A pseudo-boehmite and a method for producing the same

Abstract

This invention discloses a pseudoboehmite and its preparation method, belonging to the technical field of pseudoboehmite preparation. The method includes the following steps: S1. Adding a crystal form regulating agent to a sodium aluminate solution and an aluminum sulfate solution, performing a first-stage gelation at a pH of 4.0 to 5.5 and a temperature of 35°C to 55°C; then adding a block dispersion, performing a second-stage gelation at a pH of 7.5 to 9.0 and a temperature of 55°C to 75°C, resulting in a precursor solution after gelation; the crystal form regulating agent in the crystal form regulating agent is boric acid and citric acid; the block dispersion agent in the block dispersion is a polydimethylsiloxane-polyethylene oxide block copolymer; S2. After hydrothermal reaction, the precursor solution undergoes solid-liquid separation, collecting the solid material; the solid material is dried and graded to obtain pseudoboehmite. The pseudoboehmite prepared by this invention has high crystallinity and good thermal stability.

Description

Technical Field

[0001] This invention belongs to the field of boehmite preparation technology, specifically a boehmite and its preparation method. Background Technology

[0002] Boehmite is a key precursor for the preparation of γ-alumina supports and is widely used in catalytic cracking, hydrorefining, automotive exhaust denitrification, and lithium battery membrane coating. Currently, the mainstream industrial preparation method primarily uses sodium aluminate-aluminum sulfate dual-aluminum-source metathesis, followed by gelation, crystallization, and drying to obtain the product.

[0003] Currently, patent CN121107443A proposes a method for preparing narrow-pore pseudoboehmite, using mercaptopropionic acid-modified ZnS quantum dots as crystal form regulators and a polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer and sodium citrate complex as pore size directing agents. These are mixed and added to the system under a single pH condition, followed by aging, washing, and drying to obtain narrow-pore products with 5nm to 10nm pore size. However, this technology has significant drawbacks: the quantum dot preparation is complex, costly, and difficult to industrialize; the single-stage mixing of the crystal form regulator and pore size directing agent easily leads to intermolecular antagonism, limiting the regulation efficiency; and the single-pH gelation and single-stage aging process makes it difficult to achieve precise separation of nucleation and growth, resulting in insufficient batch stability. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides a pseudoboehmite and its preparation method. This invention uses sodium aluminate and aluminum sulfate as dual aluminum sources, employing a two-liquid co-flow segmented gelation process. During the acidic nucleation stage, a composite crystal form regulator of boric acid and citric acid is introduced, and during the alkaline growth stage, a polydimethylsiloxane-polyethylene oxide block dispersant is introduced. Combined with two-stage gradient hydrothermal crystallization, the resulting product exhibits high crystallinity and good thermal stability.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses a method for preparing pseudoboehmite, comprising the following steps: S1. A crystal form regulating solution is added to a sodium aluminate solution and an aluminum sulfate solution, and a first-stage gelation is carried out under conditions of pH 4.0 to 5.5 and temperature 35°C to 55°C; then a block dispersion is added, and a second-stage gelation is carried out under conditions of pH 7.5 to 9.0 and temperature 55°C to 75°C. After gelation, a precursor solution is obtained; the crystal form regulating agent in the crystal form regulating solution is boric acid and citric acid. The block dispersant in the block dispersion is a polydimethylsiloxane-polyethylene oxide block copolymer (PDMS-PEO). S2. After the precursor liquid undergoes a hydrothermal reaction, solid-liquid separation is performed, and the solid material is collected. After drying and grading, pseudoboehmite is obtained.

[0007] According to some embodiments of the present invention, the concentration of the sodium aluminate solution is from 1.2 mol Al / L to 2.0 mol Al / L; According to some embodiments of the present invention, the concentration of the aluminum sulfate solution is from 0.8 mol Al / L to 1.5 mol Al / L.

[0008] According to some embodiments of the present invention, the molar ratio of aluminum in the sodium aluminate solution to aluminum in the aluminum sulfate solution is 0.92:1 to 1.08:1, preferably 0.96 to 1.04:1. This molar ratio range allows for near-equimolar neutralization and gel formation, eliminating the need for additional large amounts of acid or alkali to adjust the pH, reducing salt formation and subsequent washing load. When the ratio is low, aluminum sulfate is in excess, resulting in an acidic system that easily forms amorphous aluminum gel, decreasing crystallinity and reducing pore volume. When the ratio is high, sodium aluminate is in excess, resulting in an alkaline system that easily forms gibbsite impurities, increases sodium residue, and widens and disperses pore size.

