A method for preparing a silicon-containing macroporous pseudoboehmite by carbonization

Abstract

The application relates to a method for preparing silicon-containing macroporous pseudo-boehmite by a carbonization method and belongs to the technical field of pseudo-boehmite preparation. The method comprises the following steps: performing a low-temperature carbonization reaction on a sodium metaaluminate solution and carbon dioxide gas to obtain a reaction slurry; when the low-temperature carbonization reaction is performed to the point that precipitates are separated out, adding a water glass solution into the reaction slurry, controlling the adding process of the water glass solution to be completed before the low-temperature carbonization reaction is completed, and controlling the terminal pH value of the low-temperature carbonization reaction to be alkaline, so as to obtain a silicon-containing pseudo-boehmite slurry; performing liquid-solid separation on the silicon-containing pseudo-boehmite slurry to obtain a filter cake; washing the filter cake with deionized water until the pH value of a post-washing filtrate is less than 7, so as to obtain a post-washing filter cake; and drying the post-washing filter cake to obtain silicon-containing macroporous pseudo-boehmite.

Description

Technical Field

[0001] This application relates to the field of boehmite preparation technology, and in particular to a method for preparing silica-containing macroporous boehmite by carbonization. Background Technology

[0002] Pseudoboehmite is a core precursor for alumina-based catalyst supports. After calcination, it is converted into alumina with high specific surface area, such as γ-Al₂O₃, and is widely used in catalytic reactions such as hydrorefining, hydrocracking, desulfurization, and denitrification in the petrochemical industry. Traditional alumina supports suffer from problems such as weak surface acidity, easy collapse of pore structure, and insufficient thermal stability, making it difficult to meet the requirements of diffusion of large molecules and deep impurity removal in heavy oil. Research has found that introducing silica into alumina can significantly enhance the surface acidity of the support (especially Brønsted acidity), improve pore structure stability, and enhance anti-sintering ability. Therefore, silica-containing pseudoboehmite has become a key raw material for high-performance hydrogenation catalyst supports and has become a research hotspot.

[0003] Existing carbonization methods for preparing silicon-containing pseudoboehmite have problems such as uneven silicon distribution, pore blockage leading to low pore volume and specific surface area, high sodium oxide content, complex processes, or high costs. Summary of the Invention

[0004] This application provides a method for preparing silica-containing macroporous pseudoboehmite by carbonization, in order to solve the following technical problem: how to prepare silica-containing pseudoboehmite with both macroporous volume and low sodium content. This application provides a method for preparing silica-containing macroporous pseudoboehmite by carbonization, the method comprising: Sodium aluminate solution was subjected to a low-temperature carbonization reaction with carbon dioxide gas to obtain a reaction slurry; When the low-temperature carbonization reaction proceeds to the point where precipitates are formed, water glass solution is added to the reaction slurry. The addition of water glass solution is controlled to be completed before the end of the low-temperature carbonization reaction, and the pH value at the end of the low-temperature carbonization reaction is controlled to be alkaline, so as to obtain a silica-containing pseudo-boehmite slurry. The silica-containing pseudo-boehmite slurry was subjected to liquid-solid separation to obtain a filter cake; The filter cake is washed with deionized water until the pH of the filtrate after washing is less than 7, thus obtaining the washed filter cake. The washed filter cake was dried to obtain silica-containing macroporous pseudoboehmite.

[0005] Optionally, the carbon dioxide gas is a mixture of carbon dioxide and nitrogen, wherein the volume fraction of carbon dioxide is 35% to 40%.

[0006] Optionally, during the low-temperature carbonization reaction of sodium aluminate solution with carbon dioxide gas, the flow rate of the carbon dioxide gas is 1 L / min to 5.28 L / min.

[0007] Optionally, the sodium aluminate solution has a mass concentration of 10 g / L to 30 g / L, calculated as aluminum oxide.

[0008] Optionally, the temperature of the low-temperature carbonization reaction is 10℃ to 25℃, and the endpoint pH value of the low-temperature carbonization reaction is 9.5 to 10.5.

[0009] Optionally, the mass concentration of silica in the water glass solution is 10 g / L to 30 g / L.

[0010] Optionally, the water glass solution is added over a period of 5 to 90 minutes.

[0011] Optionally, the method is implemented in a single reaction vessel via a batch reaction.

[0012] Optionally, the temperature of the deionized water used in the washing process is 60℃~100℃, and the temperature of the drying process is 80℃~150℃.

