Alumina microspheres and methods for making the same

Abstract

The application belongs to the technical field of industrial catalysts, and provides an alumina microsphere and a preparation method thereof.The method comprises the following steps: pre-solidification forming is performed on AlOOH solid sol to obtain an alumina pre-solidification gel; the alumina pre-solidification gel is placed in an alcohol solution to perform aging, and alumina gel microspheres are obtained; a temperature gradient gradient elution is performed on the alumina gel microspheres by using carbon diol, and the alumina gel microspheres after the temperature gradient gradient elution are dried and calcined to obtain alumina microspheres; wherein the alcohol solution comprises carbon octanol, carbon tetraol and an initiator, and the temperature gradient gradient elution comprises gradient temperature drop elution.The method can reduce the generation of defects of the alumina microspheres, so that the crushing strength of the alumina microspheres is improved while the specific surface area of the alumina microspheres is maintained.

Description

Technical Field

[0001] This invention relates to the field of industrial catalyst technology, specifically to an alumina microsphere and its preparation method. Background Technology

[0002] Catalytic reactions have become a crucial cornerstone of modern chemical production, and the properties of the support (such as alumina) play a vital role in the activity and selectivity of the entire catalytic reaction, as well as the safety and reliability of industrial production. Among these, the physical and chemical properties of the support, such as acid-base sites, specific surface area, dispersion of active metals, electron distribution, oxygen vacancies, and anti-coking properties, have a significant impact. The mechanical properties of the support also play a crucial role in the long-term stable operation of chemical production.

[0003] With the large-scale application of fluidized bed and moving bed reactors, the requirements for the mechanical properties of alumina microspheres are becoming increasingly stringent. While existing methods for enhancing carrier strength, such as elemental doping, process optimization, and high-pressure molding, can improve the strength of carrier microspheres to some extent, these methods significantly damage the original carrier's crystal structure and purity. Most carrier strength enhancement processes are accompanied by a decrease in reactivity. Furthermore, the crushing strength of most commercially available alumina microspheres is typically around 10 N / mm². 2 -20N / mm 2 This can cause problems such as catalyst shedding and crushing due to wear and collision of alumina microspheres in the reactor, making it difficult to meet the requirements of advanced chemical production. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] In a first aspect, the present invention provides a method for preparing alumina microspheres, comprising the following steps:

[0006] AlOOH solid sol was pre-cured to obtain alumina pre-cured gel;

[0007] The pre-cured alumina gel was aged in an alcohol solution to obtain alumina gel microspheres.

[0008] The alumina gel microspheres were subjected to a temperature gradient rinsing with carbodiol, and then dried and calcined to obtain alumina microspheres.

[0009] The alcohol solution includes C8 alcohol, C4 alcohol and an initiator, and the variable temperature gradient rinsing includes gradient cooling rinsing.

[0010] The method of this invention involves aging an alumina pre-cured gel in an alcohol solution comprising octadecanol, tetroxide, and an initiator. During aging, the monomers of the AlOOH solid solution aggregate to form AlOOH fibers, and with the removal of the solvent, the fibers aggregate to form a gel. The alcohol solution used contains both tetroxide and octadecanol. The tetroxide has a suitable hydrogen bonding effect and carbon chain length, allowing it to be directionally adsorbed onto the AlOOH fibers. As an intermediate, it helps the octadecanol, which has a weak hydrogen bonding effect and significant steric hindrance, to adsorb onto the AlOOH fibers, thereby increasing the interaction strength between the octadecanol and the AlOOH fibers and inducing the directional growth of the fibers. Furthermore, the alumina gel microspheres are subjected to gradient cooling rinsing using tetroxide, which slowly removes residual moisture from the interior of the alumina microspheres, reducing the generation of defects and thus improving the crushing strength of the alumina microspheres while maintaining a high specific surface area. This method enables the large-scale, controllable preparation of high-strength, wear-resistant catalyst carrier microspheres.

[0011] According to an embodiment of the present invention, the AlOOH solid sol is prepared by the following method: hydrolyzing, concentrating, and flash evaporating a soluble aluminum alkoxide to obtain AlOOH powder; mixing the AlOOH powder, water, and acid to obtain the AlOOH solid sol. Thus, a highly stable AlOOH solid sol can be obtained.

[0012] According to an embodiment of the present invention, in the alcohol solution, the volume ratio of the octa-ol, the tetrol and the initiator is 1:(0.2-0.5):(0.05-0.2).

[0013] According to embodiments of the present invention, the C8 alcohol comprises n-octanol and / or isooctol.

[0014] According to embodiments of the present invention, the C4 alcohol comprises n-butanol or isobutanol.

[0015] According to embodiments of the present invention, the initiator comprises trioctylamine or N,N,N',N'-tetramethylethylenediamine.

[0016] According to an embodiment of the present invention, the aging time is 1h-3h.

[0017] According to an embodiment of the present invention, the gradient cooling rinse is a three-stage cooling rinse, which includes a first rinse, a second rinse, and a third rinse performed sequentially. The temperature T1 of the first rinse is 55℃-65℃, and the time is 2min-5min; the temperature T2 of the second rinse is 45℃-55℃, and the time is 2min-5min; the temperature T3 of the third rinse is 35℃-45℃, and the time is 2min-5min; and the temperature T1 > temperature T2 > temperature T3.

[0018] According to an embodiment of the present invention, the mass ratio of the carbodiol used in each rinsing to the alumina gel microspheres is 1:(0.3-1).

[0019] According to an embodiment of the present invention, the drying temperature is 20℃-40℃ and the time is 8h-20h.

[0020] According to an embodiment of the present invention, the calcination temperature is 550℃-700℃ and the time is 3h-6h.