[0009] According to some embodiments of the present invention, the mass ratio of boric acid to citric acid in the crystal form regulator is 1:2.5 to 5.0, preferably 1:3.5 to 4.0; citric acid provides coordination regulation, and boric acid provides crystal facet selective adsorption.

[0010] According to some embodiments of the present invention, the total amount of the crystal form regulator added is 0.8% to 2.5% of the total molar amount of aluminum in the system, preferably 1.4% to 1.8%; this percentage is the molar percentage of the crystal form regulator (the sum of the amounts of boric acid and citric acid) to the total molar amount of aluminum.

[0011] According to some embodiments of the present invention, the mass concentration of the crystal form regulating solution is 8.0% to 10.0%, and the solvent is water.

[0012] According to some embodiments of the present invention, the number average molecular weight of the block dispersant is 1800 g / mol to 2200 g / mol.

[0013] According to some embodiments of the present invention, the block dispersion has a mass concentration of 3.0% to 5.0% and the solvent is water.

[0014] According to some embodiments of the present invention, the amount of the block dispersion added accounts for 0.15% to 0.45% of the total mass of the precursor liquid, preferably 0.25% to 0.30%.

[0015] According to some embodiments of the present invention, the first stage of gelation process is as follows: sodium aluminate solution and aluminum sulfate solution are added to the reactor in parallel flow, the temperature of the first stage gelation system is controlled at 35°C to 55°C, the pH value is controlled at 4.0 to 5.5, and the gelation feeding time is 30 min to 80 min; a crystal form regulating liquid is added dropwise during the first stage gelation process.

[0016] According to some embodiments of the present invention, the process of the second stage gelation is as follows: sodium aluminate solution and aluminum sulfate solution continue to be fed in a two-liquid co-flow manner, the temperature of the second stage gelation system is controlled at 55°C to 75°C, the pH value is controlled at 7.5 to 9.0, and the gelation feeding time is 15 min to 20 min; a block dispersion is added dropwise during the second stage gelation process.

[0017] According to some embodiments of the present invention, the specific steps of the hydrothermal reaction are as follows: first, keep at 92°C to 95°C for 2.0h to 2.5h, and then keep at 132°C to 135°C for 3.0h to 3.5h.

[0018] According to some embodiments of the present invention, the heating rate of the hydrothermal reaction is from 3.0°C / min to 3.5°C / min.

[0019] According to some embodiments of the present invention, the hydrothermal reaction is followed by depressurization and cooling to below 50°C.

[0020] According to some embodiments of the present invention, the solid-liquid separation is performed using a centrifugal separation process.

[0021] According to some embodiments of the present invention, the solid material is washed with water after solid-liquid separation, and the washing temperature is 50°C to 55°C.

[0022] According to some embodiments of the present invention, the drying process is a vacuum flash drying process, wherein the drying is carried out under conditions of absolute pressure of 0.075 MPa to 0.080 MPa and temperature of 95°C to 98°C for 20 to 40 minutes.

[0023] According to some embodiments of the present invention, the grading is performed by using an air classifier to control the product particle size D50 to be between 15 μm and 35 μm, preferably between 22 μm and 25 μm.

[0024] The present invention also discloses a pseudoboehmite, which is prepared by the aforementioned preparation method.

[0025] According to some embodiments of the present invention, the specific surface area of ​​the pseudoboehmite is 320 m². 2 / g up to 370m 2 / g.

[0026] According to some embodiments of the present invention, the pore volume of the pseudoboehmite is from 0.45 mL / g to 0.7 mL / g.

[0027] According to some embodiments of the present invention, the crystallinity of the pseudoboehmite is greater than or equal to 85%.

[0028] According to some embodiments of the present invention, the average grain size of the pseudoboehmite is 4 nm to 7 nm.

