A method for preparing high-purity, highly colloidal macroporous pseudoboehmite

Abstract

This application provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, belonging to the field of pseudoboehmite. The method includes: adding a high-purity aluminum salt solution and a high-purity sodium aluminate solution in parallel to a pseudoboehmite seed slurry for neutralization reaction to obtain a precursor slurry; after solid-liquid separation, adding a water-soluble alcohol to the precursor filter cake slurry to obtain an aging slurry; then subjecting the aging slurry to gradient pH aging, successively adding sodium carbonate to adjust the pH to 8-8.5 and aging for 2 hours, and adding ammonium bicarbonate to adjust the pH to 8.5-9 and aging for 1 hour; finally, after solid-liquid separation, obtaining the pseudoboehmite product. The pseudoboehmite obtained in this application has a total impurity content of Si, Fe, and Na of less than 100 ppm, a colloidal index of 98.0%-98.8%, a pore volume of 0.769-1.603 mL / g, and a specific surface area of ​​280.1-375.6 μm. 2 / g, achieving the coexistence of high purity, high colloidal solubility, and large pore volume.

Description

Technical Field

[0001] This application relates to the field of boehmite technology, and more particularly to a method for preparing high-purity, high-colloidal-solubility macroporous boehmite. Background Technology

[0002] Boehmite, also known as monohydrate alumina or pseudo-boehmite, is an important raw material for manufacturing catalyst supports. High-purity boehmite can prevent catalyst poisoning caused by impurities; suitable pore volume, pore size, and specific surface area provide effective catalytic activity; its high colloidal solubility allows it to act as a binder to enhance catalyst molding strength, while also adjusting the catalyst pore structure and acidic active site density, thus improving thermal and hydrothermal stability. Therefore, developing boehmite products that simultaneously possess high purity, high colloidal solubility, and large pore volume is of great significance.

[0003] Currently, the main methods for preparing boehmite include neutralization, carbonization, and aluminum alkoxide hydrolysis. Neutralization and carbonization are relatively simple and low-cost, but existing technologies generally suffer from a contradiction between pore volume and colloidal solubility; that is, increasing pore volume decreases the colloidal index, while increasing the colloidal index significantly reduces pore volume. It is difficult to simultaneously achieve high purity, high colloidal solubility, and large pore volume, thus failing to meet the comprehensive performance requirements of high-end catalysts such as reforming catalysts for support materials. While aluminum alkoxide hydrolysis can yield products with high purity and good colloidal solubility, its high production cost and significant environmental impact limit its large-scale application. Therefore, providing a method for preparing boehmite that achieves a balance between high purity, high colloidal solubility, and large pore volume has become a pressing technical problem in this field. Summary of the Invention

[0004] This application provides a method for preparing high-purity, highly colloidal, macroporous pseudoboehmite to solve the following technical problem: how to prepare a pseudoboehmite that simultaneously possesses high purity, high colloidal solubility, and large pore volume.

[0005] This application provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, the method comprising: An aluminum salt solution and a sodium aluminate solution were added to the boehmite seed slurry to carry out a neutralization reaction, thereby obtaining a boehmite precursor slurry. The low-temperature neutralization reaction included the following parameters: temperature of 10–30°C, time of 60–150 min, and final pH value of 6–7. The pseudoboehmite precursor slurry was subjected to solid-liquid separation to obtain precursor filter cake. A water-soluble alcohol is added to the slurry of the precursor filter cake to obtain a slurry to be aged. The slurry to be aged is subjected to gradient pH aging to obtain a pseudo-boehmite slurry. The pseudoboehmite slurry was subjected to solid-liquid separation to obtain pseudoboehmite filter cake; The pseudoboehmite filter cake is washed and dried to obtain the pseudoboehmite product.

[0006] Optionally, in the pseudoboehmite seed slurry, the pseudoboehmite seed crystals meet the following properties: purity ≥ 99.99%, and gel solubility index ≥ 98%.

[0007] Optionally, the mass of the boehmite seed crystals added is 5% to 10% of the mass of the boehmite product.

[0008] Optionally, the aluminum salt solution includes at least one of aluminum sulfate solution, aluminum chloride solution, or aluminum nitrate solution, wherein the purity of the aluminum salt solution is analytical grade, and the mass concentration of aluminum oxide in the aluminum salt solution is 50 g / L to 120 g / L.

[0009] Optionally, the sodium aluminate solution is of analytical grade, and the mass concentration of alumina in the sodium aluminate solution is 50 g / L to 120 g / L.

[0010] Optionally, the water-soluble alcohol includes at least one of propanol, butanol, isopropanol, ethylene glycol, or glycerol, and the volume of the water-soluble alcohol added is 5% to 10% of the slurry volume of the precursor filter cake.

[0011] Optionally, the step of aging the slurry to be aged using a gradient pH value to obtain a pseudo-boehmite slurry includes: Sodium carbonate is added to the slurry to be aged to adjust the pH to 8-8.5, thus obtaining the first mixed slurry; The first mixed slurry is subjected to a first aging treatment to obtain a second mixed slurry; Ammonium bicarbonate was added to the second mixed slurry to adjust the pH to 8.5-9, thus obtaining the third mixed slurry; The third mixed slurry is subjected to a second aging treatment to obtain a pseudo-boehmite slurry.

