CN108246122B - Method for synthesizing NaA molecular sieve membrane - Google Patents
Method for synthesizing NaA molecular sieve membrane Download PDFInfo
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- CN108246122B CN108246122B CN201810178837.3A CN201810178837A CN108246122B CN 108246122 B CN108246122 B CN 108246122B CN 201810178837 A CN201810178837 A CN 201810178837A CN 108246122 B CN108246122 B CN 108246122B
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- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
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Abstract
The invention discloses a method for synthesizing a NaA molecular sieve membrane, which comprises the following specific steps: 1) pre-treating the surface of the support body; 2) preparing a support surface seed crystal layer; dispersing NaA molecular sieve seed crystals in ethanol to obtain seed crystal liquid, coating the seed crystal liquid on the surface of a pretreated support body by adopting a dripping method, and drying to obtain the support body with the surface attached with the seed crystal layer; 3) preparation of NaA molecular sieve membrane: and placing the membrane in NaA molecular sieve membrane growth liquid, heating, performing hydrothermal reaction, and crystallizing to obtain the NaA molecular sieve membrane. The preparation method is simple and feasible, and is suitable for batch production; by adopting the drop coating method, the NaA molecular sieve membrane with good compactness and flatness can be generated on the alumina support body with poor hydrophilicity, and the NaA molecular sieve membrane has high repeatability and good separation performance and is suitable for popularization and application.
Description
Technical Field
The invention belongs to the technical field of molecular sieve membrane preparation, and particularly relates to a synthesis method of a NaA molecular sieve membrane.
Background
Statistically, industrial energy consumption accounts for about 32% of total energy consumption, and most of the energy is applied in the direction of material separation. The existing separation technology comprises rectification, extraction, adsorption, recrystallization and the like, wherein the rectification is the most widely applied technology, in the process, vaporization and condensation are required to be repeated continuously, a large amount of energy consumption is required, and the rectification has many low efficiency conditions in other energy utilization aspects. Compared with the traditional separation technologies, the membrane separation technology has the advantages of low energy consumption, less pollution, easiness in realizing continuous separation, easiness in coupling with other separation processes, mild use conditions, easiness in amplification and the like, and is more and more widely applied in many industrial fields.
The key point of the membrane separation technology is that the membrane component is mainly divided into an organic membrane, an inorganic membrane and a biological membrane. Compared with organic films, inorganic films have the advantages of high mechanical strength, strong chemical corrosion resistance, high temperature resistance, difficult aging and the like, and are widely applied. The NaA molecular sieve membrane is used as one of inorganic membranes, has the advantages of the inorganic membranes, simultaneously becomes the most hydrophilic molecular sieve artificially synthesized at present due to the characteristics of 0.41nm of effective pore diameter, 1 silicon-aluminum ratio and the like, and has excellent separation effect in the dehydration of organic solvents, particularly in the dehydration field of alcohol-water azeotrope systems and the like. In recent years, the fuel ethanol has great development prospect due to energy shortage, the preparation of the absolute ethanol generally adopts a rectification method, but when the water content is low, an azeotrope is generated, and 100 percent ethanol is difficult to obtain, and if a NaA molecular sieve membrane is applied to a pervaporation separation technology, the application of the fuel ethanol can be promoted.
The existing synthesis method of the NaA molecular sieve membrane mainly comprises an in-situ synthesis method, a secondary growth method, a microwave heating synthesis method, a steam phase conversion method and the like. The in-situ hydrothermal synthesis method is simple and easy to operate, but the membrane preparation method is not easy to control the thickness and the size of crystal grains of the membrane, the surface of the membrane is easy to have the problems of unevenness, cracks and the like, and the membrane separation performance and the flux are greatly influenced. The method separates the growth period and the nucleation period of crystals, firstly coats a layer of seed crystal on the surface of a support to be used as a crystal nucleus in the in-situ hydrothermal synthesis process, and when the seed crystal is used as a growth center during the hydrothermal reaction in a synthetic liquid system, the seed crystal shortens the crystallization time of the film, and plays a certain role in controlling the thickness of the film and the generation of mixed crystals; wherein, the crystal coating step on the surface of the support has important influence on the quality of the obtained NaA molecular sieve membrane.
