g. The reagent used in the alcohol washing includes anhydrous ethanol.

[0044] In a second aspect, the present invention provides boehmite, which is obtained by the preparation method described in the first aspect.

[0045] Preferably, the microscopic morphology of the boehmite is a core-shell structure, and the core material and the shell material of the core-shell structure are both boehmite.

[0046] Preferably, the D50 particle size of the boehmite is 5 to 20 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0047] Preferably, the specific surface area of the boehmite is 80 to 300 m 2 / g, for example, it can be 80m2 / g, 100m 2 / g, 120m 2 / g, 140m 2 / g, 160m 2 / g, 180m 2 / g, 200m 2 / g, 220m 2 / g, 240m 2 / g, 260m 2 / g, 280m 2 / g or 300m 2 / g, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0048] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The preparation method provided by the present invention uses ammonium alum as a raw material, mixes it with an alkaline additive and a solvent, and then performs a hydrothermal treatment to prepare boehmite. The method not only has a low preparation cost, but also obtains the boehmite in a one-step reaction, thus having the advantage of a simple preparation process. In addition, the ammonium alum used in the preparation method is an aluminum-extracted product of waste glass powder, which has a low cost, and does not require one or more impurity removal processes for the ammonium alum, thereby further simplifying the preparation process and reducing the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a flow chart of the preparation methods provided in Examples 1 to 6.

[0052] Figure 2 This is the XRD pattern of boehmite prepared by the preparation method provided in Example 1.

[0053] Figure 3This is an SEM image of boehmite prepared by the preparation method provided in Example 1. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0055] Example 1

[0056] This embodiment provides a method for preparing boehmite, and the flow chart of the preparation method is as follows: Figure 1 As shown, the preparation method includes:

[0057] (1) mixing ammonium alum, urea, anhydrous ethanol, and water to obtain a mixed solution, wherein the concentration of ammonium alum in the mixed solution is 0.67 mol / L, the molar ratio of ammonium alum to urea is 1:1, and the volume ratio of anhydrous ethanol to water is 0.5:1;

[0058] (2) subjecting the mixed solution obtained in step (1) to hydrothermal treatment at 180° C. for 12 h, filtering, washing with water twice and washing with alcohol twice, and drying at 60° C. for 10 h to obtain boehmite;

[0059] The liquid-to-solid ratio during the water washing process is 3 mL / g, and the liquid-to-solid ratio during the alcohol washing process is 3 mL / g. The reagent used in the alcohol washing includes anhydrous ethanol.

[0060] The XRD pattern of the boehmite prepared in this embodiment was obtained by X-ray diffractometer testing. Figure 2 shown.

[0061] The SEM image of the boehmite prepared in this embodiment was obtained by scanning electron microscopy. Figure 3 shown.

[0062] Example 2

[0063] This embodiment provides a method for preparing boehmite, and the flow chart of the preparation method is as follows: Figure 1 As shown, the preparation method comprises:

[0064] (1) mixing ammonium alum, urea, anhydrous ethanol, and water to obtain a mixed solution, wherein the concentration of ammonium alum in the mixed solution is 0.67 mol / L, the molar ratio of ammonium alum to urea is 1:1, and the volume ratio of anhydrous ethanol to water is 0.5:1;

[0065] (2) subjecting the mixed solution obtained in step (1) to hydrothermal treatment at 150° C. for 12 h, filtering, washing with water twice and washing with alcohol twice, and drying at 60° C. for 10 h to obtain boehmite;

[0066] The liquid-to-solid ratio during the water washing process is 3 mL / g, and the liquid-to-solid ratio during the alcohol washing process is 3 mL / g. The reagent used in the alcohol washing includes anhydrous ethanol.

[0067] Example 4

[0068] This embodiment provides a method for preparing boehmite, and the flow chart of the preparation method is as follows: Figure 1 As shown, the preparation method comprises:

[0069] (1) mixing ammonium alum, urea, anhydrous ethanol, and water to obtain a mixed solution, wherein the concentration of ammonium alum in the mixed solution is 0.67 mol / L, the molar ratio of ammonium alum to urea is 1:1, and the volume ratio of anhydrous ethanol to water is 0.5:1;

[0070] (2) subjecting the mixed solution obtained in step (1) to hydrothermal treatment at 180° C. for 8 h, filtering, washing with water twice and washing with alcohol twice, and drying at 60° C. for 10 h to obtain boehmite;

[0071] The liquid-to-solid ratio during the water washing process is 3 mL / g, and the liquid-to-solid ratio during the alcohol washing process is 3 mL / g. The reagent used in the alcohol washing includes anhydrous ethanol.

