Preparation method of alpha-Al2O3

Abstract

The invention discloses a preparation method of alpha-Al2O3, and belongs to the technical field of aluminum oxide preparation. The method comprises the following steps: (1) selecting high-purity electrolytic aluminum as an aluminum source, and dissolving the electrolytic aluminum under the action of an organic solvent and mercury monobromide to obtain alcohol aluminum salt; (2) rectifying and purifying the obtained alcohol aluminum salt in a nitrogen atmosphere at 350-400 DEG C; (3) titrating the rectified and purified alkoxide aluminum salt into an aqueous solution by adopting a titration and stirring mode, and hydrolyzing to obtain an intermediate high-purity aluminum hydroxide; and (4) carrying out calcination treatment on the high-purity aluminum hydroxide obtained in the step (3), and designing calcination parameters according to the content of alpha-Al2O3 in the required alpha-Al2O3 product to realize controllable preparation of the alpha-Al2O3 product. According to the method, the content of alpha-Al2O3 can be controlled, and the effects of reducing energy consumption, lowering the cost and improving the production efficiency can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum oxide preparation, and in particular to a method for preparing alpha-Al2O3. Background Art

[0002] α-Al2O3 is the most stable crystal structure of alumina, presenting a white micro-powder state, with high melting point, high hardness, porosity, wear resistance and corrosion resistance. Due to its excellent properties, it is used in many fields such as aerospace, electronics industry, catalyst carrier, etc. It can be prepared by pyrolysis, alcohol aluminum hydrolysis and coprecipitation. The pyrolysis preparation method of ammonium aluminum sulfate has a simple process and high product purity. It has been widely used in industry, but this process will produce waste gas to pollute the environment. Although the waste gas can be purified after a certain process, it will increase production costs and is not conducive to improving the competitiveness of enterprises; the pyrolysis preparation method of ammonium aluminum carbonate is a method improved to address the shortcomings of the pyrolysis preparation method of ammonium aluminum sulfate, but this method will produce waste liquid, and the operating conditions are strict, which is difficult to meet industrial requirements; Patent CN104891541A uses the pyrolysis method of ammonium aluminum carbonate to obtain flaky α-Al2O3 with a content of 4N level, but its aging and drying time are too long, both exceeding 12h. Sol-gel method is a newly developed technology in recent years. It can use inorganic aluminum salt as raw material or alcohol aluminum salt as raw material to produce high-purity aluminum oxide, but this method is costly and the organic solvent used is toxic and pollutes the environment; organic alcohol aluminum hydrolysis method can obtain high-purity aluminum oxide with high purity, which can well meet industrial requirements, but this method is relatively inefficient. α-Al2O3 is generally obtained by calcining Al(OH)3 at above 1200℃. Patent CN114655974A designs a method for preparing submicron-sized small original crystal α-Al2O3 for CMP polishing liquid. Aluminum hydroxide is calcined at 1100-1300℃ to obtain α-Al2O3 powder. Jun Mizuno et al. calcine aluminum hydroxide obtained by Bayer process at 1100-1500℃ to obtain α-Al2O3. Different calcination conditions will cause Al(OH)3 to generate alumina of different phases. With the change of conditions, the phase transformation will continue. Patent CN114014640A obtains a high-alumina ceramic filler whose crystal phase is mainly α-Al2O3 by calcining γ-Al2O3 at a temperature of 1370-1490°C. The α-Al2O3 content obtained by the above method is uncontrollable, and the preparation process is complicated and the cost is high. Therefore, a high-efficiency preparation method with controllable α-Al2O3 content is urgently needed to meet the α-Al2O3 content requirements of different products. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing α-Al2O3, which can realize the preparation of α-Al2O3 with controllable content, and can achieve the effects of reducing energy consumption, lowering costs and increasing production efficiency.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing α-Al2O3, the method comprising the following steps:

[0006] (1) Selecting 4N grade high-purity electrolytic aluminum as an aluminum source, using an organic solvent as a solvent, and dissolving the electrolytic aluminum in the presence of mercuric bromide as a co-solvent to obtain an alcohol aluminum salt; wherein the weight ratio of the aluminum source, the solvent, and mercuric bromide is 1:3:(0.003-0.005). The molecular formula of the organic solvent is C n H 2n+2 O2, n=4-6. The organic solvent contains two hydroxyl groups (-OH), which are connected to the methylene group so that the carboxyl group can participate in the reaction, thereby improving the dissolution efficiency and reducing the amount of solvent used; the reaction of the two carboxyl groups requires the use of a preferred catalyst (mercuric monobromide), which has a sublimation temperature of 345°C and can be volatilized and reused in the subsequent distillation process, thereby reducing the use of the catalyst.

