Preparation method of high-wear-resistance microspherical alumina

Abstract

The application discloses a preparation method of high-wear-resistance microspherical alumina, which comprises the following steps: (1) preparing an aluminum sol: using aluminum powder and hydrochloric acid to synthesize the aluminum sol, wherein the average particle size of the aluminum powder is 55-75 μ m, preferably 55-65 μ m; (2) preparing a pseudo-boehmite filter cake: using an aluminum salt and an aluminate to synthesize the pseudo-boehmite filter cake; (3) modifying the surface of the pseudo-boehmite: adding the pseudo-boehmite filter cake obtained in the step (2) into the aluminum sol obtained in the step (1) to stir and disperse, adding an alkaline solution, aging by increasing temperature, washing the slurry after dehydration until the filtrate is neutral to obtain the filter cake, and drying the filter cake to obtain the surface-modified pseudo-boehmite; and (4) preparing the high-wear-resistance microspherical alumina: adding the surface-modified pseudo-boehmite obtained in the step (3) into deionized water to make a slurry, adding an inorganic acid to gel, spraying to form, and baking to obtain the high-wear-resistance microspherical alumina. The surface of the pseudo-boehmite is modified to obtain the high-wear-resistance microspherical alumina.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of microspherical alumina with high wear resistance, and belongs to the field of chemical material synthesis. BACKGROUND

[0002] Alumina is often used as a carrier to prepare a catalyst due to its porous structure and high mechanical strength. Common alumina carriers include strip-shaped, clover-shaped, spherical carriers with a particle size of several millimeters, and microspherical carriers with a particle size of tens to hundreds of microns. The catalyst prepared by using the microspherical alumina can be used in a fluidized bed reactor. Due to a large contact area and small mass transfer resistance, the fluidized bed reactor is small in volume, high in yield and low in by-products. Since the microspherical catalyst is in a state of constant movement in the reactor, there is severe collision and friction between particles and between the particles and the inner wall of the reactor. Therefore, the wear resistance directly determines the use of the catalyst in the fluidized bed, and the wear resistance of the carrier directly determines the wear resistance of the catalyst. Therefore, it is of important practical value to prepare a microspherical alumina carrier with high wear resistance.

[0003] CN1097351A discloses a method for preparing microspheres of pseudo-boehmite-Al2O3, wherein the mass fraction of alumina in the pseudo-boehmite is 30% to 55%, the mass fraction of alumina in the aluminum sol is 21.5% to 23.5%, and the wear index of the obtained microspheres of pseudo-boehmite-Al2O3 is 0.9% to 2.5% per hour. gamma gamma The wear resistance of the microspheres of pseudo-boehmite-Al2O3 still needs to be further improved.

[0004] CN106475023A first uses amorphous alumina to prepare an aluminum sol by adding acid, then adds hexamethylenetetramine, a surfactant and liquid paraffin, fully homogenizes and emulsifies, and then sprays and forms and calcines to prepare alumina microspheres. However, the surfactant and liquid paraffin will release a large amount of organic waste gas in the calcination process, which will adversely affect the environment.

[0005] CN111468048A uses low-sodium high-viscosity pseudo-boehmite, grinds the pseudo-boehmite after slurry preparation by adding deionized water, then adds poly-methyl-acrylic-ammonium, polyethylene glycol, ammonium oleate and emulsified oil as additives, and obtains alumina microspheres with a wear index of 0.8% to 1.3% after spray forming and calcination. The grinding step has a great influence on the performance of the product and is prone to cause fluctuations in the performance of the product. In addition, the use of filter cake directly will cause the following two problems: (1) the filter cake itself has a high water content, and slurry preparation by adding water will result in a low solid content in the slurry, so that the amount of acid used in the gelatinization process increases, and the amount of pollutants generated in the calcination process also increases; (2) the filter cake is still slowly aging when placed, so that the performance of the product fluctuates.

[0006] ​CN115920904A improves the wear resistance of microspherical alumina carrier by adding water-soluble polymer such as carboxymethyl cellulose, anhydrous ethanol and propylene oxide to the pseudo-boehmite slurry. However, both anhydrous ethanol and propylene oxide used therein are highly flammable and explosive hazardous chemicals, and the safety risk of the spray forming process is high. SUMMARY

[0007] The purpose of the present application is to provide a preparation method of high wear-resistant microspherical alumina, which has high wear resistance and a wear index of ≤0.5%.