[0021] In a second aspect, the present invention proposes alumina microspheres prepared by the above method. The internal fibers and skeletal network of these alumina microspheres exhibit a composite, dense structure with a combination of long and short fibers, which improves the structural mechanical properties of the alumina microspheres while maintaining a high specific surface area. The alumina microspheres prepared by the present invention are of great significance for achieving long-term, high-performance operation of catalysts in reactors.

[0022] According to an embodiment of the present invention, the alumina microspheres have a diameter of 1.2 mm-1.5 mm, an average pore size of 6 nm-10 nm, and a specific surface area of ​​220 m². 2 / g-280m 2 / g.

[0023] According to an embodiment of the present invention, the crushing strength of the alumina microspheres is 61 N / mm². 2 -80N / mm 2 . Attached Figure Description

[0024] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0025] Figure 1 This is a scanning electron microscope image of the alumina microspheres from Example 1;

[0026] Figure 2 The image shows the pore size distribution of the alumina microspheres in Example 1.

[0027] Figure 3 This is a scanning electron microscope image of the alumina microspheres from Example 2;

[0028] Figure 4 This is a pore size distribution diagram of the alumina microspheres in Example 2;

[0029] Figure 5 The image shows a scanning electron microscope image of the alumina microspheres in Comparative Example 1.

[0030] Figure 6 The pore size distribution of the alumina microspheres in Comparative Example 1 is shown.

[0031] Figure 7 The image shows a transmission electron microscope (TEM) image of the alumina microsphere sample from Comparative Example 1.

[0032] Figure 8 This is a transmission electron microscope (TEM) image of the alumina microsphere sample from Example 2. Detailed Implementation

[0033] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0034] In one aspect of the present invention, a method for preparing alumina microspheres is provided, comprising the following steps:

[0035] (1) Preparation of alumina gel microspheres

[0036] AlOOH solid sol was pre-cured to obtain alumina pre-cured gel.

[0037] The pre-cured alumina gel was aged in an alcohol solution to obtain alumina gel microspheres.

[0038] The alcohol solution includes C8 alcohol, C4 alcohol and an initiator;

[0039] (2) Preparation of alumina microspheres

[0040] The alumina gel microspheres were subjected to a temperature gradient rinsing with carbodiol, and then dried and calcined to obtain alumina microspheres.

[0041] The variable temperature gradient rinsing includes gradient cooling rinsing.

[0042] In this invention, it is understood that the "×" in the expression "carbon × alcohol" represents the number of carbon atoms in the alcohol. For example, a carbon diol refers to an alcohol with 2 carbon atoms, and a carbon octaol refers to an alcohol with 8 carbon atoms.

[0043] In the method of this invention, the pre-cured alumina gel is aged in an alcohol solution composed of octadecanol, tetroxide, and an initiator. During this process, the monomers of the AlOOH solid sol aggregate to form AlOOH fibers. With the removal of the solvent, the fibers aggregate to form a gel. The moderate hydrogen bonding effect and moderate carbon chain length of the tetroxide allow it to be directionally adsorbed onto the AlOOH fibers. As an intermediate, it helps the octadecanol, which has a weak hydrogen bonding effect and significant steric hindrance, to adsorb onto the AlOOH fibers, thereby increasing the interaction strength between the octadecanol and the AlOOH fibers and inducing the directional growth of the fibers. Then, the alumina gel microspheres are subjected to a temperature gradient rinsing with tetroxide to slowly remove residual moisture from the interior of the alumina microspheres, reducing the generation of defects and thus improving the crushing strength of the alumina microspheres while maintaining a high specific surface area.

[0044] In some embodiments, the AlOOH sol is prepared by the following method:

[0045] Soluble aluminum alkoxides are hydrolyzed, concentrated, and flash evaporated to obtain AlOOH powder; this step yields high-purity AlOOH powder.

[0046] The AlOOH powder, water, and acid are mixed to obtain an AlOOH solid sol, which yields a stable AlOOH solid sol.

[0047] Optionally, the mass ratio of the soluble aluminum alkoxide to water is 1:(8-15), for example, 1:8, 1:9, 1:11, 1:13, 1:15, etc. This promotes the hydrolysis reaction of the soluble aluminum alkoxide, which is beneficial for obtaining alumina microspheres with high crushing strength. In addition, it can reduce the time and cost of subsequent concentration.

[0048] Furthermore, the mass ratio of the soluble aluminum alkoxide to water is 1:10.

[0049] It should be noted that crushing strength refers to the maximum load that the alumina microspheres can withstand when pressure is applied uniformly over a unit area until they fracture.

[0050] Optionally, the soluble aluminum alkoxide includes aluminum sec-butoxide or aluminum isopropoxide. The aforementioned soluble aluminum alkoxide can undergo hydrolysis in hot water to generate the corresponding alcohol and AlOOH solid sol. Furthermore, the generated alcohol can be removed by heating, thereby obtaining a high-purity AlOOH solid sol, which is beneficial for improving the crushing strength of alumina microspheres.

[0051] As an example, aluminum sec-butoxide hydrolyzes in hot water to produce sec-butanol and AlOOH solid sol. The sec-butanol can be removed by heating to obtain a high-purity AlOOH solid sol.

[0052] Optionally, the hydrolysis temperature is 85℃-98℃, such as 85℃, 88℃, 90℃, 95℃, 98℃, etc. The hydrolysis time can be 60min-120min, such as 60min, 80min, 100min, 120min, etc. The stirring speed is 200r / min-400r / min, such as 200r / min, 300r / min, 400r / min, etc. Therefore, limiting the hydrolysis temperature and time within the above ranges is beneficial for the rapid hydrolysis of soluble aluminum alkoxides to form AlOOH solid sol.

