A chitosan-regulated spherical alumina molding method

Abstract

The present invention belongs to the technical field of catalyst preparation, and discloses a method for forming spherical alumina by regulating chitosan. The method mainly comprises the following steps: preparing the aluminum sol required for dropping balls by adding pseudo-boehmite, α-Al2O3 powder, chitosan, nitric acid and cellulose, and then transferring the aluminum sol to an oil-ammonia column for dropping balls. The present invention significantly improves the adhesion phenomenon during the ball forming process by adding a modifier, improves the mechanical strength, smoothness and regularity of the spherical alumina and the color of the balls, and the process of preparing the sol does not require a high-temperature and high-pressure hydrothermal reaction, the operation process is simple, and energy consumption and production costs are effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and particularly relates to a method for forming spherical alumina by regulating chitosan. Background Art

[0002] The oil-ammonia column molding method is a commonly used method for preparing spherical catalysts. This method offers numerous advantages, including low energy consumption, high cost-effectiveness, uniform spherical formation, and high spherical strength. The method begins by preparing the sol required for sphericalization, which is then deposited into the oil-ammonia column. Sphericalization occurs within the oil layer, where surface tension influences the formation of uniformly sized spheres. Gravity forces them into the ammonia aqueous layer, where the spheres solidify. The spheres are then removed and subjected to aging and drying processes to yield the desired product. The resulting product exhibits high regularity and a smooth, rounded surface, making it widely used in large-scale industrial catalytic reaction equipment, such as fluidized and moving beds.

[0003] Chinese patent CN103011213B discloses a method for preparing spherical alumina using an oil-ammonia column, comprising simultaneously dripping an aluminum sol and a nonionic surfactant solution into the oil-ammonia column to form spheres, wherein the solvent of the nonionic surfactant solution is a mixture of water and alcohol. Chinese patent CN104891538A provides a hydrothermally stable spherical γ-Al2O3 and a method for preparing the same. The method employs pseudo-boehmite as a raw material, peptizing the slurry by acidification, then adding a pseudo-boehmite suspension to form a slurry. This slurry is then formed into a pseudo-boehmite solution of a certain viscosity, which is then formed into small spheres using an oil-ammonia column method. The spherical γ-Al2O3 is then calcined at high temperature.

[0004] The above methods require calcination during the preparation of spherical alumina, which results in high temperature and high energy consumption.

[0005] Chinese patent CN108585798B discloses a method for preparing nanoporous alumina aerogel ceramic spheres. This method utilizes the addition of polyvinyl alcohol to increase surface tension and thus improve sphericity. Sol-gel technology and aerogel drying techniques are combined to ensure the nanoporous structure of the spheres. Finally, thermal sintering is performed to obtain alumina aerogel ceramic spheres with a certain strength while retaining the nanoporous structure and high specific surface area. This method requires supercritical drying, which is complex and time-consuming.

[0006] According to existing research, the surface smoothness and regularity of spherical alumina prepared by the current spheroidization scheme are not ideal, and the energy consumption is high. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the prior art and provides a chitosan-modified spherical alumina forming method. During the preparation of the spherical alumina, chitosan, nitric acid, and cellulose are added to prepare the aluminum sol required for ball formation. An oil-ammonia column is then prepared, and the aluminum sol is finally transferred to the oil-ammonia column for ball formation. The addition of a chitosan modifier significantly improves adhesion during the ball formation process, greatly enhancing the mechanical strength, smoothness, regularity, and color of the spherical alumina. Furthermore, the sol preparation process does not require a high-temperature, high-pressure hydrothermal reaction, resulting in a simple operation and effective reduction in energy consumption and production costs.

[0008] The technical solution adopted by the present invention to solve the technical problem is:

[0009] The present invention provides a chitosan-controlled spherical alumina molding method, the method comprising the following steps:

[0010] Aluminum sol is prepared by weighing pseudo-boehmite and α-Al2O3, mixing them and adding them to a reaction vessel, adding water at room temperature and stirring to fully dissolve the pseudo-boehmite and α-Al2O3, then heating, and sequentially adding an acid solution, a cellulose solution, and a chitosan solution while stirring to peptize to obtain an aluminum sol, wherein the prepared aluminum sol has a pseudo-boehmite concentration of 5-20%, an α-Al2O3 addition amount of 5-15% of the pseudo-boehmite mass, an acid solution addition amount of 1-10% of the pseudo-boehmite mass, a cellulose addition amount of 2-8% of the pseudo-boehmite mass, and a chitosan addition amount of 3-10% of the pseudo-boehmite mass;

[0011] preparing an oil-ammonia column, the oil-ammonia column comprising an ammonia water layer and an oil layer;

[0012] Drop the ball. Put the prepared aluminum sol into a syringe and start dropping the ball from above the oil layer. Control the speed of dropping the ball. After dropping, transfer the ball to the ammonia water layer in time to solidify. Then place it in an oven to dry to obtain spherical alumina.

