Preparation method of pseudo-boehmite for chloromethane

Abstract

The application relates to the technical field of inorganic porous materials, and particularly discloses a preparation method of pseudo-boehmite for chloromethane. The preparation method comprises the following steps: S1: adding a sodium-free aluminum salt, zirconium nitrate pentahydrate and tetrabutyl titanate into a mixed solvent, adding a complexing agent, then adding nano-boehmite, uniformly mixing, adjusting the pH value to 7.5-8.0, increasing the temperature to 25-35 DEG C, mixing, adjusting the pH value to 5.5-6.0, mixing, and obtaining a uniform sol; S2: mixing urea and ammonium bicarbonate in water, adding zirconium ammonium carbonate, and obtaining a mixed solution B; S3: adding the mixed solution B into the uniform sol, uniformly mixing, performing gradient temperature reaction, performing solid-liquid separation, washing, drying, and obtaining the pseudo-boehmite for chloromethane. The pseudo-boehmite for chloromethane prepared by the application has extremely low sodium content, high specific surface area and excellent thermal stability.

Description

Technical Field

[0001] This application relates to the field of inorganic porous materials technology, and more specifically, it relates to a method for preparing chloromethane using boehmite. Background Technology

[0002] Boehmite, as a key precursor for preparing high-performance γ-alumina catalyst supports, directly determines the activity, selectivity, and lifespan of the final catalyst in industrial reactions due to its purity, pore structure, and thermal stability. In the specific scenario of chloromethane synthesis (the catalytic reaction of methanol and hydrogen chloride), the catalyst support faces unique challenges: firstly, the presence of chlorine in the reaction medium requires the support to possess extremely high phase stability to prevent structural collapse that could directly lead to catalyst deactivation; secondly, residual alkali metal impurities (especially sodium ions) in the support can undergo irreversible reactions with the reactant hydrogen chloride, potentially causing rapid chlorine poisoning of the catalyst and exacerbating high-temperature sintering of the active components, significantly reducing catalytic efficiency and stabilization period.

[0003] Chinese patent application CN119240761A discloses a method for preparing boehmite, the method comprising: neutralizing sodium aluminate and acidic aluminum salt to generate an amorphous precipitate, obtaining a first slurry; filtering the first slurry, and then pulping the filter cake obtained from the filtration to obtain a second slurry; adjusting the pH value of the second slurry to a preset pH value using an alkaline additive to age the second slurry to obtain boehmite; the alkaline additive includes at least one of the following: Na2CO3, NaOH, and NaNH2.

[0004] In this technical solution, sodium aluminate and acidic aluminum salt are used as raw materials. After neutralization reaction, precipitates are generated. In the subsequent aging process, sodium-containing alkaline additives (such as NaOH, Na2CO3, etc.) are introduced. This results in a high residual amount of sodium ions (usually calculated as Na2O) in the final product. Since scenarios such as chloromethane production are sensitive to sodium content, high sodium will aggravate chlorine poisoning of the catalyst, reduce activity and selectivity, and affect production efficiency. Summary of the Invention

[0005] To address the technical drawback of high sodium ion residue in existing boehmite, this application provides a method for preparing boehmite for chloromethane.

[0006] This application provides a method for preparing pseudoboehmite for chloromethane, using the following technical solution:

[0007] A method for preparing chloromethane using boehmite includes the following steps:

[0008] S1: At 5~15℃, add sodium-free aluminum salt, zirconium nitrate pentahydrate, and tetrabutyl titanate to a mixed solvent, add a complexing agent, then add nano-boehmite, mix evenly, first adjust the pH to 7.5~8.0, raise the temperature to 25~35℃, mix for 30~40min, then adjust the pH to 5.5~6.0, mix for 30~40min to obtain a uniform sol;

[0009] S2: Mix urea and ammonium bicarbonate and dissolve them in water, then add ammonium zirconium carbonate to obtain mixture B;

[0010] S3: Add mixture B to the homogeneous sol, mix well, and carry out a gradient temperature reaction between 70 and 180°C. Then, separate the solid and liquid, wash, and dry to obtain boehmite for chloromethane.