[0012] Optionally, the temperature of the first aging treatment is 80-100°C, and the time of the first aging treatment is 1.5-2.5 hours.

[0013] Optionally, the temperature of the second aging treatment is 80-100°C, and the time of the second aging treatment is 0.5-1.5 hours.

[0014] Optionally, the pseudoboehmite product meets the following properties: total impurity content of Si, Fe, and Na < 100 ppm; colloidal index of 98.0%–98.8%; pore volume of 0.769 mL / g–1.603 mL / g; and specific surface area of ​​280.1 m².2 / g~375.6m 2 / g.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite. Through a series of steps including seed induction, solid-liquid separation and impurity removal, pore expansion with water-soluble alcohol, gradient pH aging, and final washing and drying, the method synergistically achieves a balance between high purity, high colloidal solubility, and large pore volume in the pseudoboehmite product.

[0016] First, an aluminum salt solution and a sodium aluminate solution are added to the boehmite seed slurry for neutralization, with the reaction temperature controlled at 10–30°C, the reaction time at 60–150 min, and the final pH value at 6–7. This step induces the growth of new crystals according to a highly colloidal crystal form through the pre-existing seed crystals, laying the foundation for the high colloidal properties of the final product. Simultaneously, low-temperature neutralization promotes the formation of a loosely structured precursor, avoiding excessive densification. Second, the boehmite precursor slurry obtained from the neutralization reaction undergoes solid-liquid separation to obtain a precursor filter cake. This operation removes soluble impurities (such as sodium ions, chloride ions, or sulfate ions) from the mother liquor, ensuring the high purity of the product. Then, a water-soluble alcohol is added to the precursor filter cake slurry to obtain an aging slurry. The water-soluble alcohol can penetrate into the pores of the precursor, inhibiting pore shrinkage during subsequent aging and acting as a pore-expanding agent, creating conditions for the construction of large pore volumes. Next, the slurry to be aged is subjected to gradient pH aging. By adjusting the pH in stages (for example, first adjusting to a weakly alkaline pH to promote orderly grain arrangement, and then further adjusting to a higher pH and introducing ammonium ions to replace sodium ions), the orderly growth of grains to achieve high colloidal performance is ensured, while the pore structure is further expanded to achieve large pore volume, thus resolving the contradiction between colloidal performance and pore volume in traditional methods. Afterwards, the aged pseudoboehmite slurry is subjected to solid-liquid separation again to obtain a pseudoboehmite filter cake. This operation removes soluble byproducts generated during the aging process. Finally, the pseudoboehmite filter cake is washed and dried. The washing operation thoroughly removes residual sodium ions and other impurities to ensure product purity; the drying operation removes free water without damaging the pore structure. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart illustrating a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, as provided in an embodiment of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0022] Figure 1 This is a schematic flowchart illustrating a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, as provided in an embodiment of this application.

[0023] like Figure 1 As shown in the embodiments of this application, a method for preparing high-purity, highly colloidal macroporous pseudoboehmite is provided, the method comprising: S1. Add aluminum salt solution and sodium aluminate solution to the boehmite seed slurry to carry out a neutralization reaction to obtain the boehmite precursor slurry; the low-temperature neutralization reaction includes the following parameters: temperature 10-30℃, time 60-150min, and endpoint pH 6-7. S2. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake; S3. Add water-soluble alcohol to the slurry of the precursor filter cake to obtain the slurry to be aged; S4. The slurry to be aged is subjected to gradient pH aging to obtain pseudo-boehmite slurry. S5. The pseudoboehmite slurry is subjected to solid-liquid separation to obtain pseudoboehmite filter cake. S6. Wash and dry the pseudoboehmite filter cake to obtain the pseudoboehmite product.

[0024] It should be noted that in the preparation method of high-purity, highly colloidal macroporous boehmite, step S1 involves adding aluminum salt solution and sodium aluminate solution to the boehmite seed slurry, and carrying out a neutralization reaction at a low temperature of 10–30°C for 60–150 min, controlling the final pH value to 6–7, thereby obtaining the boehmite precursor slurry. This step, by introducing high-purity, highly colloidal boehmite seed crystals before the reaction, induces the growth of new grains according to the highly colloidal crystal form, significantly improving the colloidal properties of the final product; simultaneously, the low-temperature neutralization reaction is conducive to the formation of a precursor with uniform particle size and loose structure, laying the foundation for the subsequent construction of a macroporous structure. For example, the low-temperature neutralization reaction temperature can be 10°C, 13°C, 16°C, 19°C, 22°C, 25°C, 28°C, 30°C, etc. The low-temperature neutralization reaction time can be 60 min, 72 min, 84 min, 96 min, 110 min, 122 min, 135 min, 150 min, etc. The endpoint pH value of the low-temperature neutralization reaction can be 6.0, 6.15, 6.3, 6.45, 6.6, 6.75, 6.9, 7.0, etc.

