CN111233000B - A kind of synthetic method of low silicon aluminum ratio MTT type molecular sieve - Google Patents

Abstract

The invention relates to a method for synthesizing an MTT molecular sieve. The specific implementation steps of the synthesis method are as follows: After fully mixing the silicon source, aluminum source, template agent, and water, heat and crystallize for a certain period of time to prepare a precursor mixture; add a certain amount of aluminum source and water to the precursor mixture, and continue heating Crystallization for a certain period of time to prepare MTT molecular sieves with low silicon-aluminum ratio. The low-silicon-aluminum ratio MTT molecular sieve prepared by the invention has a Si/Al ratio as low as 5, has the characteristics of strong acidity and large acid content, and has potential applications in petroleum refining, petrochemical, coal chemical and other fields. The synthesis method provided by the invention is low in cost, safe and convenient in operation, and environment-friendly.

Description

A kind of synthetic method of low silicon aluminum ratio MTT type molecular sieve

technical field

The invention relates to a synthesis method of a molecular sieve, in particular to a synthesis method of an MTT molecular sieve with a low silicon-aluminum ratio.

Background technique

Zeolite molecular sieve is a kind of inorganic crystal material, which has the characteristics of unique pore structure, large specific surface area, and adjustable acidity. It is widely used in petroleum refining, petrochemical, coal chemical and other fields.

MTT-type molecular sieves have one-dimensional channels with teardrop-shaped ten-membered ring windows, and belong to high-silicon molecular sieves. Molecular sieves with this structure were first synthesized by C.J.Plank et al. in the 1970s. The most representative molecular sieve with MTT structure is ZSM-23, and there are also molecular sieves named KZ-1, ISI-4, EU-13, SSZ-32 and so on. Except for the channel window of the ten-membered ring, the channel diameter of ZSM-23 molecular sieve is 0.56nm×0.45nm, and there is no intersecting channel in the framework. It is precisely because its unique pore structure can meet the requirements of some reactions for shape-selective catalysis, so it shows excellent catalytic performance and potential application value in many catalytic reactions.

Molecular sieves are used in acid-catalyzed reactions, and their catalytic performance is closely related to acidity. The more molecular sieve acid, the higher the catalyst activity, and the lower the temperature required to achieve the target conversion rate. However, in the current literature reports, the Si/Al of MTT molecular sieves is generally higher than 50, which limits the increase of its acid content. By using a special template agent, some silica-alumina molecular sieves with low silica-alumina ratio can be synthesized. For example, for silica-alumina molecular sieves, Corma et al. have obtained MTW molecular sieves with Si/Al=12 (NewJ.Chem., 2016, 40, 4140) using templates synthesized in the laboratory; Jintao Li et al. The template agent obtained Si/Al=8-23 MTW type molecular sieve (Catalysis Communications, 50 (2014), 97-100). These methods for synthesizing molecular sieves with low silicon-to-alumina ratio require the use of laboratory-synthesized templates, and the high synthesis cost limits their large-scale application. The development of low-cost synthesis of MTT-type molecular sieves with a large amount of acid will likely expand the further application of this type of molecular sieves in acid-catalyzed reactions.

Contents of the invention

The purpose of the present invention is to provide a new method for the synthesis of MTT molecular sieves with low silicon-aluminum ratio.

Above-mentioned purpose, realize through following technical scheme:

1) Preparation of precursor mixture: mix silicon source, aluminum source, sodium hydroxide, organic amine, and water in a certain proportion, stir until uniform, and form precursor mixture A, in A, Al ₂ O ₃ :SiO ₂ :Na ₂ O : Organic amine: H ₂ O molar ratio is 1:80-500:1-100:1-200:1000-8000 (silicon source, aluminum source, sodium hydroxide are all calculated according to their oxide form);

2) heating and crystallizing the prepared precursor mixture A at 80°C-250°C for 5h-72h, then cooling to room temperature to obtain mixture B;

3) Add a certain amount of aluminum source and water to mixture B, stir until uniform, and obtain mixture C, in which Al ₂ O ₃ :SiO ₂ :Na ₂ O:organic amine:H ₂ O molar ratio is 1:1- 60:1-100:1-200:100-4000 (silicon source and aluminum source are calculated according to their oxide form);

4) heating and crystallizing the mixture C at 100°C-250°C for 5h-120h;

5) After the crystallization, the mixture is cooled to room temperature, filtered, washed and dried, and calcined at 300°C-600°C for 5h-36h, and the obtained solid is MTT molecular sieve with low silicon-aluminum ratio.