[0011] Preferably, the gradient heating reaction specifically involves: first heating to 70~80℃ and holding for 2~3 hours, then heating to 140~160℃ and holding for 4~5 hours, and then heating to 170~180℃ and holding for 3~4 hours.

[0012] In this technical solution, firstly, during the sol-gel construction stage, a complexing agent is used to regulate the hydrolysis of aluminum, zirconium, and titanium ions. Combined with segmented pH adjustment and the introduction of nano-boehmite seeds, the aim is to obtain a composite sol precursor with uniform composition and stable structure. Secondly, during the crystallization stage, a programmed gradient temperature increase couples the staged thermal decomposition process of urea and ammonium bicarbonate with the crystal growth of the material. The expansion effect of gas release is used to construct and expand pores in situ. Simultaneously, the ammonium zirconium carbonate in the system hydrolyzes at high temperature and interacts with the interface of the growing crystals, thereby helping to improve the structural stability of the pore walls.

[0013] Preferably, the sodium-free aluminum salt is selected from either aluminum chloride hexahydrate or aluminum nitrate nonahydrate.

[0014] Preferably, the molar ratio of the complexing agent, sodium-free aluminum salt, zirconium nitrate pentahydrate, tetrabutyl titanate, urea, ammonium bicarbonate and ammonium zirconium carbonate is (0.2~0.3):1:(0.05~0.1):(0.03~0.07):(0.8~1.2):(0.4~0.7):(0.02~0.05).

[0015] In this technical solution, by optimizing the ratio of each component, zirconium and titanium synergistic stabilization, urea-ammonium bicarbonate staged pore formation, and zirconium carbonate post-strengthening are achieved. While ensuring high porosity, the structural strength of the pore wall is maintained to the maximum extent, thereby simultaneously achieving high specific surface area, high pore volume, and excellent thermal stability.

[0016] Preferably, the amount of nanoboehmite used is 1% to 3% of the mass of sodium-free aluminum salt.

[0017] Preferably, the particle size distribution of the nanoboehmite is 5~10nm.

[0018] In this technical solution, nano-boehmite of a specific size is introduced as seed crystals to provide effective nucleation sites for the polymerization and crystallization of aluminum hydroxyl species, thereby promoting the formation and growth of pseudoboehmite phase.

[0019] Preferably, the complexing agent is selected from at least one of citric acid and tartaric acid.

[0020] In this technical solution, in the initial stage of sol preparation, it effectively inhibits the premature and rapid hydrolysis of metal ions; in the subsequent segmented pH adjustment process, the shift of complexation equilibrium allows the metal ions to be released slowly, which helps to form a more uniform precipitation environment around the seed crystals and promotes the formation of a dense and uniform precursor structure.

[0021] Preferably, the mixed solvent comprises isopropanol and water.

[0022] Preferably, in the mixed solvent, the volume ratio of isopropanol to water is (3~5):(5~7).

[0023] Preferably, in step S3, after drying, the material is dispersed in an anhydrous alcoholic solution of aluminum isopropoxide, heated to 50-60°C, water is added, and the mixture is stirred for 90-120 minutes. After solid-liquid separation, the material is washed again and dried to obtain boehmite for chloromethane.

[0024] Preferably, the amount of water used is 5% to 10% of the volume of the anhydrous alcohol solution.

[0025] Preferably, the mass concentration of aluminum isopropoxide is 1.5% to 2.5%.

[0026] Preferably, the anhydrous alcohol used in the anhydrous alcohol solution is isopropanol.

[0027] In this technical solution, aluminum isopropoxide can dissolve well and disperse uniformly in an anhydrous alcohol phase environment, adsorbing onto the surface and pores of boehmite particles. Subsequently, a limited amount of water is slowly added under heating conditions, utilizing the autocatalytic properties of the aluminum isopropoxide hydrolysis reaction to initiate a mild and controllable hydrolysis and condensation reaction. The nanoscale aluminum hydroxyl oxide generated in situ during this process can chemically bond with the hydroxyl groups on the surface of the boehmite matrix, thereby filling and bridging structural defects at the molecular level, effectively reducing surface defects, strengthening pore walls, and thus improving the material's resistance to sintering and thermal stability during subsequent high-temperature calcination and use.

