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 methyl chloride. The preparation method of the pseudo-boehmite for methyl chloride comprises the following steps: adding an aluminum ion slow-release agent into a sodium metaaluminate solution at 45-60 DEG C, dynamically adjusting the speed of the aluminum ion slow-release agent to maintain the pH of the system at 7.5-8.5, reacting for 50-120 min, performing solid-liquid separation, and then sequentially performing aging, solid-liquid separation, washing and drying to obtain the pseudo-boehmite; and the aluminum ion slow-release agent is at least one of an aluminum-organic acid complex solution and a resin loaded with aluminum ions. The preparation method effectively improves the uniformity of the pore diameter and the specific surface area of the pseudo-boehmite.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic porous materials, more particularly, it relates to a preparation method of pseudo-boehmite for methyl chloride. BACKGROUND

[0002] At present, the industrial production of methyl chloride at home and abroad mainly adopts three processes: homogeneous gas phase reaction method, gas-solid catalytic reaction method and gas-liquid phase reaction method. Although the gas-liquid phase method has the inherent defect of limited production capacity, its high selectivity characteristics exactly meet the stringent requirements of silicone monomer production on the quality of raw material methyl chloride. In the gas-liquid phase reaction method, the correlation between the structure and performance of the catalyst constitutes the core proposition of process optimization. As a key precursor of γ-Al2O3 catalyst, the microstructure of pseudo-boehmite (such as grain size, pore size distribution, surface hydroxyl content, etc.) directly affects the acid site distribution, specific surface area and pore characteristics of the alumina obtained by subsequent calcination, and then determines the mass transfer efficiency and activity stability of the catalyst in the gas-liquid interface reaction.

[0003] The preparation methods of pseudo-boehmite mainly include organic aluminum alcohol method and inorganic aluminum method, and the inorganic aluminum method can be further divided into alkali method and acid method. Since the organic aluminum alcohol method relies on toxic organic solvents and has high cost, most domestic enterprises adopt the inorganic aluminum method. In the inorganic aluminum method, the core problems of the prepared pseudo-boehmite are insufficient crystal purity, out-of-control pore structure and residual impurities, which directly restrict the activity, selectivity and life of the methyl chloride catalyst.

[0004] The patent application file with publication number CN119240761A discloses a preparation method of pseudo-boehmite, which comprises: neutralizing sodium metaaluminate and acid aluminum salt to generate amorphous precipitate, obtaining a first slurry; filtering the first slurry, and then beating the filter cake obtained by the filtering to obtain a second slurry; adjusting the pH value of the second slurry to a preset pH value by using an alkaline additive, so that the second slurry is aged to obtain pseudo-boehmite; and the preset pH value is 7.5-10.0.

[0005] In this technology, when sodium metaaluminate and acid aluminum salt are directly neutralized, the reaction rate is much higher than the mass transfer rate, resulting in the formation of local over-acid / over-base microzones: in the over-acid zone, Al 3+ diffusion lag, forming low-hydrolysis hydrated ion clusters, and in the over-base zone, AlO2 - enrichment, rapidly generating boehmite crystal nuclei, ultimately causing a multiphase nucleation system coexisting amorphous phase (over-acid zone) and crystal phase (over-base zone), thereby causing uneven grain size distribution and pore size widening, ultimately leading to the decrease of the specific surface area of pseudo-boehmite and the deterioration of the pore volume. SUMMARY

[0006] In order to improve the specific surface area and pore volume of pseudo-boehmite, the application provides a preparation method of pseudo-boehmite for methyl chloride.

[0007] The application provides a preparation method of pseudo-boehmite for methyl chloride, which adopts the following technical scheme:

[0008] The preparation method of pseudo-boehmite for methyl chloride comprises the following steps:

[0009] At 45-60 DEG C, the aluminum ion slow-release agent is added into the sodium metaaluminate solution, the pH of the system is maintained at 7.5-8.5 by dynamically adjusting the speed of the aluminum ion slow-release agent, and the reaction is carried out for 50-120 min, and then the aging, solid-liquid separation, washing and drying are sequentially carried out, and the pseudo-boehmite is obtained.