[0025] Step S2 involves solid-liquid separation of the pseudoboehmite precursor slurry to obtain a precursor filter cake. This step removes soluble impurities (such as sodium ions, chloride ions, or sulfate ions) from the reaction mother liquor through physical separation, providing pure solid material for subsequent aging treatment and preventing impurities from interfering with crystal form regulation during the aging process.

[0026] In step S3, a water-soluble alcohol is added to the slurry of the precursor filter cake to obtain the slurry to be aged. This step utilizes the water-soluble alcohol (such as propanol, butanol, ethylene glycol, glycerol, etc.) to penetrate into the pores of the pseudoboehmite precursor, effectively inhibiting pore shrinkage during the subsequent high-temperature aging process, thereby playing a role in pore expansion and ensuring the large pore volume characteristics of the product.

[0027] Step S4 involves subjecting the slurry to a gradient pH aging process to obtain a pseudoboehmite slurry. This gradient pH aging process comprises two stages: In the first stage, sodium carbonate is added to adjust the pH to 8–8.5, and aging is carried out at 80–100°C for 2 hours. This stage promotes the orderly arrangement of pseudoboehmite crystals, thereby endowing the product with high colloidal properties. In the second stage, ammonium bicarbonate is added to adjust the pH to 8.5–9, and aging continues at the same temperature for 1 hour. In this stage, ammonium ions replace sodium ions in the crystal channels and on the surface, further increasing the pore structure and achieving the coexistence of high colloidal properties and large pore volume. This resolves the technical contradiction between colloidal properties and pore volume in traditional methods.

[0028] Step S5 involves solid-liquid separation of the pseudoboehmite slurry to obtain a pseudoboehmite filter cake. This step separates the aged solid product and removes soluble byproducts generated during the aging process (such as excess carbonate, bicarbonate, and substituted sodium ions).

[0029] Step S6 involves washing and drying the pseudoboehmite filter cake to obtain the pseudoboehmite product. The washing operation involves repeatedly washing the filter cake with deionized water until the pH of the washing solution is less than 7, thoroughly removing residual sodium ions and other soluble impurities to ensure high purity (total Si, Fe, and Na impurities less than 100 ppm). The drying operation is carried out at 80–130℃ (preferably 90–110℃) to remove free water from the product while avoiding high temperature-induced pore structure collapse, ultimately yielding a product with high purity, a high colloidal index (98.0–98.8%), large pore volume (0.769–1.603 mL / g), and a suitable specific surface area (280.1–375.6 μm). 2 / g) of pseudoboehmite products.

[0030] In some embodiments, the boehmite seed crystals in the boehmite seed slurry meet the following properties: purity ≥ 99.99% and gel solubility index ≥ 98%.

[0031] Limiting the purity of boehmite seed crystals to greater than 99.99% and their colloidal index to greater than 98% ensures that the seed crystals themselves possess high purity and high colloidal properties. Seed crystals with a purity greater than 99.99% introduce extremely low levels of impurities into the reaction system, laying the foundation for the high purity of the final product; seed crystals with a colloidal index greater than 98% can effectively induce the growth of new grains according to a highly colloidal crystal form during the neutralization reaction, thereby significantly improving the colloidal properties of the product.

[0032] In some embodiments, the mass of the boehmite seed crystals added is 5% to 10% of the mass of the boehmite product.

[0033] The addition of boehmite seed crystals is limited to 5%–10% of the boehmite product mass. This range provides a sufficient number of nuclei to induce crystal growth while avoiding excessive seed crystals that could lead to excessive grain aggregation or uneven grain size distribution. This ensures suitable pore volume and specific surface area while maintaining high colloidal properties. For example, the mass percentage of boehmite seed crystals can be 5.0%, 5.7%, 6.4%, 7.1%, 7.8%, 8.5%, 9.2%, 10.0%, etc.

[0034] In some embodiments, the aluminum salt solution includes at least one of aluminum sulfate solution, aluminum chloride solution, or aluminum nitrate solution, the purity of the aluminum salt solution is analytical grade, and the mass concentration of aluminum oxide in the aluminum salt solution is 50 g / L to 120 g / L.

[0035] The aluminum salt solution is specified as at least one of aluminum sulfate, aluminum chloride, or aluminum nitrate solutions, and its purity is analytical grade. This ensures the high purity of the reaction raw materials and avoids the introduction of metal ion impurities (such as iron and silicon) into the product. The mass concentration of alumina in the aluminum salt solution is specified as 50 g / L to 120 g / L. This concentration range is beneficial for controlling the neutralization reaction rate, allowing the reaction to proceed under mild conditions, and generating a pseudoboehmite precursor with uniform particle size and loose structure. For example, the mass concentration of alumina in the aluminum salt solution can be 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, etc.

[0036] In some embodiments, the sodium aluminate solution is of analytical grade, and the mass concentration of alumina in the sodium aluminate solution is 50 g / L to 120 g / L.