[0013] Optionally, the silica-containing macroporous pseudoboehmite satisfies the following conditions: SiO2 mass fraction of 2.15%–9.02%, Na2O mass fraction <0.04%, pore volume of 1.223 mL / g–1.526 mL / g, and specific surface area of ​​346.6 m². 2 / g~458.7m 2 / g, with an average pore size of 12.9nm to 14.1nm.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing silica-containing macroporous pseudoboehmite by carbonization. The method includes: reacting sodium aluminate solution with carbon dioxide gas at low temperature to obtain a reaction slurry; when the low-temperature carbonization reaction proceeds to the point where precipitate forms, adding water glass solution to the reaction slurry, and controlling the addition of water glass solution to be completed before the end of the low-temperature carbonization reaction, and controlling the pH value of the endpoint of the low-temperature carbonization reaction to be alkaline, to obtain a silica-containing pseudoboehmite slurry; performing liquid-solid separation on the silica-containing pseudoboehmite slurry to obtain a filter cake; washing the filter cake with deionized water until the pH value of the filtrate after washing is less than 7, to obtain a washed filter cake; and drying the washed filter cake to obtain silica-containing macroporous pseudoboehmite. This application employs a low-concentration sodium aluminate solution and a low-concentration carbon dioxide mixture for carbonization at low temperatures. This significantly reduces the supersaturation and nucleation rate of the reaction system, resulting in small, moderately numerous, and loosely packed pseudo-boehmite nuclei, creating a structural basis for preserving large channels between grains. Simultaneously, the addition of water glass solution is precisely controlled until precipitates form during the low-temperature carbonization reaction. At this point, the nuclei have formed but are not yet fully aggregated. The slowly added low-concentration silicon source is uniformly adsorbed onto the nuclei surface in the form of monosilicic acid and gradually embeds itself into the growing lattice as the low-temperature carbonization reaction continues. Subsequent hot water washing and low-temperature drying effectively remove soluble sodium salts without damaging the already formed loose porous structure. This synergistic mechanism of low concentration, low temperature, stepwise silicon addition, and timing control allows silicon atoms to uniformly enter the framework during the active grain growth period, ultimately yielding a product with uniform silicon distribution, low sodium content, and large pore volume. Attached Figure Description

[0015] 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.

[0016] 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.

[0017] Figure 1 This is a schematic flowchart of a method for preparing silica-containing macroporous pseudoboehmite by carbonization, provided in an embodiment of this application. Detailed Implementation

[0018] 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.

[0019] 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.

[0020] Figure 1 This is a schematic flowchart of a method for preparing silica-containing macroporous pseudoboehmite by carbonization, provided in an embodiment of this application.

[0021] Please see Figure 1 This application provides a method for preparing silica-containing macroporous pseudoboehmite by carbonization, the method comprising: S1. Sodium aluminate solution is subjected to a low-temperature carbonization reaction with carbon dioxide gas to obtain a reaction slurry; S2. When the low-temperature carbonization reaction proceeds to the point where precipitates are formed, water glass solution is added to the reaction slurry, and the addition of water glass solution is controlled to be completed before the end of the low-temperature carbonization reaction, and the pH value at the end of the low-temperature carbonization reaction is controlled to be alkaline, so as to obtain a silica-containing pseudo-boehmite slurry. S3. The silica-containing pseudo-boehmite slurry is subjected to liquid-solid separation to obtain filter cake; S4. Wash the filter cake with deionized water until the pH value of the filtrate after washing is less than 7 to obtain the washed filter cake. S5. The washed filter cake is dried to obtain silica-containing macroporous pseudoboehmite.

[0022] Sodium aluminate solution refers to an aqueous solution used as an aluminum source, with the chemical formula NaAl(OH)4. Sodium aluminate solution is the starting material for the low-temperature carbonization reaction, reacting with carbon dioxide gas to form boehmite. The low-temperature carbonization reaction between sodium aluminate solution and carbon dioxide gas causes the aluminum species in the sodium aluminate to undergo hydrolysis and condensation reactions under the action of carbon dioxide, forming boehmite (AlOOH) precipitate, while simultaneously generating sodium carbonate. The chemical equation for this step is: NaAl(OH)4 + CO2 → AlOOH↓ + Na2CO3 + H2O. Controlling the reaction temperature at a low temperature (10℃~25℃) is to reduce the molecular thermal motion rate, slowing down the crystal nucleation rate and grain agglomeration rate. Under low-temperature conditions, the generated boehmite crystals can be loosely packed, retaining large gaps between the grains. These gaps form macropores in subsequent processing.

[0023] When the low-temperature carbonization reaction reaches the point where precipitates form, a water glass solution is added to the reaction slurry. The addition of the water glass solution is controlled to be completed before the end of the low-temperature carbonization reaction, and the final pH of the low-temperature carbonization reaction is controlled to be alkaline, resulting in a silicon-containing boehmite slurry. The water glass solution, with the chemical formula Na₂SiO₃, is an aqueous solution used as a silicon source to introduce silicon into the boehmite. Adding the water glass solution at the point of precipitate formation indicates that some boehmite crystal nuclei have already formed in the reaction slurry, but the grains have not yet fully grown. The added water glass exists in the form of monosilicic acid, which can be uniformly adsorbed on the surface of the crystal nuclei and gradually embedded into the crystal lattice as the grains grow, forming a silicon-aluminum composite framework. If water glass is added at the beginning of the reaction, silicon and aluminum react directly under strongly alkaline conditions to form hydrated sodium aluminosilicate, leading to uneven silicon distribution and increased sodium content. Controlling the addition of the water glass solution to be completed before the end of the low-temperature carbonization reaction ensures sufficient carbonization time after the water glass is added. This pure carbonization stage allows the unfixed silicon to continue reacting and precipitating, while simultaneously making the adsorbed silicon more firmly bound to the framework.

[0024] A siliceous boehmite slurry undergoes liquid-solid separation to obtain a filter cake. Liquid-solid separation refers to the process of separating the solids (siliceous boehmite) from the liquid (an aqueous solution containing soluble salts such as sodium carbonate and sodium silicate) in the siliceous boehmite slurry. The filter cake obtained after liquid-solid separation mainly consists of siliceous boehmite, while also containing a small amount of entrained mother liquor (containing soluble sodium salts). The filter cake is washed with deionized water until the pH of the filtrate after washing is less than 7, resulting in a washed filter cake. Washing the filter cake with deionized water is to remove entrained sodium carbonate and any possible residual sodium silicate and sodium aluminate. If these sodium salts are not removed, they will remain in the final product, leading to an increase in the sodium oxide mass fraction. Washing until the pH of the filtrate after washing is less than 7 is because the sodium carbonate aqueous solution is alkaline (pH approximately 11). When the pH of the filtrate drops below 7, it indicates that the sodium carbonate has been largely washed away; this endpoint determination method is simple and intuitive. The washed filter cake was dried to obtain silica-containing macroporous pseudoboehmite.