[0007] (2) The obtained aluminum alcohol salt is distilled and purified in a nitrogen atmosphere at a temperature of 350-400° C. to effectively remove impurities such as Fe, Na, and Mg contained in the intermediate; the distillation temperature can ensure the volatilization of the catalyst, realize the recycling of the catalyst, and can also effectively separate the reactants from the catalyst and the excess organic solvent. Since the organic solvent will undergo an aerobic reaction at high temperature, an inert atmosphere must be used, and a nitrogen atmosphere is preferably used. The oxygen content in industrial nitrogen is extremely low, which can prevent oxidation. Industrial argon contains a small amount of oxygen, and a vacuum environment will increase the cost, so a nitrogen atmosphere is preferably used.

[0008] (3) titrating the purified alcohol aluminum salt into an aqueous solution by titrating and stirring to obtain an intermediate high-purity aluminum hydroxide; wherein: the titration temperature (T) is 80-100°C, and the titration rate is Stirring was performed during the titration process, with a stirring speed of V=10Tr / min.

[0009] The above operations and parameter settings are mainly to control the size of the generated intermediates. Heating is required during the preparation of the intermediates. Controlling the titration speed during the titration process can control the reaction rate, which indirectly controls the size of the generated intermediates. Additional stirring can break up the newly generated mother crystals and further refine the size of the intermediates. The size of the intermediates directly affects the size of the prepared α-Al2O3 product.

[0010] (4) calcining the high-purity aluminum hydroxide obtained in step (3), designing calcination parameters according to the desired α-Al2O3 content in the α-Al2O3 product, and realizing controllable preparation of the α-Al2O3 product. The specific steps are as follows:

[0011] Under the experimental conditions of calcination temperature of 1130-1170°C, heating rate of 1-5°C / min, and holding time of 1-4h, 15 groups of calcination test schemes with different calcination parameters were designed by Box-Behnken design experiment in response surface. The aluminum hydroxide obtained in step (3) was calcined by the designed experiment, and the actual content of α-Al2O3 (α c ), and establish the response (α-Al2O3 target content (α m The relationship between )) and each factor (A, B, C) is shown in formula (1);

[0012] In formula (1), A is the calcination temperature, B is the heating rate, C is the holding time, and α c is the actual content of α-Al2O3 in the calcined product, α m It is the target content of α-Al2O3 in the calcined product.

[0013] According to formula (1) and given target content value α m , the corresponding values ​​of A, B, and C within the specified range can be obtained.

[0014] Furthermore, the objective function can be designed as the minimum error Obj between the actual content and the target content, as shown in formula (2);

[0015] Obj(A,B,C)=min(α c -α m ) (2).

[0016] Furthermore, the constraints of calcination temperature, heating rate and holding time are given by formula (3);

[0017]

[0018] The box-behnken design experiment in the response surface method is selected, which has fewer test points and the test points are the center points, so the designed test points are safer.

[0019] The design principle and beneficial effects of the present invention are as follows:

[0020] The present invention uses the molecular formula C n H 2n+2O2 (n = 4-6) organic solvent dissolves aluminum source, reducing the amount of solvent used and improving dissolution efficiency; using mercuric bromide as a dissolution catalyst can be recycled during distillation and purification; the distillation and purification temperature is 350-400 ° C to ensure the volatilization of the catalyst and realize recovery, and can also effectively separate the reactants, catalyst and excess organic solvent; the use of nitrogen atmosphere in distillation and purification can prevent oxidation; the size of the generated intermediate is controlled by titration and stirring, and the reaction rate can be controlled by controlling the titration speed during the titration process, which indirectly controls the size of the generated intermediate. The newly generated mother crystal can be broken up by additional stirring to further refine the intermediate; the box-behnken design experiment in the response surface is selected, which has fewer test points and the test points are central points, so the designed test points are safer; according to the set target α-Al2O3 purity value, the response surface intelligent algorithm is applied to reversely optimize the calcination temperature, heating rate and holding time within the specified range, which can not only achieve controllable α-Al2O3 content, but also reduce energy consumption, reduce costs and increase production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a three-dimensional response surface diagram of the calcination temperature and the heating rate of the embodiment of the present invention.

