CN101318107B - Preparation method for pure silicon beta molecular sieve film - Google Patents

Abstract

The invention pertains to the preparation field of pure silicon beta molecule sieve membrane, which in particular relates to a method for preparing highly-oriented beta molecule sieve membrane using dealuminized beta molecule sieve seeds on a plurality of carriers. The seeded carriers are prepared on a pre-treated carrier with a ratio of 2-6 mol NaOH: 10-50 mol white carbon: 2-15 mol tetraethyl ammonium hydroxide, 0.2-2 mol NAAlO2: 100-500 mol H2O, and then the molecule sieve membrane is prepared on the seeded carriers with a ratio of 0.1-10mol tetraethyl ammonium hydroxide: 0.1-10mol hydrofluoric acid: 0.05-5mol hydrofluoric acid: 0.5-50mol H2O. Suitable carriers include monocrystalline silicon wafer, glass flake, stainless steel coupons, stainless steel meshes and ceramic sheet. The membrane is continuous and compact with better repeatability, and applicable to industrial scale-up.

Description

A kind of preparation method of pure silicon beta molecular sieve membrane

technical field

The invention belongs to the field of preparation of pure silicon beta molecular sieve membranes, in particular to the preparation of highly oriented beta molecular sieves by secondary growth in a TEAOH-HF-SiO ₂ -H ₂ O gel system using dealuminated beta molecular sieve seeds on various supports membrane method.

Background technique

In recent years, more and more attention has been paid to the synthesis of molecular sieve membranes integrating catalysis and separation. Higher requirements are put forward for the quality of molecular sieve membranes used in membrane reactors, membrane selective sensors, photoelectric materials, etc., including thinness, density (no voids), and directionality. In particular, improving the orientation of the molecular sieve membrane has an important influence on the smoothness and transparency of the surface of the molecular sieve membrane. This is of great significance to the application of molecular sieve membranes in optics, photocatalysis, and devices. Recently, high-performance molecular sieve membranes have also been applied to low dielectric constant materials and anti-corrosion materials. Low dielectric materials are of great significance to overcome crosstalk and propagation delays that often occur on electronic microprocessors. The application of molecular sieve membranes in anti-corrosion materials has a good application prospect in military industry and so on. Therefore, synthesizing high-silicon continuous molecular sieve membranes, reducing the thickness of the membrane, especially increasing the order and uniformity of the membrane and improving the orientation of crystals in the membrane have become the focus of molecular sieve membrane synthesis.

The main steps of synthesis of molecular sieve membrane include: (1) treatment and preparation of carrier; (2) reaction of carrier and reaction liquid to form membrane under certain conditions. The synthesis of molecular sieve membrane mainly includes direct method and indirect method. The direct method refers to immersing the carrier in the reaction solution and reacting to form a film under certain conditions; the indirect method refers to firstly introducing a layer of uniformly dispersed molecular sieve seeds on the surface of the carrier, and then hydrothermally synthesizing the molecular sieve membrane, which is usually called a secondary method. growth method. The most direct and simplest method for molecular sieves is the direct method, which is also the most commonly used synthesis method at present. However, the molecular sieve synthesized by the direct method largely depends on the type of carrier and molecular sieve membrane, and it is difficult to obtain a defect-free and continuous molecular sieve membrane, so it lacks industrial application value. The most significant advantage of the secondary growth method is that it separates the nucleation and growth processes, inhibits the transformation of crystal nuclei into other crystals, and improves the purity of the molecular sieve membrane. In addition, the secondary growth method can shorten the nucleation and crystallization time and improve the crystallinity. In order to realize the industrial scale-up of molecular sieve membranes, in addition to selecting a suitable synthesis method, the influence of factors such as carrier and synthesis solution must also be considered. For example, in order to synthesize thin and dense molecular sieve membranes, the better choice is the gel system. The viscosity of the gel system is relatively large, and the capillary suction during the synthesis process is small, which greatly reduces the crystallization of the inner seed crystal. In contrast, gel systems have advantages over clear synthetic fluids.

