Preparation method of bimodal pore toothed spherical alumina carrier

Abstract

This application relates to the technical field of catalyst carriers, and specifically discloses a preparation method of a bimodal pore toothed spherical alumina carrier. A preparation method of a bimodal pore toothed spherical alumina carrier includes the following steps: (1) Mix pseudoboehmite, polyethylene glycol, polyacrylamide, pore expander, acidic solvent, crystal form guiding agent and deionized water, and then carry out kneading, extrusion and forming to obtain a toothed spherical green body; (2) Dry and calcine the toothed spherical green body, and a bimodal pore toothed spherical alumina carrier is obtained after the calcination is completed; the crystal form guiding agent is obtained by modifying CdSe quantum dots with an organic ligand and then grafting an amino polymer. The alumina carrier prepared by the preparation method of this application has stable performance, and the pore proportion of 4-10 nm in the alumina carrier is 65-75%, and the pore proportion of >15 nm is 10-20%, so that the alumina carrier has both good catalytic activity and mass transfer efficiency.

Description

Technical Field

[0001] This application relates to the technical field of catalyst carriers. More specifically, it relates to a preparation method of a bimodal pore toothed spherical alumina carrier. Background Art

[0002] In the field of petroleum refining, deep desulfurization is the key to improving gasoline quality. The gasoline pre-hydrogenation technology is of great significance for the desulfurization process in gasoline production. Although conventional hydrogenation can reduce sulfur content, it will cause the saturation of olefins and aromatics, reducing the octane number of gasoline. The gasoline pre-hydrogenation technology can effectively reduce the sulfur and olefin content of gasoline, reduce the loss of octane number, improve gasoline quality, and reduce the emission of harmful substances in the tail gas through selective hydrodesulfurization and de-olefination. The core of the development of gasoline pre-hydrogenation technology lies in the research and application of highly efficient supported catalysts. The new catalyst can reduce the reaction temperature and pressure, and improve the desulfurization reaction rate and selectivity. The carrier is a key part of the supported catalyst and plays a significant role. On the one hand, it can disperse the active components, improve the utilization rate of active metals, and reduce the dosage of active components; on the other hand, it provides diffusion channels for reactant and product molecules, improving the mass transfer efficiency. In terms of the performance indicators of the carrier, the pore structure has a significant impact on the performance of the catalyst. A carrier with a pore structure of appropriate size can promote the full contact between reactants and active sites, improving the reaction efficiency and mass transfer efficiency.

[0003] In related technologies, a Chinese patent document with the publication number CN116037085B discloses a macroporous alumina carrier and its preparation method, including the following: Kneading and molding the first pseudo-boehmite and the second pseudo-boehmite, and drying and calcining the molded product to obtain a macroporous alumina carrier. The alumina carrier prepared by this preparation method using two pseudo-boehmite powders with different properties has a relatively high specific surface area, pore volume, and most probable pore diameter. The proportion of pores with a pore diameter greater than 15 nm reaches 65%-80%. The macroporous alumina carrier prepared by this method has the advantages of small mass transfer resistance and high efficiency.

[0004] However, as the research on supported catalysts deepens, studies have shown that for carriers, the larger the proportion of large pores, the better, because the large proportion of large pores will inevitably lead to a small proportion of small pores. Although the mass transfer efficiency is high, the small proportion of small pores will cause the active components of the catalyst to be difficult to disperse, resulting in the reactants and active components not being able to fully contact, which is not conducive to the catalytic reaction. Therefore, the proportion of large pores and small pores needs to meet certain requirements in order for the alumina carrier to maintain a good use effect. The applicant's research shows that in alumina carriers, 4-10nm pores account for 65-75%, and >15nm pores account for 10-20%. Alumina carriers that meet this indicator can have both better catalytic activity and mass transfer efficiency for supported catalysts. Therefore, the alumina carriers prepared in the related art are difficult to meet the index requirements of 4-10nm pores accounting for 65-75% and >15nm pores accounting for 10-20%. Summary of the invention

