Preparation method of low-sulfate-radical macroporous pseudo-boehmite

Abstract

The invention relates to a preparation method of low-sulfate-radical macroporous pseudo-boehmite, and belongs to the technical field of material preparation. The method comprises the following steps: carrying out neutralization reaction on a sodium aluminate solution and an aluminum sulfate solution to obtain neutralized slurry; adding an ammonium carbonate solution into the neutralized slurry so as to adjust the pH value of the neutralized slurry to 8.5-9, and carrying out heat preservation treatment on the neutralized slurry after the pH value is adjusted so as to promote the ion exchange process to enable sulfate radicals to be transferred from a solid phase to a liquid phase so as to obtain slurry after ion exchange; sequentially carrying out suction filtration and washing on the slurry subjected to ion exchange to obtain a filter cake; pulping the filter cake again to obtain re-pulpified slurry; and sequentially carrying out aging treatment and ammonium bicarbonate solution washing on the re-pulpified slurry to obtain a low-sulfate-radical macroporous pseudo-boehmite product.

Description

Technical Field

[0001] This application relates to the field of materials preparation technology, and in particular to a method for preparing low-sulfate macroporous pseudoboehmite. Background Technology

[0002] Boehmite (chemical formula γ-AlOOH) is one of the most widely used precursor supports in the field of industrial catalysis. Through calcination, boehmite can be transformed into γ-Al₂O₃, which has a high specific surface area, abundant pore structure, and excellent stability. This transformation product plays a crucial "bridge" role in connecting the active metal component with the catalytic reaction performance. Thanks to its tunable physicochemical properties, boehmite can be adapted to various types of catalytic reactions, such as hydrogenation, dehydrogenation, catalytic oxidation, and denitration, thus occupying an irreplaceable position in many fields, including petrochemicals, environmental protection, and fine chemicals.

[0003] However, a significant issue in the preparation and application of pseudoboehmite is the adverse impact of its internal sulfate ions on catalytic performance. The presence of sulfate accelerates irreversible catalyst deactivation in multiple ways, increases operating costs, and affects production efficiency. Currently, the sulfate content in pseudoboehmite products is generally higher than 1.5%, which fails to meet the catalytic industry's demand for materials with low sulfate content, macroporous structure, and high mechanical strength. Summary of the Invention

[0004] This application provides a method for preparing low-sulfate macroporous pseudoboehmite to solve the following technical problem: how to solve the problem of excessive sulfate content in existing pseudoboehmite products. This application provides a method for preparing low-sulfate macroporous pseudoboehmite, the method comprising: The sodium aluminate solution and aluminum sulfate solution are neutralized to obtain a neutralized slurry; Ammonium carbonate solution is added to the neutralized slurry to adjust the pH of the neutralized slurry to 8.5-9. The neutralized slurry after pH adjustment is then subjected to heat treatment to promote the ion exchange process and transfer sulfate ions from the solid phase to the liquid phase, thereby obtaining the ion-exchanged slurry. The slurry after ion exchange is sequentially filtered and washed to obtain a filter cake. The filter cake is re-pulped to obtain a re-pulped slurry; The re-slurry was subjected to aging treatment and washing with ammonium bicarbonate solution in sequence to obtain the pseudoboehmite product.

[0005] Optionally, the mass concentration of alumina in the sodium aluminate solution is 160 g / L to 210 g / L.

[0006] Optionally, the aluminum oxide concentration in the aluminum sulfate solution is 40 g / L to 60 g / L.

[0007] Optionally, the mass concentration of the ammonium carbonate solution is 80 g / L to 150 g / L.

[0008] Optionally, the mass concentration of the ammonium bicarbonate solution is 30 g / L to 60 g / L.

[0009] Optionally, the temperature of the neutralization reaction is 50℃~70℃, and the pH of the neutralization slurry is 8~8.5.

[0010] Optionally, the heat preservation treatment time is 50 min to 90 min.

[0011] Optionally, the washing process involves agitation followed by rinsing.

[0012] Optionally, the solids content of the re-slurry is 70 g / L to 240 g / L, and the pH of the re-slurry is 8 to 9.

[0013] Optionally, the aging treatment is carried out at a set stirring speed, wherein the set stirring speed is 200 r / min to 300 r / min.

[0014] Optionally, the aging treatment temperature is 80–100°C, and the aging treatment time is 2–5 hours.