[0025] In some embodiments, the sodium aluminate solution has a mass concentration of 10 g / L to 30 g / L, calculated as aluminum oxide.

[0026] The concentration of sodium aluminate solution directly affects the crystal formation rate and agglomeration behavior during low-temperature carbonization. When the mass concentration based on alumina is high (e.g., greater than 30 g / L), the number of aluminate ions per unit volume of solution is large, and the pseudoboehmite small crystals generated by the low-temperature carbonization reaction appear in large quantities in a short time. The collision frequency between crystals is high, and they easily agglomerate rapidly to form a dense structure, leading to premature closure of macropore channels between crystals, and a reduction in the pore volume and pore size of the final product. By controlling the mass concentration based on alumina in the low concentration range of 10 g / L to 30 g / L, the aluminate ions are evenly dispersed, the crystal formation rate is moderate, and the small crystals have sufficient time to diffuse and rearrange in the solution, and then agglomerate in a loose manner to form macropore channels.

[0027] In some embodiments, the carbon dioxide gas is a mixture of carbon dioxide and nitrogen, wherein the volume fraction of carbon dioxide is 35% to 40%.

[0028] Carbon dioxide gas refers to the gaseous reactant used in the low-temperature carbonization reaction with sodium aluminate solution. In the embodiments of this application, the carbon dioxide gas is not pure carbon dioxide, but a mixture of carbon dioxide and nitrogen. Nitrogen, as an inert diluent component in the mixture, does not participate in the low-temperature carbonization reaction and is only used to adjust the concentration of carbon dioxide in the mixture.

[0029] The reaction between pure carbon dioxide gas and sodium aluminate solution is vigorous, easily leading to local supersaturation. This results in fine and dense boehmite crystals, which are unfavorable for the formation of macroporous structures. Diluting the carbon dioxide gas with nitrogen gas reduces the partial pressure of carbon dioxide in the reaction system, thereby slowing down the rate of the low-temperature carbonization reaction. This makes the reaction more gentle and uniform, which is conducive to the slow aggregation of small-grained boehmite into a loose macroporous structure. Secondly, when pure carbon dioxide gas is introduced into the alkaline sodium aluminate solution, a local acidic region (pH value can drop below 4) is easily formed at the gas inlet, leading to the formation of amorphous gel. Using diluted carbon dioxide gas can effectively suppress local over-acidification, ensuring that the reaction proceeds within a suitable alkaline range throughout, maintaining the purity of the product as boehmite. Finally, the gentle low-temperature carbonization reaction rate and the subsequent addition of water glass solution work synergistically to allow silicon species to be uniformly dispersed in the reaction slurry and embedded in the boehmite framework, avoiding local enrichment of silicon or the formation of hydrated sodium aluminosilicate.

[0030] If the volume fraction of carbon dioxide is higher than 40%, the reaction rate is too fast, and the low-temperature carbonization reaction is completed prematurely. This leads to a delay in the addition of water glass, preventing silicon from effectively embedding into the framework, and also reduces pore volume and specific surface area. If the volume fraction of carbon dioxide is lower than 35%, the reaction rate is too slow, the low-temperature carbonization reaction time is prolonged, production efficiency is reduced, and incomplete conversion of sodium aluminate may occur, resulting in a decrease in product yield.

[0031] In some embodiments, during the low-temperature carbonization reaction of sodium aluminate solution with carbon dioxide gas, the flow rate of the carbon dioxide gas is 1 L / min to 5.28 L / min.

[0032] The flow rate refers to the volumetric flow rate of carbon dioxide gas introduced into the sodium aluminate solution per unit time during the low-temperature carbonization reaction of sodium aluminate solution and carbon dioxide gas.

[0033] The flow rate of carbon dioxide gas directly determines the total amount of carbon dioxide entering the reaction system per unit time, thus affecting the rate of the low-temperature carbonization reaction. If the flow rate is below 1 L / min, the carbon dioxide supply is insufficient, the low-temperature carbonization reaction is too slow, and production efficiency decreases. If the flow rate is above 5.28 L / min, the carbon dioxide supply is excessive, the low-temperature carbonization reaction is too vigorous, the pH value drops too quickly, and ferrous alumina impurities are easily formed in local areas. Furthermore, the rapid agglomeration of boehmite grains leads to a decrease in pore volume and specific surface area. Secondly, the sodium aluminate solution used in this application has a mass concentration of 10 g / L to 30 g / L (low concentration) based on alumina. This low-concentration system consumes carbon dioxide at a relatively slow rate. The flow rate of carbon dioxide gas from 1 L / min to 5.28 L / min is matched with the low-concentration sodium aluminate solution to ensure that the carbon dioxide gas has sufficient dissolution and reaction time in the solution, avoiding the large amount of unreacted carbon dioxide escaping from the liquid surface due to excessive flow rate, resulting in raw material waste and reaction runaway.