[0005] In order to prepare an alumina carrier in which 4-10nm pores account for 65-75% and >15nm pores account for 10-20%, so that the alumina carrier has both good catalytic activity and mass transfer efficiency, thereby improving the reaction effect of gasoline pre-hydrogenation, promoting the further development of gasoline pre-hydrogenation technology, and achieving the purpose of improving gasoline quality, reducing production costs, and reducing environmental pollution, the present application provides a method for preparing a bimodal pore-teeth spherical alumina carrier.

[0006] The present application provides a method for preparing a bimodal porous spherical alumina carrier using the following technical solution:

[0007] A method for preparing a bimodal porous spherical alumina carrier comprises the following steps:

[0008] (1) Pseudo-boehmite, polyethylene glycol, polyacrylamide, a pore-enlarging agent, an acidic solvent, a crystal directing agent and deionized water are mixed, and then kneaded and extruded, and then processed by a tooth ball forming machine to obtain a tooth ball type blank;

[0009] (2) drying the toothed ball-shaped green body, and then calcining it at 300-400°C for 2-3 hours, and then heating it to 500-600°C for 3-5 hours, and after calcination, obtaining a bimodal porous toothed ball-shaped alumina carrier;

[0010] The crystal directing agent is obtained by modifying CdSe quantum dots with organic ligands and then grafting amino polymers.

[0011] By adopting the above technical solution, the present application controls the pore distribution and proportion of the alumina support through the cooperation of multiple means. Two pore-forming agents with different decomposition temperatures are selected and compounded. By using their different decomposition sequences and degrees during the calcination process, pore channels with corresponding pore diameters are formed at different stages. Polyethylene glycol decomposes during high-temperature calcination to form small pores of 4-10 nm, and polyacrylamide decomposes to form large pores of >15 nm. By controlling the ratio of the two and the ratio of other raw materials, the proportion of 4-10 nm pores and >15 nm pores can be accurately regulated. A crystal form guiding agent is added during the kneading process to regulate the crystal form of alumina. The pore structures formed by different crystal forms of alumina after calcination are different, which further affects the final pore distribution. At the same time, the process parameters such as the kneading time, temperature, drying temperature and time at each stage, and the calcination temperature, time, and heating rate are strictly controlled to achieve fine adjustment of the pore structure. Finally, an alumina support that meets the index requirements of 65-75% of 4-10 nm pores and 10-20% of >15 nm pores is prepared, taking into account good catalytic activity and mass transfer efficiency.

[0012] Optionally, the mass ratio of the pseudo-boehmite, polyethylene glycol, polyacrylamide, pore-expanding agent, acidic solvent, crystal form guiding agent and deionized water is (30-50):(5-8):(2-5):(1-3):(2-5):(3-5):(20-30).

[0013] By adopting the above technical solution, the above mass ratio enables the amount of pseudo-boehmite to be sufficient to form an alumina skeleton, and the amounts of additives such as polyethylene glycol and polyacrylamide can not only play corresponding plasticizing and pore-forming roles, but also have no negative impact on the performance of the support. The appropriate ratios of the pore-expanding agent, acidic solvent and crystal form guiding agent can effectively regulate the pore structure and crystal form of the support, and the amount of deionized water ensures the full mixing of the materials and the smooth progress of processing and shaping. It avoids the problem that the mixed materials are too viscous or too thin, affecting operations such as kneading and extrusion, or affecting the pore structure and crystal form of the support, resulting in the inability to meet the expected performance indicators.

[0014] Optionally, the organic ligand is preferably mercaptoacetic acid.

[0015] By adopting the above technical solution, the organic ligand is preferably mercaptoacetic acid. Mercaptoacetic acid has a suitable chemical structure and properties, and can effectively modify the CdSe quantum dots, enabling them to graft better with the amino polymer, thereby more effectively playing the role of the crystal form guiding agent, and further regulating the crystal form and pore structure of alumina, which is beneficial to the preparation of an alumina support with an ideal crystal form and pore structure.