[0013] Furthermore, the concentration of pseudo-boehmite in the aluminum sol is preferably 10-15%, the amount of α-Al2O3 added is preferably 8-10% of the mass of the pseudo-boehmite, and the amount of acid added is preferably 2-3% of the mass of the pseudo-boehmite.

[0014] Furthermore, the added amount of cellulose is preferably 3-6% of the mass of the pseudo-boehmite.

[0015] Furthermore, the added amount of chitosan is preferably 5-8% of the mass of pseudo-boehmite.

[0016] Furthermore, the acid solution is an inorganic acid or an organic acid, the inorganic acid is one or more of nitric acid, dilute sulfuric acid, hydrochloric acid, and citric acid, and the organic acid is one or more of methacrylic acid, butyric acid, and acetic acid.

[0017] Furthermore, the cellulose is one or more of cellulose ether, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose.

[0018] Furthermore, the heating temperature is 30-80° C., preferably 40-60° C. When the heating temperature is lower than 30° C., the solution is not stirred sufficiently and is not easily peptized; when the heating temperature is higher than 80° C., the solution is stirred sufficiently, is easily volatilized, and the peptization state is poor.

[0019] Furthermore, the mass concentration of the ammonia solution is 4-20%, preferably 6-12%. When the concentration of the ammonia solution is lower than 4%, it is difficult to form balls when dropped into the ammonia solution; when it is higher than 20%, the balls are uneven and have low smoothness.

[0020] The height of the ammonia layer is 10-50 cm, preferably 15-20 cm. The oil layer is any one of kerosene, glycerin and ether, and the height of the oil layer is 1-5 mm, preferably 2-3 mm.

[0021] The diameter of the needle dropper is 1-2mm. The ball dropping speed is 30-40 d / s. If the ball dropping speed is lower than 30 d / s, the ball forming process will form a tail, and the ball regularity will be low. If the ball dropping speed is higher than 40 d / s, the balls will easily mix together, and the ball formation will be irregular.

[0022] Furthermore, the ball dropping position is 2-10 cm away from the oil layer, preferably 4-6 cm.

[0023] Furthermore, the curing time is 12-24 hours.

[0024] Furthermore, the drying temperature is 50-90° C., preferably 60-80° C., and the drying time is 12-24 hours.

[0025] The advantages and positive effects of the present invention are:

[0026] The present invention adds a chitosan modifier during the preparation of spherical alumina, which significantly improves the adhesion phenomenon during the ball-forming process, improves the smoothness and regularity of the spherical alumina and the color of the balls; adds α-Al2O3 to ensure the mechanical strength of the alumina and reduce the wear of the product; adds a nitric acid solution to ensure the viscosity of the solution and form a good aluminum sol; adds a carboxymethyl cellulose solution to make the balls more regular and ensure that the particles of the balls are uniform in size; and the process of preparing the sol does not require a high-temperature and high-pressure hydrothermal reaction, has low energy consumption, good economy, and effectively reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1The figures are the ball-forming effect diagrams of alumina at various stages under different conditions, among which A1 represents the ball-dropping state of comparative example 9; A2 represents the state of the ball after solidification of comparative example 9; A3 represents the state of the ball after drying of comparative example 9; B1 represents the ball-dropping state of embodiment 2; B2 represents the state of the ball after solidification of embodiment 2; B3 represents the state of the ball after drying of embodiment 2; C1 represents the ball-dropping state of embodiment 3; C2 represents the state of the ball after solidification of embodiment 3; C3 represents the state of the ball after drying of embodiment 3. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0029] In the following examples, all reagents used were commercially available chemical reagents of analytical grade unless otherwise specified.

