CN113683099B - Method for synthesizing defective zeolite molecular sieve rich in hydroxy nest - Google Patents

Abstract

The invention provides a method for synthesizing a defective zeolite molecular sieve rich in hydroxy nest, which takes an inorganic silicon source and an organic silicon source as mixed silicon sources, and mixes the mixed silicon sources with an aluminum source and an OSDA template agent to obtain sol for crystallization; filtering, drying and roasting the obtained solid to obtain a defective zeolite molecular sieve rich in hydroxy nest; the organosilicon source is an alkylsiloxane. According to the invention, alkyl siloxane is introduced in the process of constructing a framework of the molecular sieve to form partial Si-C bond connection, and then C is burnt out in the process of roasting the molecular sieve to form a framework point defect of a single T position of the molecular sieve to form a hydroxyl nest, and the point defect almost has no influence on the crystallinity of the material, and the integrity of the molecular sieve framework is maintained to a great extent; the defect degree of the molecular sieve can be controlled relatively accurately by controlling the type and the content of the alkyl siloxane in the synthesis process, so that the defective zeolite molecular sieve rich in the hydroxy nest is obtained.

Description

A method for synthesizing defective zeolite molecular sieves rich in hydroxyl nests

Technical field

The invention belongs to the field of aluminosilicate zeolite synthesis, and specifically relates to a method for synthesizing a defective zeolite molecular sieve rich in hydroxyl nests.

Background technique

Zeolite molecular sieve is the most widely distributed inorganic microporous material in nature. Since the Swedish scientist Cronstedt first discovered natural zeolite in 1756, it has received widespread attention from scientific researchers due to its unique molecular sieving ability and good adsorption performance, and has gradually been applied in people's actual production and life. Although natural zeolites have the characteristics of wide variety, wide distribution, large reserves and low cost, they have many impurities and low purity, which limits their large-scale industrial application. Therefore, the artificial synthesis of zeolites has become a new direction of research. In the late 1940s, Barrer, an outstanding chemist in the field of molecular sieve synthesis, successfully prepared the first batch of low-silica zeolite molecular sieves using low-temperature hydrothermal synthesis technology, with a silicon-aluminum ratio of 1.0 to 1.5. In 1964, the silicon-aluminum ratio was 1.5 to 3.0. The Y-type molecular sieve was successfully synthesized and developed by Breck in the industry, and it showed excellent performance in industrial catalysis, thus promoting the development of artificially synthesized zeolites. Since then, with the development of science and technology and various innovative attempts by researchers, more and more methods have been used to synthesize zeolite molecular sieves, from the traditional hydrothermal synthesis method that simulated the formation environment of natural zeolites to the later solvothermal synthesis method and dry synthesis method. Scientific researchers have never stopped exploring the synthesis of zeolite molecular sieves through glue method, seed-assisted synthesis and solvent-free method.

But no matter which synthesis method is used, the ultimate goal is to prepare molecular sieves that are almost perfect or have few defects. With the continuous deepening of scientific research, scientists have discovered that the defect positions of the molecular sieve skeleton have certain special properties. For example, the hydroxyl nests have relatively strong acidity due to the mutual disturbance of hydrogen bonds, and are important adsorption sites during VOC adsorption. Moreover, the hydroxyl nest can accommodate certain metal ions, allowing metal heteroatoms to enter the molecular sieve skeleton; the titanium hydroxyl group TiOH in the defect position of the titanium silicon molecular sieve is the catalytic active center of the olefin epoxidation reaction. At present, the more commonly used method is to prepare zeolite molecular sieves containing defective sites through post-processing, that is, post-modification method of removing part of the framework aluminum or silicon by soaking the molecular sieve precursor in acid/alkali solution, but how to accurately control it? The location and size of defective sites without destroying the topology of the molecular sieve skeleton are major challenges in the synthesis of defective site-rich molecular sieves.

