A method for preparing a millimeter-sized alumina spherical carrier

Abstract

The application discloses a preparation method of millimeter-level alumina spherical carriers, and the preparation method comprises the following steps: forming a sol to obtain the spherical carriers through oil column forming, adding an alkali aluminum chloride sol and an alumina seed solution in the preparation process of the sol, and the mass of the alumina seed solution accounts for 0.1%-15% of the mass of the alkali aluminum chloride sol. The preparation method of the millimeter-level alumina spherical carriers improves the hydrothermal stability of the carriers, and the shrinkage of the alumina carriers is higher.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of inorganic catalytic material preparation, and particularly relates to an oil column forming method for preparing spherical alumina with high hydrothermal stability. BACKGROUND

[0002] As a catalyst and a catalyst carrier, the shape of Al2O3 has a great influence on the catalyst reaction. Common shapes of Al2O3 include spherical, strip-shaped and clover-shaped, etc. With the continuous advancement of the industrialization process of the moving bed technology, spherical alumina carriers are widely used in moving bed reactors due to good sphericity, smooth surface and high strength, and the demand is also increasing. At present, there are many studies on the preparation method of millimeter-sized alumina spherical carrier for fluidized bed at home and abroad, and the main methods include hot oil column method, oil-ammonia column method and water column method.

[0003] The hot oil column forming method for preparing spherical alumina from aluminum sol was first disclosed in patent US2620314. The aluminum sol is prepared by reacting metallic aluminum and hydrochloric acid solution, the sol is mixed with hexamethylenetetramine solution, and then is formed in a hot oil column device, and is aged in an oil bath under pressure, washed with water, dried, calcined and treated with water vapor to obtain spherical alumina. The method needs many processes, each process needs a long time, hydrochloric acid seriously corrodes the equipment, and the hydrothermal stability of the obtained alumina spheres is low.

[0004] The method disclosed in US4399119 includes reacting hydrochloric acid and gibbsite under high temperature and high pressure to obtain an aqueous solution of basic aluminum chloride, supplementing part of aluminum to adjust the aluminum content in the sol, adding ammonia water to form an aqueous sol of aluminum chloride containing ammonium chloride, mixing the sol with a gelling agent that can be decomposed during heating, forming into spherical alumina through hot oil column, aging, washing with water, drying and calcining. The method needs to be carried out under high temperature and high pressure by using hydrochloric acid to leach metallic aluminum or gibbsite, which seriously corrodes the equipment, the impurity content of the raw material is high, and the processes such as aging after forming, pressurized aging and washing with water consume a long time.

[0005] Mitsche et al. prepared an aluminum sol with a density of 1.40 g·mL -1 , an Al mass percentage of 14.2%, and an Al / Cl molar ratio of 1.15 by dissolving aluminum powder in dilute hydrochloric acid; and obtained spherical alumina particles with a specific surface area of 421 m 2 ·g -1 , a pore volume of 0.32 mL·g -1 and an average pore size of 3 nm through processes such as forming and aging.

[0006] Moser et al. used an oil column with a length of 1.5 m as an experimental platform, and investigated the influence of forming oil with different viscosities on the forming and morphology of spherical alumina. When the viscosity of the forming oil is in the range of 80-150 mm 2 ·s-1 When the viscosity of the forming oil is small, the falling speed of the droplets in the oil column is fast, and it is difficult to form. When the viscosity of the forming oil is large, the falling speed of the droplets in the oil column is slow, and it is easy to cause adhesion between the droplets, and the morphology of the obtained spherical gel particles is poor.

[0007] In CN114180607A disclosed by Professor Li Dianqing's team of Beijing University of Chemical Technology, a kind of spherical alumina with surface flower cluster lamellar structure and its preparation method are reported. Its feature is that a long-chain compound containing a large number of hydroxyl and carboxyl groups is added during the preparation of the forming sol, and the pore structure of the spherical alumina is modified. The carbonyl and hydroxyl groups will form hydrogen bonds with Al-OH in the aluminum sol during the forming process, guiding the formation of lamellar structure on the surface, and preparing spherical alumina with flower cluster lamellar structure. At the same time, key technologies such as magnetic separation-process reduction of iron-containing aluminum sol, micro-flow injection molding, spray dispersion-oil column forming, etc. are developed, which can control the preparation of spherical alumina-based carrier materials with particle size ranging from 0.1 to 3.0 mm. However, the long-chain compound containing a large number of hydroxyl and carboxyl groups introduced in this technology is an organic compound, which is decomposed during the subsequent high-temperature calcination process. Although it can increase the specific surface area and pore volume of spherical alumina, it cannot improve its hydrothermal stability.

