CN1112231C - Preparation of x-type molecular sieve film - Google Patents

Abstract

The present invention relates to a method for preparing an X type molecular sieve film, which mainly overcomes the deficiencies that the previous techniques don't relate to the film forming of X type molecular sieves on carriers and film forming processes are complicated and has long time. In the present invention, a reaction system of which the mol components of raw materials is aNa2O. bAl2O3. cSiO2. dH2O is adopted. In the reaction system, a/c=1.0 to 12.9; c/b=2 to 6; d/c=200 to 1000. in a synthetic process, a silicon source, an aluminium source and a sodium source are respectively put at both sides of a porous material pipe, and are crystallized for 36 to 168 hours under the condition that the reaction temperature is from 50 to 120 DEG C. X type molecular sieves are successfully formed on the inner surface of a porous material pipe of which the pore diameters are from 40 to 10000 angstroms through crystallization growth. Furthermore, the present invention has the characteristics of simple process of film forming operation, strong adhesive force of molecular sieves and high yield of molecular sieves, better overcomes the previous deficiencies, and can be used for industrial production.

Description

Method for preparing X-type molecular sieve membrane

The invention relates to a method for preparing X-type molecular sieve membranes.

X-type molecular sieves have larger pore diameter channels and higher porosity, and are suitable for the separation and reaction process of larger molecules. It is an ideal material for the industrialization of membrane processes.

At present, the zeolite molecular sieves obtained by artificial synthesis are all granular powders, and their size is determined by crystallization operation parameters such as crystallization liquid concentration and crystallization time. Molecular sieves have been widely used in adsorption separation and heterogeneous catalytic reactions due to their uniform pore size and high shape selectivity. However, the separation and reaction functions of molecular sieves are unified, and zeolite is synthesized on the surface of porous materials by using porous materials as carriers to form a layer of uniform zeolite molecular sieve film. It is a new type of catalytic material that can realize the simultaneous separation of some materials, which has been developed by scientific and technological workers in recent years.

Molecular sieves were used as membrane materials, and were first used as fillers in polymer membranes to improve the permeation rate and selectivity of polymer membranes. Due to the temperature resistance of polymer materials, the research in this area has been limited to the low-temperature liquid phase separation process-pervaporation process; the gas phase separation process at higher temperatures has also been studied recently, but little progress has been made. If the molecular sieve is directly formed on the surface of the ceramic carrier to form a film continuously, it not only maintains the separation and catalytic characteristics of the molecular sieve, but also greatly improves the separation effect of the porous matrix bottom membrane on the material, realizes the integration of separation and reaction, and has the advantages of an inorganic membrane. Advantages - temperature resistance, chemical corrosion resistance, swelling resistance and good mechanical strength, which has become a hot and difficult point of research. However, ceramic materials are fragile, have poor vibration resistance, and are inconvenient to process and shape, which will bring troubles to industrial applications.

USP5464798 uses γ-Al ₂ O ₃ gel coated on the inner surface of α-Al ₂ O ₃ porous ceramic tube to modify it into a carrier with a pore size of 50 angstroms, and the ceramic tube is filled with silica gel, NaOH and TPABr. The crystallization operation of the molecular sieve mother liquor is generally 2 to 3 times. The synthetic Silicalite-1 zeolite membrane significantly reduces the permeation flux of gas after membrane modification, which is generally only 3-14% of the original base membrane, and the N ₂ permeability is 5 times lower, and nC ₄ H ₁₀ is 190 times lower. Butane is 1000 times lower. Isobutane is obviously adsorbed on the membrane, and the separation coefficient of the zeolite membrane for the mixture of n-butane and isobutane can reach 22 (at room temperature).

Document WO 95 29751 uses in-situ hydrothermal crystallization on ceramic tubes and porous sintered glass tubes to synthesize Silicalite-1 membranes. The ratio of H ₂ and iC ₄ H ₁₀ permeation rates can reach 30, and can be used to study isobutane Dehydrogenation. The outer tube of the reactor is a stainless steel tube, and the inner and outer chambers of the tube are sealed with graphite gaskets, and the industrial Pt-Sn/γ-Al ₂ O ₃ catalyst is placed in the inner cavity of the membrane tube. Compared with the α-Al ₂ O ₃ membrane, the molecular sieve membrane catalytic technology can increase the yield of isobutane by 70%.