[0053] Optionally, the concentration temperature is 85℃-98℃, such as 85℃, 88℃, 90℃, 95℃, 98℃, etc. The concentration time is 1h-4h, such as 1h, 2h, 3h, 4h, etc. Therefore, limiting the concentration temperature within the above range can promote the volatilization of alcohol impurities generated by hydrolysis, resulting in a high-purity AlOOH solid sol, which is beneficial for preparing oxide microspheres with high crushing strength.

[0054] Understandably, the concentration time can be adjusted based on the selected concentration temperature and the mass ratio of soluble aluminum alkoxide to water. The concentration endpoint is reached when the total mass of soluble aluminum alkoxide and water decreases to half of its initial mass after concentration.

[0055] In some embodiments, after concentrating the hydrolysis product, the process further includes washing the AlOOH solid sol. The washing includes: first, centrifuging the AlOOH solid sol at 1000-2000 rpm for 5-10 minutes. This separates excess water from the AlOOH solid sol, facilitating subsequent washing. Then, the precipitate after centrifugation is washed at least three times with pure water at a temperature of 50-60°C (e.g., 50°C, 53°C, 55°C, 57°C, 60°C, etc.), with each wash using half the amount of water added during the hydrolysis process. Washing the AlOOH solid sol with hot water further removes impurities adhering to the solid sol surface, resulting in a higher purity AlOOH solid sol, which is beneficial for obtaining oxide microspheres with high crushing strength.

[0056] In some specific embodiments, the AlOOH solid sol is washed and then centrifuged again to separate the washing liquid and obtain the centrifuged precipitate.

[0057] In some embodiments, the centrifuged precipitate is subjected to flash evaporation to obtain AlOOH powder. The flash evaporation pressure is 0.2 bar to 0.4 bar, for example, 0.2 bar, 0.3 bar, 0.4 bar, etc., and the flash evaporation temperature is 80°C to 100°C, for example, 80°C, 90°C, 100°C, etc. The flash evaporation time is 40 min to 100 min, for example, 40 min, 60 min, 80 min, 100 min, etc. Thus, dry AlOOH powder can be obtained.

[0058] In some embodiments, the AlOOH powder, water, and acid are mixed to obtain an AlOOH solid sol. In this step, the AlOOH powder, water, and acid are mixed to cause the AlOOH powder to undergo gelation. During gelation, the acid can aggregate on the surface of the hydrolyzed AlOOH to form gel nuclei. Chloride ions and hydrogen ions are adsorbed on the surface of the gel nuclei, and under the action of electrostatic repulsion, the gel particles are not easily aggregated, thereby generating a stable monodisperse AlOOH solid sol.

[0059] In some embodiments, the mass ratio of AlOOH powder to water is 1:(3-5), for example, it can be 1:3, 1:4, 1:5, etc.

[0060] In some embodiments, the solid content of the AlOOH sol is 10wt%-25wt%.

[0061] As an example, the mass ratio of AlOOH powder to water is 1:4, and the resulting AlOOH solid sol has a mass fraction of 15 wt%.

[0062] In some embodiments, the mass ratio of AlOOH powder to acid is (5-15):1. Therefore, the acid solution can promote the hydrolysis of the AlOOH powder.

[0063] Optionally, the mass concentration of the acid is 5wt%-20wt%, for example, 5wt%, 8wt%, 10wt%, 14wt%, 16wt%, 20wt%, etc.

[0064] Optionally, the acid includes nitric acid or hydrochloric acid.

[0065] In some embodiments, the pH of the AlOOH solid sol is 3-4, such as 3, 3.2, 3.4, 3.6, 3.8, 4, etc. Therefore, limiting the pH of the AlOOH solid sol within the above range allows the formation of "acidic bridges" between AlOOH particles in a double-electron layer. These "acidic bridges" can connect multiple AlOOH particles together in a network to form a dynamic equilibrium, thereby maintaining the stability of the AlOOH solid sol and facilitating the preparation of alumina microspheres with high crushing strength.

[0066] In step (1), the AlOOH solid sol is pre-cured to induce a gel reaction, resulting in pre-cured alumina gel microspheres. These pre-cured alumina gel microspheres are then further aged to ensure complete polymerization of the AlOOH monomers, yielding the final alumina gel microspheres.

[0067] In some embodiments, a microchannel reactor can be used to pre-cur the AlOOH solid sol. Specifically, the AlOOH solid sol is mixed with a first curing agent and a second curing agent as a dispersed phase, and a mixed solution of a water extractant, an oil-soluble anionic surfactant, and an initiator is used as a continuous phase. Under the action of the continuous phase, the dispersed phase first disperses droplets within the microchannel reactor. Then, under the action of surface tension and fluid shear force, the continuous phase cuts the droplets within the microchannel, generating uniformly sized sol droplets. These uniform sol droplets form alumina pre-cured gel microspheres during the curing process. During the curing process, the alumina gel microspheres undergo the following transformation: the formed sol droplets contain a large number of AlOOH monomers. Under the combined action of the first and second curing agents, the stability of the monomers is disrupted, and the monomers gradually polymerize into AlOOH fibers. These fibers gradually overlap, ultimately forming alumina pre-cured gel microspheres.

[0068] It should be noted that a microchannel reactor is a miniature reactor with a feature size between 10 and 300 micrometers (or 1000 micrometers) manufactured using precision machining technology. The "micro" in microreactor indicates that the channels for the process fluid are at the micrometer level, rather than referring to the small size of the microreactor or the small yield of the product.

[0069] Alternatively, the microchannel reactor may include a single-channel reactor or a multi-channel reactor.

[0070] Optionally, the flow rate of the continuous phase is 1000 mL / min to 1200 mL / min.

[0071] Optionally, the flow rate of the dispersed phase is 100 mL / min to 200 mL / min.