[0008] To achieve the above purpose, the technical solution of the present application is: a preparation method of high wear-resistant microspherical alumina, comprising the following steps:

[0009] (1) Preparation of aluminum sol: aluminum sol is synthesized using aluminum powder and hydrochloric acid, the average particle size of the aluminum powder is 55 ~ 75 mu m, preferably 55 ~ 65 mu m;

[0010] (2) Preparation of pseudo-boehmite filter cake: pseudo-boehmite filter cake is synthesized using aluminum salt and aluminate;

[0011] (3) Surface modification of pseudo-boehmite: the pseudo-boehmite filter cake obtained in step (2) is added to the aluminum sol obtained in step (1) and stirred and dispersed, an alkaline solution is added, and the slurry is aged after dehydration and washing until the filtrate is neutral to obtain a filter cake, and the filter cake is dried to obtain surface-modified pseudo-boehmite;

[0012] (4) Preparation of high wear-resistant microspherical alumina: the surface-modified pseudo-boehmite obtained in step (3) is added to deionized water and slurried, then inorganic acid peptization is added, spray forming is performed, and calcination is performed to obtain high wear-resistant microspherical alumina.

[0013] Preferably, in step (1), the preparation method of the aluminum sol is: aluminum powder is added to deionized water under stirring, hydrochloric acid aqueous solution is added dropwise, and after the dropwise addition is completed, the aluminum sol is obtained by keeping the temperature at 90 ~ 99 °C for 2 ~ 4 h. Among them, the purity of the aluminum powder is generally greater than 99.9%, the mass fraction of the hydrochloric acid aqueous solution is generally 15% ~ 25%, the mass fraction of aluminum in the aluminum sol is generally 8% ~ 15%, and the viscosity of the aluminum sol is generally 5 ~ 50 mPa·s.

[0014] Preferably, in step (2), deionized water is added to a reaction kettle, and an aqueous aluminum salt solution and an aqueous aluminate solution are added dropwise in parallel under stirring, and after the dropwise addition is completed, the stirring is continued and the slurry is kept at 50-80 DEG C for 1-2 h, and then the slurry is dewatered and the filter cake is washed to neutral. The aluminum salt can be aluminum chloride, aluminum nitrate and aluminum sulfate, and the purity should be analytical pure, and the aqueous aluminum salt solution is 70-90 g / L in terms of Al2O3 content; the aluminate is generally sodium metaaluminate, and the aqueous sodium metaaluminate solution is 120-200 g / L in terms of Al2O3 content; the dropwise addition process is generally controlled at a pH value of 8.5-9.5; and the equipment used for dewatering the slurry can be a plate-and-frame filter press, a centrifuge, a belt vacuum filter and the like.

[0015] Preferably, in step (3), the mass ratio of aluminum in the aluminum sol to aluminum in the pseudo-boehmite filter cake is 1:3-1:5, the alkaline solution is generally an aqueous solution of hexamethyltetramine and / or urea, the mass fraction of the alkaline solution is 20%-40%, and the ratio of the amount of substance of N in the alkaline solution to the amount of substance of Cl in the aluminum sol is 1.0-1.2:1; and the temperature rising aging conditions are as follows: rising to 120-150 DEG C under 0.30-0.60 MPa for 4-24 h.

[0016] Preferably, in step (4), the inorganic acid is generally an aqueous nitric acid solution, the mass fraction of the nitric acid is generally 15%-25%, the amount of the added nitric acid is such that the viscosity of the slurry is controlled at 100-500 mPa·s; the inlet temperature of the spray forming is 150-250 DEG C, and the outlet temperature is 100-120 DEG C; and the calcination temperature is preferably 800-1000 DEG C.

[0017] The present application has the following beneficial effects:

[0018] (1) The present application modifies the pseudo-boehmite with an aluminum sol and an alkaline solution, and the alkaline solution is decomposed to generate ammonia after the temperature is raised, so that the aluminum sol is slowly changed from acidic to alkaline, and gradually changes into high-adhesion pseudo-boehmite under controlled conditions;

[0019] (2) The surface-modified pseudo-boehmite prepared by the present application has a surface of high-adhesion pseudo-boehmite which is changed from an aluminum sol prepared by a specific method in an alkaline environment, and this structure reacts with inorganic acid in the subsequent peptization process to play the role of a binder, greatly improving the wear resistance of the formed microspherical alumina, and the wear index is ≤0.5%. DETAILED DESCRIPTION

[0020] The present application is further described below in conjunction with examples, but does not limit the protection scope of the present application.