Document EP674939 describes the situation of synthesizing ZSM-5 molecular sieve membrane on porous α-Al ₂ O ₃ ceramic body. In the experiment, the silicon source and the aluminum source were properly configured, and the molar ratio of the final mother liquor was SiO ₂ /Al ₂ O ₃ : 102, Na ₂ O/SiO ₂ : 0.23, TPABr/SiO ₂ : 0.1, H ₂ O/SiO ₂ :200, the autoclave was placed in a heating furnace, kept at 180°C, and evenly heated for 36 hours to form a film. The prepared membrane is applied to the separation of CO ₂ in the air, It can reach 53～56, and the permeation rate of CO ₂ can reach 1.7×10 ^-7 mol/m ² .sec.Pa, while And also up to 42.

WO 93 17781 adopts the gas phase synthesis method. Firstly, molecular sieve synthesis liquid is pre-loaded on the α-Al ₂ O ₃ tube or disk, and the xerogel after film formation is hydrothermally crystallized at 130-200°C, and repeated several times. Operate film formation. The ZSM-5 zeolite membrane synthesized by this method has selective permeation effect on the mixed system of m-, p-xylene and triisopropylbenzene.

Document USP 4699892 utilizes porous carrier to synthesize A-type zeolite layer. The separability of the membrane is characterized by a mixture of 33 mol% of methane, ethane and propane, and the molar composition of the permeated gas is 73.5% of methane, 26% of ethane and 0.5% of propane.

Document JP 08257301 introduces that a Y-type zeolite membrane is synthesized on a tubular porous support. The molar composition of aluminosilicate sol for film formation is H ₂ O/SiO ₂ : 50-120, Na ₂ O/SiO ₂ : 0.5-2, SiO ₂ /Al ₂ O ₃ : 5-15, and the porous carrier is soaked in The hydrothermal crystallization in the sol forms a film. The membrane can be used as a pervaporation separation membrane, capable of separating alcohol water and alcohol-cyclohexane organic mixed system.

To sum up, none of the above-mentioned literatures involves the film formation of X-type molecular sieves on the carrier and the situation of porous material films loaded with X-type molecular sieves suitable for industrial applications. In addition, the inventors have found through experiments that the X-type molecular sieve formed on the porous material has poor adhesion to the carrier, and the amount of raw materials required for crystallization is large, that is, the yield of the synthesized X-type molecular sieve is low.

The object of the present invention is to provide a method for preparing X-type molecular sieve membranes in order to overcome the disadvantages in the prior art that do not involve X-type molecular sieves forming films on carriers. The preparation method has the characteristics of strong adhesion between the prepared X-type molecular sieve membrane and the carrier, and high yield of the obtained X-type molecular sieve.

The purpose of the present invention is achieved by the following technical solutions: a method for preparing X-type molecular sieve membranes, using aluminum source, sodium source, silica gel or silica sol and water as raw materials, and the molar composition of raw materials in the reaction system is calculated in terms of oxides It is: aNa ₂ O·bAl ₂ O ₃ ·cSiO ₂ ·dH ₂ O, a/c=1.0～12.9, c/b=2～6, d/c=200～1000, in the synthesis process, the silica gel Or make a solution of silica sol and water and place it in a glass tube or stainless steel porous material tube with a pore size of 40-10000 angstroms, place a solution of sodium source, aluminum source and water outside the porous material tube, and react at 50-120 °C Under temperature conditions, crystallize for 36 to 168 hours, and crystallize and grow X-type molecular sieves on the inner surface of the porous material tube. Before crystallization, amorphous aluminosilicate or X-type molecular sieves are pre-loaded in the porous material tube. Calculated by weight percentage, it is 0.01-0.5% of the weight of the porous material tube.

In the above technical scheme, the aluminum source is metal aluminum foil, sodium aluminate, aluminum sulfate, pseudoboehmite, aluminosilicate or aluminum alkoxide with 2 to 4 carbon atoms, and its preferred solution is sodium aluminate; the sodium source is aluminum Sodium Hydroxide or/and Sodium Hydroxide. In terms of molar ratio, the preferred range of a/c in the reaction system is 1.2 to 9.8, the preferred range of c/b is 3 to 5, and the preferred range of d/c is 250 to 800; during crystallization, the preferred range of reaction temperature 80-105°C, and the preferred range of crystallization time is 72-120 hours.

By adopting the new method for preparing the X-type molecular sieve membrane described in the invention, a uniform and continuous X-type molecular sieve thin layer can be grown on the porous material tube. It can be used for the separation of larger molecular mixture systems, and the molecular sieve pores can be modified by physical or chemical modification methods to adjust the pore size, especially in the field of separation, which can be widely used.