[0010] The aluminum ion slow-release agent is at least one of an aluminum-organic acid complex solution and a resin loaded with aluminum ions.

[0011] In the scheme, the neutralization reaction between aluminum ions and metaaluminate is always in a metastable supersaturation state by dynamically adjusting the speed of the aluminum ion slow-release agent, and the pH fluctuation is small, so that the Al 3+ cluster or rapid precipitation caused by excessive alkali is fundamentally avoided. The uniform reaction environment makes the generation rate of crystal nucleus and the growth rate of crystal grain reach a dynamic balance, promotes the ordered generation and growth of pseudo-boehmite crystal nucleus, forms a mesoporous network with concentrated pore size distribution and uniform structure, and after aging and other treatments, the structure is further optimized into a hierarchical pore system, and the specific surface area and pore volume are significantly improved.

[0012] Preferably, the molar ratio of the sodium metaaluminate to the aluminum ions in the aluminum ion slow-release agent is 1: (0.8-1.2).

[0013] Preferably, the fluctuation range of the pH is not more than ±0.05.

[0014] Preferably, the aluminum-organic acid complex solution is prepared by the following steps:

[0015] After the acidic aluminum salt solution is uniformly mixed with the organic acid, the pH is adjusted to 4.0-4.5, and the mixture is mixed for 2.5-3.5 h, and the aluminum-organic acid complex solution is obtained.

[0016] Preferably, the molar ratio of the aluminum ions to the organic acid in the acidic aluminum salt solution is 1:1.1-1:1.3.

[0017] Preferably, the organic acid is citric acid.

[0018] In the scheme, the acidic aluminum salt and citric acid form an aluminum-organic acid complex at pH 4.0-4.5, effectively inhibiting the hydrolysis of aluminum ions, so that the aluminum ions are dissociated at a controllable rate to match the hydrolysis rate of metaborate in the subsequent reaction, avoiding the formation of amorphous colloids caused by local over-concentration, thereby obtaining a mesoporous network with concentrated pore size distribution.

[0019] Preferably, the aluminum ion-loaded resin is prepared by the following steps:

[0020] The acidic aluminum salt solution is added to the reactor, and after adjusting the pH to 2.5-3.0, the strongly acidic cation exchange resin is added and mixed uniformly, heated to 55-65℃, adsorbed for 6-10h, solid-liquid separation, washed to pH 3.5-4.0, and dried to obtain.

[0021] Preferably, the molar ratio of aluminum ions in the acidic aluminum salt solution to the cation exchange groups in the strongly acidic cation exchange resin is 1:(1.2-1.4).

[0022] Preferably, the cation exchange group density of the strongly acidic cation exchange resin is not less than 4.5mmol / g.

[0023] In the scheme, the acidic aluminum salt solution is first adjusted to pH 2.5-3.0, and then exchanged with the strongly acidic cation exchange resin to help the dissociation of the cation exchange groups in the strongly acidic cation exchange resin, load aluminum ions through ion exchange, and heat to 55-65℃ to improve the ion diffusion rate. Wash to pH 3.5-4.0, the resin retains part of the protonated sites, and when mixed with sodium metaborate solution, release aluminum ions according to the pH response, thereby controlling the grain size distribution and improving the crush strength.

[0024] Preferably, when the aluminum ion slow-release agent is a complex system of aluminum-organic acid complex solution and aluminum ion-loaded resin, it is added in stages: first add the aluminum-organic acid complex solution, then add the aluminum ion-loaded resin.

[0025] In the scheme, the aluminum-organic acid complex is used to quickly dissociate to provide aluminum ions, promote the formation of high-density primary crystal nuclei in the system, and construct the initial mesoporous structure; then the slow-release mechanism of the resin microspheres is used to control the sustained and stable release of aluminum ions, guide the ordered growth and agglomeration of crystal nuclei to form secondary mesopores, so that the pseudoboehmite exhibits uniform and concentrated multi-level mesoporous distribution characteristics, effectively improving the specific surface area and pore volume of the subsequent pseudoboehmite.