[0015] Optionally, the pseudoboehmite product satisfies at least one of the following properties: specific surface area > 300 m². 2 / g, pore volume >0.8mL / g, sulfate mass fraction <1.2%.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing low-sulfate macroporous pseudoboehmite, the method comprising: neutralizing sodium aluminate solution and aluminum sulfate solution to obtain a neutralized slurry; adding ammonium carbonate solution to the neutralized slurry to adjust the pH of the neutralized slurry to 8.5-9; subjecting the pH-adjusted neutralized slurry to heat treatment to promote the ion exchange process and transfer sulfate ions from the solid phase to the liquid phase to obtain an ion-exchanged slurry; sequentially filtering and washing the ion-exchanged slurry to obtain a filter cake; re-slurrying the filter cake to obtain a re-slurry; and sequentially aging and washing with ammonium bicarbonate solution to obtain the pseudoboehmite product. By controlling the temperature and pH of the neutralization reaction, a pseudoboehmite precursor (AlOOH·xH2O) is generated. Adding a specific concentration of ammonium carbonate solution to the neutralization slurry not only adjusts the pH but also introduces carbonate ions. During subsequent heat treatment, the introduced carbonate ions undergo sufficient ion exchange with sulfate ions in the solid phase of the neutralization slurry, allowing ample time for the displaced sulfate ions to diffuse from the solid phase into the liquid phase. After ion exchange, the slurry is filtered and washed, achieving the main removal of sulfate ions. The filter cake obtained from filtration is re-slurryed to a specific solid content and pH, and aged at a set stirring speed. During aging, the weakly alkaline environment and continuous dissolution-recrystallization process perform "dynamic deep washing" of the product, removing any remaining trace amounts of sulfate ions. After aging treatment, pseudoboehmite is used to remove stubborn residual sulfate ions through ion exchange and weak alkalinity of ammonium bicarbonate solution. The resulting pseudoboehmite product has the characteristics of macroporous structure, high specific surface area and low sulfate content, which meets the needs of industrial applications. 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 The electron microscope image of boehmite 1 provided in Embodiment 1 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 "1~6" 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] This application provides a method for preparing low-sulfate macroporous pseudoboehmite, the method comprising: The sodium aluminate solution and aluminum sulfate solution are neutralized to obtain a neutralized slurry; Ammonium carbonate solution is added to the neutralized slurry to adjust the pH of the neutralized slurry to 8.5-9. The neutralized slurry after pH adjustment is then subjected to heat treatment to promote the ion exchange process and transfer sulfate ions from the solid phase to the liquid phase, thereby obtaining the ion-exchanged slurry. The slurry after ion exchange is sequentially filtered and washed to obtain a filter cake. The filter cake is re-pulped to obtain a re-pulped slurry; The re-slurry was subjected to aging treatment and washing with ammonium bicarbonate solution in sequence to obtain the pseudoboehmite product.

[0023] By controlling the temperature and pH of the neutralization reaction, a pseudoboehmite precursor (AlOOH·xH2O) is generated. Adding a specific concentration of ammonium carbonate solution to the neutralization slurry not only adjusts the pH but also introduces carbonate ions. During subsequent heat treatment, the introduced carbonate ions undergo sufficient ion exchange with sulfate ions in the solid phase of the neutralization slurry, allowing ample time for the displaced sulfate ions to diffuse from the solid phase into the liquid phase. After ion exchange, the slurry is filtered and washed, achieving the bulk removal of sulfate ions. The filter cake obtained from filtration is re-slurryed to a specific solid content and pH, and aged at a set stirring speed. During aging, the weakly alkaline environment and continuous dissolution-recrystallization process perform "dynamic deep washing" of the product, removing any remaining trace amounts of sulfate ions. After aging treatment, pseudoboehmite is used to remove stubborn residual sulfate ions through ion exchange and weak alkalinity of ammonium bicarbonate solution. The resulting pseudoboehmite product has the characteristics of macroporous structure, high specific surface area and low sulfate content, which meets the needs of industrial applications.

[0024] In some embodiments, the mass concentration of alumina in the sodium aluminate solution is 160 g / L to 210 g / L.

[0025] In the neutralization reaction, sodium aluminate solution and aluminum sulfate solution react to generate a neutralization slurry. The solid phase in the neutralization slurry is the boehmite precursor (AlOOH·xH2O). The mass concentration of alumina in the sodium aluminate solution directly affects the nucleation rate and grain growth rate of the neutralization reaction. If the mass concentration of alumina in the sodium aluminate solution is below 160 g / L, the reaction system has few particles, low supersaturation, and a slow nucleation rate, which is not conducive to the formation of a well-developed porous structure of the boehmite precursor. If the mass concentration of alumina in the sodium aluminate solution is above 210 g / L, the instantaneous supersaturation of the neutralization reaction is too high, which will lead to explosive nucleation and generate a large number of fine, disordered primary particles. These particles will accumulate randomly and will not easily form a regular macroporous structure during subsequent aging treatment. Therefore, the mass concentration of alumina in the sodium aluminate solution is 160 g / L to 210 g / L, which provides sufficient reactant concentration for the neutralization reaction to ensure a reasonable reaction rate and yield, while avoiding excessively rapid nucleation. This allows primary particles to aggregate and grow in a relatively orderly manner, laying a good foundation for the rearrangement, dissolution-recrystallization, and formation of a stable macroporous structure of the pseudoboehmite precursor in the subsequent aging treatment steps.

[0026] In some embodiments, the aluminum oxide concentration in the aluminum sulfate solution is 40 g / L to 60 g / L.

[0027] In the neutralization reaction, sodium aluminate solution (alkaline) and aluminum sulfate solution (acidic) mix rapidly, instantly generating a pseudoboehmite precursor. The structure of this pseudoboehmite precursor is the "blueprint" for the entire material structure. If the mass concentration of alumina in the aluminum sulfate solution is below 40 g / L, the neutralization reaction rate is slow, resulting in fewer crystal nuclei and potentially coarse-grained pseudoboehmite precursor particles. This makes it difficult to form a rich and well-developed porous structure. Furthermore, to achieve the same total aluminum content, a larger volume of aluminum sulfate solution needs to be processed, leading to inefficiency. If the mass concentration of alumina in the aluminum sulfate solution is above 60 g / L, similar to high-concentration sodium aluminate, the neutralization reaction will experience excessively high instantaneous supersaturation, triggering explosive nucleation and generating a large number of fine, disordered, and structurally unstable primary particles. These particles will accumulate randomly, clogging the pores. Even with subsequent aging treatment, it will be difficult to form a regular, interconnected macroporous structure in the pseudoboehmite product. By controlling the alumina concentration in the aluminum sulfate solution to be between 40 g / L and 60 g / L, matching the alumina concentration in the sodium aluminate solution, a moderate driving force for the neutralization reaction is provided. This makes the nucleation and growth process of the boehmite precursor relatively mild and controllable, which is conducive to the formation of primary particle clusters with uniform size and loose structure. This initial structure provides space for particle rearrangement and crystal growth in subsequent ion exchange processes and aging treatments, and is an important basis for the final formation of the macroporous structure of the boehmite product.