[0008] CN114180608A disclosed by Petrochemical Research Institute of China Petroleum & Chemical Corporation, a method for preparing spherical alumina is disclosed, which comprises adding an acid solution to an alumina suspension to obtain an alumina sol, adding a water-soluble organic polymer monomer and a crosslinking agent to the alumina sol to form a mixture, and dropping the mixture into a hot oil column to form a ball. This method uses the polymerization of organic polymer monomer to solidify the alumina beads, and does not use hexamethylenetetramine as a gelling agent.

[0009] CN111792659A disclosed by Liming Chemical Research and Design Institute, a method for preparing spherical alumina by oil column forming process is disclosed, characterized in that one or more of pseudo-boehmite powder and activated carbon are added to the aluminum sol, and the prepared spherical alumina has a bulk density ≤0.45 g / cm 3 , and an average compressive strength ≥40 N. It is found in practice that the addition of pseudo-boehmite powder to the aluminum sol easily causes local agglomeration of the powder and the aluminum sol into small particles, and the uniformity of the material is poor. In the subsequent hot oil column forming process, when the material is dropped into the forming oil column through the dispersion dropping tube, the needle is seriously clogged, the forming efficiency is low, and the particle sphericity is poor.

[0010] CN1048229C, published by the Tianjin Chemical Research Institute of the Ministry of Chemical Industry, discloses a process for preparing low-density, large-pore-volume spherical alumina. The process is characterized by using aluminum salts and aluminates as raw materials. First, large-grained boehmite seed crystals are prepared at 60-80℃ and pH 7-9. Then, the aluminum salts and aluminates are fed in a co-current manner to neutralize and generate alumina hydrate dominated by boehmite. When the ratio of alumina in the prepared seed crystals to the total alumina in the final neutralization product is controlled within the range of 0.05-0.45, the prepared spherical alumina exhibits large pore volume and low bulk density. This technology first prepares large-grained pseudo-boehmite seed crystals using aluminum salts and aluminates as reactants under specific conditions, and then continues to carry out a neutralization reaction using the same aluminum salts and aluminates. The characteristics of the seed crystals are the same as those of the raw materials that undergo the neutralization reaction, but the reaction conditions are different. Moreover, it does not require processes such as pressure aging, water washing, and steam pore expansion treatment, making it particularly suitable as a carrier for immobilized enzymes. However, when used in high-temperature and high-pressure scenarios such as petrochemicals that require frequent regeneration, it is prone to problems such as pore structure collapse and loss, and insufficient hydrothermal stability.

[0011] In recent years, the application fields of spherical alumina prepared by the oil column forming method as a catalyst or catalyst support have been continuously expanding, involving petrochemical, fine chemical and coal chemical industries, providing broad development space for the oil column forming method for preparing spherical alumina technology system.

[0012] The oil column molding method for preparing spherical alumina involves reacting industrial-grade hydrochloric acid with aluminum powder to synthesize basic aluminum chloride sol. After removing solid impurities from the aluminum sol, it is thoroughly mixed with a hexamethylenetetramine solution as a gelling agent. The mixed sol is then dropped into a hot oil column at 95–98°C to form the alumina. Following aging, washing, drying, and calcination, spherical alumina is obtained. This oil column molding method for preparing spherical alumina has seen its applications as a catalyst or catalyst support expanding into petrochemicals, fine chemicals, and coal chemicals. The support exhibits high sphericity, good strength, and low wear rate. However, it suffers from low hydrothermal stability; under high-temperature hydrothermal treatment conditions, the specific surface area decays rapidly, affecting the high dispersion of the active components and degrading catalytic performance.