[0016] Optionally, the amino polymer is preferably polyallylamine hydrochloride.

[0017] By adopting the above technical solution, the amino groups in polyallylamine hydrochloride can react with the active groups on the CdSe quantum dots modified with mercaptoacetic acid to achieve grafting. The amino groups on the long chain of the grafted polyallylamine hydrochloride form coordination bonds with aluminum ions, guiding the growth direction of alumina crystals. At the same time, the steric hindrance of its long chain can effectively restrict the diffusion of aluminum ions and other precursor molecules, regulate the growth rate of crystals on different crystal planes, thereby realizing the regulation of the alumina crystal form, and further realizing the regulation of the pore structure of the carrier.

[0018] Optionally, the crystal form guiding agent is prepared by the following method:

[0019] A. Mix the CdSe quantum dot dispersion with the aqueous solution of mercaptoacetic acid. Subsequently, add the Tris-HCl buffer solution to the mixed solution, adjust the pH value of the solution system to 8-9, and then oscillate and react the reaction solution at a temperature of 45-55 °C and a rotation speed of 150-200 r / min for 2-3 h. After the reaction, a CdSe quantum dot dispersion modified with mercaptoacetic acid is obtained;

[0020] B. Mix polyallylamine hydrochloride with the CdSe quantum dot dispersion modified with mercaptoacetic acid, add N-hydroxysuccinimide, and stir and react at room temperature for 12-24 h. Then, after dialysis and freeze-drying, a crystal form guiding agent is obtained.

[0021] Through the above method, the CdSe quantum dots in the crystal form guiding agent, relying on the quantum size effect, when the aluminum ions in the alumina precursor solution approach, the special electron cloud environment of the quantum dots affects the charge distribution and coordination of aluminum ions, promoting the aggregation of aluminum ions at specific positions on the surface of the quantum dots to form crystal nuclei. This fine crystal nucleus formation site can induce the formation of initial crystal nuclei with special crystal plane orientations and sizes. The initial crystal nuclei induced by the quantum size effect of CdSe quantum dots may be more inclined to grow into the γ-Al2O3 crystal form. γ-Al2O3 belongs to the cubic crystal system and has a spinel structure. There are a large number of octahedral and tetrahedral vacancies in its crystal lattice. This structural characteristic enables γ-Al2O3 to form abundant micropores and mesopores during the calcination process, and the pore size distribution is relatively concentrated in the mesopore range (2-15 nm), providing a structural basis for the formation of a high proportion of 4-10 nm pores. The subsequent grown alumina structure is more conducive to the formation of a large proportion of small pore diameters (4-10 nm) and a smaller proportion of large pore diameters (>15 nm), providing more suitable attachment sites for the active components, solving the problem that the active components are not easily dispersed, and at the same time ensuring a certain mass transfer efficiency for the large pore diameters.

[0022] During the transformation of γ-Al2O3 from precursors such as pseudo-boehmite, its pore structure undergoes a series of evolutions. During the calcination process, as the temperature rises, the moisture and organic substances in the precursor are gradually removed, and γ-Al2O3 crystals gradually form. Due to the relatively loose structure of γ-Al2O3, a large number of pores with a size of 4-10 nm are easily formed during this process. At the same time, the decomposition of pore-forming agents polyethylene glycol and polyacrylamide at different stages also cooperates with the evolution of the pore structure of γ-Al2O3 to further optimize the pore size distribution. The small pores formed by the decomposition of polyethylene glycol at a relatively low temperature can be integrated with the mesoporous structure of γ-Al2O3 itself, while the large pores formed by the decomposition of polyacrylamide at a higher temperature occupy a certain proportion in the structural framework of γ-Al2O3, thus achieving the target pore size distribution with 65-75% of pores with a size of 4-10 nm and 10-20% of pores with a size of >15 nm.