[0028] In summary, this application has the following beneficial effects:

[0029] This application constructs a homogeneous sol through multi-component synergy (zirconium, titanium, etc.) and segmented pH control. It also utilizes programmed temperature rise to couple the staged thermal decomposition of the precipitant with the material crystallization process, achieving in-situ construction of a pore structure with concentrated pore size distribution and interconnected channels. Furthermore, in-situ molecular-level reinforcement of the pore walls is carried out through alcohol phase deposition post-treatment. Ultimately, the resulting pseudoboehmite product has extremely low sodium content, high specific surface area, excellent thermal stability and structural stability, fully meeting the high-performance requirements of catalyst supports for stringent reactions such as chloromethane synthesis. Attached Figure Description

[0030] Figure 1 The BJH pore size differential distribution curve of chloromethane using pseudoboehmite in Example 1;

[0031] Figure 2 The BJH pore size differential distribution curve of chloromethane using pseudoboehmite in Example 2;

[0032] Figure 3 The BJH pore size differential distribution curve of chloromethane using pseudoboehmite in Example 4 is shown. Detailed Implementation

[0033] The present application will be further described in detail below with reference to the embodiments.

[0034] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0035] Example 1

[0036] The method for preparing chloromethane using boehmite in this embodiment includes the following steps:

[0037] S1: At 15℃, 1 mol of aluminum chloride hexahydrate, 0.05 mol of zirconium nitrate pentahydrate, and 0.03 mol of tetrabutyl titanate were added to 1.2 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 3:7). 0.2 mol of citric acid was added, followed by 1% nano-boehmite (by mass of aluminum chloride hexahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 7.5 with 8% ammonia. The temperature was raised to 25℃, and the mixture was stirred at 200 r / min for 30 min. The pH was then adjusted to 6.0 with 8% glacial acetic acid, and the mixture was stirred for another 30 min to obtain a homogeneous sol.

[0038] S2: Mix 0.8 mol of urea, 0.4 mol of ammonium bicarbonate and 1.2 L of deionized water evenly, then add 0.05 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0039] S3: At a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 70℃ at 1℃ / min and held for 2 h. The temperature was then slowly increased to 140℃ at 1℃ / min and held for 4 h. The temperature was then increased to 170℃ and held for 3 h. After cooling to room temperature naturally, the mixture was filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0040] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​395 m². 2 / g; pore volume 1.42cm 3 / g, with a most probable pore size of 9.8nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 91.6%.

[0041] Example 2

[0042] The method for preparing chloromethane using boehmite in this embodiment includes the following steps:

[0043] S1: At 10℃, 1 mol of aluminum nitrate nonahydrate, 0.1 mol of zirconium nitrate pentahydrate, and 0.07 mol of tetrabutyl titanate were added to 1.5 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 3:7). 0.3 mol of citric acid was added, followed by 3% nano-boehmite (by mass of aluminum nitrate nonahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 8.0 with 8% ammonia. The temperature was raised to 35℃, and the mixture was stirred at 200 r / min for 40 min. The pH was then adjusted to 5.5 with 8% glacial acetic acid, and the mixture was stirred for another 40 min to obtain a homogeneous sol.

[0044] S2: Mix 1.2 mol of urea, 0.6 mol of ammonium bicarbonate and 1.8 L of deionized water evenly, then add 0.05 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0045] S3: At a stirring speed of 200 r / min, mixture B is slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature is slowly increased to 80℃ at 1℃ / min and held for 3 h. The temperature is then slowly increased to 160℃ at 1℃ / min and held for 5 h. The temperature is then increased to 180℃ and held for 4 h. After cooling naturally to room temperature, the mixture is filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0046] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​405 m². 2 / g; pore volume 1.49cm 3 / g, with a most probable pore size of 10.5nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 90.4%.