[0013] Compared to the oil column forming method, the oil-ammonia column forming method is an improvement and development of the oil column forming device. This method uses boehmite as the aluminum source and ammonia as the coagulant. First, a dilute acid (nitric acid, acetic acid, etc.) is used as a solvent to react with the boehmite precursor to prepare a free-flowing sol. Then, the sol is dropped into an oil-ammonia column, with an upper layer of oil and a lower layer of ammonia at a certain concentration, through a dispersing dropper. A neutralization reaction occurs behind the ammonia layer, and the ammonia rapidly gels and solidifies to form gel spheres. The spherical alumina prepared by the oil-ammonia column method is low-cost and quick, retains the properties of the original boehmite powder, and therefore has high hydrothermal stability. The disadvantages are that the rapid coagulation rate of ammonia leads to slightly poorer sphericity and a slightly higher wear rate.

[0014] In summary, it is necessary to provide a method for preparing spherical alumina using an oil column forming process to solve the problems existing in the prior art. Summary of the Invention

[0015] The purpose of this invention is to solve the problems of poor hydrothermal stability and large specific surface area loss during repeated regeneration of spherical alumina carriers obtained by the existing oil column molding technology, and to form a spherical alumina carrier preparation technology with high hydrothermal stability, good sphericity and high particle strength.

[0016] To achieve the above objectives, the present invention provides a method for preparing millimeter-scale alumina spherical carriers, the method comprising:

[0017] The spherical carrier is obtained by molding the sol with an oil column. The sol includes basic aluminum chloride sol and alumina seed solution. The mass of the alumina seed solution accounts for 0.1% to 15% of the mass of the basic aluminum chloride sol.

[0018] The method for preparing millimeter-scale alumina spherical carriers of the present invention, wherein the mass of the alumina seed solution accounts for 0.8% to 13% of the mass of the basic aluminum chloride sol.

[0019] The method for preparing millimeter-scale alumina spherical carriers of the present invention includes the following steps in the preparation of the molded sol:

[0020] Alumina seed solution is added dropwise to basic aluminum chloride sol, and then a coagulant is added to obtain a shaped sol.

[0021] The method for preparing millimeter-scale alumina spherical carriers of the present invention includes the following steps in the preparation of the basic aluminum chloride sol:

[0022] Aqueous hydrochloric acid is added to aluminum powder to react and produce basic aluminum chloride sol.

[0023] The method for preparing millimeter-sized alumina spherical carriers of the present invention, wherein the aluminum powder has a purity of ≥99% and a particle size of 100μm-350μm;

[0024] The concentration of the hydrochloric acid aqueous solution is 12wt%-25wt%; the Al / Cl mass ratio in the reaction solution is controlled to be 0.4-2.5.

[0025] The reaction temperature is 80℃-100℃, and the reaction time is 2h-6h.

[0026] The method for preparing millimeter-scale alumina spherical carriers of the present invention includes the following steps in the preparation of the alumina seed solution:

[0027] Boehmite powder was dissolved in deionized water and stirred to obtain a suspension; nitric acid aqueous solution was added to the suspension and ultrasonically treated to form a uniformly dispersed alumina seed solution.

[0028] The method for preparing millimeter-sized alumina spherical carriers of the present invention, wherein the particle size of the pseudoboehmite powder is 150μm-300μm and the colloidal index of the pseudoboehmite powder is ≥97%.

[0029] The pseudoboehmite is at least one of SB powder, TM70 powder, and high-purity low-sodium aluminum hydroxide.

[0030] The concentration of the nitric acid aqueous solution is 10wt%-30wt%; the Al / NO3 mass ratio in the alumina seed solution is controlled to be 0.1-5;

[0031] The ultrasonic treatment time is 1-10 minutes.

[0032] The method for preparing millimeter-scale alumina spherical carriers of the present invention includes a coagulant mass fraction of 25%-45% and a coagulant accounting for 15%-30% of the total mass of the formed sol.

[0033] The coagulant is at least one of urea and hexamethylenetetramine aqueous solution, preferably a hexamethylenetetramine aqueous solution with a mass fraction of 25%-45%;

[0034] The sol-gel of the present invention is prepared in a reactor with stirring and cold bath circulation. The temperature of the material in the reactor is 0-10℃, the stirring speed is 200r / min-400r / min, and the stirring time is 20min-40min.

