CN110357123A - A kind of high crystalline multi-stage porous nano X-type molecular sieve and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of synthesis of nano X-type molecular sieves, and specifically provides a highly crystalline multi-level porous nano X-type molecular sieve and a preparation method thereof. The preparation method is to uniformly mix N-methylpyrrolidone, alkali source, aluminum source and water in a certain proportion, then slowly add silicon source, stir evenly to form a uniform sol, and hydrothermally crystallize the sol at 25-85°C for 6- After 240 hours, the product was washed to neutrality, dried, and burned to obtain a highly crystalline hierarchically porous nano X-type molecular sieve. The present invention uses N-methylpyrrolidone as a structure-directing agent to prepare X-type molecular sieves. The particle size of the product is 20-200nm, the crystallinity is high, the dispersibility is good, and it has a multi-level pore structure. It can be used as an adsorbent, an ion exchanger, and a catalyst. And carriers, or as molecular sieve seeds are widely used.

Description

A kind of highly crystalline multi-level porous nano X-type molecular sieve and its preparation method

technical field

The invention belongs to the technical field of synthesis of nanometer X-type molecular sieves, in particular to a highly crystalline multi-level porous nanometer X-type molecular sieve and a preparation method thereof.

Background technique

X-type molecular sieve (FAU) is a rigid three-dimensional framework structure composed of silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron (skeleton Si/Al ratio close to 1) connected by shared oxygen atoms. Its micropore diameter is about 0.7nm, with moderate It is acidic and has good ion exchange capacity, and has strong adsorption capacity for water and small molecule gases, and is widely used in petrochemical and other fields. However, the long micropores of traditional micron-sized molecular sieves are not conducive to the rapid transport of macromolecules, and easily cause diffusion limitation problems. The nano-processing of molecular sieve can greatly improve the catalytic reaction activity and stability, and improve the utilization rate of zeolite. This is mainly due to the large specific surface area of nano molecular sieve materials, which can expose more active sites. Therefore, it is necessary to design and construct functionally oriented nano-molecular sieve materials. The preparation of conventional nano-X molecular sieves requires the use of organic templates or synthetic systems involving high alkalinity. On the one hand, it will increase the synthesis cost of materials, and on the other hand, it limits the range of the skeleton silicon-aluminum ratio of the obtained nano-X molecular sieves. For example, Zhu Guangshan et al. (CN200510016886.X) synthesized LTA and FAU molecular sieve nanoscale crystals using tetramethylammonium hydroxide (TMAOH) as a template. The disadvantage of this method is that the expensive organic template agent TMAOH is used, which is corrosive Large, and a large amount of polluting and toxic gases will be produced when the template is calcined to remove it. Reza Fazaeli et al. synthesized nano X zeolite molecular sieves (J.Phys.Theor.Chem.IAU Iran, 2011, 8(3) 245-249) by adjusting the reaction conditions in an inorganic system, but the obtained nano zeolites were severely agglomerated, and The degree of crystallinity is not high. Hussein Awala et al. (NatureMaterials, 2015, 14, 447-451) synthesized monodisperse nanometer FAU zeolite under the condition of no organic template. The zeolite micropore crystallinity is low, and aluminum powder is used as aluminum source. A large amount of heat and hydrogen are generated in the liquid process, and the feeding process is complicated and slow, which is not conducive to large-scale industrial production.

Aiming at the problems and defects in the above-mentioned prior art, the present invention provides a method for preparing a novel structure-directing agent N-methylpyrrolidone to prepare a high-crystallinity hierarchical porous nano-X molecular sieve, which aims to reduce the manufacturing cost of the material and energy consumption, provide a new method for synthesizing hierarchically porous nano-X molecular sieves, and broaden the synthesis and application of nano-molecular sieves.

Contents of the invention

The main purpose of the present invention is to provide a highly crystalline hierarchically porous nano X-type molecular sieve and its preparation method, which can effectively solve the problems in the background technology.

