A method for preparing low-grain, high-activity, spherical boehmite

Abstract

The invention discloses a preparation method of low-crystal-grain, high-activity, spherical boehmite, which belongs to the technical field of boehmite preparation. The method comprises six steps: preparation of dilute nitric acid, preparation of sodium metaaluminate, preparation of seed material, synthesis of boehmite, preparation of boehmite wet cake and preparation of product. The pseudo-boehmite is prepared by a nitric acid method, and the pseudo-boehmite has small crystals, high activity, spherical shape, and uniform particle size distribution of pure γ-Al2O3 phase. Compared with boehmite SB powder (alcohol aluminum method), the pseudo-boehmite has low cost and is easy to operate. The pseudo-boehmite is also a special product that meets the performance requirements of synthesizing SAPO-34 molecular sieve in the production process of SmTO catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of boehmite preparation, and in particular relates to a method for preparing low-grain, high-activity, spherical boehmite. Background Art

[0002] There are generally four methods for producing pseudo-boehmite: 1. Alkali method, 2. Acid method, 3. Alcohol aluminum method SB powder, and 4. Carbon dioxide neutralization method. According to research by authoritative institutions, there is no clear dividing line between pseudo-boehmite and boehmite. The change process from pseudo-boehmite to boehmite is a process of change from serious stacking faults and defects, low order and symmetry, and grains of only 2-3 nanometers in size to relatively high crystal integrity, lattice order and symmetry, with grain sizes of hundreds of nanometers or micrometers. The range is quite wide and very regular. Small-grain pseudo-boehmite is converted into γ-Al2O3 after dehydration at 600℃ for 4 hours, while large-grain pseudo-boehmite (about 50 microns or more) is not converted into γ-Al2O3 after dehydration, but directly converted into δ-Al2O3. Only the γ-Al2O3 type has high activity and can meet the requirements of catalyst production. Summary of the invention

[0003] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing low-grain, high-activity, spherical boehmite, in which pseudo-boehmite is prepared by a nitric acid method. The pseudo-boehmite has small grains, high activity, and spherical shape. The pure γ-Al2O3 phase has uniform particle size distribution. Compared with boehmite SB powder (alcohol aluminum method), the pseudo-boehmite has low cost and is easy to operate. It is also a special product that meets the performance requirements of synthesizing SAPO-34 molecular sieves in the production process of SmTO catalysts.

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

[0005] A method for preparing low-grain, high-activity, spherical boehmite comprises the following steps:

[0006] S1: Preparation of dilute nitric acid: prepare >65% industrial nitric acid into 15-25% dilute nitric acid for standby use;

[0007] S2: Preparation of sodium aluminate: add 50L of water and 20-30kg of caustic soda to a 100L interlayer heating reaction, stir and dissolve, then slowly add 30-40kg of aluminum hydroxide powder, raise the temperature to above 90°C until all the aluminum hydroxide is dissolved, filter and obtain sodium aluminate for later use;

[0008] S3: Preparation of seed material: In the same kettle as step S2, add water and pseudo-boehmite as a starter, then heat and stir until the temperature reaches 50-60°C, start adding dilute nitric acid and sodium aluminate solution, control the pH value to 6.5-7.0, react for 1-2h and adjust the pH value to 7.4-7.6 to obtain the seed material AlOH·NaNO3·H2O hydrate;

[0009] S4: Boehmite synthesis: add the seed material obtained in step S3, add water, raise the temperature to 95-98°C, add dilute nitric acid and sodium aluminate at the same time, control the pH value of the reaction solution to be greater than 7.5, and control the reaction temperature to be greater than 95°C, react for 1-2h, then stir for 30-35min, filter, and obtain a coarse filter cake containing sodium and nitrate;

[0010] S5: Preparation of boehmite wet cake: Add water to the coarse filter cake, beat it, and then filter it, repeating three times to obtain a qualified boehmite wet cake;

[0011] S6: Product preparation: The boehmite wet cake is slurried, dried, analyzed, and packaged to obtain the boehmite product.