[0072] Example 5

[0073] This embodiment provides a method for preparing boehmite, and the flow chart of the preparation method is as follows: Figure 1 As shown, the preparation method comprises:

[0074] (1) mixing ammonium alum, urea, anhydrous ethanol, and water to obtain a mixed solution, wherein the concentration of ammonium alum in the mixed solution is 0.3 mol / L, the molar ratio of ammonium alum to urea is 1:2, and the volume ratio of anhydrous ethanol to water is 0.1:1;

[0075] (2) The mixed solution obtained in step (1) was subjected to hydrothermal treatment at 220° C. for 6 h, and then filtered, washed twice with water and twice with alcohol, and then dried at 50° C. for 12 h to obtain boehmite;

[0076] The liquid-to-solid ratio during the water washing process was 4 mL / g, and the liquid-to-solid ratio during the alcohol washing process was 4 mL / g. The reagent used in the alcohol washing included anhydrous ethanol.

[0077] Example 6

[0078] This embodiment provides a method for preparing boehmite, and the flow chart of the preparation method is as follows: Figure 1 As shown, the preparation method comprises:

[0079] (1) mixing ammonium alum, urea, anhydrous ethanol, and water to obtain a mixed solution, wherein the concentration of ammonium alum in the mixed solution is 1.5 mol / L, the molar ratio of ammonium alum to urea is 1:0.5, and the volume ratio of anhydrous ethanol to water is 0.6:1;

[0080] (2) subjecting the mixed solution obtained in step (1) to hydrothermal treatment at 150° C. for 12 h, filtering, washing with water once and washing with alcohol once, and drying at 80° C. for 6 h to obtain boehmite;

[0081] The liquid-to-solid ratio during the water washing process is 5 mL / g, and the liquid-to-solid ratio during the alcohol washing process is 5 mL / g. The reagent used in the alcohol washing includes anhydrous ethanol.

[0082] Example 7

[0083] This embodiment provides a method for preparing boehmite, which is the same as that of Example 1 except that the urea in step (1) is replaced by an equal molar amount of sodium bicarbonate.

[0084] Example 8

[0085] This embodiment provides a method for preparing boehmite, which is the same as that of Example 1 except that the urea in step (1) is replaced by an equal molar amount of ammonium bicarbonate.

[0086] Example 9

[0087] This embodiment provides a method for preparing boehmite, which is the same as that of Example 1 except that the urea in step (1) is replaced by an equal molar amount of ammonia water.

[0088] Example 10

[0089] This example provides a method for preparing boehmite, which is the same as that of Example 1 except that the concentration of ammonium alum in step (1) is 0.2 mol / L.

[0090] Example 11

[0091] This example provides a method for preparing boehmite, which is the same as that of Example 1 except that the concentration of ammonium alum in step (1) is 2.5 mol / L.

[0092] Example 12

[0093] This embodiment provides a method for preparing boehmite, which is the same as that of Example 1 except that the molar ratio of ammonium alum to urea in step (1) is 1:0.2.

[0094] Example 13

[0095] This embodiment provides a method for preparing boehmite, which is the same as that of Example 1 except that the molar ratio of ammonium alum to urea in step (1) is 1:3.

[0096] Example 14

[0097] This embodiment provides a method for preparing boehmite, which is the same as that of Example 1 except that the temperature of the hydrothermal treatment in step (2) is 120°C.

[0098] Example 15

[0099] This embodiment provides a method for preparing boehmite, which is the same as that of Example 1 except that the temperature of the hydrothermal treatment in step (2) is 240°C.