Beta molecular sieve membranes have potential applications in separation and catalytic membrane reactors due to their unique pore structure and catalytic performance. However, there are very few studies on beta molecular sieve membranes, and most of the studies on molecular sieve membranes are concentrated on the molecular sieve membranes with small and medium pores. As a beta molecular sieve with a high silicon-aluminum ratio and large pores, it has advantages that molecular sieves with small and medium pores do not have in being used as low-dielectric materials, anti-corrosion materials and optical main materials. Beta molecular sieve membranes are traditionally synthesized mainly in a silica-alumina solution system. The advantage of the beta molecular sieve membrane synthesized under this system is that the crystal grains are relatively uniform; the disadvantage is that there is no good intergrowth between the crystal grains and no orientation. In recent years, scientists at home and abroad have conducted extensive and in-depth research on the synthesis of beta molecular sieve membranes in the neutral gel system in the presence of hydrofluoric acid. The beta molecular sieve synthesized under this system has fewer defects in the membrane channel, so the hydrophobicity and thermal stability are greatly improved. But longer synthesis time, non-oriented surface, and thicker membrane section still limit the application value of beta molecular sieve membrane in industry. If the performance of the molecular sieve membrane can be improved under the premise of secondary growth and synthesis of the beta molecular sieve membrane in the neutral gel system, it will undoubtedly be beneficial to realize the industrial application of the beta molecular sieve membrane. On this basis, expanding the selection range of the carrier will be Further expand the application range of beta molecular sieve membrane.

Contents of the invention

The purpose of the present invention is to provide a rapid preparation method of pure silicon, dense and continuous beta molecular sieve membrane. The beta molecular sieve membrane synthesized by the present invention is applicable to a wide range of carriers, easy to operate, fast in synthesis speed, high in repeatability and excellent in performance, suitable for Industrial magnification.

Specific steps are as follows:

a) Pretreatment of carriers: firstly, various carriers (single crystal silicon slices, glass flakes, stainless steel flakes, stainless steel nets, and ceramic flakes) are washed and pretreated respectively. Put monocrystalline silicon slices, glass slices, stainless steel slices, and stainless steel mesh (200-400 mesh) into a mixed solution of 2-10 ml of isopropanol, 5-20 ml of ethanol, 5-20 ml of distilled water and 0.2-1 g of hydrochloric acid , ultrasonic power of 100-300 watts for 5-20 minutes, rinse with distilled water after taking it out, and dry; polish the ceramic sheet on fine sandpaper (400-800 mesh), and then ultrasonically clean it in distilled water with a power of 100-300 watts for 5-20 minutes. After 20 minutes, take it out, rinse it with distilled water, and dry it;

b) Preparation of beta molecular sieve seed solution: 2-6mol NaOH: 10-50mol white carbon black: 2-15mol tetraethylammonium hydroxide (TEAOH): 0.2-2mol NaAlO ₂ : 100-500mol H ₂ O ratio , mix and stir all raw materials until uniform, then crystallize at 80-140°C for 6-14 days, centrifuge, wash and dry to obtain nano-beta molecular sieve seed crystal powder, and then dealuminate the nano-beta molecular sieve seed crystal powder , the dealuminated seed crystal powder after dealumination treatment is made into a 10-30 g/L nanocrystal seed crystal solution with distilled water, and ammonia water is added to adjust the pH value to 9-11;

Dealumination of nano-beta zeolite seed crystals: According to the ratio of 1-5 grams of nano-beta seed crystal powder to 20-120 grams of 60% concentrated nitric acid, reflux in an oil bath at 60-120 ° C for 5-48 hours, and the product is passed through distilled water repeatedly Wash by centrifugation until neutral, then dry;

c) Preparation of seeded carriers: two different methods were used to prepare seeded carriers for different processed carriers. Immerse monocrystalline silicon wafers, glass wafers, and stainless steel wafers in 0.2% to 10% polydiallyldimethylamine hydrochloride (PDDA) solution for 5 to 20 minutes, and then put them into the dealuminated seed crystal solution to absorb crystals. Seed for 5-20 minutes, then rinse the carrier after adsorbing the seed crystal in distilled water, dry at room temperature, and form a seed crystal layer with a thickness of 0.2-0.5 microns; 2-5 drops of dealuminated seed crystal solution are dripped onto the stainless steel mesh and ceramic sheet carrier, and finally dried in a 500-700W electric furnace, and the thickness of the formed seed crystal layer is 10-30 microns;

d) Preparation of molecular sieve membrane mother liquor: 0.1-10 mol tetraethylammonium hydroxide (TEAOH): 0.1-10 mol tetraethyl orthosilicate (TEOS): 0.05-5 mol hydrofluoric acid (HF): 0.5-50 mol H ₂ O The ratio of each raw material is mixed and stirred until uniform;