[0035] The method for preparing millimeter-scale alumina spherical carriers of the present invention includes the following preparation process: the sol-gel forming process via oil column molding:

[0036] The sol is pumped to a disperser via a peristaltic pump, and then dripped into the forming column through a dispersing nozzle. The formed spheres are collected at the bottom of the hot oil column and then transferred to an aging reactor for aging. After washing, the sol is dried and calcined to obtain alumina spheres.

[0037] The method for preparing millimeter-scale alumina spherical carriers of the present invention includes a jacketed forming column, wherein the jacket is heated by a water bath or an oil bath.

[0038] The dispersing dropper drips into the hot oil in the molding column, and the temperature of the hot oil is 80℃-100℃.

[0039] The hot oil is at least one of vacuum pump oil, paraffin oil, and mineral oil;

[0040] The disperser is a needle-type disperser, and the needle can be a single needle or multiple needles.

[0041] The method for preparing the millimeter-scale alumina spherical carrier of the present invention includes an aging temperature of 120℃-150℃, a pressure of 0.5MPa-1.0MPa, and a time of 2h-6h.

[0042] The drying temperature is 60℃-120℃;

[0043] The roasting temperature is 500℃-1000℃, and the time is 4h-8h;

[0044] The alumina microspheres have a particle size of 0.1 mm to 5 mm.

[0045] The present invention discloses a method for preparing millimeter-sized alumina spherical carriers. The aluminum source in the alumina sol comprises two parts: a basic aluminum chloride sol and an alumina seed solution. The alumina seed solution exhibits excellent colloidal properties and strong adhesion. When the alumina seed solution is introduced into the basic aluminum chloride sol, it retains the characteristics of boehmite powder, resulting in narrowly distributed spherical particles. The surface hydroxyl groups of the alumina seed solution interact with the Al-OH groups in the basic aluminum chloride sol, forming hydrogen bonds. During drying and calcination, the particle shrinkage increases, and the chemical bonding between species is strengthened, effectively inhibiting high-temperature sintering and phase transformation of alumina. Microscopically, this results in a more uniform particle distribution and a tighter arrangement and bonding between particles, thereby suppressing the shrinkage and sintering between Al-OH groups under high-temperature steam, improving the hydrothermal stability of the carrier, and yielding an alumina carrier with a higher shrinkage rate.

[0046] The millimeter-sized alumina spherical supports obtained by the preparation method of this invention are mainly used as industrial catalyst supports or adsorbents. They are suitable for both fixed-bed and moving-bed processes. When used in high-temperature, high-pressure, and frequent regeneration scenarios, the pore structure is not easily lost, and the hydrothermal stability is excellent. In a fixed-bed reactor at a temperature of 600℃-700℃ and a water content of 8wt%-15wt%, the specific surface area decay of the millimeter-sized alumina spherical supports obtained by the preparation method of this invention can be controlled to within 5% over 24 hours. Attached Figure Description

[0047] Figure 1 The image shown is a SEM image of the alumina seed crystals in Example 1, magnified 1000 times.

[0048] Figure 2 SEM image of alumina seed crystals in Example 1: magnification 10000.

[0049] Figure 3SEM image of the sample without alumina seed crystals in Comparative Example 1: magnification 10000.

[0050] Figure 4 SEM image of the alumina seed sample introduced in Example 1: magnification 10000. Detailed Implementation

[0051] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Obviously, the embodiments specifically described below are merely a portion of the embodiments of the present invention, and not all of them; therefore, the present invention is not limited to the following description.

[0052] Example 1

[0053] (1) Preparation of basic aluminum chloride sol

[0054] Weigh 100g of aluminum powder with a purity ≥99% and a particle size of 100μm-200μm, and slowly add 1125g of a 15wt% hydrochloric acid aqueous solution (Al / Cl = 0.8). Control the reaction temperature at 98℃ for heating and dissolution, and reflux the reaction for 4h to obtain basic aluminum chloride sol.

[0055] (2) Preparation of alumina seed solution

[0056] Weigh 2g of pseudoboehmite with a particle size of 150μm-200μm (colloidal solubility index 99%), dissolve it in 10g of deionized water, stir to obtain a suspension, add 10g of 10wt% nitric acid aqueous solution (Al / NO3 = 1.5); sonicate for 5min to form a uniformly dispersed alumina seed solution.