X-type molecular sieve zeolite mainly forms a film on the inner surface of the carrier. Through SEM characterization, there are X-type molecular sieve zeolite crystals growing in the pores close to the inner surface of the carrier. The crystal layer grown in this layer of pores can reach 150 to 200 meters deep into the pores. Micron, connected with the X-type molecular sieve zeolite layer on the surface of the carrier, improving the adhesion of the X-type molecular sieve to the entire X-type molecular sieve zeolite layer. It can provide a larger permeation area for the carrier per unit volume, and like a single reactor tube, multiple zeolite membranes can be bundled together to form a tubular membrane separation or reactor, which can increase the area per unit volume of the membrane process , has practicability, and is beneficial to the popularization and industrialization of the membrane process.

When synthesizing the X-type molecular sieve zeolite membrane by mixing the raw materials of the reaction system first, since the gel-like starting liquid is used, the crystallization of the growth center provided by the carrier in part of the gel is beneficial to the film formation, and most of the gel is homogeneous. The phase crystallizes and forms a powdery X-type molecular sieve in the main body of the solution. After each crystallization operation, clean the X-type molecular sieve formation layer on the surface of the carrier. From the results of ultrasonic cleaning, it can be seen that most of the formation layer is the deposition layer of X-type molecular sieve powder, which is easy to remove. Each crystallization and The amount of X-type molecular sieve grown by cross-linking on the carrier is very small. After seven or eight operations, the top layer of X-type molecular sieve with a certain thickness can be formed. The method of the present invention is used to synthesize the molecular sieve top layer on the inner surface of the porous material tube. After each synthesis, the sample is washed for 30 minutes under ultrasonic waves, and the growth on the surface of the carrier is rarely washed away. After four to five times of crystallization operations, the top layer was characterized by SEM, and its thickness reached ~20 microns. A layer of crystal layer could be observed under an optical microscope. It was difficult to scrape off with a spatula. The thickness of the composite film The mechanical strength is obviously improved.

The operation method in which the main components of the starting liquid are separated on both sides of the porous material tube avoids the crystallization that occurs in the main body of the crystallization liquid that is not beneficial to film formation. Therefore, the use of fully diluted starting liquid composition can significantly reduce the amount of drugs The input amount increased the yield of X-type molecular sieve and achieved better results.

Below by embodiment the present invention will be further elaborated. 【Example 1】

The preparation method of the crystallization synthesis solution used for the coating film is as follows: Weigh 0.560 grams (30% by weight) of silica sol, add 18.680 grams of deionized water successively under stirring, stir for several minutes to form solution A, then weigh 1.9622 grams of NaOH, 0.1146 grams NaAlO ₂ , stirred and slowly added to 18.6823 g of deionized water, stirred for several minutes to form solution B.

The α-Al ₂ O ₃ porous ceramic tube used is Φ10×1.5×20 mm, with a pore diameter of 200 nm. At room temperature, the samples were washed with 1N _HNO3 solution under ultrasonic for 1 hour, washed with deionized water until neutral, left overnight at room temperature, and dried in the air. Then at room temperature, wash the sample with 1N NaOH solution under ultrasonic wave for 1 hour, wash with deionized water until it becomes neutral, overnight at room temperature, and dry in the air. Raise the temperature to 500°C, heat-treat for 2 hours, and cool naturally to room temperature.

Molecular sieve seed liquid X1 was synthesized and treated according to the following formula and conditions: in terms of molar ratio: SiO ₂ /Al ₂ O ₃ =4.0, Na ₂ O/SiO ₂ =1.29, H ₂ O/SiO ₂ =60.5, crystallized The temperature is 95°C, and the crystallization time is 9 hours; wash with deionized water until the sample is neutral. Dry at 120° C. for 3 hours, and cool to room temperature; weigh 0.2562 g of X-type molecular sieve powder, add it to 49.7584 g of deionized water, and keep stirring until the molecular sieve slurry is suspended.

Take 10 milliliters of X-type molecular sieve seed liquid X1 prepared above and pour it into a porous sample tube, pass into the tube with pressurized N2, and keep it at 345KPa until the liquid in the tube is squeezed dry. Wash the samples with deionized water. Repeat the above operation once. Leave overnight at room temperature to dry. The temperature was raised to 180° C., kept for 2 hours, and cooled to room temperature naturally.

