Preparation method of alpHa type aluminum oxide

Abstract

The invention provides a preparation method of alpHa type aluminum oxide, and belongs to the field of fine aluminum oxide. The method comprises the following steps: mixing and pulping an aluminum-containing raw material, a solvent and a control agent to obtain first slurry; adjusting the pH value of the first slurry to a set pH value; under set conditions, carrying out a hydrothermal reaction on the first slurry with a set pH value to obtain a second slurry containing Al2O3.nH2O; wherein n ranges from 1 to 1.4; adjusting the pH value of the second slurry according to the numerical value of n to obtain third slurry; carrying out solid-liquid separation on the third slurry to obtain a filter cake; and drying and grinding the filter cake to obtain the alpHa type aluminum oxide. According to the new process provided by the invention, energy is saved, the problems of hard agglomeration and surface area reduction are avoided, and the alpHa aluminum oxide with a unique structure and pore size distribution is generated. Therefore, the invention provides a novel preparation method of the alpHa type aluminum oxide.

Description

Technical Field

[0001] The present application relates to the technical field of fine alumina, and in particular to a method for preparing alpHa type alumina. Background Art

[0002] There are many alumina crystal forms, and there are more than 7 thermodynamically unstable transition crystal forms, among which the α phase is the most thermodynamically stable phase. At different temperatures, different transition phases aggregate with each other, establishing a hard cluster structure that transforms to the α phase. In fact, temperature control of various transition phases in industrial production is an important factor in obtaining the α phase.

[0003] AlpHa alumina, commonly known as corundum, is an oxide with a high melting point and can be used as a raw material for electronic materials, catalysts and structural ceramics. Alpha alumina with nano-scale crystal size has many unique properties and is widely used in the development of new materials. However, the biggest difficulty in the preparation of nano alumina powder is that the phase transition temperature of alumina is too high. Usually, transition alumina can only be transformed into alpha alumina at 1100-1250°C. In fact, the size of the grains after high-temperature phase transition is usually greater than 100nm. Therefore, the use of low-temperature phase transition is the key to the preparation of alpha alumina less than 100nm. However, due to the extremely small particle size of nano powders, they are very easy to agglomerate. Even during the low-temperature calcination process, the secondary particle size becomes very large, even reaching several microns or more than a dozen microns, thus losing the effectiveness of nano powders. This is also a thorny problem encountered by nano alpha alumina in actual production applications. Summary of the invention

[0004] The present application provides a method for preparing alpHa type alumina to solve the following technical problems: providing a new method for preparing alpHa type alumina.

[0005] The present application provides a method for preparing alpHa-type alumina, the method comprising:

[0006] Mixing and slurrying the aluminum-containing raw material, the solvent and the control agent to obtain a first slurry;

[0007] adjusting the pH value of the first slurry to a set pH value;

[0008] Under set conditions, subjecting the first slurry having a set pH value to a hydrothermal reaction to obtain a second slurry containing Al2O3·nH2O; wherein n is 1 to 1.4;

[0009] According to the value of n, adjusting the pH value of the second slurry to obtain a third slurry;

[0010] Performing solid-liquid separation on the third slurry to obtain a filter cake;

[0011] The filter cake is dried and ground to obtain alpHa type alumina.

[0012] Optionally, adjusting the pH value of the second slurry according to the value of n includes:

[0013] According to the value of n, the pH value of the second slurry is adjusted; wherein,

[0014] When 1≤n≤1.2, the pH value of the second slurry is adjusted to 6.8-7.2;

[0015] When n>1.2 and ≤1.4, the pH value of the second slurry is adjusted to 7-7.5.

[0016] Optionally, the set pH value is <7.

[0017] Optionally, the mass of the control agent is 0.1% to 9% of the total mass of the first slurry.