[0057] (3) Preparation of molding sol

[0058] Add the basic aluminum chloride sol from step (1) to a reactor with stirring and cold bath circulation, control the material temperature at 5°C, and the stirring speed at 300 r / min. Add the alumina seed solution from step (2) dropwise, with the alumina seed solution accounting for 1.8% of the mass of the basic aluminum chloride sol. Stir for 20 min. Then add 267 g of a 40% hexamethylenetetramine aqueous solution (coagulant) to the above solution, controlling the coagulant to account for 17.5% of the total mass of the shaped sol, and obtain the shaped sol.

[0059] (4) Preparation of spherical carriers by oil column molding

[0060] The shaped sol obtained in step (3) was transported to a disperser via a peristaltic pump, and then dripped into vacuum pump oil at 95°C through a dispersing nozzle (0.8 mm in diameter). The shaped microspheres were collected at the bottom of the hot oil column and then transferred to an aging reactor. The microspheres were aged at 150°C and 0.5 MPa for 6 hours to obtain alumina microspheres. After washing, the microspheres were dried at 60°C for 4 hours, then heated to 100°C for 4 hours, and finally calcined at 600°C for 4 hours to obtain alumina microspheres with a particle size of 1.5 mm-2 mm. The results of their physicochemical property tests are shown in Table 1.

[0061] Example 2

[0062] (1) Preparation of basic aluminum chloride sol

[0063] Weigh 50g of aluminum powder with a purity ≥99% and a particle size of 100μm-200μm, add it to 1125g of 15wt% hydrochloric acid aqueous solution (Al / Cl = 0.4), heat to dissolve at a controlled temperature of 95℃, and reflux for 6h to obtain basic aluminum chloride sol.

[0064] (2) Preparation of alumina seed solution

[0065] Weigh 2g of pseudoboehmite with a particle size of 200μm-300μm (colloidal solubility index 98%), dissolve it in 21g of deionized water, stir to obtain a suspension, add 147g of 10wt% nitric acid aqueous solution (Al / NO3 = 0.1) to it; sonicate for 5min to form a uniformly dispersed alumina seed solution.

[0066] (3) Preparation of molding sol

[0067] Add the basic aluminum chloride sol from step (1) to a reactor with stirring and cold bath circulation, control the material temperature at 10°C, and the stirring speed at 200 r / min. Add the alumina seed solution from step (2) dropwise, with the alumina seed solution accounting for 12.6% of the mass of the basic aluminum chloride sol. Stir for 20 min. Then add 336 g of a 40% hexamethylenetetramine aqueous solution (coagulant) to the above solution, controlling the coagulant to account for 20% of the total mass of the shaped sol, to obtain the shaped sol.

[0068] (4) Preparation of spherical carriers by oil column molding

[0069] The shaped sol obtained in step (3) was transported to a disperser via a peristaltic pump, and then dripped into vacuum pump oil at 100°C through a dispersing nozzle (0.8 mm in diameter). The shaped microspheres were collected at the bottom of the hot oil column and then transferred to an aging reactor. The microspheres were aged at 120°C and 0.8 MPa for 3 hours to obtain alumina microspheres. After washing, the microspheres were dried at 80°C for 4 hours, then heated to 110°C for 4 hours, and finally calcined at 600°C for 4 hours to obtain alumina microspheres with a particle size of 1.5 mm-2 mm. The results of their physicochemical property tests are shown in Table 1.

[0070] Example 3

[0071] (1) Preparation of basic aluminum chloride sol

[0072] Weigh 50g of aluminum powder with a purity ≥99% and a particle size of 100μm-200μm, add it to 108g of 25wt% hydrochloric acid aqueous solution (Al / Cl = 2.5), heat to dissolve at a controlled temperature of 85℃, and reflux for 6h to obtain basic aluminum chloride sol.

[0073] (2) Preparation of alumina seed solution

[0074] Weigh 2g of pseudoboehmite with a particle size of 250μm-300μm (colloidal solubility index 97%), dissolve it in 21g of deionized water, stir to obtain a suspension, add 2.9g of 10wt% nitric acid aqueous solution (Al / NO3 = 5) to it; sonicate for 1min to form a uniformly dispersed alumina seed solution.