[0047] Example 3

[0048] The method for preparing chloromethane using boehmite in this embodiment includes the following steps:

[0049] S1: At 5℃, 1 mol of aluminum nitrate nonahydrate, 0.08 mol of zirconium nitrate pentahydrate, and 0.05 mol of tetrabutyl titanate were added to 1.5 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 5:5). 0.2 mol of citric acid and 0.05 mol of tartaric acid were added, followed by 2.5% nano-boehmite (by mass of aluminum nitrate nonahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 8.0 using 8% ammonia. The temperature was raised to 35℃, and the mixture was stirred at 200 r / min for 40 min. The pH was then adjusted to 5.5 using 8% glacial acetic acid, and the mixture was stirred for another 40 min to obtain a homogeneous sol.

[0050] S2: Mix 1.0 mol of urea, 0.7 mol of ammonium bicarbonate and 1.7 L of deionized water evenly, then add 0.03 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0051] S3: At a stirring speed of 200 r / min, mixture B is slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature is slowly increased to 75℃ at 1℃ / min and held for 3 h. The temperature is then slowly increased to 150℃ at 1℃ / min and held for 5 h. The temperature is then increased to 175℃ and held for 4 h. After cooling naturally to room temperature, the mixture is filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0052] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​418 m². 2 / g; pore volume 1.58cm 3 / g, with a most probable pore size of 11.2nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 93.0%.

[0053] Example 4

[0054] The method for preparing chloromethane using boehmite in this embodiment includes the following steps:

[0055] S1: At 5℃, 1 mol of aluminum nitrate nonahydrate, 0.08 mol of zirconium nitrate pentahydrate, and 0.05 mol of tetrabutyl titanate were added to 1.5 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 5:5). 0.2 mol of citric acid and 0.05 mol of tartaric acid were added, followed by 2.5% nano-boehmite (by mass of aluminum nitrate nonahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 8.0 using 8% ammonia. The temperature was raised to 35℃, and the mixture was stirred at 200 r / min for 40 min. The pH was then adjusted to 5.5 using 8% glacial acetic acid, and the mixture was stirred for another 40 min to obtain a homogeneous sol.

[0056] S2: Mix 1.0 mol of urea, 0.7 mol of ammonium bicarbonate and 1.7 L of deionized water evenly, then add 0.03 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0057] S3: Under a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 75°C at 1°C / min and held for 3 h. The temperature was then slowly increased to 150°C at 1°C / min and held for 5 h. The temperature was then increased to 175°C and held for 4 h. After cooling naturally to room temperature, the mixture was filtered, washed three times with 55°C deionized water and once with anhydrous ethanol, and then freeze-dried at -30°C for 12 h. The mixture was dispersed in an isopropanol solution with a mass concentration of 1.5% aluminum isopropoxide and a solid-liquid ratio of 1 g: 15 mL. The temperature was increased to 50°C, and under a stirring speed of 200 r / min, 5% of the volume of deionized water (by volume of the isopropanol solution) was slowly added dropwise. The mixture was stirred for 90 min, filtered, washed twice with 55°C deionized water and once with anhydrous ethanol, and then freeze-dried at -30°C for 12 h to obtain boehmite for chloromethane.

[0058] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​408 m². 2 / g; pore volume 1.53cm 3 / g, with a most probable pore size of 11.0nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 93.8%.

[0059] Example 5

[0060] The method for preparing chloromethane using boehmite in this embodiment includes the following steps:

[0061] S1: At 5℃, 1 mol of aluminum nitrate nonahydrate, 0.08 mol of zirconium nitrate pentahydrate, and 0.05 mol of tetrabutyl titanate were added to 1.5 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 5:5). 0.2 mol of citric acid and 0.05 mol of tartaric acid were added, followed by 2.5% nano-boehmite (by mass of aluminum nitrate nonahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 8.0 using 8% ammonia. The temperature was raised to 35℃, and the mixture was stirred at 200 r / min for 40 min. The pH was then adjusted to 5.5 using 8% glacial acetic acid, and the mixture was stirred for another 40 min to obtain a homogeneous sol.