[0034] In some embodiments, the temperature of the low-temperature carbonization reaction is 10°C to 25°C, and the endpoint pH value of the low-temperature carbonization reaction is 9.5 to 10.5.

[0035] In the low-temperature carbonization reaction of sodium aluminate solution with carbon dioxide gas to form boehmite, the rates of grain formation, growth, and aggregation increase significantly with increasing temperature. Controlling the low-temperature carbonization reaction temperature between 10℃ and 25℃ allows for slower grain growth and aggregation, providing smaller grains with longer diffusion and rearrangement times in the solution. This preserves the large pore channels formed between grains, preventing them from closing due to excessively rapid aggregation. If the low-temperature carbonization reaction temperature exceeds 25℃, the grain aggregation rate accelerates, the product structure becomes more compact, leading to a decrease in pore volume and average pore size. If the low-temperature carbonization reaction temperature is below 10℃, the reaction kinetics are too slow, and low-temperature energy consumption increases.

[0036] The final pH value reflects the degree of aluminate ion conversion in the sodium aluminate solution. When the final pH value drops to 9.5–10.5, the aluminate ions in the sodium aluminate solution have been basically converted into boehmite precipitate, and the reaction is close to completion. If the final pH value is below 9.5, excessive carbon dioxide gas is introduced, and the reaction system enters a weakly alkaline or even near-neutral region, which easily leads to the formation of gibbsite impurities and wastes carbon dioxide gas. If the final pH value is above 10.5, the reaction is not yet complete, and a large number of unconverted aluminate ions remain in the solution, resulting in a lower product yield and a higher likelihood of gibbsite impurities. Furthermore, silicate ions exist as monomers under alkaline conditions (pH greater than 9), which readily bond with or isomorphously substitute for the active hydroxyl groups on the surface of boehmite grains. Controlling the final pH value at 9.5–10.5 ensures that silicon is uniformly distributed in the boehmite framework at the end of the reaction and will not precipitate due to further pH decrease. If the final pH value is below 9.5, silicate ions may polymerize to form silica gel, which is physically adsorbed on the surface of boehmite, resulting in uneven distribution of silicon (forming a silicon-coated aluminum structure) and blocking the pores. If the final pH value is above 10.5, some silicon may still remain in the solution in the form of silicate ions and cannot be effectively immobilized.

[0037] The low-temperature carbonization reaction of sodium aluminate solution with carbon dioxide gas requires sufficient time to fully convert aluminate ions into boehmite precipitate and stabilize the final pH value within the range of 9.5–10.5. In some embodiments, the total duration of the low-temperature carbonization reaction is 10 min–120 min. For higher reaction temperatures (e.g., 25°C) and higher carbon dioxide flow rates (e.g., 5.28 L / min), a shorter total duration (e.g., 10 min) can be used; for lower reaction temperatures (e.g., 10°C) and lower flow rates (e.g., 1 L / min), a longer total duration (e.g., 120 min) is required.

[0038] In some embodiments, the mass concentration of silica in the water glass solution is 10 g / L to 30 g / L.

[0039] The chemical composition of water glass is sodium silicate (Na₂SiO₃), which serves as the source of silica in the methods of this application. Aluminate ions in the sodium aluminate solution and silicate ions in the water glass solution exhibit high reactivity, readily forming hydrated sodium aluminosilicate precipitate when directly mixed. The silicon in this byproduct exists as a non-target phase, unable to enter the boehmite framework, and carries a large amount of sodium ions, leading to an increased sodium oxide content in the product that is difficult to remove by washing. By controlling the silica concentration in the water glass solution to a low range of 10 g / L to 30 g / L, the silicate ions are rapidly diluted when the water glass solution is slowly added to the reaction slurry, reducing the probability of local collisions with aluminate ions and thus inhibiting the formation of hydrated sodium aluminosilicate. Furthermore, under low concentration conditions of 10 g / L to 30 g / L, silicate ions exist stably in monomeric or oligomeric forms, exhibiting good diffusion properties. When the water glass solution is added in the middle of the reaction (when precipitates form), silicate ions can be uniformly dispersed throughout the reaction system and undergo isomorphous substitution or surface bonding with the active hydroxyl groups on the surface of the already formed boehmite crystallites, allowing silicon atoms to uniformly enter the framework positions of the boehmite. The low-temperature carbonization reaction is carried out at temperatures ranging from 10°C to 25°C. This low-temperature environment is beneficial for controlling the reaction rate. Using a low-concentration (10 g / L to 30 g / L) water glass solution further ensures a gentler silicon introduction process, preventing localized violent reactions and pore collapse caused by excessively high silicon concentrations.

[0040] In some embodiments, the water glass solution is added over a period of 5 to 90 minutes.

[0041] Water glass solution is added when precipitates appear. At this point, a large number of pseudoboehmite crystallites have formed in the reaction system, but some aluminate ions remain unconverted. Controlling the addition time of water glass solution between 5 and 90 minutes allows silicate ions to enter the reaction system slowly and continuously, competing uniformly with aluminate ions in the solution and the active sites on the crystallite surface, thus achieving a uniform distribution of silicon within the pseudoboehmite framework. After all the water glass solution has been added, the low-temperature carbonization reaction is not yet complete (because the water glass is added before the end of the total reaction time), and the reaction continues for a period of time. This period (from the completion of water glass addition to the end of the low-temperature carbonization reaction) is crucial for the final immobilization of silicon and the stability of the pore structure. Controlling the addition time of water glass between 5 and 90 minutes ensures that there is still time for silicon to fully interact with the pseudoboehmite framework after the water glass is added.

