Mo-mfi molecular sieve membrane, its preparation method and application

Abstract

The present application relates to a kind of Mo-MFI molecular sieve membrane and its preparation method and application, belong to molecular sieve membrane material preparation and separation application technical field.The present application is doped with Mo element to MFI molecular sieve membrane, significantly improve the performance of molecular sieve membrane in ethanol / water pervaporation separation.Compared with traditional MFI molecular sieve membrane and W doped MFI molecular sieve membrane, Mo doped MFI molecular sieve membrane exhibits higher permeation flux and separation factor.

Description

Technical Field

[0001] This invention relates to a Mo-MFI molecular sieve membrane, its preparation method and application, belonging to the technical field of molecular sieve membrane material preparation and separation application. Background Technology

[0002] In the field of chemical separation and purification, pervaporation technology, as a highly efficient and energy-saving separation method, is widely used in the separation of alcohols and water mixtures, especially in key industrial processes such as ethanol fermentation broth dehydration, biofuel production, and organic solvent recovery. Pervaporation-to-alcohol technology utilizes the different permeation rates of alcohol and water molecules in specific membrane materials to achieve efficient separation. This technology not only effectively improves the purity of alcohol products but also significantly reduces energy consumption and production costs, thus occupying a crucial position in modern chemical industries. With the increasing global demand for clean energy and sustainable development, the research and application of pervaporation-to-alcohol technology are receiving increasing attention, becoming an important force driving the green transformation of the chemical industry.

[0003] In existing pervaporation alcohol separation technologies, molecular sieve membranes are widely used for the separation of ethanol / water mixtures due to their unique pore structure and excellent molecular sieving performance. MFI-type molecular sieve membranes, with their good thermal and chemical stability, have shown great application potential in the field of alcohol-water separation. Previous studies have shown that introducing W element to modify the molecular sieve membrane during its preparation can effectively reduce the formation of Si-OH groups on the membrane surface, thereby improving the membrane's alcohol-water separation performance. However, its permeate flux and separation factor are not ideal. Specifically, an early patent (CN114768550A) discloses that the best-performing example, Example 1, has a permeate flux of 3.5 kg × m³. -2 ×h -1 The separation factor is 34. These performance characteristics are insufficient to meet the demands of high-throughput, high-selectivity separation in practical industrial applications.

[0004] Therefore, there is an urgent need to optimize the existing MFI-type molecular sieve membrane modification methods in order to improve the membrane's separation performance while ensuring stability. Summary of the Invention

[0005] The purpose of this invention is to provide a Mo-MFI molecular sieve membrane for pervaporation of alcohol. Compared with the prior art, by incorporating Mo atoms into the framework of the MFI molecular sieve membrane to increase the hydrophobicity of the membrane layer, the alcohol-water separation performance of the MFI molecular sieve membrane is further improved.

[0006] Specifically, this invention provides a method for preparing a Mo-MFI molecular sieve membrane, which includes the following steps: (1) Load a layer of Si-MFI seed crystals onto the support; (2) The support for the seed crystals is placed in a synthetic gel for hydrothermal crystallization, wherein the synthetic gel contains a template agent, water, a molybdenum source and a silicon source; (3) The membrane is washed, dried and calcined to obtain the Mo-MFI molecular sieve membrane.

[0007] Preferably, in step (1), the mass concentration of Si-MFI seeds in the seed solution used to load the Si-MFI seed layer is 0.5-2 wt.%, the coating time is 5-30 s, and the method of applying the seed suspension can be one or a combination of spin coating, wiping coating, dip coating or vacuum suction.

[0008] Preferably, in step (2), the template agent is selected from one of tetrabutylphosphine hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium hydroxide, preferably tetrapropylammonium hydroxide; the silicon source is selected from silica sol, tetraethyl orthosilicate, or fumed silica, preferably tetraethyl orthosilicate; the molybdenum source is selected from ammonium molybdate or sodium molybdate dihydrate, preferably sodium molybdate dihydrate; wherein, the molar ratio of the template agent, water, molybdenum source, and silicon source is SiO2:TPAOH:H2O:Na2MoO4·2H2O = 1:(0.12-0.2):(150-200):(0-0.2), preferably, SiO2:TPAOH:H2O:Na2MoO4·2H2O = 1:(0.12-0.2):(150-200):(0-0.02) (excluding 0).

[0009] Preferably, in step (2), the synthesized gel needs to be aged before hydrothermal crystallization, and the aging time is 2-10 hours.

[0010] Preferably, in step (2), the temperature of hydrothermal crystallization is 120-180 °C and the time is 6-48 h.