[0028] Secondly, the reaction between sodium aluminate solution and aluminum sulfate solution is essentially acid-base neutralization. The concentrations of sodium aluminate solution and aluminum sulfate solution directly determine the volumetric flow ratio of the two solutions when the target reaction endpoint (such as a specific pH value) is reached. Controlling the mass concentration of alumina in the aluminum sulfate solution to 40 g / L–60 g / L, and matching it with the mass concentration of alumina in the sodium aluminate solution to 160 g / L–210 g / L, ensures that the volume ratio of sodium aluminate solution and aluminum sulfate solution added is within a reasonable and easily precisely controllable range. If the concentrations of sodium aluminate solution and aluminum sulfate solution are unbalanced (e.g., aluminum sulfate is too dilute, sodium aluminate is too concentrated), it will result in one material having an extremely high flow rate and the other an extremely low flow rate. This makes pipeline mixing and metering pump control very difficult in industrial production, easily causing localized over-acidity or over-alkalinity in the neutralization reaction, leading to heterogeneity in the composition and structure of the boehmite precursor. By controlling the alumina concentration in the aluminum sulfate solution to 40 g / L–60 g / L and combining it with the alumina concentration in the sodium aluminate solution to 160 g / L–210 g / L, the stability and operability of the preparation method for low-sulfate macroporous pseudoboehmite were ensured. This allowed the neutralization reaction system to smoothly reach the preset neutralization point, generating pseudoboehmite precursors with uniform chemical composition and physical structure. This is crucial for ensuring batch-to-batch quality stability of pseudoboehmite products.

[0029] Finally, sulfate (SO4) 2-The only source of sulfate ions is aluminum sulfate solution. If the mass concentration of aluminum oxide in the aluminum sulfate solution is higher than 60 g / L, it means that a larger total amount of sulfate ions is introduced per unit volume, which will put enormous pressure on achieving the "low sulfate" goal. Controlling the mass concentration of aluminum oxide in the aluminum sulfate solution at 40 g / L to 60 g / L limits the total amount of sulfate ions entering the neutralization reaction system, fundamentally reducing the burden on the ion exchange process and filtration washing, making it easier and more reliable to achieve the core goal of "low sulfate".

[0030] In some embodiments, the mass concentration of the ammonium carbonate solution is 80 g / L to 150 g / L.

[0031] The pseudoboehmite precursor produced by the neutralization reaction has very low crystallinity, unstable structure, and underdeveloped pores. Adding ammonium carbonate solution to the slurry after neutralization to adjust the pH of the system to 8.5–9 can provide a mild and continuous alkaline environment for the neutralized system.

[0032] If the mass concentration of the ammonium carbonate solution is below 80 g / L, a large amount of low-concentration ammonium carbonate solution needs to be added to achieve the target pH value. This will excessively dilute the neutralization slurry, resulting in a very low solids content. This not only reduces the production efficiency of low-sulfate macroporous boehmite but also weakens the concentration-driving force for subsequent aging treatment, affecting crystal growth. If the mass concentration of the ammonium carbonate solution is above 150 g / L, the ammonium carbonate solution is too alkaline. Its addition can easily cause a sharp increase in the local pH of the neutralization slurry, which may lead to uncontrollable rapid precipitation or crystallization of the boehmite precursor, generating unwanted, dense impurities such as Bayerite, thus disrupting the formation of the macroporous structure of the boehmite product. By controlling the mass concentration of the ammonium carbonate solution between 80 g / L and 150 g / L, the ammonium carbonate solution can act as a mild pH adjuster and mineralizer, precisely raising and stabilizing the pH value of the neutralization slurry within a range conducive to the formation and structural optimization of the boehmite product without excessive dilution.

[0033] Sulfate ions are encapsulated or adsorbed within the solid phase of the boehmite precursor due to their affinity for the precursor surface. Ammonium carbonate solution introduces carbonate ions, which can competitively replace sulfate ions. This is because carbonate ions have a stronger competitive adsorption capacity in an alkaline environment, effectively "replacing" sulfate ions from the solid phase surface of the boehmite precursor and releasing them into the liquid phase. Maintaining the mass concentration of the ammonium carbonate solution between 80 g / L and 150 g / L ensures a sufficient concentration of carbonate ions in the neutralization reaction system without excessive amounts. These carbonate ions act as "exchange ions" during the heat treatment, continuously driving the transfer of sulfate ions from the solid phase of the boehmite precursor to the liquid phase of the neutralization slurry, thereby significantly reducing the sulfate content in the boehmite product. If the mass concentration of the ammonium carbonate solution is below 80 g / L, there is insufficient driving force to complete the deep removal process through ion exchange.

[0034] In some embodiments, the temperature of the neutralization reaction is 50°C to 70°C, and the pH of the neutralization slurry is 8 to 8.5.

[0035] Controlling the neutralization reaction temperature between 50℃ and 70℃ helps to achieve a sufficiently fast reaction rate and reasonable production efficiency, while also ensuring a good balance between the nucleation process of the boehmite precursor and particle growth.