[0075] (3) Preparation of molding sol

[0076] Add the basic aluminum chloride sol from step (1) to a reactor with stirring and cold bath circulation, control the material temperature at 2°C, and the stirring speed at 300 r / min. Add the alumina seed solution from step (2) dropwise, with the alumina seed solution accounting for 14% of the mass of the basic aluminum chloride sol. Stir for 20 min. Then add 28 g of 40% hexamethylenetetramine aqueous solution (coagulant) to the above solution, controlling the coagulant to account for 15% of the total mass of the shaped sol, and obtain the shaped sol.

[0077] (4) Preparation of spherical carriers by oil column molding

[0078] The shaped sol obtained in step (3) was transported to a disperser via a peristaltic pump, and then dripped into vacuum pump oil at 90°C through a dispersing nozzle (0.8 mm in diameter). The shaped microspheres were collected at the bottom of the hot oil column and then transferred to an aging reactor. The microspheres were aged at 140°C and 0.7 MPa for 4 hours to obtain alumina microspheres. After washing, the microspheres were dried at 60°C for 2 hours, then heated to 100°C for 4 hours, and finally calcined at 600°C for 4 hours to obtain alumina microspheres with a particle size of 1.5 mm-2 mm. The results of their physicochemical property tests are shown in Table 1.

[0079] Example 4

[0080] (1) Preparation of basic aluminum chloride sol

[0081] Weigh 100g of aluminum powder with a purity ≥99% and a particle size of 100μm-200μm, add it to 601g of a 15wt% hydrochloric acid aqueous solution (Al / Cl = 1.5), heat to dissolve at a controlled temperature of 98℃, and reflux for 2h to obtain basic aluminum chloride sol.

[0082] (2) Preparation of alumina seed solution

[0083] Weigh 2g of pseudoboehmite with a particle size of 150μm-250μm (colloidal solubility index 98%), dissolve it in 50g of deionized water, stir to obtain a suspension, add 3.7g of 20wt% nitric acid aqueous solution (Al / NO3=2); sonicate for 10min to form a uniformly dispersed alumina seed solution.

[0084] (3) Preparation of molding sol

[0085] Add the basic aluminum chloride sol from step (1) to a reactor with stirring and cold bath circulation, control the material temperature at 8°C, and the stirring speed at 300 r / min. Add the alumina seed solution from step (2) dropwise, with the alumina seed solution accounting for 7.4% of the mass of the basic aluminum chloride sol. Stir for 30 min. Then add 289 g of a 45% hexamethylenetetramine aqueous solution (coagulant) to the above solution, controlling the coagulant to account for 25% of the total mass of the shaped sol, and obtain the shaped sol.

[0086] (4) Preparation of spherical carriers by oil column molding

[0087] The shaped sol obtained in step (3) was transported to a disperser via a peristaltic pump, and then dripped into vacuum pump oil at 95°C through a dispersing dropper (0.8 mm in diameter). The shaped microspheres were collected at the bottom of the hot oil column and then transferred to an aging reactor. The microspheres were aged at 150°C and 0.5 MPa for 6 hours to obtain alumina microspheres. After washing, the microspheres were dried at 60°C for 4 hours, then heated to 120°C for 4 hours, and finally calcined at 600°C for 4 hours to obtain alumina microspheres with a particle size of 1.5 mm-2 mm. The results of their physicochemical properties are shown in Table 1.

[0088] Example 5

[0089] (1) Preparation of basic aluminum chloride sol

[0090] Weigh 100g of aluminum powder with a purity ≥99% and a particle size of 100μm-200μm, add it to 1125g of 15wt% hydrochloric acid aqueous solution (Al / Cl = 0.8), heat to dissolve at a controlled temperature of 98℃, and reflux for 4h to obtain basic aluminum chloride sol.

[0091] (2) Preparation of alumina seed solution

[0092] Weigh 1g of pseudoboehmite with a particle size of 250μm-300μm (colloidal solubility index 99%), dissolve it in 5g of deionized water, stir to obtain a suspension, add 5g of 30wt% nitric acid aqueous solution (Al / NO3 = 0.7); sonicate for 10min to form a uniformly dispersed alumina seed solution.