[0029] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0030] Compared with the prior art, the beneficial effects of the present invention are: This invention incorporates a boric acid and citric acid composite crystal form regulator in the first acidic nucleation stage to constrain crystal nucleus growth and inhibit impurity crystal formation. In the second alkaline growth stage, a PDMS-PEO block dispersant is added to create steric hindrance, preventing agglomeration and avoiding interference between additives. Combined with a two-stage gradient hydrothermal process, first, the crystal nuclei are perfected at low temperature, then the pores are optimized at high temperature. Ultimately, this results in pseudoboehmite possessing high crystallinity, narrow pore size distribution, and low agglomeration.

[0031] The pseudoboehmite product obtained by this invention has outstanding comprehensive performance and broad application prospects. It has high crystallinity and stable structure after high-temperature calcination. It exhibits better activity, strength and service life in scenarios such as heavy oil hydrogenation, catalytic cracking, tail gas treatment and new energy materials. Detailed Implementation

[0032] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0034] The raw material information used in the following examples is as follows: Polydimethylsiloxane-polyethylene oxide block copolymer (PDMS-PEO) originates from Xi'an Qiyue Biotechnology. It is an amphiphilic polymeric diblock copolymer, available in two models with number average molecular weights of 2000 g / mol and 1500 g / mol, including but not limited to the models from the above manufacturers.

[0035] [Pseudoboehmite and its preparation method] Example 1 The preparation method of pseudoboehmite in this embodiment is as follows: S1. Use a 316L jacketed reactor, pre-fill with bottom water, and start stirring; First stage gelation: Sodium aluminate solution (1.6 mol Al / L) and aluminum sulfate solution (1.1 mol Al / L) are simultaneously and uniformly added to the reactor in a two-liquid co-flow manner, controlling the molar ratio of aluminum in sodium aluminate to aluminum in aluminum sulfate to be 1.02:1; the temperature of the first stage gelation system is kept constant at 45℃, and the pH value of the system is kept stable at 4.8; the total gelation feeding time is 55 min; throughout the first stage gelation process, crystal form regulating solution (mass concentration 9.0%, boric acid:citric acid mass ratio 1:3.8) is added dropwise at a uniform rate, and the total amount of crystal form regulating solution added is calculated as 1.6 mol% of the total molar amount of aluminum in the system. No block dispersion is added in this stage.

[0036] Second stage gelation: The sodium aluminate solution and aluminum sulfate solution were continuously fed in a two-liquid co-flow without interruption; the system conditions were adjusted to control the temperature of the second stage gelation system to be constant at 63℃ and the pH value of the system to be maintained at 8.3; the feeding time of the second stage gelation was 18 min; the addition of crystal form control solution was stopped, and PDMS-PEO block dispersion (mass concentration 4.0%, PDMS-PEO number average molecular weight 2000 g / mol) was added dropwise at a uniform rate throughout the second stage gelation process, with the amount of block dispersion added accounting for 0.28% of the total mass of the precursor solution; after the gelation was completed, the precursor solution of pseudoboehmite was obtained.

[0037] S2. Transfer the precursor liquid into a closed hydrothermal reactor and maintain stirring. Heat at a constant heating rate of 3.2℃ / min. First, heat to 93℃ and hold at that temperature for 2.1h for primary pre-crystallization. Continue heating at the same rate to 133℃ and hold at that temperature for 3.1h for deep crystallization. After the hydrothermal reaction is complete, stop heating and allow the pressure to release naturally to cool to below 50℃.

[0038] After hydrothermal treatment, the material is separated into solid and liquid components by centrifugation. The solid material is collected and washed with deionized water at a constant temperature of 52°C. After thorough stirring and impregnation, it is centrifuged again. The washing process is repeated twice. The washed solid filter cake is then sent to a vacuum flash dryer. The drying vacuum is controlled at 0.078 MPa and the drying temperature at 96°C for 30 minutes. Low-temperature vacuum flash drying is used for rapid dehydration to avoid grain sintering and pore collapse.

[0039] After drying, the material is pulverized and classified by an air classifier; the median diameter of the finished product is controlled to be D50=23μm.

[0040] Example 2 The difference between this embodiment and Embodiment 1 is as follows: The molar ratio of aluminum in sodium aluminate to that in aluminum sulfate is 0.92:1; The other raw materials, steps and parameters are the same as in Example 1.