[0018] Optionally, the control agent includes: one or more of a grain control agent, a guide control agent and a specific surface control agent; and / or,

[0019] The grain control agent includes: one or more of ammonium salt, sodium salt, potassium salt, acid and base; and / or,

[0020] The guide control agent includes: one or more of aluminum nitrate, aluminum chloride, ammonium chloride, aluminum oxide and organic acid; and / or,

[0021] The specific surface control agent includes: one or more of an ionic surfactant, a non-ionic carboxylic acid surfactant and a benzenesulfonic acid surfactant.

[0022] Optionally, the mass of the aluminum-containing raw material is 60% to 95% of the total mass of the first slurry.

[0023] Optionally, the aluminum-containing raw material includes: one or more of aluminum salts, aluminum hydroxide, hydrous aluminum oxide, derivatives of aluminum hydroxide and derivatives of hydrous aluminum oxide.

[0024] Optionally, the parameters of the hydrothermal reaction include: temperature of 80°C to 300°C, insulation time of 3h to 10h, and stirring speed of 120rpm / min to 180rpm / min.

[0025] Optionally, the grinding time is greater than 10 hours.

[0026] Optionally, after obtaining the second slurry containing Al2O3·nH2O, the method comprises:

[0027] When n>1.4, the pH value of the second slurry is adjusted to a set pH value, and the second slurry with the set pH value is subjected to a hydrothermal reaction until n is 1 to 1.4.

[0028] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0029] The embodiment of the present application provides a method for preparing alpHa type alumina, which includes: mixing and slurrying aluminum-containing raw materials, solvents and control agents to obtain a first slurry; adjusting the pH value of the first slurry to a set pH value; under set conditions, subjecting the first slurry having a set pH value to a hydrothermal reaction to obtain a second slurry containing Al2O3·nH2O; wherein n is 1 to 1.4; adjusting the pH value of the second slurry according to the value of n to obtain a third slurry; subjecting the third slurry to solid-liquid separation to obtain a filter cake; and drying and grinding the filter cake to obtain alpHa type alumina. First, compared with the traditional process of preparing alpHa type alumina by high-temperature calcination of trihydrate alumina or monohydrate alumina, the present method does not undergo a high-temperature calcination process, and thus can significantly save energy. Secondly, in the traditional process, high-temperature calcination often leads to hard agglomeration between alumina powder particles, affecting the dispersibility and use effect of the product. However, the present method can effectively avoid the generation of hard agglomeration through hydrothermal reaction and subsequent filtering, drying, ball milling and other steps. Thirdly, in the traditional process, small particles of alumina powder may adhere to and adsorb on large particles, resulting in a rapid reduction in surface area. However, this method can generate alumina hydrate intermediates with specific structures and properties by precisely controlling the pH value and reaction conditions of the slurry. These intermediates can maintain a high specific surface area during subsequent processing. Thus, a new method for preparing alpHa-type alumina is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the description, are used to explain the principles of the present application.

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1 A schematic flow chart of a method for preparing alpHa-type alumina provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0034] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0035] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one-to-one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0036] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0037] Figure 1 A schematic flow chart of a method for preparing alpHa-type alumina provided in an embodiment of the present application.

[0038] like Figure 1 As shown, the present application provides a method for preparing alpHa type alumina, the method comprising:

[0039] S1, mixing and slurrying the aluminum-containing raw material, the solvent and the control agent to obtain a first slurry;

[0040] In some embodiments, the solvent is water and the like.

[0041] In some embodiments, the mass of the control agent is 0.1% to 9% of the total mass of the first slurry.

[0042] The control agent controls the key parameters such as the crystal form, particle size, and specific surface area of ​​Al2O3·nH2O by adjusting the chemical and physical properties of the slurry, thereby affecting the performance of the final alpHa-type alumina. Exemplarily, the mass of the control agent can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc. of the total mass of the first slurry.

[0043] In some embodiments, the control agent includes: one or more of a grain control agent, a guide control agent and a specific surface control agent; and / or,

[0044] The grain control agent includes: one or more of ammonium salt, sodium salt, potassium salt, acid and base; and / or,

[0045] The guiding control agent includes: one or more of aluminum nitrate, aluminum chloride, ammonium chloride, aluminum oxide and organic acid; and / or,

[0046] The specific surface control agent includes: one or more of an ionic surfactant, a non-ionic carboxylic acid surfactant and a benzenesulfonic acid surfactant.

