Preparation method of spherical aluminum oxide

Abstract

The invention discloses a preparation method of spherical aluminum oxide. The preparation method comprises the following steps: mixing a proper amount of pseudo-boehmite and basic aluminum chloride sol to obtain mixed sol; adding the mixed sol into a balling column, and sequentially aging and roasting to obtain spherical aluminum oxide; wherein the upper layer in the column cavity of the balling column is an oil phase, and the lower layer is a salt phase. The method of mixing and peptizing the pseudo-boehmite and the basic aluminum chloride is used, so that the flowability and the solid content of a balling solution are increased, and the hydrothermal stability is improved. In the balling process, a mixed solution of inorganic ammonium salt and organic amine is adopted as a forming solution, and compared with ammonia water, poison and pollution can be remarkably reduced, so that the production process is safer, green and environmentally friendly. The spherical alumina carrier prepared by the method disclosed by the invention is uniform in particle size distribution (1.6-1.8 mm), large in surface area, suitable in pore structure, high in mechanical strength and good in hydrothermal stability.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst carrier preparation, and particularly relates to a method for preparing spherical alumina with high hydrothermal stability. Background Art

[0002] In industrial applications, when alumina is used as a catalyst, catalyst carrier, and adsorbent, it has shapes such as spheres, cylinders, strips, and clover leaves. Since the surface of spherical alumina is smooth, the friction coefficient is low during use, which makes the sliding wear rate low, and can improve the fluidity and adsorption effect of the reactants. Spherical alumina has a large specific surface area, suitable pore volume and pore size distribution, and high mechanical strength, which is conducive to the conduct of various reactions. Among them, spherical alumina with excellent sphericity and a particle size in the range of 1.6-2.0mm shows good fluidity and can be used to prepare moving bed reactor catalysts. There are many commonly used methods for preparing spherical alumina with uniform particles, mainly oil column molding method and oil-ammonia column molding method.

[0003] The oil column molding method for preparing spherical alumina involves reacting hydrochloric acid with aluminum powder to synthesize a basic aluminum chloride sol. This sol is then thoroughly mixed with a gelling agent, hexamethylenetetramine solution, and the resulting mixture is dripped into a hot oil column to form the sol. The mixture is then aged, washed, dried, and calcined to produce the spherical alumina. Patent CN116253345A discloses a method for preparing spherical alumina using hot oil column molding. This method involves mixing an aluminum chloride sol with deionized water, adding glycerol diglycidyl ether and tetrahydrophthalic anhydride, and then dripping the mixture into a hot oil column for aging, drying, and calcining to produce the spherical alumina. Patent CN105502447B involves adding urea and deionized water to the aluminum sol, stirring them uniformly. Hexamethylenetetramine and the sol mixture are then added and dripped into a hot oil column. The mixture is then washed, dried, and calcined to produce the spherical alumina. The hexamethylenetetramine and urea added during the molding process can generate ammonia nitrogen pollution, creating environmental pressure. The hot oil column forming process consumes a lot of energy. Under high-temperature hydrothermal treatment conditions, the specific surface area of ​​spherical alumina decreases rapidly, resulting in catalyst deactivation.

[0004] Compared to the oil column forming method, the oil-ammonia column forming method is an improved and developed method based on the oil column forming apparatus. This method uses pseudo-boehmite as the aluminum source and ammonia as the coagulant. First, a dilute acid is used as a peptizing agent to prepare a sol with the pseudo-boehmite. This sol is then dripped into the oil-ammonia column by gravity. A neutralization reaction occurs behind the ammonia layer, and the gel quickly solidifies into gel spheres. The gel spheres are then aged, washed, dried, and calcined to produce spherical alumina. The oil-ammonia column method produces spherical alumina in a short time, retaining the properties of the original pseudo-boehmite powder and thus having high hydrothermal stability. However, the disadvantages are that the pseudo-boehmite sol has a low solids content (less than 23%) and poor fluidity. Furthermore, the ammonia solution in this method has a strong odor, making it difficult to meet environmental protection requirements in actual production.