[0072] As examples, the first curing agent is a temperature-initiated curing agent with reverse temperature-sensitive properties. It is liquid at low temperatures and entangled between chains at high temperatures, presenting a semi-solid form and promoting the sol-gel reaction. The second curing agent is an internal pH-initiated curing agent, which is easily decomposed by heat at high temperatures to generate ammonia gas. This ammonia gas can neutralize the acid added to the AlOOH solid sol, disrupting the most stable pH environment of the AlOOH solid sol and causing the AlOOH solid sol to become unstable and transform into a gel.

[0073] Optionally, the first curing agent includes at least one of methylcellulose, polyvinyl alcohol, polyacrylamide, or polyethylene glycol, and the second curing agent includes at least one of hexamethylenetetramine and urea. Thus, by selecting the aforementioned first and second curing agents, the stable AlOOH solid sol can be further promoted to gelation, thereby obtaining alumina pre-cured gel microspheres.

[0074] Optionally, in the dispersed phase, the mass ratio of the AlOOH solid sol, the first curing agent, and the second curing agent is 1:(0.002-0.3):(0.005-0.3), for example, 1:0.002:0.008, 1:0.005:0.005, 1:0.005:0.3, 1:0.3:0.005, 1:0.1:0.2, etc. Therefore, limiting the mass ratio of the AlOOH solid sol, the first curing agent, and the second curing agent to the above range is beneficial for promoting the gelation transformation of the AlOOH solid sol, thereby obtaining alumina pre-cured gel microspheres.

[0075] Optionally, the first curing agent includes at least one of methylcellulose, polyvinyl alcohol, polyacrylamide, or polyethylene glycol.

[0076] Optionally, the second curing agent includes at least one of hexamethylenetetramine and urea.

[0077] In some embodiments, in the continuous phase, the water extractant can extract water from the sol microspheres through the water difference between the interior of the AlOOH solid sol and the continuous phase, accelerating the gelation transformation process of the sol; the oil-soluble anionic surfactant can be adsorbed on the outside of the droplets, reducing surface tension and improving interfacial interactions; the initiator is an external pH curing initiator, which can diffuse from the continuous phase into the sol droplets, neutralize the acid added to the sol, disrupt the most stable pH environment of the sol, and cause the sol to become unstable and transform into a gel.

[0078] Optionally, in the continuous phase, the mass fraction of the water extractant is 67%-97.5%, for example, 67%, 70%, 83%, 85%, 90%, 97.5%, etc.; the mass fraction of the oil-soluble anionic surfactant is 1.5%-3%, for example, 1.5%, 2%, 2.5%, 3%, etc.; and the mass fraction of the initiator is 1%-30%, for example, 1%, 10%, 15%, 20%, 25%, 30%, etc. Thus, limiting the mass fractions of the water extractant, the oil-soluble anionic surfactant, and the initiator to the above ranges is beneficial for promoting the transformation of AlOOH solid sol into gelation, thereby obtaining alumina pre-cured gel microspheres.

[0079] Optionally, the oil-soluble anionic surfactant includes at least one of Span 85 and Dow Corning 749.

[0080] Optionally, the initiator includes trioctylamine and / or N,N,N',N'-tetramethylethylenediamine.

[0081] Optionally, the water extraction agent comprises octadecanol. Thus, the octadecanol, due to its partial water solubility and relatively long carbon chain, can partially dissolve in the AlOOH solid sol due to hydroxyl groups and hydrogen bonding, and is directionally adsorbed onto the AlOOH fibers under the influence of hydrogen bonding. The longer carbon chain provides a higher steric foci, thereby preventing AlOOH monomers from growing along the fiber sidewalls. Therefore, during the pre-curing stage, the AlOOH monomers in the AlOOH solid sol can only be adsorbed at both ends of the already aggregated AlOOH fibers, inducing axial fiber growth and constructing a long fiber structure.

[0082] As a water extraction agent, the C8 alcohol can be a monohydric alcohol or a polyhydric alcohol. As a specific example, the C8 alcohol is n-octanol and / or isooctol.

[0083] In some embodiments, the pre-curing temperature is 80℃-95℃, such as 80℃, 83℃, 86℃, 90℃, 93℃, 95℃, etc., and the pre-curing time is 1min-3min, such as 1min, 1.5min, 2min, 2.5min, 3min, etc. Thus, during the pre-curing process, under the combined action of the continuous phase and the dispersed phase, the dispersed phase droplets can rapidly gel in the microchannels and ultimately complete the pre-curing process, obtaining alumina pre-cured gel microspheres.

[0084] In some embodiments, the stability of some AlOOH monomers within the pre-cured gel microspheres is disrupted under the combined action of a first curing agent and a second curing agent. The monomers gradually polymerize into AlOOH fibers, which then gradually overlap to ultimately form alumina pre-cured gel microspheres. However, some AlOOH monomers within the pre-cured microspheres remain incompletely polymerized. During the aging stage, the polymerization of all monomers must continue to complete to obtain alumina gel microspheres. The pre-cured gel microspheres are collected and placed in the alcohol solution for further aging.

[0085] In some embodiments, the alcohol solution comprises a mixed solution of octadecanol, tetroxide, and an initiator. Thus, octadecanol, tetroxide, and the initiator are mixed to form the alcohol solution. The moderate hydrogen bonding effect and moderate carbon chain length of tetroxide allow it to be directionally adsorbed onto AlOOH fibers. As an intermediate, it helps octadecanol, which has a weak hydrogen bonding effect and a large steric hindrance, to adsorb onto AlOOH fibers, thereby increasing the interaction strength between octadecanol and AlOOH fibers and inducing directional fiber growth. However, if the alcohol solution contains only octadecanol, its weak hydrogen bonding effect and high steric hindrance make it difficult for it to directly adsorb onto AlOOH fibers, which is detrimental to inducing axial fiber growth. Therefore, this advantage cannot be achieved by octadecanol and the initiator alone.