[0026] Preferably, the molar ratio of aluminum ions in the aluminum-organic acid complex solution to aluminum ions in the aluminum ion-loaded resin is (60%-70%):(30%-40%).

[0027] Preferably, the aging step is aging at 80-100℃ for 2-4h, then cooling to 60-80℃, and hydrothermal treatment for 40-60min.

[0028] Preferably, the acidic aluminum salt solution is at least one selected from aluminum sulfate solution, aluminum nitrate solution or aluminum chloride solution.

[0029] In summary, the present application has the following beneficial effects:

[0030] 1. The present application adopts aluminum-organic acid complex solution, controls slow release of aluminum ions through dynamic coordination, suppresses violent boiling nucleation and agglomeration, forms uniform mesoporous structure, improves specific surface area and pore volume, and the residual organic acid is decomposed into CO2 and H2O in the subsequent calcination process, forms through pores at the same time, and the residual group can control the distribution of surface acid sites, providing a chemical environment basis for the subsequent loading of catalytically active sites.

[0031] 2. The present application preferably adopts resin loaded with aluminum ions, loads aluminum source through ion exchange, relies on the spatial confinement effect of resin pores to realize slow release of aluminum ions, and forms a phased synergistic mechanism with the rapid dissociation of aluminum-organic acid complex: the complex provides high-density crystal nuclei in the early stage, and the resin slowly releases aluminum ions in the later stage to guide the ordered growth of crystal grains along the template pore wall, suppresses the formation of large pores, and forms uniform mesopores. DETAILED DESCRIPTION

[0032] The present application is further described below in conjunction with examples.

[0033] The raw materials of the examples and comparative examples of the present application are all ordinary commercial products unless otherwise specified.

[0034] In the following examples and comparative examples:

[0035] The strong acid cation exchange resin is D001 type, and the exchange capacity is ≥4.5mmol / g, wherein the particle size distribution between 0.315-0.6mm accounts for about 95%;

[0036] During the maintenance of the pH of the reaction system, according to the pH monitoring results, 0.5mol / L ammonia water was added dropwise to assist the adjustment; the aluminum-citric acid complex solution or the resin microspheres loaded with aluminum ions was used as the main agent, and the ammonia water was only used for auxiliary adjustment in response to accidental pH fluctuations.

[0037] Example 1

[0038] The preparation method of pseudoboehmite for methyl chloride in the example comprises the following steps:

[0039] S1: In a constant temperature water bath at 30℃, 400 mL of aluminum nitrate solution with a concentration of 1.25 mol / L was mixed uniformly with 0.6 mol of citric acid, 0.5 mol / L of ammonia water was used to adjust the pH to about 4.0, and the mixture was stirred for 3 h to obtain an aluminum-citric acid complex solution;

[0040] S2: 500 mL of sodium metaaluminate solution with a concentration of 1 mol / L was injected into the reaction kettle, preheated to 50℃, the aluminum-citric acid complex solution was pumped in at an initial flow rate of 5 mL / min by a peristaltic pump, and the addition rate of the aluminum-citric acid complex solution was dynamically adjusted (range 5-12 mL / min) by real-time monitoring by an online pH sensor (accuracy ±0.01) to maintain the pH of the reaction system at 8.0±0.03, the temperature was kept at 50℃, and the reaction was carried out for 60 min to obtain a slurry;

[0041] The slurry was transferred to an aging kettle, heated to 90℃ at a rate of 5℃ / min, stirred at a rate of 300 rpm for aging for 3 h, then transferred to a hydrothermal reaction kettle, cooled to 70℃, hydrothermally treated for 50 min, cooled to room temperature, vacuum filtered, the filter cake was washed with deionized water until the conductivity of the washing liquid was <50 μS / cm, and then transferred to a blast drying oven, dried at 110℃ until the weight was constant.

