Method for preparing highly efficient separation molecular sieve membrane by hydro-organic solvent thermal method, highly efficient separation molecular sieve membrane and application thereof

Abstract

The present invention provides a method for preparing a highly efficient separation molecular sieve membrane by hydro-organic solvent thermal treatment, the highly efficient separation molecular sieve membrane and its application. By adding an organic solvent with a volume ratio of 1% - 40% to the molecular sieve membrane synthesis solution to replace part of the water as a solvent, it effectively promotes the continuous and uniform movement of the active components for preparing the molecular sieve membrane from the main body of the synthesis solution to the surface of the carrier; the structural microelement layers of the layered molecular sieve are used to induce the active components moving to the surface of the carrier to be uniformly transformed into the target molecular sieve, and finally crosslinked to construct a dense molecular sieve membrane. The prepared highly efficient separation molecular sieve membrane can be used for the separation of small molecule mixtures, the separation efficiency for methanol and methyl tert-butyl ether is higher than 5000, and the permeation flux of methanol is higher than 1.6 kg·m<supgt;-2< / supgt;·h<supgt;-1< / supgt>.

Description

Technical Field

[0001] The present invention belongs to the field of membrane separation, and particularly relates to a method for preparing a highly efficient separation molecular sieve membrane by hydrothermal treatment with water-organic solvent, a highly efficient separation molecular sieve membrane, and an application thereof. Background Art

[0002] Molecular sieve membranes have shown great potential in the separation field due to their adjustable and uniform pore sizes, pore sizes similar to molecular sizes, high chemical stability, thermal stability, and mechanical strength. However, during the preparation of molecular sieve membranes, the irregular deposition of active components on the surface of the support results in defective membrane layers. The defect pore sizes are much larger than the crystal cavities of the molecular sieves, causing the mixture to pass through the membrane layer without discrimination, weakening or even completely eliminating the molecular sieving effect, and reducing the separation performance of the molecular sieve membrane.

[0003] In-situ growth method and secondary growth method in the water system are the most commonly used methods to eliminate the defects of the membrane layer. The in-situ growth method directly places the support in the synthesis solution for the nucleation of molecular sieve particles and the growth of molecular sieve membranes. In comparison, the secondary growth method separates the nucleation process and the crystal growth step, avoiding the uneven distribution of crystal nuclei on the surface of the support, and thus preparing a more dense and uniform molecular sieve membrane layer. From this, other improved methods are derived, including microwave heating method, gas phase conversion method, adding organic matter method, and gel conversion method, etc.

[0004] However, as the preparation process of the molecular sieve membrane progresses, the active components that are converted into molecular sieve crystals on the surface of the support are rapidly consumed, and the active components in the main body of the synthesis solution are difficult to move uniformly and quickly to the surface of the support to provide sufficient nutrients for the growth of the molecular sieve membrane. On the one hand, due to the similar composition of the main body of the synthesis solution and the support interface, the active components can only move slowly to the surface of the support by molecular diffusion; on the other hand, the active components in the main body of the synthesis solution will also be consumed due to nucleation and crystallization.

[0005] Therefore, how to continuously and uniformly move the active components in the main body of the synthesis solution to the surface of the support is the key to preparing a defect-free molecular sieve membrane. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a highly efficient separation molecular sieve membrane by hydrothermal treatment with water-organic solvent. By adding a certain proportion of organic solvent to the molecular sieve membrane synthesis solution to replace part of the water as the solvent, it effectively promotes the continuous and uniform movement of the active components for preparing the molecular sieve membrane from the main body of the synthesis solution to the surface of the support; using the structural microelement layer of the layered molecular sieve to induce the active components moving to the surface of the support to be uniformly converted into the target molecular sieve, and finally cross-linking to construct a dense molecular sieve membrane.

[0007] Another purpose of the present invention is to provide a highly efficient separation molecular sieve membrane, which is prepared by the above method, and the membrane layer is dense and uniform, has good stability, high repeatability, and excellent performance.