[0012] Furthermore, the concentration of sodium aluminate obtained in step S2 is 280-300 g / L.

[0013] Furthermore, in step S3, the amount of water added is 40-50 L, and the amount of pseudo-boehmite added is 3-5 kg.

[0014] Furthermore, the D50 of the pseudo-boehmite in step S3 is 1.88-2.02 um.

[0015] Furthermore, in step S3, the total amount of the diluted nitric acid and the sodium aluminate solution added is 20-25% by weight.

[0016] Furthermore, the AlOH·NaNO3·H2O hydrate of the seed material obtained in step S3 is an emulsion without precipitation or stratification, and has small grains. The D50 measured by the HYL-1073 laser particle size analyzer is 2-2.2 um.

[0017] Furthermore, in step S4, the amount of seed material added is 15-25 L, and the amount of water added is 20-30 L.

[0018] Furthermore, after the reaction in step S4 is completed, the D50 is measured to be 1.78-2.06 um.

[0019] The beneficial effects of the present invention are as follows: (1) the present invention adopts the nitric acid method to prepare pseudo-boehmite, which has small crystals, high activity, spherical shape, and uniform particle size distribution of pure γ-Al2O3 phase. Compared with boehmite SB powder (alcohol aluminum method), it has low cost and is easy to operate. It is also a special product that meets the performance requirements of synthesizing SAPO-34 molecular sieve in the production process of SmTO catalyst;

[0020] (2) The present invention utilizes dilute nitric acid and sodium aluminate solution, uses pseudo-boehmite as an initiator, and prepares a seed material AlOH·NaNO3·H2O hydrate, controls the particle size, and generates a spherical body with small grains, that is, controls the generation of the γ-Al2O3 phase type. The γ-Al2O3 phase type has high activity and is low in cost and easy to operate compared with boehmite SB powder (alcohol aluminum method). DETAILED DESCRIPTION

[0021] In order to better understand the present invention, the embodiments of the present invention are described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0022] Embodiment 1:

[0023] A method for preparing low-grain, high-activity, spherical boehmite comprises the following steps:

[0024] S1: Preparation of dilute nitric acid: 66% industrial nitric acid is prepared into 15% dilute nitric acid for later use;

[0025] S2: Preparation of sodium aluminate: add 50L of water and 20kg of caustic soda to a 100L interlayer heating reaction, stir and dissolve, then slowly add 36kg of aluminum hydroxide powder, heat to 92°C until all aluminum hydroxide is dissolved, filter, and obtain a sodium aluminate concentration of 280g / L for standby use;

[0026] S3: Preparation of seed material: In the same kettle as step S2, add 40L of water and 5kg of pseudo-boehmite as a starter, the D50 of the pseudo-boehmite is 2.02um, then heat and stir until the temperature reaches 50°C, start adding dilute nitric acid and sodium aluminate solution, the total amount of which accounts for 25% by mass, control the pH value to 7.0, react for 1h and adjust the pH value to 7.4 to obtain a seed material AlOH·NaNO3·H2O hydrate. The obtained seed material AlOH·NaNO3·H2O hydrate is a milky body without precipitation or stratification, with small grains, and the D50 measured by HYL-1073 laser particle size analyzer is 2.2um;

[0027] S4: Boehmite synthesis: add 15L of seed material obtained in step S3, add 30L of water, raise the temperature to 95°C, add dilute nitric acid and sodium aluminate at the same time, control the pH value of the reaction solution to be greater than 7.5, and control the reaction temperature to be greater than 95°C, react for 1h, and after the reaction is completed, the D50 is measured to be 2.0um, then stir for 30min, filter, and obtain a coarse filter cake containing sodium and nitrate;

[0028] S5: Preparation of boehmite wet cake: Add water to the coarse filter cake, beat it, and then filter it, repeating three times to obtain a qualified boehmite wet cake;

[0029] S6: Product preparation: The boehmite wet cake is slurried, dried, analyzed, and packaged to obtain the boehmite product.