In the method, the silicon source in step 1) is one or more of silica sol, water glass, white carbon black, orthoethyl silicate;

In the method, the aluminum source in step 1) is one or more of aluminum isopropoxide, sodium metaaluminate, pseudoboehmite, aluminum sulfate, and aluminum nitrate;

In the method, the organic amine in step 1) is one or more of dimethylamine, N,N-dimethylformamide, pyrrolidine, n-propylamine, isopropylamine, n-butylamine and the like.

In the method, step 1) in the mixture A, the molar ratio of Al ₂ O ₃ :SiO ₂ :Na ₂ O:organic amine:H ₂ O is 1:80-200:1-50:1-100:3000-6000.

In the method, step 2) the preferred crystallization temperature of mixture A is 100°C-200°C; the preferred crystallization time is 10h-48h.

In the method, step 3) the molar ratio of Al ₂ O ₃ :SiO ₂ :Na ₂ O:organic amine:H ₂ O in the mixture C is 1:10-40:1-30:1-50:200-2000.

In the method, step 4) the preferred crystallization temperature of mixture C is 100°C-200°C; the preferred crystallization time is 12h-100h.

In the method, the preferred calcination temperature in step 5) is 450°C-550°C; the preferred calcination time is 12h-24h.

The silicon source, the aluminum source, and the template are crystallized at a certain temperature for a certain period of time to form a low-crystallinity MTT molecular sieve. At this time, the system not only contains a low-crystallinity MTT molecular sieve, but also contains silicon-aluminum amorphous substances, templates, and water. . After the aluminum source is added to this system, the MTT molecular sieve with low crystallinity acts as a seed crystal. During the crystallization process at a certain temperature, the added aluminum source is more likely to enter the molecular sieve under the action of the seed crystal. As a result, more aluminum enters into the molecular sieve framework, and after crystallization, MTT molecular sieves with low silicon-aluminum ratio are produced.

Compared with the MTT type molecular sieve synthesized by the prior art, the MTT type molecular sieve synthesis method of the present invention has the following characteristics:

(1) A new synthesis method for MTT molecular sieves with low silicon-aluminum ratio is provided.

(2) The prepared MTT molecular sieve has more acid content.

(3) The synthesis method is low in cost, only needs to be synthesized by using a commercial template, and is easy to operate and has strong economic efficiency.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but it should be pointed out that the content of the present invention is not limited thereto.

Comparative example 1

Weigh 11.9g of sodium hydroxide, 56.8g of dimethylamine (40% aqueous solution), 3.7g of aluminum sulfate, add 256g of water, and after fully stirring, add 100g of 30% silica sol to it, after stirring evenly, move the mixed solution into Put it into a polytetrafluoroethylene-lined stainless steel reaction kettle, put it in an oven at 175°C, crystallize for 4 days, cool to room temperature, wash with deionized water for 3 times, dry it in an oven at 120°C, and bake at 550°C for 12 hours. MTT molecular sieves were prepared. The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

Comparative example 2

Weigh 11.9g of sodium hydroxide, 56.8g of dimethylamine (40% aqueous solution), 11.1g of aluminum sulfate, add 256g of water, and after fully stirring, add 100g of 30% silica sol to it, after stirring evenly, move the mixed solution into Put it into a polytetrafluoroethylene-lined stainless steel reaction kettle, put it in an oven at 175°C, crystallize for 4 days, cool to room temperature, wash with deionized water for 3 times, dry it in an oven at 120°C, and bake at 550°C for 12 hours. Amorphous products were obtained, and MTT molecular sieves were not obtained. The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