[0042] In some embodiments, the method is implemented in a single reaction vessel via a batch reaction.

[0043] A single reaction vessel refers to a single reaction container used to hold a sodium aluminate solution and carry out a low-temperature carbonization reaction. A single reaction vessel is distinct from a multi-stage reaction system consisting of two or more reaction vessels connected in series. All chemical reaction steps of the method in this application (from the low-temperature carbonization reaction of the sodium aluminate solution with carbon dioxide gas, to the addition of water glass solution, and finally to obtaining a silica-containing pseudoboehmite slurry) are completed within the same reaction vessel, without transferring the reactants to another reaction vessel in between.

[0044] A batch reaction refers to a reaction operation mode in which reactants (including sodium aluminate solution, carbon dioxide gas, and water glass solution) are added to a single reaction vessel in batches according to the time sequence defined in the embodiments of this application. The reaction proceeds within a single reaction vessel until the endpoint is reached. Then, the resulting silica-containing pseudoboehmite slurry is completely removed before the next batch operation begins. Batch reactions differ from continuous reactions (in continuous reactions, materials continuously enter the reactor, products continuously flow out, and the materials within the reactor maintain a dynamic equilibrium).

[0045] The entire process of low-temperature carbonization and water glass solution addition is completed in a single reaction vessel, eliminating the need to transfer the reaction slurry from one vessel to another. This avoids the mechanical shear forces exerted on the pseudoboehmite grain agglomerates by pumping or pipeline flow during transfer. Such mechanical shear forces can disrupt the already formed macroporous and porous structure, leading to a decrease in pore volume and specific surface area. The single reaction vessel allows for gentle grain growth in a static environment, helping to maintain the macroporous structure.

[0046] In batch reactions, the sodium aluminate solution is added to the reaction vessel all at once, allowing for accurate recording of the reaction start time. This enables precise control over the addition of water glass solution when precipitate forms during the low-temperature carbonization reaction. In continuous reactions, the constant flow of materials makes it difficult to precisely define the reaction start time and achieve sequential control over the addition of water glass solution when precipitate forms. Furthermore, in batch reactions, the total amount of material in the reaction vessel is fixed, and the cumulative amount of carbon dioxide gas introduced corresponds directly to the reaction progress. The pH value of the slurry can be monitored in real time using an online pH meter. When the pH value reaches 9.5–10.5, the introduction of carbon dioxide gas is stopped, clearly defining the reaction endpoint.

[0047] In some embodiments, the temperature of the deionized water used in the washing process is 60°C to 100°C, and the temperature of the drying process is 80°C to 150°C.

[0048] During the low-temperature carbonization reaction, sodium ions in the system mainly exist as sodium carbonate, sodium bicarbonate, and a small amount of hydrated sodium aluminosilicate. The solubility of these sodium salts in high-temperature water is significantly higher than in room-temperature water. The goal of the washing step is to remove most of the soluble sodium salts, reducing the residual sodium content in the filter cake to an extremely low level. Heating deionized water to 60℃~100℃ can significantly increase the dissolution rate and amount of sodium ions, thus multiplying the washing efficiency. If deionized water below 60℃ is used, sodium salts dissolve slowly, requiring more washing water and a longer washing time to reduce the Na2O content to below 0.04%. If the deionized water temperature is above 100℃, although the washing effect is better, the water boils at atmospheric pressure, making operation inconvenient and increasing energy consumption.

[0049] Boehmite contains a certain amount of water of crystallization, which is only removed at higher temperatures. Controlling the drying temperature between 80℃ and 150℃ effectively removes both free and adsorbed water (physical water) from the filter cake, ensuring a stable dry state while preventing excessive loss of water of crystallization. If the drying temperature is below 80℃, free water is difficult to remove completely, resulting in a high moisture content, easy clumping, and the need for additional drying before subsequent use. If the drying temperature is above 150℃, the boehmite begins to lose its water of crystallization, gradually transforming into monohydrate boehmite, leading to a change in crystal phase and a sharp decrease in pore volume and specific surface area. The target product of this method is silica-containing macroporous boehmite (not calcined alumina), therefore the drying temperature must be controlled below 150℃. Furthermore, the drying temperature significantly affects the pore structure. Within the range of 80℃ to 150℃, moisture evaporates slowly, and the pore structure remains largely intact during drying, without collapsing due to drastic dehydration.

[0050] In some embodiments, the silica-containing macroporous pseudoboehmite satisfies the following conditions: SiO2 mass fraction of 2.15%–9.02%, Na2O mass fraction <0.04%, pore volume of 1.223 mL / g–1.526 mL / g, and specific surface area of ​​346.6 m². 2 / g~458.7m 2 / g, with an average pore size of 12.9nm to 14.1nm.

[0051] The above five product characteristic parameters collectively define the material properties of silica-containing macroporous pseudoboehmite. The mass fraction of SiO2 reflects the amount of silicon introduced into the silica-containing macroporous pseudoboehmite, the mass fraction of Na2O is a key indicator for measuring product purity, the pore volume reflects the total volume of pores within a unit mass of product, the specific surface area reflects the number of surface active sites in the product, and the average pore diameter reflects the average width of the product's pores.

[0052] 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.