[0021] Example 1

[0022] (1) Preparation of aluminum sol: 3.22 kg of deionized water was added into a reaction kettle, high-purity aluminum powder (average particle size 63.0 mu m) 0.37 kg was added under stirring, 3.26 kg of 20% mass fraction hydrochloric acid aqueous solution was added, after dropwise addition was completed, 90 ~ 95 °C continued to stir and keep for 2 h, aluminum sol was obtained, in which the mass fraction of Al was 10.3%;

[0023] (2) Preparation of pseudo-boehmite filter cake: 3.94 kg of analytical pure aluminum sulfate was weighed and prepared into aluminum sulfate aqueous solution, in which the content of Al2O3 was 80 g / L. 4.20 kg of sodium metaaluminate solid was weighed and prepared into sodium metaaluminate solution, in which the content of Al2O3 was 200 g / L. Deionized water 9.00 kg was added into a reaction kettle, aluminum sulfate solution and sodium metaaluminate solution were added by concurrent flow under stirring, the pH value was controlled to be 9.0, after dropwise addition was completed, stirring was continued and aging was carried out at 60 °C for 1 h. After aging, the slurry was transferred into a centrifuge, after liquid removal, deionized water was used for washing until the filtrate was neutral to obtain a pseudo-boehmite filter cake;

[0024] (3) Surface modification of pseudo-boehmite: the pseudo-boehmite filter cake prepared in step (2) was redispersed in the aluminum sol prepared in step (1) at room temperature, 1.03 kg of 30% hexamethylenetetramine aqueous solution was added, after pressurization to 0.40 MPa and heating to 130 °C, aging was carried out for 24 h, liquid removal was carried out again, deionized water was used for washing until the filtrate was neutral to obtain a filter cake. The filter cake was flash dried to obtain surface-modified pseudo-boehmite. The ratio of the mass of aluminum in the aluminum sol to the mass of aluminum in the filter cake was 1:3;

[0025] (4) Preparation of high-wear-resistance microspherical alumina: the surface-modified pseudo-boehmite obtained in step (3) was redispersed in 9.33 kg of deionized water to make a slurry, 1.56 kg of 20% mass fraction nitric acid aqueous solution was added again, until the viscosity of the slurry was 200 mPa·s, the inlet air temperature was controlled to be 200 ~ 210 °C and the outlet air temperature was controlled to be 110 ~ 120 °C during spray forming, the intermediate product after forming was calcined at 900 °C for 4 h to obtain high-wear-resistance microspherical alumina.

[0026] Example 2

[0027] High-purity aluminum powder with an average particle size of 55 mu m was used, and other conditions were the same as in Example 1.

[0028] Example 3

[0029] High-purity aluminum powder with an average particle size of 75 mu m was used, and other conditions were the same as in Example 1.

[0030] Example 4

[0031] In the reaction kettle, 2.11 kg of deionized water was added, and high-purity aluminum powder (average particle size 60.0 mu m) 0.28 kg was added under stirring, 1.95 kg of 20% mass fraction hydrochloric acid aqueous solution was added, and after the dropwise addition was completed, 90 ~ 95 °C continued to be stirred for 2 h, to obtain an aluminum sol, wherein the mass fraction of Al was 9.5%. 40% urea aqueous solution 0.96 kg was added, and the ratio of the mass of aluminum in the aluminum sol to the mass of aluminum in the filter cake was 1:5. The rest was the same as Example 1.

[0032] Example 5

[0033] In step (1), the average particle size of high-purity aluminum powder was 65.0 mu m, in step (3), the aging temperature was 145 °C, and the aging time was 6 h, and the rest was the same as Example 1.

[0034] Comparative Example 1

[0035] Analyzed pure aluminum sulfate 3.94 kg was weighed to prepare an aluminum sulfate aqueous solution, wherein the Al2O3 content was 80 g / L. Sodium metaaluminate solid 4.20 kg was weighed to prepare a sodium metaaluminate solution, wherein the Al2O3 content was 200 g / L. Deionized water 3.22 kg was added to the reaction kettle, and the aluminum sulfate solution and the sodium metaaluminate solution were added dropwise in parallel under stirring, and the pH value was controlled at 9.0. After the dropwise addition was completed, the stirring was continued, and the aging was carried out at 60 °C for 1 h. After the aging, the slurry was transferred to a centrifuge, and after the liquid was removed, deionized water was used for washing until the filtrate became neutral to obtain a boehmite filter cake; the filter cake was flash dried to obtain boehmite. The boehmite was reslurried in 7.00 kg of deionized water, 1.17 kg of 20% mass fraction nitric acid aqueous solution was added again, the slurry viscosity was 200 mPa•s, the inlet air temperature was controlled at 200 ~ 210 °C, the outlet air temperature was controlled at 110 ~ 120 °C during the spray forming, and the formed intermediate product was calcined at 900 °C for 4 h to obtain high-wear-resistance microspherical alumina.