e) Preparation of molecular sieve membrane: put the seed crystal carrier and the mother liquor of the molecular sieve membrane together in a reaction kettle for crystallization at 140-170°C for 2-5 days, then wash and dry; finally wash and dry the beta molecular sieve membrane in Calcination in a tube furnace at 500-700°C for 8-12 hours, and finally form a film with a thickness of 1-3 microns on a single crystal silicon wafer, glass wafer, and stainless steel wafer carrier, and on a stainless steel mesh and ceramic wafer carrier The thickness of the formed film is 12-32 micrometers.

Among them, the molecular sieve membrane mother liquor prepared with 0.3-0.8mol TEAOH, 0.5-5mol TEOS, 0.2-2mol HF, and 2-10molH ₂ O has the best quality of beta molecular sieve membrane.

The centrifugation described in the above steps is to centrifuge the dealuminated beta nanocrystal solution on a centrifuge to obtain a uniform nanocrystal solution, which is first centrifuged at 3000 to 5000 rpm for 5 to 20 minutes to remove the lower layer. For large-particle nanocrystals, centrifuge at 8,000 to 10,000 rpm for 10 to 30 minutes to remove the supernatant and retain the solid below;

Water washing is to pour off the upper layer solution after centrifugation, then add distilled water, repeat 3 to 5 times;

Drying is to dry the centrifuged solid seed crystal powder in an oven at 70-80°C.

Said water in the above-mentioned method all refers to distilled water.

The beta molecular sieve membrane synthesized by the invention is tested by X-ray diffraction and scanning electron microscope photos, showing that no miscellaneous crystals are formed, and a layer of dense and continuous membrane is formed on the surface of the membrane.

The beta molecular sieve membrane synthesized by the present invention is tested by an inductively coupled plasma atomic emission spectrometer (ICP-AES) and shows that when the dealuminated beta molecular sieve seed crystal is used, the Si/Al ratio of the generated beta molecular sieve membrane reaches 5014.3.

By adopting the beta molecular sieve membrane synthesized by the present invention, the synthesis period is relatively short, only about two days.

The beta molecular sieve membrane synthesized by the invention is relatively thin, continuous and dense on various supports such as single crystal silicon sheet, glass sheet, stainless steel sheet, etc., has good repeatability, and is suitable for industrial amplification.

Description of drawings

Fig. 1: the scanning electron micrograph picture of the front and side of the beta molecular sieve membrane on the surface of the single crystal silicon wafer carrier prepared in Example 1;

Fig. 2: the scanning electron micrograph figure and the X-ray diffraction figure of the beta molecular sieve membrane front side of the single crystal silicon chip carrier surface prepared in embodiment 2;

Fig. 3: the scanning electron micrograph figure and the X-ray diffraction figure of the beta molecular sieve film front side of the single crystal silicon wafer carrier surface prepared in embodiment 3;

Fig. 4: the scanning electron micrograph figure of the beta molecular sieve membrane front and side of the glass flake carrier surface that embodiment 4 prepares;

Fig. 5: the scanning electron micrograph figure and the X-ray diffraction figure of the beta molecular sieve membrane front side of the glass flake carrier surface prepared in embodiment 5;

Fig. 6: the scanning electron micrograph figure of the beta molecular sieve membrane front and side of the surface of the stainless steel sheet carrier prepared in embodiment 6;

Fig. 7: the scanning electron micrograph figure and the X-ray diffraction figure of the beta molecular sieve membrane front surface of the stainless steel sheet carrier surface prepared in embodiment 7;

Fig. 8: the scanning electron micrograph figure of the beta molecular sieve membrane front and side of the surface of the stainless steel net carrier prepared in embodiment 8;

Fig. 9: the scanning electron micrograph picture and the X-ray diffraction picture of the beta molecular sieve membrane front side of the surface of the stainless steel net carrier prepared in embodiment 9;

Fig. 10: the scanning electron micrograph figure of the beta molecular sieve membrane front and side of the surface of the ceramic sheet carrier prepared in embodiment 10;

Figure 11: Scanning electron micrographs and X-ray diffraction images of the front surface of the beta molecular sieve membrane on the surface of the ceramic sheet carrier prepared in Example 11.