[0036] If the neutralization reaction temperature is below 50℃, the reaction rate and molecular thermal motion speed are slow, resulting in a small-sized and low-activity boehmite precursor. This precursor structure may be too "stable," hindering structural rearrangement and crystal growth during subsequent ion exchange and aging processes, making it difficult to form a well-developed macroporous structure in the boehmite product. If the neutralization reaction temperature is above 70℃, the reaction rate is too fast, easily leading to explosive nucleation and the generation of a large number of fine, disordered nanoparticles. These particles will tightly pack together, forming small and tortuous channels. Furthermore, a neutralization temperature above 70℃ accelerates the transformation of the boehmite precursor into a more thermodynamically stable crystalline phase (such as Bayerite), rather than generating boehmite with high pore volume and abundant mesoporous structure.

[0037] At higher temperatures, the solubility of ions generally increases, and thermal motion intensifies. Neutralization reactions conducted at 50℃~70℃ allow more sulfate ions from the aluminum sulfate solution to be excluded from the solid phase of the boehmite precursor particles at the moment of precursor formation, or to be weakly adsorbed on the surface of the boehmite precursor, rather than being tightly encapsulated within its structure.

[0038] The neutralization reaction of sodium aluminate and aluminum sulfate involves an aluminum hydrolysis-precipitation equilibrium. Under weakly alkaline conditions (pH 8–8.5), aluminum ions combine with hydroxide ions to primarily form boehmite precursors, rather than other crystalline phases (such as gibbsite). If the pH is too low (<8), aluminum precipitation is incomplete, easily forming colloidal or amorphous precipitates, leading to difficulties in subsequent filtration and poor product pore structure. If the pH is too high (>8.5), sodium aluminate may not react completely, residual aluminum species will affect product purity, and the precipitate is easily redissolved, reducing yield.

[0039] In some embodiments, the heat preservation treatment time is 50 min to 90 min.

[0040] Sulfate ions are encapsulated or adsorbed within the boehmite precursor, and its removal is a diffusion-controlled kinetic process. The removal of sulfate ions requires time to complete the following steps: carbonate ions diffuse from the bulk liquid phase to the surface of the boehmite precursor solid particles; as the reaction proceeds, the pH gradually increases, macroporous structures gradually form, and carbonate ions exchange with sulfate ions in the boehmite precursor solid phase; the displaced sulfate ions diffuse from the interior of the boehmite precursor solid phase to the surface of the boehmite precursor; and sulfate ions further diffuse from the surface of the boehmite precursor back into the bulk liquid phase. If the holding time is less than 50 minutes, the sulfate removal process cannot proceed sufficiently, and the ion exchange process only occurs on the surface and shallow layer of the boehmite precursor. A large number of sulfate ions inside the boehmite precursor cannot be displaced and diffused out in time, resulting in a persistently high sulfate content in the final boehmite product. While a holding time exceeding 90 minutes might improve sulfate removal, the improvement is limited. Within 50–90 minutes, most exchangeable sulfate ions have already been removed. Further extending the holding time offers limited improvement to the purity of the boehmite product and may even reduce the production efficiency of the boehmite preparation method, increasing energy consumption. Furthermore, holding times exceeding 90 minutes may cause slow changes in the boehmite precursor structure that are detrimental to macropore formation in the final product. Therefore, controlling the holding time to 50–90 minutes provides sufficient and necessary reaction and diffusion time for the ion exchange process, ensuring that sulfate ions within the solid phase of the boehmite precursor are deeply and thoroughly replaced, thereby significantly reducing the sulfate content in the final boehmite product.

[0041] In some embodiments, the washing is a combination of agitation and rinsing.

[0042] After heat treatment, the ion-exchange slurry is filtered to obtain a filter cake. The filter cake is then washed and re-slurryed to obtain a re-slurry. Washing involves agitation and rinsing. Agitation involves re-mixing the filter cake with fresh washing liquid (such as deionized water) to break up any clumps, allowing the washing liquid to fully penetrate the filter cake and dissolve and displace the sulfate-containing mother liquor remaining between particles and in the pores. Rinsing occurs during filtration, where the washing liquid is evenly sprayed (drizzled) onto the surface of the filter cake. The concentration difference and liquid flow continuously wash away and remove residual sulfate ions from the surface and shallow layers of the filter cake. Agitation achieves deep internal cleaning, while rinsing provides continuous surface rinsing and displacement. The combination of these two methods maximizes the physical separation of sulfate ions that have transferred to the liquid phase from the solid phase, providing a purer intermediate for subsequent steps.

[0043] In some embodiments, the solids content of the re-slurry is 70 g / L to 240 g / L, and the pH of the re-slurry is 8 to 9.

[0044] A solids content of 70 g / L to 240 g / L in the re-slurry provides the optimal interparticle interaction environment for the aging process, enabling the construction of the ideal pore structure of the boehmite product. If the solids content of the re-slurry is below 70 g / L, the slurry is too thin, resulting in large distances between solid particles and weak interaction forces. During aging, the "dissolution-recrystallization" process of the solid particles may tend to generate independent, small-sized boehmite crystals rather than a robust framework of interconnected, porous boehmite products. This can lead to boehmite products with potentially large pore volumes, poor strength, wide pore size distribution, and difficulty in forming regular large pores. If the solids content of the re-slurry is above 240 g / L, the slurry becomes too viscous, resembling a paste, which severely hinders mass and heat transfer during the aging process, resulting in uneven aging. Under high pressure and density, the dense packing of solid particles leaves insufficient space for the growth of boehmite pores, easily leading to the formation of small, tortuous pores. They may even agglomerate during aging treatment, preventing the formation of large pores. However, under conditions where the solid content of the re-slurry is 70 g / L to 240 g / L, there is sufficiently frequent contact and interaction between the solid particles. This allows for synergistic and orderly mass transport and crystal growth during the aging process, which is beneficial for forming a stable structure with high strength, concentrated pore size distribution, and, in particular, an ideal proportion of large pores.

