A method for synthesizing pure silicon MWW molecular sieves and its application

Abstract

This invention discloses a method for synthesizing pure silicon MWW molecular sieves using a steam crystallization method, and further synthesizing titanium-containing MWW molecular sieves from the obtained pure silicon MWW molecular sieves. The method includes the following steps: (1) mixing a silicon source, seed crystals, an organic template agent, and water uniformly; (2) evaporating and grinding the solid-liquid mixture from step (1) to obtain a dry powder; (3) crystallizing the powder from step (2) in high-pressure steam containing an organic template agent for several hours, followed by washing and drying to obtain a pure silicon MWW molecular sieve carrier; (4) mixing the pure silicon MWW molecular sieve obtained in (3) with an inorganic titanium source and a strong acid, refluxing for several hours, followed by washing, drying, and calcining to obtain a titanium-containing MWW molecular sieve. Compared with the traditional hot water method, the pure silicon molecular sieve synthesized by this invention uses nearly 60% less template agent and 90% less water, and the synthesis cycle is shortened by 60%. The sample has high crystallinity and good hydrothermal stability, which is beneficial for industrial production and can be further applied to the synthesis of other heteroatom molecular sieves.

Description

Technical Field

[0001] This invention relates to a method for preparing pure silicon MWW molecular sieves, belonging to the field of inorganic synthesis. Background Technology

[0002] In 1998, Corma et al. (Journal of Physical Chemistry B, 1998, 102(1):44-51) successfully synthesized ITQ-1 molecular sieves using a classical hydrothermal method without alkali metals. However, this method requires a large amount of template agent and has a long synthesis cycle and complex operation. In 2001, Wu et al. (Journal of Physical Chemistry B, 2001, 105(150):2897-2905) first used boric acid as a crystallization aid and piperidine or hexamethyleneimine as template agents to successfully synthesize titanium-containing MWW molecular sieves hydrothermally without alkali metals. This synthesis method requires the addition of boric acid as a crystallization aid, but the utilization rate of boric acid is very low and a large amount of wastewater is generated.

[0003] In 2005, Wu et al. (Catalysis Today, 2005, 99(1-2):233-240) successfully synthesized titanium-containing MWW molecular sieves for the first time using a dry gel method. The basic process involves mixing silicon source, titanium source, and boric acid to obtain a dry gel, which is then crystallized under the action of piperidine or hexamethyleneimine vapor. This method requires only a small amount of water and template agent to achieve crystallization, but it still suffers from problems such as low efficiency of titanium addition, generally larger particle size of synthesized molecular sieve crystals compared to the classical hydrothermal method, and lower activity in the hexene epoxidation reaction. In 2012, Corma et al. (Chemistry of Material, 2012, 24(22):4371-4775) obtained Ti-YNU-1 molecular sieve with expanded pore structure by adding titanium addition after hydrothermal synthesis of pure silicon MWW molecular sieve.

[0004] In 2018, Ge et al. (Applied Catalysis A-General, 2018, 564:218-225) successfully synthesized a boron-degraded ERB-1 support using a dry gel method, and then performed hydrothermal titanium loading to obtain a titanium-containing MWW molecular sieve with catalytic activity comparable to that obtained by the classical hydrothermal method. However, the boron-degraded support obtained by this method still requires the addition of boric acid during the synthesis process and subsequent acid elution to remove boron, and cannot directly obtain pure silicon MWW molecular sieves; at the same time, its secondary hydrothermal titanium loading still does not get rid of the problem of excessive use of template agents and solvents in traditional secondary hydrothermal synthesis.

[0005] Currently, there is no method that can simultaneously solve the problems of large organic template agent usage, long synthesis cycle, and low crystallinity in the synthesis of pure silicon MWW molecular sieves. This method can simultaneously solve the problems of long synthesis cycle, large template agent usage, and large water requirement for crystallization associated with the classical hydrothermal method. It facilitates a more efficient synthesis of pure silicon MWW molecular sieves with good hydrothermal stability and high specific surface area, which is beneficial for large-scale industrial production. Summary of the Invention

[0006] The purpose of this invention is to provide an efficient and rapid method for synthesizing pure silicon MWW molecular sieves and to apply it to the synthesis of titanium-containing MWW molecular sieves. Its key features include the use of a steam crystallization method to synthesize pure silicon MWW molecular sieves, which is simple in procedure, has a short synthesis cycle, requires a small amount of template agent, and exhibits high hydrothermal stability; furthermore, the synthesized titanium-containing MWW molecular sieves show high catalytic activity.