[0030] Example 1

[0031] A chitosan-controlled spherical aluminum oxide molding method comprises the following steps:

[0032] Aluminum sol was prepared by weighing 60 g of pseudo-boehmite and 6 g of α-Al2O3 and adding them to a reaction vessel. Deionized water was added at room temperature to fully dissolve the solids. The mixture was then heated to 40°C and stirred while adding nitric acid solution to a concentration of 3% of the mass of the pseudo-boehmite. A carboxymethyl cellulose solution was added to a concentration of 5% of the mass of the pseudo-boehmite. A chitosan solution was added to a concentration of 6% of the mass of the pseudo-boehmite. After constant volume, the mass concentration of the pseudo-boehmite in the aluminum sol was 15%. The mixture was peptized for 60 minutes to obtain the aluminum sol.

[0033] Prepare the oil-ammonia column, the ammonia water layer uses ammonia water with a mass concentration of 8% and a filling height of 15 cm, and the oil layer uses kerosene with a filling height of 2 mm; for ball dropping, put the prepared sol into a syringe, and start dropping the ball 5 cm above the liquid surface of the oil layer, controlling the speed to squeeze out a ball about two seconds. After dropping, transfer the ball to ammonia water in time to solidify for 12 hours, and then place it in an oven at 80°C for 12 hours.

[0034] We scored the regularity, tailing, and color of the balls during the dropping process, and listed them in Table 1.

[0035] The scoring criteria are as follows:

[0036] Regularity: 5 points, smooth; 4 points, relatively smooth; 3 points, not too smooth; 2 points, with burrs; 1 point, with many burrs.

[0037] Adhesion condition: 5 points, no tailing; 4 points, a little tailing; 3 points, large tailing; 2 points, obvious tailing; 1 point, obvious and large tailing that cannot form a ball.

[0038] Color: 5 points white; 4 points dark white; 3 points grayish white; 2 points slightly yellow; 1 point transparent.

[0039] It can be seen from the data in Table 1 that, through the method provided in the present invention, Example 1 has the best ball-forming state, high mechanical strength, good ball-forming regularity, and the ball-forming size is uniform overall.

[0040] Example 2

[0041] The molding method is the same as that of Example 1, except that the amount of chitosan added is 5% of the mass of pseudo-boehmite. The test results are listed in Table 1. Figure 1 B1, B2, and B3 in the table.

[0042] Example 3

[0043] The molding method is the same as that of Example 1, except that the amount of chitosan added is 6.5% of the mass of pseudo-boehmite. The test results are listed in Table 1. Figure 1 C1, C2, and C3 in the .

[0044] Comparative Example 1

[0045] The molding method is the same as that of Example 1, except that the mass of α-Al2O3 is 2 g. The test results are listed in Table 1.

[0046] Comparative Example 2

[0047] The molding method is the same as that of Example 1, except that the mass of α-Al2O3 is 20 g. The test results are listed in Table 1.

[0048] In Comparative Example 1-2, the quality of α-Al2O3 was changed. The purpose of adding α-Al2O3 was to ensure the mechanical strength of alumina, reduce the cost of pelletizing, and reduce product losses.

[0049] Comparative Example 3

[0050] The molding method was the same as in Example 1, except that the amount of carboxymethyl cellulose added was 1% of the mass of the pseudo-boehmite. The test results are listed in Table 1.

[0051] Comparative Example 4

[0052] The molding method was the same as in Example 1, except that the amount of carboxymethyl cellulose added was 10% of the mass of the pseudo-boehmite. The test results are listed in Table 1.

[0053] In comparative examples 3-4, the amount of carboxymethyl cellulose added was changed. The purpose of adding carboxymethyl cellulose was to make the balls more regular and smooth. A small amount of carboxymethyl cellulose added resulted in inconsistent ball sizes, while a large amount of carboxymethyl cellulose added increased the viscosity of the aluminum sol, making it difficult to form regular spheres.

[0054] Comparative Example 5

[0055] The molding method was the same as in Example 1, except that the amount of nitric acid added was 0.5% of the mass of the pseudo-boehmite. The test results are listed in Table 1.

[0056] Comparative Example 6

[0057] The molding method was the same as in Example 1, except that the amount of nitric acid added was 12% of the mass of the pseudo-boehmite. The test results are listed in Table 1.

[0058] In Comparative Example 5-6, the amount of nitric acid added was changed. The addition of nitric acid would change the viscosity of the aluminum sol. If the viscosity was too low, no spherical shape would be formed, and if the viscosity was too high, tailing would occur.