[0042] Example 2

[0043] The preparation method of the pseudoboehmite for chloromethane in this example comprises the following steps:

[0044] S1: In a constant temperature water bath at 25℃, 400 mL of aluminum sulfate solution with a concentration of 0.625 mol / L was mixed uniformly with 0.55 mol of citric acid, 0.5 mol / L of ammonia water was used to adjust the pH to about 4.5, and the mixture was stirred for 3.5 h to obtain an aluminum-citric acid complex solution;

[0045] S2: 600 mL of sodium metaaluminate solution with a concentration of 1 mol / L was injected into the reaction kettle, preheated to 60℃, the aluminum-citric acid complex solution was pumped in at an initial flow rate of 5 mL / min by a peristaltic pump, and the addition rate of the aluminum-citric acid complex solution was dynamically adjusted (range 5-12 mL / min) by real-time monitoring by an online pH sensor (accuracy ±0.01) to maintain the pH of the reaction system at 8.5±0.05, the temperature was kept at 60℃, and the reaction was carried out for 50 min to obtain a slurry;

[0046] The slurry was transferred to an aging kettle, heated to 80℃ at a rate of 5℃ / min, stirred at a rate of 300 rpm for aging for 4 h, then transferred to a hydrothermal reaction kettle, cooled to 60℃, hydrothermally treated for 60 min, cooled to room temperature, vacuum filtered, the filter cake was washed with deionized water until the conductivity of the washing liquid was <50 μS / cm, and then transferred to a blast drying oven, dried at 110℃ until the weight was constant.

[0047] Example 3

[0048] The preparation method of pseudoboehmite for chloromethane in this example comprises the following steps:

[0049] S1: In a constant temperature water bath at 25℃, mix 500mL of aluminum chloride solution with a concentration of 1.25mol / L with 0.81mol of citric acid uniformly, adjust the pH to about 4.0 with 0.5mol / L of ammonia water, and stir and mix for 2.5h to obtain an aluminum-citric acid complex solution;

[0050] S2: Inject 500mL of sodium metaaluminate solution with a concentration of 1mol / L into the reaction kettle, preheat to 45℃, pump the aluminum-citric acid complex solution into the reaction kettle at an initial flow rate of 5mL / min through a peristaltic pump, and monitor in real time through an online pH sensor (accuracy ±0.01) to dynamically adjust the addition rate of the aluminum-citric acid complex solution (range 5~12mL / min) and maintain the pH of the reaction system at 7.8±0.05, constant temperature 45℃, reaction for 90min to obtain a slurry;

[0051] Transfer the slurry to an aging kettle, heat to 100℃ at a rate of 5℃ / min, stir at a rate of 300rpm for 2h, then transfer to a hydrothermal reaction kettle, cool to 80℃, hydrothermal treatment for 40min, cool to room temperature, vacuum filtration, wash the filter cake with deionized water until the conductivity of the washing liquid is <50μS / cm, and then transfer to a forced air drying oven, dry at 110℃ until the weight is constant.

[0052] Example 4

[0053] The preparation method of pseudoboehmite for chloromethane in this example comprises the following steps:

[0054] S1: Add 450mL of aluminum nitrate solution with a concentration of 0.5mol / L into the reactor, adjust the pH to 3.0 with 0.1mol / L of nitric acid solution, add 70g of strongly acidic cation exchange resin, heat to 65℃, oscillate for 6h for adsorption, after filtration, wash with deionized water until the pH is 4.0, and vacuum dry at 60℃ until the weight is constant to obtain aluminum ion loaded resin microspheres;

[0055] S2: Inject 225mL of sodium metaaluminate solution with a concentration of 1mol / L into the reaction kettle, preheat to 60℃, initially add the aluminum ion loaded resin microspheres at a rate of 0.8g / min, continuously stir at a rate of 200rpm, monitor in real time through an online pH sensor (accuracy ±0.01) to dynamically adjust the addition rate of the aluminum ion loaded resin microspheres (range 0.8~1.5g / min), maintain the pH of the reaction system at 7.5±0.05, and react for 120min to filter out the resin microspheres to obtain a slurry.