[0047] It should be noted that grain control agents include ammonium salts (such as ammonium chloride, ammonium sulfate, etc.), sodium salts (such as sodium chloride, sodium sulfate, etc.), potassium salts (such as potassium chloride, potassium sulfate, etc.), acids (such as hydrochloric acid, sulfuric acid, etc.) and alkalis (such as sodium hydroxide, potassium hydroxide, etc.). These substances control the grain size and shape of aluminum hydroxide by affecting the pH value, ionic strength and other conditions of the solution.

[0048] Direction control agents: including aluminum nitrate, aluminum chloride, ammonium chloride, aluminum oxide and organic acids (such as acetic acid, citric acid, etc.). They can be used as crystal nucleation agents or lattice directing agents to promote the formation of aluminum hydroxide of a specific crystal form.

[0049] Specific surface control agents: including ionic surfactants (such as sodium dodecyl sulfate, hexadecyl trimethyl ammonium bromide, etc.), non-ionic carboxylic acid surfactants (such as polyethylene glycol fatty acid esters, sorbitan fatty acid esters, etc.) and benzene sulfonic acid surfactants. These substances change the surface properties and charge state of aluminum hydroxide particles by adsorbing on their surface, thereby affecting the dispersion, agglomeration degree and specific surface area of ​​the particles.

[0050] In some embodiments, the mass of the aluminum-containing raw material is 60% to 95% of the total mass of the first slurry.

[0051] The aluminum-containing raw material is the main source of ingredients for preparing alpHa-type alumina. The mass proportion of the aluminum-containing raw material in the first slurry is 60% to 95%, which ensures the full utilization of the raw material and also provides sufficient space for the addition of solvents and control agents. Exemplarily, the mass of the aluminum-containing raw material can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc. of the total mass of the first slurry.

[0052] In some embodiments, the aluminum-containing raw material includes one or more of aluminum salts, aluminum hydroxide, hydrous aluminum oxide, derivatives of aluminum hydroxide, and derivatives of hydrous aluminum oxide.

[0053] It should be noted that if the raw material used is aluminum salt, it is necessary to first react the aluminum salt with the pH control agent at room temperature, and filter the resulting reactant, and then add water to the filtrate and stir and slurry it; if the aluminum-containing raw material used is aluminum hydroxide, hydrous aluminum oxide, aluminum hydroxide, and its derivatives after treatment with hydrous aluminum oxide, aluminum hydroxide, hydrous aluminum oxide, aluminum hydroxide, and its derivatives after treatment with hydrous aluminum oxide can be directly added with water and stirred to slurry it at room temperature (when slurrying at room temperature, whether a pH adjuster needs to be added depends on the pH value of the aluminum-containing raw material slurry. If the pH value of the slurry is too low or too high, a pH adjuster needs to be added).

[0054] S2, adjusting the pH value of the first slurry to a set pH value;

[0055] In some embodiments, the set pH value is <7.

[0056] Limiting the pH value of the first slurry to less than 7 is conducive to the generation of the desired alumina hydrate intermediate product. By precisely controlling the pH value, the crystal form, particle size and structure of these intermediate products can be regulated, laying a good foundation for the subsequent conversion into alpHa-type alumina. On the one hand, when the pH value is too high, the aluminum ions in the solution are easily combined with hydroxide ions to form water-insoluble precipitates, which may not be the desired intermediate products, resulting in waste of raw materials and increased subsequent processing costs. Controlling the pH value within 7 can effectively avoid this situation and ensure the efficient use of raw materials. On the other hand, if the pH value is too low, the generated alumina hydrate intermediate product may dissolve in water, which will not only reduce production efficiency, but also cause the substances dissolved in water to form impurities in the later stage, affecting the purity of the final alumina. By maintaining an appropriate pH value, it can be ensured that the intermediate product remains stable in the solution, avoiding unnecessary dissolution and the introduction of impurities. In addition, precise control of the pH value helps to obtain alumina hydrate intermediate products with specific structures and properties, which can be more easily converted into high-quality alpHa-type alumina in subsequent processing. Therefore, controlling the pH value within 7 helps to improve the quality and performance of the final product. Exemplarily, the pH value of the first slurry can be 1, 2, 3, 4, 5, 6, 6.5, etc.