Example 1

Weigh 11.9g of sodium hydroxide, 56.8g of dimethylamine (40% aqueous solution), 3.7g of aluminum sulfate, add 256g of water, and after fully stirring, add 100g of 30% silica sol to it, after stirring evenly, move the mixed solution into Put it into a polytetrafluoroethylene-lined stainless steel reaction kettle, put it in an oven at 170°C, keep it for 1 day, cool to room temperature and take it out, then add 7.4g of aluminum sulfate and 18g of water to it, stir the mixture evenly, and then transfer it to the In a polytetrafluoroethylene-lined stainless steel reaction kettle, heat up to 175°C and keep it for 2 days, then cool to room temperature, wash with deionized water for 3 times, dry in an oven at 120°C, and roast at 550°C for 12 hours to obtain MTT type Molecular sieve. The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

Example 2

Weigh 11.9g of sodium hydroxide, 35.6g of pyrrolidine, 3.7g of aluminum sulfate, add 256g of water, and after stirring fully, add 100g of 30% silica sol to it, after stirring evenly, transfer the mixed solution into polytetrafluoroethylene Put it into a lined stainless steel reaction kettle, put it in an oven at 170°C, keep it for 1 day, cool it to room temperature, take it out, add 9.6g of aluminum sulfate and 18g of water into it, stir it evenly, and then transfer the mixture to the Teflon liner In a stainless steel reaction kettle, the temperature was raised to 175 ° C for 2 days, cooled to room temperature, washed with deionized water for 3 times, dried in an oven at 120 ° C, and roasted at 550 ° C for 12 hours to obtain MTT molecular sieves. The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

Example 3

Weigh 11.9g of sodium hydroxide, 36.5g of N,N-dimethylformamide, 3.7g of aluminum sulfate, add 256g of water, stir well, add 100g of 30% silica sol to it, stir evenly, and mix Move it into a polytetrafluoroethylene-lined stainless steel reaction kettle, put it in an oven at 175°C, keep it for 10 hours, cool it to room temperature and take it out, then add 11.1g of aluminum sulfate and 18g of water to it, stir it evenly, and then move the mixture into the In a polytetrafluoroethylene-lined stainless steel reaction kettle, heat up to 175°C and keep it for 2 days, then cool to room temperature, wash with deionized water for 3 times, dry in an oven at 120°C, and roast at 550°C for 12 hours to obtain MTT type Molecular sieve. The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

Example 4

Weigh 11.9g of sodium hydroxide, 36.5g of N,N-dimethylformamide, 3.7g of aluminum sulfate, add 256g of water, stir well, add 100g of 30% silica sol to it, stir evenly, and mix Move it into a polytetrafluoroethylene-lined stainless steel reaction kettle, put it in an oven at 175°C, and keep it for 18 hours. After cooling to room temperature and taking it out, add 13g of aluminum sulfate and 18g of water to it, stir evenly, and then move the mixture into a polytetrafluoroethylene In a stainless steel reaction kettle lined with tetrafluoroethylene, the temperature was raised to 175°C and kept for 2 days, then cooled to room temperature, washed with deionized water for 3 times, dried in an oven at 120°C, and roasted at 550°C for 12 hours to obtain MTT molecular sieves. . The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

Example 5

Weigh 11.9g of sodium hydroxide, 36.5g of isobutylamine, 3.7g of aluminum sulfate, add 256g of water, and after fully stirring, add 100g of 30% silica sol to it, after stirring evenly, transfer the mixed solution into polytetrafluoroethylene Put it into a lined stainless steel reaction kettle, put it in an oven at 175°C, keep it for 30 hours, cool it to room temperature and take it out, then add 29.6g of aluminum sulfate and 36g of water into it, stir it evenly, and then transfer the mixture to the PTFE liner In a stainless steel reaction kettle, the temperature was raised to 175 ° C for 30 h, cooled to room temperature, washed with deionized water for 3 times, dried in an oven at 120 ° C, and roasted at 550 ° C for 12 h to obtain MTT molecular sieves. The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

