MOR molecular sieve membrane and preparation method thereof

Abstract

The present invention provides a MOR molecular sieve membrane and a preparation method thereof, wherein the preparation method of the MOR molecular sieve membrane comprises the following steps: S1, mixing an aluminum source, an alkali solution, a silicon source, a fluoride salt, an organic alcohol and water to obtain a synthetic sol; S2, coating a seed solution on the surface of a porous carrier to obtain a seed layer; S3, coating the synthetic sol on the surface of the seed layer, and performing three temperature-variable crystallizations to obtain a MOR molecular sieve membrane; in step S1, the molar ratio of SiO2, Na2O, Al2O3, ROH, NaF and H2O is 1: (0.1-0.35): (0.03-0.15): (0.2-2): (0.1-0.5): (10-100). The present invention adds an organic alcohol to improve the crystallinity and overall structural integrity of the MOR molecular sieve membrane structure.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane separation materials, and in particular relates to a MOR molecular sieve membrane and a preparation method thereof. Background Art

[0002] MOR molecular sieve membrane is a membrane structure made of MOR type (Mordenite type) molecular sieve. MOR type molecular sieve is a kind of zeolite material with a unique pore structure. Its framework structure is mainly composed of silicon oxygen tetrahedron (SiO4) and has a highly regular pore and pore system. MOR type molecular sieve membrane is a membrane prepared on the basis of the crystal structure of this molecular sieve, and is usually used in gas separation, catalysis, adsorption and other applications. At present, the materials for preparing MOR molecular sieve membrane are composed of silicon source, aluminum source, fluorine source and alkali solution. The prepared MOR type molecular sieve membrane has low crystallinity and is prone to defects. Summary of the invention

[0003] In view of this, the present invention provides a MOR molecular sieve membrane and a preparation method thereof, which improves the crystallinity and overall structural integrity of the MOR molecular sieve membrane.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] In one aspect, the present invention provides a method for preparing a MOR molecular sieve membrane, comprising the following steps:

[0006] S1, mixing the aluminum source, alkali solution, silicon source, fluoride salt, organic alcohol and water to obtain a synthetic sol;

[0007] S2, coating a seed solution on the surface of the porous support to obtain a seed layer;

[0008] S3, after coating the synthetic sol on the surface of the seed layer, performing temperature-variable crystallization three times, first at high temperature, then at low temperature, and then at high temperature, to obtain a MOR molecular sieve membrane;

[0009] In step S1, the aluminum source, alkali solution, silicon source, fluoride salt, organic alcohol and water are mixed, aged at room temperature for 6-8 hours, and stirred at a speed of 400-600 rpm to obtain a synthetic sol; and / or,

[0010] In step S1, the synthetic sol obtained contains SiO2, Na2O, Al2O3, ROH, NaF and H2O, and the molar ratio of SiO2, Na2O, Al2O3, ROH, NaF and H2O is 1: (0.1-0.35): (0.03-0.15): (0.2-2): (0.1-0.5): (10-100).

[0011] Preferably, in step S2, the specific step of coating the seed solution on the surface of the porous support is to coat the pure phase mordenite molecular sieve crystals on the porous ceramic support by a coating method; and / or,

[0012] In step S2, after the seed solution is coated on the surface of the porous carrier, it is dried at a temperature of 80-100° C. for 6-8 hours to obtain a seed layer.

[0013] Preferably, in step S3, the synthetic sol is coated on the surface of the seed layer, and the specific step is to immerse the seed layer in the synthetic sol.

[0014] Preferably, the seed layer is immersed in the synthetic sol for a period of 0.5-30 min.

[0015] Preferably, in step S3, the specific temperature conditions for performing three temperature-variable crystallizations of first high temperature, then low temperature, and then high temperature are: first crystallize at a temperature of 130-190°C for 0.5-6h, then crystallize at a temperature of 25-80°C for 0.5-6h, and finally crystallize at a temperature of 130-190°C for 0.5-6h.

[0016] Preferably, in step S3, the container for performing the three-time temperature-variable crystallization, first at high temperature, then at low temperature, and then at high temperature, is a reactor, and the bottom of the reactor contains organic alcohol or water.

[0017] On the other hand, the present invention provides a MOR molecular sieve membrane, which is prepared by the MOR molecular sieve membrane preparation method, and the raw materials for preparing the MOR molecular sieve membrane include: aluminum source, alkali solution, silicon source, fluoride salt, organic alcohol and water, and the organic alcohol includes at least one of methanol, ethanol, isopropanol, butanol and ethylene glycol.