At present, there are many methods for coating crystal, such as hot dipping, vacuum coating, and wiping. The most widely applied hot dipping method is that the support body is subjected to heat treatment, hot air is formed inside the support body, the support body is rapidly cooled to form negative pressure when being immersed in liquid crystal, and the seed crystal is adsorbed on the surface of the support body to form a seed crystal layer under the push of pressure difference; in the process, the coating time is short, the distribution of the crystal seeds is not uniform enough, and the surface of the carrier cannot be completely covered even if the crystal coating is repeated for many times. Several other coating methods also make it difficult to achieve a uniform distribution of the seeds on the support. The quality of seed crystal coating has great influence on the thickness, uniformity, compactness and the like of the NaA molecular sieve membrane, thereby influencing the performance of the membrane.
Disclosure of Invention
The invention aims to solve the technical problems of uneven seed crystal distribution, low compactness and the like in the preparation process of the existing NaA molecular sieve membrane by a secondary growth method, and provides a synthesis process for uniformly and compactly coating seed crystals on a support body with poor hydrophilicity by a dripping method and preparing a compact and flat molecular sieve membrane by hydrothermal reaction.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for synthesizing a NaA molecular sieve membrane is characterized by comprising the following steps:
1) pre-treating the surface of the support body; polishing an aluminum oxide plate, placing the aluminum oxide plate in water for ultrasonic oscillation cleaning, then sequentially soaking the aluminum oxide plate in a hydrochloric acid solution and a sodium hydroxide solution, then ultrasonically oscillating and washing the aluminum oxide plate to be neutral, drying and taking out for later use;
2) preparing a support surface seed crystal layer; mixing and stirring a silicon source, an aluminum source, an alkali source and water uniformly, placing the mixture in a reaction kettle for crystallization, and then performing suction filtration and drying to obtain NaA molecular sieve seed crystals; dissolving NaA molecular sieve seed crystals in an ethanol solution to prepare a liquid crystal, coating the liquid crystal seed crystals on the surface of the alumina plate pretreated in the step 1) by adopting a dripping method, and drying to obtain a support body with the surface covered with the seed crystal layer;
3) preparing a NaA molecular sieve membrane; mixing and stirring a silicon source, an aluminum source, an alkali source and water uniformly to obtain a NaA molecular sieve membrane growth solution; and (3) soaking the support body with the surface covered with the seed crystal layer obtained in the step 2) in a reaction kettle filled with NaA molecular sieve membrane growth liquid for hydrothermal crystallization, rapidly cooling after the reaction is finished, and washing and drying to obtain the NaA molecular sieve membrane on an alumina plate.
In the scheme, the grinding step in the step 1) adopts abrasive paper for grinding, and the models of the abrasive paper are preferably 800# and 1200 #.
In the scheme, the concentration of the hydrochloric acid and the sodium hydroxide in the step 1) is 0.5-4 mol/L.
In the scheme, the drying temperature in the step 1) is 50-80 ℃, and the drying time is 10-24 h.
In the scheme, the aluminum source in the step 2) and the step 3) is one of aluminum chloride, aluminum hydroxide and sodium metaaluminate; the silicon source is one of water glass, sodium silicate, silica sol and silicon dioxide; the alkali source is sodium hydroxide.
In the above scheme, the addition amounts of the alkali source, the silicon source and the aluminum source in step 2) and step 3) are respectively added with the introduced Na2O、SiO2And Al2O3The mol ratio of the alkali source, the silicon source, the aluminum source and the water is based on Al2O3:Na2O:SiO2:H2O is 1 (0.5-3), (1-3) and (100-200).
In the scheme, the average particle size of the NaA molecular sieve seed crystal obtained in the step 2) is 1-5 μm.
In the scheme, the concentration of the NaA molecular sieve seed crystal in the liquid crystal is 2-5 g/L.
Preferably, the concentration of the NaA molecular sieve seed crystal in the liquid crystal liquid is 3-4 g/L.