[0086] Furthermore, the volume ratio of the octadecyl alcohol, the tetroxide, and the initiator is 1:(0.2-0.5):(0.05-0.2). Examples include 1:0.2:0.05, 1:0.2:0.2, 1:0.3:0.2, 1:0.5:0.05, and 1:0.5:0.2. Within this range, the octadecyl alcohol and tetroxide exhibit the strongest directional adsorption effect on the fibers.

[0087] In step (1), the type of C8 alcohol may be the same as or different from the C8 alcohol selected in the pre-curing stage. As some examples, the C8 alcohol is n-octanol and / or isooctol.

[0088] In step (1), the C4T alcohol possesses a certain degree of water solubility, a suitable carbon chain length, and a suitable hydrogen bonding effect. The C4T alcohol can dissolve in the alumina pre-cured gel during the aging stage and, under the action of hydrogen bonds, is directionally adsorbed onto the already formed AlOOH fibers. The suitable carbon chain length and hydrogen bonding effect do not affect fiber growth or the polymerization of AlOOH monomers. The C4T alcohol can be a monohydric alcohol or a polyhydric alcohol. As some examples, the C4T alcohol includes n-butanol and / or isobutanol.

[0089] Optionally, the initiator includes trioctylamine and / or N,N,N',N'-tetramethylethylenediamine.

[0090] In some embodiments, the aging time is 1-3 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc. As a preferred example, the aging time is 2 hours.

[0091] In step (2), the alumina gel microspheres are subjected to variable temperature gradient rinsing, drying, and calcination using carbodiols to obtain alumina microspheres. The variable temperature gradient rinsing includes gradient cooling rinsing. The carbodiols possess superior water solubility, ultra-short carbon chain length, and strong hydrogen bonding. The carbodiols can adsorb residual water and AlOOH monomers within the aged alumina gel microspheres through hydrogen bonding. Simultaneously, the ultra-short carbon chains result in minimal steric hindrance between the carbodiols, allowing a large amount of carbodiol to aggregate on the AlOOH monomers, preventing monomer polymerization. Furthermore, the use of octa-ols and tetrols in the aging step increases the interaction strength between carbodiols and octa-ols. The carbodiols carry monomers and fill the long fiber network structure constructed by the octa-ols, building a dense alumina skeleton, thereby significantly improving the mechanical properties and structural strength of the alumina microspheres.

[0092] It is understood that the gradient cooling rinsing refers to rinsing the alumina gel microspheres at a certain temperature first, then cooling down and continuing the rinsing process, and so on, with each stage of cooling decreasing gradually. The number of stages in the gradient cooling rinsing can be adjusted according to actual rinsing needs, such as 2, 3, 4, 5, 6, 10, 20, etc.

[0093] In step (2), the gradient cooling rinsing process removes the moisture inside the microspheres and promotes the stable and orderly assembly of the monomers, while minimizing the possibility of hollow or defective interiors caused by rapid dehydration of the alumina gel microspheres, thereby improving the crushing strength of the alumina microspheres.

[0094] In some embodiments, the gradient cooling rinse is a three-stage cooling rinse, including a first rinse, a second rinse, and a third rinse performed sequentially.

[0095] The first rinsing includes: immersing alumina gel microspheres in carbon glycol, and controlling the temperature T1 of the first rinsing to be 55℃-65℃, such as 65℃, 60℃, 55℃, etc., and the time to be 2min-5min, such as 2min, 3min, 4min, 5min, etc.

[0096] The second rinsing includes taking out the alumina gel microspheres after the first soaking, immersing them in carbohydric alcohol, and controlling the temperature T2 of the second rinsing to be 45℃-55℃, such as 55℃, 50℃, 45℃, etc., and the time to be 2min-5min, such as 2min, 3min, 4min, 5min, etc.

[0097] The third rinsing includes taking out the alumina gel microspheres after the second soaking, immersing them in carbohydric alcohol, and controlling the temperature T3 of the second rinsing to be 35℃-45℃, such as 35℃, 40℃, 45℃, etc., and the time to be 2min-5min, such as 2min, 3min, 4min, 5min, etc.

[0098] Furthermore, during the variable temperature gradient rinsing process, it is necessary to control the temperature T1 > temperature T2 > temperature T3. This ensures that the alumina gel microspheres can be fully mixed with the carbodiol, which facilitates the penetration of the carbodiol into the interior of the alumina gel microspheres.

[0099] In some embodiments, the mass ratio of carbohydric alcohol to alumina gel microspheres used in each rinsing is 1:(0.3-1), for example, 1:0.3, 1:0.5, 1:0.8, 1:1, etc. This ensures that while the alumina gel microspheres are immersed in carbohydric alcohol, the added alcohol does not reach saturation water content, allowing residual water within the alumina gel microspheres to continuously diffuse outwards, thereby obtaining alumina microspheres with high crushing strength.

[0100] It is understood that carbohydrics can include at least one of monohydric alcohols and dihydric alcohols. As examples, carbohydrics include ethanol, ethylene glycol, etc.

[0101] In step (2), the alumina gel microspheres after rinsing are dried. During the volatilization of carbodiol, the remaining water in the alumina gel microspheres can be stably removed. At the same time, the assembly between the remaining monomers and the constructed AlOOH fibers is completed. Finally, the dried alumina gel microspheres are calcined, which can dehydrate AlOOH and transform it into an Al-O-Al structure, thus obtaining alumina microspheres with high crushing strength.