[0037] The purity of the sodium aluminate solution is limited to analytical grade to ensure high purity of the raw material and prevent contamination of the product by impurities such as sodium, silicon, and iron. The mass concentration of alumina in the sodium aluminate solution is limited to 50 g / L to 120 g / L, matching the concentration of the aluminum salt solution to ensure stoichiometric balance between the aluminum and alkali sources during the neutralization reaction, thereby obtaining a precursor with a single crystalline phase and high purity. For example, the mass concentration of alumina in the sodium aluminate solution can be 50 g / L, 62 g / L, 74 g / L, 86 g / L, 93 g / L, 101 g / L, 112 g / L, 120 g / L, etc.

[0038] In some embodiments, the water-soluble alcohol includes at least one of propanol, butanol, isopropanol, ethylene glycol, or glycerol, and the volume of the water-soluble alcohol added is 5% to 10% of the slurry volume of the precursor filter cake.

[0039] The water-soluble alcohol is specified to include at least one of propanol, butanol, isopropanol, ethylene glycol, or glycerol. These water-soluble alcohols are well dispersed in the aqueous slurry and effectively penetrate into the pores of the precursor filter cake. The added volume of the water-soluble alcohol is specified to be 5% to 10% of the slurry volume of the precursor filter cake. This volume ratio is sufficient to form effective steric hindrance during subsequent high-temperature aging, inhibiting pore shrinkage and thus expanding the pores to ensure the macropore volume characteristics of the product. For example, the volume percentage of the water-soluble alcohol added can be 5.0%, 5.8%, 6.6%, 7.4%, 8.2%, 8.8%, 9.4%, 10.0%, etc.

[0040] In some embodiments, the slurry to be aged is subjected to gradient pH aging to obtain a pseudo-boehmite slurry, including: Sodium carbonate is added to the slurry to be aged to adjust the pH to 8-8.5, thus obtaining the first mixed slurry; The first mixed slurry is subjected to a first aging treatment to obtain a second mixed slurry; Ammonium bicarbonate was added to the second mixed slurry to adjust the pH to 8.5-9, thus obtaining the third mixed slurry; The third mixed slurry was subjected to a second aging treatment to obtain a pseudo-boehmite slurry.

[0041] This stepwise gradient regulation method can optimize the grain arrangement and pore structure in stages: In the first stage, sodium carbonate is used to promote the orderly arrangement of grains in a weakly alkaline environment (pH 8-8.5) to achieve high colloidal performance; in the second stage, ammonium bicarbonate is used to further increase the pH to 8.5-9, introducing ammonium ions to replace sodium ions in the grain pores and on the surface, further increasing the pore structure, thereby achieving the coexistence of high colloidal performance and large pore volume.

[0042] In some embodiments, the temperature of the first aging treatment is 80–100°C, and the time of the first aging treatment is 1.5–2.5 h.

[0043] The temperature for the first aging treatment is limited to 80–100°C, and the time is limited to 1.5–2.5 h (preferably 2 h). This temperature range provides sufficient energy for the orderly rearrangement of grains while avoiding excessive temperature that could cause channel collapse; the aging time of 1.5–2.5 h ensures that the grain arrangement is fully completed, forming a stable, highly colloidal crystal form. For example, the first aging treatment temperature can be 80°C, 83°C, 86°C, 89°C, 92°C, 95°C, 98°C, 100°C, etc. The first aging treatment time can be 1.5 h, 1.65 h, 1.8 h, 1.95 h, 2.1 h, 2.25 h, 2.4 h, 2.5 h, etc.

[0044] In some embodiments, the temperature of the second aging treatment is 80–100°C, and the time of the second aging treatment is 0.5–1.5 h.

[0045] The temperature for the second aging treatment is limited to 80–100°C, and the time is limited to 0.5–1.5 h (preferably 1 h). The same temperature range as the first aging treatment ensures the continuity of the aging process and avoids the adverse effects of temperature fluctuations on the grain structure; the 0.5–1.5 h time is sufficient to complete the substitution of sodium ions by ammonium ions and further expansion of pores, while preventing over-aging that could lead to a decrease in specific surface area. For example, the temperature for the second aging treatment can be 80°C, 82°C, 85°C, 88°C, 91°C, 94°C, 97°C, 100°C, etc. The time for the second aging treatment can be 0.5 h, 0.65 h, 0.8 h, 0.95 h, 1.1 h, 1.25 h, 1.4 h, 1.5 h, etc.

[0046] In some embodiments, the pseudoboehmite product meets the following properties: total impurity content of Si, Fe, and Na < 100 ppm, colloidal index of 98.0%–98.8%, pore volume of 0.769 mL / g–1.603 mL / g, and specific surface area of ​​280.1 m². 2 / g~375.6m 2 / g.

[0047] This application achieves simultaneous compliance with various performance indicators of the product by using high-purity raw materials and washing to ensure purity, seeding and first-stage aging to ensure gel solubility, and water-soluble alcohol and second-stage aging to synergistically expand pores and maintain a suitable specific surface area.

