阅读说明：本技术 一种高纯片状勃姆石及其制备方法 (High-purity flaky boehmite and preparation method thereof ) 是由 梁武洋 刘中清 赵峰 邓兆敬 王倩 于 2021-10-28 设计创作，主要内容包括：本发明提供了一种高纯片状勃姆石及其制备方法。该方法包括：将铝源、铵盐混合得到不加入水的反应体系,或者,将铝源、铵盐、水混合得到加入少量水的反应体系,其中,在所述加入少量水的反应体系中,加入的水的量≤15wt％；将反应体系升温至170-250℃,反应4-48h；对反应产物进行洗涤、干燥得到所述片状勃姆石。本发明还提供了利用上述方法制备的高纯片状勃姆石。本发明提供了一种低能耗、低成本、易操作、易放大的直接制备高纯片状勃姆石的生产方法,所有制得的勃姆石具有形状规整、结晶度高、以及粒度分布窄等优势,勃姆石的边长为0.4-2.0μm,勃姆石结晶度>99％,勃姆石纯度>99.9％。(The invention provides high-purity flaky boehmite and a preparation method thereof. The method comprises the following steps: mixing an aluminum source and an ammonium salt to obtain a reaction system without water, or mixing the aluminum source, the ammonium salt and water to obtain a reaction system with a small amount of water, wherein the amount of the added water in the reaction system with the small amount of water is less than or equal to 15 wt%; heating the reaction system to 170 ℃ and 250 ℃, and reacting for 4-48 h; and washing and drying the reaction product to obtain the flaky boehmite. The invention also provides high-purity flaky boehmite prepared by the method. The invention provides a production method for directly preparing high-purity flaky boehmite with low energy consumption, low cost, easy operation and easy amplification, all prepared boehmite has the advantages of regular shape, high crystallinity, narrow particle size distribution and the like, the side length of the boehmite is 0.4-2.0 mu m, the crystallinity of the boehmite is more than 99%, and the purity of the boehmite is more than 99.9%.)

1. A method for preparing high-purity flaky boehmite, which comprises the following steps:

mixing an aluminum source and an ammonium salt to obtain a reaction system without adding water, or mixing the aluminum source, the ammonium salt and water to obtain a reaction system with adding a small amount of water, wherein the amount of the added water in the reaction system with adding the small amount of water is less than or equal to 15 wt%, and the preference is that the water content is less than or equal to 15 wt%, and the preference is that<10 wt%; NH in ammonium salts₄ ⁺The molar ratio of Al in the reaction system is 0.01-0.30: 1, preferably 0.05 to 0.20: 1;

heating the reaction system to 170-250 ℃, preferably to 220-250 ℃; reacting for 4-48h, preferably 8-16 h;

and washing and drying the reaction product to obtain the flaky boehmite.

2. The method of claim 1, wherein the aluminum source comprises one or a combination of two or more of aluminum hydroxide, quick-release powder, pseudoboehmite, gamma-alumina; preferably, the aluminum source is aluminum hydroxide and/or gamma-alumina;

more preferably, the aluminum source is a combination of aluminum hydroxide and gamma-alumina, wherein the weight ratio of the aluminum source to the gamma-alumina is preferably 0.01 to 0.50, more preferably 0.05 to 0.20.

3. The method of claim 2, wherein the aluminum hydroxide is in the form of flakes having a thickness of less than 500nm and a width of 0.5-2 μm; the width is more preferably 0.5 to 1 μm.

4. The method according to claim 1, wherein the ammonium salt comprises one or more of ammonium chloride, ammonium acetate, ammonium oxalate, ammonium sulfate, ammonium citrate and crystal water compounds corresponding to the ammonium salt; ammonium chloride and/or ammonium sulfate are preferred.

5. The method of claim 1, wherein the water added to the reaction system to which the small amount of water is added comprises one or a combination of two or more of deionized water, distilled water, high purity water and reverse osmosis water.

6. The method as claimed in claim 1, wherein the temperature increase rate in the step of increasing the temperature of the reaction system to 170-250 ℃ is 1-6 ℃/min.

7. The method of claim 1, wherein the washing agent comprises one or more of deionized water, distilled water, high purity water, reverse osmosis water, absolute ethanol, and 95% ethanol.