[0007] The method for synthesizing pure silicon MWW molecular sieves and its application as described in this invention includes the following steps:

[0008] (1) Preparation of dry powder: Silicon source, organic amine template agent and water are thoroughly mixed in a molar ratio of 1:0.05~0.26:20~90, and then seed crystals equivalent to 0.01%~20% of the mass of silicon source are added. After aging at 25℃~90℃ for 1~6 hours, the hydrogel is evaporated in an oil bath at 40~110℃ and ground to obtain dry powder;

[0009] (2) Crystallization: The dry powder obtained in step (1) is added to a polytetrafluoroethylene container. The organic amine template agent and water are placed in a high-pressure reactor with a polytetrafluoroethylene liner at a molar ratio of 1:10 to 80. The polytetrafluoroethylene container is placed in the liner and statically crystallized at a constant temperature of 130 to 220°C for 0.5 to 5 days. After washing and drying, the crystallized sample is used to obtain pure silicon MWW molecular sieve.

[0010] (3) Preparation of titanium-containing MWW molecular sieve: The pure silicon MWW molecular sieve obtained in step (2) is placed in an atmospheric pressure container, and then an inorganic titanium source and 0.5-6 mol / L strong acid are added. The titanium is refluxed for 0.5-8 hours at a reflux temperature of 40-100℃. After the titanium is refluxed, the solid is filtered or centrifuged and washed until neutral. After drying, grinding and calcining, titanium-containing MWW molecular sieve is obtained. The silicon-to-titanium ratio is 2-100 and the solid-to-liquid ratio is 10-60.

[0011] In step (1), the silicon source is one or more of tetraethyl orthosilicate, silica, silica gel and silica sol; the seed crystal is one or more of ITQ-1, B-MWW and DB-MWW.

[0012] In steps (1) and (2), the organic template agent is one or more of piperidine, hexamethyleneimine, ethylenediamine, and N,N,N-trimethyl-1-adamantyl ammonium hydroxide.

[0013] In step (3), the inorganic titanium source is one or more of titanium tetrachloride, titanium sulfate, fluorotitanic acid, and ammonium fluorotitanate; the strong acid is one or more of hydrochloric acid, sulfuric acid, and nitric acid; the calcination temperature is 450-700℃, and the calcination time is 3-18 hours.

[0014] The pure silicon MWW molecular sieve prepared by the synthesis method provided in this invention can be used in the synthesis of titanium-containing MWW molecular sieves, tin-containing MWW molecular sieves, iron-containing MWW molecular sieves, and gallium-containing MWW molecular sieves. Among them, the titanium-containing MWW molecular sieve exhibits good catalytic performance in the epoxidation reaction of 1-hexene.

[0015] Compared with the prior art, the present invention has the following significant advantages:

[0016] 1. Compared with the traditional dry gel method, this invention disperses organic template agents in the dry powder and polytetrafluoroethylene liner based on the properties of different types of organic template agents. This reduces the amount of organic template agent and water used, and enables the synthesis of highly crystalline pure silicon MWW molecular sieves in a short time. Furthermore, it can be applied to the synthesis of titanium-containing molecular sieves.

[0017] 2. Compared with the traditional hydrothermal synthesis method, the amount of organic amine template agent and water used in this invention is greatly reduced, and the synthesis cycle is short, the product yield is high, and the pollution is low. In the traditional hydrothermal method, the residual substances dissolved in the solvent are directly discharged as pollutants, while in this invention, there is almost no residual crystallization waste liquid discharge.

[0018] 3. Compared with the two-step synthesis method, the present invention obtains pure silicon MWW molecular sieve in one step, without the need for subsequent strong acid treatment, and can be directly applied to the synthesis of other heteroatom molecular sieves. In contrast, the two-step synthesis method requires the addition of aluminum or boron sources as crystallization aids, and requires a large amount of strong acid for a long time to remove aluminum or boron. Furthermore, the obtained molecular sieve cannot be guaranteed to be completely pure silicon, and the residual aluminum and boron elements will provide additional acid sites in the catalytic reaction, which is not conducive to the catalytic reaction. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the pure silicon MWW molecular sieve obtained in Example 1. Figure 2 The image shows the XRD pattern of the titanium-containing MWW molecular sieve obtained in Example 1. Detailed Implementation

[0020] The invention will be further illustrated below with specific examples. Each embodiment only lists the technical data for each step.