Contents of the invention

In order to make full use of the special properties of molecular sieve defects, the present invention provides a synthesis method of defective zeolite molecular sieves rich in hydroxyl holes, using inorganic silicon sources and organic silicon sources of alkyl siloxane as mixed silicon sources and conventional aluminum The source and template agent are mixed for crystallization. During the process of building the framework of the molecular sieve, due to the introduction of alkylsiloxane, some Si-C bonds are formed. Subsequently, during the roasting process of the molecular sieve, C is burned away to form a single T site of the molecular sieve. Defects in the skeleton point form hydroxyl nests. During the synthesis process, the degree of molecular sieve defects can be controlled relatively precisely by controlling the type and content of alkylsiloxane, thereby obtaining a defective zeolite molecular sieve rich in hydroxyl nests.

The technical solution of the present invention is as follows:

A method for synthesizing defective zeolite molecular sieves rich in hydroxyl nests, including the following steps:

S1 uses inorganic silicon source (Inorg-Si) and organic silicon source (Org-Si) as mixed silicon sources, mix them with aluminum source and OSDA template agent to obtain a sol, and then crystallize;

S2 is filtered, dried and roasted to obtain a defective zeolite molecular sieve rich in hydroxyl nests;

The organic silicon source is an alkylsiloxane, and the molar ratio of SiO ₂ -Inorg-Si (SiO ₂ in the inorganic silicon source) and SiO _{2 -} Org-Si (SiO ₂ in the organic silicon source) in the sol is 1: 0.001～0.2.

The zeolite molecular sieve is ZSM-5 zeolite molecular sieve, Beta zeolite molecular sieve, MCM22 zeolite molecular sieve or SSZ13 zeolite molecular sieve.

The zeolite molecular sieve is ZSM-5 zeolite molecular sieve, and the S1 specifically includes the following steps:

(1) Preparation of the initial raw material silicon solution: Under vigorous stirring, mix the inorganic silicon source, organic silicon source, sodium hydroxide and water evenly to prepare the initial raw material silicon solution and stir thoroughly;

(2) Preparation of the initial raw material aluminum solution: Under vigorous stirring, mix the aluminum source, sulfuric acid, and water evenly to prepare the initial raw material aluminum solution and stir thoroughly;

(3) Slowly drop the completely dissolved initial raw material aluminum solution into the initial raw material silicon solution, add OSDA, and stir at room temperature for 4 to 10 hours to obtain a sol. The molar composition of the sol is:

18Na ₂ O: 96.8～99.9SiO ₂ -Inorg-Si (SiO ₂ in inorganic silicon source): 0.1～3.2SiO ₂ -Org-Si (SiO ₂ in organic silicon source): 0.5～4Al ₂ O ₃ :12SO ₄ ^{2 -} :4000H ₂ O:16.5～40.7OSDA;

(4) Put the obtained sol into a polytetrafluoroethylene-lined autoclave to perform a hydrothermal crystallization reaction. The hydrothermal crystallization temperature is 130°C to 190°C, and the hydrothermal crystallization time is 5 minutes to 48 hours.

The zeolite molecular sieve is Beta zeolite molecular sieve, and the S1 specifically includes the following steps:

(1) Preparation of the initial raw material silicon solution: Under vigorous stirring, mix the inorganic silicon source, organic silicon source, sodium hydroxide, and water evenly to prepare the initial raw material silicon solution and stir thoroughly;

(2) The initial raw material silicon solution is slowly added to the aluminum source and OSDA under vigorous stirring. After continuing to stir vigorously for 5 to 120 minutes, a shear emulsifier is used for 10 minutes of high-speed shear emulsification treatment to obtain a sol. The molar composition of the sol is: :

8.9～16.4Na ₂ O: 26.2～59.6SiO ₂ -Inorg-Si (SiO ₂ in inorganic silicon source): 0.4～3.8SiO ₂ -Org-Si (SiO ₂ in organic silicon source): 1Al ₂ O ₃ : 480～ 960H ₂ O:10～40OSDA;

(3) Put the obtained sol into a polytetrafluoroethylene-lined autoclave to perform a hydrothermal crystallization reaction. The hydrothermal crystallization temperature is 120°C to 160°C, and the hydrothermal crystallization time is 5 minutes to 28 hours.

The inorganic silicon source is selected from one or more of silica sol, white carbon black, water glass and solid silica gel.

The alkylsiloxane is methylsiloxane. Further, the methylsiloxane is dimethylsiloxane, dimethyldimethoxysilane, dimethyldiethoxysilane and One or more of methyltriethoxysilane.