[0102] Optionally, the drying temperature is 20℃-40℃, such as 20℃, 25℃, 30℃, 35℃, 40℃, etc., and the drying time is 8h-20h, such as 8h, 10h, 15h, 20h, etc. Therefore, limiting the drying parameters to the above range can effectively remove excess carbodiol from the interior of the alumina gel microspheres. The volatilization of carbodiol can induce the stable removal of remaining solvent within the alumina gel microspheres, thereby obtaining alumina microspheres with high crushing strength.

[0103] Optionally, the calcination temperature is 550℃-700℃, such as 550℃, 600℃, 650℃, 700℃, etc., and the calcination time is 3h-6h, such as 3h, 4h, 5h, 6h, etc. Therefore, limiting the calcination parameters within the above range can further promote the dehydration of AlOOH molecules, transforming them into an Al-O-Al structure, thereby obtaining alumina microspheres with high crushing strength.

[0104] In a second aspect, the present invention proposes alumina microspheres prepared by the above method. These alumina microspheres exhibit a composite, dense structure with a combination of long and short fibers within their internal fiber and skeletal network. This structure enhances the structural mechanical properties of the alumina microspheres while maintaining a high specific surface area, thereby enabling large-scale, controllable preparation of high-strength, wear-resistant catalyst support microspheres. This is of great significance for achieving long-term, high-performance operation of catalysts within reactors.

[0105] Optionally, the diameter of the alumina microspheres is 1.2mm-1.5mm, such as 1.2mm, 1.25mm, 1.3mm, 1.4mm, 1.5mm, etc.

[0106] Optionally, the alumina microspheres have a porous structure with a pore size of 6nm-10nm, such as 6nm, 7nm, 8nm, 9nm, 10nm, etc. This facilitates catalyst loading onto alumina and reduces catalyst agglomeration.

[0107] Optionally, the specific surface area of ​​the alumina microspheres is 220 m². 2 / g-280m 2 / g, for example 220m 2 / g、240m 2 / g、260m 2 / g、280m 2 / g etc. This facilitates catalyst loading onto alumina and reduces catalyst agglomeration.

[0108] Optionally, the crushing strength of the alumina microspheres is 61 N / mm². 2 -80N / mm 2 For example, 61 N / mm 2 65N / mm 2 70N / mm 2 75N / mm 2 80N / mm 2 wait.

[0109] Optionally, the pore volume of the alumina microspheres is 0.3 mL / g to 1 mL / g.

[0110] The present invention will be described below through specific embodiments. It should be noted that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0111] Example 1

[0112] (1) 2000g of aluminum sec-butoxide was added to 20000g of pure water at 95℃ and stirred and hydrolyzed for 120min at 300r / min. Then, it was concentrated at 95℃ for 3h, so that the total mass after concentration was about 11000g. The resulting mixture was washed three times with 10000g of water each time with hot water at 60℃. Then, it was flash-evaporated at 90℃ and 0.2bar for 60min to obtain AlOOH raw material powder.

[0113] (2) Take out 500g of AlOOH raw material powder, add 2000g of pure water, and then mix it with 50g of 20wt% nitric acid to obtain a stable AlOOH solid sol with pH 4.

[0114] (3) 2550g of stable AlOOH solid sol was mixed with 6g of polyvinyl alcohol and 20g of hexamethylenetetramine and stirred evenly at 250r / min to form a dispersed phase. A solution of n-octanol containing 15wt% trioctylamine and 2wt% Span85 was prepared as a continuous phase. Subsequently, in a 200-channel T-type droplet shearing microfluidic module, the continuous phase with a flow rate of 1170mL / min was used to shear the dispersed phase with a flow rate of 140mL / min to form dispersed phase droplets. The dispersed phase droplets underwent preliminary gelation in a microfluidic system at 90℃ for 3min. Then, the alumina pre-cured gel microspheres were collected into a raw material tank containing 5L n-octanol, 2.5L n-butanol and 1L trioctylamine and aged for 1h to obtain alumina gel microspheres.

[0115] (4) Collect 450g of alumina gel microspheres and immediately immerse them in 1000mL of ethanol at 60℃. Stir the microspheres in the ethanol slowly for 3min to complete the first gradient rinsing. Then collect the soaked alumina gel microspheres and immediately immerse them in 1000mL of ethanol at 50℃. Stir the microspheres in the ethanol slowly for 3min to complete the second gradient rinsing. Finally, use the same method to complete the third rinsing with 1000mL of ethanol at 40℃. Then dry them at 30℃ for 12h. Finally, calcine the dried alumina gel microspheres at 600℃ for 6h to obtain alumina microspheres.

[0116] Figure 1 The scanning electron microscope (SEM) images of the alumina microspheres obtained in Example 1 are shown. As can be seen from the figures, the alumina microspheres prepared in Example 1 exhibit uniform particle size, sphericity, surface smoothness, and other properties, with evenly distributed pores. Furthermore, based on… Figure 1 The size of 50 microspheres was statistically analyzed using a scale, and the average value was calculated, yielding an alumina microsphere diameter of 1.42 mm.

[0117] Figure 2The figure shows the pore size distribution of the alumina microspheres obtained in Example 1. The pore size was obtained by performing nitrogen adsorption-desorption tests using a Micromeritics ASAP 2460 physical adsorption workstation (USA). The specific surface area and pore volume were then obtained by fitting the curve using the BET multi-point method. The vertical axis of the figure represents the differential calculated value of the logarithmic distribution of pore area and pore diameter in the pore size distribution diagram. As shown in the figure, the average pore size of the alumina microspheres obtained in this example is 7.25 nm. Figure 2 The curves were fitted using the BET multi-point method and the BJH method, yielding a specific surface area of ​​235.41 m² for the alumina microspheres. 2 / g, pore volume is 0.56mL / g.