In the above scheme, the seed crystal liquid is dropwise added to the surface of the support body by the dripping method until the seed crystal liquid completely covers the support body, and the dripping speed is 30-60 drops/min.
Preferably, the dripping height is 0.5-10 cm; the diameter of the injector is 0.2-1 cm.
Preferably, the corresponding dripping amount of the surface of the support body is 0.5-1 ml/cm2。
More preferably, the dripping area of the support surface corresponding to each dripping point (dripping position of the injector) is 1cm2The following.
In the scheme, the surface of the support body which is not covered with the seed crystal layer is wrapped and protected by a material (preferably polytetrafluoroethylene gummed paper) which does not influence the crystallization reaction, and then the support body is placed in a NaA molecular sieve membrane growth liquid for hydrothermal synthesis crystallization treatment.
In the scheme, the drying temperature in the step 2) is 50-100 ℃.
Preferably, the drying time in the step 2) is 2-3 h.
In the scheme, the mixing speed of the mixing and stirring in the step 2) and the step 3) is 60-500 r/min, the stirring time is 3-5 h, and the stirring temperature is room temperature.
In the scheme, the hydrothermal crystallization temperature is 60-120 ℃, and the time is 1-6 h.
In the scheme, the alumina plate is formed by pressing alumina particles, the size range of the alumina particles is 10-30 mu m, and the pore size distribution range formed among the particles is 0.5-1 mu m.
Preferably, the equivalent diameter of the surface of the aluminum oxide plate is 1-10 cm.
The principle of the invention is as follows: dripping NaA seed crystal onto a support body by adopting a dripping method, wherein when the liquid drop meets the support body, the liquid has a spreading tendency, and the seed crystal liquid completely covers the support body along with continuous dripping to form a solution layer; at a proper temperature (drying temperature after dropping coating), the NaA particles undergo a self-assembly process in ethanol to form an ordered structure spontaneously, and the ordered structure is arranged flatly together, and a uniform seed crystal layer is formed finally along with the evaporation of the ethanol.
The invention has the beneficial effects that:
1) the invention firstly proposes to adopt a dripping coating method, obtain a uniform and compact NaA molecular sieve crystal seed layer on a support body with poor hydrophilicity by pretreating the surface of the support body, regulating and controlling the liquid crystal and drying conditions, and further crystallize to prepare the NaA molecular sieve membrane; the method is simple, convenient and easy to operate, has good repeatability, makes up the problem that other crystal coating methods are limited by hydrophilicity, and is suitable for popularization and application.
2) The seed crystal dispersing agent adopted by the invention is ethanol, and the evaporation speed of the ethanol, the polarity of the ethanol and the interaction between NaA particles are important factors for promoting the leveling and uniform distribution of the seed crystal layer.
3) The NaA molecular sieve membrane obtained by the invention is flat and compact, has higher permeability and separation performance, and has higher industrial application value.
Drawings
FIG. 1 is a scanning electron microscope image of a NaA molecular sieve seed layer obtained in example 1 of the present invention.
FIG. 2 is a scanning electron microscope image of the NaA molecular sieve membrane obtained in example 2 of the present invention.
FIG. 3 shows the NaA molecular sieve membrane obtained in example 2 of the present invention and its X-ray diffraction pattern
FIG. 4 is a scanning electron microscope image of the NaA molecular sieve membrane obtained in example 3 of the present invention.
FIG. 5 is a scanning electron microscope image of the NaA molecular sieve membrane obtained in example 4 of the present invention.
FIG. 6 is a scanning electron micrograph of the NaA molecular sieve membrane obtained in comparative example 1.
FIG. 7 is a scanning electron micrograph of the NaA molecular sieve seed layer obtained in comparative example 2.
FIG. 8 is a scanning electron micrograph of a NaA molecular sieve seed layer obtained in comparative example 3.
Detailed Description
For a better understanding of the present invention, the following further illustrates the present invention with reference to specific examples and drawings, but the present invention is not limited to the following examples.
In the following examples, the alumina plate (. alpha. -Al)2O3The plate) is a circular support body formed by pressing large-particle alumina (10-30 mu m), and the pore size distribution range formed among particles is 0.5-1 mu m; the diameter of the alumina plate is 1-3 cm.