The aluminum source is one or more of alumina, aluminum nitrate, sodium metaaluminate and aluminum isopropoxide.

In the synthesis of the ZSM-5 zeolite molecular sieve, OSDA is one or more of methylamine, ethylamine, propylamine, n-butylamine, tetrapropylammonium hydroxide and tetrapropylammonium bromide.

In the synthesis of the Beta zeolite molecular sieve, OSDA is at least one of tetraethyl bromide and tetraethylammonium hydroxide. ,

The drying temperature described in step S2 is 110°C, and the drying time is 8 hours; the roasting temperature is 500-600°C, and the roasting time is 10 hours.

Compared with existing modification technology, the beneficial effects of the present invention are as follows:

The traditional post-processing method - acid and alkali treatment to remove part of the skeleton silicon or aluminum is difficult to control the degree of removal, and the post-processing method to remove skeleton atoms is generally removed in pieces to form large defect vacancies, thus Destroy the crystallinity and skeleton integrity of the material to a certain extent. This method uses inorganic silicon sources and organic silicon sources such as siloxane as a mixed silicon source and conventional aluminum sources and template agents for mixed crystallization. In the process of building the molecular sieve skeleton, due to the introduction of organic silicone as part of the silicon source, the formation of Part of the Si-C bonds are removed, and then C is burned away during the roasting process of the molecular sieve to form skeleton point defects at the single T position of the molecular sieve to form hydroxyl nests. This point defect has almost no effect on the crystallinity of the material, and greatly maintains the integrity of the molecular sieve skeleton. What's more important is that the hydroxyl nest formed by this single T-site defect has the greatest interference with hydrogen bonds and has the most unique chemical properties. Therefore, this method can relatively accurately control the degree of molecular sieve defects by controlling the type and content of siloxane during the synthesis process, thereby obtaining a defective zeolite molecular sieve rich in hydroxyl nests.

Description of the drawings

Figure 1 shows the XRD spectra of Comparative Example D1# and Example Samples 1# and 2#.

Figure 2 is the hydroxyl infrared spectrum of Comparative Example D1# and Example Samples 1-3#.

Figure 3 is the hydroxyl infrared spectrum of Comparative Example D2# and Example Samples 6# and 9#.

Detailed ways

Comparative example 1

Weigh 0.75g NaOH and 50g sodium silicate (SiO ₂ mass fraction 60%, Na ₂ O mass fraction 10%) and add to 22.5g deionized water, stir evenly with a magnetic stirrer; then completely dissolve 4.28g aluminum sulfate In 5g of water, slowly add 2.25g of concentrated sulfuric acid (98%); slowly drop the completely dissolved aluminum sulfate solution into the solution containing sodium silicate, add 25.9g of tetrapropylammonium hydroxide TPAOH, and stir at room temperature for 6 hours. A sol is obtained. The molar composition of the sol is: 18Na ₂ O:100SiO ₂ :2.5Al ₂ O ₃ :12SO ₄ ^2- :4000H ₂ O:25.4TPAOH; the obtained sol is put into an autoclave lined with polytetrafluoroethylene. , controlling the hydrothermal crystallization temperature to 170°C and the hydrothermal crystallization time to 26 hours; after filtration, drying at 110°C for 8 hours, and roasting at 540°C for 10 hours, fully crystallized ZSM-5 was obtained, recorded as D1#.

Comparative example 2

Mix 60g white carbon black, 21.6g sodium hydroxide and 32g water evenly, slowly add 4.9g sodium metaaluminate under vigorous stirring, then add 73.5g tetraethylammonium hydroxide, continue stirring vigorously for 1 hour and then use shearing The emulsifier performs 10 minutes of high-speed shear emulsification treatment to obtain a sol. The molar composition of the sol is: 8.9Na ₂ O: 30SiO ₂ : 1Al ₂ O ₃ : 960H ₂ O: 15TEAOH; put the obtained sol into a polytetraethylene-lined In the autoclave of vinyl fluoride, the crystallization temperature is 150°C and the hydrothermal crystallization time is 48 hours; after filtration, drying at 110°C for 8 hours, and roasting at 540°C for 10 hours, a fully crystallized Beta molecular sieve is obtained, recorded as D2# .