[0118] Example 2

[0119] Alumina microspheres were prepared according to the method in Example 1, except that the aging time was 2 hours, the temperature of the first rinsing was 65°C, the temperature of the second rinsing was 50°C, and the temperature of the third rinsing was 35°C.

[0120] Figure 3 The scanning electron microscope (SEM) images of the alumina microspheres obtained in Example 2 are shown. The images demonstrate that the alumina microspheres prepared in Example 2 exhibit uniform particle size, sphericity, surface smoothness, and other properties, with evenly distributed pores. According to... Figure 3 The size of 50 microspheres was statistically analyzed using a scale, and the average value was calculated, yielding an alumina microsphere diameter of 1.39 mm.

[0121] Figure 4 The figure shows the pore size distribution of the alumina microspheres obtained in Example 2. As can be seen from the figure, the average pore size of the alumina microspheres obtained in this example is 7.01 nm. Figure 4 The curves were fitted using the BET multi-point method and the BJH method, yielding a specific surface area of ​​254.24 m² for the alumina microspheres. 2 / g, pore volume is 0.55mL / g.

[0122] Example 3

[0123] Alumina microspheres were prepared in accordance with the method of Example 1, except that the aging time was 3 hours.

[0124] Example 4

[0125] Alumina microspheres were prepared according to the method in Example 1, except that the temperature of the first rinsing was 65°C, the temperature of the second rinsing was 50°C, and the temperature of the third rinsing was 35°C.

[0126] Example 5

[0127] Alumina microspheres were prepared in accordance with the method of Example 1, except that the aging time was 2 hours.

[0128] Example 6

[0129] Alumina microspheres were prepared according to the method in Example 1, except that the aging time was 3 hours, the temperature of the first rinsing was 65°C, the temperature of the second rinsing was 50°C, and the temperature of the third rinsing was 35°C.

[0130] Example 7

[0131] Alumina microspheres were prepared according to the method in Example 1, except that the volume ratio of n-octanol, n-butanol, and trioctylamine was 1:0.3:0.2, and the volume of n-octanol was 5L; the aging time was 2h; the temperature of the first rinse was 65°C; the temperature of the second rinse was 50°C; and the temperature of the third rinse was 35°C.

[0132] Example 8

[0133] Alumina microspheres were prepared according to the method in Example 1, except that the volume ratio of n-octanol, n-butanol, and trioctylamine was 1:0.2:0.2, and the volume of n-octanol was 5L; the aging time was 2h; the temperature of the first rinse was 65°C; the temperature of the second rinse was 50°C; and the temperature of the third rinse was 35°C.

[0134] Example 9

[0135] Alumina microspheres were prepared according to the method in Example 1, except that the volume ratio of n-octanol, n-butanol, and trioctylamine was 1:0.5:0.1, and the volume of n-octanol was 5L; the aging time was 2h; the temperature of the first rinse was 65°C; the temperature of the second rinse was 50°C; and the temperature of the third rinse was 35°C.

[0136] Example 10

[0137] Alumina microspheres were prepared according to the method in Example 1, except that the volume ratio of n-octanol, n-butanol, and trioctylamine was 1:0.5:0.05, and the volume of n-octanol was 5L; the aging time was 2h; the temperature of the first rinse was 65°C; the temperature of the second rinse was 50°C; and the temperature of the third rinse was 35°C.

[0138] Example 11

[0139] Alumina microspheres were prepared according to the method in Example 1, except that the aging time was 2 hours, the temperature of the first rinsing was 65°C, the temperature of the second rinsing was 50°C, the temperature of the third rinsing was 35°C, and the drying temperature was 25°C.

[0140] Example 12

[0141] Alumina microspheres were prepared according to the method in Example 1, except that the aging time was 2 hours, the temperature of the first rinsing was 65°C, the temperature of the second rinsing was 50°C, the temperature of the third rinsing was 35°C, and the drying time was 20 hours.

[0142] Comparative Example 1

[0143] Alumina microspheres were prepared according to the method in Example 1, except that the alumina gel microspheres were not washed, but were directly dried at 30°C for 12 hours, and then calcined at 600°C for 6 hours to obtain alumina microspheres.

[0144] Figure 5 The scanning electron microscope images of the alumina microspheres obtained in Comparative Example 1 are shown. As can be seen from the figures, the particle size, sphericity, and surface smoothness of the alumina microspheres prepared in Comparative Example 1 are slightly inferior to those in Examples 1 and 2. According to... Figure 5 The size of 50 microspheres was statistically analyzed using a scale, and the average value was calculated, yielding an alumina microsphere diameter of 1.46 mm.

[0145] Figure 6 The pore size distribution of the alumina microspheres obtained in Comparative Example 1 is shown. As can be seen from the figure, the average pore size of the alumina microspheres obtained in this example is 9.26 nm. Figure 6 The curve was fitted using the BET multi-point method and the BJH method, yielding a specific surface area of ​​258 m². 2 / g, pore volume is 0.73mL / g.

[0146] Comparative Example 2

[0147] Alumina microspheres were prepared according to the method in Example 1, except that the rinsing process was as follows: the aged alumina gel microspheres were collected and immediately immersed in 1000 mL of ethanol at 80 °C, and the microspheres in the ethanol were slowly stirred. The immersion time was 3 min. The subsequent two rinsing processes were completed in the same way. The microspheres were then dried at 30 °C for 12 h. The dried alumina gel microspheres were then calcined at 600 °C for 6 h to obtain alumina microspheres.

[0148] Comparative Example 3

[0149] Alumina microspheres were prepared according to the method in Example 1, except that the aging method was different. Specifically, the pre-cured alumina gel microspheres were collected in a raw material tank containing 6.25 L of n-octanol and 1.25 L of trioctylamine and aged for 1 hour.