Example 1
A method for synthesizing a NaA molecular sieve membrane comprises the following steps:
1) using 800# and 1200# sandpaper to pair alpha-Al in sequence2O3Polishing a plate (with the diameter of 1cm), placing the plate in water, performing ultrasonic oscillation to wash away residual powder, sequentially soaking the plate in 2mol/L hydrochloric acid and sodium hydroxide solution for 24 hours respectively, performing ultrasonic oscillation for 15min, washing the plate to be neutral by using deionized water, placing the plate in a 60 ℃ drying oven, and drying the plate for 12 hours, and taking the plate out for later use;
2) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate and hydrogen according to the molar ratio of O to the sodium metaaluminate of 1:2:2:1200.8g of sodium oxide, 3g of 30% silica sol and 19.8g of deionized water, mixing and stirring at room temperature for 3h (stirring speed of 300r/min), putting into a stainless steel reaction kettle, reacting at 100 ℃ for 4h, performing suction filtration, drying (80 ℃), and preparing NaA molecular sieve seed crystals; dissolving the obtained NaA molecular sieve seed crystal in ethanol, stirring well, preparing 3g/L liquid crystal, taking the prepared liquid crystal with an injector with the diameter of 0.3cm, and separating by the distance of alpha-Al2O3The center of the plate surface is 1cm high as the dripping center, and the seed crystal is dripped on the alumina plate at the speed of about 1 drop/second (the corresponding dripping amount on the surface of the support is 0.5-1 ml/cm)2) Completely covering the surface of the support body with the seed crystal liquid, and drying at 80 ℃ for 2.5h to obtain the support body with the surface covered with the seed crystal layer for later use;
3) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2 to 120, stirring at room temperature for 3 hours (the stirring speed is 300r/min) to prepare a molecular sieve membrane growth solution, wrapping the back surface (the surface without the seed crystal layer) of the support body with polytetrafluoroethylene adhesive tape, placing the support body into a reaction kettle containing the molecular sieve membrane growth solution, reacting at 100 ℃ for 3 hours, washing with tap water after the reaction is finished, rapidly cooling, taking out the support body, washing with deionized water to be neutral, and drying to obtain the NaA molecular sieve membrane.
Fig. 1 is an SEM of the NaA molecular sieve seed crystal layer obtained in this example at different magnifications, which shows that the NaA seed crystal is uniformly and smoothly distributed on the surface of the support; the average particle size is about 1.5 to 2 μm.
Example 2
A method for synthesizing a NaA molecular sieve membrane comprises the following steps:
1) using 800# and 1200# sandpaper to pair alpha-Al in sequence2O3Polishing a plate (with the diameter of 1cm), placing the plate in water, performing ultrasonic oscillation to wash away residual powder, sequentially soaking the plate in 2mol/L hydrochloric acid and sodium hydroxide solution for 24 hours respectively, performing ultrasonic oscillation for 15min, washing the plate to be neutral by using deionized water, placing the plate in a 60 ℃ drying oven, and drying the plate for 12 hours, and taking the plate out for later use;
2) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2:2:150, mixing and stirring at room temperature for 3h (stirring speed of 500r/min), putting into a stainless steel reaction kettle, reacting at 100 ℃ for 4h, performing suction filtration, and drying (80 ℃) to obtain NaA molecular sieve seed crystals; dissolving the obtained NaA molecular sieve seed crystal in ethanol, stirring well, preparing 3g/L liquid crystal, taking the prepared liquid crystal with an injector with the diameter of 0.3cm, and separating by the distance of alpha-Al2O3The center of the plate surface is 1cm high as the dripping center, and the seed crystal is dripped on the alumina plate at the speed of about 1 drop/second (the corresponding dripping amount on the surface of the support is 0.5-1 ml/cm)2) Completely covering the surface of the support body with the seed crystal liquid, and drying at 80 ℃ for 2.5h to obtain the support body with the surface covered with the seed crystal layer for later use;
3) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2 to 150, stirring at room temperature for 3 hours (stirring speed of 500r/min) to prepare a molecular sieve membrane growth solution, wrapping the back surface (the surface without the seed crystal layer) of the support body with polytetrafluoroethylene adhesive tape, placing the support body with the seed crystal layer covered on the surface, reacting in a reaction kettle containing the molecular sieve membrane growth solution at 120 ℃ for 3 hours, flushing with tap water after the reaction is finished, rapidly cooling, taking out the support body, washing with deionized water to be neutral, and drying to obtain the NaA molecular sieve membrane.