[0048] Regarding high purity (total impurity content <100ppm): This performance is mainly achieved through the following steps. First, the aluminum salt solution and sodium aluminate solution used in step S1 are both analytical grade, with an alumina concentration of 50–120 g / L in both the aluminum salt solution and the sodium aluminate solution, thus controlling the introduction of impurities such as iron and silicon from the source of the raw materials. Second, the boehmite seed crystals added in step S1 have a purity greater than 99.99%, further preventing the introduction of additional impurities by the seed crystals. Third, step S2 involves solid-liquid separation of the boehmite precursor slurry to obtain a precursor filter cake. This operation removes soluble impurities such as sodium ions, chloride ions, or sulfate ions dissolved in the reaction mother liquor. Finally, in steps S5 and S6, the pseudoboehmite filter cake is thoroughly washed (until the pH value is less than 7) to completely remove residual sodium carbonate and ammonium bicarbonate introduced during the aging process, as well as sodium ions displaced by ammonium ions. Simultaneously, the drying temperature is controlled at 80–130°C to avoid potential impurity enrichment at high temperatures. Through these multiple purification measures, the total content of Si, Fe, and Na impurities in the final product is controlled below 100 ppm.

[0049] Regarding the high colloidal index (98.0%–98.8%): This performance is mainly attributed to the synergistic effect of seed induction and the first stage of gradient pH aging. In step S1, a neutralization reaction is carried out in the presence of boehmite seed slurry. The colloidal index of the seed crystals is greater than 98%, indicating high purity. This allows the nascent crystals to grow in a highly colloidal crystal form, thus endowing the precursor with excellent colloidal potential. Subsequently, in the gradient pH aging process of step S4, sodium carbonate is added in the first stage to adjust the pH to 8–8.5, and a first aging treatment is carried out at 80–100℃ for 1.5–2.5 hours. This weakly alkaline high-temperature aging condition promotes the orderly arrangement of boehmite crystals, resulting in a more complete and uniform crystal form, further consolidating the high colloidal performance. The combination of these two steps ensures that the colloidal index of the final product consistently reaches 98.0%–98.8%.

[0050] Regarding macropore volume (0.769–1.603 mL / g) and suitable specific surface area (280.1–375.6 μm) 2 / g): This performance relies on the pore-expanding effect of water-soluble alcohol and the structural regulation of the second stage of gradient pH aging. In step S3, 5%–10% by volume of water-soluble alcohol (such as propanol, butanol, isopropanol, ethylene glycol, or glycerol) is added to the precursor filter cake slurry. These alcohol molecules can penetrate into the precursor pores and form steric hindrance during subsequent high-temperature aging, effectively inhibiting the shrinkage of pores caused by grain rearrangement, thereby expanding the pores and ensuring the formation of large pore volume. In the gradient pH aging of step S4, ammonium bicarbonate is added to the second mixed slurry in the second stage to adjust the pH to 8.5–9, and the second aging treatment is carried out at 80–100℃ for 0.5–1.5 h. In this stage, ammonium ions enter the grain pores and surface, replacing some sodium ions. Due to the thermal decomposition of ammonium ions leaving more voids, the pore structure is further expanded, and the pore volume is significantly increased to 0.769–1.603 mL / g. Meanwhile, because the original framework of the grains was not excessively damaged, the specific surface area was maintained at 280.1–375.6 m². 2 The appropriate range of / g ensures both the sufficiency of catalytic active sites and avoids the decrease in thermal stability caused by excessively high specific surface area.

[0051] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0052] Example 1 This embodiment provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 12g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 0.5mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 80g / L and a high-purity aluminum chloride solution with an equivalent alumina concentration of 80g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 20℃, the reaction time is 75min, and the final pH value is 6.9, obtaining a boehmite precursor slurry.

[0053] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0054] S31. The precursor filter cake is slurried with deionized water, 200 mL of propanol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0055] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.5, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0056] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a high-purity, high-colloidal macroporous pseudoboehmite filter cake.

[0057] S61. The high-purity, high-colloidal-solubility macroporous pseudoboehmite filter cake was dried at 110℃ to obtain high-purity, high-colloidal-solubility macroporous pseudoboehmite. The final mass of the pseudoboehmite product obtained was 232g.

[0058] Example 2 This embodiment provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 20g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 0.7mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 100g / L and a high-purity aluminum chloride solution with an equivalent alumina concentration of 100g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 18℃, the reaction time is 90min, and the final pH value is 6.7, obtaining a boehmite precursor slurry.

[0059] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0060] S31. The precursor filter cake is slurried with deionized water, 200 mL of butanol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0061] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8.2, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.6, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0062] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a high-purity, high-colloidal macroporous pseudoboehmite filter cake.

[0063] S61. The high-purity, high-colloidal-solubility macroporous pseudoboehmite filter cake was dried at 100℃ to obtain high-purity, high-colloidal-solubility macroporous pseudoboehmite. The final mass of the pseudoboehmite product obtained was 297g.

[0064] Example 3 This embodiment provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 20g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 0.8mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 100g / L and a high-purity aluminum sulfate solution with an equivalent alumina concentration of 100g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 22℃, the reaction time is 105min, and the final pH value is 6.7, obtaining a boehmite precursor slurry.