[0018] Preferably, the aluminum source is sodium metaaluminate; and / or,

[0019] The alkali solution is sodium hydroxide or potassium hydroxide; and / or,

[0020] The silicon source is silica sol; and / or,

[0021] The fluoride salt is sodium fluoride or potassium fluoride.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) In the present invention, organic alcohol is added to the raw materials for preparing the MOR molecular sieve membrane. On the one hand, the organic alcohol as a solvent helps to adjust the viscosity and fluidity of the synthetic sol, thereby affecting the growth process of the seed crystal. An appropriate organic alcohol solvent can make the synthetic sol more evenly coated on the surface of the carrier, and reduce bubbles or unevenness during the coating process, thereby promoting uniform crystallization. On the other hand, the organic alcohol plays a certain role in activating the seed crystal layer, making it easier for the seed crystal to grow on the surface of the carrier. It can interact with other components in the solution, such as silicon source, aluminum source and fluoride salt, to optimize the formation and deposition of the seed crystal, thereby promoting the smooth progress of the crystallization process. On the third hand, the organic alcohol has good solubility and stability, can help stabilize the pH value of the reaction solution, control the chemical environment of the solution, make the synthesis process of the MOR type molecular sieve membrane more stable, and avoid adverse side reactions or crystal defects during the crystal growth process. On the fourth hand, the organic alcohol promotes more uniform crystallization, reduces the formation of amorphous regions, and improves the size and quality of the crystal by affecting the surface tension and interface of the reaction system. This is crucial for improving crystallinity. Fifthly, the addition of organic alcohols regulates the hydration degree in the reaction system, thereby optimizing the crystallization process of the MOR molecular sieve membrane. Appropriate hydration can promote the stable growth of crystals, reduce the formation of bubbles and pores, and thus improve the crystallinity and overall structural integrity of the membrane.

[0024] (2) The present invention performs three temperature-variable crystallizations in the preparation of MOR molecular sieve membranes, first at high temperature, then at low temperature, and then at high temperature. Compared with constant temperature crystallization, temperature-variable crystallization helps to control the detailed changes in the crystal structure, thereby optimizing the pore size and pore distribution of the MOR molecular sieve membrane. High temperature is conducive to promoting the formation of larger pore structures, while low temperature can help improve the uniformity of the pore structure, ultimately improving the porosity and screening efficiency of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The surface (a) and cross-section (b) SEM images of the MOR molecular sieve membrane provided in Example 1 of the present invention;

[0026] Figure 2 The SEM images of the surface (a) and cross section (b) of the MOR molecular sieve membrane provided in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand the present invention more clearly.

[0028] Example 1

[0029] Provided is a MOR molecular sieve membrane. Raw materials for preparing the MOR molecular sieve membrane include silica sol, sodium hydroxide, sodium metaaluminate, sodium fluoride, ethylene glycol and water.

[0030] The preparation method of MOR molecular sieve membrane is as follows: silica sol, sodium hydroxide, sodium aluminate and sodium fluoride are mixed, and a certain amount of water and ethylene glycol are added, and the mixture is hydrolyzed and aged at room temperature to form a synthetic gel. The components of the synthetic gel are SiO2, Na2O, Al2O3, ROH (the organic alcohol here is ethylene glycol), and NaF. The molar ratio of SiO2, Na2O, Al2O3, ROH, and NaF is 1:0.1:0.03:0.2:0.1:10. The synthetic sol is aged at room temperature for 6 hours, and the stirring speed is 400 rpm. The pure phase mordenite molecular sieve crystals are coated on a porous ceramic support by a coating method, and the support is dried in an oven at 80°C for 6 hours after treatment. Then the seeded support is immersed in the synthetic gel for 0.5min while hot, and the temperature of the seeded support is 80°C. The carrier coated with the synthetic gel is placed in a stainless steel reactor, and 1 / 4 volume of water is put into the bottom of the reactor. The variable temperature gel conversion process is divided into three steps. The temperature and time of the first step are 130°C and 0.5h respectively, the temperature and time of the second step are 25°C and 0.5h respectively, and the temperature and time of the third step are 130°C and 0.5h respectively. Finally, distilled water is used to wash the alkaline solution on the surface of the crystallized mordenite molecular sieve membrane.

[0031] Example 2

[0032] Provided is a MOR molecular sieve membrane. Raw materials for preparing the MOR molecular sieve membrane include silica sol, sodium hydroxide, sodium metaaluminate, sodium fluoride, ethylene glycol and water.