Fig. 2 and 3 are SEM image and XRD image of the NaA molecular sieve membrane obtained in this example, respectively. It can be seen from fig. 2 that a dense, flat NaA molecular sieve membrane was formed on the alumina plate, and the side view shows that the NaA molecular sieve membrane was tightly bonded to the alumina plate, and no detachment was observed. The XRD pattern in fig. 3 shows that the drop coating process has successfully coated NaA molecular sieve seeds on alumina plates and produced NaA molecular sieve membranes.
Example 3
A method for synthesizing a NaA molecular sieve membrane comprises the following steps:
1) using 800# and 1200# sandpaper to pair alpha-Al in sequence2O3Polishing a plate (with the diameter of 3cm), placing the plate in water, performing ultrasonic oscillation to wash away residual powder, sequentially soaking the plate in 2mol/L hydrochloric acid and sodium hydroxide solution for 24 hours respectively, performing ultrasonic oscillation for 15min, washing the plate to be neutral by using deionized water, placing the plate in a 60 ℃ drying oven, and drying the plate for 12 hours, and taking the plate out for later use;
2) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2:2:120, mixing and stirring at room temperature for 3 hours (the stirring speed is 300r/min), putting into a stainless steel reaction kettle, reacting at 100 ℃ for 4 hours, performing suction filtration, and drying (80 ℃) to obtain NaA molecular sieve seed crystals; dissolving the obtained NaA molecular sieve seed crystal in ethanol, stirring well, preparing 3g/L liquid crystal, taking the prepared liquid crystal with an injector with the diameter of 0.3cm, and separating by the distance of alpha-Al2O3The center of the plate surface is 2cm high as the dripping center, and the seed crystal is dripped on the alumina plate at the speed of about 1 drop/second (the corresponding dripping amount on the surface of the support is 0.5-1 ml/cm)2) Completely covering the surface of the support body with the seed crystal liquid, and drying at 80 ℃ for 2.5h to obtain the support body with the surface covered with the seed crystal layer for later use;
3) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2 to 120, stirring at room temperature for 3 hours (the stirring speed is 300r/min) to prepare a molecular sieve membrane growth solution, wrapping the back surface (the surface without the seed crystal layer) of the support body with polytetrafluoroethylene adhesive tape, placing the support body into a reaction kettle containing the molecular sieve membrane growth solution, reacting at 100 ℃ for 5 hours, washing with tap water after the reaction is finished, rapidly cooling, taking out the support body, washing with deionized water to be neutral, and drying to obtain the NaA molecular sieve membrane.
Fig. 4 is an SEM image of the NaA zeolite membrane prepared in this example, and it can be seen that the obtained zeolite membrane has a flat and dense surface.