In order to achieve the above object, the technical scheme that the present invention takes is:

A preparation method of highly crystalline hierarchical porous nano X-type molecular sieve, the preparation method comprises the following steps:

Step 1: Add a certain amount of alkali source and aluminum source into deionized water, and stir until completely dissolved;

Step 2: Add a certain amount of N-methylpyrrolidone into the solution in Step 1, stir and mix evenly to obtain Solution A;

Step 3: under the condition of strong stirring of solution A, slowly add the silicon source and keep stirring to obtain sol B;

Step 4: Transfer Sol B to a reaction vessel, and crystallize at 25-85°C for 6-240 hours;

Step 5: After the reaction is completed, the solid product is subjected to solid-liquid separation, washing, drying, and high-temperature calcination to obtain a highly crystalline multi-level porous nano X-type molecular sieve.

Preferably, the alkali source is an inorganic alkali source, based on the amount of theoretically generated _M2O , the aluminum source is based on the theoretically generated amount of _Al2O3 , the silicon source is based on the theoretically generated amount of _SiO2 , and N _- methylpyrrolidone NMP for short, the molar ratio of each component in the sol B is M ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O:NMP=1.0-15:1.0:1.8-15:40-450:0.6-13.8 , M represents an alkali metal.

Preferably, the alkali source is one or more of sodium hydroxide, sodium oxide, sodium carbonate;

The aluminum source is one of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, pseudoboehmite, aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum powder, aluminum isopropoxide, aluminum acetate or Various.

Preferably, the silicon source is one or more of water glass, white carbon black, sodium silicate, silica sol, tetraethyl orthosilicate, silica gel, and diatomaceous earth.

Preferably, stir vigorously, and the number of revolutions is 400-1500 revolutions per minute.

Preferably, the slow addition rate of the silicon source is 0.001 mol/min˜5 mol/min.

Preferably, the reaction vessel is a closed polytetrafluoroethylene reaction kettle or a glass flask.

Preferably, the heating device used under the condition of 25-85°C is one or more of oven, oil bath, water bath, sand bath, electric heating mantle, microwave oven, and the crystallization condition is standing or 200-1000 rpm min stir.

Preferably, the heating rate of the high-temperature calcination is 0.2-5°C min ^-1 , the temperature is raised to 300-700°C, and the calcination is 0.5-48h.

And, a highly crystalline hierarchically porous nano X-type molecular sieve, the highly crystalline hierarchically porous nano X-type molecular sieve has a mesoporous structure, a particle size of (20-200)nm, and a specific surface area of not less than 420m ² g ^{- 1.} The external area is not less than 50m ² g ^-1 ; the silicon-aluminum ratio is 0.9-1.6.

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

(1) The present invention uses cheap small-molecular organic matter (N-methylpyrrolidone) as a structure-directing agent to synthesize highly crystalline multi-level nano-X molecular sieves. Large-scale production and application are realized, and the prepared highly crystalline multi-level nano X-type molecular sieve has the characteristics of high crystallinity, small product particle size, large specific surface area, and a multi-level pore structure.

(2) The X-type molecular sieve prepared by the present invention has a particle size between 20 and 200nm, and the product has a small particle size, good monodispersity, high crystallinity, large specific surface area, and has a multi-level pore structure characteristic. There are potential application prospects in the fields of chemical industry, energy and electronics.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings without making creative efforts.

