CN108793185A - A kind of preparation method of nano-ZSM-5 molecular sieve - Google Patents

Abstract

The invention belongs to the technical field of zeolite molecular sieve synthesis, and aims to provide a green and convenient nano ZSM-5 molecular sieve preparation method, in particular to a synthesis system by adding a high molecular polymer, a silicon source, an aluminum source, an organic structure-guided Stir the agent and deionized water evenly to form a sol-gel of molecular sieve synthesis precursor, then make the above-mentioned sol-gel into a dry gel, and then use the steam-assisted crystallization method to obtain the nano ZSM‑5 molecular sieve. The nano ZSM-5 molecular sieve prepared by this method has the characteristics of high crystallinity, adjustable grain size between 10-100nm, meso-microporous composite hierarchical pore structure, large specific surface area and the like. The preparation method of nanometer ZSM‑5 molecular sieve provided by the present invention not only avoids technical defects such as the difficulty of separating and collecting nanometer molecular sieves from mother liquor and discharges a large amount of synthetic waste liquid, but also improves the synthesis efficiency, and is a simple, efficient and environment-friendly synthesis method. The route has a certain industrial application prospect.

Description

A kind of preparation method of nano ZSM-5 molecular sieve

technical field

The invention relates to the technical field of synthesis of zeolite molecular sieves, in particular to provide a green and simple preparation method of nanometer ZSM-5 molecular sieves.

Background technique

ZSM-5 molecular sieve is a new type of crystalline aluminosilicate material successfully developed in 1972 by Mobile Oil Company of the United States. Due to its excellent channel shape selectivity, suitable acidity and good hydrothermal stability, it has gradually become one of the most important catalytic materials in the petroleum refining and chemical industry. However, because it only contains micropores, the mass transfer and diffusion capacity is limited, which not only cannot effectively catalyze the conversion of macromolecular raw materials, but also easily causes catalyst carbon deposition and deactivation. Compared with conventional micron ZSM-5 molecular sieves, the grain size of nano ZSM-5 molecular sieves is generally less than 100nm, which can significantly shorten the intracrystalline diffusion path, and also has a larger external specific surface area, high acid site accessibility and exposed pores The advantages of high mouth density make nano molecular sieves have higher reactivity and stability, and exhibit excellent catalytic performance.

For a long time, the preparation technology of nano molecular sieves has attracted much attention. Patent CN106698463A discloses a method for synthesizing nano ZSM-5 molecular sieves. The specific synthesis process is as follows: firstly, the organic template agent, silicon source, aluminum source, inorganic base and deionized water are mixed and stirred evenly to obtain a gel, and then the gel is mixed evenly with macroporous carbon, and the macroporous carbon is used to limit the growth of molecular sieve crystals. Nano ZSM-5 molecular sieves were prepared with a lower dosage of organic template. Patent CN1958453A discloses a preparation method for synthesizing small-grain ZSM-5 molecular sieves by using the seed crystal method, which specifically includes dissolving the silicon source in an acidic solution, and then sequentially adding a template agent and an aluminum source to the above-mentioned silicon source solution, and then adding A small amount of molecular sieve seeds are prepared by hydrothermal crystallization method to prepare small crystal molecular sieves. Patent CN101428818B discloses a method of interfering with the growth of crystal nuclei. Specifically, a structure-directing agent organic base isopropylamine is added to the ZSM-5 molecular sieve synthesis system to synthesize ZSM-23 molecular sieves. By increasing the amount of the above-mentioned isopropylamine Controlling it in a proper range can get nanometer ZSM-5 molecular sieve. Patent CN102745714A provides a method for preparing small-grain ZSM-5 molecular sieves. In the preparation process, the organosilicon source and the alcohol solvent are mixed uniformly to obtain an alcohol solution containing a silicon source, and then the template agent is dissolved in an aqueous solution of an inorganic alkali, and the aluminum source and the alcohol solution containing a silicon source are added to the template agent. In the alkaline solution, fully stir and mix to form an emulsion, and liquid crystallize the above emulsion to obtain a small-grain ZSM-5 molecular sieve. Patent CN101182004B discloses a synthetic method for preparing nano-molecular sieves by adding hydrocarbon component surfactants to the molecular sieve synthesis precursor solution to form a super-solubilization system of oil-in-melts and regulating the grain size of molecular sieves. Patent CN104192859A discloses a method for rapidly preparing small-grain ZSM-5 molecular sieves. In the preparation method, the prepared silicon-alumina mixed sol is placed under low temperature conditions for nucleation, and then crystallized at an elevated temperature to obtain a small-grain ZSM-5 molecular sieve.