8. The method as claimed in claim 1, wherein the drying temperature is 100-150 ℃.

9. High purity flaky boehmite produced by the method according to any one of claims 1 to 8;

preferably, the high purity flaky boehmite has an edge length of 0.4 to 2.0 μm;

preferably, the thickness of the plate-like boehmite is below 500nm, more preferably below 300 nm.

10. The high purity flaky boehmite according to claim 9, wherein the high purity flaky boehmite has a crystallinity of > 99% and a purity of > 99.9%.

Technical Field

The invention relates to high-purity flaky boehmite and a preparation method thereof, belonging to the technical field of inorganic material preparation.

Background

Boehmite of the molecular formula gamma-Al₂O₃·H₂O, also known as boehmite, is a partially dehydrated aluminum hydroxide. Boehmite is fine white crystal in appearance, belongs to an orthorhombic system and has a layered structure; within the single structural layer, oxygen ions (O)^2-) Aluminum ions (Al) arranged at the vertices of octahedron in cubic close packing³⁺) In the center of the octahedron, hydroxyl (OH)^-) Is positioned on the surface of the laminated structure, and the layers are connected by hydrogen bonds. In addition, boehmite has high thermal conductivity, good thermal stability and low bulk density, and can release water vapor, absorb a large amount of heat and decompose Al₂O₃Covering the surface of the substrate, the flame retardant can delay the burning rate and achieve the flame retardant effect. Due to its good microstructure and thermal stability, boehmite is widely used in the fields of ceramic materials, semiconductor materials, coating materials, flame retardant materials, catalysts, carriers, and the like; more notably, due to the characteristics of low density, soft texture, good thermal conductivity, good organic matter compatibility and the like, the boehmite gradually replaces the traditional Al₂O₃And TiO₂The hard materials are used for coating the lithium battery diaphragm; in addition, the safety performance and energy density of the lithium battery can be actively improved by coating the lithium battery diaphragm with boehmite; under the era background of realizing the aim of 'double carbon', boehmite has a very wide application prospect as a preferred material of a new energy battery cell diaphragm and a pole piece coating material.

The properties of boehmite materials tend to vary due to variations in their particle size and morphology; the preparation of high-purity boehmite with small particle size from cheap and easily available industrial raw materials is the focus of the current industrial research. A common preparation method is a hydrothermal method, for example: CN 106186008A discloses a hydrothermal preparation method of boehmite for a lithium battery diaphragm coating, which takes aluminum chloride hexahydrate and aluminum nitrate nonahydrate as aluminum sources, and obtains rhombohedral boehmite with the particle size of about 800nm after the steps of precipitation, aging, filtration, hydrothermal treatment, washing, drying and the like. The method uses inorganic aluminum salt with relatively high price as an aluminum source, and has complex flow and high production and operation cost. Also, non-hydrothermal methods such as CN 111453751 a disclose a method for preparing high-purity boehmite by controlling the reaction ratio and gas flow rate of high-temperature water vapor and aluminum alkoxide to control the reaction progress to prepare high-purity nano-bulk boehmite; the method does not produce boehmite by hydrothermal method, and the prepared boehmite has narrow particle size distribution, good dispersibility and high purity; however, the operation is complicated, and the aluminum alkoxide with high price is used as the aluminum source, which is not beneficial to industrial scale-up.

As described above, in the production of high-purity boehmite, the use of expensive inorganic or organic aluminum salts as an aluminum source is mainly relied on, and the raw material cost is extremely high, and mass production is difficult. In the aspect of boehmite morphology control, the morphology is mainly controlled in the form of adding additives, which can result in high residual amounts of metal impurities in the product.

Disclosure of Invention

In order to solve the above technical problems, it is an object of the present invention to provide a method for preparing high purity flaky boehmite by one-step transcrystallization heating without adding water or with adding a small amount of water.