Fig. 1 is the X-ray diffraction pattern (XRD) of the highly crystalline multi-level porous nano-X molecular sieve prepared in Example 1 of the present invention;

Fig. 2 is the scanning electron micrograph (SEM) of the highly crystalline hierarchically porous nano X-type molecular sieve prepared in Example 1 of the present invention;

Fig. 3 is the transmission electron micrograph (TEM) of the high crystallinity hierarchical porous nano-X type molecular sieve prepared by the embodiment of the present invention 1;

Fig. ₄ is the N adsorption/desorption isotherm curve of the highly crystalline multi-stage porous nano X-type molecular sieve prepared in Example 1 of the present invention;

Fig. 5 is the BJH pore size distribution diagram of the highly crystalline multi-stage porous nano X-type molecular sieve prepared in Example 1 of the present invention;

Fig. 6 is an X-ray diffraction pattern (XRD) of the highly crystalline hierarchically porous nano X-type molecular sieve prepared in Example 2 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Example 1

(1) Add 0.5g of sodium hydroxide and 1.2g of sodium aluminate into 6.7g of deionized water, and stir until a clear solution;

(2) Add 3g of N-methylpyrrolidone (NMP) to the step (1) solution;

(3) Under the rapid stirring of the solution in step (2) (rotating speed is 500 rpm), slowly drop (0.005mol min ^-1 , calculated as SiO ₂ ) 3.88g water glass (wherein the content of active ingredient is SiO ₂ 27.13wt%, Na ₂ O 8.74wt%), and continued stirring for 3h to obtain a homogeneous sol;

(4) Put the sol obtained in step (3) into a stainless steel reaction kettle lined with polytetrafluoroethylene, crystallize at a constant temperature of 75°C for 60 hours, and the molar ratio of each component in the reaction precursor is Na ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O:NMP＝1.43:1.0:2.4:70.2:4.1;

(5) After the crystallization is completed, the solid product is centrifuged and washed until neutral, dried in a blast oven at 50°C for 24h, and calcined at a constant temperature of 400°C in air for 5h (the heating rate is 1°C min ^-1 ), to obtain Nano X molecular sieve.

The sample prepared in Example 1 (hereinafter referred to as Nano-X) was characterized and analyzed.

The phase characterization of Nano-X samples was carried out by X-ray diffractometer. The results are shown in Figure 1. The XRD spectrum of the Nano-X sample is completely consistent with the characteristic peaks of the standard X-type molecular sieve, indicating that the synthesized Nano-X sample is an X-type molecular sieve.

The Si/Al ratio of the Nano-X sample was analyzed by X-ray fluorescence spectroscopy to be 1.5.

The morphology of Nano-X samples was characterized by scanning electron microscopy. As shown in Figure 2, the shape of the Nano-X sample has a particle size of about 50-100 nm, and the particle size distribution is uniform, indicating that the synthesized sample is nanoscale. Transmission electron microscopy (Figure 3) further confirmed the particle size of the synthesized Nano-X samples. There are a large number of mesopores between the Nano-X nanoparticles, which will facilitate the rapid transport of catalytic macromolecular substances.

The pore structure analysis of Nano-X samples was carried out by _N2 adsorption-desorption analyzer. As shown in Fig. 4, the _N2 adsorption-desorption isotherm shows a typical IV-type adsorption isotherm, indicating that Nano-X has a hierarchical porous structure, which is consistent with the TEM analysis results. Through calculation, its BET specific surface area is 704m ² g ^-1 , and its external area is 89m ² g ^-1 . The micropore diameter of Nano-X is 0.56nm, and the mesopore diameter distribution diagram is shown in Figure 5. The mesopore diameter is between 4.9nm and 16nm, concentrated around 8.9nm.

Example 2

(1) Add 0.5g of sodium hydroxide and 1.2g of sodium aluminate into 6.7g of deionized water, and stir until a clear solution;

(2) Add 4g of N-methylpyrrolidone (NMP) to the step (1) solution;

(3) Under strong stirring of the solution in step (2) (rotating speed is 500 rpm), slowly dropwise (0.005mol min ^-1 , calculated as SiO ₂ ) 3.88g of water glass (wherein the active ingredient content is SiO ₂ 27.13wt%, Na ₂ O 8.74wt%), and continued stirring for 3h to obtain a homogeneous sol;

(4) Put the sol obtained in step (3) into a hydrothermal reaction kettle, crystallize at a constant temperature of 75°C for 60 hours, and the molar ratio of each component in the reaction precursor is Na ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O:NMP＝1.43:1.0:2.4:70.2:5.5;

(5) After the crystallization is completed, the solid product is centrifuged and washed until neutral, dried in a blast oven at 50°C for 24h, and calcined at a constant temperature of 400°C in air for 5h (the heating rate is 1°C min ^-1 ), to obtain Nano X molecular sieve.