[0021] Example 1:

[0022] Step 1: Preparation of dry powder

[0023] Take 20g of silica (Shanghai Shanbo Industrial Co., Ltd.), 1.7g of piperidine (Sinopharm Chemical Reagent Co., Ltd.), 1g of seed crystal, and 500g of water, mix thoroughly, age at room temperature (25℃) for 1 hour, then evaporate to dryness at 80℃, and grind to obtain dry powder. In the preparation of the dry powder, the molar ratio of silicon source to template agent is 20, the molar ratio of silicon to water is 0.012, the seed crystal is DB-MWW, and the seed crystal mass is 5% of the silicon source mass.

[0024] Step 2: Crystallization

[0025] The dry powder obtained in the first step was placed in a small polytetrafluoroethylene (PTFE) container. Then, 16g of piperidine (from Sinopharm Chemical Reagent Co., Ltd.) and 34g of water were placed in a high-pressure reactor lined with PTFE, and the small container was placed inside. Static crystallization was then carried out at 170℃ for 12 hours. After removal, the mixture was washed with deionized water until neutral, then dried overnight, and ground to obtain pure silicon MWW molecular sieve. The molar ratio of template agent to water during crystallization was 0.1.

[0026] Step 3: Preparation of titanium-containing MWW molecular sieves

[0027] Take 10g of the pure silicon MWW molecular sieve obtained in step two, 2g of titanium sulfate (Sinopharm Chemical Reagent Co., Ltd.), and 200ml of 0.5mol / L nitric acid, mix them and add them to an atmospheric pressure container. Reflux at 60℃ for 0.5 hours. After titanium addition, wash the resulting solid with deionized water until neutral, dry overnight, grind, and calcine at 550℃ for 12 hours to obtain titanium-containing MWW molecular sieve. The silicon-to-titanium ratio of the mixture is 20, and the solid-to-liquid ratio is 10.

[0028] Example 2: Same as Example 1, except that in the first step, the silicon source is silica gel, the organic template agent is ethylenediamine, the seed crystal is B-MWW, the aging temperature is 40℃, the aging time is 2 hours, and the evaporation temperature is 90℃. During the dry powder preparation process, the molar ratio of silicon source, organic template agent, and water is 1:0.1:80, and the seed crystal mass is 10% of the silicon source mass. In the second step, the organic template agent is hexamethyleneimine, the static crystallization time is 24 hours, and the crystallization temperature is 160℃. During the crystallization process, the molar ratio of template agent to water is 0.05. In the third step, the inorganic titanium source is ammonium fluorotitanate, the strong acid is 1 mol / L sulfuric acid, the reflux temperature is 70℃, and the reflux time is 3 hours. The molar ratio of Si in the support to the inorganic titanium source is 1:0.1, the solid-liquid ratio is 20, the calcination temperature is 500℃, and the calcination time is 6 hours.

[0029] Example 3: Same as Example 1, except that in the first step, the silicon source is tetraethyl orthosilicate, the organic template agent is N,N,N-trimethyl-1-adamantyl ammonium hydroxide, the seed crystal is ITQ-1, the aging temperature is 50℃, the aging time is 0.5 hours, and the evaporation temperature is 70℃. During the dry powder preparation process, the molar ratio of silicon source, organic template agent, and water is 1:0.15:70, and the seed crystal mass is 15% of the silicon source mass. In the second step, the organic template agent is hexamethyleneimine, the static crystallization time is 48 hours, and the crystallization temperature is 150℃. During the crystallization process, the molar ratio of template agent to water is 0.03. In the third step, the inorganic titanium source is titanium tetrachloride, the strong acid is 2 mol / L hydrochloric acid, the reflux temperature is 80℃, and the reflux time is 1 hour. The molar ratio of Si in the support to the inorganic titanium source is 1:0.1, the solid-liquid ratio is 30, the calcination temperature is 450℃, and the calcination time is 18 hours.

[0030] Example 4: Same as Example 1, except that in the first step, the silicon source is silica sol, the organic template agent is hexamethyleneimine, the seed crystal is B-MWW, the aging temperature is 60℃, the aging time is 3 hours, and the evaporation temperature is 100℃. During the dry powder preparation process, the molar ratio of silicon source, organic template agent, and water is 1:0.2:60, and the seed crystal mass is 20% of the silicon source mass. In the second step, the organic template agent is ethylenediamine, the static crystallization time is 60 hours, and the crystallization temperature is 200℃; the molar ratio of template agent to water during crystallization is 0.025. In the third step, the inorganic titanium source is fluorotitanic acid, the strong acid is 1 mol / L nitric acid, the reflux temperature is 90℃, and the reflux time is 4 hours. The molar ratio of Si in the carrier to the inorganic titanium source is 1:0.02, the solid-liquid ratio is 40, the calcination temperature is 600℃, and the calcination time is 8 hours.