In order to achieve the above object, the present invention provides a method for preparing high-purity flaky boehmite, comprising the steps of:

mixing an aluminum source and an ammonium salt to obtain a reaction system without adding water, or mixing the aluminum source, the ammonium salt and water to obtain a reaction system with adding a small amount of water, wherein the amount of the added water in the reaction system with adding the small amount of water is less than or equal to 15 wt%, and the preference is that the water content is less than or equal to 15 wt%, and the preference is that<10 wt%; NH in ammonium salts₄ ⁺The molar ratio of Al in the reaction system is 0.01-0.30: 1, preferably 0.05 to 0.20: 1;

heating the reaction system to 170-250 ℃, preferably to 220-250 ℃; reacting for 4-48h, preferably 8-16 h;

and washing and drying the reaction product to obtain the flaky boehmite.

In the above method, preferably, the aluminum source includes, but is not limited to, one or a combination of two or more of aluminum hydroxide, quick-release powder, pseudoboehmite, γ -alumina, and the like; more preferably, the aluminum source is aluminum hydroxide and/or gamma-alumina. Wherein, the aluminum hydroxide is preferably in a sheet shape, the thickness of the sheet-shaped aluminum hydroxide is less than 500nm, the width of the sheet-shaped aluminum hydroxide is 0.5-2 μm, and the width of the sheet-shaped aluminum hydroxide is preferably 0.5-1 μm. When the aluminum source is a combination of aluminum hydroxide and gamma-alumina, the weight ratio of the two (aluminum hydroxide: gamma-alumina) is preferably 0.01 to 0.50: 1, more preferably 0.05 to 0.20: 1.

in the method, the content of crystal water of aluminum hydroxide (also called alumina trihydrate) and pseudo-boehmite (also called alumina monohydrate) is higher than that of boehmite, and the heating crystal transformation from the aluminum hydroxide and the pseudo-boehmite is actually a dehydration process.

The size of boehmite can be adjusted and controlled by adding aluminum oxide compounds with different crystal forms such as quick-release powder, gamma-alumina and the like as a second aluminum source. In addition, the invention can also utilize water precipitated in the crystal transformation process as a solvent to dissolve additives such as salts and the like, and control the morphology of boehmite.

In the method, the morphology of boehmite can be controlled by adding ammonium salt, and anions in the ammonium salt can be adsorbed on the surface of boehmite in a manner of being coordinated with Al ions, so that different crystal planes have different growth rates, and boehmite with different morphologies is prepared. In addition, aluminum hydroxide is crystallized into boehmite, and two ways exist simultaneously: solid phase transformation and liquid phase transformation, the amount of Al dissolved in solution in the reaction system and the rate of deposition of dissolved Al onto the boehmite surface vary from anion to anion due to coordination of anions with Al ions, and these factors can also affect the nucleation and growth rates of boehmite grains, and thus boehmite grain size. Preferably, the ammonium salt includes but is not limited to one or a combination of more than two of ammonium chloride, ammonium acetate, ammonium oxalate, ammonium sulfate, ammonium citrate and corresponding crystal water compounds of the ammonium salt; more preferably ammonium chloride and/or ammonium sulphate. The ammonium salt may be added in the form of an ammonium salt solution; wherein, no matter what form the ammonium salt is added, the amount of water additionally added to the reaction system to which a small amount of water is added is controlled to be not more than 15 wt%. The selection of ammonium salts as additives according to the invention brings about the following advantages: the ammonium salt has good water solubility and high solubility, is convenient to elute, is easy to decompose and volatilize when being heated, does not introduce other metal ions, and is beneficial to improving the purity of the product.

In the above method, preferably, the water added to the reaction system to which a small amount of water is added includes one or a combination of two or more of deionized water, distilled water, high-purity water, reverse osmosis water, and the like.

In the above method, it is preferable that the temperature increase rate in the course of increasing the temperature of the reaction system to 170-250 ℃ is 1-6 ℃/min.

In the above method, preferably, the washing agent used for washing comprises one or a combination of two or more of deionized water, distilled water, high purity water, reverse osmosis water, absolute ethyl alcohol and 95% ethyl alcohol. Washing may comprise 2-3 washing processes, for example 3 washes with water or ethanol.

In the above method, preferably, the temperature of the drying is 100-150 ℃.

High purity flaky boehmite is prepared by the above method, and the high purity flaky boehmite can be directly prepared without grinding in the whole preparation process (i.e., the above method provided by the present invention does not include a grinding step).

