CN108246122B - Method for synthesizing NaA molecular sieve membrane - Google Patents

Abstract

The invention discloses a method for synthesizing a NaA molecular sieve membrane. The specific steps are: 1) pretreatment on the surface of a support body; 2) preparation of a seed layer on the surface of the support body; dispersing the NaA molecular sieve crystal seeds in ethanol to obtain the crystal seeds 3) Preparation of NaA molecular sieve film: placed in NaA molecular sieve film growth liquid , heating for hydrothermal reaction and crystallization to obtain NaA molecular sieve membrane. The preparation method involved in the invention is simple and feasible, and is suitable for mass production; by adopting the drop coating method, a NaA molecular sieve membrane with good compactness and good flatness can be formed on the alumina support body with poor hydrophilicity, and the repeatability is High, good separation performance, suitable for popularization and application.

Description

A kind of synthetic method of NaA molecular sieve membrane

technical field

The invention belongs to the technical field of molecular sieve membrane preparation, in particular to a synthesis method of NaA molecular sieve membrane.

Background technique

According to statistics, industrial energy consumption accounts for about 32% of the total energy consumption, and most of this energy is used in the direction of material separation. Existing separation technologies include rectification, extraction, adsorption, recrystallization, etc. Among them, rectification is the most widely used. In this process, repeated vaporization and condensation are required, which requires a lot of energy consumption, and rectification is used in other There are many inefficiencies in energy utilization. Compared with these traditional separation technologies, membrane separation technology has the advantages of low energy consumption, less pollution, easy to achieve continuous separation, easy coupling with other separation processes, mild conditions of use, and easy amplification. widely.

The key to membrane separation technology lies in membrane components, which are mainly divided into organic membranes, inorganic membranes and biological membranes. Compared with organic films, inorganic films have the advantages of high mechanical strength, strong chemical corrosion resistance, high temperature resistance, and not easy to age, and have been widely used. As a kind of inorganic membrane, NaA molecular sieve membrane not only has the advantages of inorganic membrane, but also has the characteristics of effective pore size of 0.41nm and silicon-aluminum ratio of 1, making it the most hydrophilic synthetic membrane at present. Molecular sieve, and it has excellent separation effect in the dehydration of organic solvents, especially in the field of dehydration of alcohol-water azeotrope systems. In recent years, there is a shortage of energy, and fuel ethanol has great development prospects. The preparation of anhydrous ethanol generally adopts the method of rectification, but when the water content is small, azeotropes are generated, and it is difficult to obtain 100% ethanol. The application of molecular sieve membrane to pervaporation separation technology will promote the application of fuel ethanol.

At present, the synthesis methods of NaA molecular sieve membranes mainly include in-situ synthesis, secondary growth, microwave heating synthesis, and vapor phase inversion. The in-situ hydrothermal synthesis method is simple and easy to operate, but this method of membrane production is not easy to control the thickness of the membrane and the size of the grains, and the membrane surface is prone to unevenness and cracks. have a greater impact. At present, the most widely used method is the secondary growth method. This method separates the growth phase and the nucleation phase of the crystal. First, a layer of seed crystals is coated on the surface of the support, which is used as the crystal nucleus in the in-situ hydrothermal synthesis process. , when the hydrothermal reaction is carried out in the synthesis liquid system, it acts as the growth center, which shortens the crystallization time of the film, and plays a certain role in controlling the thickness of the film and the formation of miscellaneous crystals; The coating step has an important influence on the quality of the obtained NaA molecular sieve membrane.

At present, there are many methods of coating crystal, such as hot dipping method, vacuum coating method, wipe coating method, etc. Among them, the most widely used hot dipping method is to form hot air inside the support body after heat treatment, and rapidly cool to form a negative pressure when immersed in the seed liquid. Seed layer: In this process, the coating time is short, the distribution of the seeds is not uniform enough, and the surface of the carrier cannot be completely covered even if the coating is repeated for many times. Several other coating methods are also difficult to achieve uniform distribution of seeds on the support. The quality of seed coating has a great influence on the thickness, uniformity and compactness of NaA molecular sieve membrane, thus affecting the performance of the membrane.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to solve the problems of uneven distribution of crystal seeds and low compactness existing in the preparation process of the existing NaA molecular sieve film secondary growth method, and to provide a method for uniform and dense seed crystals through a drop coating method. The synthetic process of coating on a support body with poor hydrophilicity and preparing a dense and smooth molecular sieve membrane through hydrothermal reaction, the obtained molecular sieve membrane has high separation performance and large permeation flux, and the involved preparation process is simple and convenient, High repeatability, suitable for promotion and application.