[0033] The preparation method of MOR molecular sieve membrane is as follows: silica sol, sodium hydroxide, sodium aluminate and sodium fluoride are mixed, and a certain amount of water and ethylene glycol are added, and the mixture is hydrolyzed and aged at room temperature to form a synthetic gel. The components of the synthetic gel are SiO2, Na2O, Al2O3, ROH, and NaF, and the molar ratio of SiO2, Na2O, Al2O3, ROH, and NaF is 1:0.25:0.1:1:0.3:50. The synthetic sol is aged at room temperature for 7 hours, and the stirring speed is 500 rpm. The pure phase mordenite molecular sieve crystals are coated on a porous ceramic support by a coating method, and the support is dried in an oven at 90°C for 7 hours after treatment. Then the seeded support is immersed in the synthetic gel while hot for 15 minutes, and the temperature of the seeded support is 90°C. The carrier coated with the synthetic gel is placed in a stainless steel reactor, and 1 / 4 volume of water is placed at the bottom of the reactor. The variable temperature gel conversion process is divided into three steps. The temperature and time of the first step are 170°C and 2h respectively, the temperature and time of the second step are 60°C and 3h respectively, and the temperature and time of the third step are 170°C and 2h respectively. Finally, distilled water is used to wash the alkaline solution on the surface of the crystallized mordenite molecular sieve membrane.

[0034] Example 3

[0035] Provided is a MOR molecular sieve membrane. Raw materials for preparing the MOR molecular sieve membrane include silica sol, sodium hydroxide, sodium metaaluminate, sodium fluoride, ethylene glycol and water.

[0036] The preparation method of MOR molecular sieve membrane is as follows: silica sol, sodium hydroxide, sodium aluminate and sodium fluoride are mixed, and a certain amount of water and ethylene glycol are added, and the mixture is hydrolyzed and aged at room temperature to form a synthetic gel. The components of the synthetic gel are SiO2, Na2O, Al2O3, ROH, and NaF, and the molar ratio of SiO2, Na2O, Al2O3, ROH, and NaF is 1:0.35:0.15:2:0.5:100. The synthetic sol is aged at room temperature for 8 hours, and the stirring speed is 600 rpm. The pure phase mordenite molecular sieve crystals are coated on a porous ceramic support by a coating method, and the support is dried in an oven at 100°C for 8 hours after treatment. Then the seeded support is immersed in the synthetic gel while hot for 30 minutes, and the temperature of the seeded support is 100°C. The carrier coated with the synthetic gel is placed in a stainless steel reactor, and 1 / 4 volume of water is placed at the bottom of the reactor. The variable temperature gel conversion process is divided into three steps. The temperature and time of the first step are 190°C and 1h, respectively; the temperature and time of the second step are 80°C and 6h, respectively; the temperature and time of the third step are 190°C and 1h, respectively; finally, distilled water is used to wash the alkaline solution on the surface of the crystallized mordenite molecular sieve membrane.

[0037] Example 4

[0038] A MOR molecular sieve membrane is provided. The raw materials and preparation method of the MOR molecular sieve membrane are the same as those in Example 2, except that the organic alcohol is ethanol.

[0039] Example 5

[0040] A MOR molecular sieve membrane is provided. The raw materials and preparation method of the MOR molecular sieve membrane are the same as those in Example 2, except that the organic alcohol is ethanol, and during the preparation process, ethanol is placed at the bottom of the reactor.

[0041] Example 6

[0042] A MOR molecular sieve membrane is provided. The raw materials and preparation method for preparing the MOR molecular sieve membrane are the same as those in Example 2, except that, during the preparation process, the temperature and time of the first step are 160°C and 4h respectively, the temperature and time of the second step are 60°C and 3h respectively, and the temperature and time of the third step are 160°C and 4h respectively.

[0043] Example 7

[0044] A MOR molecular sieve membrane is provided. The raw materials and preparation method for preparing the MOR molecular sieve membrane are the same as those in Example 2, except that, during the preparation process, the variable temperature gel conversion process is divided into three steps in total, the temperature and time of the first step are 150°C and 5h respectively, the temperature and time of the second step are 80°C and 3h respectively, and the temperature and time of the third step are 150°C and 5h respectively.

[0045] Comparative Example 1

[0046] A MOR molecular sieve membrane is provided. The raw materials and preparation method for preparing the MOR molecular sieve membrane are the same as those in Example 2, except that the raw materials for preparing the MOR molecular sieve membrane do not include organic alcohol.

[0047] Comparative Example 2

[0048] A MOR molecular sieve membrane is provided. The raw materials and preparation method for preparing the MOR molecular sieve membrane are the same as those in Example 2, except that the raw materials for preparing the MOR molecular sieve membrane do not include organic alcohol, and during the preparation process, no liquid is added to the reactor.

[0049] Comparative Example 3

[0050] A MOR molecular sieve membrane is provided. The raw materials and preparation method for preparing the MOR molecular sieve membrane are the same as those in Example 2, except that during the preparation process, constant temperature crystallization is adopted in a reactor at a temperature of 170° C. for 6 hours.