The X-ray diffraction (XRD) of the sample is shown in Figure 6, which shows that the synthesized sample is a pure phase of X-type molecular sieve. The particle size is about 70nm. Using X-ray fluorescence spectroscopic analysis, the Si/Al ratio of the sample was 1.51. The N ₂ adsorption-desorption isotherm curve is similar to that in Figure 4, and the BET specific surface area is calculated to be 588m ² g ^-1 , and the external surface area is 116m ² g ^-1 .

Example 3

(1) Add 0.5g of sodium hydroxide and 1.2g of sodium aluminate into 6.7g of deionized water, and stir until a clear solution;

(2) Slowly add 2g of N-methylpyrrolidone (NMP) to the step (1) solution;

(3) Under strong stirring of the solution in step (2) (rotating speed is 500 rpm), slowly drop (0.007mol min ^-1 , calculated as SiO ₂ ) 3.88g of water glass (wherein the content of active ingredient is SiO ₂ 27.13 wt%, Na ₂ O 8.74wt%), and continued to stir for 4h to obtain a homogeneous sol, which was left to stand for 24h;

(4) Put the sol obtained in step (3) into a hydrothermal reaction kettle, crystallize at a constant temperature of 70°C for 24 hours, and the molar ratio of each component in the reaction precursor is Na ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O:NMP＝1.43:1.0:2.4:70.2:2.8;

(5) After the crystallization is completed, the solid product is centrifuged and washed until neutral, dried in a blast oven at 50°C for 24h, and calcined at a constant temperature of 400°C in air for 5h (the heating rate is 1°C min ^-1 ), to obtain Nano X molecular sieve.

The X-ray diffraction pattern of the sample is basically the same as that in Figure 1, and the particle size is about 90nm. Its BET specific surface area is 597m ² g ^-1 , and its outer surface area is 50m ² g ^-1 .

Example 4

(1) Add 2.67g of sodium hydroxide and 1.21g of sodium aluminate into 25g of deionized water, and stir until a clear solution;

(2) Add 4g of N-methylpyrrolidone (NMP) to the solution of step (1), and put it into an ice bath immediately;

(3) Slowly add 1.715g of white carbon black (0.008mol min ^-1 ) to the solution in step (2) under the conditions of 0°C ice bath and rapid stirring (rotation speed: 600 rpm), and continue to mix in the ice bath Stir for 2h to obtain a homogeneous sol, and let stand for 24h;

(4) Put the sol obtained in step (3) into a hydrothermal reaction kettle, and crystallize at a constant temperature of 60°C for 48 hours, wherein the molar ratio of each component in the reaction precursor is Na ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O:NMP＝4.52:1.0:3.87:188:5.46;

(5) After the crystallization is completed, the solid product is centrifuged and washed until neutral, dried in a blast oven at 50°C for 24h, and calcined at a constant temperature of 400°C in air for 5h (the heating rate is 1°C min ^-1 ), to obtain Nano X molecular sieve.

The X-ray diffraction pattern of the sample is basically the same as that in Figure 1, the particle size distribution is between 100 and 200nm, the BET specific surface area is 497m ² g ^-1 , and the external surface area is 116m ² g ^-1 .