[0057] S3, under set conditions, subjecting the first slurry having a set pH value to a hydrothermal reaction to obtain a second slurry containing Al2O3·nH2O; wherein n is 1 to 1.4;

[0058] It should be noted that Al2O3·nH2O is aluminum oxide hydrate, wherein n represents the molar ratio of water molecules to aluminum oxide molecules.

[0059] In some embodiments, the parameters of the hydrothermal reaction include: temperature of 80° C. to 300° C., insulation time of 3 h to 10 h, and stirring speed of 120 rpm / min to 180 rpm / min.

[0060] The temperature is limited to 80℃~300℃, and the holding time is 3h~10h. The aluminum ions in the slurry can react effectively with the hydroxide ions to generate the required alumina hydrate. At the same time, it not only ensures the efficient progress of the reaction, but also avoids the risk of explosion of the high-pressure container due to excessive temperature. Within this temperature range, the pressure bearing capacity of the high-pressure container can be effectively guaranteed, thereby ensuring the safety of the production process. In addition, the appropriate temperature and holding time are conducive to the generation of alumina hydrate intermediates with specific structures and properties. These intermediates can be more easily converted into high-quality alpHa-type alumina in the subsequent processing process. At the same time, a good stirring effect helps to improve the reaction rate and product quality, and also helps to prevent local overheating or uneven reaction. The stirring speed is limited to 120rpm / min~180rpm / min, and the slurry can be fully stirred and mixed, thereby ensuring uniform contact and reaction between the reactants. Exemplarily, the temperature of the hydrothermal reaction parameters can be 80°C, 100°C, 120°C, 150°C, 180°C, 220°C, 250°C, 300°C, etc., the insulation time can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc., and the stirring speed can be 120rpm / min, 130rpm / min, 140rpm / min, 150rpm / min, 160rpm / min, 170rpm / min, 180rpm / min, etc.

[0061] According to the value of n, the pH value of the second slurry is adjusted; wherein,

[0062] When 1≤n≤1.2, the pH value of the second slurry is adjusted to 6.8-7.2;

[0063] When n>1.2 and ≤1.4, the pH value of the second slurry is adjusted to 7-7.5.

[0064] The hydrothermal reaction of the first slurry to generate a second slurry containing Al2O3·nH2O (where n is 1 to 1.4) is a key step. Next, adjusting the pH of the second slurry according to the value of n, as well as the subsequent treatment of the secondary slurry, are important factors to ensure that pure phase alpha alumina is finally obtained.

[0065] When 1≤n≤1.2, the pH value of the second slurry is adjusted to 6.8-7.2. This range of pH values ​​helps to generate a specific pure phase intermediate product, which can be more easily converted into pure phase alpHa type alumina in the subsequent ball milling process. This is because at this pH value, the concentration and activity of aluminum ions and hydroxide ions in the solution reach a balance point, which is conducive to the formation of a stable alumina hydrate intermediate product with a specific structure.

[0066] When n>1.2 and ≤1.4, the pH value of the second slurry is adjusted to 7-7.5. This slightly higher pH range is conducive to the generation of another pure phase intermediate product, which can obtain pure phase alpHa type alumina during direct ball milling. By accurately controlling the pH value of the second slurry, it is possible to ensure the generation of pure phase intermediate products and ultimately convert them into pure phase alpHa type alumina.