The preparation method of high-purity flaky boehmite provided by the invention aiming at the defects of the prior art is a production method for directly preparing the high-purity flaky boehmite with low energy consumption, low cost and easy operation, the method adopts cheap industrial products as raw materials, and the high-purity flaky boehmite can be prepared by heating and crystal transformation, wherein the side length of the boehmite is 0.4-2.0 mu m; the boehmite prepared by the method has the advantages of high purity, regular sheet shape, high crystallinity, narrow particle size distribution and the like; the method also has the advantages and characteristics of simple process, small equipment corrosivity, less washing wastewater, suitability for large-scale industrial production and the like.

The invention also provides flaky boehmite which is high-purity flaky boehmite and is prepared by the method provided by the invention.

According to a specific embodiment of the present invention, preferably, the above flake-like boehmite has an edge length of 0.4 to 2.0 μm.

According to a particular embodiment of the present invention, preferably, the above flake-like boehmite has a thickness of less than 500nm, more preferably less than 300 nm.

According to a particular embodiment of the present invention, preferably, the above flake-like boehmite has a crystallinity of > 99% and a purity of > 99.9%.

Compared with the prior art, the technical scheme of the invention has the following advantages:

1) the method is a low-cost boehmite preparation method, is different from the traditional solvothermal and hydrothermal synthesis methods, and can be used for preparing boehmite under the condition of not additionally adding water or adding a small amount of water, so that the energy consumption caused by heating the solvent in the preparation process is greatly reduced, and the production cost is greatly reduced.

2) The method is safer and more convenient, boehmite is prepared under the condition of no water or little water, and compared with the traditional solvothermal and hydrothermal synthesis methods, the method has the advantages that the pressure of a reaction system is low, the requirement on the strength of production equipment is greatly reduced, and the equipment cost is greatly reduced; meanwhile, no high-temperature and high-heat mother liquor is generated after the reaction, so that the subsequent operations such as filtration, washing and the like are very convenient, and the operation cost is greatly reduced.

3) The method of the invention takes cheap industrial products such as aluminum hydroxide, quick-release powder, pseudo-boehmite, gamma-alumina and the like as raw materials to further reduce the cost of the raw materials.

4) The method of the invention uses ammonium salt as an additive to further control the morphology of boehmite, and the prepared boehmite has the advantages of regular shape, high crystallinity, narrow particle size distribution and the like. Meanwhile, the ammonium salt is easy to dissolve in water, is convenient to elute, is easy to decompose and volatilize when being heated, does not introduce other metal ions, and improves the product purity.

5) The whole preparation process of the method of the invention does not need grinding, and the high-purity flaky boehmite is directly prepared, wherein the side length of the flaky boehmite is 0.4-2 mu m.

In conclusion, compared with the prior art, the invention provides a production method for directly preparing high-purity flaky boehmite with low energy consumption, low cost, easy operation and easy amplification, all prepared boehmite has the advantages of regular shape, high crystallinity, narrow particle size distribution and the like, the side length of the boehmite is 0.4-2.0 mu m, the crystallinity of the boehmite is more than 99%, and the purity of the boehmite is more than 99.9%.

Drawings

Fig. 1 is an XRD pattern of a sample of high purity flaky boehmite prepared in example 6.

Fig. 2 is an SEM image of a sample of high purity flaky boehmite prepared in example 1.

Fig. 3 is an SEM image of a sample of high purity flaky boehmite prepared in example 6.

Fig. 4 is an SEM image of a boehmite sample prepared in comparative example 1.

Fig. 5 is an SEM image of a boehmite sample prepared in comparative example 2.

Fig. 6 is an SEM image of a boehmite sample prepared in comparative example 3.

Fig. 7 is an SEM image of a boehmite sample prepared in comparative example 4.

Detailed Description

The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.