To achieve the above object, the technical scheme adopted in the present invention is:

A kind of synthetic method of NaA molecular sieve membrane, is characterized in that, comprises the following steps:

1) Pretreatment of the surface of the support body; the alumina plate is polished, placed in water for ultrasonic vibration cleaning, then immersed in hydrochloric acid solution and sodium hydroxide solution in turn, then ultrasonically washed with water to neutrality, dried, and taken out for use;

2) Preparation of the crystal seed layer on the surface of the support; the silicon source, the aluminum source, the alkali source and the water are mixed and stirred uniformly, placed in the reaction kettle for crystallization, and then suction filtered and dried to obtain the NaA molecular sieve crystal seed; The NaA molecular sieve crystal seeds are dissolved in the ethanol solution to prepare the seed crystal liquid, and the drop coating method is used to coat the seed crystal liquid on the surface of the alumina plate pretreated in step 1), and dry to obtain a surface covered with the seed crystal layer. support body;

3) Preparation of NaA molecular sieve membrane; the silicon source, aluminum source, alkali source and water are mixed and stirred evenly to obtain a NaA molecular sieve membrane growth solution; the support body covered with the seed layer on the surface obtained in step 2) is immersed in a NaA molecular sieve membrane The hydrothermal crystallization is carried out in the reaction kettle of the growth liquid, and after the reaction is completed, it is rapidly cooled, washed with water, and dried to obtain a NaA molecular sieve film on the alumina plate.

In the above scheme, the grinding step described in step 1) is carried out with sandpaper, and the sandpaper model is preferably 800# and 1200#.

In the above scheme, the concentration of hydrochloric acid and sodium hydroxide described in step 1) is 0.5-4mol/L.

In the above scheme, the drying temperature in step 1) is 50-80° C., and the drying time is 10-24 h.

In the above scheme, the aluminum source described in the step 2) and the step 3) is one of aluminum chloride, aluminum hydroxide, and sodium metaaluminate; the silicon source is water glass, sodium silicate, silica sol, two A kind of silicon oxide; the alkali source is sodium hydroxide.

In the above scheme, the addition amounts of the alkali source, silicon source and aluminum source described in step 2) and step 3) are respectively the Na ₂ O, SiO ₂ and Al ₂ O ₃ introduced by them, and the alkali source, silicon source, The molar ratio of the aluminum source and water is calculated as Al ₂ O ₃ :Na ₂ O:SiO ₂ :H ₂ O as 1:(0.5-3):(1-3):(100-200).

In the above scheme, the average particle size of the NaA molecular sieve seeds in step 2) is 1-5 μm.

In the above scheme, the concentration of NaA molecular sieve seeds in the seed liquid is 2-5 g/L.

Preferably, the concentration of NaA molecular sieve seeds in the seed solution is 3-4 g/L.

In the above solution, in the drop coating method, the seed liquid is added dropwise to the surface of the support until the seed liquid completely covers the support, and the dropping rate is 30-60 drops/min.

Preferably, the drop coating height is 0.5-10 cm; the diameter of the syringe is 0.2-1 cm.

Preferably, the drop coating amount corresponding to the surface of the support is 0.5-1 ml/cm ² .

More preferably, the drop-coating area on the surface of the support corresponding to each drop-coating point (drop-in position of the syringe) is 1 cm ² or less.

In the above-mentioned scheme, the support body uses the material (preferably polytetrafluoroethylene tape) that does not affect the crystallization reaction to wrap and protect the side that does not cover the seed layer, and then is placed in the NaA molecular sieve film growth solution for hydrothermal treatment. Synthetic crystallization treatment.

In the above scheme, the drying temperature in step 2) is 50-100°C.

Preferably, the drying time in step 2) is 2-3h.

In the above scheme, the stirring speed of the mixing and stirring described in step 2) and step 3) is 60～500r/min, the stirring time is 3～5h, and the stirring temperature is room temperature.

In the above scheme, the hydrothermal crystallization temperature is 60-120° C., and the time is 1-6 h.