[0031] Example 5: Same as Example 1, except that in the first step, the silicon source is silica gel, the organic template agent is N,N,N-trimethyl-1-adamantyl ammonium hydroxide, the seed crystal is ITQ-1, the aging temperature is 70℃, the aging time is 6 hours, and the evaporation temperature is 110℃. During the dry powder preparation process, the molar ratio of silicon source, organic template agent, and water is 1:0.22:50, and the seed crystal mass is 1% of the silicon source mass. In the second step, the organic template agent is ethylenediamine, the static crystallization time is 120 hours, and the crystallization temperature is 220℃; the molar ratio of template agent to water during crystallization is 0.02. In the third step, the inorganic titanium source is titanium tetrachloride, the strong acid is 1 mol / L sulfuric acid, the reflux temperature is 50℃, and the reflux time is 3 hours. The molar ratio of Si in the support to the inorganic titanium source is 1:0.04, the solid-liquid ratio is 50, the calcination temperature is 650℃, and the calcination time is 10 hours.

[0032] Example 6: Same as Example 1, except that in the first step, the silicon source is tetraethyl orthosilicate, the organic template agent is hexamethyleneimine, the seed crystal is B-MWW, the evaporation temperature is 90℃, the aging time is 3 hours, and the evaporation temperature is 50℃. The molar ratio of silicon source, organic template agent, and water in the dry powder preparation process is 1:0.26:40, and the seed crystal mass is 2% of the silicon source mass. In the second step, the organic template agent is hexamethyleneimine, the static crystallization time is 96 hours, and the crystallization temperature is 210℃; the molar ratio of template agent to water during crystallization is 0.015. In the third step, the inorganic titanium source is ammonium fluorotitanate, the strong acid is 6 mol / L nitric acid, the reflux temperature is 40℃, and the reflux time is 2 hours. The molar ratio of Si in the support to the inorganic titanium source is 1:0.025, and the solid-liquid ratio is 60. The calcination temperature is 700℃, and the calcination time is 14 hours.

[0033] Comparative Example 1

[0034] This comparative study describes the synthesis of pure silicon MWW molecular sieves using the traditional hydrothermal method described by Corma et al. (Journal of Physical Chemistry B, 1998, 102(1):44-51); and the further synthesis of titanium-containing MWW molecular sieves using the liquid-solid phase titanium-addition method. First, 26.9 mL of water was placed in a normal pressure container, followed by the sequential addition of N,N,N-trimethyl-1-adamantyl ammonium hydroxide (TMAdaOH), hexamethyleneimine (HMI), and a silicon source. After thorough mixing and aging at room temperature for 1 hour, the mixture was transferred to a high-pressure reactor with a polytetrafluoroethylene liner and dynamically crystallized at 160°C for 120 hours to obtain pure silicon MWW molecular sieves. These were then mixed with a mixture of titanium sulfate and 1 mol / L nitric acid to obtain titanium-containing MWW molecular sieves. The sol molar ratio during crystallization was Si:TMAdaOH:HMI:H2O = 1:0.27:0.3:30, and the solution molar ratio during titanium addition was Si:Ti = 1:0.05.

[0035] Comparative Example 2

[0036] This comparative study describes the synthesis of highly boron-degraded MWW molecular sieves using the dry gel method described by Ge et al. (Applied Catalysis A-General, 2018, 564:218-225), followed by titanium deposition in a liquid-solid phase to obtain titanium-containing MWW molecular sieves. First, silicon source, boron source, seed crystals, and water were thoroughly mixed and aged for 0.5 hours, then evaporated to dryness at 80°C to obtain a dry powder. The dry powder was placed in a pressure vessel containing piperidine and water for static crystallization at a constant temperature of 170°C for 2 days. The resulting solid was washed, dried, acid-washed, and calcined to obtain highly boron-degraded MWW molecular sieves. These were then mixed with a mixed solution of titanium sulfate and 1 mol / L nitric acid to deposit titanium and obtain titanium-containing MWW molecular sieves. The seed crystals were DB-MWW, the molar ratio of the dry powder was Si:B:H₂O = 1:0.2:0.3:80, the molar ratio of the solution for titanium deposition was Si:Ti = 1:0.05, and the seed crystal mass was 10% of the silicon source mass.

[0037] The titanium-containing MWW molecular sieves obtained in Examples 1 to 6 and the titanium-containing MWW molecular sieves in Comparative Examples 1 to 2 were subjected to activity tests. The epoxidation of 1-hexene was used as a probe reaction. The conditions were: 10 mmol of 1-hexene, 10 mmol of hydrogen peroxide, 10 ml of solvent acetonitrile, 0.5 g of internal standard cyclohexanone, 0.05 g of catalyst, reaction temperature of 60 °C, and reaction time of 2 h.