[0100] Comparative Example 1

[0101] This comparative example provides a method for preparing boehmite, which comprises:

[0102] (1) dissolving aluminum nitrate in ethanol to form a mixed solution;

[0103] (2) adding hydrochloric acid catalyst to adjust the pH of the mixed solution obtained in step (1) to 5, thereby inducing the hydrolysis of aluminum nitrate to generate hydroxyaluminum intermediates, and forming a three-dimensional network sol through a condensation reaction;

[0104] (3) The three-dimensional network sol obtained in step (2) is aged for 24 hours, and then the solvent is removed by atmospheric drying, vacuum drying or freeze drying to obtain a gel;

[0105] (4) calcining the gel obtained in step (3) at 600° C. to promote boehmite crystallization and form boehmite.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing boehmite, which comprises:

[0108] (1) Using polyethylene oxide as a template, aluminum nitrate and the template are dissolved in water to form a homogeneous system;

[0109] (3) heating the homogeneous system obtained in step (1) at 160° C. for 24 hours, wherein the template guides the directional growth of the boehmite to form boehmite containing the template;

[0110] (4) removing the template-containing boehmite obtained in step (2) by calcination or solvent extraction to obtain boehmite.

[0111] The content of each element in the ammonium alum used in the above examples was tested by atomic absorption spectrophotometry, and the content of each element in the ammonium alum obtained by the test is shown in Table 1 and Table 2;

[0112] The contents of the elements in the boehmite obtained in the above examples and comparative examples were tested by atomic absorption spectrophotometry. The contents of the elements in the boehmite obtained by the tests are shown in Tables 3 and 4.

[0113] The specific surface areas of the boehmite obtained in the above examples and comparative examples were tested using a gas adsorption method. The specific surface areas of the boehmite obtained by the test are shown in Table 5.

[0114] The D50 particle size of the boehmite obtained in the above examples and comparative examples was tested using a laser particle size analyzer. The D50 particle size of the boehmite obtained by the test is shown in Table 3.

[0115] Table 1

[0116]

[0117] Table 2

[0118]

[0119] Table 3

[0120]

[0121] Table 4

[0122]

[0123]

[0124] Table 5

[0125]

[0126]

[0127] From Tables 1 to 5, we can get:

[0128] (1) The boehmite prepared by the boehmite preparation method provided in Examples 1 to 6 of the present invention has a high specific surface area, a suitable D50 particle size, and a high purity;

[0129] (2) By comparing Example 1 with Examples 7 and 8, it can be seen that when urea is used as an alkaline additive; firstly, since the alkaline additive can slowly release hydroxide in the hydrothermal reaction, thereby controlling the formation of boehmite, excessive alkalinity will promote the formation of aluminum hydroxide, and the rate of urea releasing hydroxide is slow, which is conducive to the hydrothermal reaction to form boehmite; secondly, since urea does not contain impurity elements such as Na, while creating a weak alkaline environment, the purity of the boehmite finally prepared is improved;

[0130] (3) By comparing Example 1 with Example 9, it can be seen that since the alkaline additive can slowly release hydroxide in the hydrothermal reaction, thereby controlling the formation of boehmite, excessive alkalinity will promote the formation of aluminum hydroxide. Therefore, using any one of urea, sodium bicarbonate, sodium carbonate or ammonium bicarbonate, or a combination of at least two thereof as the alkaline additive is conducive to the formation of boehmite;

[0131] (4) By comparing Example 1 with Examples 10 and 11, it can be seen that the concentration of ammonium alum in step (1) of the present invention affects the performance of the prepared boehmite; when the concentration of ammonium alum is 0.5-2 mol / L, the prepared boehmite has better performance, which is because when the concentration of ammonium alum is 0.5-2 mol / L, the hydrolysis rate of aluminum ions and the crystal nucleation reach a dynamic balance; not only is it avoided that the crystal nucleation rate is too slow due to the low concentration of ammonium alum, which ultimately causes the coarsening of the boehmite grains; it can also avoid the agglomeration of boehmite particles caused by the high concentration of ammonium alum; ammonium alum of appropriate concentration can form small-sized nanoparticles through uniform nucleation to increase the specific surface area, and can also form a uniform plate-like morphology through the directional growth of the layered structure, reducing the pore blockage caused by disordered accumulation; in addition, ammonium alum of appropriate concentration can also inhibit the encapsulation effect of impurity ions, making it easier to remove impurities in the aluminum salt by washing, thereby improving the purity of the boehmite;