[0023] The amino groups on polyallylamine hydrochloride form coordination bonds with aluminum ions, which, like a "molecular switch", determine the addition direction and position of aluminum atoms during crystal growth, guiding the growth of alumina crystals along specific lattice directions. At the same time, the steric hindrance of the polymer long chain restricts the diffusion and approach paths of surrounding aluminum ions and other precursor molecules, changing the growth rates of different crystal planes of the crystal and regulating the crystal form of alumina to tend to grow into the γ-Al2O3 crystal form. The γ-Al2O3 crystal form is beneficial to forming a pore size distribution that meets the requirements of 65-75% of pores with a size of 4-10 nm and 10-20% of pores with a size of >15 nm, taking into account both catalytic activity and mass transfer efficiency.

[0024] Optionally, in step A, the mass concentration of the CdSe quantum dot dispersion is 5%-20%; the mass concentration of the mercaptoacetic acid aqueous solution is 5%-15%; the mass ratio of the CdSe quantum dot dispersion to the mercaptoacetic acid aqueous solution is 1:(5-10).

[0025] Optionally, in step B, the mass ratio of polyallylamine hydrochloride to the mercaptoacetic acid-modified CdSe quantum dot dispersion is 1:(15-20).

[0026] By adopting the above technical solutions, the appropriate mass ratio enables polyallylamine hydrochloride to fully react with the modified quantum dots to form a stable grafted structure, and its coordination effect and steric hindrance effect of amino groups with aluminum ions can better play their roles in regulating the crystal form and pore structure of alumina.

[0027] Optionally, in step B, the addition amount of N-hydroxysuccinimide is 1%-5% of the mass of the mercaptoacetic acid-modified CdSe quantum dot dispersion.

[0028] By adopting the above technical solution, N-hydroxysuccinimide is used as an activator. If the addition amount is too much, side reactions may occur, affecting the quality of the crystal form guiding agent; if the addition amount is too little, the reaction may not be fully activated, resulting in insufficient grafting reaction. An appropriate addition amount can enable the grafting reaction to proceed smoothly, obtaining a crystal form guiding agent with appropriate structure and properties to meet the requirements for regulating the crystal form and pore structure of alumina.

[0029] Optionally, the acidic solvent is one of nitric acid or acetic acid.

[0030] Optionally, the pore-expanding agent is one of ammonium carbonate or ammonium bicarbonate.

[0031] By adopting the above technical solution, ammonium carbonate or ammonium bicarbonate will decompose to produce gas during the calcination process, leaving pores, effectively increasing the pore diameter and pore volume of the carrier, realizing the regulation of the pore structure of the carrier, and preparing an alumina carrier with a bimodal pore structure to meet specific performance requirements.

[0032] In summary, the present application has the following beneficial effects:

[0033] 1. The present application selects at least two pore-forming agents with different decomposition temperatures for compounding, and uses their decomposition characteristics at different stages during the calcination process to accurately construct pores with a size of 4-10 nm and pores larger than 15 nm. When kneading, a crystal form guiding agent is added. With the quantum size effect of CdSe quantum dots, the charge distribution and coordination of aluminum ions are affected, prompting crystal nuclei to form at specific positions on the surface of the quantum dots, and then inducing the formation of a γ-Al2O3 crystal form that is prone to form a high proportion of 4-10 nm pores. At the same time, the amino groups on the grafted chain of polyallylamine hydrochloride coordinate with aluminum ions, and the steric hindrance of the long chain jointly regulates the crystal form of alumina. The difference in crystal form further affects the evolution of the pore structure. By strictly controlling a series of process parameters such as kneading, drying, and calcination, finally, the proportion of 4-10 nm pores in the prepared alumina carrier reaches 65-75%, and the proportion of pores larger than 15 nm reaches 10-20%. This takes into account good catalytic activity and mass transfer efficiency, which is beneficial to improving the gasoline pre-hydrogenation reaction effect.