It can be seen that although there are many synthesis techniques for nano ZSM-5 molecular sieves, most of them are induced to form nano ZSM-5 molecular sieves by adding molecular sieve seeds, organic structure directing agents and other substances in the synthesis system; Inorganic salts, organic alcohols or surfactants are added to the system to adjust the grain size of molecular sieves to prepare nano-molecular sieves; some synthesis techniques also fine-tune crystallization conditions and crystallization temperature, especially low-temperature crystallization induction to form nano-molecular sieves. However, the above-mentioned synthesis process often has technical defects such as complex process, low synthesis efficiency, difficult separation and collection of nano-molecular sieve products from the mother liquor, the need for a large amount of structure-directing agent, high synthesis cost, and the discharge of a large amount of synthetic waste liquid to pollute the environment. This greatly limits the industrial production and application of nano ZSM-5 molecular sieves. Therefore, it is very necessary and urgent to develop a green and simple synthesis route of nano-molecular sieves.

Contents of the invention

The invention provides a simple, efficient, environment-friendly and easy-to-industrial production method for overcoming the defects of difficult product separation and collection, low synthesis efficiency and environmental pollution in the existing nano ZSM-5 molecular sieve synthesis technology. The nano ZSM-5 molecular sieve prepared by the method has the characteristics of high crystallinity, meso-microporous composite hierarchical pore structure, large specific surface area, large micropore specific surface area and micropore volume, and the like.

The method for preparing nanometer ZSM-5 molecular sieves in the present invention is specifically, the initial synthetic sol-gel is prepared by adding a mixture formed by high molecular polymer, silicon source, aluminum source, organic structure directing agent and deionized water in the synthesis system, and then The above-mentioned sol-gel is made into a dry gel, and then the nanometer ZSM-5 molecular sieve is obtained by a steam-assisted crystallization method.

The present invention also provides a preparation method of the above-mentioned nano ZSM-5 molecular sieve, the specific synthesis steps are as follows:

(1) Dissolve a certain amount of polymer in deionized water, stir at room temperature for 2-12 hours, and prepare a uniform mixed solution A;

(2) Add a certain amount of silicon source and aluminum source in sequence, and stir in a water bath at 20-80°C for 0-24 hours to obtain a uniformly mixed solution B;

(3) In the stirring state, add the organic structure directing agent dropwise to the above mixed solution B, continue stirring in a water bath at 20-80°C for 0-24 hours, and fully age to obtain a sol-gel mixture, wherein the molar composition of the raw materials is as follows : 50～100SiO ₂ :0～2Al ₂ O ₃ :5～15SDA:0～5X:4000H ₂ O, wherein, X represents high molecular polymer, SDA represents organic structure directing agent;

(4) placing the above-mentioned initial sol-gel mixture in a constant temperature oven, and drying at 25-120° C. for 0-48 hours to obtain molecular sieve synthetic dry glue;

(5) Then transfer the above-mentioned molecular sieve synthetic dry glue to a polytetrafluoroethylene-lined stainless steel crystallization kettle, and use steam-assisted crystallization to prepare nano-molecular sieves, wherein the crystallization temperature is 100-200 ° C, and the crystallization time 8～72h;

(6) After the crystallization is completed, the obtained product is subjected to suction filtration, washing, and drying to obtain a solid product, that is, the original powder of nano ZSM-5 molecular sieve; Roasting at ℃ for 4-12 hours to remove the organic matter and obtain the nano ZSM-5 molecular sieve product.

The raw material used in the present invention is specifically preferably as follows:

In the above preparation method, the silicon source used can be one or two silicon source systems of glass, silicic acid, silica sol, fumed silica, white carbon black or tetraethyl orthosilicate; wherein, the silicon source is preferably Tetraethyl orthosilicate.

In the above-mentioned preparation method, the aluminum source adopted can be one or more mixtures in sodium aluminate, aluminum isopropoxide, aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydroxide, pseudo-boehmite; wherein , preferably the aluminum source is aluminum isopropoxide.