Example 1

Weigh 0.75g NaOH and 49.8g sodium silicate (SiO ₂ mass fraction 60%, Na ₂ O mass fraction 10%) and add them to 22.5g deionized water. Add 0.36g methyltriethoxysilane and stir with a magnetic stirrer. Uniform; then completely dissolve 4.28g aluminum sulfate in 5g water, slowly add 2.25g concentrated sulfuric acid (98%); slowly drop the completely dissolved aluminum sulfate solution into the solution containing sodium silicate, add 25.9g tetrapropyl Ammonium hydroxide TPAOH, stir at room temperature for 6 hours to obtain a sol. The molar composition of the sol is: 18Na ₂ O: 99.6SiO ₂ -Inorg-Si: 0.4SiO ₂ -Org-Si: 2.5Al ₂ O ₃ :12SO ₄ ^2- : 4000H ₂ O: 25.4TPAOH; put the obtained sol into an autoclave lined with polytetrafluoroethylene, control the hydrothermal crystallization temperature to 170°C and the hydrothermal crystallization time to 25 hours; the solid obtained is filtered and dried at 110°C After roasting at 540°C for 8 hours and 10 hours, a defective ZM-5 zeolite molecular sieve rich in hydroxyl nests was obtained. The obtained product was recorded as sample 1#.

Example 2

Weigh 0.75g NaOH and 49.25g sodium silicate (SiO ₂ mass fraction 60%, Na ₂ O mass fraction 10%) and add to 22.5g deionized water, add 1.34g methyltriethoxysilane and stir with a magnetic stirrer Uniform; then completely dissolve 4.28g aluminum sulfate in 5g water, slowly add 2.25g concentrated sulfuric acid (98%); slowly drop the completely dissolved aluminum sulfate solution into the solution containing sodium silicate, add 30.7g tetrapropyl Ammonium hydroxide TPAOH, stir at room temperature for 6 hours to obtain a sol. The molar composition of the sol is: 18Na ₂ O: 98.5SiO ₂ -Inorg-Si: 1.5SiO ₂ -Org-Si: 2.5Al ₂ O ₃ :12SO ₄ ^2- : 4000H ₂ O: 30.2TPAOH; put the obtained sol into an autoclave lined with polytetrafluoroethylene, control the hydrothermal crystallization temperature to 170°C and the hydrothermal crystallization time to 25 hours; the solid obtained is filtered and dried at 110°C After roasting at 540°C for 8 hours and 10 hours, a defective ZM-5 zeolite molecular sieve rich in hydroxyl nests was obtained. The obtained product was recorded as sample 2#.

Example 3

Weigh 0.75g NaOH and 48.6g sodium silicate (SiO ₂ mass fraction 60%, Na ₂ O mass fraction 10%) and add them to 22.5g deionized water. Add 2.50g methyltriethoxysilane and stir with a magnetic stirrer. Uniform; then completely dissolve 4.28g aluminum sulfate in 5g water, slowly add 2.25g concentrated sulfuric acid (98%); slowly drop the completely dissolved aluminum sulfate solution into the solution containing sodium silicate, add 30.7g tetrapropyl Ammonium hydroxide TPAOH, stir at room temperature for 6 hours to obtain a sol. The molar composition of the sol is: 18Na ₂ O: 97.2SiO ₂ -Inorg-Si: 2.8SiO ₂ -Org-Si: 2.5Al ₂ O ₃ :12SO ₄ ^2- : 4000H ₂ O: 30.2TPAOH; put the obtained sol into an autoclave lined with polytetrafluoroethylene, control the hydrothermal crystallization temperature to 170°C and the hydrothermal crystallization time to 25 hours; the solid obtained is filtered and dried at 110°C After roasting at 540°C for 8 hours and 10 hours, a defective ZM-5 zeolite molecular sieve rich in hydroxyl nests was obtained. The obtained product was recorded as sample 3#.

Example 4-5

The operation is the same as in Example 3, except that the source and quality of silicone are changed. See Table 1. Other operations are the same.