[0034] 2. The method of the present application precisely sets the mass ratio of each raw material, enabling pseudoboehmite to form a framework, additives to play roles such as plasticizing and pore-forming, pore-expanding agents, acidic solvents, and crystal form guiding agents to effectively regulate the pore structure and crystal form, and deionized water to ensure the mixing and forming of materials. Therefore, it can avoid abnormal material states from affecting the operation and the performance of the carrier, ensuring the successful and efficient preparation of a high-performance alumina carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a detection graph of the change in pore diameter and pore volume of the alumina carrier in Example 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The present application will be further described in detail below in conjunction with embodiments.

[0037] The pore volume of pseudo-boehmite is 0.6 - 0.7 mL / g; polyethylene glycol is PEG400 purchased from Hai'an Petrochemical Factory in Jiangsu Province; polyacrylamide is CD-0046 purchased from Shandong Chengda Chemical Technology Co., Ltd.; the CdSe quantum dot dispersion is purchased from Nanjing Muke Nano Technology Co., Ltd., and the liquid phase of the CdSe quantum dot dispersion is ethanol.

[0038] Preparation Examples of Crystal Structure-directing Agent

[0039] Preparation Example 1

[0040] The crystal structure-directing agent is prepared by the following method:

[0041] A. Mix 1 kg of a 5% CdSe quantum dot dispersion with 5 kg of a 5% aqueous mercaptoacetic acid solution. Then, slowly add Tris-HCl buffer solution to the mixed solution to adjust the pH value of the solution system to 8 - 9. Then, react the reaction solution at a temperature of 45°C and a rotation speed of 150 r / min for 2 h. After the reaction, a mercaptoacetic acid-modified CdSe quantum dot dispersion is obtained;

[0042] B. Mix 0.1 kg of polyallylamine hydrochloride with 1.5 kg of the mercaptoacetic acid-modified CdSe quantum dot dispersion, add 0.015 kg of N-hydroxysuccinimide, and stir and react at room temperature for 12 h. Then, transfer the reaction solution to a dialysis bag, dialyze with deionized water for 48 h, and then perform freeze-drying to obtain the crystal structure-directing agent.

[0043] Preparation Example 2

[0044] The crystal structure-directing agent is prepared by the following method:

[0045] A. Mix 1 kg of a 12% CdSe quantum dot dispersion with 8 kg of a 10% aqueous mercaptoacetic acid solution. Then, slowly add Tris-HCl buffer solution to the mixed solution to adjust the pH value of the solution system to 8 - 9. Then, react the reaction solution at a temperature of 50°C and a rotation speed of 175 r / min for 2.5 h. After the reaction, a mercaptoacetic acid-modified CdSe quantum dot dispersion is obtained;

[0046] B. Mix 0.1 kg of polyallylamine hydrochloride with 1.8 kg of the mercaptoacetic acid-modified CdSe quantum dot dispersion, add 0.054 kg of N-hydroxysuccinimide, and stir and react at room temperature for 18 h. Then, transfer the reaction solution to a dialysis bag, dialyze with deionized water for 48 h, and then perform freeze-drying to obtain the crystal structure-directing agent.

[0047] Preparation Example 3

[0048] The crystal form guiding agent is prepared by the following method:

[0049] A. Mix 1 kg of CdSe quantum dot dispersion with a mass concentration of 20% and 10 kg of mercaptoacetic acid aqueous solution with a mass concentration of 15%. Then slowly add Tris-HCl buffer solution to the mixed solution, adjust the pH value of the solution system to 8-9, and then react the reaction solution at a temperature of 55°C with a rotation speed of 200 r / min for 3 h. After the reaction, a mercaptoacetic acid-modified CdSe quantum dot dispersion is obtained;

[0050] B. Mix 0.1 kg of polyallylamine hydrochloride with 2.0 kg of mercaptoacetic acid-modified CdSe quantum dot dispersion, add 0.10 kg of N-hydroxysuccinimide, stir and react at room temperature for 24 h, then transfer the reaction solution to a dialysis bag, dialyze with deionized water for 48 h, and then perform freeze-drying to obtain the crystal form guiding agent.