[0062] S2: Mix 1.0 mol of urea, 0.7 mol of ammonium bicarbonate and 1.7 L of deionized water evenly, then add 0.03 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0063] S3: Under a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 75℃ at 1℃ / min and held for 3 h. The temperature was then slowly increased to 150℃ at 1℃ / min and held for 5 h. The temperature was then increased to 175℃ and held for 4 h. After cooling naturally to room temperature, the mixture was filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h. The mixture was dispersed in an isopropanol solution with a mass concentration of 2.5% aluminum isopropoxide and a solid-liquid ratio of 1 g: 15 mL. The temperature was increased to 60℃, and under a stirring speed of 200 r / min, 10% of the volume of deionized water (by volume of the isopropanol solution) was slowly added dropwise. The mixture was stirred for 90 min, filtered, washed twice with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0064] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​402 m². 2 / g; pore volume 1.50cm 3 / g, with a most probable pore size of 10.7nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 94.5%.

[0065] Comparative Example 1

[0066] The comparative example of chloromethane preparation using boehmite includes the following steps:

[0067] S1: At 15℃, 1 mol of aluminum chloride hexahydrate and 0.05 mol of zirconium nitrate pentahydrate were added to 1.2 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 3:7), 0.2 mol of citric acid were added, and then 1% of nano-boehmite (by mass of aluminum chloride hexahydrate) was added. The mixture was stirred evenly, and the pH was adjusted to 7.5 with 8% ammonia water. The temperature was raised to 25℃, and the mixture was stirred at 200 r / min for 30 min. The pH was then adjusted to 6.0 with 8% glacial acetic acid, and the mixture was stirred for another 30 min to obtain a uniform sol.

[0068] S2: Mix 0.8 mol of urea, 0.4 mol of ammonium bicarbonate and 1.2 L of deionized water evenly, then add 0.05 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0069] S3: At a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 70℃ at 1℃ / min and held for 2 h. The temperature was then slowly increased to 140℃ at 1℃ / min and held for 4 h. The temperature was then increased to 170℃ and held for 3 h. After cooling to room temperature naturally, the mixture was filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0070] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​385 m². 2 / g; pore volume 1.39cm 3 / g, with a most probable pore size of 9.5nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 87.9%.

[0071] Comparative Example 2

[0072] The comparative example of chloromethane preparation using boehmite includes the following steps:

[0073] S1: At 15℃, 1 mol of aluminum chloride hexahydrate and 0.03 mol of tetrabutyl titanate were added to 1.2 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 3:7), 0.2 mol of citric acid were added, and then 1% of nano-boehmite (by mass of aluminum chloride hexahydrate) was added. The mixture was stirred evenly, and the pH was adjusted to 7.5 with 8% ammonia water. The temperature was raised to 25℃, and the mixture was stirred at 200 r / min for 30 min. The pH was then adjusted to 6.0 with 8% glacial acetic acid, and the mixture was stirred for another 30 min to obtain a uniform sol.

[0074] S2: Mix 0.8 mol of urea, 0.4 mol of ammonium bicarbonate and 1.2 L of deionized water evenly, then add 0.05 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0075] S3: At a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 70℃ at 1℃ / min and held for 2 h. The temperature was then slowly increased to 140℃ at 1℃ / min and held for 4 h. The temperature was then increased to 170℃ and held for 3 h. After cooling to room temperature naturally, the mixture was filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0076] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​390 m². 2 / g; pore volume 1.41cm 3 / g, with a most probable pore size of 10.0nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 88.6%.

[0077] Comparative Example 3

[0078] The comparative example of chloromethane preparation using boehmite includes the following steps:

[0079] S1: At 15℃, 1 mol of aluminum chloride hexahydrate, 0.05 mol of zirconium nitrate pentahydrate, and 0.03 mol of tetrabutyl titanate were added to 1.2 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 3:7). 0.2 mol of citric acid was added, followed by 1% nano-boehmite (by mass of aluminum chloride hexahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 7.5 with 8% ammonia. The temperature was raised to 25℃, and the mixture was stirred at 200 r / min for 30 min. The pH was then adjusted to 6.0 with 8% glacial acetic acid, and the mixture was stirred for another 30 min to obtain a homogeneous sol.