[0008] The last object of the present invention is to provide an application of a highly efficient separation molecular sieve membrane for effectively separating small molecule mixtures, especially for separating methanol and methyl tert-butyl ether.

[0009] The specific technical solution of the present invention is as follows:

[0010] A method for preparing a highly efficient separation molecular sieve membrane by hydrothermal treatment with water-organic solvent, comprising the following steps:

[0011] 1) Prepare a molecular sieve membrane synthesis solution using water and an organic solvent as solvents;

[0012] 2) Assemble a microelement layer of a layered molecular sieve structure on the surface of the carrier;

[0013] 3) Place the carrier treated in step 2) into the molecular sieve membrane synthesis solution prepared in step 1) for crystallization synthesis to obtain a highly efficient separation molecular sieve membrane.

[0014] In step 1), the volume of the organic solvent used accounts for 1%-40% of the total volume of water and the organic solvent.

[0015] The organic solvent is an organic solvent that can be miscible or partially miscible with water;

[0016] The organic solvent is selected from one or more of alcohol organic solvents, ketone organic solvents, ether organic solvents or amide organic solvents that can be miscible or partially miscible with water;

[0017] Preferably, the alcohol organic solvents include but are not limited to one or several of methanol, ethanol, propanol, ethylene glycol, propylene glycol or butylene glycol;

[0018] The ketone organic solvent includes but is not limited to acetone;

[0019] The ether organic solvent includes but is not limited to tetrahydrofuran

[0020] The amide organic solvent includes but is not limited to N,N-dimethylformamide;

[0021] In step 1), the preparation method of the molecular sieve membrane synthesis solution is: place the aluminum source, silicon source and alkali source required for synthesizing the molecular sieve membrane in water, and dropwise add the organic solvent after they are fully dissolved;

[0022] Or, the preparation method of the molecular sieve membrane synthesis solution in step 1) is: disperse the organic solvent in water to obtain a mixed liquid solvent, and then place the aluminum source, silicon source and alkali source required for synthesizing the molecular sieve membrane in the mixed liquid solvent.

[0023] In the preparation process of the molecular sieve membrane synthesis solution in step 1), after adding the aluminum source, silicon source and alkali source, stir at room temperature for 1h-48h to obtain the molecular sieve membrane synthesis solution.

[0024] The aluminum source includes, but is not limited to, the following raw materials: aluminum isopropoxide, sodium aluminate, aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum hydroxide, or alumina.

[0025] The silicon source includes, but is not limited to, the following raw materials: sodium silicate, silica sol, tetraethyl orthosilicate, or silicon oxide.

[0026] The base source is selected as sodium hydroxide;

[0027] Furthermore, a template agent can also be added in the preparation of the molecular sieve membrane synthesis solution in step 1).

[0028] The template agent includes, but is not limited to, the following raw materials: tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, tetraethylammonium hydroxide, tetraethylammonium bromide, or tetraethylammonium chloride.

[0029] The carrier material in step 2) is hydrophilic alumina or hydrophilic titanium oxide; or a hydrophobic hollow structure material after hydrophilic treatment. The carrier pattern is sheet-like, single-tube type, multi-channel type, or hollow fiber type;

[0030] The layered molecular sieves assembled on the carrier surface in step 2) include, but are not limited to, molecular sieves of the following structural types: CDO, MWW, FER, layered MFI, layered AFO, or layered MOF molecular sieves.

[0031] The layered molecular sieves in step 2) have the same or similar structural units as the molecular sieves in the target molecular sieve membrane, such as having the same secondary structural units, layered fragments, etc. For example, both MWW and CHA molecular sieves contain double six-membered ring secondary structural units, both CDO and MFI molecular sieves contain mor secondary structural units, and MWW and SOD molecular sieves contain similar layered fragments.