[0051] Preparation Example 4

[0052] The crystal form guiding agent is different from that in Preparation Example 3 in that an equal amount of polyaniline is used instead of polyallylamine hydrochloride to participate in the grafting reaction in this preparation example.

[0053] Example

[0054] Example 1

[0055] A method for preparing a bimodal pore toothball-shaped alumina carrier includes the following steps:

[0056] (1) Weigh the raw materials according to the material dosage ratio shown in Table 1. Among them, ammonium carbonate is selected as the pore-expanding agent, nitric acid with a mass concentration of 8% is selected as the acidic solvent, and the crystal form guiding agent prepared in Preparation Example 1 is selected as the crystal form guiding agent. Then mix the weighed pseudo-boehmite, polyethylene glycol, polyacrylamide, pore-expanding agent, acidic solvent, crystal form guiding agent and deionized water, and then perform kneading and extrusion. When extruding, the feeding frequency is 15 Hz and the extrusion frequency is 10 Hz. The extruded strip-shaped material is processed by a toothball forming machine to obtain a toothball-shaped blank;

[0057] (2) Dry the toothball-shaped blank at a drying temperature of 100°C for 8 h; then calcine at 300°C for 2 h, and then raise the temperature to 500°C and calcine for 3 h. After the calcination is completed, a bimodal pore toothball-shaped alumina carrier is obtained.

[0058] Example 2

[0059] A method for preparing a bimodal pore toothball-shaped alumina carrier includes the following steps:

[0060] (1) Weigh the raw materials according to the dosage ratio of substances shown in Table 1. Among them, the pore former is ammonium carbonate, the acidic solvent is nitric acid with a mass concentration of 8%, and the crystal form guiding agent is the crystal form guiding agent prepared in Preparation Example 2. Then mix the weighed pseudo-boehmite, polyethylene glycol, polyacrylamide, pore former, acidic solvent, crystal form guiding agent and deionized water, and then carry out kneading and extrusion. When extruding, the feeding frequency is 15 Hz and the extrusion frequency is 10 Hz. The extruded strip-shaped material is processed by a tooth ball forming machine to obtain a tooth ball-shaped green body;

[0061] (2) Dry the tooth ball-shaped green body at a drying temperature of 90 °C for 8 h; then calcine it at 350 °C for 3 h, and then raise the temperature to 550 °C and calcine it for 4 h. After the calcination is completed, a bimodal pore tooth ball-shaped alumina carrier is obtained.

[0062] Example 3

[0063] A preparation method of a bimodal pore tooth ball-shaped alumina carrier, comprising the following steps:

[0064] (1) Weigh the raw materials according to the dosage ratio of substances shown in Table 1. Among them, the pore former is ammonium carbonate, the acidic solvent is nitric acid with a mass concentration of 8%, and the crystal form guiding agent is the crystal form guiding agent prepared in Preparation Example 3. Then mix the weighed pseudo-boehmite, polyethylene glycol, polyacrylamide, pore former, acidic solvent, crystal form guiding agent and deionized water, and then carry out kneading and extrusion. When extruding, the feeding frequency is 15 Hz and the extrusion frequency is 10 Hz. The extruded strip-shaped material is processed by a tooth ball forming machine to obtain a tooth ball-shaped green body;

[0065] (2) Dry the tooth ball-shaped green body at a drying temperature of 90 °C for 8 h; then calcine it at 350 °C for 3 h, and then raise the temperature to 550 °C and calcine it for 4 h. After the calcination is completed, a bimodal pore tooth ball-shaped alumina carrier is obtained.