[0080] S2: Mix 0.8 mol of urea, 0.4 mol of ammonium bicarbonate and 1.2 L of deionized water until homogeneous to obtain mixture B;

[0081] S3: At a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 70℃ at 1℃ / min and held for 2 h. The temperature was then slowly increased to 140℃ at 1℃ / min and held for 4 h. The temperature was then increased to 170℃ and held for 3 h. After cooling to room temperature naturally, the mixture was filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0082] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​395 m². 2 / g; pore volume 1.43cm 3 / g, with a most probable pore size of 10.2nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 89.3%.

[0083] Comparative Example 4

[0084] The comparative example of chloromethane preparation using boehmite includes the following steps:

[0085] S1: At 15℃, 1 mol of aluminum chloride hexahydrate, 0.05 mol of zirconium nitrate pentahydrate, and 0.03 mol of tetrabutyl titanate were added to 1.2 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 3:7). 0.2 mol of citric acid was added, followed by 1% nano-boehmite (by mass of aluminum chloride hexahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 7.5 with 8% ammonia. The temperature was raised to 25℃, and the mixture was stirred at 200 r / min for 30 min. The pH was then adjusted to 6.0 with 8% glacial acetic acid, and the mixture was stirred for another 30 min to obtain a homogeneous sol.

[0086] S2: Mix 1.2 mol of ammonium bicarbonate and 1.2 L of deionized water evenly, then add 0.05 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0087] S3: At a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 70℃ at 1℃ / min and held for 2 h. The temperature was then slowly increased to 140℃ at 1℃ / min and held for 4 h. The temperature was then increased to 170℃ and held for 3 h. After cooling to room temperature naturally, the mixture was filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0088] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​311 m². 2 / g; pore volume 1.11cm 3 / g, with a most probable pore size of 14.5nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 82.3%.

[0089] Comparative Example 5

[0090] The comparative example of chloromethane preparation using boehmite includes the following steps:

[0091] S1: At 15℃, 1 mol of aluminum chloride hexahydrate, 0.05 mol of zirconium nitrate pentahydrate, and 0.03 mol of tetrabutyl titanate were added to 1.2 L of isopropanol aqueous solution (isopropanol and deionized water volume ratio 3:7). 0.2 mol of citric acid was added, followed by 1% nano-boehmite (by mass of aluminum chloride hexahydrate). The mixture was thoroughly mixed, and the pH was adjusted to 7.5 with 8% ammonia. The temperature was raised to 25℃, and the mixture was stirred at 200 r / min for 30 min. The pH was then adjusted to 6.0 with 8% glacial acetic acid, and the mixture was stirred for another 30 min to obtain a homogeneous sol.

[0092] S2: Mix 1.2 mol of urea and 1.2 L of deionized water evenly, then add 0.05 mol of ammonium zirconium carbonate and stir to mix evenly to obtain mixture B;

[0093] S3: At a stirring speed of 200 r / min, mixture B was slowly added dropwise to the homogeneous sol. After stirring for 30 min, the temperature was slowly increased to 70℃ at 1℃ / min and held for 2 h. The temperature was then slowly increased to 140℃ at 1℃ / min and held for 4 h. The temperature was then increased to 170℃ and held for 3 h. After cooling to room temperature naturally, the mixture was filtered, washed three times with 55℃ deionized water and once with anhydrous ethanol, and then freeze-dried at -30℃ for 12 h to obtain boehmite for chloromethane.

[0094] The performance test results of using pseudoboehmite for chloromethane are as follows: Na₂O content not exceeding 30 ppm; BET specific surface area of ​​382 m². 2 / g; pore volume 1.31cm 3 / g, with a most probable pore size of 13.0nm; after calcination at 600℃ for 4h, the specific surface area retention rate is 86.5%.

[0095] The performance test data from Examples 1 and Comparative Examples 1-5 show that, compared with Example 1, the absence of titanium or the absence of early zirconium both resulted in a simultaneous decrease in the specific surface area, pore volume, and thermal stability at 600℃ of the product. This indicates that the synergistic introduction of zirconium and titanium helps to improve the thermal stability of the pore structure. Meanwhile, the pore volume of Example 1 remained at a high level, indicating that the synergistic effect did not sacrifice the pore structure while ensuring excellent thermal stability.