Example 4
A method for synthesizing a NaA molecular sieve membrane comprises the following steps:
1) using 800# and 1200# sandpaper to pair alpha-Al in sequence2O3Polishing a plate (with the diameter of 3cm), placing the plate in water, performing ultrasonic oscillation to wash away residual powder, sequentially soaking the plate in 2mol/L hydrochloric acid and sodium hydroxide solution for 24 hours respectively, performing ultrasonic oscillation for 15min, washing the plate to be neutral by using deionized water, placing the plate in a 60 ℃ drying oven, and drying the plate for 12 hours, and taking the plate out for later use;
2) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2:2:120, mixing and stirring at room temperature for 3h (the stirring speed is 400r/min), putting into a stainless steel reaction kettle, reacting at 100 ℃ for 4h, performing suction filtration, and drying (80 ℃) to obtain NaA molecular sieve seed crystals; dissolving the obtained NaA molecular sieve seed crystal in ethanol, stirring well, preparing 3g/L liquid crystal, taking the prepared liquid crystal with an injector with the diameter of 0.3cm, and separating by the distance of alpha-Al2O3The center of the plate surface is 2cm high as the dripping center, and the seed crystal is dripped on the alumina plate at the speed of about 1 drop/second (the corresponding dripping amount on the surface of the support is 0.5-1 ml/cm)2) Completely covering the surface of the support body with the seed crystal liquid, and drying at 80 ℃ for 2.5h to obtain the support body with the surface covered with the seed crystal layer for later use;
3) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of 1:2:2:120, stirring at room temperature for 4.5h (the stirring speed is 400r/min) to prepare a molecular sieve membrane growth solution, wrapping the back surface (the surface without the seed crystal layer) of the support body with polytetrafluoroethylene adhesive tape, placing the support body with the seed crystal layer covered on the surface, reacting for 3h at 100 ℃, rapidly cooling by using tap water after the reaction is finished, taking out the support body, washing to be neutral by using the deionized water, and drying to obtain the NaA molecular sieve membrane.
Fig. 5 is an SEM image of the NaA zeolite membrane prepared in this example, and it can be seen that the obtained zeolite membrane has a flat and dense surface.
Comparative example 1
A method for synthesizing a NaA molecular sieve membrane comprises the following steps:
1) using 800# and 1200# sandpaper to pair alpha-Al in sequence2O3Polishing a plate (with the diameter of 1cm), placing the plate in water, performing ultrasonic oscillation to wash away residual powder, sequentially soaking the plate in 2mol/L hydrochloric acid and sodium hydroxide solution for 24 hours respectively, performing ultrasonic oscillation for 15min, washing the plate to be neutral by using deionized water, placing the plate in a 60 ℃ drying oven, and drying the plate for 12 hours, and taking the plate out for later use;
2) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2:2:120, mixing and stirring at room temperature for 3 hours (the stirring speed is 300r/min), putting into a stainless steel reaction kettle, reacting at 100 ℃ for 4 hours, performing suction filtration, and drying (80 ℃) to obtain NaA molecular sieve seed crystals; dissolving the obtained NaA molecular sieve seed crystal in ethanol, uniformly stirring, preparing 3g/L of liquid crystal, wrapping one side of an alumina plate with polytetrafluoroethylene gummed paper, covering the alumina plate with the seed crystal by adopting a hot dipping method, and drying at 80 ℃ to obtain a support body with the surface covered with a seed crystal layer for later use;
3) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2 to 120, stirring at room temperature for 4.5 hours (the stirring speed is 300r/min) to prepare a molecular sieve membrane growth solution, putting the support body with the surface covered with the seed crystal layer into a reaction kettle containing the molecular sieve membrane growth solution, reacting for 3 hours at 100 ℃, washing with tap water for rapid cooling after the reaction is finished, taking out the support body, washing with deionized water to be neutral, and drying to obtain the NaA molecular sieve membrane.
Fig. 6 is an SEM image of the NaA molecular sieve membrane obtained in the present comparative example, which shows that the obtained molecular sieve membrane does not exhibit a compact state, and an alumina plate is leaked in a part of the area, which is mainly caused by the fact that the hot dipping method cannot obtain a uniform and compact seed layer for the alumina plate.