[0005] Patent CN118239504A discloses a method for preparing spherical alumina using an oil-ammonia column. This method involves mixing pseudo-boehmite with deionized water and then adding nitric acid to produce an aluminum sol. This sol is then dripped into an oil-ammonia column containing an oil phase and an organic amine layer. A surfactant is then added to the interface, followed by aging, filtration, drying, and calcination to produce spherical alumina. This method uses an organic amine instead of aqueous ammonia, reducing ammonia volatilization. However, its disadvantages include poor fluidity and low solids content.

[0006] The preparation of spherical alumina, the oil column molding method and the oil ammonia column molding method currently used both have problems. The main problems are poor fluidity of the molding liquid, low solid content resulting in low molding efficiency, poor hydrothermal stability of the spherical alumina product, and environmental pollution caused by the production process. Summary of the Invention

[0007] In response to the above problems, the present invention provides a method for preparing spherical alumina with higher production efficiency, excellent catalyst thermal stability, lower preparation cost and more environmentally friendly process.

[0008] To achieve the above results, the present invention adopts the following technical solutions:

[0009] A method for preparing spherical alumina comprises: mixing appropriate amounts of pseudo-boehmite and basic aluminum chloride sol to obtain a mixed sol; adding the mixed sol to a spherical column, aging, and calcining the column to obtain spherical alumina; wherein the spherical column, as a primary component of a spherical carrier forming device, generally has a two-phase layered structure (e.g., an oil-ammonia column) within its column cavity. In the present invention, the upper layer within the column cavity of the spherical column is an oil phase, and the lower layer is a salt phase.

[0010] Furthermore, the salt phase is an organic amine aqueous solution, an inorganic ammonium salt aqueous solution or a mixed aqueous solution of the two.

[0011] Furthermore, the organic amine is any one of dimethylformamide, dimethylacetamide, triethylamine, cyclopropylamine, and formamide, preferably cyclopropylamine or dimethylformamide;

[0012] The inorganic ammonium salt is any one of ammonium carbonate, ammonium bicarbonate, ammonium chloride, and ammonium nitrate, preferably ammonium carbonate.

[0013] Furthermore, when the salt phase is a mixed aqueous solution of an organic amine and an inorganic ammonium salt, the volume ratio of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution used for mixing is 1:3 to 3:1, and the mass fractions of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution are both 1 to 50%.

[0014] Preferably, when the salt phase is a mixed aqueous solution of an organic amine and an inorganic ammonium salt, the volume ratio of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution used for mixing is 1:3 or 1:1, and the mass fractions of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution are both 5-25%.

[0015] Furthermore, the oil phase is any one of kerosene, petroleum ether, gasoline, kerosene, white oil, diesel, and cyclohexane.

[0016] Furthermore, the mass fraction of the pseudo-boehmite in the mixed sol is 25-33%.

[0017] Furthermore, the aging time is 2 to 6 hours; the aging temperature is 90 to 150° C.; the roasting temperature is 550 to 650° C., and the roasting time is 3 to 6 hours.

[0018] Furthermore, the height of the oil phase is 2 to 20 cm, and the height of the salt phase is 40 to 100 cm.

[0019] The present invention utilizes a mixed peptization method of pseudo-boehmite and basic aluminum chloride to increase the fluidity and solid content of the spheroidizing solution and enhance hydrothermal stability. The present invention utilizes a mixed solution of an inorganic ammonium salt and an organic amine as the forming liquid during the spheroidizing process, significantly reducing toxicity and pollution compared to aqueous ammonia, making the production process safer, greener, and more environmentally friendly. The spherical alumina carrier prepared by the present method exhibits a uniform particle size distribution (1.6 to 1.8 mm), a large surface area, a suitable pore structure, high mechanical strength, and good hydrothermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the spherical alumina product obtained in Example 1 of the present invention. Specific implementation plan

[0021] The technical solution of the invention is further described below in conjunction with specific embodiments.