[0022] Figure 2 It is a three-dimensional response surface diagram of the calcination temperature and the holding time of the embodiment of the present invention.

[0023] Figure 3 It is a three-dimensional response surface diagram of the heating rate and the holding time of the embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to further understand the present invention, the present invention is described below in conjunction with examples, but the examples are only for further elaboration of the features and advantages of the present invention, rather than for limiting the claims of the present invention.

[0025] The calcination temperature of traditional α-Al2O3 preparation needs to reach above 1200℃, and the common methods are ammonium aluminum sulfate pyrolysis method and ammonium aluminum carbonate pyrolysis method. The preparation process is complicated, the cycle is long, pollutant gas is released, and energy loss is high. Therefore, the present invention proposes a preparation method of α-Al2O3, by selecting 4N grade high-purity electrolytic aluminum as aluminum source, using organic solvent as solvent (organic solvent molecular formula: C n H 2n+2O2, n = 4-6), mercuric monobromide is used as a co-solvent to dissolve electrolytic aluminum to obtain alcohol aluminum salt, which is then distilled and purified and then hydrolyzed to obtain an intermediate high-purity aluminum hydroxide. A model is established within the specified range of each factor through response surface and reverse optimization intelligent algorithms to achieve calcination conditions with a controllable target α-Al2O3 content, so as to reduce costs, shorten the preparation cycle, and improve production efficiency.

[0026] Embodiment 1:

[0027] The controllable preparation process of α-Al2O3 in this embodiment is as follows:

[0028] (1) Select high-purity electrolytic aluminum as the aluminum source, with a purity greater than 99.99%, and use an organic solvent as the solvent. The molecular formula of the organic solvent is C4H 10 O2, using mercuric bromide as a dissolution catalyst to dissolve electrolytic aluminum to obtain alcohol aluminum salt, wherein the weight ratio of the aluminum source, the solvent and the mercuric bromide is 1:3:0.003.

[0029] (2) The obtained aluminum alcohol salt is purified by distillation in a nitrogen atmosphere at a temperature of 350-400° C. to remove impurities such as Fe, Na, and Mg contained in the aluminum alcohol salt.

[0030] (3) The alcohol aluminum salt after distillation and purification is titrated into an aqueous solution for hydrolysis by a titration and stirring method to obtain an intermediate high-purity aluminum hydroxide, wherein the titration temperature (T) is 80° C., the titration speed v is 3.75 ml / min, and the stirring speed V is 800 r / min.

[0031] (4) For the high-purity aluminum hydroxide prepared by the aluminum alcohol hydrolysis method, the target content of α-Al2O3 was set to 0.9, and the model obtained by the response surface was optimized. The process is as follows:

[0032] Under the experimental conditions of calcination temperature of 1130-1170°C, heating rate of 1-5°C / min, and holding time of 1-4h, 15 groups of calcination test schemes with different calcination parameters were designed by Box-Behnken design experiment in response surface, as shown in Table 1. The aluminum hydroxide obtained in step (3) was calcined by the designed experiment, and the actual content of α-Al2O3 (α c ), and establish the response (α-Al2O3 target content (α m The relationship between )) and each factor (A, B, C) is shown in formula (1);

[0033] α m =-204.77071+0.35082×A+0.59085×B-4.43456×C

[0034] -6.75E-4×A×B-4.125E-3×A×C+2.41667E-3×B×C(1);

[0035] -1.50125E-4×A 2 +0.027988×B 2 -0.018356×C 2

[0036] In formula (1), A is the calcination temperature, B is the heating rate, C is the holding time, and α c is the actual content of α-Al2O3 in the calcined product, α m It is the target content of α-Al2O3 in the calcined product.

[0037] According to formula (1) and given target content value α m , the best A=1169.39℃、B=4.95℃ / min、C=2.92h、α m =90%, based on Figure 1-Figure 3 The response surface diagram obtained shows that the optimal value of the factor is located at the optimal position. The design objective function is the minimum error Obj between the actual content and the target content, as shown in formula (2). In this embodiment, the minimum error Obj is set to min (99.34% - 99%) = 0.34%;

[0038] Obj(A,B,C)=min(α c -α m ) (2).