[0059] Comparative Example 7

[0060] The molding method is the same as that of Example 1, except that the amount of chitosan added is 2% of the mass of pseudo-boehmite. The test results are listed in Table 1.

[0061] Comparative Example 8

[0062] The molding method is the same as that of Example 1, except that the amount of chitosan added is 12% of the mass of pseudo-boehmite. The test results are listed in Table 1.

[0063] Comparative Examples 7-8 change the amount of chitosan added. The addition of chitosan will change the mechanical strength, smoothness and regularity of spherical alumina and the color of the balls. A small amount of chitosan added will result in low mechanical strength and uneven balls, while a large amount of chitosan added will result in low regularity and uneven color.

[0064] Comparative Example 9

[0065] The molding method was the same as in Example 1, except that the chitosan solution was not added. The test results are listed in Table 1.

[0066] When chitosan is not added in Comparative Example 9, the mechanical strength of the spherical alumina is poor, it is not smooth and the spheres are irregular. The details are shown in Table 1. The sphere forming process is shown in Figure 1 A1, A2, and A3 in the table.

[0067] Comparative Example 10

[0068] The molding method is the same as that of Example 1, except that α-Al2O3 is not added. The test results are listed in Table 1.

[0069] In Comparative Example 10, when α-Al2O3 is not added, the mechanical strength of the spherical alumina is poor and the product is subject to much wear.

[0070] Comparative Example 11

[0071] The molding method is the same as that of Example 1, except that carboxymethyl cellulose is not added. The test results are listed in Table 1.

[0072] In Comparative Example 11, when no carboxymethyl cellulose was added, the regularity of the spherical alumina was low and the particle size was uneven.

[0073] Comparative Example 12

[0074] The molding method is the same as that of Example 1, except that the nitric acid solution is not added. The test results are listed in Table 1.

[0075] In Comparative Example 12, when no nitric acid was added, the viscosity of the spherical alumina was too low and it was difficult to form a sphere.

[0076] Table 1

[0077]

[0078]

[0079] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

Claims

1. A method for forming spherical alumina by regulating chitosan, characterized in that: The following steps are involved: Aluminum sol is prepared by weighing pseudo-boehmite and α-Al2O3, mixing the two and adding them to a reaction container, adding water at room temperature and stirring to fully dissolve the pseudo-boehmite and α-Al2O3, then heating, and sequentially adding an acid solution, a cellulose solution, and a chitosan solution while stirring to peptize to obtain an aluminum sol, wherein the prepared aluminum sol has a pseudo-boehmite concentration of 5-20%, an α-Al2O3 addition amount of 5-15% by weight of the pseudo-boehmite, an acid solution addition amount of 1-10% by weight of the pseudo-boehmite, an cellulose addition amount of 2-8% by weight of the pseudo-boehmite, and an chitosan addition amount of 3-10% by weight of the pseudo-boehmite; preparing an oil-ammonia column, the oil-ammonia column comprising an ammonia water layer and an oil layer; Drop the ball. Put the prepared aluminum sol into a syringe and start dropping the ball from above the oil layer. Control the speed of dropping the ball. After dropping, transfer the ball to the ammonia water layer in time to solidify. Then place it in an oven to dry to obtain spherical alumina.

2. The molding method according to claim 1, characterized in that The acid solution is an inorganic acid or an organic acid, the inorganic acid is one or more of nitric acid, dilute sulfuric acid, hydrochloric acid, and citric acid, and the organic acid is one or more of methacrylic acid, butyric acid, and acetic acid.

3. The molding method according to claim 1, characterized in that The cellulose is one or more of cellulose ether, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose.

4. The molding method according to claim 1, characterized in that The heating temperature is 30-80℃.

5. The molding method according to claim 1, characterized in that The mass concentration of the ammonia water is 4-20%, the height of the ammonia water layer is 10-50 cm, the oil layer is any one of kerosene, glycerin and ether, and the height of the oil layer is 1-5 mm.

6. The molding method according to claim 1, characterized in that The ball dropping position is 2-10 cm above the oil layer, and the ball dropping speed is 30-40 d / s.

7. The molding method according to claim 1, characterized in that: The curing time is 12-24h.

8. The molding method according to claim 1, characterized in that: The drying temperature is 50-90℃ and the drying time is 12-24h.

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