[0066] Table 1 Raw material dosage and ratio in Examples 1-3 (kg)

[0067]

[0068] Example 4

[0069] A preparation method of a bimodal pore tooth ball-shaped alumina carrier, which is different from Example 1 in that: the pore former in step (1) of this example is ammonium bicarbonate.

[0070] Example 5

[0071] A preparation method of a bimodal pore tooth ball-shaped alumina carrier, which is different from Example 1 in that: the acidic solvent in step (1) of this example is acetic acid with a mass concentration of 15%.

[0072] Example 6

[0073] A preparation method of a bimodal pore toothed spherical alumina support, which is different from Example 1 in that: the crystal form guiding agent in step (1) of this example is the crystal form guiding agent prepared in Preparation Example 4.

[0074] Comparative example

[0075] Comparative Example 1

[0076] An alumina support was prepared according to Example 5 in the patent document with the publication number CN116037085B and the name "A macroporous alumina support and its preparation method".

[0077] Comparative Example 2

[0078] A preparation method of a bimodal pore toothed spherical alumina support, which is different from Example 1 in that: in this comparative example, no crystal form guiding agent was added to the raw materials in step (1), and the difference was made up with pseudoboehmite.

[0079] Comparative Example 3

[0080] A preparation method of a bimodal pore toothed spherical alumina support, which is different from Example 1 in that: in step (1) of this comparative example, an equal amount of untreated CdSe quantum dot dispersion liquid was used instead of the crystal form guiding agent.

[0081] Comparative Example 4

[0082] A preparation method of a bimodal pore toothed spherical alumina support, which is different from Example 1 in that: in step (1) of this comparative example, polyethylene glycol was not added, and the difference was made up with pseudoboehmite.

[0083] Performance detection test

[0084] The performance indexes of the alumina supports prepared in Examples 1-6 and Comparative Examples 1-6 were detected, and the results are shown in Table 2.

[0085] Table 2 Detection results

[0086]

[0087] The particle size of the alumina supports prepared in Examples 1-5 is between 3.02 and 3.12 mm, the pore volume is between 0.56 and 0.62 mL / g, the bulk density is between 0.62 and 0.68 g / mL, and the physical property parameters are basically stable. And the prepared alumina support meets the index requirements of 65-75% of pores with a diameter of 4-10 nm and 10-20% of pores with a diameter > 15 nm. The prepared alumina support can take into account good catalytic activity and mass transfer efficiency, which is beneficial to improving the reaction effect of gasoline pre-hydrogenation.

[0088] The pore volume ratio of 4 - 10 nm of the alumina support prepared in Comparative Example 1 is only 11.23%, while the pore volume ratio of >15 nm is as high as 68.92%, which is difficult to meet the pore ratio index expected in this application.

[0089] In Comparative Example 2, no crystal form directing agent was added during the preparation process. The pore volume ratio of 4 - 10 nm of the obtained alumina support is 23.52%, and the pore volume ratio of >15 nm is 45.21%. Due to the lack of the crystal form directing agent, the effect of the crystal form directing agent on aluminum ions cannot be utilized to induce the formation of γ - Al2O3 crystal form that is beneficial to the formation of a high proportion of 4 - 10 nm pores, and the pore structure cannot be optimized through crystal form regulation, resulting in an insufficient proportion of 4 - 10 nm pores and a relatively high proportion of >15 nm pores.

[0090] In Comparative Example 3, an equal amount of untreated CdSe quantum dot dispersion liquid was used to replace the crystal form directing agent. The pore volume ratio of 4 - 10 nm of the prepared alumina support is 52.16%, and the pore volume ratio of >15 nm is 5.62%. The untreated CdSe quantum dot dispersion liquid has not undergone processes such as mercaptoacetic acid modification and grafting with amino polymers, and cannot effectively exert the influence on the charge distribution and coordination of aluminum ions, and cannot induce the formation of alumina with a suitable crystal form, so the pore structure cannot be accurately regulated, resulting in the non - compliance of the proportion of 4 - 10 nm pores and an overly low proportion of >15 nm pores.