[0039] The constraints of calcination temperature, heating rate and holding time are given by formula (3);

[0040]

[0041] The best calcination conditions obtained through the above optimization in this embodiment are calcination temperature of 1169.39°C, heating rate of 4.95°C / min, and insulation time of 2.92h. The aluminum hydroxide obtained by calcining under similar conditions obtains α-Al2O3 with an actual content of 99.34%, which is 0.34% different from the target content value.

[0042] Embodiment 2:

[0043] The controllable preparation process of α-Al2O3 in this embodiment is as follows:

[0044] (1) Select high-purity electrolytic aluminum as the aluminum source, with a purity greater than 99.99%, and use an organic solvent as the solvent. The molecular formula of the organic solvent is C6H 14O2, using mercuric bromide as a dissolution catalyst to dissolve electrolytic aluminum to obtain alcohol aluminum salt, wherein the weight ratio of the aluminum source, the solvent and the mercuric bromide is 1:3:0.005.

[0045] (2) The obtained aluminum alcohol salt is purified by distillation in a nitrogen atmosphere at a temperature of 350 to 400° C. to remove impurities such as Fe, Na, and Mg contained in the aluminum alcohol salt.

[0046] (3) The alcohol aluminum salt after distillation and purification is titrated into an aqueous solution for hydrolysis by a titration and stirring method to obtain an intermediate high-purity aluminum hydroxide, wherein the titration temperature (T) is 100° C., the titration speed v is 1.7 ml / min, and the stirring speed V is 900 r / min.

[0047] (4) For the high-purity aluminum hydroxide prepared by the aluminum alcohol hydrolysis method, the target content of α-Al2O3 was set to 0.7, and the model obtained by the response surface was optimized. The process is as follows:

[0048] Under the experimental conditions of calcination temperature of 1130-1170°C, heating rate of 1-5°C / min, and holding time of 1-4h, 15 groups of calcination test schemes with different calcination parameters were designed by Box-Behnken design experiment in response surface, as shown in Table 1. The aluminum hydroxide obtained in step (3) was calcined by the designed experiment, and the actual content of α-Al2O3 (α c ), and the relationship between the response and each factor is established based on the obtained analysis results. The relationship is shown in formula (1);

[0049]

[0050] In formula (1), A is the calcination temperature, B is the heating rate, C is the holding time, and α c is the actual content of α-Al2O3 in the calcined product, α m It is the target content of α-Al2O3 in the calcined product.

[0051] According to formula (1) and given target content value α m , and the best A=1149.89℃、B=4.79℃ / min、C=3.1h、α m =70%, based on Figure 1-Figure 3 The response surface diagram obtained shows that the optimal value of the factor is located at the optimal position. The design objective function is the minimum error Obj between the actual content and the target content, as shown in formula (2). In this embodiment, the minimum error Obj is set to min (67.84% - 70%) = 2.16%;

[0052] Obj(A,B,C)=min(αc -α m ) (2).

[0053] The constraints of calcination temperature, heating rate and holding time are given by formula (3);

[0054]

[0055] The best calcination conditions obtained through the above optimization in this embodiment are calcination temperature of 1149.89°C, heating rate of 4.79°C / min, and insulation time of 3.1h. The aluminum hydroxide obtained by calcining under similar conditions obtains an actual content of 67.84% of α-Al2O3, which is 2.16% different from the target content value.

[0056] Comparative Example 1:

[0057] The preparation process of α-Al2O3 in this example is as follows:

[0058] (1) Select high-purity electrolytic aluminum as the aluminum source, with a purity greater than 99.99%, and use an organic solvent as the solvent. The molecular formula of the organic solvent is C4H 10 O2, using mercuric bromide as a dissolution catalyst to dissolve electrolytic aluminum to obtain alcohol aluminum salt.

[0059] (2) The obtained aluminum alcohol salt is purified by distillation in a nitrogen atmosphere at a temperature of 350-400° C. to remove impurities such as Fe, Na, and Mg contained in the aluminum alcohol salt.

[0060] (3) The alcohol aluminum salt after distillation and purification is titrated into an aqueous solution for hydrolysis by a titration and stirring method to obtain an intermediate high-purity aluminum hydroxide, wherein the titration temperature (T) is 80° C., the titration speed v is 3.75 ml / min, and the stirring speed V is 800 r / min.