[0053] Example 1 Add 5 liters of sodium aluminate solution, with a mass concentration of 20 g / L (calculated as alumina), to the reaction vessel. Introduce carbon dioxide gas into the reaction vessel; this gas is a mixture of carbon dioxide and nitrogen, with a carbon dioxide volume fraction of 35%, at a flow rate of 5.28 L / min. Perform a low-temperature carbonization reaction between the sodium aluminate solution and the carbon dioxide gas at 16°C to obtain a reaction slurry. When the low-temperature carbonization reaction reaches the point where precipitate forms, add 0.3 liters of water glass solution, with a silica mass concentration of 10 g / L. Control the addition time of the water glass solution to 5 minutes, ensuring all water glass solution is added before the end of the low-temperature carbonization reaction. The endpoint pH of the low-temperature carbonization reaction is 10.0, yielding a silica-containing pseudoboehmite slurry.

[0054] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 110°C to obtain silica-containing macroporous pseudoboehmite. Measurements showed that the silica-containing macroporous pseudoboehmite obtained in this example contained 2.15% silica by mass, 0.04% sodium oxide by mass, had a pore volume of 1.223 mL / g, and a specific surface area of ​​346.6 m². 2 / g, with an average pore size of 14.1nm and a boehmite impurity content of 0.5%.

[0055] Example 2 5 liters of sodium aluminate solution with a mass concentration of 20 g / L (calculated as alumina) was added to the reaction vessel. Carbon dioxide gas, a mixture of carbon dioxide and nitrogen with a volume fraction of 35% (carbon dioxide), was introduced into the reaction vessel at a flow rate of 5.14 L / min. The sodium aluminate solution and carbon dioxide gas were subjected to a low-temperature carbonization reaction at 18°C ​​to obtain a reaction slurry. When precipitate formed during the low-temperature carbonization reaction, 0.3 liters of water glass solution with a silica mass concentration of 20 g / L was added to the reaction slurry. The addition time of the water glass solution was controlled at 15 minutes, and all the water glass solution was added before the end of the low-temperature carbonization reaction. The final pH value of the low-temperature carbonization reaction was 10.2, yielding a silica-containing pseudoboehmite slurry.

[0056] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 110°C to obtain silica-containing macroporous pseudoboehmite. Analysis showed that the silica-containing macroporous pseudoboehmite obtained in this example contained 4.32% silica by mass, 0.03% sodium oxide by mass, had a pore volume of 1.354 mL / g, and a specific surface area of ​​407.0 m². 2 / g, with an average pore size of 13.3nm and a boehmite impurity content of 0.5%.

[0057] Example 3 Five liters of sodium aluminate solution with a mass concentration of 19 g / L (calculated as alumina) were added to the reaction vessel. Carbon dioxide gas, a mixture of carbon dioxide and nitrogen with a volume fraction of 35% (2.57 L / min), was then introduced into the vessel. The sodium aluminate solution and carbon dioxide gas were subjected to a low-temperature carbonization reaction at 20°C to obtain a reaction slurry. When precipitate formed during the low-temperature carbonization reaction, 0.2 liters of water glass solution with a silica mass concentration of 30 g / L was added to the reaction slurry. The addition time of the water glass solution was controlled at 20 minutes, and all the water glass solution was added before the end of the low-temperature carbonization reaction. The final pH value of the low-temperature carbonization reaction was 10.5, yielding a silica-containing pseudo-boehmite slurry.

[0058] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 100°C to obtain silica-containing macroporous pseudoboehmite. Analysis showed that the silica-containing macroporous pseudoboehmite obtained in this example contained 4.41% silica by mass, 0.03% sodium oxide by mass, had a pore volume of 1.362 mL / g, and a specific surface area of ​​419.2 m². 2 / g, with an average pore size of 12.9nm and a boehmite impurity content of 0.5%.

[0059] Example 4 Add 5 liters of sodium aluminate solution, with a mass concentration of 22 g / L (calculated as alumina), to the reaction vessel. Introduce carbon dioxide gas into the reaction vessel; this gas is a mixture of carbon dioxide and nitrogen, with a carbon dioxide volume fraction of 35%, at a flow rate of 1.94 L / min. Perform a low-temperature carbonization reaction between the sodium aluminate solution and the carbon dioxide gas at 22°C to obtain a reaction slurry. When the low-temperature carbonization reaction reaches the point where precipitate forms, add 0.5 liters of water glass solution, with a silica mass concentration of 26 g / L. Control the addition time of the water glass solution to 35 minutes, ensuring all water glass solution is added before the end of the low-temperature carbonization reaction. The endpoint pH of the low-temperature carbonization reaction is 10.0, yielding a silica-containing pseudoboehmite slurry.

[0060] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 100°C to obtain silica-containing macroporous pseudoboehmite. Analysis showed that the silica-containing macroporous pseudoboehmite obtained in this example contained 8.37% silica by mass, 0.04% sodium oxide by mass, had a pore volume of 1.478 mL / g, and a specific surface area of ​​434.3 m². 2 / g, with an average pore size of 13.6nm and a boehmite impurity content of 0.5%.