[0056] Wherein, after the complete addition of the aluminum ion loaded resin microspheres, 0.5 mol / L ammonia water is used as an auxiliary condition, the maximum pH is not more than 8.0, the fluctuation range is controlled within ±0.05, and the reaction is completed until the pH is stable;

[0057] The slurry is transferred into an aging kettle, and is heated to 90℃ at a rate of 5℃ / min, and is stirred at a rate of 300 rpm for 3h, and then is transferred into a hydrothermal reaction kettle, and is cooled to 70℃, and is hydrothermally treated for 50 min, and is cooled to room temperature, and is vacuum filtered, and the filter cake is washed with deionized water until the conductivity of the washing liquid is less than 50 μS / cm, and is transferred into a blast drying oven, and is dried at 110℃ until the weight is constant, and is obtained.

[0058] Example 5

[0059] The difference between this example and Example 4 is that:

[0060] Step S1: 450 mL of 0.5 mol / L aluminum nitrate solution is added into the reactor, and 0.1 mol / L nitric acid solution is used to adjust the pH to 2.5, 60 g of strong acid cation exchange resin is added, and the temperature is increased to 55℃, and is oscillated for adsorption for 10h, and after filtration, deionized water is used for washing until the pH is 3.5, and is vacuum dried at 60℃ until the weight is constant, and the aluminum ion loaded resin microspheres are obtained;

[0061] The others are the same as Example 4.

[0062] Example 6

[0063] The preparation method of the chloromethane using the pseudo-boehmite in this example comprises the following steps:

[0064] S1: 280 mL of 1.25 mol / L aluminum nitrate solution is mixed with 0.42 mol of citric acid uniformly in a constant temperature water bath at 30℃, 0.5 mol / L ammonia water is used to adjust the pH to about 4.0, and the mixture is stirred for 3h to obtain an aluminum-citric acid complex solution;

[0065] S2: 300 mL of 0.5 mol / L aluminum nitrate solution is added into the reactor, and 0.1 mol / L nitric acid solution is used to adjust the pH to 2.5, 45 g of strong acid cation exchange resin is added, the temperature is increased to 60℃, and is oscillated for adsorption for 8h, and after filtration, deionized water is used for washing until the pH is 3.5, and is vacuum dried at 60℃ until the weight is constant, and the aluminum ion loaded resin microspheres are obtained;

[0066] S3: 500 mL of sodium metaaluminate solution with a concentration of 1 mol / L was injected into the reactor, preheated to 55℃, and the aluminum-citric acid complex solution was pumped in at an initial flow rate of 5 mL / min by using a peristaltic pump, and the addition rate of the aluminum-citric acid complex solution was dynamically adjusted (range 5-12 mL / min) by monitoring in real time through an online pH sensor (accuracy ±0.01) to maintain the pH of the reaction system at 8.0±0.03. After 50 min of reaction, at the end of the reaction, i.e. when the aluminum-citric acid complex solution was completely pumped in for about 5 min, the aluminum ion-loaded resin microspheres were simultaneously introduced at an initial rate of 0.2 g / min to increase the pH of the system to 8.2±0.03. After the aluminum-citric acid complex solution was completely pumped in, the aluminum ion-loaded resin microspheres were introduced at a rate of 0.8 g / min, and the addition rate of the aluminum ion-loaded resin microspheres was dynamically adjusted (range 0.8-1.5 g / min) to maintain the pH of the reaction system at 8.5±0.05. The reaction was carried out for 70 min, and the resin microspheres were filtered out to obtain a slurry;

[0067] After the aluminum ion-loaded resin microspheres were completely added, 0.5 mol / L of ammonia water was used as an auxiliary condition, and the fluctuation range was controlled at ±0.05 until the reaction was completed.