[0032] The specific operation of assembling the layered molecular sieve structural unit layer on the carrier surface in step 2) is: assembling the layered molecular sieve on the carrier surface, and then soaking it in an acidic or alkaline solution for 0.5 h - 12 h. Preferably, the soaking temperature is 20°C - 100°C;

[0033] The assembly of the layered molecular sieve in step 2) means that the layered molecular sieve is tiled on the surface of the porous carrier in a single layer or multiple layers through methods such as layer-by-layer dip coating, rubbing coating, spraying, spin coating, self-assembly, or vacuum filtration, as well as combinations of these methods.

[0034] The acidic or alkaline solution in step 2) refers to: the acidic or alkaline target molecular sieve membrane synthesis solution, or an alkaline solution with a mass concentration of 0.5% - 30% or an acidic solution with a mass concentration of 0.5% - 30%.

[0035] If the acidic or alkaline solution is an alkaline solution with a mass concentration of 0.5%-30% or an acidic solution with a mass concentration of 0.5%-30%, after treatment, the carrier needs to be slowly taken out of the solution and transferred to the target molecular sieve membrane synthesis solution for crystallization synthesis.

[0036] The crystallization synthesis described in step 3) refers to microwave or hydrothermal synthesis, and the reaction is carried out at 30-250 °C for 0.5-96 h.

[0037] After the crystallization synthesis reaction in step 3) is completed, when the temperature of the synthesis solution drops to room temperature, the carrier is washed with deionized water and dried to obtain a dense and defect-free target molecular sieve membrane grown on the surface of the porous carrier.

[0038] The washing means repeatedly washing with deionized water several times until the pH value of the washing liquid is 7;

[0039] The drying means drying at 60-100 °C for 24 h.

[0040] The molecular sieve membrane synthesized in step 3) includes, but is not limited to, the following types of molecular sieve membranes: LTA, MFI, SOD, FAU, ZIF, CHA, or MOF molecular sieve membranes.

[0041] Furthermore, in step 3), when the template agent that cannot be removed by drying is contained in the molecular sieve membrane synthesis solution, the template agent is removed by calcination after drying.

[0042] A highly efficient separation molecular sieve membrane provided by the present invention is prepared by the above method; the membrane layer of the highly efficient separation molecular sieve membrane is uniform and has no obvious defects on the surface.

[0043] The application of the highly efficient separation molecular sieve membrane provided by the present invention is used for effectively separating small molecule mixtures, especially the separation of methanol and methyl tert-butyl ether; the separation efficiency of methanol and methyl tert-butyl ether is higher than 5000, and the permeation flux of methanol is higher than 1.6 kg·m -2 ·h -1 .

[0044] Compared with the prior art, in the present invention, a certain proportion of organic solvent is added to the molecular sieve membrane synthesis solution to replace part of the water, and the structural microelement layer of the layered molecular sieve is used to induce the construction of a dense molecular sieve membrane. First, the water-organic solvent system can prevent the active components from nucleating and crystallizing in the main body of the synthesis solution, reduce the consumption of the active components in the main body of the synthesis solution, and ensure that there are sufficient active components in the synthesis solution. Secondly, the organic solvent system can promote the continuous and uniform transfer of the active components from the main body of the synthesis solution to the surface of the carrier, providing sufficient and uniformly distributed active components for the growth of the molecular sieve membrane on the surface of the carrier. Finally, the uniform distribution of the structural microelement layer on the surface of the carrier is obtained by utilizing the characteristics of the layered molecular sieve being easily dispersed and deposited on the surface of the carrier. The structural microelement layer induces the active components to be uniformly converted into the target molecular sieve on the surface of the carrier. As the active components on the surface of the carrier are continuously converted into the target molecular sieve, the content of the active components on the surface of the carrier decreases, promoting the further movement of the active components in the main body of the synthesis solution to the surface of the carrier. The water-organic solvent system ensures sufficient and uniform active components on the surface of the carrier, while the structural microelement of the layered molecular sieve ensures that the active components are converted into the target molecular sieve on the surface of the carrier, and the target molecular sieve is finally cross-linked to construct a dense molecular sieve membrane. The obtained highly efficient separation molecular sieve membrane can be used for the separation of small molecule mixtures. The separation efficiency of methanol and methyl tert-butyl ether is higher than 5000, and the permeation flux of methanol is higher than 1.6 kg·m -2 ·h -1 。 Description of the Drawings

