Preparation method of molecular sieve membrane

Abstract

The invention provides a molecular sieve membrane preparation method, which comprises: S1, coating the outer surface of a porous carrier tube with a seed crystal suspension, drying, and curing to obtain a target porous carrier tube; and S2, putting the target porous carrier tube in the membrane synthesis gel solution for dip-coating, then putting the dip-coated target porous carrier tube in a microwave reaction kettle, carrying out a crystallization reaction under microwave pulses, and cooling through a water vapor cooling system to obtain the molecular sieve membrane. The microwave pulse modulation technology is combined with the water vapor cooling system for cooling, efficient, low-energy-consumption and environment-friendly molecular sieve membrane preparation can be achieved, the performance of the molecular sieve membrane is remarkably improved, the cost is reduced, and the method can be suitable for the fields of gas separation, organic solvent dehydration, environmental protection and the like and has wide industrial application potential.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic membrane preparation, and particularly relates to a method for preparing a molecular sieve membrane. Background Art

[0002] Molecular sieve membranes, due to their exceptional chemical, mechanical, and thermal stability, anti-fouling capabilities, and tunable pore structure and surface hydrophilicity and hydrophobicity, have been widely recognized as one of the most promising membrane materials in recent years. They have demonstrated tremendous potential for applications in areas such as gas separation and solvent dehydration. However, despite significant progress in the preparation of existing molecular sieve membranes, they still face several technical challenges that directly restrict their performance and the feasibility of their industrial applications.

[0003] (1) Inaccurate temperature control: In the traditional preparation process of zeolite membranes, especially when performing crystallization reactions in microwave reactors, microwave heating often uses continuous heating. This heating method may cause local excessive temperatures, thereby causing uneven stress on the membrane surface or cracking of the membrane layer. Although existing studies have used microwave heating to improve reaction efficiency, due to large temperature fluctuations during the heating process, the surface and internal structure of the membrane cannot be uniformly formed, resulting in unstable pore structure of the membrane and reduced flux. Therefore, inaccurate temperature control remains a key factor limiting the quality and performance of zeolite membranes.

[0004] (2) Uneven cooling process: Traditional molecular sieve membrane cooling methods usually rely on air cooling or rapid cooling in a water bath. Such methods may cause the membrane surface temperature to change too quickly, resulting in cracks on the membrane surface or structural deformation. Especially after the high-temperature crystallization reaction, the rapid cooling of the membrane will generate thermal stress, which will affect the long-term stability and separation performance of the membrane. Uneven temperature during the cooling process will lead to uneven micro-stress distribution in the membrane, which seriously affects the reliability and performance of the membrane. Therefore, the uniformity of the cooling process remains a major challenge in membrane preparation.

[0005] (3) Uneven distribution of seeds: In many existing methods for preparing molecular sieve membranes, the distribution of seeds is usually relatively uneven, especially in the liquid phase method. The dispersion of seeds directly affects the crystal orientation and pore structure of the membrane. In order to obtain high-quality molecular sieve membranes, it is necessary to precisely control the deposition and distribution of seeds. However, existing technologies often find it difficult to finely control the distribution of seeds, resulting in uneven pore structure of the membrane, which in turn affects the separation performance and stability of the membrane. Therefore, how to ensure the uniform distribution of seeds has become a key issue in improving membrane performance.

[0006] (4) High energy consumption and high cost: Existing zeolite membrane preparation methods, especially the hydrothermal synthesis process, usually require a large amount of energy for heating and have a long reaction time, resulting in high energy consumption and high cost. In addition, the large amount of solvents and chemical reagents used in the reaction process also brings about waste emissions and environmental problems. These factors increase the economic cost and environmental burden of membrane preparation, limiting its application on an industrial scale. Therefore, reducing energy consumption, improving preparation efficiency and reducing environmental pollution remain important directions for optimizing zeolite membrane preparation methods.

[0007] In summary, current molecular sieve membrane preparation methods have significant deficiencies in temperature control, cooling processes, seed distribution, energy consumption, and cost. These issues directly impact membrane preparation efficiency, performance stability, and the feasibility of industrial applications. Therefore, technological innovations addressing these issues, particularly in precise temperature control, seed distribution control, and energy consumption reduction, are of great research significance and have broad application prospects. Summary of the Invention

[0008] In view of this, the present invention provides a method for preparing molecular sieve membranes. By combining microwave pulse modulation technology with water vapor cooling system cooling, it can achieve efficient, low-energy consumption, and environmentally friendly molecular sieve membrane preparation, significantly improve the performance of molecular sieve membranes, and reduce costs. It can be applied to gas separation, organic solvent dehydration, environmental protection fields, etc., and has broad industrial application potential.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing a molecular sieve membrane, comprising the following steps: S1, coating the seed crystal suspension on the outer surface of the porous carrier tube, drying and solidifying it to obtain the target porous carrier tube; S2. Dip-coating the target porous carrier tube in a membrane synthesis gel solution, then placing the dip-coated target porous carrier tube into a microwave reactor, performing a crystallization reaction under microwave pulses, and then cooling the tube through a water vapor cooling system to obtain a molecular sieve membrane.