[0036] Comparative Example 2

[0037] The step (3) "adding 30% methenamine aqueous solution 1.03 kg" in Example 1 was removed, and the rest was the same as Example 1.

[0038] Comparative Example 3

[0039] High-purity aluminum powder with an average particle size of 100 mu m was used, and the rest was the same as Example 1.

[0040] Comparative Example 4

[0041] High-purity aluminum powder with an average particle size of 40mu Example 4. The sol viscosity was greater than 1000 mPa-s and became a gel after standing, which could not be modified subsequently.

[0042] The attrition index was determined according to the method of YS / T 438.2-2013 Determination of physical properties of sand-like alumina Part 2: Determination of attrition index. The attrition index was calculated by the mass percentage of the fine powder collected within one hour of the injection treatment to the total loading sample. The attrition index reflects the fine powder generation rate of the sample after the attrition test. The greater the value, the worse the wear resistance of the sample. The smaller the attrition index, the better the wear resistance of the sample. The attrition indexes of Examples 1-5 and Comparative Examples 1-3 are shown in Table 1.

[0043] Table 1 Attrition index of microspherical alumina

[0044] mu Wear Index 0.2% Example 1 0.1% Example 2 0.5% Example 3 0.4% Example 4 0.4% Example 5 7.3% Comparative Example 1 6.7% Comparative Example 2 Comparative Example 3 2.4%

Claims

1. A method for preparing high-wear-resistance microspherical alumina, comprising the following steps: (1) Preparation of aluminum sol: aluminum sol is synthesized using aluminum powder and hydrochloric acid, the average particle diameter of the aluminum powder is 55 ~ 75 μ m; (2) preparing a pseudo-boehmite filter cake: synthesizing a pseudo-boehmite filter cake using an aluminum salt and an aluminate; (3) surface modification of the pseudo-boehmite: adding the pseudo-boehmite filter cake obtained in step (2) to the aluminum sol obtained in step (1) and stirring and dispersing, adding an alkaline solution, aging by increasing the temperature, washing the slurry after dehydration until the filtrate is neutral to obtain a filter cake, and drying the filter cake to obtain surface-modified pseudo-boehmite; (4) preparing high-wear-resistance microspherical alumina: adding the surface-modified pseudo-boehmite obtained in step (3) to deionized water and slushing, adding an inorganic acid peptizer, spray forming, and calcining to obtain high-wear-resistance microspherical alumina; The microspherical alumina has a wear index of ≤0.5%.

2. The production method according to claim 1, characterized by, In step (1), the aluminum sol is prepared by adding aluminum powder to deionized water under stirring, and then adding hydrochloric acid solution dropwise, and keeping the temperature at 90-99 °C for 2-4 h after the dropwise addition is completed.

3. The production method according to claim 1 or 2, characterized by, In step (1), the mass fraction of aluminum in the aluminum sol is 8%-15%.

4. The production method according to claim 1, characterized by, In step (2), deionized water is added to a reaction kettle, and an aluminum salt aqueous solution and an aluminate aqueous solution are added dropwise in parallel under stirring, and the stirring is continued and the temperature is kept at 50-80 °C for 1-2 h after the dropwise addition is completed, and then the slurry is dehydrated and the filter cake is washed until neutral.

5. The production method according to claim 4, characterized by, In step (2), the aluminum salt is selected from aluminum chloride, aluminum nitrate, or aluminum sulfate, and the aluminate is sodium metaaluminate.

6. The method of claim 1, wherein, In step (3), the alkaline solution is an aqueous solution of hexamethylenetetramine and / or urea.

7. The production method according to claim 6, characterized by In step (3), the ratio of the amount of substance of N element in the alkaline solution to the amount of substance of Cl element in the aluminum sol is 1.0-1.2:

1.

8. The production method according to claim 1, characterized by, In step (1), the average particle diameter of the aluminum powder is 55 ~ 65 μ m.

9. The production method according to claim 1, characterized by, In step (3), the ratio of the mass of aluminum in the aluminum sol to the mass of aluminum in the pseudo-boehmite filter cake is 1:3-1:

5.

10. The production method according to claim 1, characterized by, In step (3), the aging conditions are as follows: increasing the temperature to 120-150 °C under a pressure of 0.30-0.60 MPa for 4-24 h.

11. The production method according to claim 1, characterized by, In step (4), the inorganic acid is an aqueous nitric acid solution, and the mass fraction of nitric acid is 15%-25%.

12. The production method according to claim 1, characterized by, In step (4), the inlet temperature for spray forming is 150-250 °C, the outlet temperature is 100-120 °C, and the calcination temperature is 800-1000 °C.