[0067] This preparation process not only improves the purity and performance of the product, but also reduces production costs and energy consumption. At the same time, the precise control of the pH value also reflects the fine regulation of reaction conditions in chemical synthesis, which is the key to achieving the preparation of high-performance materials. Exemplarily, when n is 1.1, the pH value of the second slurry can be adjusted to 6.8, 6.9, 7.0, 7.1, 7.2, etc., when n is 1.2, the pH value of the second slurry can be adjusted to 6.8, 6.9, 7.0, 7.1, 7.2, etc., when n is 1.3, the pH value of the second slurry can be adjusted to 7, 7.1, 7.2, 7.3, 7.4, 7.5, etc., when n is 1.4, the pH value of the second slurry can be adjusted to 7, 7.1, 7.2, 7.3, 7.4, 7.5, etc.

[0068] In some embodiments, after obtaining the second slurry containing Al2O3·nH2O, the method includes:

[0069] When n>1.4, the pH value of the second slurry is adjusted to a set pH value, and the second slurry with the set pH value is subjected to a hydrothermal reaction until n is 1 to 1.4.

[0070] S4. According to the value of n, the pH value of the second slurry is adjusted to obtain a third slurry;

[0071] S5, performing solid-liquid separation on the third slurry to obtain a filter cake;

[0072] It should be noted that during the solid-liquid separation and the washing process after solid-liquid separation, the pH value of the final product must be controlled between 7 and 7.5. Only when the pH of the filtered and washed product is controlled within the acidic or slightly alkaline range can the pure phase intermediate product obtained be converted into pure phase alpHa alumina during the subsequent ball milling.

[0073] S6. Drying and grinding the filter cake to obtain alpHa type alumina.

[0074] In some embodiments, adjusting the pH value of the second slurry according to the value of n comprises:

[0075] In some embodiments, the grinding time is greater than 10 h.

[0076] The advantages of preparing alpHa-type alumina provided in this application are specifically:

[0077] (1) Energy saving: Compared with the traditional process of preparing alpHa alumina by high-temperature calcination of alumina trihydrate or alumina monohydrate, this method does not go through a high-temperature calcination process, thus significantly saving energy.

[0078] (2) Avoiding hard agglomeration: In traditional processes, high-temperature calcination often causes hard agglomeration between alumina powder particles, affecting the dispersibility and use effect of the product. However, this method can effectively avoid the generation of hard agglomeration through hydrothermal reaction and subsequent filtration, drying, ball milling and other steps.

[0079] (3) Maintaining a high specific surface area: In traditional processes, small particles of alumina powder may adhere to and adsorb on large particles, resulting in a rapid decrease in surface area. However, this method can generate alumina hydrate intermediates with specific structures and properties by precisely controlling the pH value of the slurry and reaction conditions. These intermediates can maintain a high specific surface area during subsequent processing.

[0080] (4) High product purity: This method can ensure the generation of pure intermediate products by precisely controlling the pH value of the slurry, reaction temperature, insulation time, stirring speed and other parameters, and finally convert them into pure alpHa-type alumina. This preparation process not only improves the purity of the product, but also reduces production costs and energy consumption.

[0081] (5) Flexible process: The type and amount of the control agent in this method can be adjusted as needed to optimize key parameters such as the crystal form, particle size, specific surface area, etc. of the product. In addition, the pH value of the second slurry can be adjusted according to the value of n to meet the needs of different raw materials and reaction conditions.

[0082] (6) Environmentally friendly: This method avoids the harmful gases and dust pollution that may be generated during high-temperature calcination, and is more environmentally friendly.

[0083] (7) Wide application fields: The alpHa-type alumina prepared by this method has a unique structure and pore size distribution, and can be re-calcined, formed, composited, etc. as needed to meet the application requirements of different fields. For example, it can be used in catalytic cracking, abrasives, ceramics, coatings, plastics, rubber, papermaking, inks and other fields.

[0084] (8) High production efficiency: This method can significantly improve production efficiency and reduce production costs by optimizing reaction conditions and process flow.

[0085] In summary, the method for preparing alpHa-type alumina has the advantages of significant energy saving, avoiding hard agglomeration, maintaining high specific surface area, high product purity, flexible process, environmental friendliness, wide application field and high production efficiency. These advantages make this method an effective and feasible choice for preparing high-quality alpHa-type alumina.