[0093] (3) Preparation of molding sol

[0094] Add the basic aluminum chloride sol from step (1) to a reactor with stirring and cold bath circulation, control the material temperature at 5°C, and the stirring speed at 300 r / min. Add the alumina seed solution from step (2) dropwise, with the alumina seed solution accounting for 0.9% of the mass of the basic aluminum chloride sol. Stir for 20 min. Then add 267 g of a 40% hexamethylenetetramine aqueous solution (coagulant) to the above solution, controlling the coagulant to account for 17.8% of the total mass of the shaped sol, and obtain the shaped sol.

[0095] (4) Preparation of spherical carriers by oil column molding

[0096] The shaped sol obtained in step (3) was transported to a disperser via a peristaltic pump, and then dripped into vacuum pump oil at 95°C through a dispersing dropper (0.8 mm in diameter). The shaped microspheres were collected at the bottom of the hot oil column and then transferred to an aging reactor. The microspheres were aged at 150°C and 0.5 MPa for 6 hours to obtain alumina microspheres. After washing, the microspheres were dried at 60°C for 4 hours, then heated to 120°C for 4 hours, and finally calcined at 600°C for 4 hours to obtain alumina microspheres with a particle size of 1.5 mm-2 mm. The results of their physicochemical properties are shown in Table 1.

[0097] Example 6

[0098] Alumina microspheres were prepared according to the method in Example 1, except that the oil phase used in step (4) for preparing the spherical carrier by oil column molding was mineral oil, and the molding temperature was 100℃. The results of its physicochemical performance testing are shown in Table 1.

[0099] Example 7

[0100] Alumina microspheres were prepared according to the method in Example 1, except that the concentration of the hexamethylenetetramine aqueous solution was 30% in step (3) of the preparation of the sol. The results of its physicochemical properties are shown in Table 1.

[0101] Example 8

[0102] Alumina microspheres were prepared according to the method of Example 1. The difference was that in the preparation of the sol in step (3), the coagulant was 305 g of urea solution with a mass fraction of 30%. The results of its physicochemical performance test are shown in Table 1.

[0103] Comparative Example 1

[0104] (1) Preparation of basic aluminum chloride sol

[0105] Weigh 100g of aluminum powder with a purity ≥99% and a particle size of 100μm-200μm, add it to 1125g of 15wt% hydrochloric acid aqueous solution (Al / Cl=0.8), control the reaction temperature at 98℃ for heating and dissolution, and reflux the reaction for 4h to obtain basic aluminum chloride sol.

[0106] (2) Preparation of molding sol

[0107] Add the basic aluminum chloride sol from step (1) to a reactor with stirring and cold bath circulation, control the material temperature at 5°C and the stirring speed at 300 r / min, then add 267 g of 40% hexamethylenetetramine aqueous solution (coagulant) to the above solution, controlling the coagulant to account for 17.9% of the total mass of the shaped sol, and obtain the shaped sol.

[0108] (3) Preparation of spherical carriers by oil column molding

[0109] The shaped sol obtained in step (2) was transported to a disperser via a peristaltic pump, and then dripped into vacuum pump oil at 95°C through a dispersing nozzle (0.8 mm in diameter). The shaped microspheres were collected at the bottom of the hot oil column and then transferred to an aging reactor. The microspheres were aged at 150°C and 0.5 MPa for 6 hours to obtain alumina microspheres. After washing, the microspheres were dried at 60°C for 4 hours, then heated to 100°C for 4 hours, and finally calcined at 600°C for 4 hours to obtain alumina microspheres with a particle size of 1.5 mm-2 mm. The results of their physicochemical property tests are shown in Table 1.

[0110] Comparative Example 2

[0111] (1) Preparation of basic aluminum chloride sol

[0112] Weigh 100g of aluminum powder with a purity ≥99% and a particle size of 100μm-200μm, add it to 1350g of hydrochloric acid aqueous solution with a concentration of 10wt%, control the reaction temperature at 95℃ for heating and dissolving, and reflux the reaction for 4h to obtain basic aluminum chloride sol.

[0113] (2) Add 7% by weight of boehmite and 400g by weight of 35% hexamethylenetetramine aqueous solution to the aluminum sol. After mixing evenly, drop the mixture into an oil column at 95°C using a dispersing dropper.