[0010] Preferably, in step S1 , the coating method includes vacuum suction dipping.

[0011] Preferably, the vacuum suction dipping time is 10 to 30 seconds.

[0012] Preferably, in step S1: The seed suspension includes a large seed suspension and a small seed suspension, and the seed suspension is coated on the outer surface of the porous carrier tube specifically by sequentially coating the large seed suspension and the small seed suspension on the outer surface of the porous carrier tube; wherein the mass concentration of the large seed suspension is 0.5-3.0wt%, the particle size of the large seed is 500 nm-2 μm, the mass concentration of the small seed suspension is 0.5-3.0wt%, and the particle size of the small seed is 50-300 nm; and / or, The drying temperature is 70-80°C and the drying time is 2-8 hours; and / or, The curing temperature is 150~200 ℃ and the curing time is 6~10 h.

[0013] Preferably, in step S2: The microwave pulse has a power of 300-600 W, a frequency of 2.45 GHz, and a pulse period of 10-60 s; the microwave source may be used to output the pulse mode; and / or, The reaction temperature is 100-180°C and the reaction time is 20-300 min; and / or, The water vapor temperature of the water vapor cooling system is 20~40℃, and the water vapor flow rate is 0.1~1.0 m 3 / h, cooling time is 1~10 min.

[0014] Preferably, in step S2: The components of the membrane synthesis gel solution include a silicon source, an aluminum source, an alkali source and water; and / or, When the dip-coated target porous support tube is placed in a microwave reactor, there is 0.5 to 5.0 mL of water at the bottom of the microwave reactor.

[0015] Preferably, before step S1, the method further includes: S01. Clean the porous carrier tube by ultrasonic cleaning and then calcine.

[0016] Preferably, in step S01: The number of ultrasonic cleanings shall be no less than three times, with each ultrasonic cleaning lasting 15 to 30 minutes; and / or, The porous carrier tube has an average pore size of 2-3 μm and a porosity of 30-40%; and / or The calcination temperature is 500~600 ℃ and the time is 4~8 h.

[0017] Preferably, in step S01, a surfactant is added during ultrasonic cleaning to improve the surface affinity of the porous carrier tube.

[0018] Preferably, the surfactant comprises at least one of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), cetyltrimethylammonium bromide (CTAB) and polyethyleneimine (PEI); and / or, The added concentration of the surfactant is 0.05-1.0 wt %.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) In the preparation method of the molecular sieve membrane provided by the present invention, the local temperature can be controlled by microwave pulse modulation technology to avoid local overheating problems, and cooling by a water vapor cooling system can provide a uniform and mild cooling environment, reducing thermal stress and surface defects; microwave pulse modulation technology combined with cooling by a water vapor cooling system can make the surface and internal structure of the molecular sieve membrane more uniform, significantly improve the pore structure, crystal orientation and separation performance of the molecular sieve membrane, thereby enhancing the performance and stability of the molecular sieve membrane.

[0020] (2) The preparation method of the molecular sieve membrane provided by the present invention can improve reaction efficiency, reduce dependence on traditional high-temperature heating, and reduce energy consumption. It can also reduce the use of solvents and chemical reagents and reduce waste emissions, thus meeting the requirements of green manufacturing and sustainable development.

[0021] (3) The preparation method of the molecular sieve membrane provided by the present invention can reduce costs and produce high-performance molecular sieve membranes, which can be applied to multiple fields such as gas separation, organic solvent dehydration, and environmental protection, and have broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM image of the Silicalite-1 molecular sieve membrane provided in Example 1 of the present invention; Figure 2 This is a SEM image of the ZSM-5 molecular sieve membrane provided in Example 4 of the present invention; Figure 3 This is the XRD pattern of the ZSM-5 molecular sieve membrane provided in Example 4 of the present invention; Figure 4 This is a SEM image of the Silicalite-1 molecular sieve membrane provided in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to specific embodiments so that those skilled in the art can understand the present invention more clearly.