[0150] Comparative Example 4

[0151] Alumina microspheres were prepared using a rolling spherical method. Specifically, AlOOH raw material powder was produced by reacting aluminum sulfate with sodium aluminate. The powder was placed in a rotating table, and a binder was added. The powder gradually rolled under the rotation of the turntable and the drive of centrifugal force, continuously adhering AlOOH powder. Finally, the resulting spheres were calcined to form alumina microspheres. The average diameter of the alumina microspheres obtained in Comparative Example 4 was 2 mm.

[0152] The experimental parameters for Examples 1-12 and Comparative Examples 1-4 are shown in Table 1.

[0153] Table 1

[0154]

[0155] " / " indicates no.

[0156] Testing and Analysis

[0157] Under the same conditions, the crushing strength of the alumina microspheres prepared in Examples 1-12 and Comparative Examples 1-4 was tested. The specific test methods are as follows:

[0158] Crushing strength: The test was conducted using a YHKC-2A particle strength tester. A microsphere was placed in the tester, and the pressure detection element was turned on to continuously press down on the microsphere. When the microsphere broke, the instrument displayed the maximum pressure value on the microsphere. The experiment was repeated 10 times to obtain the average value of the maximum pressure on the microsphere during crushing. Crushing strength = average value of maximum pressure / (π × microsphere radius 2).

[0159] The test results of the alumina microspheres in Examples 1-12 and Comparative Examples 1-4 are shown in Table 2.

[0160] Table 2

[0161] Example 1 71.78 Example 2 78.83 Example 3 74.69 Example 4 72.96 Example 5 77.34 Example 6 75.98 Example 7 74.32 Example 8 70.69 Example 9 71.30 Example 10 68.56 Example 11 76.32 Example 12 71.40 Comparative Example 1 31.90 Comparative Example 2 21.76 Comparative Example 3 38.15 Comparative Example 4 12.06

[0162] As shown in the table above, the alumina microspheres prepared by the method of the present invention maintain a high specific surface area while also possessing high crushing strength. Compared with Example 1, the alumina microspheres of Comparative Example 1 have a higher specific surface area, but their crushing strength is lower. This is because the internal structure of the alumina microsphere carrier does not form a dense skeletal structure of long and short fiber combinations, thus resulting in poorer strength even with a relatively similar specific surface area.

[0163] Figure 7 Transmission electron microscopy (TEM) images of the alumina microsphere sample from Comparative Example 1 are shown. Because the alumina gel microspheres were not subjected to gradient cooling rinsing with carbohydric alcohol, a dense skeletal structure of long and short fibers was not formed within the microsphere carrier. Therefore, even with a relatively similar specific surface area, the carrier exhibited poor compressive strength.

[0164] Figure 8 Transmission electron microscopy (TEM) images of the alumina microsphere sample from Example 2 are shown. It can be seen that the combined use of octa-ol and tetrol during the aging stage induced and promoted the growth of long AlOOH fibers, while the gradient cooling rinsing with carbodiol during the rinsing stage induced the directional growth of short AlOOH fibers. The internal structure of the carrier exhibits a dense skeletal structure of long and short fibers, significantly improving the carrier's compressive strength.

[0165] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. All patents and publications related to this invention are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0166] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0167] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing alumina microspheres, characterized in that, Includes the following steps: AlOOH solid sol was pre-cured to obtain alumina pre-cured gel; The pre-cured alumina gel was aged in an alcohol solution to obtain alumina gel microspheres. The alumina gel microspheres were subjected to a temperature gradient rinsing with carbodiol, and then dried and calcined to obtain alumina microspheres. The alcohol solution includes octadecanol, tetroxide and an initiator, and the variable temperature gradient rinsing includes gradient cooling rinsing. The initiator includes trioctylamine and / or N,N,N',N'-tetramethylethylenediamine; In the alcohol solution, the volume ratio of the octa-ol, the tetrol, and the initiator is 1:(0.2-0.5):(0.05-0.2); The gradient cooling rinsing is a three-stage cooling rinsing, which includes a first rinsing, a second rinsing, and a third rinsing performed sequentially. The temperature T1 of the first rinse is 55℃-65℃, and the time is 2min-5min; The temperature T2 of the second rinsing is 45℃-55℃, and the time is 2min-5min; The temperature T3 of the third rinse is 35℃-45℃, and the time is 2min-5min; Furthermore, temperature T1 > temperature T2 > temperature T3.

2. The preparation method according to claim 1, characterized in that, The AlOOH solid sol was prepared by the following method: Soluble aluminum alkoxides are hydrolyzed, concentrated, and flash evaporated to obtain AlOOH powder; The AlOOH powder, water, and acid are mixed to obtain an AlOOH solid sol.

3. The preparation method according to claim 1, characterized in that, The C8 alcohols include n-octanol and / or isooctol; The C4 alcohols include n-butanol and / or isobutanol.

4. The preparation method according to claim 1, characterized in that, The aging time is 1-3 hours.

5. The preparation method according to claim 1, characterized in that, The mass ratio of carbon glycol to the alumina gel microspheres used in each rinsing is 1:(0.3-1).

6. The preparation method according to any one of claims 1-5, characterized in that, The drying temperature is 20℃-40℃, and the time is 8h-20h; and / or, The roasting temperature is 550℃-700℃, and the time is 3h-6h.

7. Alumina microspheres prepared by the preparation method according to any one of claims 1-6, characterized in that, The alumina microspheres have a diameter of 1.2 mm-1.5 mm, an average pore size of 6 nm-10 nm, and a specific surface area of ​​220 m². 2 / g-280m 2 / g, crushing strength is 61N / mm 2 -80N / mm 2 .

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