[0041] Example 3 The difference between this embodiment and Embodiment 1 is as follows: The mass ratio of boric acid to citric acid in the crystal form control solution is 1:2.0; The other raw materials, steps and parameters are the same as in Example 1.

[0042] Example 4 The difference between this embodiment and Embodiment 1 is as follows: The temperature of the first-stage gelation system was kept constant at 52℃, and the pH value of the system was kept stable at 4.2. The other raw materials, steps and parameters are the same as in Example 1.

[0043] Example 5 The difference between this embodiment and Embodiment 1 is as follows: The temperature of the second-stage gelation system was kept constant at 58℃, and the pH value of the system was kept stable at 8.8. The other raw materials, steps and parameters are the same as in Example 1.

[0044] Example 6 The difference between this embodiment and Embodiment 1 is as follows: The block dispersion was added at a rate of 0.20% of the total mass of the precursor solution. The other raw materials, steps and parameters are the same as in Example 1.

[0045] Example 7 The difference between this embodiment and Embodiment 1 is as follows: The number-average molecular weight of PDMS-PEO used in the block dispersion was 1500 g / mol; The other raw materials, steps and parameters are the same as in Example 1.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: S1. Use a 316L jacketed reactor of the same specifications, add bottom water in advance and start stirring; First stage of gelation: Sodium aluminate solution and aluminum sulfate solution are added to the reactor simultaneously in parallel flow; the system temperature is controlled at 45℃, the pH value is stabilized at 4.8, and the feeding time is 55min; throughout the first stage of gelation, a pre-mixed crystal form regulating solution and block dispersion mixture are added dropwise at a uniform speed.

[0047] The second stage of gelation: The dual aluminum source solutions were continuously fed in a parallel flow without interruption; the operating conditions were adjusted to raise the system temperature to 63℃ and stabilize the pH at 8.3, with a feeding time of 18 minutes; the remaining mixed additive solution was continued to be added dropwise at a uniform rate, without separate additions throughout the process; the two additives were always mixed and added synchronously; after gelation, the precursor solution was obtained. In this comparative example, the crystal form regulating solution and dispersion were pre-mixed and added together throughout the process, without segmented addition.

[0048] The other raw materials, steps and parameters are the same as in Example 1.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: The molar ratio of aluminum in sodium aluminate solution to aluminum in aluminum sulfate solution is 1.2:1. The other raw materials, steps and parameters are the same as in Example 1.

[0050] [Example of Results] The pseudoboehmite prepared in the above embodiments and comparative examples was subjected to the following tests, and the test results are shown in Tables 1 to 3.

[0051] Example 1—Specific Surface Area and Pore Volume (GB / T 19587) Table 1 Specific surface area and pore volume table

[0052] Example 2—Crystallization and Average Grain Size (XRD Method) Table 2 Crystallinity and Average Grain Size

[0053] Example 3—Retention rate of specific surface area after calcination The boehmite sample was placed in a muffle furnace and calcined at 550℃ for 4 hours. After natural cooling, the BET specific surface area was re-measured according to GB / T 19587. The retention rate was calculated as follows: Retention rate = Specific surface area after calcination / Specific surface area before calcination × 100%.

[0054] Table 3. Specific Surface Area Retention Rate after Calcination

[0055] The following points should be noted in conjunction with Tables 1 to 3: Example Group: Example 3: The boric acid / citric acid ratio was unbalanced. The low citric acid ratio resulted in insufficient crystal form constraint, significantly reduced pore volume and crystallinity, and decreased calcination specific surface area retention. Example 7: The dispersant had a small molecular weight, resulting in poor dispersion and coating performance, disordered grain growth, and easy structural collapse.

[0056] Comparative Example Group: In Comparative Example 1, the two additives were mixed and added, resulting in mutual interference, poor crystallization, heavy agglomeration, the worst pore structure, and a significant decrease in crystallinity; after calcination, the structure was severely damaged, and the thermal stability was the worst. In Comparative Example 2, the Al molar ratio in the sodium aluminate solution and aluminum sulfate solution exceeded the range, making the system more alkaline, increasing impurities, and resulting in a poor pore structure; the imbalance of the Al ratio also led to more impurities and incomplete crystal forms.