[0045] Boehmite is an aluminum hydroxyl compound stable under weakly alkaline conditions, and pH is one of the most critical factors controlling its formation and transformation. If the pH of the resizing slurry is below 8, the slurry environment is acidic or neutral, which is unfavorable for the stability and growth of boehmite. The resizing slurry system may tend to generate amorphous aluminum hydroxide or undergo a phase transformation to more acidic conditions such as gibbsite, failing to obtain highly crystalline boehmite products. If the pH of the resizing slurry is above 9, the strongly alkaline environment will cause the boehmite precursor to dissolve, entering the slurry solution as aluminate ions. This will lead to a violent recrystallization during the aging process, potentially generating gibbsite variants such as Bayerite, or producing boehmite products with uneven particle size and dense structure, thus damaging the macroporous structure of the boehmite product. Precisely controlling the pH of the re-slurry within the weakly alkaline range of 8–9 provides the perfect thermodynamic driving force and kinetic conditions for the heterogeneous crystallization and growth of boehmite. At a pH of 8–9, the boehmite precursor can undergo slow and controllable dissolution, and precipitate and grow well-crystallized, lamellar or fibrous interwoven boehmite crystals along the correct crystallographic path. This interwoven structure is the key to forming the macropores of the boehmite product.

[0046] In some embodiments, the aging treatment is carried out at a set stirring speed, which is 200 r / min to 300 r / min.

[0047] Aging is a continuous and lengthy process. Under static or stirring speeds below 200 rpm, the boehmite precursor will settle to the bottom of the reactor due to gravity. If the stirring speed is below 200 rpm during aging, severe sedimentation will occur, resulting in excessively high material concentration at the bottom of the reactor, forming viscous slurries or even scaling on the reactor walls and agitator. The material deposited at the bottom of the reactor will come into contact with the heating surface, leading to localized overheating, abnormal rapid crystallization, or the formation of impurities such as Bayerite. The supernatant in the reactor will become clear, while the bottom will remain a paste. This will result in significant differences in the structure and properties of the upper and lower parts of the same batch of boehmite product, leading to a complete loss of quality control for the boehmite product. Therefore, controlling the stirring speed during the aging process at 200 r / min to 300 r / min provides sufficient suspending force to ensure that all boehmite precursors are uniformly dispersed in the liquid phase, forming a stable suspension system. This guarantees a consistent temperature distribution throughout the reactor, ensuring that all boehmite precursors undergo aging under the same thermodynamic conditions. Reactants and byproducts are also uniformly distributed within the aging system, avoiding concentration gradients. Setting the stirring speed during the aging process to 200 r / min to 300 r / min results in highly uniform properties and good reproducibility of the final boehmite product within each batch.

[0048] Secondly, the aging process is essentially a dynamic equilibrium of "dissolution-recrystallization" in the solid phase of the boehmite precursor. Molecules on the surface of the boehmite precursor particles dissolve into the liquid phase and then recrystallize in a more energy-favorable location. This process requires material transport in the liquid phase. If the stirring speed during the aging process is lower than 200 r / min, the mass transfer rate will be slow, and the dissolved aluminum species can only move within a very small diffusion layer around the boehmite precursor, resulting in low mass exchange efficiency. This will make the aging process extremely slow, and any trace amounts of sulfate ions that may remain cannot be effectively removed from the surface of the boehmite precursor.

[0049] In some embodiments, the aging treatment temperature is 80–100°C, and the aging treatment time is 2–5 hours.

[0050] The aging process follows the Ostwald ripening principle, where small, unstable particles or disordered phases dissolve and recrystallize on the surface of larger, more stable crystals. This process requires energy to overcome the energy barrier. If the aging temperature is below 80°C, the molecular kinetic energy is insufficient, and the kinetic rates of dissolution and recrystallization are too slow. The aging process becomes extremely lengthy or even stalls, and the pseudoboehmite precursor cannot be effectively converted into a well-crystallized pseudoboehmite product. The product may remain amorphous or have very low crystallinity, poor structural strength, and underdeveloped pores. If the aging treatment temperature exceeds 100℃, the driving force is too strong and the reaction rate is too fast, which may lead to the following problems: the formation of impurities such as Bayerite—in a high-temperature, strongly alkaline environment, the aging treatment system is prone to transforming into the more thermodynamically stable gibbsite, rather than forming the metastable pseudoboehmite target product; and structural densification—excessive crystallization leads to coarse and densely packed pseudoboehmite crystals, which in turn destroys the already formed macroporous structure of pseudoboehmite, resulting in a wider pore size distribution and a decrease in specific surface area and pore volume in the pseudoboehmite product. Therefore, controlling the aging treatment temperature at 80–100℃ provides sufficient thermal energy for the aging process, driving the pseudoboehmite precursor to undergo moderate and controllable dissolution-recrystallization, ensuring that the reaction proceeds at a reasonable rate towards the formation of a pure-phase, highly crystalline pseudoboehmite product, while effectively inhibiting the formation of impurities such as Bayerite.