[0011] Preferably, in step (3), the calcination environment is air, oxygen, ozone or a mixture of oxygen and ozone, the heating rate is 0.2-0.5 ℃ / min, the calcination temperature is 200-450 ℃, and the calcination time is 24-96 h.

[0012] The present invention also provides a Mo-MFI molecular sieve membrane prepared by the above preparation method, wherein the molecular sieve membrane contains the element Mo.

[0013] The Mo-MFI molecular sieve membrane prepared in this invention is used for alcohol permeation in alcohol-water separation. Its ethanol flux is ≥5 J / kg×m³ in a 5 wt.% ethanol / water system at 60 °C. -2 ×h -1 and / or separation factor ≥ 50.

[0014] Compared with the prior art, the present invention has the following advantages: This invention employs Mo to dope and modify MFI molecular sieve membranes, increasing the membrane's hydrophobicity and significantly improving its performance in alcohol-water systems. Compared to traditional MFI molecular sieve membranes and W-doped MFI molecular sieve membranes, the Mo-doped MFI molecular sieve membrane exhibits higher permeation flux and separation factor. This improvement is attributed to Mo's ability to more readily replace Si in the MFI molecular sieve membrane framework, repairing silanol defects, increasing membrane surface hydrophobicity, and resulting in a molecular sieve membrane with superior alcohol-water separation performance.

[0015] The method for preparing Mo-doped MFI molecular sieve membranes of the present invention achieves uniform distribution and efficient doping of Mo in the molecular sieve membrane by precisely controlling the doping concentration. Even with low doping levels, the Mo-doped MFI molecular sieve membrane still exhibits excellent performance in ethanol / water system applications, meeting the requirements for high throughput and high separation factor in practical industrial applications. Attached Figure Description

[0016] Figure 1 The XRD patterns are of the molecular sieve membranes prepared in Example 1 and Comparative Example 1 of this invention. Figure 2 The images show the surface and cross-sectional SEM images of the molecular sieve membrane prepared in Example 1 of this invention. Figure 3 The image shows the EDX elemental distribution of the molecular sieve membrane prepared in Example 1 of this invention. Figure 4 The image shows the contact angles of the molecular sieve membranes prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] Example 1 The specific preparation method of Mo-MFI molecular sieve membrane is as follows: (1) Preparation of seed crystals: The synthesis solution was prepared by mixing 1SiO2:0.12TPAOH:19.2H2O and aged in a bottle for 6 h according to the molar ratio. The reaction was carried out at 150 °C for 48 h. The obtained product Si-MFI was centrifuged and dried.

[0019] (2) The seed crystals prepared in step (1) are uniformly coated on the YSZ carrier by dip-coating method. Specifically, the molecular sieve prepared in step (1) is made into a seed crystal suspension of 0.5 wt.%, the carrier is immersed in the seed crystal suspension for 30 s, and then dried at 60 ℃ for 12 h.

[0020] (3) Preparation of Mo-MFI molecular sieve membrane: The synthesis solution was prepared by mixing SiO2:0.12 TPAOH:180H2O:0.02 Na2MO4·2H2O and aged at room temperature for 6 h.

[0021] After fixing the carrier with the seed layer prepared in step (2), place it in the reaction vessel and react with the membrane synthesis gel in step (3) at 140 °C for 12 h.

[0022] The membrane after reaction was washed with deionized water, dried at 60 °C for 12 h, and then calcined in a muffle furnace at 450 °C in air for 8 h, with heating and cooling rates of 1 °C / min, to remove the template agent. The prepared molecular sieve membrane was labeled Mo-0.02-MFI.

[0023] Example 2 Steps (1) and (2) are the same as in Example 1.

[0024] The preparation process of step (3) is basically the same as that of step (3) in Example 1. The difference is that the molar ratio of each substance in the gel of the final synthesized molecular sieve membrane is 1SiO2:0.12TPAOH:180H2O:0.06Na2MO4·2H2O, and the molecular sieve membrane prepared is labeled as Mo-0.06-MFI.

[0025] Example 3 Steps (1) and (2) are the same as in Example 1.

[0026] The preparation process of step (3) is basically the same as that of step (3) in Example 1. The difference is that the molar ratio of each substance in the gel of the final synthesized molecular sieve membrane is 1SiO2:0.12TPAOH:180H2O:0.08Na2MO4·2H2O, and the molecular sieve membrane prepared is labeled as Mo-0.08-MFI.

[0027] Comparative Example 1 Steps (1) and (2) are the same as in Example 1.

[0028] Step (3) is basically the same as step (3) in Example 1, except that the membrane synthesis solution is formulated as 1SiO2:0.12TPAOH:180H2O. The molecular sieve membrane obtained is labeled as Si-MFI.