[0091] In Comparative Example 4, no polyethylene glycol was added. The pore volume ratio of 4 - 10 nm is 15.36%, and the pore volume ratio of >15 nm is 48.32%. Polyethylene glycol is a key pore - forming agent for forming 4 - 10 nm small pores during high - temperature calcination. After the lack of polyethylene glycol, sufficient 4 - 10 nm small pores cannot be decomposed and formed at the corresponding temperature, resulting in a significant decrease in the proportion of 4 - 10 nm pores, while the proportion of >15 nm large pores formed by the decomposition of polyacrylamide relatively increases.

[0092] This specific embodiment is only an explanation of this application, and it does not limit this application. Those skilled in the art can make modifications without creative contributions to this embodiment after reading this specification, but as long as it is within the scope of the claims of this application, it is protected by the patent law.

Claims

1. A preparation method of a bimodal pore toothed spherical alumina carrier, characterized in that, It includes the following steps: (1) Mix pseudoboehmite, polyethylene glycol, polyacrylamide, pore former, acidic solvent, crystal form directing agent and deionized water, then carry out kneading and extrusion, and then process with a tooth ball forming machine to obtain a tooth ball shaped blank; (2) Dry the tooth ball shaped blank, then calcine it at 300 - 400 °C for 2 - 3 h, then raise the temperature to 500 - 600 °C and calcine for 3 - 5 h. After the calcination is completed, a bimodal pore tooth ball shaped alumina support is obtained; The crystal form directing agent is prepared by the following method: A. Disperse the CdSe quantum dot dispersion in an aqueous solution of mercaptoacetic acid. Subsequently, add a Tris-HCl buffer solution to the mixed solution, adjust the pH value of the solution system to 8 - 9, and then oscillate and react the reaction solution at a temperature of 45 - 55 °C and a rotation speed of 150 - 200 r / min for 2 - 3 h. After the reaction is completed, a mercaptoacetic acid modified CdSe quantum dot dispersion is obtained; B. Mix polyallylamine hydrochloride with the mercaptoacetic acid modified CdSe quantum dot dispersion, add N-hydroxysuccinimide, and stir and react at room temperature for 12 - 24 h, and then carry out dialysis and freeze drying to obtain the crystal form directing agent; In step B, the addition amount of N-hydroxysuccinimide is 1% - 5% of the mass of the mercaptoacetic acid modified CdSe quantum dot dispersion. The mass ratio of the pseudoboehmite, polyethylene glycol, polyacrylamide, pore former, acidic solvent, crystal form directing agent and deionized water is (30 - 50):(5 - 8):(2 - 5):(1 - 3):(2 - 5):(3 - 5):(20 - 30).

2. The preparation method of a bimodal pore toothed spherical alumina carrier according to claim 1, characterized in that: In step A, the mass concentration of the CdSe quantum dot dispersion is 5% - 20%; the mass concentration of the aqueous solution of mercaptoacetic acid is 5% - 15%; the mass ratio of the CdSe quantum dot dispersion to the aqueous solution of mercaptoacetic acid is 1:(5 - 10).

3. The preparation method of a bimodal pore toothed spherical alumina carrier according to claim 1, characterized in that: In step B, the mass ratio of polyallylamine hydrochloride to the mercaptoacetic acid modified CdSe quantum dot dispersion is 1:(15 - 20).

4. The preparation method of a bimodal pore toothed spherical alumina carrier according to claim 1, characterized in that: The acidic solvent is one of nitric acid or acetic acid.

5. The preparation method of a bimodal pore toothed spherical alumina carrier according to claim 1, characterized in that: The pore former is one of ammonium carbonate or ammonium bicarbonate.

6. The preparation method of a bimodal pore toothed spherical alumina carrier according to claim 1, characterized in that: ​

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