In the above solution, the alumina plate is formed by pressing alumina particles, the size of the alumina particles is in the range of 10-30 μm, and the pore size distribution formed between the particles is in the range of 0.5-1 μm.

Preferably, the equivalent diameter of the surface of the alumina plate used is 1-10 cm.

The principle of the present invention is as follows: using the method of drip coating, drop the NaA seed crystal on the support body, when the droplet encounters the support body, the liquid has a tendency to spread, and with the continuous drip coating, the seed crystal liquid will support The body is completely covered to form a layer of solution; at a suitable temperature (drying temperature after drop coating), the NaA particles undergo a self-assembly process in ethanol, spontaneously form an ordered structure, and are evenly arranged together. The evaporation of ethanol eventually forms a uniform seed layer.

The beneficial effects of the present invention are:

1) The present invention proposes for the first time that a drop coating method is adopted to obtain a uniform and dense NaA molecular sieve seed layer on a support whose hydrophilicity is not very good through pretreatment of the surface of the support, regulation of the seed liquid and drying conditions, The NaA molecular sieve membrane is prepared by further crystallization; the method is simple, convenient, easy to operate, and has good repeatability, which makes up for the problem that other coating methods are limited by hydrophilicity, and is suitable for popularization and application.

2) The crystal seed dispersant used in the present invention is ethanol, and the interaction between the evaporation speed of ethanol, the polarity of ethanol and the NaA particles is an important factor for promoting the smooth and uniform distribution of the seed crystal layer.

3) The NaA molecular sieve membrane obtained by the present invention is flat and compact, has high permeability and separation performance, and has high industrial application value.

Description of drawings

1 is a scanning electron microscope image of the NaA molecular sieve seed layer obtained in Example 1 of the present invention.

2 is a scanning electron microscope image of the NaA molecular sieve membrane obtained in Example 2 of the present invention.

Fig. 3 is the NaA molecular sieve membrane and X-ray diffractogram obtained in Example 2 of the present invention

4 is a scanning electron microscope image of the NaA molecular sieve membrane obtained in Example 3 of the present invention.

5 is a scanning electron microscope image of the NaA molecular sieve membrane obtained in Example 4 of the present invention.

6 is a scanning electron microscope image of the NaA molecular sieve membrane obtained in Comparative Example 1.

7 is a scanning electron microscope image of the NaA molecular sieve seed layer obtained in Comparative Example 2.

8 is a scanning electron microscope image of the NaA molecular sieve seed layer obtained in Comparative Example 3.

Detailed ways

In order to better understand the present invention, the content of the present invention is further explained below with reference to specific embodiments and accompanying drawings, but the content of the present invention is not limited to the following embodiments.

In the following examples, the alumina plate (α-Al ₂ O ₃ plate) is a circular support formed by pressing large-particle alumina (10-30 μm), and the pore size distribution between the particles is 0.5-1 μm; The diameter of the alumina plate is 1 to 3 cm.

Example 1

A kind of synthetic method of NaA molecular sieve membrane, its preparation method comprises the steps:

1) Use 800# and 1200# sandpaper in turn to polish the α-Al ₂ O ₃ plate (diameter 1cm), place it in water and carry out ultrasonic vibration to wash off the residual powder, and then add 2mol/L hydrochloric acid and sodium hydroxide solution in turn. Soak for 24 hours, then ultrasonically shake for 15 minutes, wash with deionized water until neutral, and place them in a 60°C oven to dry for 12 hours, then take them out for use;

2) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, mixed and stirred at room temperature for 3h (stirring rate 300r/min), put into a stainless steel reaction kettle, reacted at 100°C for 4h, suction filtered, and dried (80°C) to obtain NaA molecular sieve seeds Dissolve the gained NaA molecular sieve crystal seeds in ethanol and stir evenly, prepare 3g/L seed crystal liquid, take the prepared seed crystal liquid with a syringe with a diameter of 0.3cm, and take the distance α-Al ₂ O ₃ plate surface circle center 1cm high At the center of the drop coating, apply the seed crystal droplet on the alumina plate at a speed of about 1 drop/second (the drop coating amount corresponding to the surface of the support body is 0.5-1ml/cm ² ), so that the seed crystal solution completely covers the support. The surface of the body was baked at 80°C for 2.5 hours to obtain a support body covered with a seed layer, which was used for later use;

3) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, stirred at room temperature for 3h (stirring rate 300r/min) to obtain a molecular sieve film growth solution, and the back surface of the support whose surface was covered with the seed layer was wrapped with polytetrafluoroethylene tape (without the seed layer) one side), put it into the reaction kettle filled with molecular sieve film growth liquid, react at 100 ° C for 3 hours, rinse with tap water and rapidly cool after the reaction, take out the support, wash with deionized water to neutrality and dry, A NaA molecular sieve membrane was obtained.