As shown in Figure 1, it can be seen that the symbiosis between crystals is very good, the surface is dense and flat, and the thickness of the film is 2.0 microns;

As shown in Figure 2, it can be seen from the scanning electron microscope photo that the crystal intergrowth is very good, the surface of the film is dense and smooth, and the characteristic peak of the (101) crystal plane of beta at 7.88 degrees appears in the X-ray diffraction pattern, which shows that the synthesis The product is indeed the desired product, and the peak intensity is very high, which proves that the crystallinity is good.

As shown in Figure 3, it can be seen from the scanning electron microscope that the symbiosis between the crystals is still very good. Although the film is still very dense, the surface is not smooth, and the characteristic peak of the (101) crystal plane of beta appears in the X-ray diffraction diagram. It can be seen from the figure The synthetic product is indeed the desired product, and the peak intensity is still high, and the crystallinity is better;

As shown in Figure 4, it can be seen that the symbiosis between crystals is very good, the surface is dense and smooth, and the thickness of the film is 2.3 microns. The (101) crystal plane characteristic peak of beta appeared in the X-ray diffraction diagram, and it can be seen from the figure that the synthesized product is indeed the desired product, and the peak intensity is still very high, and the crystallinity is better;

As shown in Figure 5, it can be seen that the symbiosis between crystals is better, the surface is denser and smoother, the characteristic peak of beta appears in the X-ray diffraction pattern, and the crystallinity is poor;

As shown in Figure 6, it can be seen from the scanning electron microscope photo that the crystal intergrowth is better, the film is very dense and smooth, and the thickness of the film is 1.6 microns;

As shown in Figure 7, the scanning electron microscope photo shows that the crystal intergrowth is better, and the surface is denser and smoother. The characteristic peak of beta appeared in the X-ray diffraction diagram, and it can be seen from the figure that the synthesized product is indeed the desired product, but the crystallinity is relatively poor;

As shown in Figure 8, it can be seen from the scanning electron microscope photo that the symbiosis between crystals is better, the film is very dense and flat, and the thickness of the film is 23.7 microns;

As shown in FIG. 9 , the scanning electron microscope photo shows that the symbiosis between crystals is poor, and the surface is denser and smoother. The characteristic peak of beta appeared in the X-ray diffraction diagram, and it can be seen from the figure that the synthesized product is indeed the desired product, and the crystallinity is better;

As shown in Figure 10, it can be seen from the scanning electron microscope photo that the crystals are well intergrown, the film is very dense and smooth, and the thickness of the film is 15.3 microns;

As shown in Figure 11, the scanning electron microscope photo shows that the intergrowth of crystals is better, and the surface is dense and smooth, but there are small grains on the surface. The characteristic peak of beta appeared in the X-ray diffraction pattern, and it can be seen from the figure that the synthesized product is indeed the desired product, and the crystallinity is better.

Detailed ways

The following application examples will further elaborate the present invention:

Example 1

A method for preparing a beta molecular sieve membrane with a single crystal silicon wafer (Beijing Institute of Nonferrous Metals) as a carrier.

Step 1 Preparation of seed crystals: the reaction ratio of nano-beta molecular sieve seed crystal solution is: 4.5molNaOH: 25mol _SiO2 (white carbon black): 9.0mol tetraethylammonium hydroxide (TEAOH): _0.5molNaAlO2 : 360mol _H2 O. Add 3.0 grams of white carbon black to a mixed solution of 5.89 grams, 45%wt tetraethylammonium hydroxide solution, 0.36 grams of sodium hydroxide, 0.082 grams of sodium aluminate, and 9.72 grams of distilled water, and stir until uniform on an electromagnetic stirrer. Then the reaction mixed solution was transferred to the lining of the reaction kettle, the kettle was installed, sealed, and crystallized at 100° C. for 10 days. The product is repeatedly centrifuged, washed with water, and the aqueous solution is neutralized, then dried; dealumination of nano-beta zeolite seed crystals: add 60 g of 60% concentrated nitric acid to 1 g of beta zeolite seeds, and reflux in an oil bath at 80 ° C for 24 hours, the product was repeatedly centrifuged and washed with distilled water to neutrality, and then dried; the nano-beta molecular sieve crystal seed crystal was dealt with to form a 10g/L seed crystal emulsion. The value is 10.