[0030] Embodiment 2:

[0031] A method for preparing low-grain, high-activity, spherical boehmite comprises the following steps:

[0032] S1: Preparation of dilute nitric acid: 68% industrial nitric acid is prepared into 25% dilute nitric acid for later use;

[0033] S2: Preparation of sodium aluminate: add 50L of water and 30kg of caustic soda to a 100L interlayer heating reaction, stir and dissolve, then slowly add 30kg of aluminum hydroxide powder, raise the temperature to 93°C until the aluminum hydroxide is completely dissolved, filter, and obtain a sodium aluminate concentration of 300g / L for standby use;

[0034] S3: Preparation of seed material: In the same kettle as step S2, add 50L of water and 3kg of pseudo-boehmite as a starter, the D50 of the pseudo-boehmite is 2.0um, then heat and stir until the temperature reaches 60°C, start adding dilute nitric acid and sodium aluminate solution, the total amount added accounts for 20% by weight, control the pH value to 6.5, react for 2h and adjust the pH value to 7.6 to obtain the seed material AlOH·NaNO3·H2O hydrate. The obtained seed material AlOH·NaNO3·H2O hydrate is a milky body without precipitation or stratification, with small grains, and the D50 is 2um measured by HYL-1073 laser particle size analyzer;

[0035] S4: Boehmite synthesis: add 25L of seed material obtained in step S3, add 20L of water, raise the temperature to 98°C, add dilute nitric acid and sodium aluminate at the same time, control the pH value of the reaction solution to be greater than 7.5, and control the reaction temperature to be greater than 95°C, react for 2h, and after the reaction is completed, the D50 is measured to be 1.96um, then stir for 35min, filter, and obtain a coarse filter cake containing sodium and nitrate;

[0036] S5: Preparation of boehmite wet cake: Add water to the coarse filter cake, beat it, and then filter it, repeating three times to obtain a qualified boehmite wet cake;

[0037] S6: Product preparation: The boehmite wet cake is slurried, dried, analyzed, and packaged to obtain the boehmite product.

[0038] Embodiment 3:

[0039] A method for preparing low-grain, high-activity, spherical boehmite comprises the following steps:

[0040] S1: Preparation of dilute nitric acid: 67% industrial nitric acid is prepared into 20% dilute nitric acid for later use;

[0041] S2: Preparation of sodium aluminate: add 50L of water and 25kg of caustic soda to a 100L interlayer heating reaction, stir and dissolve, then slowly add 40kg of aluminum hydroxide powder, heat to 93°C until all aluminum hydroxide is dissolved, filter, and obtain a sodium aluminate concentration of 285g / L for standby use;

[0042] S3: Preparation of seed material: In the same kettle as step S2, add 42L of water and 4kg of pseudo-boehmite as a starter, the D50 of the pseudo-boehmite is 1.98um, then heat and stir until the temperature reaches 55°C, start adding dilute nitric acid and sodium aluminate solution, the total amount added accounts for 23% by weight, control the pH value to 6.9, react for 1.5h and adjust the pH value to 7.5 to obtain the seed material AlOH·NaNO3·H2O hydrate. The obtained seed material AlOH·NaNO3·H2O hydrate is a milky body without precipitation or stratification, with small grains, and the D50 measured by HYL-1073 laser particle size analyzer is 2.1um;

[0043] S4: Boehmite synthesis: add 20L of seed material obtained in step S3, add 28L of water, raise the temperature to 96°C, add dilute nitric acid and sodium aluminate at the same time, control the pH value of the reaction solution to be greater than 7.5, and control the reaction temperature to be greater than 95°C, react for 1.8h, and after the reaction is completed, the D50 is measured to be 2.06um, then stir for 32min, filter, and obtain a coarse filter cake containing sodium and nitrate;

[0044] S5: Preparation of boehmite wet cake: Add water to the coarse filter cake, beat it, and then filter it, repeating three times to obtain a qualified boehmite wet cake;

[0045] S6: Product preparation: The boehmite wet cake is slurried, dried, analyzed, and packaged to obtain the boehmite product.