[0086] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0087] Example 1

[0088] 25.6 moles of alumina trihydrate produced by the Bayer process, 0.25 moles of ammonium sulfate, and 5.12 moles of aluminum hydrate are added with water and mixed evenly, stirred at 150 rpm for 30 minutes at room temperature, and nitric acid is added to adjust the pH value of the solution to about 3 to obtain a first slurry; the first slurry is heated to 180°C and reacted at the same speed for 3 hours to obtain a second slurry after the reaction is completed; the second slurry is filtered and dried at 120°C, and the obtained product has a crystalline water content of 1.1. The dried second slurry is ball-milled for more than 10 hours until alpHa alumina is obtained.

[0089] Example 2

[0090] 1.15 moles of aluminum hydroxide trihydrate produced by the Bayer process, 0.15 moles of high-temperature calcined Bayer aluminum hydroxide trihydrate, 0.1 moles of ammonium sulfate and an appropriate amount of water are mixed evenly, and the pH is adjusted to about 3 with nitric acid, and the stirring speed is 150 rpm for 40 minutes to obtain a first slurry; the first slurry is heated to 200°C and kept warm for 2 hours, and a second slurry is obtained after the reaction is completed; the second slurry is filtered and dried, and it is found that the obtained hydrous aluminum oxide is between 1.3 moles, and the pH value of the second slurry is adjusted by adding ammonia water until the pH value of the second slurry is between 6.8 and 7.5. The second slurry is stirred for 2 hours, and then the second slurry is filtered, washed and dried, and the dried material is ground for more than 10 hours to obtain a new type of alpHa type aluminum oxide.

[0091] Example 3

[0092] In terms of molar ratio, 25.6 mol of alumina trihydrate produced by the Bayer process, 0.25 mol of ammonium sulfate, 5.12 mol of aluminum hydrate, and some water are mixed evenly, the pH value is adjusted to about 3 by nitric acid, and the mixture is stirred at 150 rpm for 30 minutes at room temperature to obtain a first slurry; the first slurry is heated to 180°C and reacted at the same speed for 3 hours, and a second slurry is obtained after the reaction is completed; a part of the second slurry is filtered, washed, and dried, and the crystal water content of the dried product is more than 1.4 mol, and the pH value of the second slurry is adjusted to between 6.8 and 7.5; the second slurry after the pH value is adjusted is heated to 180°C and reacted at a speed of 150 rpm for 3 hours to obtain a third slurry, and the third slurry obtained by hydrothermal treatment is filtered, washed, and dried to obtain a product with a crystal water content of less than 1.4; the filtered and dried product of the third slurry is ball-milled for more than 10 hours until alpHa alumina is obtained.

[0093] The performance of the alpHa alumina obtained in Examples 1 to 3 was measured, and the results are shown in Table 1.

[0094] Table 1 Properties of alpHa alumina obtained in Examples 1 to 3

[0095] Group purity,% Particle size d50, nm <![CDATA[Specific surface area, m 2 / g]]> Pore ​​size, nm Example 1 99.95 36.4 521 3.4 Example 2 99.94 36.7 527 3.8 Example 3 99.92 36.3 529 3.6

[0096] As shown in Table 1, the purity of the alpHa alumina obtained in the embodiment is greater than 99.0%, the particle size d50 is 36nm-37nm, and the specific surface area is greater than 500m 2 / g, the pore size is 3nm~4nm, alpHa alumina has a unique structure and pore size distribution.

[0097] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0098] In the embodiments of the present application, compared with the traditional calcination of alumina trihydrate and alumina monohydrate to alpha alumina products, this new process of directly converting aluminum-containing raw materials into alpha alumina through hydrothermal reaction, filtration, drying, and ball milling, firstly, the new process does not go through a high-temperature calcination process, which can save a lot of energy; secondly, it will not produce hard agglomerates; thirdly, it will not cause the small particles of alumina powder to adhere to and adsorb on large particles, resulting in a rapid reduction in surface area. The alpha alumina generated by this new process has a unique structure and pore size distribution. It can be subsequently processed according to different processes such as re-calcination, molding, and compounding, and can be applied to various fields such as catalytic cracking and abrasives.