In the above preparation method, the high molecular polymer used may be one or more mixtures of polyvinylpyrrolidone, polyacrylamide, polystyrene, polyurethane, etc., wherein the high molecular polymer is preferably polyvinylpyrrolidone;

In the above-mentioned preparation method, the organic structure-directing agent SDA adopted can be one or more mixtures in tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, wherein, preferably the organic structure-directing agent SDA is tetrapropyl ammonium hydroxide;

Among the present invention, the preference of part processing conditions is as follows:

In the above preparation method, the drying temperature for drying the initial sol-gel mixture to prepare dry glue is preferably 80-100° C., and the drying time is preferably 12-24 hours;

In the above preparation method, during the crystallization process of the molecular sieve synthetic dry glue by steam-assisted crystallization, the crystallization temperature is preferably 120-180° C., and the crystallization time is preferably 4-72 hours.

Compared with the prior art, the present invention has the following beneficial effects.

(1) Polyvinylpyrrolidone is a cheap and easy-to-obtain commercial reagent, which is non-polluting to the environment, has a wide range of industrial uses, and is extremely soluble in water. The polyvinylpyrrolidone is easily removed by washing.

(2) The present invention adopts dry glue transformation method to prepare nanometer ZSM-5 molecular sieve, prepare dry glue by synthetic sol-gel of molecular sieve, then carry out crystal transformation through water vapor assisted crystallization, not only reduce solvent water in the crystallization kettle It occupies less space, and also has the advantages of mild preparation conditions, easy operation, high synthesis efficiency, almost no discharge of synthetic waste liquid, and is conducive to the separation of molecular sieve products and mother liquor. Exploring efficient and safe synthetic routes and products has certain industrial application value.

Description of drawings

In order to facilitate the understanding of those skilled in the art, the present invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 is the XRD spectrogram of the nanometer ZSM-5 molecular sieve sample that the embodiment of the present invention synthesizes;

Fig. 2 is the SEM figure of the nano ZSM-5 molecular sieve sample synthesized by the embodiment of the present invention 1;

Fig. 3 is the TEM figure of the nano ZSM-5 molecular sieve sample synthesized by the embodiment of the present invention 1;

Fig. 4 is the N of the nanometer ZSM-5 molecular sieve sample synthesized by the embodiment of the present invention ₁ Adsorption-desorption isotherm;

Fig. 5 is the SEM figure of the nano ZSM-5 molecular sieve sample synthesized by the embodiment of the present invention 2;

Fig. 6 is the SEM figure of the nano ZSM-5 molecular sieve sample synthesized by the embodiment of the present invention 3;

Fig. 7 is the SEM image of the nano ZSM-5 molecular sieve sample synthesized in Example 4 of the present invention.

Detailed ways

Example 1

The feature of the nano ZSM-5 molecular sieve prepared by the present invention is characterized by the following methods:

The phase structure and crystallinity of molecular sieves were characterized by powder X-ray diffraction (XRD).

The crystal morphology and size of molecular sieves can be observed intuitively by scanning electron microscope (SEM) and transmission electron microscope (TEM).

The nitrogen adsorption experiment was used to measure the surface area, isotherm adsorption curve and pore size distribution of the molecular sieve, and judge its pore structure.

A kind of preparation method of nanometer ZSM-5 molecular sieve, the high molecular polymer polyvinylpyrrolidone of 3.2g is dissolved in the deionized water of 40.0g, room temperature is stirred to fully dissolving, forms mixed solution A; Adds the aluminum source of 0.2g and 10.4g of silicon source, continue to stir at constant temperature until it is uniformly mixed to form solution B; then add 3.0g of structure directing agent dropwise to solution B to form a mixed solution, and stir and age the above mixed solution in a constant temperature water bath at 60°C for 24 hours to form a sol-gel Dry the above-mentioned sol-gel to obtain dry glue, transfer the ground dry glue to a crystallization kettle, use steam-assisted crystallization method to realize the molecular sieve crystallization process, crystallize at 180°C for 36h, and the obtained product is filtered and dried Dry to obtain molecular sieve powder. Put the original molecular sieve powder in a muffle furnace and roast at 550°C for 6 hours to remove organic matter, and obtain nanometer ZSM-5 molecular sieve.