Example 5

(1) Add 2.67g of sodium hydroxide and 1.21g of sodium aluminate into 25g of deionized water, and stir until a clear solution;

(2) Add 3g of N-methylpyrrolidone (NMP) to the solution of step (1), and put it into an ice bath immediately;

(3) Slowly add 1.715g of white carbon black (0.005mol min ^-1 ) to the solution in step (2) under the conditions of 0°C ice bath and rapid stirring (speed: 600 rpm), and continue stirring in the ice bath 2h, to obtain a homogeneous sol, let stand for 24h;

(4) Put the sol obtained in step (3) into a round-bottomed flask with a condenser, crystallize at a constant temperature of 80°C for 36h, and the molar ratio of each component in the reaction precursor is Na ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O:NMP＝4.52:1.0:3.87:188:5.46;

(5) After the crystallization is completed, the solid product is centrifuged and washed until neutral, dried in a blast oven at 50°C for 24h, and calcined at a constant temperature of 400°C in air for 5h (the heating rate is 1°C min ^-1 ), to obtain Nano X molecular sieve.

The X-ray diffraction pattern of the sample is basically the same as that in Figure 1, the particle size is about 100nm, the BET specific surface area is 452m ² g ^-1 , and the external area is 100m ² g ^-1 .

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (10)

1. a preparation method of highly crystalline multi-stage porous nanometer X-type molecular sieve, is characterized in that, the preparation method comprises the steps: Step 1: Add a certain amount of alkali source and aluminum source into deionized water, stir until completely dissolved; Step 2: Add a certain amount of N-methylpyrrolidone into the solution in Step 1, stir and mix evenly to obtain Solution A; Step 3: Under the condition of strong stirring, the solution A is slowly added with the silicon source, and the stirring is continued to obtain the sol B; Step 4: Put sol B into a reaction vessel, and crystallize at 25-85°C for 6-240 hours; Step 5: After the reaction is completed, the solid product is subjected to solid-liquid separation, washing, drying, and high-temperature calcination to obtain a highly crystalline nano-hierarchical X-type molecular sieve. 2. The preparation method as claimed in claim ₁ , characterized in that, the alkali source is an inorganic alkali source, according to the theoretically generated _M2O amount, the aluminum source according to the theoretically generated _Al2O3 amount, and the silicon source According to the amount of theoretically generated SiO ₂ , N-methylpyrrolidone is referred to as NMP, and the molar ratio of each component in the sol B is M ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O:NMP=1.0-15: 1.0:1.8-15:40-450:0.6-13.8, M represents alkali metal. 3. preparation method as claimed in claim 1, is characterized in that, described alkali source is one or more in sodium hydroxide, sodium oxide, sodium carbonate; The aluminum source is one of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, pseudoboehmite, aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum powder, aluminum isopropoxide, aluminum acetate or Various. 4. preparation method as claimed in claim 1 is characterized in that, described silicon source is a kind of in water glass, white carbon black, sodium silicate, silica sol, tetraethyl orthosilicate, silica gel, diatomite or more. 5. The preparation method according to claim 1, characterized in that, in step 3, the stirring rotation speed of the vigorous stirring is 400-1500 rpm. 6. The preparation method according to claim 1, characterized in that, in step 3, the rate of slowly adding silicon source is 0.001 mol/min˜5 mol/min. 7. The preparation method according to claim 1, wherein in step 4, the reaction vessel is one or more of a closed polytetrafluoroethylene reactor and a glass flask. 8. The preparation method according to claim 1, characterized in that, in step 4, the heating device used under the condition of 25-85°C is one of oven, oil bath, water bath, sand bath, electric heating mantle, microwave oven or Various, the crystallization condition is standing still or stirring at 200-1000 rpm. 9. The preparation method according to claim 1, characterized in that, the heating rate of the high-temperature calcination is 0.2-5°C min ^-1 , the temperature is raised to 300-700°C, and the calcination is 0.5-48h. 10. A highly crystalline multi-level porous nano X-type molecular sieve, characterized in that the highly crystalline multi-level porous nano-X type molecular sieve has a mesoporous structure with a particle size of (20-200) nm and a specific surface area of not less than 420m ² g ^-1 , the outer surface area is not less than 50m ² g ^-1 ; the silicon-aluminum ratio is 0.9-1.6.