Centrifugation is to firstly centrifuge at 3000 rpm for 5 minutes to remove the larger particles in the lower layer, and then centrifuge at 8000 rpm for 15 minutes to remove the supernatant and retain the solid below.

Water washing is to pour off the supernatant solution after centrifugation, and then add distilled water, repeating 3 times.

Drying is to dry the centrifuged solid seed crystal powder in an oven at 80°C.

Step 2 Preparation of seed crystal carrier: put the monocrystalline silicon wafer into a mixed solution of 5 ml of isopropanol, 10 ml of ethanol, 10 ml of distilled water and 0.5 g of hydrochloric acid, ultrasonic (KQ-100DE type numerical control ultrasonic cleaner, Kunshan City Ultrasonic Instrument Co., Ltd.) 100 watts for washing for 10 minutes; take it out, rinse it with distilled water, and dry; soak the carrier after drying in 0.5% polydiallyldimethylamine hydrochloride (PDDA) solution for 10 minutes After taking it out, rinse off the PDDA solution on the surface with distilled water, then put it into the 10g/L dealuminated seed crystal emulsion for 10 minutes, and finally rinse the carrier for adsorbing the seed crystal with distilled water, and let it dry naturally. The thickness of the formed seed crystal layer is is 0.35 microns.

Step 3 Preparation of molecular sieve membrane: The ratio of the reaction mother liquor is: 0.5mol TEAOH: 1.0mol TEOS: 0.5mol HF: 8.0mol H ₂ O. Add 9.47 grams of TEOS to a mixed solution of 7.44 grams, 45%wt tetraethylammonium hydroxide solution and 1.77 grams of distilled water, stir on a magnetic stirrer for 6h until uniform, and then transfer the homogeneous gel to the seeding The carrier was placed vertically in the reaction kettle in advance, and finally 1 ml of hydrofluoric acid (HF) was slowly added to the gel, the kettle was filled, sealed, and crystallized at 140°C for 2 days. After the reaction, the reaction film was taken out, and the product was repeatedly washed with distilled water for 3 times, then dried in an oven at 80°C, and calcined at 500°C for 8 hours to remove the template agent. A beta molecular sieve membrane (M1) with a single crystal silicon wafer as a carrier is obtained, with a thickness of 2.0 microns.

Example 2

A method for preparing a beta molecular sieve membrane using a single crystal silicon chip as a carrier.

Except that the carrier was dropped into 10g/L seed crystal emulsion to prolong for 12 minutes, the others were the same as in Example 1 to obtain a beta molecular sieve membrane (M2) with a single crystal silicon chip as a carrier, with a thickness of 2.2 microns.

Example 3

A method for preparing a beta molecular sieve membrane using a single crystal silicon chip as a carrier.

Except that the seed crystal carrier was laid flat on the bottom of the kettle, the others were the same as in Example 1 to obtain a beta molecular sieve membrane (M3) with a single crystal silicon chip as a carrier, with a thickness of 2.5 microns.

Example 4

A method for preparing a beta molecular sieve membrane with a glass sheet (Changchun Huayu Glass Instrument Co., Ltd.) as a carrier.

Except changing carrier into glass sheet, other is identical with embodiment 1, obtains the beta molecular sieve membrane (M4) that takes glass sheet as carrier, and thickness is 2.3 microns.

Example 5

The invention discloses a method for preparing a beta molecular sieve membrane with a glass sheet as a carrier.

Except that carrier is changed into glass sheet, the silicon source of reaction mother liquor is changed into and adds 2.73 grams of white carbon blacks, other is the same as embodiment 1, obtains the beta molecular sieve membrane (M5) with glass sheet as carrier, and thickness is 2.2 microns.

Example 6

A method for preparing a beta molecular sieve membrane with a stainless steel sheet (Changchun Xiangchen Chemical Co., Ltd.) as a carrier.

Except that the carrier is changed into a stainless steel sheet, the others are the same as in Example 1 to obtain a beta molecular sieve membrane (M6) with a stainless steel sheet as a carrier, and the thickness is 1.6 microns.

Example 7

A method for preparing a beta molecular sieve membrane with a stainless steel sheet as a carrier.

Except that the carrier is changed into a stainless steel sheet, and the silicon source of the reaction mother liquid is changed into 2.73 grams of white carbon black, the others are the same as in Example 1 to obtain a beta molecular sieve membrane (M7) with a stainless steel sheet as a carrier, and the thickness is 1.5 microns.