[0038] Chromatographic analysis method: Chromatographic column: Agilent 6890; Capillary column: Agilent 19091J-413. Gas conditions: Hydrogen flow rate: 40 mL / min; Air flow rate: 450 mL / L; Split ratio: 3. The temperature program was as follows: initial temperature 50℃, residence time 2 min, heating rate 5℃ / min, final temperature 250℃, residence time 1 min.

[0039] The catalytic results of titanium-containing MWW molecular sieves in the n-hexene epoxidation reaction of Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0040] The XRD patterns of the pure silicon MWW molecular sieves obtained in Examples 2-6 are all consistent with... Figure 1 Consistent with typical pure silica MWW molecular sieves; the XRD patterns of the obtained titanium-containing MWW molecular sieves are all consistent with... Figure 2 Consistent, it is a typical titanium-containing MWW molecular sieve.

[0041] Figure 1 and Figure 2In the study, the molecular sieve exhibited typical MWW structural characteristic peaks: 2θ = 7.22°, 7.90°, 9.54°, 14.42°, 16.14°, 22.64°, 23.72°, and 26.14°; 2θ = 6.35° corresponds to the (002) crystal plane diffraction peak of MWW. X-ray powder diffractometer (XRD) was used with Cu-Kα as the X-ray source. The testing conditions were: voltage 45 kV, current 40 mA, scanning range 0°–45°, and scanning rate 0.1313° / s.

[0042] The examples described above only illustrate some of the most representative embodiments of the present invention, but the present invention is not limited to the specific details of the above embodiments. Based on the technical concept of the present invention, those skilled in the art can arbitrarily combine various different embodiments of the present invention. Therefore, any improvements made based on the technical concept of the present invention should be covered within the scope of protection of the present invention. To avoid unnecessary repetition, the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and the present invention will not further describe the various possible combinations.

[0043] Table 1

[0044]

Claims

1. A method for synthesizing pure silicon MWW molecular sieves, characterized in that... Includes the following steps: (1) Preparation of dry powder: Silicon source, organic amine template agent and water are thoroughly mixed in a molar ratio of 1:0.05~0.26:20~90, and then seed crystals equivalent to 0.01%~20% of the mass of silicon source are added. After aging at 25~90℃ for 1~6 hours, the hydrogel is evaporated in an oil bath at 40~110℃ and ground to obtain dry powder; (2) Place the dry powder obtained in step (1) into a polytetrafluoroethylene container, place the organic amine template agent and water in a high-pressure reactor lined with polytetrafluoroethylene at a molar ratio of 1:10 to 80, place the polytetrafluoroethylene container containing the dry powder in the liner, and statically crystallize at a constant temperature of 130 to 220°C for 0.5 to 5 days. After washing and drying the crystallized solid, pure silicon MWW molecular sieve is obtained; the silicon source is one or more of tetraethyl orthosilicate, silica, silica gel and silica sol; the seed crystal is one or more of ITQ-1, B-MWW and DB-MWW; the organic amine template agent is one or more of piperidine, hexamethyleneimine, ethylenediamine, N,N,N-trimethyl-1-adamantyl ammonium hydroxide.

2. The application of the pure silicon MWW molecular sieve obtained by the synthesis method according to claim 1, wherein the pure silicon MWW molecular sieve is placed in an atmospheric pressure container, and then an inorganic titanium source and 0.5-6 mol / L strong acid are added, and the mixture is refluxed for 0.5-8 hours to coat with titanium at a reflux temperature of 40-100°C. After the titanium coating is completed, the solid is filtered or centrifuged and washed until neutral. After drying, grinding, and calcining, titanium-containing MWW molecular sieve is obtained; wherein the silicon-to-titanium ratio is 2-100, and the solid-to-liquid ratio is 10-60.

3. The application of the pure silicon MWW molecular sieve according to claim 2, characterized in that: The inorganic titanium source is one or more of titanium tetrachloride, titanium sulfate, fluorotitanic acid, and ammonium fluorotitanate.

4. The application of the pure silicon MWW molecular sieve according to claim 2, characterized in that: Strong acids are one or more of hydrochloric acid, sulfuric acid, and nitric acid.

5. The application of the pure silicon MWW molecular sieve according to claim 2, characterized in that: The roasting temperature is 450–700℃, and the roasting time is 3–18 hours.

Images