Table 1 Defective ZM-5 zeolite molecular sieves rich in hydroxyl nests obtained from different silicone sources and qualities

Example number Sample serial number Silicone source types Silicone source quality Example 4 4# Dimethyldiethoxysilane 2.22g Example 5 5# dimethylsiloxane 1.49g

Example 6

Mix 60g white carbon black, 3.6g methyltriethoxysilane, 21.6g sodium hydroxide, and 32g water evenly, slowly add 4.9g sodium metaaluminate under vigorous stirring, and then add 73.5g tetraethylammonium hydroxide , continue stirring vigorously for 1 hour, and then use a shear emulsifier to perform high-speed shear emulsification treatment for 10 minutes; a sol is obtained, and the molar composition of the sol is: 8.9Na ₂ O: 30SiO ₂ (Inorg-Si): 0.6SiO ₂ (Org- Si): 1Al ₂ O ₃ : 960H ₂ O: 15TEAOH; put the obtained sol into an autoclave lined with polytetrafluoroethylene, the crystallization temperature is 150°C, and the hydrothermal crystallization time is 48 hours; after filtration, After drying at 110°C for 8 hours and calcining at 540°C for 10 hours, a defective Beta zeolite molecular sieve rich in hydroxyl nests was obtained. The obtained product was recorded as sample 6#.

Example 7-9

The operation is the same as in Example 6, except that the source and quality of organic silicon are changed, and other operations are the same.

Table 2 Defective Beta zeolite molecular sieves rich in hydroxyl nests obtained from different sources and qualities of silicone

Example number Sample serial number Silicone source types Silicone source quality Example 7 7# Methyltriethoxysilane 4.8g Example 8 8# Dimethyldiethoxysilane 3.2g Example 9 9# Dimethyldimethoxysilane 2.4g

Example 10

The samples prepared in the above examples were characterized by XRD. Taking Comparative Example D1# and Example Samples 1# and 2# as examples, their XRD spectra are shown in Figure 1; Comparative Example D1# and Example Samples 1-5# are relatively Crystallinity data are shown in Table 3. The results show that all samples conform to the structural characteristics of ZSM-5 through XRD analysis, that is, the solid samples obtained are all ZSM-5 molecular sieves, and due to the introduction of the organic silicon source, the skeleton of the defective molecular sieve prepared is complete, and the relative crystallinity of the samples is not visible. dropped significantly.

Table 3 Relative crystallinity of different samples

Sample serial number Relative crystallinity D1# 100% 1# 97.3% 2# 99.1% 3# 98.8% 4# 99.4% 5# 98.9%

Example 11

The samples prepared in the above examples were characterized by infrared hydroxyl groups. The hydroxyl infrared spectra of Comparative Example D1# and Example Samples 1-3# are shown in Figure 2. The results show that Comparative Example D1# has no vibration at 3500cm ^-1 , indicating that the sample does not have hydroxyl nests, while the samples with introduced organic silicon sources can see clear peaks at 3500cm ^-1 , indicating that these samples have abundant hydroxyl nests. Defect locations, and as the amount of silicone source increases, the degree of material defects also increases significantly.

Example 12

The Beta series samples were characterized by infrared hydroxyl groups. The hydroxyl infrared spectra of Comparative Example D2# and Example Samples 6# and 9# are shown in Figure 3. In addition, the XRD test showed that the skeletons of the 6# and 9# defective molecular sieves were intact. It has the same effect as the ZSM-5 series.

Claims (10)

1. A method for synthesizing a defective zeolite molecular sieve rich in hydroxy nest is characterized in that: the method comprises the following steps:

s1, inorganic silicon source Inorg-Si and organic silicon source Org-Si are used as mixed silicon sources, and are mixed with an aluminum source and an OSDA template agent to obtain sol for crystallization;

s2, filtering, drying and roasting the obtained solid to obtain a defective zeolite molecular sieve rich in hydroxy nest;

the organosilicon source is alkyl siloxane, and SiO in the sol ₂ -Inorg-Si and SiO _2- The molar ratio of the Org-Si is 1:0.001-0.2.

