A method for rapidly synthesizing single-layer MWW molecular sieves by adding organic amine cosolvents

Abstract

The invention discloses a method for rapidly synthesizing a single-layer MWW molecular sieve by adding an organic amine cosolvent, using silica sol as a silicon source, sodium metaaluminate as an aluminum source, hexamethyleneimine and dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride as structure-directing agents, and organic amines such as ethylenediamine and diethylamine as cosolvents, to synthesize the single-layer MWW molecular sieve by a one-step hydrothermal method. The synthesis method of the present invention is simple and easy, has a high yield of the synthesized product, and by adding organic amine cosolvents such as ethylenediamine and diethylamine, the nucleation rate is effectively accelerated, thereby greatly shortening the crystallization time, and obtaining a single-layer MWW molecular sieve with good crystallinity, which provides a possibility for application in industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieves and porous materials, and particularly relates to a method for rapidly synthesizing a single-layer MWW molecular sieve by adding an organic amine cosolvent. Background Art

[0002] MCM-22 is a layered molecular sieve with MWW topology. Due to its unique pore structure, it is widely used in catalytic cracking and alkylation reactions. In 1994, Leonowicz et al. conducted an in-depth study on the structure of MCM-22 and proposed the MWW cage {4 3 5 6 6 3 [4 3 ]} is its primary structural unit. Horizontally, oxygen bridges connect the MWW cages to form a monolayer of MCM-22, approximately 2.5 nm thick. Vertically, the monolayers are connected by intralayer ten-membered ring channels. MCM-22P, the precursor of MCM-22, has a two-dimensional layered structure consisting of orderly stacked MWW monolayers in the vertical direction. The interlayer forces are hydrogen bonds formed between Si-OH groups. Because hydrogen bonds are weak, they can be post-processed. For example, single-layer molecular sieves can be prepared by swelling MCM-22P followed by ultrasonic exfoliation.

[0003] ITQ-2 is a zeolite molecular sieve material with a single-layer structure. It was initially obtained by swelling MCM-22P with a cationic surfactant (CTAB) under alkaline conditions (TPAOH), followed by ultrasonic exfoliation. Compared to MCM-22, ITQ-2 has the advantages of a large external surface area, short diffusion paths, and easily accessible acidic sites, making it more conducive to reactions involving large molecules. However, the traditional preparation method is relatively cumbersome, involving three steps: synthesis of MCM-22P, swelling, and exfoliation. The rigorous swelling process (pH = 13.0-13.8, T = 80°C) can lead to partial amorphization of the molecular sieve. Therefore, the one-step hydrothermal synthesis of single-layer MWW molecular sieves has become a research hotspot.

[0004] Luo et al. (Chem. Sci. 2015, 6, 6320-6324) successfully synthesized a single-layer MWW nanosheet molecular sieve in one step using a self-designed novel bifunctional structure-directing agent (denoted as Ada-i-16) in 2015. Margarit et al. (Angew. Chem. Int. Ed. 2015, 54, 13724-13728) also used a self-designed structure-directing agent C 16The combined action of DC1 and HMI enabled the one-step synthesis of the MWW-type two-dimensional layered molecular sieve DS-ITQ-2. However, the aforementioned research suffers from the high cost and difficulty in obtaining custom-designed templates with specialized structures, making them unsuitable for industrial production. Chinese patent CN 110615446A reports the controlled synthesis of monolayer to oligolayer MWW nanosheet zeolites using a commonly used commercial long-chain amphoteric organosilane (TPOAC) as an auxiliary structure-directing agent. However, this method only achieved monolayer MWW zeolites after 14 days under low alkalinity conditions, and the long crystallization time makes it unsuitable for industrial application. Summary of the Invention

[0005] The present invention aims to provide a method for synthesizing a single-layer MWW molecular sieve in a short time by adding an organic amine cosolvent to a gel for synthesizing a single-layer MWW molecular sieve directed by a dual-template agent to accelerate the nucleation process.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention consists of the following steps:

[0007] Step 1: weighing raw materials sodium hydroxide, sodium metaaluminate, silica sol, hexamethyleneimine, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, deionized water, and organic amine cosolvent according to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.10-0.15, HMI / SiO2=0.25-0.35, TPOAC / SiO2=0.025-0.035, organic amine cosolvent / SiO2=0.1-0.8, and H2O / SiO2=45-52, wherein HMI is hexamethyleneimine, TPOAC is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and the organic amine cosolvent is any one or more of ethylenediamine, diethylamine, triethylamine, and mercaptoethylamine;

