CN114307689A - A kind of preparation method of wet gel conversion synthesis A-type zeolite membrane - Google Patents

Abstract

The invention provides a preparation method of wet gel conversion synthesis A-type zeolite membrane, belonging to the field of zeolite membrane material and the technical field of organic dehydration. The invention adopts the wet gel conversion method to prepare the A-type zeolite membrane, coats the surface of the carrier after the crystal coating with a certain proportion of the gel synthesis solution, crystallizes at a high temperature, the surface grows uniformly and continuously, and the membrane thickness is about 4 μm. It has higher permeate water flux and separation factor during pervaporation. Compared with high silicon-aluminum ratio zeolite membrane, it has better permeate water flux. Using this method can solve the problem of industrial scale-up of flat supports and reduce the cost of membrane preparation. .

Description

A kind of preparation method of wet gel conversion synthesis A-type zeolite membrane

technical field

The invention belongs to the field of zeolite membrane material and the technical field of organic dehydration, in particular to a preparation method for synthesizing A-type zeolite membrane by wet gel conversion.

Background technique

With the rapid development of my country's chemical industry, the refining of organic compounds has become more and more important in petrochemical, fine chemical, organic chemical, pharmaceutical and chemical fields, and the biggest problem in the process of organic refining is the dehydration of organic compounds. Whether in chemical synthesis or wastewater treatment, the presence of moisture is an insurmountable gap for organic matter. Organic matter often forms an azeotrope with water, which increases the difficulty of its dehydration. Therefore, it is urgent to find a practical and effective method for dehydration of organic matter. Dehydration of organic matter has attracted the attention of researchers and governments around the world, and is a research hotspot in the field of engineering.

A major problem currently faced by the ethanol dehydration industry is that ethanol and water can form azeotropes. At 78.15°C, the 97.2% ethanol aqueous solution by mass fraction or volume fraction forms an azeotrope that cannot be separated by traditional distillation methods. The traditional rectification method can achieve effective separation only for 10-85wt% ethanol solution. If the proportion of ethanol water is close to the composition of azeotrope, and the ethanol content exceeds 86%, the energy consumption required by traditional rectification will be greater. Especially when the target product is anhydrous ethanol, the reflux ratio of the equipment is required to be higher. The dehydration and separation of ethanol solution and most organic solvents is usually divided into two stages. Generally, the solution is concentrated to about 92% in the conventional distillation method, and then the concentrated solution is specially treated to obtain absolute ethanol and other high-purity organic compounds. Commonly used dehydration purification methods include rectification, liquid-liquid extraction and adsorption. For rectification, the process is very mature, but the energy consumption is too high, and the introduction of components is easy to cause pollution [Jaime J A, Rodríguez G, Gil ID. Industrial & Engineering Chemistry Research, 2018, 57(29): 9615-9626.], Adsorption The treatment capacity is large and the energy consumption is also low, but the regeneration is more complicated [Moulai S, Ghezini R, Hasnaoui A, et al. Research on Chemical Intermediates, 2019, 45(3): 1653-1668]. Low, pollution-free, and easy to regenerate, it is widely welcomed by everyone, but the processing capacity is small.

Compared with organic membrane materials, inorganic zeolite membrane materials not only have high mechanical stability and anti-biofouling properties, but also have regular crystalline pores, adjustable framework silicon-alumina ratio (hydrophilic and hydrophobic) and other characteristics, so inorganic zeolite membranes are used in inorganic zeolite membranes. It not only has good stability for organic dehydration, but also has excellent separation factor and high permeate water flux.

The traditional hydrothermal synthesis method is widely used due to its mature technology, convenience and simplicity, but film formation requires multiple crystallizations. Masuda et al. used multiple in-situ synthesis methods to prepare zeolite membranes, trying to increase the number of synthesis times. Thickening to compensate [Masuda T, Hara H. Microporous Mater, 1995, 3(4-5):565-571]. At present, NaA zeolite molecular sieve membranes are mostly prepared by secondary growth method, which can greatly reduce the number of crystallization [Liu Guangrui, Yang Jianhua, Wang Lei, et al. Progress in Chemical Industry, 2019, 38(12):8.] . Due to the lack of solvent in the zeolite crystallization process, the wet gel conversion method effectively reduces its own pressure and eliminates many potential safety hazards. It can also be synthesized quickly at higher temperatures, and the mechanical strength of the membrane is also improved to a certain extent, which is more conducive to the reaction mechanism. research, thereby promoting the improvement of crystallinity. The wet gel conversion method saves more raw materials, and only needs to coat the gel layer once to crystallize, which is of great significance for environmental pollution and industrial scale-up.