2. The method for synthesizing a defective zeolite molecular sieve rich in hydroxy-acid cells according to claim 1, wherein: the zeolite molecular sieve is a ZSM-5 zeolite molecular sieve, and the S1 specifically comprises the following steps:

(1) Preparing an initial raw material silicon solution: under intense stirring, uniformly mixing an inorganic silicon source, an organic silicon source, sodium hydroxide and water to prepare an initial raw material silicon solution, and fully stirring;

(2) Preparing an initial raw material aluminum solution: uniformly mixing an aluminum source, sulfuric acid and water under vigorous stirring to prepare an initial raw material aluminum solution, and fully stirring;

(3) Slowly dripping the completely dissolved initial raw material aluminum solution into the initial raw material silicon solution, adding OSDA, and stirring at room temperature for 4-10 hours to obtain sol, wherein the mol composition of the sol is as follows: 18Na ₂ O : 96.8~99.9SiO ₂ -Inorg-Si : 0.1~3.2SiO ₂ -Org-Si :0.5~4Al ₂ O ₃ : 12SO ₄ ^2- : 4000H ₂ O : 16.5~40.7OSDA；

(4) And filling the obtained sol into an autoclave lined with polytetrafluoroethylene for hydrothermal crystallization reaction, wherein the hydrothermal crystallization temperature is 130-190 ℃, and the hydrothermal crystallization time is 5 minutes-48 hours.

3. The method for synthesizing a defective zeolite molecular sieve rich in hydroxy-acid cells according to claim 1, wherein: the zeolite molecular sieve is Beta zeolite molecular sieve, and the S1 specifically comprises the following steps:

(1) Preparing an initial raw material silicon solution: under intense stirring, uniformly mixing an inorganic silicon source, an organic silicon source, sodium hydroxide and water to prepare an initial raw material silicon solution, and fully stirring;

(2) Slowly adding an aluminum source and OSDA into an initial raw material silicon solution under intense stirring, continuously and vigorously stirring for 5-120 minutes, and then carrying out high-speed shearing and emulsifying treatment for 10 minutes by adopting a shearing and emulsifying machine to obtain sol, wherein the molar composition of the sol is as follows: 8.9 to 16.4Na ₂ O : 26.2~59.6SiO ₂ -Inorg-Si : 0.4~3.8SiO ₂ -Org-Si : 1Al ₂ O ₃ : 480~960H ₂ O : 10~40OSDA；

(3) And filling the obtained sol into an autoclave lined with polytetrafluoroethylene for hydrothermal crystallization reaction, wherein the hydrothermal crystallization temperature is 120-160 ℃, and the hydrothermal crystallization time is 5 minutes-28 hours.

4. A method of synthesizing a defective zeolite molecular sieve rich in hydroxy-pits according to any one of claims 1 to 3, wherein: the inorganic silicon source is selected from one or more of silica sol, white carbon black, water glass and solid silica gel.

5. A method of synthesizing a defective zeolite molecular sieve rich in hydroxy-pits according to any one of claims 1 to 3, wherein: the alkyl siloxane is methyl siloxane.

6. The method for synthesizing a defective zeolite molecular sieve rich in hydroxy-acid cells according to claim 5, wherein: the methyl siloxane is one or more of dimethyl siloxane, dimethyl dimethoxy silane, dimethyl diethoxy silane and methyl triethoxy silane.

7. A method of synthesizing a defective zeolite molecular sieve rich in hydroxy-pits according to any one of claims 1 to 3, wherein: the aluminum source is one or more of aluminum oxide, aluminum nitrate, sodium metaaluminate and aluminum isopropoxide.

8. A method of synthesizing a defective zeolite molecular sieve rich in hydroxy-acid cells according to claim 2, wherein: the OSDA is one or more of methylamine, ethylamine, propylamine, n-butylamine, tetrapropylammonium hydroxide and tetrapropylammonium bromide.

9. A method of synthesizing a defective zeolite molecular sieve rich in hydroxy-acid cells according to claim 3, wherein: the OSDA is at least one of tetraethyl bromide and tetraethyl ammonium hydroxide.

10. A method of synthesizing a defective zeolite molecular sieve rich in hydroxy-pits according to any one of claims 1 to 3, wherein: and in the step S2, the roasting temperature is 500-600 ℃ and the roasting time is 10 hours.