Comparative example 2
A method for synthesizing a NaA molecular sieve membrane comprises the following steps:
1) using 800# and 1200# sandpaper to pair alpha-Al in sequence2O3Polishing a plate (with the diameter of 1cm), placing the plate in water, performing ultrasonic oscillation to wash away residual powder, sequentially soaking the plate in 2mol/L hydrochloric acid and sodium hydroxide solution for 24 hours respectively, performing ultrasonic oscillation for 15min, washing the plate to be neutral by using deionized water, placing the plate in a 60 ℃ drying oven, and drying the plate for 12 hours, and taking the plate out for later use;
2) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2:2:120, mixing and stirring at room temperature for 3 hours (the stirring speed is 300r/min), putting into a stainless steel reaction kettle, reacting at 100 ℃ for 4 hours, performing suction filtration, and drying (80 ℃) to obtain NaA molecular sieve seed crystals; dissolving the obtained NaA molecular sieve seed crystal in acetonitrile, uniformly stirring, preparing 3g/L of liquid crystal, taking the prepared liquid crystal by using an injector with the diameter of 0.3cm, dripping the seed crystal on an alumina plate at the speed of about 1 drop/second to ensure that the seed crystal completely covers the surface of a support body, and drying for 2.5 hours at the temperature of 80 ℃ to obtain the support body with the surface covered with the seed crystal layer for later use;
3) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2 to 120, stirring at room temperature for 4.5 hours (the stirring speed is 300r/min) to prepare a molecular sieve membrane growth solution, putting the support body with the surface covered with the seed crystal layer into a reaction kettle containing the molecular sieve membrane growth solution, reacting for 3 hours at 100 ℃, washing with tap water for rapid cooling after the reaction is finished, taking out the support body, washing with deionized water to be neutral, and drying to obtain the NaA molecular sieve membrane.
FIG. 7 is an SEM image of the NaA molecular sieve seed crystal layer obtained in the comparative example, and it can be seen that the obtained molecular sieve seed crystal has very uneven distribution and has unevenness.
Comparative example 3
A method for synthesizing a NaA molecular sieve membrane comprises the following steps:
1) using 800# and 1200# sandpaper to pair alpha-Al in sequence2O3The plate (diameter 1cm) was polishedPlacing the powder in water for ultrasonic oscillation to wash away residual powder, sequentially soaking in 2mol/L hydrochloric acid and sodium hydroxide solution for 24h respectively, then ultrasonic oscillation for 15min to be washed to be neutral by deionized water, placing the solution in a 60 ℃ oven for drying for 12h, and taking out for later use;
2) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2:2:120, mixing and stirring at room temperature for 3 hours (the stirring speed is 300r/min), putting into a stainless steel reaction kettle, reacting at 100 ℃ for 4 hours, performing suction filtration, and drying (80 ℃) to obtain NaA molecular sieve seed crystals; dissolving the obtained NaA molecular sieve seed crystal in ethanol, stirring well, preparing 6g/L liquid crystal, taking the prepared liquid crystal with an injector with the diameter of 0.3cm, and separating by the distance of alpha-Al2O3The center of the plate surface is 1cm high as the dripping center, the seed crystal is dripped on the alumina plate at the speed of about 1 drop/second to completely cover the surface of the support body, and the support body with the surface covered with the seed crystal layer is obtained after drying for 2.5 hours at the temperature of 80 ℃ for standby;
3) according to Al2O3:Na2O:SiO2:H2Weighing 1.64g of sodium metaaluminate, 0.8g of sodium hydroxide, 3g of 30% silica sol and 19.8g of deionized water according to the molar ratio of O to 2 to 120, stirring at room temperature for 3 hours (the stirring speed is 300r/min) to prepare a molecular sieve membrane growth solution, wrapping the back surface (the surface without the seed crystal layer) of the support body with polytetrafluoroethylene adhesive tape, placing the support body into a reaction kettle containing the molecular sieve membrane growth solution, reacting at 100 ℃ for 3 hours, washing with tap water after the reaction is finished, rapidly cooling, taking out the support body, washing with deionized water to be neutral, and drying to obtain the NaA molecular sieve membrane.
Fig. 8 is an SEM of the NaA molecular sieve seed layer obtained in this example, and it can be seen that the NaA seed crystal is not uniformly distributed on the surface of the support, and has an uneven phenomenon.
Application example
The NaA molecular sieve membranes obtained in examples 1-4 were subjected to ethanol/water permeability tests, and the results are shown in Table 1.
TABLE 1 results of ethanol/Water Permeability test of NaA molecular sieve membranes obtained in examples 1 to 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 results show that the NaA molecular sieve membrane obtained by the invention has higher permeability and separation performance.
It is apparent that the above embodiments are only examples for clearly illustrating and do not limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications are therefore intended to be included within the scope of the invention as claimed.