SUMMARY OF THE INVENTION

Aiming at the problems of high cost and great damage to the mechanical strength of the membrane by the traditional synthesis method of the above-mentioned organic dehydration process, the present invention proposes a preparation method for synthesizing the A-type zeolite membrane by the wet gel conversion method.

Technical scheme of the present invention:

A preparation method for synthesizing A-type zeolite membrane by wet gel conversion. The surface of a porous carrier is modified, coated with a crystal seed liquid to obtain a crystal seed layer, and coated with a coating liquid to obtain a gel layer; and then the carrier is crystallized Then, the A-type zeolite molecular sieve membrane is obtained; the porous carrier is modified and then introduced into crystal seeds and directly coated with a gel solution to prepare a gel, which is directly converted into a molecular sieve membrane in a vapor environment, and the synthesis pressure is adjusted during the synthesis process. to control the film quality. In this method, a seed layer is pre-coated on an inexpensive macroporous carrier, and the A-type zeolite molecular sieve membrane prepared by the gel method has excellent separation performance and certain stability. The method has high repeatability, effective solvent saving and high membrane performance.

Specific steps are as follows:

(1) Modified carrier: after wetting the porous carrier with deionized water, wipe the alumina powder with uniform particle size on the surface of the porous carrier, dry it and wipe it with absorbent cotton;

(2) Coating seed layer: Disperse A-type zeolite molecular sieve crystal seeds in deionized water to obtain A-type zeolite molecular sieve seed crystal liquid, coat the seed crystal liquid on the surface of the porous carrier, and then dry it with absorbent cotton to obtain Uniform dense, defect-free seed layer;

(3) Preparation of gel solution: using silica sol as the silicon source, sodium metaaluminate as the aluminum source, and sodium hydroxide as the alkali source, mix the aluminum source, the alkali source and the silicon source, and continue to stir and age for 4 to 6 hours to form A stable SiO ₂ -Na ₂ O-Al ₂ O ₃ -H ₂ O system; wherein, the molar ratios of the components are: SiO ₂ /Al ₂ O ₃ =1-5, H ₂ O/SiO ₂ =50-60 , Na ₂ O/SiO ₂ =1～2;

(4) Coating the gel layer: using the gel solution obtained in the step (3) as a coating solution, uniformly coat the surface of the porous carrier obtained in the step (2);

(5) Crystallization: before crystallization, add water that accounts for 0.1 to 2% of the volume of the still body to adjust the vapor pressure in the still; then place the porous carrier obtained in step (4) in the autoclave at Crystallize at 80～120℃ for 3～5.5h.

The crystallization reaction conditions are 3-5.5 hours at 80-120° C., and the crystallization time decreases with the increase of the crystallization temperature. The preferred crystallization reaction conditions are 100° C. for 4 hours.

In step (2), the content of the A-type zeolite molecular sieve in the A-type zeolite molecular sieve crystal seed liquid is 0.5-2%, the A-type zeolite molecular sieve crystal particle size is 0.2-3 μm, and preferably the A-type zeolite molecular sieve size is 0.5-3 μm of the carrier aperture. 1 times.

In step (2), the method for introducing the A-type zeolite molecular sieve seed liquid into the seed layer on the surface of the porous carrier is dipping method, hot dipping method, variable temperature thermal dipping method, vacuum coating crystal method, spraying method, wiping method or spin coating.

In step (3), the preparation conditions of the gel solution are: stirring at 20-50° C. for 4-6 hours.

The preparation process of the A-type zeolite membrane synthesis solution is to stir and dissolve sodium hydroxide and sodium aluminate in water, add silica sol after the solution is clarified, and stir and age for 4-6 hours.