[0045] Figure 1 SEM image of the FAU molecular sieve membrane obtained in Example 1;

[0046] Figure 2 SEM image of the MFI molecular sieve membrane obtained in Example 2;

[0047] Figure 3 SEM image of the NaA molecular sieve membrane obtained in Example 3;

[0048] Figure 4 SEM image of the FAU molecular sieve membrane obtained in Comparative Example 1;

[0049] Figure 5 Schematic diagram of the preparation method of the present invention. Detailed Embodiments

[0050] The present invention will be further described below through examples.

[0051] Example 1

[0052] A method for thermally preparing a highly efficient separation molecular sieve membrane with a water-organic solvent, comprising the following steps:

[0053] 1) Uniformly disperse the layered ITQ-1 molecular sieve (a type of MWW molecular sieve) into absolute ethanol and ultrasonically disperse it for 0.5 h to obtain an ITQ-1 molecular sieve ethanol suspension with a concentration of 1 g / L. Then, use the dip-coating method to assemble an ITQ-1 molecular sieve layer on the surface of a hydrophilic alumina single-tube carrier.

[0054] 2) Dissolve sodium aluminate and sodium hydroxide in deionized water, continuously stir for 2 h until completely dissolved and cool to room temperature to obtain a mixed solution. Then, under stirring conditions, dropwise add the sodium silicate solution to the above mixed solution. After stirring for 2 h, dropwise add the organic solvent propylene glycol and continue to stir at room temperature for 24 h to obtain a molecular sieve membrane synthesis solution with a molar ratio of 45Na 2 O:Al 2 O 3 :12SiO 2 ,Al 3+ content of 0.089 mol / L and a propylene glycol volume content of 15%.

[0055] 3) Place the carrier treated in step 1) in the synthesis solution prepared in step 2) and let it stand at 30 °C for 30 min.

[0056] 4) Transfer the molecular sieve membrane synthesis solution containing the carrier treated in step 3) to a crystallization kettle together, make the synthesis solution cover the carrier, seal it and carry out hydrothermal crystallization, and maintain it at 60 °C for 24 h.

[0057] 5) After crystallization is completed, take out the carrier, then wash it repeatedly with deionized water until the pH value of the washing solution is 7, and then dry it at 60 °C for 24 h to obtain a FAU molecular sieve membrane.

[0058] Figure 1 This is the SEM image of the FAU molecular sieve membrane obtained in Example 1. As can be seen from the figure, a dense, flat and defect-free FAU molecular sieve membrane is formed on the surface of the carrier.

[0059] Place the FAU molecular sieve membrane prepared in step 5) in a pervaporation device, introduce a 10% methyl tert-butyl ether methanol solution at 75 °C, and conduct pervaporation testing on the membrane material. The separation efficiency of methanol and methyl tert-butyl ether is higher than 5000, and the permeation flux of methanol is higher than 1.6 kg·m -2 ·h -1 .

[0060] Example 2

[0061] A method for hydrothermally preparing a highly efficient separation molecular sieve membrane from water-organic solvents, comprising the following steps:

[0062] 1) Uniformly disperse the layered UZM-25 molecular sieve (a kind of CDO molecular sieve) into anhydrous methanol, and ultrasonically disperse it for 1 h to obtain a UZM-25 molecular sieve methanol suspension with a concentration of 5 g / L. Then, use the spin-coating method to spin-coat a UZM-25 molecular sieve layer on the surface of the flaky hydrophilic titanium oxide support. Subsequently, place the support vertically in a 10% hydrochloric acid solution and let it stand at 40 °C for 12 h.