[0024] Example 1 A method for preparing a Silicalite-1 molecular sieve membrane comprises the following steps: S1. Clean a porous carrier tube with a pore size of 2 μm by ultrasonic cleaning for 20 min, three times in a row. During the cleaning process, 0.5 wt% PVA (polyvinyl alcohol) is added to improve the surface affinity of the porous carrier tube. After cleaning, the tube is calcined at 550°C for 4 h to remove impurities and set aside. S2. Small seed crystals with a particle size of 50 nm are prepared into a small seed crystal suspension with a concentration of 1.5 wt%, and large seed crystals with a particle size of 1 μm are prepared into a large seed crystal suspension with a concentration of 2 wt%. The large seed crystal suspension is first sucked for 10 s, and then the small seed crystal suspension is sucked for 10 s. The large seed crystal suspension and the small seed crystal suspension are sequentially dip-coated on the outer surface of the porous carrier tube. The coated porous carrier tube is dried at 70° C. for 4 h, and then cured at 150° C. for 8 h to obtain the target porous carrier tube. S3. Dip the target porous carrier tube into the membrane synthesis gel solution. The components of the membrane synthesis gel solution are tetraethyl silicate, sodium hydroxide, tetrapropylammonium hydroxide and water. Ensure that its pH value is 11-12 before the reaction. Place the dipped target porous carrier tube into a microwave reactor. The water content at the bottom is 1.5 mL. During the microwave heating process, a pulse mode (power 300 W, frequency 2.45 GHz, pulse period 30 s) is adopted. The reaction temperature is set to 140 ° C and the reaction time is 2 h. After the reaction is completed, take out the porous carrier tube and use a water vapor cooling system for rapid cooling. The water vapor temperature is set to 30 ° C and the water vapor flow rate is 0.5 m 3 / h, cooling time is 5 min, and Silicalite-1 molecular sieve membrane is obtained.

[0025] Figure 1 This is a scanning electron microscope (SEM) image of the prepared Silicalite-1 molecular sieve membrane. The prepared Silicalite-1 molecular sieve membrane was applied to the pervaporation dehydration of a 5 wt% low-concentration ethanol aqueous solution at an operating temperature of 50°C, with a permeation flux of 1.650 L·m -2 ·h -1 The water content of the permeating liquid is 97.5wt%.

[0026] Example 2 A method for preparing a Silicalite-1 molecular sieve membrane is described with reference to Example 1, except that: In step S3: During the microwave heating process, the pulse mode (power 450 W, frequency 2.45 GHz, pulse period 10 s) was adopted, the reaction temperature was set to 100 °C, the reaction time was 5 h; the water vapor temperature was set to 20 °C, the water vapor flow rate was 0.1 m 3 / h, cooling time is 1 min.

[0027] The prepared Silicalite-1 molecular sieve membrane was applied to the pervaporation dehydration of 5 wt% low-concentration ethanol aqueous solution at an operating temperature of 50°C, and the permeate flux was 1.592 L·m -2 ·h -1 The water content of the permeated liquid is 97.29 wt%.

[0028] Example 3 A method for preparing a Silicalite-1 molecular sieve membrane is described with reference to Example 1, except that: In step S3, during the microwave heating process, the pulse mode (power 600 W, frequency 2.45 GHz, pulse period 60 s) was adopted, the reaction temperature was set to 180 °C, the reaction time was 20 min; the water vapor temperature was set to 40 °C, the water vapor flow rate was 1 m 3 / h, cooling time is 10 min.

[0029] The prepared Silicalite-1 molecular sieve membrane was applied to the pervaporation dehydration of 5 wt% low-concentration ethanol aqueous solution at an operating temperature of 50°C, and the permeate flux was 1.952 L·m -2 ·h -1 The water content of the permeating liquid is 98.97 wt%.