[0046] Comparative Example 1:

[0047] A method for preparing pseudo-boehmite, characterized by comprising:

[0048] 1) dissolving the organic alcohol aluminum in an alcohol solvent, heating the solvent under stirring, to obtain a first suspension;

[0049] 2) mixing the first suspension with deionized water, continuing heating, and aging to obtain a second suspension;

[0050] 3) separating the second suspension into solid and liquid to retain the solid phase;

[0051] 4) washing the solid phase with an alcohol solvent;

[0052] 5) Drying and crushing the washed solid phase to obtain pseudo-boehmite.

[0053] Comparative Example 2:

[0054] The difference between Comparative Example 2 and Example 1 is that hydrochloric acid is used to adjust the pH value in step S3 and step S4, and the other technical contents are the same as those in Example 1.

[0055] The properties of the boehmite products prepared in the above examples and comparative examples were tested, and the test results are shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] The above description of the embodiments is to facilitate the understanding and use of the present invention by those skilled in the art. Those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the principles of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing low-grain, high-activity, spherical boehmite, characterized in that: The following steps are involved: S1: Preparation of dilute nitric acid: prepare industrial nitric acid with a concentration of >65% into dilute nitric acid with a concentration of 15-25% for later use; S2: Preparation of sodium aluminate: add 50L of water and 20-30kg of caustic soda to a 100L interlayer heating reaction, stir and dissolve, then slowly add 30-40kg of aluminum hydroxide powder, raise the temperature to above 90°C until all the aluminum hydroxide is dissolved, filter and obtain sodium aluminate for later use; S3: Preparation of seed material: In the same kettle as step S2, add water and pseudo-boehmite as a starter, then heat and stir until the temperature reaches 50-60°C, start adding dilute nitric acid and sodium aluminate solution, control the pH value to 6.5-7.0, react for 1-2h and adjust the pH value to 7.4-7.6 to obtain a seed material AlOH•NaNO3•H2O hydrate, wherein the total amount of the dilute nitric acid and sodium aluminate solution added accounts for 20-25% by weight; S4: Boehmite synthesis: add the seed material obtained in step S3, add water, raise the temperature to 95-98°C, add dilute nitric acid and sodium aluminate at the same time, control the pH value of the reaction solution to be greater than 7.5, and control the reaction temperature to be greater than 95°C, react for 1-2h, and after the reaction is completed, the D50 is measured to be 1.78-2.06um, then stir for 30-35min, filter, and obtain a coarse filter cake containing sodium and nitrate; S5: Preparation of boehmite wet cake: Add water to the coarse filter cake, beat it, and then filter it, repeating three times to obtain a qualified boehmite wet cake; S6: Product preparation: The boehmite wet cake is slurried, dried, analyzed, and packaged to obtain the boehmite product.

2. The method for preparing low-grain, high-activity, spherical boehmite according to claim 1, characterized in that: The concentration of sodium aluminate obtained in step S2 is 280-300 g / L.

3. The method for preparing low-grain, high-activity, spherical boehmite according to claim 1, characterized in that: In the step S3, the amount of water added is 40-50 L, and the amount of pseudo-boehmite added is 3-5 kg.

4. The method for preparing low-grain, high-activity, spherical boehmite according to claim 1, characterized in that: The D50 of the pseudo-boehmite in step S3 is 1.88-2.02 um.

5. The method for preparing low-grain, high-activity, spherical boehmite according to claim 1, characterized in that: The AlOH•NaNO3•H2O hydrated body of the seed material obtained in step S3 is an emulsion without precipitation or stratification, and has small crystal grains. The D50 is 2-2.2 um as measured by HYL-1073 laser particle size analyzer.

6. The method for preparing low-grain, high-activity, spherical boehmite according to claim 1, characterized in that: In step S4, the amount of seed material added is 15-25 L, and the amount of water added is 20-30 L.

Images