Example 1

The embodiment provides a preparation method of high-purity flaky boehmite, which comprises the following specific steps: 350g of aluminum hydroxide (the content of the aluminum hydroxide is more than 99.7 percent, wherein most of impurities are Na and Si, and the content is about 1000ppm) with the particle size of 5 mu m and 5g of ammonium chloride are uniformly mixed, then the mixture is put into a 1L autoclave, the temperature is raised to 250 ℃ at the rate of 4 ℃/min, and the temperature is kept for 10 hours. And (3) cooling, filtering and separating, washing with deionized water, and drying in an oven at 150 ℃ to obtain the high-purity flaky boehmite. The side length of boehmite of the product is 0.8-1.5 mu m, the thickness is about 300nm, the crystallinity of the boehmite is 99.5 percent, the purity of the boehmite is 99.92 percent, and Na is added⁺Content (wt.)322ppm。

The SEM image of the high purity flaky boehmite sample prepared in this example is shown in FIG. 2, wherein 10 lattices in FIG. 2 represent 5 μm and one lattice represents 500 nm. As can be seen from fig. 2: the flaky boehmite sample prepared by the embodiment has the advantages of regular shape, good size uniformity and good dispersibility.

Example 2

The embodiment provides a preparation method of high-purity flaky boehmite, which comprises the following specific steps: 370g of pseudo-boehmite, 20g of quick-release powder, 10g of ammonium sulfate and 10g of water are uniformly mixed and then are put into a 1L high-pressure kettle, the temperature is raised to 240 ℃ at the speed of 5 ℃/min, and the temperature is kept for 12 h. And (3) cooling, filtering and separating, washing with deionized water, and drying in an oven at 130 ℃ to obtain the high-purity flaky boehmite.

The total amount of the material was 410g, 10g of additional water was added, and the amount of additional water added in the system was 10/410-2.43%.

The side length of boehmite of the product is 0.8-2.0 mu m, the thickness is about 350nm, the crystallinity of the boehmite is 99.5 percent, the purity of the boehmite is 99.96 percent, and Na is added⁺The content was 219 ppm.

Example 3

The embodiment provides a preparation method of high-purity flaky boehmite, which comprises the following specific steps: 370g of aluminum hydroxide having a particle size of 5 μm (the content of aluminum hydroxide and the content of impurities are the same as in example 1), 20g of quick-release powder, 5g of ammonium chloride and 5g of ammonium oxalate were placed in a 1L autoclave, the temperature was raised to 220 ℃ at a rate of 6 ℃/min, and the temperature was maintained for 16 hours. And (3) cooling, filtering and separating, washing with deionized water, and drying in an oven at 120 ℃ to obtain the high-purity flaky boehmite.

The side length of boehmite of the product is 1.2-2.0 mu m, the thickness is about 250nm, the crystallinity of the boehmite is 99.7 percent, and the purity of the boehmite is>99.91％，Na⁺The content was 245 ppm.

Example 4

The embodiment provides a preparation method of high-purity flaky boehmite, which comprises the following specific steps: 390g of aluminum hydroxide with the particle size of 2 μm (the content of the aluminum hydroxide and the content of impurities are the same as those in example 1), 5g of ammonium citrate and 5g of ammonium sulfate are uniformly mixed, then the mixture is put into an autoclave, the temperature is controlled to be raised to 200 ℃ at 4 ℃/min, and the temperature is kept for 24 hours. And (3) cooling, filtering and separating, washing with deionized water, and drying in an oven at 120 ℃ to obtain the high-purity flaky boehmite.

The boehmite of the product has a length of about 0.8-1.5 μm, a thickness of about 80nm, a boehmite crystallinity of 99.6%, a boehmite purity of 99.93%, and Na⁺The content was 267 ppm.

Example 5

The embodiment provides a preparation method of high-purity flaky boehmite, which comprises the following specific steps: 370g of aluminum hydroxide with the particle size of 2 mu m (the content of the aluminum hydroxide and the content of impurities are the same as in example 1), 20g of quick-release powder, 5g of ammonium citrate and 5g of ammonium sulfate are uniformly mixed, then the mixture is put into an autoclave, the temperature is controlled to be raised to 200 ℃ at 4 ℃/min, and the temperature is kept for 24 hours. And (3) cooling, filtering and separating, washing with deionized water, and drying in an oven at 120 ℃ to obtain the high-purity flaky boehmite.

The boehmite of the product has a length of about 0.6-1.2 μm, a thickness of about 80nm, a boehmite crystallinity of 99.4%, a boehmite purity of 99.94%, and Na⁺The content was 208 ppm.