Claims (9)
1. A method for synthesizing a NaA molecular sieve membrane is characterized by comprising the following steps:
1) pre-treating the surface of the support body; polishing an aluminum oxide plate, placing the aluminum oxide plate in water for ultrasonic oscillation cleaning, then sequentially soaking the aluminum oxide plate in a hydrochloric acid solution and a sodium hydroxide solution, then ultrasonically oscillating and washing the aluminum oxide plate to be neutral, drying the aluminum oxide plate, and taking the aluminum oxide plate out for later use;
2) preparing a support surface seed crystal layer; mixing and stirring a silicon source, an aluminum source, an alkali source and water uniformly, placing the mixture in a reaction kettle for crystallization treatment, and then performing suction filtration and drying to obtain NaA molecular sieve crystal seeds; dispersing NaA molecular sieve seed crystals in ethanol to prepare a seed crystal liquid, coating the seed crystal liquid on the surface of the alumina plate pretreated in the step 1) by adopting a dripping method, and drying;
the concentration of NaA molecular sieve crystal seeds in the liquid crystal is 2-5 g/L; the drying temperature is 50-100 ℃;
3) preparing a NaA molecular sieve membrane; mixing and stirring a silicon source, an aluminum source, an alkali source and water uniformly to prepare a NaA molecular sieve membrane growth solution; and (3) soaking the support body with the surface covered with the seed crystal layer obtained in the step 2) in a reaction kettle filled with NaA molecular sieve membrane growth liquid for hydrothermal crystallization, rapidly cooling after the reaction is finished, and washing and drying to obtain the NaA molecular sieve membrane on an alumina plate.
2. The synthesis method according to claim 1, wherein the concentration of the hydrochloric acid and the sodium hydroxide in the step 1) is 0.5-4 mol/L.
3. The synthesis method of claim 1, wherein the aluminum source in step 2) and step 3) is one of aluminum chloride, aluminum hydroxide and sodium metaaluminate; the silicon source is one of sodium silicate, silica sol and silicon dioxide; the alkali source is sodium hydroxide.
4. The method of synthesis according to claim 1, characterized in that steps 2) andthe adding amounts of the alkali source, the silicon source and the aluminum source in the step 3) are respectively the Na introduced by the adding amounts2O、SiO2And Al2O3The mol ratio of the alkali source, the silicon source, the aluminum source and the water is based on Al2O3:Na2O:SiO2: H2O is 1 (0.5-3), (1-3) and (100-200).
5. The synthesis method according to claim 1, wherein the average particle size of the NaA molecular sieve seed crystals is 1-5 μm.
6. The synthesis method of claim 1, wherein the seed solution is dropwise added to the surface of the support body by the dropping method until the seed solution completely covers the support body, the dropping speed is 30-60 drops/min, and the corresponding dropping amount on the surface of the support body is 0.5-1 ml/cm2。
7. The synthesis method according to claim 1, wherein the temperature of the hydrothermal synthesis crystallization treatment is 60-120 ℃ and the time is 1-6 h.
8. The synthesis method according to claim 1, wherein the alumina plate is formed by pressing alumina particles, the size range of the alumina particles is 10-30 μm, and the pore size distribution range formed between the particles is 0.5-1 μm.
9. A NaA molecular sieve membrane prepared by the synthesis method of any one of claims 1 to 8.
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| CN111013405A (en) * | 2019-12-25 | 2020-04-17 | 江门谦信化工发展有限公司 | Ethanol/water system molecular sieve composite membrane and preparation method and application thereof |
| CN111992050B (en) * | 2020-09-10 | 2022-05-17 | 南京惟新环保装备技术研究院有限公司 | Carrier surface modified hydrophilic molecular sieve membrane and preparation method thereof |
| CN112371081A (en) * | 2020-10-19 | 2021-02-19 | 西安工程大学 | Preparation method of attapulgite-based NaA molecular sieve membrane support |
| CN113198334B (en) * | 2021-05-07 | 2021-11-30 | 宿州中粮生物化学有限公司 | NaA molecular sieve membrane and preparation method and application thereof |
| CN114225718A (en) * | 2021-12-24 | 2022-03-25 | 中国科学院上海硅酸盐研究所 | NaA molecular sieve membrane on surface of porous silicon nitride ceramic and preparation method thereof |
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