[0022] Example 1

[0023] (1) Preparation of basic aluminum chloride sol

[0024] Weigh 24 g of aluminum powder, add 815 g of 5% hydrochloric acid aqueous solution, heat to dissolve, condense and reflux for 4 h to obtain basic aluminum chloride sol.

[0025] (2) Preparation of alumina sol

[0026] 446 g of pseudo-boehmite (produced by Sasol, Germany) was weighed and added to the basic aluminum chloride sol prepared in step (1). The mixture was stirred and peptized for 20 min to obtain an alumina sol (spheroidizing solution). The mass fraction of the pseudo-boehmite in the sol was 30%.

[0027] (3) Molding

[0028] In the spherical column of the carrier forming device for preparing spherical alumina, the upper layer is an oil phase and the lower layer is a salt phase. The upper oil phase is 8 cm thick kerosene and the lower salt phase is a 60 cm thick mixed solution of ammonium carbonate and cyclopropylamine, both with a mass fraction of 10%, wherein the volume ratio of ammonium carbonate to cyclopropylamine is 3:1. The alumina sol prepared in step (2) is dripped into the spherical column, aged at 100°C for 3 hours, and calcined at 600°C for 5 hours to obtain spherical alumina. The spherical alumina product has good sphericity, large surface area, and uniform particle size distribution (such as Figure 1 shown).

[0029] Example 2

[0030] (1) Preparation of basic aluminum chloride sol

[0031] The basic aluminum chloride sol was prepared in the same manner as in step (1) of Example 1.

[0032] (2) Preparation of alumina sol

[0033] 534 g of pseudo-boehmite was weighed, and the basic aluminum chloride sol prepared in step (1) was added thereto, and the mixture was stirred and peptized for 20 minutes to obtain an aluminum oxide sol. The mass fraction of the pseudo-boehmite in the sol was 33%.

[0034] (3) Molding

[0035] The molding is carried out in the same manner as in step (3) of Example 1.

[0036] Example 3

[0037] (1) Preparation of basic aluminum chloride sol

[0038] The basic aluminum chloride sol was prepared in the same manner as in step (1) of Example 1.

[0039] (2) Preparation of alumina sol

[0040] 323 g of pseudo-boehmite was weighed, and the basic aluminum chloride sol prepared in step (1) was added thereto, and the mixture was stirred and peptized for 20 min to obtain an alumina sol. The mass fraction of the pseudo-boehmite in the sol was 25%.

[0041] (3) Molding

[0042] The molding is carried out in the same manner as in step (3) of Example 1.

[0043] Example 4

[0044] (1) Preparation of basic aluminum chloride sol

[0045] The basic aluminum chloride sol was prepared in the same manner as in step (1) of Example 1.

[0046] (2) Preparation of alumina sol

[0047] Alumina sol was prepared in the same manner as in step (2) of Example 1.

[0048] (3) Molding

[0049] The upper layer of the spherical column is an oil phase, and the lower layer is a salt phase. The upper oil phase is 8 cm thick kerosene, and the lower salt phase is a 60 cm thick mixed solution of ammonium carbonate and cyclopropylamine, both with a mass fraction of 10%, wherein the volume ratio of ammonium carbonate to cyclopropylamine is 1:1. The alumina sol prepared in step (2) is dropped into the spherical column, aged at 100°C for 3 hours, and calcined at 600°C for 5 hours to obtain spherical alumina.

[0050] Example 5

[0051] (1) Preparation of basic aluminum chloride sol

[0052] The basic aluminum chloride sol was prepared in the same manner as in step (1) of Example 1.

[0053] (2) Preparation of alumina sol

[0054] Alumina sol was prepared in the same manner as in step (2) of Example 1.