[0061] Example 5 Add 5 liters of sodium aluminate solution, with a mass concentration of 25 g / L (calculated as alumina), to the reaction vessel. Introduce carbon dioxide gas into the reaction vessel; this gas is a mixture of carbon dioxide and nitrogen, with a carbon dioxide volume fraction of 35%, at a flow rate of 1.00 L / min. Perform a low-temperature carbonization reaction between the sodium aluminate solution and the carbon dioxide gas at 25°C to obtain a reaction slurry. When the low-temperature carbonization reaction reaches the point where precipitate forms, add 1.0 liter of water glass solution, with a silica mass concentration of 15 g / L. Control the addition time of the water glass solution to 70 minutes, ensuring all water glass solution is added before the end of the low-temperature carbonization reaction. The endpoint pH of the low-temperature carbonization reaction is 10.2, yielding a silica-containing pseudoboehmite slurry.

[0062] A siliceous pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 120°C to obtain siliceous macroporous pseudoboehmite. Measurements showed that the siliceous macroporous pseudoboehmite obtained in this example contained 9.02% silica by mass, 0.04% sodium oxide by mass, had a pore volume of 1.526 mL / g, and a specific surface area of ​​458.7 m². 2 / g, with an average pore size of 13.3nm and a boehmite impurity content of 0.5%.

[0063] Comparative Example 1 Add 5 liters of sodium aluminate solution, with a mass concentration of 50 g / L (calculated as alumina), to the reaction vessel. Introduce carbon dioxide gas into the reaction vessel; this gas is a mixture of carbon dioxide and nitrogen, with a carbon dioxide volume fraction of 35%, at a flow rate of 5.28 L / min. Perform a low-temperature carbonization reaction between the sodium aluminate solution and the carbon dioxide gas at 16°C to obtain a reaction slurry. When the low-temperature carbonization reaction reaches the point where precipitate forms, add 0.3 liters of water glass solution, with a silica mass concentration of 10 g / L. Control the addition time of the water glass solution to 5 minutes, and add all the water glass solution before the end of the low-temperature carbonization reaction. The endpoint pH of the low-temperature carbonization reaction is 10.0, yielding a silica-containing pseudo-boehmite slurry.

[0064] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 110°C to obtain silica-containing macroporous pseudoboehmite. The silica-containing macroporous pseudoboehmite obtained in this comparative example was found to contain 0.91% silica by mass, 0.06% sodium oxide by mass, with a pore volume of 0.661 mL / g and a specific surface area of ​​286.4 m². 2 / g, with an average pore size of 9.25nm and a boehmite impurity content of 0.5%.

[0065] Comparative Example 2 Add 5 liters of sodium aluminate solution, with a mass concentration of 20 g / L (calculated as alumina), to the reaction vessel. Introduce carbon dioxide gas into the reaction vessel; this gas is a mixture of carbon dioxide and nitrogen, with a carbon dioxide volume fraction of 35%, at a flow rate of 5.14 L / min. Perform a low-temperature carbonization reaction between the sodium aluminate solution and the carbon dioxide gas at 29°C to obtain a reaction slurry. When the low-temperature carbonization reaction reaches the point where precipitate forms, add 0.3 liters of water glass solution, with a silica mass concentration of 20 g / L. Control the addition time of the water glass solution to 15 minutes, ensuring all water glass solution is added before the end of the low-temperature carbonization reaction. The endpoint pH of the low-temperature carbonization reaction is 10.2, yielding a silica-containing pseudoboehmite slurry.

[0066] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 110°C to obtain silica-containing macroporous pseudoboehmite. The silica-containing macroporous pseudoboehmite obtained in this comparative example was found to contain 4.48% silica by mass, 0.04% sodium oxide by mass, with a pore volume of 0.979 mL / g and a specific surface area of ​​319.2 m². 2 / g, with an average pore size of 12.3nm. The content of gibbsite impurities is 0.5%.

[0067] Comparative Example 3 Five liters of sodium aluminate solution with a mass concentration of 19 g / L (calculated as alumina) were added to the reaction vessel. Carbon dioxide gas, a mixture of carbon dioxide and nitrogen with a volume fraction of 35% (2.57 L / min), was then introduced into the vessel. The sodium aluminate solution and carbon dioxide gas were subjected to a low-temperature carbonization reaction at 20°C to obtain a reaction slurry. When precipitate formed during the low-temperature carbonization reaction, 0.2 liters of water glass solution with a silica mass concentration of 30 g / L was added to the reaction slurry. The addition time of the water glass solution was controlled at 20 minutes, and all the water glass solution was added before the end of the low-temperature carbonization reaction. The final pH value of the low-temperature carbonization reaction was 11.5, yielding a silica-containing pseudoboehmite slurry.

[0068] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80°C until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 100°C to obtain silica-containing macroporous pseudoboehmite. Analysis showed that the silica-containing macroporous pseudoboehmite obtained in this comparative example contained 4.67% silica by mass, 0.03% sodium oxide by mass, a pore volume of 1.248 mL / g, and a specific surface area of ​​345.1 m². 2 / g, with an average pore size of 14.5nm and a boehmite impurity content of 2%.

[0069] Comparative Example 4 Add 5 liters of sodium aluminate solution, with a mass concentration of 22 g / L (calculated as alumina), to the reaction vessel. Introduce carbon dioxide gas into the reaction vessel; this gas is a mixture of carbon dioxide and nitrogen, with a carbon dioxide volume fraction of 35%, at a flow rate of 1.94 L / min. Perform a low-temperature carbonization reaction between the sodium aluminate solution and the carbon dioxide gas at 22°C to obtain a reaction slurry. When precipitate forms during the low-temperature carbonization reaction, rapidly add 0.5 liters of water glass solution (with a silica mass concentration of 26 g / L) to the reaction slurry over 2 minutes. The addition of the water glass solution must be completed before the end of the low-temperature carbonization reaction. The final pH value of the low-temperature carbonization reaction is 10.0, yielding a silica-containing pseudoboehmite slurry.