[0029] The pervaporation performance of the membrane is represented by the permeate flux J and the separation factor α. Permeate flux J = W / (A×Δt), unit: kg·m³. -2 ·h -1 Separation factor α = Ye•Xw / (Yw•Xe), where W is the amount of component permeating through the membrane (kg); A is the effective membrane area (m²). 2; Δt is the operating time, h; Ye and Yw represent the mass fractions of ethanol and water on the permeate side, respectively, and Xe and Xw represent the mass fractions of ethanol and water in the feed, respectively.

[0030] Characterization results The XRD patterns of the molecular sieve membranes prepared in Example 1 and Comparative Example 1 are shown below. Figure 1 As shown. The surface and cross-sectional SEM images of the Mo-0.02-MFI molecular sieve membrane prepared in Example 1 are shown below. Figure 2 As shown in the figure, the crystals on the film surface all exhibit a regular cuboid morphology, with inter-crystal growth forming a continuous and dense film layer. There are no obvious intergranular defects, and the film thickness is approximately 3 μm. Figure 3 The EDX elemental distribution map shows that the prepared membrane contains Mo atoms, and there are no obvious Mo species clusters in the entire image area, indicating that all introduced Mo species are highly dispersed in the molecular sieve membrane.

[0031] The effect of Mo on the hydrophobicity of the membrane surface was evaluated using the water contact angle (WCA) test. Figure 4 As shown in Table 1, the WCA value of the Si-MFI membrane prepared in Comparative Example 1 was 81.5°, while that of the Mo-MFI membrane prepared in Example 1 was significantly improved to 124.5°, which is higher than the 119° value of the W-MFI molecular sieve membrane in patent CN114768550A, indicating that the Mo-MFI molecular sieve membrane has better hydrophobicity. The Mo-MFI molecular sieve membranes synthesized in Examples 1-3 and the Si-MFI molecular sieve membrane synthesized in Comparative Example 1 were used for pervaporation separation of ethanol / water. The test conditions were: feed liquid of 5 wt.% ethanol / water system, experimental temperature of 60℃, and membrane permeate side pressure of 200 Pa. The experimental results are shown in Table 1. The performance was best when the Mo doping amount was 0.02, with an ethanol flux of 5.1 and a separation factor of 58, which were significantly improved compared with the Si-MFI molecular sieve membrane in Comparative Example 1 in both permeate flux and separation factor. Moreover, in this embodiment 1, with a lower metal doping amount, the permeation flux and separation factor are both higher than those in the inventor's earlier patent application CN114768550A.

[0032] Table 1 Performance test results of different embodiments and comparative examples Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a Mo-MFI molecular sieve membrane, characterized in that, The steps include the following: (1) Load a layer of Si-MFI seed crystals onto a support; (2) The seed-supported carrier is placed in a synthetic gel for hydrothermal crystallization, wherein the synthetic gel contains a template agent, water, a molybdenum source and a silicon source; wherein the molar ratio of silicon source, template agent, water and molybdenum source is SiO2:TPAOH:H2O:Na2MoO4·2H2O =1:(0.12-0.2):(150-200):(0-0.02), and the content of molybdenum source is not 0; (3) The membrane formed in step (2) is washed, dried, and calcined to obtain the Mo-MFI molecular sieve membrane; the water flux of the Mo-MFI molecular sieve membrane at 60 °C and in a 5 wt% ethanol / water system is ≥5 kg×m -2 ×h -1 and / or separation factor ≥ 50.

2. The preparation method according to claim 1, characterized in that, In step (1), the carrier is made of porous inorganic material; the carrier configuration is hollow fiber, sheet or tube; the mass concentration of Si-MFI seeds in the seed solution used to load the Si-MFI seed layer is 0.5-2 wt%, the coating time is 5-30 s, and the seed suspension is applied by one or a combination of spin coating, wiping coating, dip coating or vacuum suction.

3. The preparation method according to claim 1, characterized in that, In step (2), the silicon source is selected from silica sol, tetraethyl orthosilicate or fumed silica.

4. The preparation method according to claim 1, characterized in that, In step (2), the synthesized gel needs to be aged before hydrothermal crystallization, and the aging time is 2-10 h.

5. The preparation method according to claim 1, characterized in that, In step (2), the temperature for hydrothermal crystallization is 120-180 ℃ and the time is 6-48 h.

6. The preparation method according to claim 1, characterized in that, In step (3), the calcination environment is air, oxygen, ozone or a mixture of oxygen and ozone, the heating rate is 0.2-0.5 ℃ / min, the calcination temperature is 200-450 ℃, and the calcination time is 24-96 h.

7. A Mo-MFI molecular sieve membrane prepared by the preparation method according to claim 1, characterized in that... The molecular sieve membrane contains the element Mo.

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