[0055] (3) Molding

[0056] The upper layer of the spherical column is an oil phase, and the lower layer is a salt phase. The upper oil phase is 8 cm thick kerosene, and the lower salt phase is a 60 cm thick mixed solution of ammonium carbonate and cyclopropylamine, both of which have a mass fraction of 10%, wherein the volume ratio of ammonium carbonate to cyclopropylamine is 1:3. The alumina sol prepared in step (2) is dripped into the spherical column, aged at 100°C for 3 hours, and calcined at 600°C for 5 hours to obtain spherical alumina.

[0057] Example 6

[0058] (1) Preparation of basic aluminum chloride sol

[0059] The basic aluminum chloride sol was prepared in the same manner as in step (1) of Example 1.

[0060] (2) Preparation of alumina sol

[0061] Alumina sol was prepared in the same manner as in step (2) of Example 1.

[0062] (3) Molding

[0063] The upper layer of the spherical column is an oil phase, and the lower layer is a salt phase. The upper oil phase is 8 cm thick kerosene, and the lower salt phase is 60 cm thick ammonium carbonate solution with a mass fraction of 10%. The alumina sol prepared in step (2) is dripped into the spherical column, aged at 100°C for 3 hours, and calcined at 600°C for 5 hours to obtain spherical alumina.

[0064] Example 7

[0065] (1) Preparation of basic aluminum chloride sol

[0066] The basic aluminum chloride sol was prepared in the same manner as in step (1) of Example 1.

[0067] (2) Preparation of alumina sol

[0068] Alumina sol was prepared in the same manner as in step (2) of Example 1.

[0069] (3) Molding

[0070] The upper layer of the spherical column is an oil phase, and the lower layer is a salt phase. The upper oil phase is 8 cm thick kerosene, and the lower salt phase is 60 cm thick cyclopropylamine solution with a mass fraction of 10%. The alumina sol prepared in step (2) is dropped into the spherical column, aged at 100°C for 3 hours, and calcined at 600°C for 5 hours to obtain spherical alumina.

[0071] Comparative Example 1

[0072] (1) Preparation of basic aluminum chloride sol

[0073] The basic aluminum chloride sol was prepared in the same manner as in step (1) of Example 1.

[0074] (2) Oil column forming

[0075] The oil phase of the hot oil column consisted of 180 cm of liquid paraffin (Sinopharm Group Chemical Reagent Beijing Co., Ltd.) with a mass fraction of 8%. The aluminum chloride sol (sphering solution) prepared in step (1) and the hexamethylenetetramine solution were mixed and stirred and then dripped into the hot oil column. The mixture was aged at 100°C for 3 hours, washed, dried, and calcined at 600°C for 5 hours to obtain spherical alumina. During the experiment, it was found that the sphericity of the obtained product was poor.

[0076] Comparative Example 2

[0077] (1) Preparation of alumina sol

[0078] 50 g of pseudo-boehmite was weighed, added to 94 g of deionized water, stirred for 10 min, and then added with 0.5 ml of nitric acid, stirred and peptized for 20 min to obtain an alumina sol. The mass fraction of the pseudo-boehmite in the mixed sol was 25%.

[0079] (2) Oil-ammonia column molding

[0080] The upper layer of the oil-ammonia column is an oil phase, and the lower layer is a salt phase. The upper oil phase is 8 cm thick kerosene, and the lower salt phase is 60 cm thick ammonia aqueous solution with a mass fraction of 10%. The alumina sol (spherical solution) prepared in step (1) is dropped into the oil-ammonia column, aged at 100°C for 3 hours, and calcined at 600°C for 5 hours to obtain spherical alumina.

[0081] The spheroidizing solution prepared in Example 1 exhibited excellent flow properties, with a viscosity of up to 2560 mP·s. As shown in Table 1, this example exhibited optimal performance in terms of roundness, adhesion, tailing, and hardness, with a comprehensive score significantly superior to that of the other examples (scores ≥14 points) and the comparative example (highest score of only 10 points), fully demonstrating the superior performance of the spheroidizing solution of the present invention.