Example 6

Weigh 11.9g of sodium hydroxide, 36.5g of n-butylamine, 3.7g of aluminum sulfate, add 256g of water, after fully stirring, add 100g of 30% silica sol to it, after stirring evenly, transfer the mixed solution into polytetrafluoroethylene In the lined stainless steel reaction kettle, put it in an oven at 170°C and keep it for 30 hours. After cooling to room temperature, take it out, then add 62.9g of aluminum sulfate and 36g of water into it, stir it evenly, and then transfer the mixture to the polytetrafluoroethylene lining In a stainless steel reaction kettle, the temperature was raised to 175 ° C for 2 days, cooled to room temperature, washed with deionized water for 3 times, dried in an oven at 120 ° C, and roasted at 550 ° C for 12 hours to obtain MTT molecular sieves. The Si/Al and acid content characterization results of the obtained MTT molecular sieves are summarized in Table 1.

The characterization results of molecular sieve crystal form, Si/Al and acid content obtained in Table 1 Comparative Examples and Examples

The low silicon-aluminum ratio MTT molecular sieve prepared by the invention has a Si/Al ratio as low as 5, has the characteristics of strong acidity and large acid content, and has potential applications in petroleum refining, petrochemical, coal chemical and other fields. The synthesis method provided by the invention has the advantages of low cost, safe and convenient operation, and environmental friendliness.

Claims (6)

1. a kind of synthetic method of low silicon-aluminum ratio MTT type molecular sieve is characterized in that: take organic amine as template agent, use silicon source, aluminum source and sodium hydroxide to synthesize low silicon-aluminum ratio MTT type molecular sieve; comprise the following steps: 1) Preparation of precursor mixture: mix silicon source, aluminum source, sodium hydroxide, organic amine, and water in a certain proportion, stir until uniform, and form precursor mixture A, in A, Al ₂ O ₃ :SiO ₂ :Na ₂ O : organic amine: H ₂ O molar ratio is 1:80-500:1-100:1-200:1000-8000; 2) Heat and crystallize the prepared precursor mixture A at 80°C-250°C for 5h-72h, then cool to room temperature to obtain mixture B; 3) Add a certain amount of aluminum source and water to mixture B, stir until uniform, and obtain mixture C, the molar ratio of Al ₂ O ₃ :SiO ₂ :Na ₂ O:organic amine:H ₂ O in C is 1:1- 60:1-100:1-200:100-4000; 4) Heat and crystallize the mixture C at 100°C-250°C for 5h-120h; 5) After the crystallization is completed, cool the mixture to room temperature, filter, wash and dry, and roast at 300°C-600°C for 5h-36h, and the obtained solid is MTT molecular sieve with low silicon-aluminum ratio; The silicon source in step 1) is one or more of silica sol, water glass, white carbon black, orthoethyl silicate; The aluminum source is one or more of aluminum isopropoxide, sodium metaaluminate, pseudoboehmite, aluminum sulfate, and aluminum nitrate; The organic amine is one or more of dimethylamine, N,N-dimethylformamide, pyrrolidine, n-propylamine, isopropylamine, n-butylamine, etc.; The silicon-aluminum ratio of the low-silicon-aluminum ratio MTT molecular sieve is 5-30. 2. according to the described synthetic method of claim 1, it is characterized in that: step 1) Al ₂ O ₃ : SiO ₂ : Na ₂ O: organic amine: H ₂ O molar ratio in the mixture A is 1:80-200:1 -50:1-100:3000-6000. 3. The synthesis method according to claim 1, characterized in that: step 2) the crystallization temperature of the mixture A is 100°C-200°C; the crystallization time is 10h-48h. 4. The synthesis method according to claim 1, characterized in that: step 3) in the mixture C, the molar ratio of _Al2O3 : _SiO2 :Na2O:organic amine: _H2O is ₁ :10-40: ₁ -30:1-50:200-2000. 5. The synthesis method according to claim 1, characterized in that: step 4) the crystallization temperature of the mixture C is 100°C-200°C; the crystallization time is 12h-100h. 6. The synthesis method according to claim 1, characterized in that: the calcination temperature in step 5) is 450°C-550°C; the calcination time is 6h-24h.