Take 5 ml of the above-prepared solution A and pour it into a porous tube, then take 5 ml of solution B and pour it into a stainless steel crystallization kettle, put the sample vertically into the synthesis kettle, seal the kettle, and let it stand at room temperature for 48 hours. Move the crystallization kettle into a heating oven that has been preheated to 80°C, and conduct hydrothermal crystallization under self-generated pressure for 120 hours without stirring. After the synthesis, the crystallization kettle was quenched with tap water, and the lid was opened. The samples were washed with deionized water under ultrasound for 30 minutes, and further washed until the carrier was neutral. The temperature was raised to 120° C. for 4 hours, and then the temperature was lowered to room temperature. Repeat the above film-making process four times. After the last crystallization operation, the temperature was raised to 450° C. and baked for 4 hours, and then the temperature was lowered to room temperature.

The inner surface of the crystallized carrier was characterized by XRD and SEM. XRD shows the X-type molecular sieve crystal pattern; SEM shows that there is a top layer on the inner surface, and the cross-section SEM shows that the thickness is about 10-15 microns. Molecular sieves also grow in the carrier channel under the top layer, forming a transition layer, which reaches a depth of 100 microns.

Mix the same silicon-aluminum composition to prepare a gel-like crystallization initial solution, but put the aluminum source, sodium source, and silicon source into the porous ceramic tube at the same time, and synthesize the X-type molecular sieve membrane according to the above conditions. After five times of repeated crystallization Chemical operation, the thickness of the obtained molecular sieve layer is about 15-20 microns. Because the surface adhesion layer is very thin, it is not easy to detect its adhesion to the carrier surface, so the experiment is tested by empirical methods. Scrape firmly on the molecular sieve layer with a medicine spoon. With the synthetic method of the present invention, the molecular sieve layer loaded on the carrier is firmly combined with the carrier, which is difficult to scrape off. However, when scraping vigorously with the aforementioned method in the past, the load layer is easily broken. Many molecular sieve powders are produced. It shows that with the method of the present invention, the surface molecular sieve layer is well attached to the carrier, and a firm top layer can be formed on the carrier. [Example 2]

The preparation method of the crystallization synthesis liquid used for the coating film is as follows: Weigh 1.2823 grams (30% by weight) of silica sol, add 14.010 grams of deionized water successively under stirring, stir for several minutes to form solution A, then weigh 0.5313 grams of NaOH, 0.2624 grams of NaAlO ₂ was stirred and slowly added to 13.983 g of deionized water, and stirred for several minutes to form solution B.

The α-Al ₂ O ₃ porous ceramic tube used is Φ10×1.5×20 mm, with a pore diameter of 4500 nm. At room temperature, the samples were washed with 1N _HNO3 solution under ultrasonic for 1 hour, washed with deionized water until neutral, left overnight at room temperature, and dried in the air. Then at room temperature, wash the sample with 1N NaOH solution under ultrasonic wave for 1 hour, wash with deionized water until it becomes neutral, overnight at room temperature, and dry in the air. Raise the temperature to 500°C, heat-treat for 2 hours, and cool naturally to room temperature.

Take 5 ml of the above-prepared solution A and pour it into the above-mentioned porous tube, then take 5 ml of the solution B and pour it into a stainless steel crystallization kettle, put the sample vertically into the synthesis kettle, seal the kettle, and let it stand at room temperature for 48 hours. Move the crystallization kettle into a heating oven that has been preheated to 95°C, and conduct hydrothermal crystallization under self-generated pressure for 72 hours without stirring. After the synthesis, the crystallization kettle was quenched with tap water, and the lid was opened. The samples were washed with deionized water under ultrasound for 30 minutes, and further washed until the carrier was neutral. The temperature was raised to 120° C. for 4 hours, and then the temperature was lowered to room temperature. Repeat the above film-making process four times. After the last crystallization operation, the temperature was raised to 450° C. and baked for 4 hours, and then the temperature was lowered to room temperature.

Use the same silicon-aluminum composition to mix and prepare a gel-like crystallization starting solution. Just put the aluminum source, sodium source, and silicon source into the above-mentioned porous ceramic tube at the same time, and synthesize an X-type molecular sieve membrane according to the above-mentioned conditions. After six times of repeated crystallization Operation, recording the molecular sieve loading and observing the thickness of the molecular sieve loading layer through an electron microscope. Table 1 shows the growth and change of carrier weight gain and film thickness when synthesized by the above two methods.