As can be seen from Figures 1-4, it can be seen from the XRD spectrum that the prepared molecular sieve has a typical MFI framework structure, and the purity and crystallinity of the ZSM-5 molecular sieve sample are relatively high; Regular appearance, microspheres assembled by nanocrystals; from the TEM image, the grain size of nano ZSM-5 molecular sieve is about 10-20nm; from the hysteresis ring in the N ₂ - adsorption-desorption isotherm, it can be seen that the nano-ZSM-5 molecular sieve The sample has a certain amount of mesoporous structure.

Example 2

A preparation method of nanometer ZSM-5 molecular sieves, comprising: dissolving 1.6g of high molecular polymer polyvinylpyrrolidone in 40.0g of deionized water, stirring at room temperature until completely dissolved to form mixed solution A; adding 0.2g of aluminum source in turn and 10.4g of silicon source, continue to stir at constant temperature until they are uniformly mixed to form solution B; then add 3.0g of structure directing agent dropwise to solution B to form a mixed solution, and stir and age the above mixed solution in a constant temperature water bath at 60°C for 24 hours to form a sol-gel Glue; Dry the above-mentioned sol-gel to obtain dry glue, transfer the ground dry glue to a crystallization kettle, use steam-assisted crystallization to realize the molecular sieve crystallization process, crystallize at 180°C for 36h, and the obtained product is filtered, Dry to obtain the molecular sieve powder. Put the original molecular sieve powder in a muffle furnace and roast at 550°C for 6 hours to remove organic matter, and obtain nanometer ZSM-5 molecular sieve. As shown in Figure 5, the macroscopic morphology of the prepared nano-ZSM-5 molecular sieve sample is a grape-like aggregate formed by the self-assembly of many grains with a size of about 50 nm.

Example 3

A kind of preparation method of nanometer ZSM-5 molecular sieve: the polymer polyvinylpyrrolidone of 6.4g is dissolved in the deionized water of 40.0g, stirs at room temperature until completely dissolving, forms mixed solution A; Adds the aluminum source of 0.2g and 10.4g of silicon source, continue to stir at constant temperature until it is uniformly mixed to form solution B; then add 3.0g of structure directing agent dropwise to solution B to form a mixed solution, and stir and age the above mixed solution in a constant temperature water bath at 60°C for 24 hours to form a sol-gel Dry the above-mentioned sol-gel to obtain dry glue, transfer the ground dry glue to a crystallization kettle, use steam-assisted crystallization method to realize the molecular sieve crystallization process, crystallize at 180°C for 36h, and the obtained product is filtered and dried Dry to obtain molecular sieve powder. Put the original molecular sieve powder in a muffle furnace and roast at 550°C for 6 hours to remove organic matter, and obtain nano ZSM-5 molecular sieve; Ellipsoidal aggregates formed by the self-assembly of grains.

Example 4

A kind of preparation method of nanometer ZSM-5 molecular sieve, the high molecular polymer polyvinylpyrrolidone of 3.2g is dissolved in the deionized water of 40.0g, room temperature is stirred to fully dissolving, forms mixed solution A; Adds the aluminum source of 0.1g and 10.4g of silicon source, continue to stir at constant temperature until it is uniformly mixed to form solution B; then add 3.0g of structure directing agent dropwise to solution B to form a mixed solution, and stir and age the above mixed solution in a constant temperature water bath at 60°C for 24 hours to form a sol-gel Dry the above-mentioned sol-gel to obtain dry glue, transfer the ground dry glue to a crystallization kettle, use steam-assisted crystallization method to realize the molecular sieve crystallization process, crystallize at 180°C for 36h, and the obtained product is filtered and dried Dry to obtain molecular sieve powder. Put the raw molecular sieve powder in a muffle furnace and roast at 550°C for 6 hours to remove organic matter, and obtain sodium-type nano ZSM-5 molecular sieve. Put the original molecular sieve powder in a muffle furnace and roast at 550°C for 6 hours to remove organic matter, and obtain nanometer ZSM-5 molecular sieve. As shown in Figure 7, the macroscopic morphology of the prepared nano ZSM-5 molecular sieve sample is an irregular aggregate formed by the self-assembly of many crystal grains with a size of about 20-50 nm.