Example 8

A preparation method of a beta molecular sieve membrane with a stainless steel mesh (300 mesh, Xinxiang Bashan Precision Filter Material Co., Ltd.) as a carrier.

1. Preparation of molecular sieve seed crystals: same as in Example 1;

2. Preparation of the seed crystal carrier: the pretreatment of the stainless steel mesh carrier is the same as in Example 1; the carrier after drying is coated with 3 drops of the prepared dealuminated seed crystal emulsion, and then placed on an electric stove with a power of 600 watts Prepare the closely arranged seed crystal layer by rapid drying and set aside, the thickness of the seed crystal layer is 22.0 microns;

3. The preparation of molecular sieve membrane: same as embodiment 1;

A beta molecular sieve membrane (M8) with a stainless steel mesh as a carrier is obtained, and the thickness is 23.7 microns.

The following is the Si/Al ratio of the dealuminated beta molecular sieve seed and M8beta molecular sieve membrane tested by plasma emission spectroscopy.

Table 1: Si/Al ratio of dealuminated beta molecular sieve seeds and M8 beta molecular sieve membrane

Si(wt%) Al(wt%) Si/Al(mol/mol)

beta dealuminated seed 30.5 0.03 980.4

M8beta molecular sieve membrane 36.4 0.007 5014.3

Example 9

The invention discloses a method for preparing a beta molecular sieve membrane with a stainless steel mesh as a carrier.

The reaction solution of the molecular sieve membrane is: 0.6mol TEAOH: 1.0mol TEOS: 0.5mol HF: 8.0mol H ₂ O, 9.47 grams of TEOS are added to the mixed solution of 8.93 grams of tetraethylammonium hydroxide (45%) and 0.96 grams of distilled water Chinese and foreign, other is the same as embodiment 8, obtains the beta molecular sieve membrane (M9) that is carrier with stainless steel mesh. Thickness is 22.3 microns

Example 10

A method for preparing a beta molecular sieve membrane with a ceramic sheet (product of Dalian Institute of Chemical Physics) as a carrier.

1. Preparation of molecular sieve seed crystals: same as in Example 1;

2. Preparation of the seed crystal carrier: the carrier ceramic sheet was first polished on fine sandpaper (600 mesh), then ultrasonically cleaned at 100 watts for 10 minutes, then rinsed with distilled water, and dried for use. The dried carrier is coated with 3 drops of dealuminated seed crystal emulsion, and then quickly dried on an electric furnace with a power of 600 watts to prepare a closely arranged seed crystal layer for use, and the thickness of the seed crystal layer is 13.8 microns;

3. The preparation of molecular sieve membrane: same as embodiment 1;

A beta molecular sieve membrane (M10) with a stainless steel mesh as a carrier is obtained. Thickness is 15.3 microns

Example 11

The invention discloses a method for preparing a beta molecular sieve membrane with a ceramic sheet as a carrier.

The reaction solution ratio of the molecular sieve membrane is: 0.5mol TEAOH: 0.9mol TEOS: 0.5mol HFmol: 8.0mol _H2O . Except that 8.52 grams of TEOS were added to the mixed solution of 7.44 grams of tetraethylammonium hydroxide (45%) and 1.77 grams of distilled water, the others were the same as in Example 10 to obtain the beta molecular sieve membrane (M11) with the ceramic sheet as the carrier. The thickness is 15.7 microns.

Table 2 shows the results of secondary growth hydrothermally synthesized beta molecular sieve membranes in different carriers and conditions in the above examples.

Table 2: Results of secondary growth hydrothermal synthesis of beta molecular sieve membranes under different carriers and conditions

Membrane number Film thickness (um) Membrane surface morphology film orientation M1 2.0 Dense, smooth good M2 2.2 Dense, smooth good M3 2.5 denser and smoother better M4 2.3 Dense, smooth good M5 2.2 Relatively dense and smooth better M6 1.6 Dense, smooth good M7 1.5 denser and smoother better M8 23.7 Dense, smooth good M9 22.3 denser and smoother better M10 15.3 Dense, smoother good M11 15.7 Dense, smoother better

Claims (6)