[0030] Example 4 A method for preparing a ZSM-5 molecular sieve membrane comprises the following steps: S1. Clean a porous support tube with a pore size of 1 μm by ultrasonic cleaning for 30 min, three times in a row. During the cleaning process, 0.1 wt% CTAB (cetyltrimethylammonium bromide) is added to improve the surface affinity of the porous support tube. After cleaning, the tube is calcined at 600°C for 6 h to remove impurities and set aside. S2. Small seed crystals with a particle size of 100 nm are prepared into a 1 wt% small seed suspension, and large seed crystals with a particle size of 2 μm are prepared into a 2.5 wt% large seed suspension. The large seed suspension is first sucked for 15 s, and then the small seed suspension is sucked for 15 s. The large seed suspension and the small seed suspension are sequentially dip-coated on the outer surface of the porous carrier tube. The coated porous carrier tube is dried at 80° C. for 2 h, and then cured at 180° C. for 6 h to obtain the target porous carrier tube. S3. Dip the target porous carrier tube into the membrane synthesis gel solution. The components of the membrane synthesis gel solution are tetraethoxysilane, sodium aluminate, sodium hydroxide and water. Ensure that its pH value is 11-12 before the reaction. Place the dipped target porous carrier tube into a microwave reactor. The water content at the bottom is 3 mL. During the microwave heating process, a pulse mode (power 500 W, frequency 2.45 GHz, pulse period 50 s) is adopted. The reaction temperature is set to 180 ° C and the reaction time is 1 h. After the reaction is completed, take out the porous carrier tube and use a water vapor cooling system for rapid cooling. The water vapor temperature is set to 20 ° C and the water vapor flow rate is 1.0 m 3 / h, cooling time is 8 min, and ZSM-5 molecular sieve membrane is obtained.

[0031] Figure 2 This is a scanning electron microscope (SEM) image of the prepared ZSM-5 molecular sieve membrane; Figure 3 is the (XRD) pattern of the prepared ZSM-5 molecular sieve membrane, Figure 3 Typical ZSM-5 zeolite phase characteristic peaks were observed, indicating that the prepared zeolite membrane was a ZSM-5 zeolite membrane. The prepared ZSM-5 zeolite membrane was applied to the pervaporation dehydration of a 10 wt% isopropanol aqueous solution at an operating temperature of 80°C, and the permeate flux was 2.164 L·m -2 ·h -1 , the water content of the permeate liquid is 99.375 wt% Comparative Example 1 A method for preparing a Silicalite-1 molecular sieve membrane is described with reference to Example 1, except that: In step S3, instead of using a water vapor cooling system for rapid cooling, a conventional water bath is used for cooling. The temperature of the water bath is 20° C., and the cooling time is 30 min.

[0032] Figure 4 This is a scanning electron microscope (SEM) image of the prepared Silicalite-1 molecular sieve membrane. The prepared Silicalite-1 molecular sieve membrane was applied to the pervaporation dehydration of a 5 wt% low-concentration ethanol aqueous solution at an operating temperature of 50°C, with a permeation flux of 1.281 L·m -2 ·h -1 The water content of the permeating liquid is 92.43 wt%.

[0033] Comparative Example 2 A method for preparing a Silicalite-1 molecular sieve membrane is described with reference to Example 1, except that: In step S3, the dip-coated porous carrier tube was placed in a microwave reactor with a bottom water content of 1.5 mL. Microwave continuous heating was adopted. During the microwave heating process, the microwave power was 300 W, the reaction temperature was set to 140°C, and the reaction time was 2 h.

[0034] The prepared Silicalite-1 molecular sieve membrane was applied to the pervaporation dehydration of 5 wt% low-concentration ethanol aqueous solution at an operating temperature of 50 °C, and the permeation flux was 1.457·m -2 ·h -1 The water content of the permeating liquid is 92.30wt%.

[0035] Comparative Example 3 A method for preparing a Silicalite-1 molecular sieve membrane is described with reference to Example 1, except that: In step S3, the dip-coated porous carrier tube was placed in a microwave reactor with a bottom water content of 1.5 mL. Microwave continuous heating was adopted. During the microwave heating process, the microwave power was 300 W, the reaction temperature was set to 140°C, and the reaction time was 2 h. Instead of using a water vapor cooling system for rapid cooling, a conventional water bath was used for cooling. The water bath temperature was 20°C and the cooling time was 30 min.

[0036] The prepared Silicalite-1 molecular sieve membrane was applied to the pervaporation dehydration of 5 wt% low-concentration ethanol aqueous solution at an operating temperature of 50 °C, and the permeation flux was 1.224·m -2 ·h -1 The water content of the permeating liquid is 83.58wt%.

[0037] Comparative Example 4 A method for preparing a ZSM-5 molecular sieve membrane is described with reference to Example 4, except that: In step S3, the dip-coated porous carrier tube was placed in a microwave reactor with a bottom water content of 3 mL. Microwave continuous heating was adopted. During the microwave heating process, the microwave power was 500 W, the reaction temperature was set to 180° C., and the reaction time was 1 h.