[0068] The slurry was transferred to an aging kettle, heated to 90℃ at a rate of 5℃ / min, and stirred at a rate of 300 rpm for 3 h. Then it was transferred into a hydrothermal reaction kettle, cooled to 70℃, and hydrothermally treated for 50 min. After cooling to room temperature, vacuum filtration was performed, and the filter cake was washed with deionized water until the conductivity of the washing liquid was <50 μS / cm. Then it was transferred into a blast drying oven and dried at 110℃ until the weight was constant.

[0069] Example 7

[0070] The preparation method of the pseudoboehmite for chloromethane in this example comprises the following steps:

[0071] S1: In a constant temperature water bath at 30℃, 240 mL of aluminum nitrate solution with a concentration of 1.25 mol / L was uniformly mixed with 0.36 mol of citric acid. The pH was adjusted to about 4.0 by using 0.5 mol / L of ammonia water, and the mixture was stirred for 3 h to obtain an aluminum-citric acid complex solution.

[0072] S2: 400 mL of aluminum nitrate solution with a concentration of 0.5 mol / L was added to the reactor, and the pH was adjusted to 2.5 by using 0.1 mol / L of nitric acid solution. 55 g of strong acid cation exchange resin was added, and the temperature was increased to 60℃. The adsorption was performed by oscillation for 8 h. After filtration, the filter cake was washed with deionized water until the pH was 3.5. The aluminum ion-loaded resin microspheres were dried at 60℃ under vacuum until the weight was constant.

[0073] S3: 500 mL of sodium metaaluminate solution with a concentration of 1 mol / L was injected into the reactor, preheated to 55℃, and the aluminum-citric acid complex solution was pumped in at an initial flow rate of 5 mL / min by a peristaltic pump, and the addition rate of the aluminum-citric acid complex solution was dynamically adjusted (range 5-12 mL / min) by real-time monitoring by an online pH sensor (accuracy ±0.01) to maintain the pH of the reaction system at 8.0±0.03, and after 50 min of reaction, the pH of the system was increased to 8.2±0.03 by simultaneously adding the aluminum ion-loaded resin microspheres at an initial rate of 0.2 g / min at the end of the reaction, i.e., when the aluminum-citric acid complex solution was completely pumped in for about 5 min, and the addition rate of the aluminum ion-loaded resin microspheres was dynamically adjusted (range 0.8-1.5 g / min) at a rate of 0.8 g / min after the aluminum-citric acid complex solution was completely pumped in to maintain the pH of the reaction system at 8.5±0.05, and the reaction was carried out for 70 min, and the resin microspheres were filtered out to obtain a slurry;

[0074] After the aluminum ion-loaded resin microspheres were completely added, 0.5 mol / L of ammonia water was used as an auxiliary condition, and the fluctuation range was controlled at ±0.05 until the reaction was completed;

[0075] The slurry was transferred to an aging kettle, heated to 90℃ at a rate of 5℃ / min, and stirred at a rate of 300 rpm for 3 h, then transferred to a hydrothermal reaction kettle, cooled to 70℃, and hydrothermally treated for 50 min, cooled to room temperature, vacuum filtered, and the filter cake was washed with deionized water until the conductivity of the washing liquid was <50 μS / cm, then transferred to a blast drying oven, and dried at 110℃ until the weight was constant.

[0076] Example 8

[0077] The difference between this example and Example 7 is:

[0078] Step S3: 500 mL of sodium metaaluminate solution with a concentration of 1 mol / L was injected into the reactor, preheated to 55℃, and the aluminum-citric acid complex solution was pumped in at an initial flow rate of 5 mL / min by a peristaltic pump, and the addition rate of the aluminum-citric acid complex solution was dynamically adjusted (range 5-12 mL / min) by real-time monitoring by an online pH sensor (accuracy ±0.01) to maintain the pH of the reaction system at 8.0±0.05, and after 50 min of reaction, the resin microspheres were filtered out to obtain a slurry;

[0079] The slurry was transferred to an aging kettle, heated to 90°C at a rate of 5°C / min, and stirred at a rate of 300 rpm for 3 h, then transferred to a hydrothermal reaction kettle, cooled to 70°C, and hydrothermally treated for 50 min. After cooling to room temperature, the slurry was vacuum filtered, the filter cake was washed with deionized water until the conductivity of the wash water was < 50 μS / cm, and the filter cake was transferred to a forced air drying oven and dried at 110°C until the weight was constant.