[0061] (4) The high-purity aluminum hydroxide obtained by the alcohol aluminum hydrolysis method was directly calcined at a calcination temperature of 1170°C, a heating rate of 5°C / min, and a holding time of 1 h to obtain α-Al2O3 with a content of 18.76%.

[0062] Comparative Example 2:

[0063] The preparation process of α-Al2O3 in this example is as follows:

[0064] (1) Select high-purity electrolytic aluminum as the aluminum source, with a purity greater than 99.99%, and use an organic solvent as the solvent. The molecular formula of the organic solvent is C6H 14 O2, using mercuric bromide as a dissolution catalyst to dissolve electrolytic aluminum to obtain alcohol aluminum salt.

[0065] (2) The obtained aluminum alcohol salt is purified by distillation in a nitrogen atmosphere at a temperature of 350-400° C. to remove impurities such as Fe, Na, and Mg contained in the aluminum alcohol salt.

[0066] (3) The alcohol aluminum salt after distillation and purification is titrated into an aqueous solution for hydrolysis by a titration and stirring method to obtain an intermediate high-purity aluminum hydroxide, wherein the titration temperature (T) is 100° C., the titration speed v is 1.7 ml / min, and the stirring speed V is 900 r / min.

[0067] (4) The high-purity aluminum hydroxide obtained by the alcohol aluminum hydrolysis method was directly calcined at a calcination temperature of 1190°C, a heating rate of 5°C / min, and a holding time of 1 h to obtain α-Al2O3 with a content of 50.26%.

[0068] Table 1 Box-Behnken experimental design table

[0069]

Claims

1. A method for preparing α-Al2O3, characterized in that: The method comprises the following steps: (1) selecting 4N grade high-purity electrolytic aluminum as an aluminum source, using an organic solvent as a solvent, and dissolving the electrolytic aluminum in the presence of mercuric bromide as a co-solvent to obtain an aluminum alcohol salt; (2) the obtained aluminum alcohol salt is subjected to distillation purification under a nitrogen atmosphere at a temperature of 350-400° C. to effectively remove impurities contained in the intermediate; (3) titrating the purified alcohol aluminum salt into an aqueous solution by titrating and stirring to obtain an intermediate high-purity aluminum hydroxide; (4) calcining the high-purity aluminum hydroxide obtained in step (3), designing calcination parameters according to the desired α-Al2O3 content in the α-Al2O3 product, and realizing controllable preparation of the α-Al2O3 product.

2. The method for preparing α-Al2O3 according to claim 1, characterized in that: In step (1), the molecular formula of the organic solvent is C n H 2n+2 O2, n=4-6.

3. The method for preparing α-Al2O3 according to claim 1 or 2, characterized in that: The organic solvent contains two hydroxyl groups (-OH), which are connected to the methylene group.

4. The method for preparing α-Al2O3 according to claim 1, characterized in that: In step (1), the weight ratio of the aluminum source, the dissolving agent and the mercuric monobromide is 1:(2-5):(0.003-0.005).

5. The method for preparing α-Al2O3 according to claim 1, characterized in that: In step (3), the titration temperature (T) is 80-100°C and the titration rate is Stirring was performed during the titration process, with a stirring speed of V = 10T r / min.

6. The method for preparing α-Al2O3 according to claim 1, characterized in that: The specific process of step (4) is as follows: under the experimental conditions of calcination temperature of 1130-1170°C, heating rate of 1-5°C / min, and holding time of 1-4h, a total of 15 groups of calcination test schemes with different calcination parameters are designed through the box-behnken design experiment in the response surface, and the aluminum hydroxide obtained in step (3) is calcined through the designed experiment, and the actual content of α-Al2O3 (α c ), and the target content of α-Al2O3 in the calcined product (α m ) and the relationship between each factor, as shown in formula (1); In formula (1), A is the calcination temperature, B is the heating rate, C is the holding time, and α c is the actual content of α-Al2O3 in the calcined product, α m is the target content of α-Al2O3 in the calcined product; According to formula (1) and given target content value α m , the corresponding values ​​of A, B, and C within the specified range can be obtained.

7. The method for preparing α-Al2O3 according to claim 6, characterized in that: The objective function can be designed as the minimum error Obj between the actual content and the target content, as shown in formula (2); Obj(A,B,C)=min(α c -a m ) (2).

8. The method for preparing α-Al2O3 according to claim 6, characterized in that: The constraints of calcination temperature, heating rate and holding time are given by formula (3);

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