[0051] Furthermore, the transformation from boehmite precursor to well-crystallized boehmite product is a slow structural rearrangement process, requiring time for atoms and ions to find their correct positions within the boehmite lattice. If the aging process is less than 2 hours, it is insufficient, resulting in a partially crystallized "semi-finished product" with an incomplete crystal structure, weak pore wall strength, and a tendency for pores to collapse during subsequent processing. While the specific surface area and pore volume may appear high, the structural stability is poor, and it may contain unconverted boehmite precursors. If the aging process exceeds 5 hours, it leads to over-aging. In the later stages of boehmite crystal growth, to reduce surface energy, smaller boehmite crystals are "swallowed" by larger ones, causing an increase in the average crystal size, a decrease in total pore volume and specific surface area, and a shift in pore size distribution towards larger pores, although the number of large pores may decrease, resulting in a coarsening of the structure. This is also detrimental to maintaining the ideal pore structure of the boehmite product. Excessively long aging times are also economically unreasonable.

[0052] Throughout the lengthy aging process, the slurry is maintained in an alkaline environment with a pH of 8-9. This alkaline environment provides a final opportunity for the removal of residual, deeply encapsulated trace amounts of sulfate ions. The continuous ion exchange and dissolution-recrystallization process exposes and releases these remaining sulfate ions into the liquid phase. Compared to a brief filtration wash, the prolonged aging process is equivalent to a dynamic, deep washing and purification process, further solidifying the "low sulfate" characteristic of the boehmite product.

[0053] In some embodiments, the mass concentration of the ammonium bicarbonate solution is 30 g / L to 60 g / L.

[0054] After aging, the re-slurry is sequentially filtered, washed with a weakly alkaline ammonium bicarbonate solution, washed with deionized water, and dried to obtain pseudoboehmite. Following the preceding ion exchange, filtration, stirring, rinsing, and aging treatments, most of the sulfate ions have been removed. However, a very small amount of sulfate ions may still be deeply adsorbed within the crystals or strongly bound to Al-OH active sites. The ammonium bicarbonate solution is weakly alkaline (pH approximately 7.8-8.2), providing HCO3-. - Ions can continue to react with residual SO4 2- Competitive adsorption or ion exchange occurs, displacing the last remaining stubborn sulfate ions. Furthermore, the mildly alkaline environment of the ammonium bicarbonate solution does not cause the drastic dissolution of boehmite as a strong alkali, but it is sufficient to disrupt some of the stronger bonds between sulfate and aluminum species, releasing sulfate ions into the liquid phase. In the embodiments of this application, the mass concentration of the ammonium bicarbonate solution is 30 g / L to 60 g / L. Concentrations below 30 g / L result in incomplete washing, while concentrations above 60 g / L may lead to waste or unnecessary side reactions.

[0055] In some embodiments, the pseudoboehmite product satisfies at least one of the following properties: specific surface area > 300 m². 2 / g, pore volume >0.8mL / g, sulfate mass fraction <1.2%.

[0056] Sulfate is an acidic group, which is particularly harmful when boehmite is used as a catalyst support. It poisons the active sites of the catalyst (especially the metal sites), reducing the catalyst's thermal stability and activity. By controlling the mass fraction of sulfate in the boehmite product to below 1.2%, a high-purity support material level was achieved, ensuring that the catalysts prepared using the boehmite product have high activity and long lifespan.

[0057] Pore ​​volume is an indicator that measures the total amount of pore space inside a material. A pore volume greater than 0.8 mL / g for pseudoboehmite products is a very high value, indicating that pseudoboehmite products have extremely rich pores. Abundant pores mean that pseudoboehmite products can load more active metal components and provide ample space for the diffusion and transport of chemical reactants and products. This is particularly beneficial for macromolecular reactions, effectively reducing diffusion limitations and preventing carbon buildup and pore blockage.

[0058] Specific surface area is the total surface area per unit mass of material. The specific surface area of ​​pseudoboehmite products is greater than 300 m². 2 / g belongs to high specific surface area materials. The high specific surface area of ​​pseudoboehmite products means that there are a large number of active sites available for exposure. When pseudoboehmite products are used as catalyst supports, active metals such as cobalt, molybdenum and nickel can be highly dispersed into tiny particles, thereby significantly improving catalytic efficiency.

[0059] 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 / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0060] Example 1 At 60°C, an aluminum sulfate solution with an alumina content of 50 g / L and a sodium aluminate solution with an alumina content of 180 g / L were pumped into a reaction vessel using a peristaltic pump. The pH was adjusted to 8.5 by adjusting the flow rate to obtain a neutralized slurry. 80 g / L ammonium carbonate was added to adjust the pH of the neutralized slurry to 9. After holding the neutralized slurry at this temperature for 1 hour, it was filtered and washed by stirring and rinsing. Deionized water was used to make slurries with solid contents of 70 g / L, 100 g / L, and 140 g / L, respectively. The pH was adjusted to 8.5 using ammonium carbonate solution to obtain a re-slurry. The re-slurry was heated to 90°C and aged for 3 hours with a stirring speed of 200 r / min. After filtration, it was washed first with a 30 g / L ammonium bicarbonate solution and then with deionized water. Finally, it was dried to obtain pseudoboehmite 1, pseudoboehmite 2, and pseudoboehmite 3.

[0061] The specific surface area of ​​pseudoboehmite 1 is 302.7 m². 2 / g, pore volume is 1.10 mL / g, SO4 2- The content is 1.56%; the specific surface area of ​​pseudoboehmite 2 is 311.3 m². 2 / g, pore volume is 1.16 mL / g, SO4 2- The content was 1.39%; the specific surface area of ​​pseudoboehmite 3 was 303.6 m². 2 / g, pore volume is 0.89 mL / g, SO4 2- The content is 1.63%.