[0065] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0066] S31. The precursor filter cake is slurried with deionized water, 200 mL of isopropanol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0067] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8.4, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.8, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0068] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a high-purity, high-colloidal macroporous pseudoboehmite filter cake.

[0069] S61. The high-purity, high-colloidal-solubility macroporous pseudoboehmite filter cake is dried at 100℃ to obtain high-purity, high-colloidal-solubility macroporous pseudoboehmite. The final mass of the pseudoboehmite product obtained is 300g.

[0070] Example 4 This embodiment provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 15g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 0.9mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 90g / L and a high-purity aluminum sulfate solution with an equivalent alumina concentration of 90g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 25℃, the reaction time is 120min, and the final pH value is 6.5, obtaining a boehmite precursor slurry.

[0071] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0072] S31. The precursor filter cake is slurried with deionized water, 200 mL of ethylene glycol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0073] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8.1, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.7, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0074] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a high-purity, high-colloidal macroporous pseudoboehmite filter cake.

[0075] S61. The high-purity, high-colloidal-solubility macroporous pseudoboehmite filter cake is dried at 100℃ to obtain high-purity, high-colloidal-solubility macroporous pseudoboehmite. The final mass of the pseudoboehmite product obtained is 264g.

[0076] Example 5 This embodiment provides a method for preparing high-purity, highly colloidal macroporous pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 12g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 1.0mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 80g / L and a high-purity aluminum sulfate solution with an equivalent alumina concentration of 80g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 19℃, the reaction time is 140min, and the final pH value is 6.2, obtaining a boehmite precursor slurry.

[0077] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0078] S31. The precursor filter cake is slurried with deionized water, 200 mL of glycerol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0079] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.5, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0080] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a high-purity, high-colloidal macroporous pseudoboehmite filter cake.

[0081] S61. The high-purity, high-colloidal-solubility macroporous pseudoboehmite filter cake was dried at 90℃ to obtain high-purity, high-colloidal-solubility macroporous pseudoboehmite. The final mass of the pseudoboehmite product obtained was 232g.

[0082] Comparative Example 1 This comparative example provides a method for preparing pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor. Without adding boehmite seed crystals, slowly add a high-purity sodium aluminate solution with an alumina concentration of 80g / L and a high-purity aluminum chloride solution with an alumina concentration of 80g / L in parallel to carry out a neutralization reaction. The reaction temperature is 20℃, the reaction time is 75min, and the final pH value is 6.9, to obtain a boehmite precursor slurry.

[0083] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0084] S31. The precursor filter cake is slurried with deionized water, 200 mL of propanol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0085] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.5, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0086] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a pseudoboehmite filter cake.

[0087] S61. The pseudoboehmite filter cake is dried at 110°C to obtain the pseudoboehmite product. The final mass of the pseudoboehmite product is 220g.

[0088] Comparative Example 2 This comparative example provides a method for preparing pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 20g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 0.7mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 100g / L and a high-purity aluminum chloride solution with an equivalent alumina concentration of 100g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 18℃, the reaction time is 90min, and the final pH value is 6.7, obtaining a boehmite precursor slurry.

[0089] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0090] S31. The precursor filter cake is slurried with deionized water without adding water-soluble alcohol, and stirred evenly to obtain the slurry to be aged. The total volume of the slurry after slurrying the precursor filter cake is 4000 mL.

[0091] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8.2, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.6, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0092] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a pseudoboehmite filter cake.

[0093] S61. The pseudoboehmite filter cake is dried at 100°C to obtain the pseudoboehmite product. The final mass of the pseudoboehmite product is 297g.

[0094] Comparative Example 3 This comparative example provides a method for preparing pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 20g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 80%, and a pore volume of 0.8mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 100g / L and a high-purity aluminum sulfate solution with an equivalent alumina concentration of 100g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 22℃, the reaction time is 105min, and the final pH value is 7.5, obtaining a boehmite precursor slurry.

[0095] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0096] S31. The precursor filter cake is slurried with deionized water, 200 mL of isopropanol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0097] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8.4, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.8, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0098] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a pseudoboehmite filter cake.

[0099] S61. The pseudoboehmite filter cake is dried at 100℃ to obtain the pseudoboehmite product. The final mass of the pseudoboehmite product obtained is 300g.

[0100] Comparative Example 4 This comparative example provides a method for preparing pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 15g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 0.9mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 90g / L and a high-purity aluminum sulfate solution with an equivalent alumina concentration of 90g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 25℃, the reaction time is 120min, and the final pH value is 6.5, obtaining a boehmite precursor slurry.

[0101] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0102] S31. The precursor filter cake is slurried with deionized water, 200 mL of ethylene glycol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0103] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 8.1, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 9.5, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0104] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a pseudoboehmite filter cake.

[0105] S61. The pseudoboehmite filter cake is dried at 100°C to obtain the pseudoboehmite product. The final mass of the pseudoboehmite product is 264g.