In step (4), the method for preparing the gel layer is dipping method, spin coating method, flow method, vacuum method, spraying method or spin coating method; single-channel tubular type, hollow fiber carrier is preferably dipping method; multi-channel tubular type and The plate carrier is preferably a flow method.

In step (5), the crystallization temperature is 80-120° C., and the crystallization time is 3-5.5 h.

The material of the porous carrier is alumina, zirconia, mullite, and porous metal; the form of the porous carrier is single-channel and multi-channel tubular, plate, and hollow fibers; the pore diameter of the porous carrier is 0.02-40 μm.

The crystallization heating method adopts conventional heating and microwave.

The porous carrier is an α-Al ₂ O ₃ tube, a hollow fiber or a stainless steel tube, preferably an α-Al ₂ O ₃ tube.

The pore size of the porous carrier is 0.5-5 μm, preferably the pore size of the carrier is 2-3 μm.

The alumina particle modification method is rubbing method, hot dipping method or spraying method, preferably rubbing method.

After the carrier film was formed, the surface impurities were quickly washed with clean water and soaked in deionized water for 12 h.

The A-type zeolite molecular sieve membrane has a flux of 2.62 kg·m ^-2 ·h ^-1 to 90 wt.% ethanol/water at a temperature of 75° C., and the separation factor is greater than 10,000.

Beneficial effects of the present invention: A-type zeolite membrane is used for pervaporation of alcohols dehydration, has higher separation factor, and has larger permeation flux than zeolite membrane with high silicon-aluminum ratio, and operates by wet gel conversion method Low cost and easier than traditional hydrothermal methods.

Description of drawings

Figure 1 is a schematic diagram of a pervaporation (PV) device, wherein a magnetic stirrer, b water bath, c membrane tube, d membrane module, e raw material storage tank, f cold trap, g liquid nitrogen, h buffer bottle, i vacuum meter , j vacuum pump;

Fig. 2 is A-type zeolite membrane surface scanning electron microscope (SEM) figure;

Fig. 3 is A-type zeolite membrane cross section scanning electron microscope (SEM) figure;

Fig. 4 is the hydrothermal stability diagram of A-type zeolite membrane pervaporation;

Figure 5 is an x-ray diffraction pattern (XRD) pattern of the A-type zeolite membrane, wherein a is the membrane and b is the crystal.

Detailed ways

The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

(1) Modified carrier: after wetting the porous carrier with deionized water, rubbed 3 μm alumina powder on the surface of the porous carrier, and then put it in a 100°C oven to dry;

(2) Handling the carrier: After the modified carrier is dried, dry the carrier with absorbent cotton.

(3) Coating seed layer: Disperse A-type zeolite molecular sieve crystal seeds in deionized water to obtain A-type zeolite molecular sieve crystal seed liquid, and coat the seed crystal liquid on the surface of the porous carrier to obtain uniform, dense, defect-free crystals seed layer;

(4) Preparation of gel solution: the present invention uses the synthetic solution as the gel coating solution, wherein the content of water is less; the synthetic solution uses silica sol as the silicon source, sodium metaaluminate as the aluminum source, and sodium hydroxide as the Alkali source, add aluminum source, alkali source and silicon source to mix, continue to stir and age for 4-6 hours to form a stable SiO ₂ -Na ₂ O-Al ₂ O ₃ -H ₂ O system. Wherein, the molar ratio of each component is: SiO ₂ /Al ₂ O ₃ =1-5, H ₂ O/SiO ₂ =50-60, Na ₂ O/SiO ₂ =1-2;

(5) Handling the carrier: After the crystal-coated carrier is cured, dry the carrier with absorbent cotton.

(6) Coating gel layer: take the gel solution obtained in (4) as a coating solution, and evenly coat it on the surface of the carrier;

(7) Crystallization: The carrier is placed in an autoclave and crystallized at 80-120° C. for 3-5.5 hours.