[0070] A siliceous pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80℃ until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 100℃ to obtain siliceous macroporous pseudoboehmite. The siliceous macroporous pseudoboehmite obtained in this comparative example was found to contain 8.28% silica by mass, 0.15% sodium oxide by mass, a pore volume of 1.002 mL / g, and a specific surface area of ​​369.3 m². 2 / g, with an average pore size of 10.8nm. The content of gibbsite impurities is 0.5%.

[0071] Comparative Example 5 Add 5 liters of sodium aluminate solution, with a mass concentration of 25 g / L (calculated as alumina), to the reaction vessel. Introduce carbon dioxide gas into the reaction vessel; this gas is a mixture of carbon dioxide and nitrogen, with a carbon dioxide volume fraction of 35%, at a flow rate of 1.00 L / min. Perform a low-temperature carbonization reaction between the sodium aluminate solution and the carbon dioxide gas at 25°C to obtain a reaction slurry. When the low-temperature carbonization reaction reaches the point where precipitate forms, add 1 liter of water glass solution, with a silica mass concentration of 75 g / L. Control the addition time of the water glass solution to 70 minutes, ensuring all water glass solution is added before the end of the low-temperature carbonization reaction. The endpoint pH of the low-temperature carbonization reaction is 10.2, yielding a silica-containing pseudoboehmite slurry.

[0072] A silica-containing pseudoboehmite slurry was subjected to liquid-solid separation to obtain a filter cake. The filter cake was washed with deionized water at 80℃ until the pH of the filtrate was less than 7, yielding a washed filter cake. The washed filter cake was then dried at 120℃ to obtain silica-containing macroporous pseudoboehmite. The silica-containing macroporous pseudoboehmite obtained in this comparative example was determined to contain 33.1% silica by mass, 0.10% sodium oxide by mass, with a pore volume of 0.807 mL / g and a specific surface area of ​​378.5 m². 2 / g, with an average pore size of 8.53nm. The content of gibbsite impurities is 0.5%.

[0073] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: This application employs a single-tank batch reaction, where all reaction steps (from the low-temperature carbonization reaction of sodium aluminate solution with carbon dioxide gas, to the addition of water glass solution, and finally to the obtaining of a silica-containing pseudo-boehmite slurry) are completed in the same reaction tank. This eliminates the need for multi-stage reactors in series or parallel-flow feeding systems, as well as complex equipment such as gas-liquid mixing pumps. Compared to multi-stage continuous carbonization methods, this application significantly reduces equipment investment, simplifies the operation process, and lowers the difficulty of process control. Furthermore, the low-concentration reaction system exhibits lower corrosivity to equipment, and both high-temperature washing and low-temperature drying are routine unit operations, facilitating scale-up from laboratory to industrial production.

[0074] 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 silica-containing macroporous pseudoboehmite by carbonization, characterized in that, The method includes: Sodium aluminate solution was subjected to a low-temperature carbonization reaction with carbon dioxide gas to obtain a reaction slurry; When the low-temperature carbonization reaction proceeds to the point where precipitates are formed, water glass solution is added to the reaction slurry. The addition of water glass solution is controlled to be completed before the end of the low-temperature carbonization reaction, and the pH value at the end of the low-temperature carbonization reaction is controlled to be alkaline, so as to obtain a silica-containing pseudo-boehmite slurry. The silica-containing pseudo-boehmite slurry was subjected to liquid-solid separation to obtain a filter cake; The filter cake is washed with deionized water until the pH of the filtrate after washing is less than 7, thus obtaining the washed filter cake. The washed filter cake was dried to obtain silica-containing macroporous pseudoboehmite.

2. The method according to claim 1, characterized in that, The carbon dioxide gas is a mixture of carbon dioxide and nitrogen, wherein the volume fraction of carbon dioxide is 35% to 40%.

3. The method according to claim 1, characterized in that, During the low-temperature carbonization reaction of sodium aluminate solution with carbon dioxide gas, the flow rate of the carbon dioxide gas is 1 L / min to 5.28 L / min.

4. The method according to claim 1, characterized in that, The sodium aluminate solution has a mass concentration of 10 g / L to 30 g / L, calculated as aluminum oxide.

5. The method according to claim 1, characterized in that, The temperature of the low-temperature carbonization reaction is 10℃~25℃, and the final pH value of the low-temperature carbonization reaction is 9.5~10.

5.

6. The method according to claim 1, characterized in that, The mass concentration of silica in the water glass solution is 10 g / L to 30 g / L.

7. The method according to claim 1, characterized in that, The water glass solution is added over a period of 5 to 90 minutes.

8. The method according to claim 1, characterized in that, The method is implemented in a single reaction vessel via a batch reaction.

9. The method according to claim 1, characterized in that, The temperature of the deionized water used in the washing process is 60℃~100℃, and the temperature of the drying process is 80℃~150℃.

10. The method according to claim 1, characterized in that, The silica-containing macroporous pseudoboehmite meets the following requirements: SiO2 mass fraction of 2.15%–9.02%, Na2O mass fraction <0.04%, pore volume of 1.223 mL / g–1.526 mL / g, and specific surface area of ​​346.6 m². 2 / g~458.7m 2 / g, with an average pore size of 12.9nm to 14.1nm.

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