[0106] Comparative Example 5 This comparative example provides a method for preparing pseudoboehmite, which includes the following steps: S11. Add 0.5L of bottom water to a 5L reactor, then add 12g of boehmite seed crystals with a purity of 99.99%, a colloidal index of 98%, and a pore volume of 1.0mL / g. Stir until homogeneous to obtain a boehmite seed crystal slurry. Slowly add a high-purity sodium aluminate solution with an alumina concentration of 80g / L and a high-purity aluminum sulfate solution with an equivalent alumina concentration of 80g / L to the boehmite seed crystal slurry in parallel flow to carry out a neutralization reaction. The reaction temperature is 19℃, the reaction time is 140min, and the final pH value is 6.2, obtaining a boehmite precursor slurry.

[0107] S21. The pseudoboehmite precursor slurry is subjected to solid-liquid separation to obtain precursor filter cake.

[0108] S31. The precursor filter cake is slurried with deionized water, 200 mL of glycerol is added, and the mixture is stirred evenly to obtain the slurry to be aged. The total volume of the slurry after the precursor filter cake is slurried is 4000 mL.

[0109] S41. The slurry to be aged is subjected to gradient pH aging: First, sodium carbonate is added to adjust the pH to 7.5, and the first aging treatment is carried out at 80℃ for 2 hours; then ammonium bicarbonate is added to adjust the pH to 8.5, and the second aging treatment is carried out at 80℃ for 1 hour to obtain pseudo-boehmite slurry.

[0110] S51. Filter and wash the pseudoboehmite slurry using deionized water at 80°C until the pH value is less than 7, to obtain a pseudoboehmite filter cake.

[0111] S61. The pseudoboehmite filter cake is dried at 90°C to obtain the pseudoboehmite product. The final mass of the pseudoboehmite product is 232g.

[0112] The performance of the pseudoboehmite products obtained in Examples 1-5 and Comparative Examples 1-5 was measured, and the results are shown in Table 1.

[0113] Table 1. Performance of the pseudoboehmite products of Examples 1-5 and Comparative Examples 1-5

[0114] As shown in Table 1, the pseudoboehmite products prepared in Examples 1-5 had Si impurity contents of 31-42 ppm, Fe impurity contents of 17-21 ppm, and Na impurity contents of 17-20 ppm, with a total impurity content of less than 100 ppm; a colloidal index of 98.0%-99.7%; a pore volume of 0.769-1.603 mL / g; and a specific surface area of ​​280.1-375.6 m². 2 / g. The products of the embodiments of this application simultaneously achieve the goals of high purity, high colloidal solubility, and large pore volume.

[0115] Comparative Example 1, due to the absence of high-purity, highly colloidal boehmite seed crystals during synthesis, suffered from insufficient induction of grain growth, resulting in a product colloidal index dropping to 95.1%. While other indicators were acceptable, the colloidal performance was inadequate. Comparative Example 2, lacking the addition of water-soluble alcohol before aging, experienced significant pore shrinkage during high-temperature aging, with a pore volume of only 0.782 mL / g, far lower than the pore volume levels under the same seed conditions in the examples. Comparative Example 3, with a high pH value of 7.5 at the neutralization reaction endpoint, resulted in excessively coarse initial grain growth, reducing the product pore volume to 0.905 mL / g and the specific surface area to 298.2 μm. 2 / g, with severe structural densification. In Comparative Example 4, the pH was adjusted to 9.5 during the second stage of gradient aging. Although the colloidal index increased to 99.6%, the excessively alkaline environment caused the pore structure to collapse, resulting in a pore volume of only 0.834 mL / g and a specific surface area of ​​only 257.9 μm. 2 / g. In Comparative Example 5, the pH was adjusted to 7.5 in the first stage of gradient aging, resulting in imperfect grain arrangement and insufficient crystallinity in the initial aging stage. The product's colloidal index decreased significantly to 90.9%. Although the pore volume and specific surface area increased, the core property of high colloidal solubility was lost.

[0116] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: (1) High purity assurance: This invention uses high-purity aluminum salt solution and high-purity sodium aluminate solution of analytical grade as raw materials, and introduces high-purity, high-colloidal soluble boehmite seed crystals with a purity greater than 99.99% before the neutralization reaction. Combined with subsequent solid-liquid separation and washing until the pH value is less than 7, the reaction mother liquor and impurities such as sodium, silicon, and iron introduced during the aging process are effectively removed, so that the total content of Si, Fe, and Na impurities in the final product is less than 100 ppm, which meets the stringent requirements of high-end catalysts for carrier purity.

[0117] (2) Achievement of high colloidal properties: By pre-adding high-purity, high-colloidal-solubilized pseudoboehmite seed crystals with a colloidal index greater than 98%, the newly formed grains are induced to grow according to the high colloidal crystal form; then, combined with the first stage of gradient pH aging (adding sodium carbonate to adjust the pH to 8-8.5, aging at 80-100℃ for 2h), the orderly arrangement of the grains is promoted, so that the colloidal index of the product can be stably reached 98.0%-98.8%, which can be used as a high-efficiency binder to enhance the molding strength of the catalyst.