[0051] Performance testing and results

[0052] Separation performance test: The separation performance of the mordenite molecular sieve membrane in a 10wt% water / ethanol mixed solution (75°C) was evaluated by pervaporation technology. The pervaporation separation results are shown in Appendix Table 1. The pervaporation performance of the membrane is represented by two parameters: permeation flux J and the percentage of water permeated. Permeation flux J represents the total mass of material that permeates through a unit area of ​​the membrane per unit time, in kg·m -2 ·h -1 The contents of organic matter and water in the measured components were detected by Shimadzu GC-14C gas chromatography. Figure 1 The surface and cross-sectional SEM images of the molecular sieve membrane of Example 2 are shown, and the surface (a) and cross-sectional SEM images (b) of the MOR molecular sieve membrane provided in Comparative Example 3 are shown. Figure 2 , Figure 1 The mordenite crystals in the zeolite are ellipsoidal, the crystals grow alternately, and the symbiosis is good. The thickness of the molecular sieve crystal layer is about 5μm.

[0053] Table 1 Pervaporation performance of mordenite molecular sieve membrane (10wt% water / ethanol, 75℃)

[0054]

[0055] Combined with Table 1, it can be concluded that the MOR zeolite membrane with excellent separation performance can be effectively prepared by organic alcohol-assisted crystallization agent and variable temperature steam gel conversion method. The type and content of organic alcohol and the synthesis temperature and time during the variable temperature steam gel conversion method have a great influence on the performance of the zeolite membrane.

[0056] The specific raw materials not described in the present invention are all existing materials and can be directly purchased from the market.

[0057] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a MOR molecular sieve membrane, characterized in that: The following steps are involved: S1, mixing an aluminum source, an alkali solution, a silicon source, a fluoride salt, an organic alcohol and water to obtain a synthetic sol; S2, coating a seed solution on the surface of the porous support to obtain a seed layer; S3, after coating the synthetic sol on the surface of the seed layer, performing temperature-variable crystallization three times, first at high temperature, then at low temperature, and then at high temperature, to obtain a MOR molecular sieve membrane; In step S1, the aluminum source, alkali solution, silicon source, fluoride salt, organic alcohol and water are mixed, aged at room temperature for 6-8 hours, and stirred at a speed of 400-600 rpm to obtain a synthetic sol; and / or, In step S1, the obtained synthetic sol contains SiO2, Na2O, Al2O3, ROH, NaF and H2O, and the molar ratio of SiO2, Na2O, Al2O3, ROH, NaF and H2O is 1: (0.1-0.35): (0.03-0.15): (0.2-2): (0.1-0.5): (10-100); In step S3, the container for performing three temperature-changing crystallizations, first at high temperature, then at low temperature, and then at high temperature, is a reactor, and the bottom of the reactor contains organic alcohol or water; In step S1 , the organic alcohol includes at least one of methanol, ethanol, isopropanol, butanol and ethylene glycol.

2. The preparation method according to claim 1, characterized in that: In step S2, the specific step of coating the seed solution on the surface of the porous support is to coat the pure phase mordenite molecular sieve crystals on the porous ceramic support by a coating method; and / or, In step S2, after the seed solution is coated on the surface of the porous carrier, it is dried at a temperature of 80-100° C. for 6-8 hours to obtain a seed layer.

3. The preparation method according to claim 1, characterized in that: In step S3, the synthetic sol is coated on the surface of the seed layer, and the specific step is to immerse the seed layer in the synthetic sol.

4. The preparation method according to claim 3, characterized in that: The seed layer is immersed in the synthetic sol for 0.5-30 minutes.

5. The preparation method according to claim 1, characterized in that: In step S3, the specific temperature conditions for performing three temperature-variable crystallizations of high temperature, low temperature, and high temperature are: first crystallize at 130-190°C for 0.5-6h, then crystallize at 25-80°C for 0.5-6h, and finally crystallize at 130-190°C for 0.5-6h.

6. A MOR molecular sieve membrane, characterized in that: The MOR molecular sieve membrane is prepared by the method for preparing the MOR molecular sieve membrane according to any one of claims 1 to 5, and the raw materials for preparing the MOR molecular sieve membrane include: aluminum source, alkali solution, silicon source, fluoride salt, organic alcohol and water.

7. The MOR molecular sieve membrane according to claim 6, characterized in that: The aluminum source is sodium metaaluminate; and / or, The alkali solution is sodium hydroxide or potassium hydroxide; and / or, The silicon source is silica sol; and / or, The fluoride salt is sodium fluoride or potassium fluoride.

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