[0057] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing pseudo-boehmite, characterized by, Includes the following steps: S1. Add crystal form regulating solution to sodium aluminate solution and aluminum sulfate solution, and carry out the first stage of gelation under the conditions of pH value of 4.0 to 5.5 and temperature of 35℃ to 55℃; then add block dispersion solution, and carry out the second stage of gelation under the conditions of pH value of 7.5 to 9.0 and temperature of 55℃ to 75℃. After the gelation is completed, the precursor solution is obtained. The crystal form regulating agents in the crystal form regulating solution are boric acid and citric acid; The block dispersant in the block dispersion is a polydimethylsiloxane-polyethylene oxide block copolymer; S2. After the precursor liquid undergoes a hydrothermal reaction, solid-liquid separation is performed, and the solid material is collected. After drying and grading, pseudoboehmite is obtained.

2. The preparation method according to claim 1, characterized in that, The molar ratio of aluminum in sodium aluminate solution to aluminum in aluminum sulfate solution is 0.92:1 to 1.08:1; And / or, the concentration of aluminum in the sodium aluminate solution is from 1.2 mol Al / L to 2.0 mol Al / L; And / or, the aluminum concentration in the aluminum sulfate solution is from 0.8 mol Al / L to 1.5 mol Al / L.

3. The preparation method according to claim 1, characterized in that, The mass ratio of boric acid to citric acid in the crystal form regulator is 1:2.5 to 1:5.0; And / or, the total amount of the crystal form regulator added is 0.8% to 2.5% of the total molar amount of aluminum in the system; And / or, the mass concentration of the crystal form regulating solution is 8.0% to 10.0%, and the solvent is water.

4. The preparation method according to claim 1, characterized in that, The number-average molecular weight of the block dispersant is from 1800 g / mol to 2200 g / mol; And / or, the block dispersion has a mass concentration of 3.0% to 5.0% and the solvent is water; And / or, the amount of the block dispersion added is 0.15% to 0.45% of the total mass of the precursor liquid.

5. The preparation method according to claim 1, characterized in that, The first stage of gelation process is as follows: sodium aluminate solution and aluminum sulfate solution are added to the reactor in a two-liquid co-flow manner, the temperature of the first stage gelation system is controlled at 35℃ to 55℃, the pH value is 4.0 to 5.5, and the gelation feeding time is 30 min to 80 min; crystal form regulating liquid is added dropwise during the first stage gelation process; And / or, the second stage of gelation process is as follows: sodium aluminate solution and aluminum sulfate solution continue to be fed in a two-liquid co-flow manner, the temperature of the second stage gelation system is controlled at 55℃ to 75℃, the pH value is 7.5 to 9.0, and the gelation feeding time is 15 min to 20 min; block dispersion is added dropwise during the second stage gelation process.

6. The preparation method according to claim 1, characterized in that, The specific steps of the hydrothermal reaction are as follows: first, keep the temperature at 92℃ to 95℃ for 2.0h to 2.5h, and then keep the temperature at 132℃ to 135℃ for 3.0h to 3.5h. And / or, the heating rate of the hydrothermal reaction is from 3.0 °C / min to 3.5 °C / min.

7. The preparation method according to claim 1, characterized in that, The solid-liquid separation is performed using a centrifugal separation process; after solid-liquid separation, the solid material is washed with water at a temperature of 50°C to 55°C. And / or, the drying process is a vacuum flash drying process, wherein the drying is carried out under an absolute pressure of 0.075 MPa to 0.080 MPa and a temperature of 95°C to 98°C for 20 to 40 minutes; And / or, the grading is performed using an air classifier to control the product particle size D50 between 15 μm and 35 μm.

8. A pseudoboehmite, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The pseudoboehmite as described in claim 8, characterized in that, The pseudo-boehmite has a specific surface area of 320 m 2 / g to 370 m 2 / g; And / or, the pore volume of the pseudoboehmite is from 0.45 mL / g to 0.70 mL / g.

10. The pseudoboehmite as described in claim 8, characterized in that, The crystallinity of the pseudoboehmite is greater than or equal to 85%; And / or, the average grain size of the pseudoboehmite is 4 nm to 7 nm.

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