[0038] The prepared ZSM-5 molecular sieve membrane was applied to the pervaporation dehydration of 10 wt% isopropanol aqueous solution at an operating temperature of 80 °C, and the permeate flux was 1.031 L·m -2 ·h -1 The water content of the permeating liquid is 65.248 wt%.

[0039] Conclusion: Figure 1 and Figure 4 It can be seen that compared with Comparative Example 1, the Silicalite-1 molecular sieve membrane prepared in Example 1 is more uniform and dense. Figure 2 and Figure 3 It can be seen that the ZSM-5 molecular sieve membrane prepared in Example 4 is uniform and dense; thus, it is shown that the present invention can make the prepared molecular sieve membrane more uniform and dense; compared with Comparative Examples 1 to 3, the permeation flux and the water content of the permeated liquid of the Silicalite-1 molecular sieve membrane prepared in Examples 1 to 3 are significantly increased, and compared with Comparative Example 4, the permeation flux and the water content of the permeated liquid of the ZSM-5 molecular sieve membrane prepared in Example 4 are significantly increased; thus, it is shown that the present invention can improve the performance of the molecular sieve membrane by combining microwave pulse modulation technology with water vapor cooling system cooling.

[0040] The raw materials not specifically described in the present invention are all existing materials that can be directly purchased from the market.

[0041] The above is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a molecular sieve membrane, characterized in that: The following steps are involved: S1, coating the seed crystal suspension on the outer surface of the porous carrier tube, drying and solidifying it to obtain the target porous carrier tube; S2. Dip-coating the target porous carrier tube in a membrane synthesis gel solution, then placing the dip-coated target porous carrier tube into a microwave reactor, performing a crystallization reaction under microwave pulses, and then cooling the tube through a water vapor cooling system to obtain a molecular sieve membrane.

2. The method for preparing a molecular sieve membrane according to claim 1, wherein: In step S1 , the coating method includes vacuum suction dipping.

3. The method for preparing a molecular sieve membrane according to claim 2, wherein: The vacuum suction dipping process has a suction time of 10 to 30 seconds.

4. The method for preparing a molecular sieve membrane according to claim 1, wherein: In step S1: The seed suspension includes a large seed suspension and a small seed suspension, and the seed suspension is coated on the outer surface of the porous carrier tube specifically by sequentially coating the large seed suspension and the small seed suspension on the outer surface of the porous carrier tube; wherein the mass concentration of the large seed suspension is 0.5-3.0wt%, the particle size of the large seed is 500 nm-2 μm, the mass concentration of the small seed suspension is 0.5-3.0wt%, and the particle size of the small seed is 50-300 nm; and / or, The drying temperature is 70-80°C and the drying time is 2-8 hours; and / or, The curing temperature is 150~200 ℃ and the curing time is 6~10 h.

5. The method for preparing a molecular sieve membrane according to claim 1, wherein: In step S2: The microwave pulse has a power of 300-600 W, a frequency of 2.45 GHz, and a pulse period of 10-60 s; and / or, The reaction temperature is 100-180°C and the reaction time is 20-300 min; and / or, The water vapor temperature of the water vapor cooling system is 20~40℃, and the water vapor flow rate is 0.1~1.0 m 3 / h, cooling time is 1~10 min.

6. The method for preparing a molecular sieve membrane according to claim 1, wherein: In step S2: The components of the membrane synthesis gel solution include a silicon source, an aluminum source, an alkali source and water; and / or, When the dip-coated target porous support tube is placed in a microwave reactor, there is 0.5 to 5.0 mL of water at the bottom of the microwave reactor.

7. The method for preparing a molecular sieve membrane according to claim 1, wherein: Before step S1, the method further includes: S01. Clean the porous carrier tube by ultrasonic cleaning and then calcine.

8. The method for preparing a molecular sieve membrane according to claim 7, wherein: In step S01: The number of ultrasonic cleanings shall be no less than three times, with each ultrasonic cleaning lasting 15 to 30 minutes; and / or, The porous carrier tube has an average pore size of 2-3 μm and a porosity of 30-40%; and / or The calcination temperature is 500~600 ℃ and the time is 4~8 h.

9. The method for preparing a molecular sieve membrane according to claim 7, wherein: In step S01 , a surfactant is added during ultrasonic cleaning.

10. The method for preparing a molecular sieve membrane according to claim 9, characterized in that: The surfactant comprises at least one of polyvinyl pyrrolidone, polyvinyl alcohol, cetyltrimethylammonium bromide and polyethyleneimine; and / or, The added concentration of the surfactant is 0.05-1.0 wt %.

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