[0080] Example 7.

[0081] Comparative Example 1

[0082] The preparation method of chloromethane using pseudo-boehmite in the present comparative example included the following steps:

[0083] A 500 mL sodium metaaluminate solution having a concentration of 1 mol / L was injected into a reaction kettle, preheated to 50°C, and 400 mL of an aluminum nitrate solution having a concentration of 1.25 mol / L was added at one time. The temperature was maintained at 50°C, and the reaction was carried out for 60 min to obtain a slurry.

[0084] The slurry was transferred to an aging kettle, heated to 90°C at a rate of 5°C / min, and stirred at a rate of 300 rpm for 3 h, then transferred to a hydrothermal reaction kettle, cooled to 70°C, and hydrothermally treated for 50 min. After cooling to room temperature, the slurry was vacuum filtered, the filter cake was washed with deionized water until the conductivity of the wash water was < 50 μS / cm, and the filter cake was transferred to a forced air drying oven and dried at 110°C until the weight was constant.

[0085] Comparative Example 2

[0086] The preparation method of chloromethane using pseudo-boehmite in the present comparative example included the following steps:

[0087] S1: In a constant temperature water bath at 30°C, 400 mL of an aluminum nitrate solution having a concentration of 1.25 mol / L was mixed with 0.65 mol of citric acid, and the pH was adjusted to about 4.0 using 0.5 mol / L of ammonia water. The mixture was stirred for 3 h to obtain an aluminum-citric acid complex solution.

[0088] S2: A 500 mL sodium metaaluminate solution having a concentration of 1 mol / L was injected into a reaction kettle, preheated to 50°C, and the aluminum-citric acid complex solution was pumped into the reaction kettle at a constant flow rate of 8.0 mL / min using a peristaltic pump. The temperature was maintained at 50°C, and the reaction was carried out for 60 min to obtain a slurry.

[0089] The slurry was transferred to an aging kettle, heated to 90°C at a rate of 5°C / min, and stirred at a rate of 300 rpm for 3 h, then transferred to a hydrothermal reaction kettle, cooled to 70°C, and hydrothermally treated for 50 min. After cooling to room temperature, the slurry was vacuum filtered, the filter cake was washed with deionized water until the conductivity of the wash water was < 50 μS / cm, and the filter cake was transferred to a forced air drying oven and dried at 110°C until the weight was constant.

[0090] Performance test

[0091] The pseudoboehmite prepared in Examples 1-7 and Comparative Examples 1-2 was taken respectively, pre-sintered in a sintering furnace at 550℃±10℃ for 2h, and cooled to room temperature with the furnace. The performance was detected by referring to YS / T1161.3-2016 Pseudoboehmite Analysis Method Part 3: Determination of Pore Volume and Specific Surface Area by Nitrogen Adsorption Method. The detection results are shown in Table 1.

[0092] Table 1 Performance detection data of the pseudoboehmite prepared in Examples 1-7 and Comparative Examples 1-2

[0093]

[0094] By analyzing the performance detection data in Table 1:

[0095] In Examples 1-3, the aluminum-citric acid complex system was used to dynamically control the release rate of aluminum ions and the alkaline environment, which effectively inhibited the violent boiling nucleation and promoted the uniform growth of crystal grains, forming relatively uniform mesoporous structures and inhibiting the generation of large pores. In Comparative Examples 1-2, direct mixing or constant flow rate resulted in large pH fluctuations or instantaneous precipitation, and the crystal grains were easily aggregated to form micron-sized particles, with a high proportion of large pore diameters, and the specific surface area and pore volume were significantly deteriorated.