[0063] 2) Dissolve sodium aluminate in deionized water, add sodium hydroxide and 2 M aqueous solution of tetrapropylammonium hydroxide (TPAOH) as a template while stirring, and continuously stir for 2 h until it is completely dissolved and cooled to room temperature. Then, dropwise add silica sol to the above-obtained solution drop by drop while stirring, and then dropwise add the organic solvent acetone, and stir at room temperature for 24 h to obtain a molecular sieve membrane synthesis solution with a molar ratio of 1 TPAOH:4.5 NaOH:0.012 NaAlO 2 :6SiO 2 ,Al 3+ content of 0.6×10 6 mol / L and an acetone volume content of 5%.

[0064] 3) Place the support treated in step 1) into the synthesis solution prepared in step 2) so that the synthesis solution covers the support, and then transfer the synthesis solution containing the flaky titanium oxide support to an oven for hydrothermal crystallization, and maintain it at 180 °C for 12 h.

[0065] 4) After crystallization, take out the support, and then wash it repeatedly with deionized water several times until the pH value of the washing solution is 7, then dry it at 80 °C for 24 h, then heat it to 550 °C at a heating rate of 1 °C / min, and keep it at this temperature for 10 h for calcination to remove the template agent, obtaining an MFI molecular sieve membrane.

[0066] Figure 2 This is the SEM image of the MFI molecular sieve membrane obtained in Example 2. As can be seen from the figure, a dense, flat and defect-free MFI molecular sieve membrane is formed on the surface of the support.

[0067] Example 3

[0068] A method for preparing a highly efficient separation molecular sieve membrane by hydrothermal treatment of water-organic solvents, comprising the following steps:

[0069] 1) Use the rubbing method to rub an AMH-3 molecular sieve layer on the surface of a single-tube hydrophilic alumina support, and then place the support vertically in a 1% nitric acid solution and let it stand at 90 °C for 6 h.

[0070] 2) Dissolve sodium aluminate in deionized water. While stirring, add sodium hydroxide and continuously stir for 2 h until it is completely dissolved and cooled to room temperature. Then, dropwise add it to the stirred sodium silicate solution, and then dropwise add the organic solvent N,N-dimethylformamide. Stir at room temperature for 12 h to obtain a molecular sieve membrane synthesis solution with a molar ratio of 50Na 2 O:1Al 2 O 3 :5SiO 2 ,Al 3+ content of 0.089 mol / L and N,N-dimethylformamide volume content of 30%.

[0071] 3) Place the carrier treated in step 1) into the synthesis solution prepared in step 2). Then, transfer the synthesis solution containing the single-channel tubular alumina carrier to an oven for hydrothermal crystallization and maintain it at 80 °C for 24 h.

[0072] 4) After crystallization is completed, take out the carrier, and then repeatedly wash it with deionized water several times until the pH value of the washing liquid is 7. Then, dry it to obtain the LTA molecular sieve membrane.

[0073] Figure 3 This is the SEM image of the LTA molecular sieve membrane obtained in Example 3. As can be seen from the figure, a dense, flat and defect-free LTA molecular sieve membrane is formed on the inner wall of the porous ceramic tube.

[0074] Place the LTA molecular sieve membrane prepared in step 4) into a pervaporation device, introduce a 10% methyl tert-butyl ether / methanol solution at 75 °C, and conduct pervaporation testing on the membrane material. The separation efficiency of methanol and methyl tert-butyl ether is higher than 10000, and the permeation flux of methanol is higher than 1.8 kg·m -2 ·h -1 .

[0075] Comparative Example 1

[0076] A method for preparing a molecular sieve membrane, comprising the following steps:

[0077] 1) Polish the outer wall of an alumina ceramic hollow fiber carrier with a length of 500 mm successively with 200-mesh, 1000-mesh and 2000-mesh sandpapers until the outer wall of the carrier is smooth. Place the polished ceramic carrier in water for ultrasonic washing to remove the residual powder, and then place it in deionized water for ultrasonic washing until the washing water is neutral. Finally, place it in an 80 °C oven and dry it for 18 h for use.