Fig. 1 is the SEM under different magnifications of the NaA molecular sieve seed layer obtained in the present embodiment. It can be seen that the NaA seeds are distributed evenly and flat on the surface of the support body; the average particle size is about 1.5-2 μm.

Example 2

A kind of synthetic method of NaA molecular sieve membrane, its preparation method comprises the steps:

1) Use 800# and 1200# sandpaper in turn to polish the α-Al ₂ O ₃ plate (diameter 1cm), place it in water and carry out ultrasonic vibration to wash off the residual powder, and then add 2mol/L hydrochloric acid and sodium hydroxide solution in turn. Soak for 24 hours, then ultrasonically shake for 15 minutes, wash with deionized water until neutral, and place them in a 60°C oven to dry for 12 hours, then take them out for use;

2) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:150, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, mixed and stirred at room temperature for 3h (stirring rate 500r/min), put into a stainless steel reaction kettle, reacted at 100°C for 4h, suction filtered, and dried (80°C) to obtain NaA molecular sieve seeds Dissolve the gained NaA molecular sieve crystal seeds in ethanol and stir evenly, prepare 3g/L seed crystal liquid, take the prepared seed crystal liquid with a syringe with a diameter of 0.3cm, and take the distance α-Al ₂ O ₃ plate surface circle center 1cm high At the center of the drop coating, apply the seed crystal droplet on the alumina plate at a speed of about 1 drop/second (the drop coating amount corresponding to the surface of the support body is 0.5-1ml/cm ² ), so that the seed crystal solution completely covers the support. The surface of the body was baked at 80°C for 2.5 hours to obtain a support body covered with a seed layer, which was used for later use;

3) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:150, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, stirred at room temperature for 3h (stirring rate 500r/min) to obtain a molecular sieve film growth solution, and the back surface of the support whose surface was covered with the seed layer was wrapped with polytetrafluoroethylene tape (without the seed layer) one side), put it into the reaction kettle filled with the molecular sieve film growth solution, react at 120 ° C for 3 hours, rinse with tap water and rapidly cool after the reaction, take out the support, wash with deionized water to neutrality and dry, A NaA molecular sieve membrane was obtained.

FIG. 2 and FIG. 3 are the SEM image and the XRD image of the NaA molecular sieve membrane obtained in this example, respectively. It can be seen from Figure 2 that a dense and flat NaA molecular sieve membrane is formed on the alumina plate, and the side view shows that the NaA molecular sieve membrane and the alumina plate are tightly bound, and there is no separation. The XRD pattern in Figure 3 shows that the NaA molecular sieve seed crystals have been successfully coated on the alumina plate by the drop coating method and a NaA molecular sieve film is formed.

Example 3

A kind of synthetic method of NaA molecular sieve membrane, its preparation method comprises the steps:

1) Use 800# and 1200# sandpapers in turn to polish the α-Al ₂ O ₃ plate (diameter 3cm), place it in water and carry out ultrasonic vibration to wash off the residual powder, and then add 2mol/L hydrochloric acid and sodium hydroxide solution in turn. Soak for 24 hours, then ultrasonically shake for 15 minutes, wash with deionized water until neutral, and place them in a 60°C oven to dry for 12 hours, then take them out for use;

2) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, mixed and stirred at room temperature for 3h (stirring rate 300r/min), put into a stainless steel reaction kettle, reacted at 100°C for 4h, suction filtered, and dried (80°C) to obtain NaA molecular sieve seeds Dissolve the gained NaA molecular sieve crystal seeds in ethanol and stir evenly, prepare 3g/L seed crystal liquid, take the prepared seed crystal liquid with a syringe with a diameter of 0.3cm, and take a distance of 2cm from the center of the surface of the α-Al ₂ O ₃ plate. At the center of the drop coating, apply the seed crystal droplet on the alumina plate at a speed of about 1 drop/second (the drop coating amount corresponding to the surface of the support body is 0.5-1ml/cm ² ), so that the seed crystal solution completely covers the support. The surface of the body was baked at 80°C for 2.5 hours to obtain a support body covered with a seed layer, which was used for later use;

3) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, stirred at room temperature for 3h (stirring rate 300r/min) to obtain a molecular sieve film growth solution, and the back surface of the support whose surface was covered with the seed layer was wrapped with polytetrafluoroethylene tape (without the seed layer) one side), put it into the reaction kettle filled with molecular sieve membrane growth liquid, react at 100 ° C for 5 hours, rinse with tap water and rapidly cool after the reaction, take out the support, wash with deionized water to neutrality and dry, A NaA molecular sieve membrane was obtained.