[0096] In Examples 4-5, the resin microspheres loaded with aluminum ions were used, and the release speed of aluminum ions was slightly slower, and the initial aluminum ion concentration was lower, resulting in slightly lower nucleation and growth synergy efficiency, and slightly lower mesoporous uniformity. However, during the slow release of aluminum ions, the limited crystal nuclei gradually aggregated due to the ample growth space, forming relatively uniform particles, so the average pore diameter remained in a relatively stable range. However, the lack of nucleation led to a decrease in mesoporous packing structure, and the specific surface area and pore volume decreased.

[0097] In Examples 6-7, the aluminum-citric acid complex and the resin microspheres loaded with aluminum ions were used in a phased synergistic manner. The aluminum-citric acid complex released aluminum ions relatively quickly in the early stage, forming a high-density nanoscale primary crystal nucleus, and then the resin microspheres slowly released aluminum ions, guiding the ordered growth of crystal grains, avoiding local supersaturation, and inhibiting the disorderly growth of crystal nuclei into large particles, allowing small crystal nuclei to dissolve and deposit orderly on the surface of large crystal nuclei, forming mesoporous cascade growth. In Example 8, the resin microspheres loaded with aluminum ions were added first, and the release of aluminum ions was limited by the exchange kinetics of the resin in the early stage, resulting in a relatively low initial aluminum ion concentration, which led to a small number of nucleation and easy formation of large-size primary particles, which destroyed the small pore structure and increased the number of large pores, resulting in a decrease in specific surface area.

[0098] The embodiments are only illustrative of the present application, and are not intended to limit the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing chloromethane using boehmite, characterized in that, Includes the following steps: At 45~60℃, aluminum ion slow-release agent is added to sodium aluminate solution. The pH of the system is maintained at 7.5~8.5 by dynamically adjusting the rate of aluminum ion slow-release agent. The reaction is carried out for 50~120 min, followed by solid-liquid separation. Then, aging, solid-liquid separation, washing and drying are performed in sequence to obtain the product. The aluminum ion slow-release agent is a compound system of aluminum-organic acid complex solution and aluminum ion-loaded resin, and is added in stages: first the aluminum-organic acid complex solution is added, and then the aluminum ion-loaded resin is added. The organic acid is citric acid; The molar ratio of sodium aluminate to aluminum ions in the aluminum ion slow-release agent is 1:(0.8~1.2). The molar ratio of aluminum ions in the aluminum-organic acid complex solution to aluminum ions in the aluminum-loaded resin is (60%~70%):(30%~40%). The aging process is as follows: aging at 80~100℃ for 2~4 hours, then cooling to 60~80℃ and hydrothermal treatment for 40~60 minutes.

2. The method for preparing pseudoboehmite for chloromethane according to claim 1, characterized in that, The aluminum-organic acid complex solution is prepared by the following steps: After mixing the acidic aluminum salt solution with the organic acid evenly, adjust the pH to 4.0~4.5 and mix for 2.5~3.5 hours to obtain the final product.

3. A method for preparing pseudoboehmite for chloromethane according to claim 2, characterized in that, The molar ratio of aluminum ions to organic acids in the acidic aluminum salt solution is 1:1.1 to 1:1.

3.

4. A method for preparing pseudoboehmite for chloromethane according to claim 1, characterized in that, The aluminum ion-loaded resin is prepared by the following steps: Add an acidic aluminum salt solution to the reactor, adjust the pH to 2.5-3.0, add a strong acidic cation exchange resin and mix thoroughly. Heat to 55-65℃ and adsorb for 6-10 hours. Separate the solid and liquid, wash until the pH is 3.5-4.0, and dry to obtain the final product.

5. A method for preparing pseudoboehmite for chloromethane according to claim 4, characterized in that, The molar ratio of aluminum ions in the acidic aluminum salt solution to cation exchange groups in the strongly acidic cation exchange resin is 1:(1.2~1.4).

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