[0062] Comparative Example 1 At 60°C, an aluminum sulfate solution with an alumina content of 50 g / L and a sodium aluminate solution with an alumina content of 180 g / L were pumped into a reaction vessel using a peristaltic pump. The pH was adjusted to 8.5 by regulating the flow rate to obtain a neutralized slurry. 80 g / L ammonium carbonate was added to adjust the pH of the neutralized slurry to 9. After heating to 90°C, the slurry was aged for 3 hours with a stirring speed of 200 r / min. The mixture was then filtered, washed first with a 30 g / L ammonium bicarbonate solution, then washed with deionized water, and finally dried to obtain pseudoboehmite. The specific surface area of ​​the obtained pseudoboehmite was 302 m². 2 / g, pore volume is 1.12 mL / g, SO4 2- The content is 2.86%.

[0063] Example 2 At 60°C, an aluminum sulfate solution with an alumina content of 50 g / L and a sodium aluminate solution with an alumina content of 200 g / L were pumped into a reactor using a peristaltic pump. The pH was adjusted to 8.5 by adjusting the flow rate to obtain a neutralized slurry. 80 g / L ammonium carbonate was added to adjust the pH of the neutralized slurry to 9. After holding the neutralized slurry at this temperature for 1 hour, it was filtered and washed by stirring and rinsing. Deionized water was used to pulp the slurry at a solid content of 100 g / L, and the pH was adjusted to 8.5 using ammonium carbonate solution to obtain a re-pulped slurry. The re-pulped slurry was heated to 90°C and aged for 2.5 hours at stirring speeds of 200 r / min and 300 r / min, respectively. After filtration, the slurry was first washed with a 40 g / L ammonium bicarbonate solution, then washed with deionized water, and finally dried to obtain pseudoboehmite 4 and pseudoboehmite 5.

[0064] The specific surface area of ​​pseudoboehmite 4 reaches 332.6 m². 2 / g, pore volume reaches 1.10 mL / g, SO4 2- Content 1.72%; specific surface area of ​​pseudoboehmite 5 reaches 355.8 m². 2 / g, pore volume reaches 1.11 mL / g, SO4 2- Content 1.84%.

[0065] Comparative Example 2 At 60°C, an aluminum sulfate solution with an alumina content of 50 g / L and a sodium aluminate solution with an alumina content of 200 g / L were pumped into a reaction vessel using a peristaltic pump. The pH was adjusted to 8 by regulating the flow rate to obtain a neutralized slurry. 80 g / L ammonium carbonate was added to adjust the pH of the neutralized slurry to 8.5. After holding the neutralized slurry at this temperature for 1 hour, it was filtered and washed using a combination of agitation and rinsing. The slurry was then pulped using deionized water at a solids content of 100 g / L, and the pH was adjusted to 8.5 using ammonium carbonate solution to obtain a re-slurry. The re-slurry was heated to 90°C and statically aged for 2.5 hours, followed by filtration. The slurry was first washed with a 40 g / L ammonium bicarbonate solution, then washed with deionized water, and finally dried to obtain pseudoboehmite. The specific surface area of ​​the obtained pseudoboehmite reached 355.7 m². 2 / g, pore volume reaches 1.07 mL / g, SO4 2- Content 3.52%.

[0066] Comparative Example 3 The preparation steps are basically the same as in Example 2, except that: the neutralized slurry is kept warm for 2 hours and 3 hours respectively, then filtered, stirred and rinsed, and then directly pulped with deionized water at a solid content of 240 g / L.

[0067] The specific surface area of ​​the pseudoboehmite obtained after heat preservation for 2 hours reached 321 m². 2 / g, pore volume reaches 1.05 mL / g, SO4 2- Content 1.97%. The specific surface area of ​​the pseudoboehmite obtained after heat treatment for 3 hours reached 335 m². 2 / g, pore volume reaches 1.03mL / g, SO4 2- Content 2.04%.

[0068] Example 3 At 60°C, an aluminum sulfate solution with an alumina content of 50 g / L and a sodium aluminate solution with an alumina content of 200 g / L were pumped into a reaction vessel using a peristaltic pump. The pH was adjusted to 8 by adjusting the flow rate to obtain a neutralized slurry. 80 g / L ammonium carbonate was added to adjust the pH of the neutralized slurry to 8.5. After holding the neutralized slurry at this temperature for 1 hour, it was filtered and washed by stirring and rinsing. Deionized water was used to pulp the slurry at solid contents of 100 g / L, 147 g / L, and 240 g / L, respectively. The pH was adjusted to 9 using ammonium carbonate solution to obtain a re-pulped slurry. The re-pulped slurry was heated to 95°C and aged for 2.5 hours with a stirring speed of 200 r / min. After filtration, it was washed first with a 50 g / L ammonium bicarbonate solution, then washed with deionized water, and finally dried to obtain pseudoboehmite 6, pseudoboehmite 7, and pseudoboehmite 8.

[0069] The specific surface area of ​​pseudoboehmite 6 reaches 344.3 m². 2 / g, pore volume reaches 0.84 mL / g, SO4 2- The content was 0.93%; the specific surface area of ​​pseudoboehmite 7 reached 343.4 m². 2 / g, pore volume reaches 0.84 mL / g, SO4 2- Content 1.09%; the specific surface area of ​​pseudoboehmite 8 reaches 348.8 m². 2 / g, pore volume reaches 0.88 mL / g, SO4 2- Content 1.51%.

[0070] Comparative Example 4 The preparation steps are basically the same as in Example 3, except that: after keeping the neutralized slurry warm for 1 hour, it is filtered without stirring or rinsing, and deionized water is used directly to slurry with a solid content of 240 g / L.

[0071] The specific surface area of ​​the obtained pseudoboehmite reached 341 m². 2 / g, pore volume reaches 0.85 mL / g, SO4 2- Content 2.68%.