FIG. 4 is a SEM image of the NaA molecular sieve membrane obtained in this example, and it can be seen from the figure that the surface of the obtained molecular sieve membrane is smooth and dense.

Example 4

A kind of synthetic method of NaA molecular sieve membrane, its preparation method comprises the steps:

1) Use 800# and 1200# sandpapers in turn to polish the α-Al ₂ O ₃ plate (diameter 3cm), place it in water and carry out ultrasonic vibration to wash off the residual powder, and then add 2mol/L hydrochloric acid and sodium hydroxide solution in turn. Soak for 24 hours, then ultrasonically shake for 15 minutes, wash with deionized water until neutral, and place them in a 60°C oven to dry for 12 hours, then take them out for use;

2) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, mixed and stirred at room temperature for 3h (stirring rate 400r/min), put into a stainless steel reaction kettle, reacted at 100°C for 4h, suction filtered, and dried (80°C) to obtain NaA molecular sieve seeds Dissolve the gained NaA molecular sieve crystal seeds in ethanol and stir evenly, prepare 3g/L seed crystal liquid, take the prepared seed crystal liquid with a syringe with a diameter of 0.3cm, and take a distance of 2cm from the center of the surface of the α-Al ₂ O ₃ plate. At the center of the drop coating, apply the seed crystal droplet on the alumina plate at a speed of about 1 drop/second (the drop coating amount corresponding to the surface of the support body is 0.5-1ml/cm ² ), so that the seed crystal solution completely covers the support. The surface of the body was baked at 80°C for 2.5 hours to obtain a support body covered with a seed layer, which was used for later use;

3) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8 g of deionized water, stirred at room temperature for 4.5 h (stirring rate 400 r/min) to obtain a molecular sieve membrane growth liquid, and the back surface of the support whose surface was covered with the seed layer was wrapped with polytetrafluoroethylene tape (without the seed layer). side), put it into the reaction kettle filled with molecular sieve film growth liquid, react at 100 ° C for 3 hours, rinse with tap water and rapidly cool after the reaction, take out the support, wash with deionized water to neutrality and dry , to obtain a NaA molecular sieve membrane.

FIG. 5 is a SEM image of the NaA molecular sieve membrane obtained in this example, and it can be seen from the figure that the surface of the obtained molecular sieve membrane is smooth and dense.

Comparative Example 1

A kind of synthetic method of NaA molecular sieve membrane, its preparation method comprises the steps:

1) Use 800# and 1200# sandpaper in turn to polish the α-Al ₂ O ₃ plate (diameter 1cm), place it in water and carry out ultrasonic vibration to wash off the residual powder, and then add 2mol/L hydrochloric acid and sodium hydroxide solution in turn. Soak for 24 hours, then ultrasonically shake for 15 minutes, wash with deionized water until neutral, and place them in a 60°C oven to dry for 12 hours, then take them out for use;

2) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, mixed and stirred at room temperature for 3h (stirring rate 300r/min), put into a stainless steel reaction kettle, reacted at 100°C for 4h, suction filtered, and dried (80°C) to obtain NaA molecular sieve seeds ; Dissolve the obtained NaA molecular sieve crystal seeds in ethanol and stir evenly, prepare 3 g/L crystal seed solution, wrap one side of the alumina plate with polytetrafluoroethylene tape, and use the hot dipping method to make the alumina plate covered with crystal seeds, 80 ℃ condition Dry down to obtain the support body covered with the seed crystal layer, which is for later use;

3) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, stirred at room temperature for 4.5h (stirring rate 300r/min) to obtain a molecular sieve film growth liquid, put the support of the obtained surface covering the seed layer into the reaction kettle filled with the molecular sieve film growth liquid, in the The reaction was carried out at 100° C. for 3 hours. After the reaction was completed, it was rinsed with tap water and rapidly cooled. The support was taken out, washed with deionized water until neutral, and dried to obtain a NaA molecular sieve membrane.