[0008] Step 2: Sodium hydroxide and sodium aluminate are dissolved in deionized water in sequence, and silica sol is gradually added dropwise under stirring, and stirred at room temperature for 20 to 30 minutes. Then, hexamethyleneimine, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and an organic amine cosolvent are added, and stirring is continued at room temperature for 1 to 2 hours;

[0009] Step 3: The mixed solution obtained in step 2 is transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and stirred and crystallized at 150°C under closed conditions for 3 to 6 days. After the reaction is completed, the hydrothermal reactor is taken out and quenched in cold water. The reaction solution is centrifuged and washed with water until neutral, and finally dried at 80 to 120°C.

[0010] Step 4: Grind the solid product dried in step 3 into powder, and then calcine it in a muffle furnace at 500-550° C. for 6 hours to obtain a single-layer MWW molecular sieve.

[0011] In the above step 1, the raw materials are preferably weighed according to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.15, HMI / SiO2=0.3, TPOAC / SiO2=0.035, organic amine cosolvent / SiO2=0.5, and H2O / SiO2=51.4.

[0012] In the above step 3, the crystallization is preferably carried out under closed conditions at 150° C. and 50-60 rpm with stirring for 4-5 days.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention uses silica sol as a silicon source, sodium metaaluminate as an aluminum source, hexamethyleneimine and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride as structure-directing agents, and organic amines such as ethylenediamine and diethylamine as cosolvents to synthesize a single-layer MWW molecular sieve using a one-step hydrothermal method. The preparation method is simple and easy, with a high yield of the synthesized product. Furthermore, the addition of organic amine cosolvents such as ethylenediamine and diethylamine effectively accelerates the nucleation rate, significantly shortening the crystallization time. This results in a single-layer MWW molecular sieve with excellent crystallinity, paving the way for its application in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 1 is the XRD pattern of MCM-22, Comparative Example 1 and MWW molecular sieve prepared in Example 1.

[0016] Figure 2 It is the N2- adsorption-desorption isotherm diagram of MCM-22 molecular sieve and the single-layer MWW molecular sieve prepared in Example 1.

[0017] Figure 3 This is a TEM image of the single-layer MWW molecular sieve prepared in Example 1.

[0018] Figure 4 1 is the XRD pattern of the single-layer MWW molecular sieve prepared in Examples 2 to 5. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and actual cases, but the protection scope of the present invention is not limited to these embodiments.

[0020] Example 1

[0021] 1. According to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.15, HMI / SiO2=0.3, TPOAC / SiO2=0.035, EDA / SiO2=0.5, H2O / SiO2=51.4, weigh 0.123g sodium hydroxide, 0.127g sodium metaaluminate, 2.325g silica sol, 0.469g HMI, 0.64g TPOAC, 0.465g EDA, and 12.54g deionized water.

[0022] 2. Dissolve 0.123 g of sodium hydroxide and 0.127 g of sodium metaaluminate in 12.54 g of deionized water in sequence. After complete dissolution, add 2.325 g of silica sol dropwise under stirring. Stir at room temperature for 30 minutes. Then, add 0.469 g of HMI, 0.64 g of TPOAC, and 0.465 g of EDA in sequence. Continue stirring at room temperature for 2 hours.

[0023] 3. The mixed solution obtained in step 2 was transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reactor was placed in a homogeneous reactor. The reaction was carried out at a speed of 60 rpm and 150°C for 114 hours. After the reaction was completed, the hydrothermal reactor was taken out and quenched in cold water. The reaction solution was centrifuged and washed with water until neutral. Finally, the sample was dried at 120°C for 12 hours.

[0024] 4. The solid product dried in step 3 was ground into powder and calcined in a muffle furnace at 550° C. for 6 hours to obtain a single-layer MWW molecular sieve with a yield of 95.5%.

[0025] Comparative Example 1

[0026] In Example 1, ethylenediamine was not added, and the other steps were the same as those in Example 1.