The preferred embodiments of the invention disclosed above are only to help illustrate the invention. The preferred embodiments are not exhaustive in all detail, nor are the inventions limited to specific embodiments described. Obviously, many modifications and variations can be made based on the contents of this specification. This description selects and specifically describes these embodiments in order to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The invention is to be limited only by the claims, along with their full scope and equivalents.

Claims (7)

1. a kind of preparation method of nano-ZSM-5 molecular sieve, which is characterized in that including following synthesis step：：

(1) high molecular polymer, silicon source, silicon source, Organic structure directing agent and deionized water are stirred well to uniformly mixed, shape At Zeolite synthesis collosol and gel, then above-mentioned collosol and gel is dried, dry glue is made；

(2) dry glue obtained above is fully ground, is transferred in the stainless steel crystallizing kettle of polytetrafluoroethyllining lining, is steamed using water Vapour auxiliary crystallization method, crystallization temperature is 100-200 DEG C, crystallization time 6-72h, after the completion of waiting for crystallization, detaches solid product, does Dry, roasting removing organic matter obtains nano-ZSM-5 molecular sieve.

2. a kind of preparation method of nano-ZSM-5 molecular sieve according to claim 1, which is characterized in that specifically include as Lower synthesis step：

(1) high molecular polymer is dissolved in deionized water, stirs 2~12h at room temperature, homogeneous mixture solotion A is made；

(2) a certain amount of silicon source and silicon source are sequentially added, 20~80 DEG C of constant temperature water baths stirrings 0~for 24 hours, obtain homogeneous mixture solotion B；

(3) under stirring, Organic structure directing agent is added dropwise into above-mentioned mixed solution B, continues in 20~80 DEG C of water Bath constant temperature stirring 0~for 24 hours, collosol and gel mixture is made in abundant aging, and wherein feed molar composition is as follows：50~ 100SiO₂:0~2Al₂O₃:5~15SDA:0~5X:4000H₂O, wherein X represents high molecular polymer, and SDA represents organic knot Structure directed agents；

(4) above-mentioned starting sol gel mixture is placed in constant temperature oven, dry 0~48h, is divided at 25~120 DEG C Son sieve synthesis dry glue；

(5) and then by above-mentioned Zeolite synthesis dry glue it is transferred in the stainless steel crystallizing kettle of polytetrafluoroethyllining lining, is steamed using water Vapour auxiliary crystallization method prepares nano molecular sieve, wherein crystallization temperature is 100~200 DEG C, and crystallization time is 8~72h；

(6) after the completion of waiting for crystallization, products obtained therefrom is filtered, is washed, dries and obtains solid product, is i.e. nano-ZSM-5 molecule Sieve original powder；Above-mentioned nano-ZSM-5 molecular sieve original powder is roasted to 4~8h in Muffle furnace, removing is therein to be had at 500~600 DEG C Machine object obtains nano-ZSM-5 molecular sieve product.

3. a kind of preparation method of nano-ZSM-5 molecular sieve according to claim 2, which is characterized in that in step (3) In, be made collosol and gel aging temperature be 20~80 DEG C, ageing time be 0~for 24 hours.

4. a kind of preparation method of nano-ZSM-5 molecular sieve according to claim 1, it is characterised in that：In step (1) In, the high molecular polymer be one kind in polyvinylpyrrolidone, polyacrylamide, polystyrene, polyurethane etc. or A variety of mixtures.

5. a kind of preparation method of nano-ZSM-5 molecular sieve according to claim 1, it is characterised in that：In step (1) In, the Organic structure directing agent is one kind in tetraethyl ammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide Or a variety of mixtures.

6. a kind of preparation method of nano-ZSM-5 molecular sieve according to claim 1, it is characterised in that：In step (1) Silicon source used in Zeolite synthesis is one kind or more in tetraethyl orthosilicate, aerosil, white carbon or Ludox Kind mixture；Silicon source used in Zeolite synthesis is aluminum sulfate, aluminum nitrate, sodium metaaluminate, boehmite, boehmite or different One or more mixtures in aluminium propoxide.

7. a kind of preparation method of nano-ZSM-5 molecular sieve according to claim 1, it is characterised in that：In step (2) In, the crystallization method for preparing nano-ZSM-5 molecular sieve is dry gel conversion method.