Fig. 6 is the SEM image of the NaA molecular sieve film obtained by the comparative example. It can be seen from the figure that the obtained molecular sieve film is not in a tight state, and there are alumina plates leaking in some areas. This is mainly because the hot dip method cannot make the alumina plates uniform. due to a compact seed layer.

Comparative Example 2

A kind of synthetic method of NaA molecular sieve membrane, its preparation method comprises the steps:

1) Use 800# and 1200# sandpaper in turn to polish the α-Al ₂ O ₃ plate (diameter 1cm), place it in water and carry out ultrasonic vibration to wash off the residual powder, and then add 2mol/L hydrochloric acid and sodium hydroxide solution in turn. Soak for 24 hours, then ultrasonically shake for 15 minutes, wash with deionized water until neutral, and place them in a 60°C oven to dry for 12 hours, then take them out for use;

2) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, mixed and stirred at room temperature for 3h (stirring rate 300r/min), put into a stainless steel reaction kettle, reacted at 100°C for 4h, suction filtered, and dried (80°C) to obtain NaA molecular sieve seeds Dissolve the gained NaA molecular sieve crystal seed in acetonitrile and stir evenly, prepare 3g/L seed crystal liquid, take the prepared seed crystal liquid with a syringe with a diameter of 0.3cm, and drop the crystal seed liquid at a speed of about 1 drop/second. Coat it on an alumina plate so that the seed crystal liquid completely covers the surface of the support, and bake it at 80°C for 2.5 hours to obtain a support with the surface covered with the seed layer, which is ready for use;

3) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, stirred at room temperature for 4.5h (stirring rate 300r/min) to obtain a molecular sieve film growth liquid, put the support of the obtained surface covering the seed layer into the reaction kettle filled with the molecular sieve film growth liquid, in the The reaction was carried out at 100° C. for 3 hours. After the reaction was completed, it was rinsed with tap water and rapidly cooled. The support was taken out, washed with deionized water until neutral, and dried to obtain a NaA molecular sieve membrane.

Fig. 7 is the SEM image of the NaA molecular sieve seed crystal layer obtained by the comparative example, and it can be seen from the figure that the distribution of the obtained molecular sieve seed crystal is very uneven, and there is a phenomenon of unevenness.

Comparative Example 3

A kind of synthetic method of NaA molecular sieve membrane, its preparation method comprises the steps:

1) Use 800# and 1200# sandpaper in turn to polish the α-Al ₂ O ₃ plate (diameter 1cm), place it in water and carry out ultrasonic vibration to wash off the residual powder, and then add 2mol/L hydrochloric acid and sodium hydroxide solution in turn. Soak for 24 hours, then ultrasonically shake for 15 minutes, wash with deionized water until neutral, and place them in a 60°C oven to dry for 12 hours, then take them out for use;

2) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, mixed and stirred at room temperature for 3h (stirring rate 300r/min), put into a stainless steel reaction kettle, reacted at 100°C for 4h, suction filtered, and dried (80°C) to obtain NaA molecular sieve seeds Dissolve the gained NaA molecular sieve crystal seeds in ethanol and stir evenly, prepare 6g/L seed crystal liquid, take the prepared seed crystal liquid with a syringe with a diameter of 0.3cm, and take a distance of 1cm from the center of the surface of the α-Al ₂ O ₃ plate. At the drop coating center, apply the seed crystal droplet on the alumina plate at a speed of about 1 drop/second, so that the seed crystal liquid completely covers the surface of the support, and bake it at 80 °C for 2.5 hours to obtain a surface covered with a seed crystal layer. The support body, spare;

3) According to the molar ratio of Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O of 1:2:2:120, weigh 1.64 g of sodium metaaluminate, 0.8 g of sodium hydroxide, and 3 g of 30% silica sol , 19.8g of deionized water, stirred at room temperature for 3h (stirring rate 300r/min) to obtain a molecular sieve film growth solution, and the back surface of the support whose surface was covered with the seed layer was wrapped with polytetrafluoroethylene tape (without the seed layer) one side), put it into the reaction kettle filled with molecular sieve film growth liquid, react at 100 ° C for 3 hours, rinse with tap water and rapidly cool after the reaction, take out the support, wash with deionized water to neutrality and dry, A NaA molecular sieve membrane was obtained.