1. a preparation method of pure silicon beta molecular sieve membrane, its steps are as follows: a) Pretreatment of the carrier: first, the monocrystalline silicon wafer, glass sheet, stainless steel sheet, stainless steel mesh or ceramic sheet carrier are respectively washed and pretreated; b) Preparation of beta molecular sieve seed solution: 2-6mol NaOH: 10-50mol white carbon black: 2-15mol tetraethylammonium hydroxide: 0.2-2mol NaAlO ₂ : 100-500mol H ₂ O ratio, each The raw materials are mixed and stirred until uniform, and then crystallized at a temperature of 80-140°C for 6-14 days. The beta nanocrystal solution obtained after crystallization is centrifuged, washed with water, and dried to obtain nano-beta molecular sieve seed crystal powder, and then dealuminated. The dealuminated molecular sieve seed crystal powder is obtained; finally, the dealuminated molecular sieve seed crystal powder is prepared into a 10-30 g/L seed crystal solution with distilled water, and the pH value is adjusted to 9-11; c) Preparation of seed crystal carrier: immerse the pre-washed single crystal silicon slice, glass slice or stainless steel slice into 0.2%-10% polydiallyldimethylamine hydrochloride solution for 5-20 minutes, Then put it into the seed crystal solution to absorb the seed crystal for 5-20 minutes, then wash the carrier after adsorbing the seed crystal in distilled water, and dry it at room temperature, and the thickness of the formed seed crystal layer is 0.2-0.5 microns; or 2-5 Drop the seed crystal solution onto the pre-washed stainless steel mesh or ceramic sheet carrier, and finally dry it on a 500-700W electric furnace to form a seed crystal layer with a thickness of 10-30 microns; d) Preparation of molecular sieve membrane mother liquor: mix and stir all raw materials until uniform according to the ratio of 0.1-10 mol tetraethylammonium hydroxide: 0.1-10 mol ethyl orthosilicate: 0.05-5 mol HF: 0.5-50 mol H ₂ O; e) Preparation of molecular sieve membrane: put the seed crystal carrier and the mother liquid of the molecular sieve membrane together in a reaction kettle for crystallization at 140-170°C for 2-5 days, then wash and dry; then wash and dry the beta molecular sieve membrane Calcination in a tube furnace at 500-700°C for 8-12 hours, and finally form a film with a thickness of 1-3 microns on a single crystal silicon wafer, glass wafer or stainless steel wafer carrier, and on a stainless steel mesh or ceramic wafer carrier The thickness of the formed film is 12-32 microns. 2. the preparation method of pure silicon beta molecular sieve membrane as claimed in claim 1 is characterized in that: the washing pretreatment of carrier is to put monocrystalline silicon sheet, glass sheet, stainless steel sheet or stainless steel net into 2～10 milliliters of isopropyl Alcohol, 5-20ml ethanol, 5-20ml distilled water and 0.2-1g hydrochloric acid mixed solution, ultrasonic power 100-300 watts, wash for 5-20 minutes, rinse with distilled water after taking out, dry; Grind on 800-mesh fine sandpaper, then ultrasonically clean in distilled water with a power of 100-300 watts for 5-20 minutes, take it out, rinse it with distilled water, and dry it. 3. The preparation method of pure silicon beta molecular sieve membrane as claimed in claim 1, characterized in that: the molecular sieve membrane is prepared according to the ratio of 0.3～0.8mol TEAOH, 0.5～5mol TEOS, 0.2～2mol HF, 2～10mol _H2O mother liquor. 4. the preparation method of pure silicon beta molecular sieve membrane as claimed in claim 1 is characterized in that: in step b), centrifugation is the beta nanocrystal solution obtained after crystallization is centrifugally obtained the solution of uniform nanocrystal on centrifuge, It is first centrifuged at 3000-5000 rpm for 5-20 minutes to remove the nanocrystals with larger particles in the lower layer, and then centrifuged at 8000-10000 rpm for 10-30 minutes to remove the supernatant and leave Take the solid below. 5. the preparation method of pure silicon beta molecular sieve membrane as claimed in claim 1 is characterized in that: in step b), dealumination is to add the concentrated nitric acid of 20～120 grams 60% according to 1～5 gram beta molecular sieve seed crystal powders Ratio, reflux in an oil bath at 60-120°C for 5-48 hours, and the product is repeatedly centrifuged and washed with distilled water to neutrality, and then dried. 6. the preparation method of pure silicon beta molecular sieve membrane as claimed in claim 1 is characterized in that: in the step b), be to regulate the pH value of seed crystal solution with ammoniacal liquor. the

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