[0027] Depend on Figure 1 It can be seen that MCM-22 presents a clear (002) diffraction peak, and the (101) and (102) diffraction peaks between 2θ=8°~10° are obviously split, indicating that the MWW layer is highly ordered. The XRD spectrum of the sample in Comparative Example 1 clearly shows that the diffraction peak intensity is low, and the sample contains a large amount of amorphous material, indicating that when ethylenediamine is not added, the crystallization time is too short to form a single-layer MWW molecular sieve with good crystallinity. The XRD spectrum of the sample obtained in Example 1 has no (002) diffraction peak, and the (101) and (102) diffraction peaks merge into a broad peak, indicating that the organosilane is uniformly bonded to the MWW lamellae, causing the MWW lamellae to be disordered along the c-axis, and a single-layer MWW molecular sieve with good crystallinity is obtained in a short time. By Figure 2It can be seen that in the high pressure region, compared with MCM-22, the two isotherms of the single-layer MWW molecular sieve obtained in Example 1 do not overlap to form a hysteresis loop, which is a typical adsorption isotherm of mesoporous materials, indicating that mesopores exist in the crystallized product. Figure 3 It can be seen that the MWW molecular sieve prepared in Example 1 is a single-layer nanosheet.

[0028] Example 2

[0029] 1. According to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.15, HMI / SiO2=0.3, TPOAC / SiO2=0.035, EDA / SiO2=0.8, H2O / SiO2=51.4, weigh 0.123g sodium hydroxide, 0.127g sodium metaaluminate, 2.325g silica sol, 0.469g HMI, 0.64g TPOAC, 0.744g EDA, and 12.54g deionized water.

[0030] 2. Dissolve 0.123 g of sodium hydroxide and 0.127 g of sodium metaaluminate in 12.54 g of deionized water in sequence. After complete dissolution, add 2.325 g of silica sol dropwise under stirring. Stir at room temperature for 30 minutes. Then, add 0.469 g of HMI, 0.64 g of TPOAC, and 0.744 g of EDA in sequence. Continue stirring at room temperature for 2 hours.

[0031] 3. Transfer the mixed solution obtained in step 2 to a polytetrafluoroethylene-lined hydrothermal reactor, place the hydrothermal reactor in a homogeneous reactor, and react at a speed of 60 rpm and 150°C for 114 hours. After the reaction is completed, take out the hydrothermal reactor and quench it in cold water. The reaction solution is centrifuged and washed with water until neutral. Finally, the sample is dried at 120°C for 12 hours.

[0032] 4. Grind the solid product dried in step 3 into powder, place it in a muffle furnace and roast it at 550 ° C for 6 hours to obtain a single-layer MWW molecular sieve (see Figure 4 ), with a yield of 95.8%.

[0033] Example 3

[0034] 1. According to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.15, HMI / SiO2=0.3, TPOAC / SiO2=0.035, MEA / SiO2=0.2, H2O / SiO2=51.4, weigh 0.123g sodium hydroxide, 0.127g sodium metaaluminate, 2.325g silica sol, 0.469g HMI, 0.64g TPOAC, 0.238g MEA, and 12.54g deionized water.

[0035] 2. Dissolve 0.123 g of sodium hydroxide and 0.127 g of sodium metaaluminate in 12.54 g of deionized water in sequence. After complete dissolution, add 2.325 g of silica sol dropwise under stirring. Stir at room temperature for 30 minutes. Then, add 0.469 g of HMI, 0.64 g of TPOAC, and 0.238 g of MEA in sequence. Continue stirring at room temperature for 2 hours.

[0036] 3. The mixed solution obtained in step 2 was transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reactor was placed in a homogeneous reactor. The reaction was carried out at a speed of 60 rpm and 150°C for 5 days. After the reaction was completed, the hydrothermal reactor was taken out and quenched in cold water. The reaction solution was centrifuged and washed with water until neutral. Finally, the sample was dried at 120°C for 12 hours.

[0037] 4. Grind the solid product dried in step 3 into powder, place it in a muffle furnace and roast it at 550 ° C for 6 hours to obtain a single-layer MWW molecular sieve (see Figure 4 ), with a yield of 95.1%.

[0038] Example 4

[0039] 1. According to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.15, HMI / SiO2=0.3, TPOAC / SiO2=0.035, TEA / SiO2=0.5, H2O / SiO2=51.4, weigh 0.123g sodium hydroxide, 0.127g sodium metaaluminate, 2.325g silica sol, 0.469g HMI, 0.64g TPOAC, 0.78g TEA, and 12.54g deionized water.

[0040] 2. Dissolve 0.123 g of sodium hydroxide and 0.127 g of sodium metaaluminate in 12.54 g of deionized water in sequence. After complete dissolution, add 2.325 g of silica sol dropwise under stirring. Stir at room temperature for 30 minutes. Then, add 0.469 g of HMI, 0.64 g of TPOAC, and 0.78 g of TEA in sequence. Continue stirring at room temperature for 2 hours.