[0114] The experiment revealed that during the mixing of basic aluminum chloride sol and boehmite, numerous agglomerated particles appeared in the basic aluminum chloride sol. Even after further ultrasonic dispersion, the material uniformity remained poor. When dispensed through a dispersing dropper, needle blockage was easily caused, resulting in poor particle size uniformity and low forming efficiency. The physicochemical properties test results are shown in Table 1.

[0115] Performance Evaluation

[0116] The alumina microsphere samples prepared in the examples and comparative examples were added to a fixed-bed reactor and hydrothermally treated for 24 h at a temperature of 650 °C and a water content of 12 wt%. The specific surface area results of the alumina microsphere samples are shown in Table 1.

[0117] Table 1 Performance parameters of the samples prepared in the examples and comparative examples.

[0118]

[0119]

[0120] As can be seen from the results in Table 1, the alumina spherical carrier prepared by this invention has the advantages of high particle strength and strong hydrothermal stability compared with the spherical alumina prepared without alumina seed crystals.

[0121] The alumina microspheres obtained in Example 1 and Comparative Example 1 were characterized, and the results are shown in the figure. Figures 1-4 .Depend onFigure 1 , Figure 2 As can be seen, the alumina seed crystals were magnified by SEM at 1000 and 10000 magnifications, respectively. The alumina seed crystal solution retained the characteristics of the pseudoboehmite raw powder, which consisted of spherical particles with a narrow particle distribution. Figure 3 , Figure 4 The images show SEM images of the carriers prepared before and after the addition of alumina seed crystals in Comparative Example 1 and Example 1, respectively. It can be seen that after the addition of alumina seed crystal solution, the microscopic size shows a more uniform particle distribution and a tighter arrangement and bonding between particles.

[0122] The embodiments described above are merely preferred embodiments of the present invention and are by no means intended to limit the implementation of the present invention. Those skilled in the art can make other variations or equivalent embodiments based on the above description. It is impossible to exhaustively list all possible implementations here. Any obvious variations, modifications, or equivalent alterations derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing millimeter-scale alumina spherical carriers, characterized in that, include: The spherical carrier is obtained by molding the sol with an oil column. The sol includes basic aluminum chloride sol and alumina seed solution. The mass of the alumina seed solution accounts for 0.1% to 15% of the mass of the basic aluminum chloride sol. The preparation process of the shaped sol includes: dropping an alumina seed solution into a basic aluminum chloride sol, and then adding a coagulant to obtain the shaped sol; The preparation process of the basic aluminum chloride sol includes: adding hydrochloric acid aqueous solution to aluminum powder and reacting to obtain basic aluminum chloride sol; The preparation process of the alumina seed solution includes: dissolving boehmite powder in deionized water and stirring to obtain a suspension; adding nitric acid aqueous solution to the suspension and ultrasonically treating it to form a uniformly dispersed alumina seed solution.

2. The method for preparing millimeter-scale alumina spherical carriers according to claim 1, characterized in that, The mass of the alumina seed solution accounts for 0.8% to 13% of the mass of the basic aluminum chloride sol.

3. The method for preparing millimeter-scale alumina spherical carriers according to claim 1, characterized in that, The aluminum powder has a particle size of 100μm-350μm; the Al / Cl mass ratio in the reaction solution is controlled to be 0.4-2.

5.

4. The method for preparing millimeter-scale alumina spherical carriers according to claim 1, characterized in that, The gel solubility index of the pseudoboehmite powder is ≥97%, and the particle size of the pseudoboehmite powder is 150μm-300μm.

5. The method for preparing millimeter-scale alumina spherical carriers according to claim 1, characterized in that, The pseudoboehmite is at least one of SB powder, TM70 powder, and high-purity low-sodium aluminum hydroxide.

6. The method for preparing millimeter-scale alumina spherical carrier according to claim 1, characterized in that, The concentration of the nitric acid aqueous solution is 10wt%-30wt%, and the Al / NO3 mass ratio in the alumina seed solution is controlled to be 0.1-5.

7. The method for preparing millimeter-scale alumina spherical carriers according to claim 1, characterized in that, The ultrasonic treatment time is 1-10 minutes.

8. The method for preparing millimeter-scale alumina spherical carrier according to claim 1, characterized in that, The mass fraction of the coagulant is 25%-45%; the coagulant accounts for 15%-30% of the total mass of the sol; the coagulant is at least one of urea and hexamethylenetetramine aqueous solution.

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