In the step (3), the content of the A-type zeolite molecular sieve in the A-type zeolite molecular sieve seed liquid is 0.5-2%, and the A-type zeolite molecular sieve crystal particle size in the A-type zeolite molecular sieve liquid is 0.2-3 μm.

In the step (3), the method of introducing the A-type zeolite molecular sieve seed liquid into the seed layer on the surface of the porous carrier is dipping method, hot dipping method, variable temperature thermal dipping method, vacuum coating crystal method, spraying method, rubbing method, etc. A coating method or a spin coating method, preferably a variable temperature dipping method.

In the step (4), the preparation conditions of the gel solution are: stirring at 20-50° C. for 4-6 hours, preferably stirring at 30° C. for 4 hours.

In the step (6), the method of coating the gel layer is dipping method, hot dipping method, vacuum method, spraying method, wiping method or spin coating method, preferably dipping method.

In the step (7), the crystallization temperature is 80-120°C, and the crystallization time is 3-5.5h, preferably the crystallization temperature is 100°C, and the crystallization time is 4h.

In order to further describe the present invention, several specific implementation examples are given below, but the patent rights are not limited to the following examples.

Example 1

(1) Pretreatment α-Al ₂ O ₃ carrier tube: the outer diameter of the tube is 12 mm, the inner diameter of the tube is 8 mm, the average pore diameter is 2-3 μm, and the porosity is about 30-40%; the outer surface of the carrier tube is sanded with 800-mesh and 1500-mesh sandpaper. Grind one after another; use deionized water to ultrasonically remove the residual sand on the carrier tube, repeat several times until the water used for washing the tube no longer becomes turbid, and then use acid and alkali ultrasonic vibration in turn to remove the residues in the carrier pores , and washed with deionized water until neutral; finally, the tube was dried in an oven, and then placed in a muffle furnace for calcination at 550 ° C for 6 hours, and both ends were sealed for use;

(2) placing the carrier tube obtained in step (1) in deionized water for 10 to 15 s, and then rubbing and modifying it with 3 μm spherical alumina powder to obtain a modified carrier;

(3) The carrier tube obtained in step (2) was preheated at 175°C for 3 to 4 hours, and then quickly immersed in suspension I of large seed crystals (3 μm) with a mass concentration of 2 wt.%, at 80°C overnight Drying and curing at 175°C for 3-4 hours to obtain the seed layer supported carrier I;

(4) Wipe off the seed crystals on the surface of the carrier with absorbent cotton, and place the seed layer supported carrier I at 80°C for 3 to 4 hours, and then immerse it into a small seed crystal (200 nm) with a mass concentration of 0.5 wt.% to suspend In liquid II, drying at 80°C overnight, and curing at 175°C for 3 to 4 hours to obtain seed layer supported carrier II;

(5) A synthesis solution was prepared with a molar ratio of 1Al ₂ O ₃ : 2SiO ₂ : 2Na ₂ O : 100H ₂ O, and the mixture was stirred and aged for 4-6 hours at room temperature;

(6) Immerse the carrier tube II in the synthesis solution for about 15-20 s to obtain the supported carrier III with a gel layer

(7) Load carrier III obtained in (6) into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, and place it in an oven at 100° C. for crystallization for 4 hours;

(8) The synthesized A-type molecular sieve zeolite membrane was washed with deionized water until neutral, and dried in an oven at 50°C.

Example 2

Except (7), all other steps are identical with embodiment 1;

Change the synthesis conditions, add 1 mL of water at the bottom of the kettle, synthesize the A-type zeolite molecular sieve membrane, and carry out the pervaporation test of 90wt.% ethanol/water at 75 °C. The flux and separation factor of the membrane are 1.30 kg m, respectively. ^-2 · h ^-1 , 1491.

Example 3

The A-type zeolite molecular sieve membrane prepared in Example 1 was used to separate the 90 wt.% ethanol/water system for a time-dependent test, and the test results are shown in FIG. 4 . After 10h of testing, the total flux decreased from the initial 2.62kg·m-2·h-1 to about 2.32kg·m-2·h-1, and the water content on the permeate side remained basically unchanged.