Table 1 Comparison of molecular sieve membranes synthesized from gel-state and clear-state starting solutions Crystallization times gel starting solution Clear starting solution (the present invention) Carrier weight gain, % Film thickness, microns Carrier weight gain, % Film thickness, microns 1357 0.27 31.38 82.06 152.73 20 0.74 51.52 132.49 18

In the method of the present invention, the crystallized product loaded on the carrier is not easy to fall off in the ultrasonic treatment after crystallization, which is conducive to the rapid growth of the molecular sieve layer, thereby accelerating the film forming speed, and realizing the same thickness of the molecular sieve covering layer and the loading capacity of the molecular sieve , with the method of the present invention, the amount of medicines can be saved up to 30% to 40%. [Example 3]

The preparation method of the crystallization synthesis liquid used in the coating film is as follows: weigh 0.560 grams (30% by weight) of silica sol, add 18.680 grams of deionized water successively under stirring, stir for several minutes to form solution A, then weigh 0.1146 grams of NaAlO ₂ , 1.9622 Slowly add 18.6823 g of deionized water to 1 g of NaOH with stirring, and stir for several minutes to form solution B.

The α-Al ₂ O ₃ porous ceramic tube used is Φ10×1.5×20 mm, with a pore diameter of 50 nm. At room temperature, the sample was washed with 1N HCl solution under ultrasonic for 1 hour, washed with deionized water until it was neutral, left overnight at room temperature, and dried in the air. Then at room temperature, wash the sample with 1N NaOH solution under ultrasonic wave for 1 hour, wash with deionized water until it becomes neutral, overnight at room temperature, and dry in the air. Raise the temperature to 500°C, heat-treat for 2 hours, and cool naturally to room temperature.

Take 5 ml of the above-prepared solution A and pour it into a porous tube, then take 5 ml of solution B and pour it into a stainless steel crystallization kettle, put the sample vertically into the synthesis kettle, seal the kettle, and let it stand at room temperature for 48 hours. Move the crystallization kettle into a heating oven that has been preheated to 95°C, and conduct hydrothermal crystallization under self-generated pressure for 96 hours without stirring. After the synthesis, the crystallization kettle was quenched with tap water, and the lid was opened. The samples were washed with deionized water under ultrasound for 30 minutes, and further washed until the carrier was neutral. The temperature was raised to 120° C. for 4 hours, and then the temperature was lowered to room temperature. Repeat the above film-making process three times. After the last crystallization operation, the temperature was raised to 450° C. and baked for 4 hours, and then the temperature was lowered to room temperature.

The inner surface of the crystallized carrier was characterized by XRD and SEM, and XRD showed that it was an X-type crystal pattern. SEM shows that there is a top layer on the inner surface with a thickness of about 5-10 microns, molecular sieves also grow in the carrier channel under the top layer, and there is a transition layer. Test the amount of gas permeating through the membrane with single-component steam at normal pressure and 300°C, collect and cool it, and calculate the permeation flux of (C ₄ H ₉ ) ₃ N to be 1.18×10 ^-7 mol/ ^m2 .sec.Pa, while the permeation flux of (C ₄ F ₉ ) ₃ N is 2.46×10 ^-9 mol/m ² .sec.Pa, and the selectivity reaches 48. The transmission rate of (C ₄ H ₉ ) ₃ N and (C ₄ F ₉ ) ₃ N passing through the ceramic tube at the same temperature is 2.84. 【Example 4】

The preparation method of the crystallization synthesis liquid used in the coating film is as follows: weigh 0.5640 grams (30% by weight) of silica sol, add 18.820 grams of deionized water successively under stirring, stir for several minutes to form solution A, then weigh 0.1154 grams of NaAlO ₂ , 1.6837 Gram of NaOH, slowly add 18.819 g of deionized water with stirring, and stir for several minutes to form solution B.

The α-Al ₂ O ₃ porous ceramic tube used is Φ10×1.5×20 mm, with a pore diameter of 100 nm. At room temperature, the samples were washed with 1N _HNO3 solution under ultrasonic for 1 hour, washed with deionized water until neutral, left overnight at room temperature, and dried in the air. Then at room temperature, wash the sample with 1N NaOH solution under ultrasonic wave for 1 hour, wash with deionized water until it becomes neutral, overnight at room temperature, and dry in the air. Raise the temperature to 500°C, heat-treat for 2 hours, and cool naturally to room temperature.

Molecular sieve seed liquid X1 was synthesized and treated according to the following formula and conditions: SiO ₂ /Al ₂ O ₃ =4.0, Na ₂ O/SiO ₂ =1.29, H ₂ O/SiO ₂ =60.5, crystallization temperature 95°C, The drying time was 9 hours; washed with deionized water until the sample was neutral. Dry at 120° C. for 3 hours, and cool to room temperature; weigh 0.2562 g of X-type molecular sieve powder, add it to 49.7584 g of deionized water, and keep stirring until the molecular sieve slurry is suspended.