[0118] (3) Coexistence of macropore volume and high colloidal solubility: To address the problem of the conflict between pore volume and colloidal solubility in traditional methods, this invention adds 5-10% by volume of water-soluble alcohol (such as propanol, butanol, ethylene glycol, glycerol, etc.) to the precursor filter cake slurry before aging. The alcohol molecules penetrate into the pores to inhibit pore shrinkage during high-temperature aging. At the same time, ammonium bicarbonate is added in the second stage of gradient aging to adjust the pH to 8.5-9, using ammonium ions to replace sodium ions to further expand the pore structure. The synergistic effect of the two results in a product pore volume of 0.769-1.603 mL / g, while maintaining the colloidal index, thus achieving the coexistence of high colloidal solubility and macropore volume.

[0119] (4) Suitable specific surface area: While achieving large pore volume, the specific surface area of ​​the product of the present invention is controlled between 280.1 and 375.6 m². 2 Within the range of / g, it provides sufficient active sites for catalytic reactions while avoiding the decrease in thermal stability caused by excessively high specific surface area, resulting in excellent overall performance.

[0120] (5) Mild process conditions and controllable production costs: The present invention adopts the neutralization method, with a reaction temperature of 10-30℃, an aging temperature of 80-100℃, and a drying temperature of 80-130℃. It does not require high temperature and high pressure (unlike the 105-250℃ hydrothermal treatment in the aluminum alkoxide hydrolysis method), and the equipment requirements are low. The raw materials are conventional analytical pure aluminum salts and sodium aluminate, which avoids the use of high-cost raw materials such as high carbon alcohols in the aluminum alkoxide hydrolysis method. The production cost is significantly lower than that of imported products, and the environmental pressure is small.

[0121] (6) Product performance substitutes for imports: Through the above technical means, the pseudoboehmite prepared by the present invention has reached or exceeded the level of similar imported products (such as SB powder) in terms of key indicators such as purity, colloidal index, pore volume and specific surface area, filling the domestic technology gap. It is suitable for manufacturing high-end reforming catalysts and can effectively replace foreign imported products.

[0122] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing high-purity, highly colloidal macroporous pseudoboehmite, characterized in that, The method includes: An aluminum salt solution and a sodium aluminate solution were added to the boehmite seed slurry to carry out a neutralization reaction, thereby obtaining a boehmite precursor slurry. The low-temperature neutralization reaction included the following parameters: temperature of 10–30°C, time of 60–150 min, and final pH value of 6–7. The pseudoboehmite precursor slurry was subjected to solid-liquid separation to obtain precursor filter cake. A water-soluble alcohol is added to the slurry of the precursor filter cake to obtain a slurry to be aged. The slurry to be aged is subjected to gradient pH aging to obtain a pseudo-boehmite slurry. The pseudoboehmite slurry was subjected to solid-liquid separation to obtain pseudoboehmite filter cake; The pseudoboehmite filter cake is washed and dried to obtain the pseudoboehmite product.

2. The method according to claim 1, characterized in that, In the pseudoboehmite seed slurry, the pseudoboehmite seed crystals meet the following properties: purity ≥ 99.99%, and gel solubility index ≥ 98%.

3. The method according to claim 2, characterized in that, The mass of the pseudoboehmite seed crystals added is 5% to 10% of the mass of the pseudoboehmite product.

4. The method according to claim 1, characterized in that, The aluminum salt solution includes at least one of aluminum sulfate solution, aluminum chloride solution, or aluminum nitrate solution, wherein the purity of the aluminum salt solution is analytical grade, and the mass concentration of aluminum oxide in the aluminum salt solution is 50 g / L to 120 g / L.

5. The method according to claim 1, characterized in that, The sodium aluminate solution is of analytical grade, and the mass concentration of alumina in the sodium aluminate solution is 50 g / L to 120 g / L.

6. The method according to claim 1, characterized in that, The water-soluble alcohol includes at least one of propanol, butanol, isopropanol, ethylene glycol, or glycerol, and the volume of the water-soluble alcohol added is 5% to 10% of the slurry volume of the precursor filter cake.

7. The method according to claim 1, characterized in that, The step of aging the slurry to be aged using a gradient pH value to obtain a pseudo-boehmite slurry includes: Sodium carbonate is added to the slurry to be aged to adjust the pH to 8-8.5, thus obtaining the first mixed slurry; The first mixed slurry is subjected to a first aging treatment to obtain a second mixed slurry; Ammonium bicarbonate was added to the second mixed slurry to adjust the pH to 8.5-9, thus obtaining the third mixed slurry; The third mixed slurry is subjected to a second aging treatment to obtain a pseudo-boehmite slurry.

8. The method according to claim 7, characterized in that, The temperature of the first aging treatment is 80-100℃, and the time of the first aging treatment is 1.5h-2.5h.

9. The method according to claim 7, characterized in that, The temperature of the second aging treatment is 80-100℃, and the time of the second aging treatment is 0.5h-1.5h.

10. The method according to claim 1, characterized in that, The pseudoboehmite product meets the following properties: total impurity content of Si, Fe, and Na < 100 ppm; colloidal index of 98.0%–98.8%; pore volume of 0.769 mL / g–1.603 mL / g; and specific surface area of ​​280.1 m². 2 / g~375.6m 2 / g.

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