FIG. 8 is the SEM of the NaA molecular sieve seed layer obtained in this example, it can be seen that the distribution of NaA seeds on the surface of the support is very uneven, and there are uneven phenomena.

Application example

The NaA molecular sieve membranes obtained in Examples 1-4 were subjected to the permeability test of ethanol/water, and the results are shown in Table 1.

Table 1 Ethanol/water permeability test results of NaA molecular sieve membranes obtained in Examples 1-4

Numbering Vacuum-MPa Flux g/h Example 1 0.025 234.92 Example 2 0.035 379.74 Example 3 0.045 489.16 Example 4 0.055 464.28

The above results show that the NaA molecular sieve membrane obtained in the present invention has higher permeability and separation performance.

Obviously, the above-mentioned embodiments are only examples for clear illustration, and are not intended to limit the implementation manner. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. However, the obvious changes or changes derived therefrom still fall within the protection scope of the present invention.

Claims (9)

1. a synthetic method of NaA molecular sieve membrane, is characterized in that, comprises the following steps: 1) Pretreatment of the surface of the support body; the alumina plate is polished, placed in water for ultrasonic vibration cleaning, then immersed in hydrochloric acid solution and sodium hydroxide solution in turn, washed with ultrasonic vibration until neutral, dried, and taken out for use; 2) Preparation of the seed layer on the surface of the support; the silicon source, the aluminum source, the alkali source and the water are mixed and stirred evenly, placed in a reaction kettle for crystallization, and then filtered and dried to obtain NaA molecular sieve crystal seeds ; Disperse the NaA molecular sieve crystal seeds in ethanol to prepare a seed crystal liquid, and apply the drop coating method to the surface of the alumina plate pretreated in step 1), and dry the seed liquid; The concentration of NaA molecular sieve crystal seeds in the crystal seed liquid is 2~5g/L; the drying temperature is 50~100°C; 3) Preparation of NaA molecular sieve membrane; the silicon source, aluminum source, alkali source and water are mixed and stirred evenly to prepare a NaA molecular sieve membrane growth solution; the support body with the surface covered with the seed crystal layer obtained in step 2) is immersed in a solution containing NaA molecular sieve The hydrothermal crystallization is carried out in the reaction kettle of the film growth liquid, and after the reaction is completed, it is rapidly cooled, washed with water, and dried to obtain the NaA molecular sieve film on the alumina plate. 2. The synthetic method according to claim 1, wherein the concentration of hydrochloric acid and sodium hydroxide described in step 1) is 0.5-4 mol/L. 3. The synthetic method according to claim 1, wherein the aluminum source described in step 2) and step 3) is one of aluminum chloride, aluminum hydroxide and sodium metaaluminate; the silicon source is silicon One of sodium, silica sol and silicon dioxide; the alkali source is sodium hydroxide. 4. synthetic method according to claim 1 is characterized in that, the addition amount of alkali source, silicon source and aluminum source described in step 2) and step 3) are respectively Na ₂ O, SiO ₂ and Al that it introduces ₂ O ₃ shall prevail, and the molar ratio of alkali source, silicon source, aluminum source and water shall be calculated as Al ₂ O ₃ : Na ₂ O : SiO ₂ : H ₂ O as 1:(0.5~3):(1~3) :(100~200). 5. synthetic method according to claim 1, is characterized in that, the average particle diameter of described NaA molecular sieve crystal seed is 1～5 μm. 6. synthetic method according to claim 1, is characterized in that, described drop coating method adds dropwise to the surface of support body until seed crystal liquid completely covers support body, and the dripping speed is 30～60 drops/ min, the drop coating amount corresponding to the surface of the support is 0.5-1 ml/cm ² . 7. synthetic method according to claim 1, is characterized in that, the temperature of described hydrothermal synthesis crystallization treatment is 60～120 ℃, and the time is 1～6h. 8 . The synthesis method according to claim 1 , wherein the alumina plate is formed by pressing alumina particles, the size of the alumina particles ranges from 10 to 30 μm, and the pore size distribution between the particles ranges from 0.5 to 30 μm. 9 . 1 μm. 9. the NaA molecular sieve membrane prepared by the synthetic method of any one of claims 1 to 8.

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