Example 6

The embodiment provides a preparation method of high-purity flaky boehmite, which comprises the following specific steps: 370g of aluminum hydroxide with the particle size of 2 mu m, 20g of gamma-alumina, 5g of ammonium citrate and 5g of ammonium sulfate are uniformly mixed and then are put into an autoclave, the temperature is controlled to be raised to 200 ℃ at 4 ℃/min, and the temperature is kept for 24 h. And (3) cooling, filtering and separating, washing with deionized water, and drying in an oven at 120 ℃ to obtain the high-purity flaky boehmite.

The boehmite of the product has a length of about 0.4-0.8 μm, a thickness of about 50nm, a boehmite crystallinity of 99.3%, a boehmite purity of 99.93%, and Na⁺The content was 189 ppm.

The XRD patterns and SEM patterns of the high purity flaky boehmite samples prepared in this example are shown in fig. 1 and 3, respectively. As can be seen from fig. 3: the flaky boehmite sample prepared by the embodiment has the advantages of regular shape, good size uniformity and good dispersibility.

Comparative example 1

Comparative example 1 reference example 1, comparative example 1 differs from example 1 in that: the same procedure as in example 1 was repeated except that 5g of ammonium chloride was replaced with 5g of potassium sulfate. The product obtained is a cubic boehmite having an edge length of 1.5-2.5μ m, boehmite crystallinity 99.2%, boehmite purity 99.68%, Na⁺537ppm, K⁺The content was about 692 ppm.

The SEM image of the boehmite sample prepared in this comparative example is shown in fig. 4. As can be seen from fig. 4: this comparative example produced cubic boehmite having an edge length of 1.5 to 2.5. mu.m.

Comparative example 2

Comparative example 2 reference example 1, comparative example 2 differs from example 1 in that: the same procedures as in example 1 were repeated except for replacing 5g of ammonium chloride with 5g of magnesium sulfate. The obtained product is rhombohedral flaky boehmite, the side length of boehmite is 1.5-2.5 μm, the crystallinity of boehmite is 99.9%, the purity of boehmite is 99.63%, and Na⁺588ppm of Mg²⁺The content was 753 ppm.

The SEM image of the boehmite sample prepared in this comparative example is shown in fig. 5. As can be seen from fig. 5: this comparative example produced rhombohedral flake boehmite having side lengths of 1.5 to 2.5 μm.

Comparative example 3

Comparative example 3 reference example 1, comparative example 3 differs from example 1 in that: the same procedure as in example 1 was repeated except that 5g of ammonium chloride was replaced with 5g of zinc sulfate. The product obtained is a cubic boehmite having an edge length of 1.5 to 2.5 μm, a boehmite crystallinity of 99.9%, a boehmite purity of 99.56%, Na⁺737ppm, Zn²⁺The content was about 1228 ppm.

The SEM image of the boehmite sample prepared in this comparative example is shown in fig. 6. As can be seen from fig. 6: this comparative example produced cubic boehmite having an edge length of 1.5 to 2.5. mu.m.

Comparative example 4

Comparative example 4 is referred to example 2, and comparative example 4 differs from example 2 in that: the same procedures as in example 2 were repeated except that 10g of ammonium sulfate was replaced with 8g of magnesium sulfate. The product obtained is a parallelepipedal boehmite having an edge length of 2.0 to 2.5 μm and a boehmite crystallinity of>99.9%, boehmite purity 99.50%, Na⁺Content 644ppm, Mg²⁺The content is about 1667 ppm.

The SEM image of the boehmite sample prepared in this comparative example is shown in fig. 7. As can be seen from fig. 7: this comparative example produces a parallelepipedal boehmite having an edge length of 2.0 to 2.5. mu.m.

From the contents of examples 1 to 6 and comparative examples 1 to 4, it can be seen that: the boehmite prepared by the preparation method of the invention is flaky with the side length within the range of 0.4-2.0 mu m under the condition of no water or only adding a small amount of water, and the crystallinity of the boehmite can reach more than 99 percent, and the impurity content is very low, and the purity of the boehmite can reach more than 99.9 percent. And the flaky boehmite has regular appearance and uniform size.