[0072] Example 4 At 60°C, an aluminum sulfate solution with an alumina content of 50 g / L and a sodium aluminate solution with an alumina content of 180 g / L were pumped into a reactor using a peristaltic pump. The pH was adjusted to 8.5 by adjusting the flow rate to obtain a neutralized slurry. 80 g / L ammonium carbonate was added to adjust the pH of the neutralized slurry to 9. After holding the neutralized slurry at this temperature for 1 hour, it was filtered and washed by stirring and rinsing. Deionized water was used to pulp the slurry at solid contents of 100 g / L, 180 g / L, and 240 g / L, respectively. The pH was adjusted to 9 using ammonium carbonate solution to obtain a re-pulped slurry. The re-pulped slurry was heated to 95°C and aged for 2.5 hours with a stirring speed of 200 r / min. After filtration, it was washed first with a 35 g / L ammonium bicarbonate solution, then washed with deionized water, and finally dried to obtain pseudoboehmite 9, pseudoboehmite 10, and pseudoboehmite 11.

[0073] The specific surface area of ​​pseudoboehmite 9 reaches 350.3 m². 2 / g, pore volume reaches 1.08mL / g, SO4 2- Content 0.73%; specific surface area of ​​pseudoboehmite 10 reaches 358.9 m². 2 / g, pore volume reaches 1.11 mL / g, SO4 2- With a content of 0.89%, the specific surface area of ​​pseudoboehmite 11 reaches 353.6 m². 2 / g, pore volume reaches 1.13 mL / g, SO4 2- Content 1.16%.

[0074] Comparative Example 5 At 60°C, an aluminum sulfate solution with an alumina content of 50 g / L and a sodium aluminate solution with an alumina content of 180 g / L were pumped into a reaction vessel using a peristaltic pump. The pH was adjusted to 8.5 by regulating the flow rate to obtain a neutralized slurry. 80 g / L ammonium carbonate was added to adjust the pH of the neutralized slurry to 9. After holding the neutralized slurry at this temperature for 1 hour, it was filtered and washed using a combination of agitation and rinsing. Deionized water was used to create a slurry with a solids content of 240 g / L. The pH was adjusted to 9 using ammonium carbonate solution to obtain a re-slurry. The re-slurry was heated to 95°C and aged for 2.5 hours with a stirring speed of 200 r / min. It was then filtered without washing with ammonium bicarbonate solution. The resulting product, boehmite, had a specific surface area of ​​351.2 m². 2 / g, pore volume reaches 1.1 mL / g, SO4 2- Content 2.59%.

[0075] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The embodiments of the present invention solve the problem of excessive sulfate content in existing pseudoboehmite products and meet the needs of the catalysis industry for low sulfate materials.

[0076] The embodiments of the present invention prepare pseudoboehmite with a macroporous structure. The macroporous structure is beneficial to the diffusion and mass transfer of reactants in the catalytic reaction, thereby improving the catalytic efficiency.

[0077] In this embodiment of the invention, the low sulfate content and macroporous structure work together to significantly improve the catalytic performance of boehmite.

[0078] Appendix Figure 1 Detailed explanation: Figure 1 The image shows an electron microscope image of boehmite 1 provided in Embodiment 1 of this application; as can be seen from the image, boehmite 1 has a macroporous structure and a loose structure.

[0079] 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 in this application.

Claims

1. A method for preparing low-sulfate macroporous pseudoboehmite, characterized in that, The method includes: The sodium aluminate solution and aluminum sulfate solution are neutralized to obtain a neutralized slurry; Ammonium carbonate solution is added to the neutralized slurry to adjust the pH of the neutralized slurry to 8.5-9. The neutralized slurry after pH adjustment is then subjected to heat treatment to promote the ion exchange process and transfer sulfate ions from the solid phase to the liquid phase, thereby obtaining the ion-exchanged slurry. The slurry after ion exchange is sequentially filtered and washed to obtain a filter cake. The filter cake is re-pulped to obtain a re-pulped slurry; The re-slurry was subjected to aging treatment and washing with ammonium bicarbonate solution in sequence to obtain the pseudoboehmite product.

2. The method according to claim 1, characterized in that, The sodium aluminate solution contains aluminum oxide at a mass concentration of 160 g / L to 210 g / L.

3. The method according to claim 1, characterized in that, The aluminum sulfate solution contains aluminum oxide at a mass concentration of 40 g / L to 60 g / L.

4. The method according to claim 1, characterized in that, The ammonium carbonate solution has a mass concentration of 80 g / L to 150 g / L; and / or, The mass concentration of the ammonium bicarbonate solution is 30 g / L to 60 g / L.

5. The method according to claim 1, characterized in that, The neutralization reaction is carried out at a temperature of 50℃ to 70℃. The pH of the neutralized slurry is 8 to 8.

5.

6. The method according to claim 1, characterized in that, The heat preservation treatment time is 50 min to 90 min; and / or, The washing process involves agitation followed by rinsing.

7. The method according to claim 1, characterized in that, The solids content of the re-slurry is 70 g / L to 240 g / L, and the pH of the re-slurry is 8 to 9.

8. The method according to claim 1, characterized in that, The aging process is carried out at a set stirring speed, which is 200 r / min to 300 r / min.

9. The method according to claim 1, characterized in that, The aging treatment temperature is 80-100℃, and the aging treatment time is 2-5 hours.

10. The method according to claim 1, characterized in that, The pseudoboehmite product meets at least one of the following properties: specific surface area > 300 m² 2 / g, pore volume >0.8mL / g, sulfate mass fraction <1.2%.

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