Comparative Example 1

The A-type zeolite molecular sieve membrane was synthesized by conventional in-situ hydrothermal synthesis method. Step by step, the synthetic liquid after aging is slowly introduced into the reaction kettle along the inner lining wall of the kettle, and crystallized at high temperature. It can be seen from Table 1 that the separation factor of the direct in situ synthesis on the macroporous carrier is only 1.45 and the flux reaches 23.53 kg·m ² ·h ^-1 , indicating that the NaA zeolite membrane grown in situ is discontinuous and dense.

Table 1 Flux and separation factor of Example 1 and Comparative Example 1

Claims (8)

1. a preparation method of wet gel conversion synthesis A-type zeolite membrane, carrying out modification on porous carrier surface, coating seed liquid to obtain crystal seed layer, coating coating liquid to obtain gel layer; then described carrier crystal After chemical treatment, the A-type zeolite molecular sieve membrane is obtained; it is characterized in that the porous carrier is modified and then introduced into crystal seeds and directly coated with a gel solution to prepare a gel, which is directly converted into a molecular sieve membrane in a vapor environment, and then synthesized During the process, the quality of the film formation is controlled by adjusting the synthesis pressure; the specific steps are as follows: (1) Modified carrier: after wetting the porous carrier with deionized water, wipe the alumina powder with uniform particle size on the surface of the porous carrier, dry it and wipe it with absorbent cotton; (2) Coating seed layer: Disperse A-type zeolite molecular sieve crystal seeds in deionized water to obtain A-type zeolite molecular sieve seed crystal liquid, coat the seed crystal liquid on the surface of the porous carrier, and then dry it with absorbent cotton to obtain Uniform dense, defect-free seed layer; (3) Preparation of gel solution: using silica sol as the silicon source, sodium metaaluminate as the aluminum source, and sodium hydroxide as the alkali source, mix the aluminum source, the alkali source and the silicon source, and continue to stir and age for 4 to 6 hours to form A stable SiO ₂ -Na ₂ O-Al ₂ O ₃ -H ₂ O system; wherein, the molar ratios of the components are: SiO ₂ /Al ₂ O ₃ =1-5, H ₂ O/SiO ₂ =50-60 , Na ₂ O/SiO ₂ =1～2; (4) Coating the gel layer: using the gel solution obtained in the step (3) as a coating solution, uniformly coat the surface of the porous carrier obtained in the step (2); (5) Crystallization: before crystallization, add water that accounts for 0.1 to 2% of the volume of the still body to adjust the vapor pressure in the still; then place the porous carrier obtained in step (4) in the autoclave at Crystallize at 80～120℃ for 3～5.5h. 2. preparation method according to claim 1 is characterized in that, in step (2), the content of A-type zeolite molecular sieve in A-type zeolite molecular sieve crystal seed liquid is 0.5～2%, and A-type zeolite molecular sieve crystal particle size is 0.2～3μm. 3. preparation method according to claim 1 is characterized in that, in step (2), the method for introducing A-type zeolite molecular sieve crystal seed liquid into the seed layer on the porous carrier surface is dipping method, hot dipping method, temperature change Hot dip, vacuum coating, spray coating, wipe coating or spin coating. 4 . The preparation method according to claim 1 , wherein, in step (3), the preparation conditions of the gel solution are: stirring at 20-50° C. for 4-6 hours. 5 . 5. The preparation method according to claim 1, wherein the material of the porous carrier is alumina, zirconia, mullite, porous metal; the form of the porous carrier is a single-channel tubular type, a multi-channel tubular type , plate type, hollow fiber; the pore size of the porous carrier is 0.02-40 μm. 6. preparation method according to claim 1 is characterized in that, in step (4), the method for preparing gel layer is dipping method, spin coating method, flow method, vacuum method, spraying method or spin coating method; Channel tube type, hollow fiber carrier selection impregnation method; multi-channel tube type, plate type carrier selection flow method. 7 . The preparation method according to claim 1 , wherein, in step (5), the crystallization temperature is 80-120° C., and the crystallization time is 3-5.5 h. 8 . 8 . The preparation method according to claim 1 , wherein the crystallization heating method adopts conventional heating and microwave. 9 .

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