[0082] Table 1 Comparison of the properties of the spheroidizing solutions obtained in the examples and comparative examples

[0083]

[0084] The spherical alumina prepared in the present invention exhibits a variety of excellent properties. Table 2 shows a comparison of its performance with that of conventional spherical alumina products obtained in Comparative Examples 1 and 2. Table 2 shows that the spherical alumina prepared in the present invention exhibits superior performance in terms of crushing strength, specific surface area, and hydrothermal stability.

[0085] Specifically, when the mass fraction of pseudo-boehmite in the mixed sol is 30%, the resulting product achieves a crushing strength of 64 N / grain. The products of each embodiment of the present invention outperformed those of Comparative Examples 1 and 2 in terms of specific surface area and hydrothermal stability. The specific surface area of ​​the product of Comparative Example 1 decreased by 21% after 18 hours of hydrothermal treatment, and its hydrothermal stability was significantly inferior to that of the product of the present invention.

[0086] Table 2 Performance data of spherical alumina

[0087]

[0088] The spherical alumina produced by the present invention achieves a significant increase in solid content, a significant increase in production efficiency, and effective control of production costs. In addition, the reagent raw materials used in the present invention are substantially non-toxic and have the characteristics of being green and environmentally friendly.

Claims

1. A method for preparing spherical alumina, characterized in that: An appropriate amount of pseudo-boehmite and basic aluminum chloride sol are mixed to obtain a mixed sol; the mixed sol is added into a spherical column, and after aging and roasting, a spherical alumina product is obtained; wherein the upper layer in the column cavity of the spherical column is an oil phase, and the lower layer is a salt phase.

2. The method for preparing spherical alumina according to claim 1, wherein: The salt phase is an organic amine aqueous solution, an inorganic ammonium salt aqueous solution or a mixed aqueous solution of the two.

3. The method for preparing spherical alumina according to claim 2, wherein: The organic amine is any one of dimethylformamide, dimethylacetamide, triethylamine, cyclopropylamine and formamide; the inorganic ammonium salt is any one of ammonium carbonate, ammonium bicarbonate, ammonium chloride and ammonium nitrate.

4. The method for preparing spherical alumina according to claim 3, wherein: The organic amine is cyclopropylamine or dimethylformamide, and the inorganic ammonium salt is ammonium carbonate.

5. The method for preparing spherical alumina according to claim 3, wherein: When the salt phase is a mixed aqueous solution of organic amine and inorganic ammonium salt, the volume ratio of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution used for mixing is 1:3 to 3:1, and the mass fractions of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution are both 1 to 50%.

6. The method for preparing spherical alumina according to claim 5, wherein: When the salt phase is a mixed aqueous solution of organic amine and inorganic ammonium salt, the volume ratio of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution used for mixing is 1:3 or 1:1, and the mass fractions of the organic amine aqueous solution and the inorganic ammonium salt aqueous solution are both 5-25%.

7. The method for preparing spherical alumina according to any one of claims 1 to 6, characterized in that: The oil phase is any one of kerosene, petroleum ether, gasoline, kerosene, white oil, diesel, and cyclohexane.

8. The method for preparing spherical alumina according to claim 7, wherein: The mass fraction of the pseudo-boehmite in the mixed sol is 25-33%.

9. The method for preparing spherical alumina according to claim 8, wherein: The aging time is 2 to 6 hours, and the aging temperature is 90 to 150° C.; the roasting temperature is 550 to 650° C., and the roasting time is 3 to 6 hours.

10. The method for preparing spherical alumina according to claim 9, wherein: The height of the oil phase in the spherical column cavity is 2 to 20 cm, and the height of the salt phase is 40 to 100 cm.

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