[0096] The absence of ammonium zirconium carbonate significantly reduced thermal stability, indicating that it had a certain strengthening effect on the pore walls during the high-temperature crystallization stage. Although Comparative Example 4 had a larger pore diameter, its specific surface area, pore volume, and thermal stability were all poor, indicating that single low-temperature pore formation resulted in a fragile, irregular, and easily collapsed structure. Comparative Example 5 also performed worse than the examples, indicating that the lack of an initial pore template limited the effect of high-temperature pore expansion.

[0097] As can be seen from the performance test data of Examples 1-3, by gradually optimizing key process parameters such as aluminum salt type, complexing agent system, mixed solvent ratio and amount of nano-boehmite, the performance of the obtained pseudoboehmite for chloromethane all showed excellent and stable high levels.

[0098] As can be seen from the performance test data of Examples 3-5, after the aluminum isopropoxide alcohol phase post-treatment, the material achieves a significant improvement in thermal stability with a small loss in specific surface area and pore volume.

[0099] Combination Figures 1-3 The differential pore size distribution curves of chloromethane prepared using boehmite in Examples 1-2 and Example 4 all exhibit typical single-peak characteristics. The curves rise rapidly in the small pore size region and reach a clear peak in the mesoporous range of 9-11 nm, then decline gently without obvious tailing or secondary impurities. This characteristic clearly demonstrates that the product prepared by this application achieves highly concentrated and uniform development of its pore structure within a specific mesoporous range.

[0100] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing chloromethane using boehmite, characterized in that, Includes the following steps: S1: At 5~15℃, add sodium-free aluminum salt, zirconium nitrate pentahydrate, and tetrabutyl titanate to a mixed solvent, add a complexing agent, then add nano-boehmite, mix evenly, first adjust the pH to 7.5~8.0, raise the temperature to 25~35℃, mix for 30~40min, then adjust the pH to 5.5~6.0, mix for 30~40min to obtain a uniform sol; S2: Mix urea and ammonium bicarbonate and dissolve them in water, then add ammonium zirconium carbonate to obtain mixture B; S3: Add mixture B to the homogeneous sol, mix well, first heat to 70~80℃, keep at this temperature for 2~3h, continue to heat to 140~160℃, keep at this temperature for 4~5h, continue to heat to 170~180℃, keep at this temperature for 3~4h, then separate the solid and liquid, wash, dry, disperse in an anhydrous alcoholic solution of aluminum isopropoxide, heat to 50~60℃, add water, mix for 90~120min, separate the solid and liquid, wash again, dry, and obtain boehmite for chloromethane.

2. The method for preparing boehmite for chloromethane according to claim 1, characterized in that, The molar ratio of the complexing agent, sodium-free aluminum salt, zirconium nitrate pentahydrate, tetrabutyl titanate, urea, ammonium bicarbonate and ammonium zirconium carbonate is (0.2~0.3):1:(0.05~0.1):(0.03~0.07):(0.8~1.2):(0.4~0.7):(0.02~0.05).

3. The method for preparing boehmite for chloromethane according to claim 1, characterized in that, The amount of nanoboehmite used is 1% to 3% of the mass of sodium-free aluminum salt.

4. The method for preparing boehmite for chloromethane according to claim 1, characterized in that, The complexing agent is selected from at least one of citric acid and tartaric acid.

5. The method for preparing boehmite for chloromethane according to claim 1, characterized in that, The mixed solvent includes isopropanol and water.

6. The method for preparing boehmite for chloromethane according to claim 1, characterized in that, The amount of water used is 5% to 10% of the volume of the anhydrous alcohol solution.

7. The method for preparing boehmite for chloromethane according to claim 1, characterized in that, The mass concentration of aluminum isopropoxide is 1.5% to 2.5%.

8. The method for preparing pseudoboehmite for chloromethane according to claim 1, characterized in that, The anhydrous alcohol used in the anhydrous alcohol solution is isopropanol.

Images