[0099] In the embodiments of the present application, in order to overcome the problem that the nano powder in the prior art has an extremely small particle size and is very easy to agglomerate, even during the low-temperature calcination process, the secondary particle size becomes very large, even reaching several microns or more than ten microns, thereby losing the effectiveness of the nano powder. Therefore, a new process for preparing alpHa-type alumina with a high specific surface area is developed using aluminum hydroxide as a raw material. First, this process is different from the ordinary alpHa alumina calcination process. Second, it is based on the aluminum hydroxide raw material and directly converts aluminum hydroxide into a new alpHa-type alumina with a high specific surface area through hydrothermal, filtration, drying, and ball milling.

[0100] In the embodiments of the present application, efficient conversion from aluminum-containing raw materials to alpHa-type alumina is achieved by precisely controlling the ratio of raw materials, solvents, and control agents, as well as reaction conditions (such as pH value, temperature, time, etc.) throughout the preparation process.

[0101] In the embodiments of the present application, harmful gases and dust pollution that may be generated during high-temperature calcination are avoided, which is more environmentally friendly.

[0102] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing alpHa type alumina, the method comprising: Mixing and slurrying the aluminum-containing raw material, the solvent and the control agent to obtain a first slurry; adjusting the pH value of the first slurry to a set pH value; Under set conditions, subjecting the first slurry having a set pH value to a hydrothermal reaction to obtain a second slurry containing Al2O3·nH2O; wherein n is 1 to 1.4; According to the value of n, adjusting the pH value of the second slurry to obtain a third slurry; Performing solid-liquid separation on the third slurry to obtain a filter cake; The filter cake is dried and ground to obtain alpHa type alumina.

2. The method according to claim 1, characterized in that The step of adjusting the pH value of the second slurry according to the value of n comprises: According to the value of n, the pH value of the second slurry is adjusted; wherein, When 1≤n≤1.2, the pH value of the second slurry is adjusted to 6.8-7.2; When n>1.2 and ≤1.4, the pH value of the second slurry is adjusted to 7-7.

5.

3. The method according to claim 1, characterized in that The set pH value is <7.

4. The method according to claim 1, characterized in that: The mass of the control agent is 0.1% to 9% of the total mass of the first slurry.

5. The method according to claim 4, characterized in that The control agent includes: one or more of a grain control agent, a guide control agent and a specific surface control agent; and / or, The grain control agent includes: one or more of ammonium salt, sodium salt, potassium salt, acid and base; and / or, The guide control agent includes: one or more of aluminum nitrate, aluminum chloride, ammonium chloride, aluminum oxide and organic acid; and / or, The specific surface control agent includes: one or more of an ionic surfactant, a non-ionic carboxylic acid surfactant and a benzenesulfonic acid surfactant.

6. The method according to claim 1, characterized in that The mass of the aluminum-containing raw material is 60% to 95% of the total mass of the first slurry.

7. The method according to claim 6, characterized in that The aluminum-containing raw materials include: one or more of aluminum salts, aluminum hydroxide, hydrous aluminum oxide, aluminum hydroxide-treated derivatives, and hydrous aluminum oxide-treated derivatives.

8. The method according to claim 1, characterized in that The parameters of the hydrothermal reaction include: temperature of 80° C. to 300° C., insulation time of 3 h to 10 h, and stirring speed of 120 rpm / min to 180 rpm / min.

9. The method according to claim 1, characterized in that: The grinding time is greater than 10 hours.

10. The method according to claim 1, characterized in that After obtaining the second slurry containing Al2O3·nH2O, the method comprises: When n>1.4, the pH value of the second slurry is adjusted to a set pH value, and the second slurry with the set pH value is subjected to a hydrothermal reaction until n is 1 to 1.4.

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