Take X110 milliliters of X-type molecular sieve seed crystal liquid prepared above and pour it into a porous sample tube, pass into the tube with pressurized N2, and keep it at 345KPa until the liquid in the tube is squeezed dry. Wash the samples with deionized water. Repeat the above operation once. Leave overnight at room temperature to dry. Raise the temperature to 180°C, keep it for 2 hours, and cool to room temperature naturally.

Take 5 ml of the above-prepared solution A and pour it into a porous tube, then take 5 ml of solution B and pour it into a stainless steel crystallization kettle, put the sample vertically into the synthesis kettle, seal the kettle, and let it stand at room temperature for 48 hours. Move the crystallization kettle into a heating oven preheated to 105°C, and conduct hydrothermal crystallization under self-generated pressure for 120 hours without stirring. After the synthesis, the crystallization kettle was quenched with tap water, and the lid was opened. The samples were washed with deionized water under ultrasound for 30 minutes, and further washed until the carrier was neutral. The temperature was raised to 120° C. for 4 hours, and then the temperature was lowered to room temperature. Repeat the above film-making process four times. After the last crystallization operation, the temperature was raised to 450° C. and baked for 4 hours, and then the temperature was lowered to room temperature.

The inner surface of the carrier was used for XRD and SEM characterization, and the XRD pattern showed the crystal morphology of X-type molecular sieve. SEM photos show that there is a layer of X-type molecular sieve on the inner surface, and the thickness of the surface film is about 8-14 microns. Test the amount of gas permeating through the membrane with single-component steam at normal pressure and 300°C, collect and cool it, and calculate the permeation flux of (C ₄ H ₉ ) ₃ N to be 9.42×10 ^-7 mol/ ^m2 .sec.Pa, while the permeation flux of (C ₄ F ₉ ) ₃ N is 2.38×10 ^-8 mol/m ² .sec.Pa, and the selectivity reaches 39. The transmission rate of (C ₄ H ₉ ) ₃ N and (C ₄ F ₉ ) ₃ N passing through the ceramic tube at the same temperature is 2.33. This result is consistent with the traditional adsorption behavior of (C ₄ H ₉ ) ₃ N and (C ₄ F ₉ ) ₃ N on X-type molecular sieves, indicating that the X-type molecular sieve membranes formed on porous supports have no large defects, and zeolite The X-type molecular sieve channel of the layer is the main channel through which (C ₄ H ₉ ) ₃ N and (C ₄ F ₉ ) ₃ N pass through.

Claims (5)

1. A method for preparing X-type molecular sieve membranes, using aluminum source, sodium source, silica gel or silica sol and water as raw materials, the molar composition of raw materials in the reaction system is calculated as oxides: aNa ₂ O bAl ₂ O ₃ cSiO _2. dH ₂ O, a/c=1.0~12.9, c/b=2~6, d/c=200~1000, characterized in that silica gel or silica sol and water are first prepared into a solution and placed in a pore size of 40~ In a 10,000 angstrom glass tube or stainless steel porous material tube, place a solution of sodium source, aluminum source and water outside the porous material tube, and crystallize for 36-168 hours at a reaction temperature of 50-120°C. X-type molecular sieve is crystallized on the inner surface of the tube, wherein before crystallization, amorphous aluminosilicate or X-type molecular sieve is preloaded in the porous material tube, and the preloading amount is 0.01-0.5% of the weight of the porous material tube in weight percentage . 2. The method for preparing X-type molecular sieve membrane according to claim 1, characterized in that the aluminum source is metal aluminum foil, sodium aluminate, aluminum sulfate, pseudo-boehmite, aluminosilicate or aluminum alloy with 2 to 4 carbon atoms Aluminum alkoxide; the sodium source is sodium aluminate or/and sodium hydroxide. 3. The method for preparing X-type molecular sieve membrane according to claim 2, characterized in that the aluminum source is sodium aluminate. 4. The method for preparing X-type molecular sieve membrane according to claim 1, characterized in that a/c is 1.2-9.8, c/b is 3-5, and d/c is 250-800 in terms of molar ratio. 5. The method for preparing X-type molecular sieve membrane according to claim 1, characterized in that the reaction temperature is 80-105°C, and the crystallization time is 72-120 hours.