[0132] (5) By comparing Example 1 with Examples 12 and 13, it can be seen that the molar ratio of ammonium alum to urea in step (1) of the present invention affects the performance of the prepared boehmite; when the molar ratio of ammonium alum to urea is 1:(0.5-2), the prepared boehmite has better performance. This is because when the molar ratio of ammonium alum to urea is 1:(0.5-2), it can ensure that ammonium alum can release enough hydroxide to form boehmite at an appropriate rate, and can also avoid the excessively fast generation rate of hydroxide, which leads to the formation of aluminum hydroxide;

[0133] (6) By comparing Example 1 with Examples 14 and 15, it can be seen that the temperature of the hydrothermal treatment in step (2) of the present invention affects the properties of the prepared boehmite; when the temperature of the hydrothermal treatment is 150-220°C, the prepared boehmite has better properties. This is because this temperature range can not only promote the uniform hydrolysis of ammonium alum and the nucleation of boehmite, but also generate a large number of fine crystal nuclei, thereby inhibiting excessive particle growth and agglomeration;

[0134] (7) By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the preparation method provided by the present invention uses ammonium alum as a raw material, mixes it with an alkaline additive and a solvent, and then performs hydrothermal treatment to prepare boehmite. This method not only has a low preparation cost, but also obtains boehmite in a one-step reaction, thus having the advantage of a simple preparation process. In addition, the preparation method does not require one or more impurity removal processes for ammonium alum, thereby further simplifying the preparation process and reducing the preparation cost.

[0135] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing boehmite, characterized in that: The preparation method comprises: A mixed solution is obtained by mixing ammonium alum, an alkaline additive and a solvent, and the mixed solution is hydrothermally treated to obtain boehmite.

2. The preparation method according to claim 1, characterized in that The concentration of ammonium alum in the mixed solution is 0.3-1.5 mol / L.

3. The preparation method according to claim 1, characterized in that The alkaline additive includes any one of urea, sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonia water or sodium hydroxide, or a combination of at least two thereof; Preferably, the alkaline additive comprises any one or a combination of at least two of urea, sodium bicarbonate, sodium carbonate or ammonium bicarbonate, preferably urea; Preferably, the molar ratio of ammonium alum to alkaline additive in the mixture is 1:(0.5-2).

4. The preparation method according to claim 1, characterized in that A dispersant is also mixed into the mixing; Preferably, the dispersant comprises anhydrous ethanol, and the solvent comprises water; Preferably, the volume ratio of the dispersant to the solvent in the mixture is (0.1-0.6):

1.

5. The preparation method according to claim 1, characterized in that The temperature of the hydrothermal treatment is 150-220° C., and the time is 6-12 hours.

6. The preparation method according to claim 1, characterized in that The preparation method further comprises filtering, washing with water, washing with alcohol and drying in sequence after the hydrothermal treatment; Preferably, the liquid-to-solid ratio during the water washing process is 3 to 5 mL / g; Preferably, the liquid-to-solid ratio during the alcohol washing process is 3-5 mL / g.

7. The preparation method according to claim 1, characterized in that The preparation method comprises: (1) mixing ammonium alum, urea, anhydrous ethanol, and water to obtain a mixed solution, wherein the concentration of ammonium alum in the mixed solution is 0.3 to 1.5 mol / L, the molar ratio of ammonium alum to urea is 1:(0.5 to 2), and the volume ratio of anhydrous ethanol to water is (0.1 to 0.6):1; (2) subjecting the mixed solution obtained in step (1) to hydrothermal treatment at 150-220° C. for 6-12 hours, filtering, washing with water 1-2 times, and washing with alcohol 1-2 times, and drying at 50-80° C. for 6-12 hours to obtain boehmite; The liquid-to-solid ratio in the water washing process is 3-5 mL / g, and the liquid-to-solid ratio in the alcohol washing process is 3-5 mL / g. The reagent used in the alcohol washing includes anhydrous ethanol.

8. A boehmite, characterized in that The boehmite is obtained by the preparation method according to any one of claims 1 to 7.

9. The boehmite according to claim 8, characterized in that The microscopic morphology of the boehmite is a core-shell structure, and both the core material and the shell material of the core-shell structure are boehmite.

10. The boehmite according to claim 8, characterized in that The boehmite has a D50 particle size of 5 to 20 μm; Preferably, the specific surface area of the boehmite is 80 to 300 m 2 / g.

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