[0041] 3. The mixed solution obtained in step 2 was transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reactor was placed in a homogeneous reactor. The reaction was carried out at a speed of 60 rpm and 150°C for 114 hours. After the reaction was completed, the hydrothermal reactor was taken out and quenched in cold water. The reaction solution was centrifuged and washed with water until neutral. Finally, the sample was dried at 120°C for 12 hours.

[0042] 4. Grind the solid product dried in step 3 into powder, place it in a muffle furnace and roast it at 550 ° C for 6 hours to obtain a single-layer MWW molecular sieve (see Figure 4 ), with a yield of 95.4%.

[0043] Example 5

[0044] 1. According to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.15, HMI / SiO2=0.3, TPOAC / SiO2=0.03, DEA / SiO2=0.5, H2O / SiO2=45, weigh 0.123g sodium hydroxide, 0.127g sodium metaaluminate, 2.325g silica sol, 0.469g HMI, 0.54g TPOAC, 0.566g DEA, and 10.8g deionized water.

[0045] 2. Dissolve 0.123 g of sodium hydroxide and 0.127 g of sodium metaaluminate in 10.8 g of deionized water in sequence. After complete dissolution, add 2.325 g of silica sol dropwise under stirring. Stir at room temperature for 30 minutes. Then, add 0.469 g of HMI, 0.54 g of TPOAC, and 0.566 g of DEA in sequence. Continue stirring at room temperature for 2 hours.

[0046] 3. The mixed solution obtained in step 2 was transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reactor was placed in a homogeneous reactor. The reaction was carried out at a speed of 60 rpm and 150°C for 6 days. After the reaction was completed, the hydrothermal reactor was taken out and quenched in cold water. The reaction solution was centrifuged and washed with water until neutral. Finally, the sample was dried at 120°C for 12 hours.

[0047] 4. Grind the solid product dried in step 3 into powder, place it in a muffle furnace and roast it at 550 ° C for 6 hours to obtain a single-layer MWW molecular sieve (see Figure 4 ), with a yield of 94.6%.

Claims

1. A method for rapidly synthesizing a single-layer MWW molecular sieve by adding an organic amine cosolvent, characterized in that The method consists of the following steps: Step 1: weighing raw materials sodium hydroxide, sodium metaaluminate, silica sol, hexamethyleneimine, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, deionized water, and organic amine cosolvent according to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.10-0.15, HMI / SiO2=0.25-0.35, TPOAC / SiO2=0.025-0.035, organic amine cosolvent / SiO2=0.1-0.8, and H2O / SiO2=45-52, wherein HMI is hexamethyleneimine, TPOAC is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, and the organic amine cosolvent is any one or more of ethylenediamine, diethylamine, triethylamine, and mercaptoethylamine; Step 2: Sodium hydroxide and sodium aluminate are dissolved in deionized water in sequence, and silica sol is gradually added dropwise under stirring, and stirred at room temperature for 20 to 30 minutes. Then, hexamethyleneimine, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride and an organic amine cosolvent are added, and stirring is continued at room temperature for 1 to 2 hours; Step 3: The mixed solution obtained in step 2 is transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and stirred and crystallized at 150°C under closed conditions for 3 to 6 days. After the reaction is completed, the hydrothermal reactor is taken out and quenched in cold water. The reaction solution is centrifuged and washed with water until neutral, and finally dried at 80 to 120°C. Step 4: Grind the solid product dried in step 3 into powder, and then calcine it in a muffle furnace at 500-550° C. for 6 hours to obtain a single-layer MWW molecular sieve.

2. The method for rapidly synthesizing a single-layer MWW molecular sieve by adding an organic amine cosolvent according to claim 1, characterized in that: In step 1, the raw materials are weighed according to the molar ratio of SiO2 / Al2O3=30, NaOH / SiO2=0.15, HMI / SiO2=0.3, TPOAC / SiO2=0.035, organic amine cosolvent / SiO2=0.5, and H2O / SiO2=51.

4.

3. The method for rapidly synthesizing a single-layer MWW molecular sieve by adding an organic amine cosolvent according to claim 1, characterized in that: In step 3, crystallization is carried out under closed conditions at 150° C. and 50 to 60 rpm with stirring for 4 to 5 days.

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