[0078] 2) Dissolve sodium aluminate in deionized water. While stirring, add sodium hydroxide and continuously stir for 2 h until it is completely dissolved and cooled to room temperature. Then, dropwise add silica sol to the above-mentioned solution under high-speed stirring and stir at room temperature for 48 h to obtain a molar ratio of 53Na 2O:1Al 2 O 3 :6SiO 2 ,Al 3+ a synthetic solution with an Al content of 0.089 mol / L.

[0079] 3) Place the carrier pretreated in step 1) into the synthetic solution prepared in step 2), then transfer the synthetic solution containing the single-channel tubular ceramic carrier to an oven for hydrothermal crystallization, and maintain it at 80 °C for 24 h.

[0080] 4) After crystallization is completed, take out the carrier, then wash it repeatedly with deionized water several times until the pH value of the washing solution is 7, and then obtain the FAU zeolite membrane after drying.

[0081] Figure 4 SEM image of the FAU zeolite membrane obtained in Comparative Example 1. As can be seen from the figure, there are many defects in the FAU zeolite membrane grown on the surface of the porous ceramic carrier.

[0082] Place the FAU zeolite membrane prepared in step 4) into a pervaporation device, introduce a 10% methyl tert-butyl ether / methanol solution at 75 °C, and conduct a pervaporation test on the membrane material. The separation efficiency of methanol and methyl tert-butyl ether is only 40.

Claims

1. A method for preparing a highly efficient separation molecular sieve membrane by hydrothermal treatment in water-organic solvent, characterized in that, the method comprises the following steps: 1) Prepare a molecular sieve membrane synthesis solution using water and an organic solvent as solvents; 2) Assemble a microelement layer of a layered molecular sieve structure on the surface of the support; 3) Place the support treated in step 2) into the molecular sieve membrane synthesis solution prepared in step 1) for crystallization synthesis to obtain a highly efficient separation molecular sieve membrane; the organic solvent described in step 1) is an organic solvent that can be miscible or partially miscible with water; the volume of the organic solvent used in step 1) accounts for 1%-40% of the total volume of water and the organic solvent.

2. The method according to claim 1, characterized in that, the preparation method of the molecular sieve membrane synthesis solution in step 1) is: place the aluminum source, silicon source and alkali source required for synthesizing the molecular sieve membrane in water, and slowly add the organic solvent dropwise after it is fully dissolved; or, the preparation method of the molecular sieve membrane synthesis solution in step 1) is: disperse the organic solvent into water to obtain a mixed liquid solvent, and then place the aluminum source, silicon source and alkali source required for synthesizing the molecular sieve membrane in the mixed liquid solvent.

3. The method according to claim 1, characterized in that, the layered molecular sieve assembled on the surface of the support in step 2) includes molecular sieves of the following structural types: one of CDO, MWW, FER, layered MFI, layered AFO or layered MOF molecular sieve.

4. The method according to claim 1 or 3, characterized in that, the layered molecular sieve described in step 2) has the same or similar microelement structure as the molecular sieve in the target molecular sieve membrane.

5. The method according to claim 1, characterized in that, the crystallization synthesis in step 3) means reacting at 30-250 °C for 0.5-96 h.

6. The method according to claim 1 or 5, characterized in that, the molecular sieve membrane synthesized in step 3) includes one of the following types of molecular sieve membranes: LTA, MFI, SOD, FAU, ZIF, CHA or MOF molecular sieve membrane.

7. A highly efficient separation molecular sieve membrane prepared by the method according to any one of claims 1-6.

8. An application of a highly efficient separation molecular sieve membrane prepared by the method according to any one of claims 1-6, characterized in that, it is used for the separation of methanol and methyl tert-butyl ether.

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