A method for MOF gel induced preparation of covalent organic framework membranes and applications in aromatic hydrocarbon separation

Abstract

The application discloses a method for preparing a covalent organic framework film by MOF gel induction and application in aromatic hydrocarbon separation. Specifically, the application uses MOF gel as a catalyst, controls monomer diffusion and catalytic polymerization at an interface by adjusting the concentration of the MOF gel, and prepares a covalent organic framework film material. The surface of the film material is smooth, dense and defect-free, and the film material has the characteristics of high permeation flux and molecular sieving in the application of catalytic diesel aromatic separation. In addition, the covalent organic framework film prepared by the application has the characteristics of good crystallinity, strong mechanical properties and strong chemical stability, and realizes the assembly strategy of the dual role of MOF gel as a catalyst and water phase.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing a covalent organic framework film through MOF gel induction and belongs to the technical field of covalent organic framework film preparation. BACKGROUND

[0002] Catalytic cracking diesel, also known as catalytic diesel, is the main product of a heavy oil catalytic cracking unit, and has a carbon number distribution concentrated in 10-25, belonging to poor-quality diesel. The catalytic diesel has complex components, and the components cover chain alkanes, naphthenes and various aromatic hydrocarbons. A high content (40-60 wt%) of polycyclic aromatic hydrocarbons is easy to cause low cetane number and aggravate combustion carbon deposition and other adverse effects, and seriously hinders oil product upgrading. Under the background of excess refining capacity and shrinking diesel demand, deep separation of alkanes and aromatic hydrocarbons in catalytic diesel is an important way for clean and value-added utilization of catalytic diesel.

[0003] Catalytic diesel aromatic hydrocarbon removal processes mainly include hydrofining, solvent extraction and adsorption, but have problems such as high energy consumption or large solvent consumption. Membrane separation has the advantages of low energy consumption, simple process and small equipment investment, and is expected to be applied to catalytic diesel aromatic hydrocarbon separation. At present, for the separation of alkane and aromatic hydrocarbon mixtures, especially for the separation of light components (such as benzene / cyclohexane) with a carbon number less than 7, organic solvent reverse osmosis membranes are more suitable for the separation of catalytic diesel with a molecular weight of about 200 Da.

[0004] Crystalline polymer covalent organic framework materials (COFs) based on dynamic covalent chemistry have attracted extensive attention in the field of membranes. The realization of high flux and high selectivity membranes not only depends on the rich micropores of COFs, but also depends on the preparation of ultra-thin defect-free membranes. The preparation of polyamide reverse osmosis membranes using oil-water interfacial polymerization technology has been widely used in industry, and is expected to provide guidance for the preparation of large-area COF thin films. The physical and chemical properties of the interface (interfacial tension, mechanical stability, catalytic activity) determine the diffusion kinetics of monomers and the microenvironment of the polymerization process, and are crucial to the crystallization growth of COF membranes. In the preparation process of COF membranes, the solubility of macromolecular monomers in water is poor, and an acid (such as acetic acid, trifluoroacetic acid, scandium trifluoromethane sulfonate and p-toluenesulfonic acid) is often introduced as a catalyst to improve the reaction activity. Therefore, a better layout is to place the catalyst in the water phase, and place the two monomers in the oil phase at the same time. In order to ensure the good crystallinity of COF, the reaction time can be as long as several days. In large-scale preparation, the interface properties are easily affected by mechanical disturbance and non-steady-state diffusion, resulting in defects in the generated membrane. This greatly limits the preparation of high permeation flux and high selectivity COF membrane materials. SUMMARY

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned background technology, and for the first time, use MOF gel as a catalyst and the aqueous phase in interfacial polymerization to construct a gel-liquid interface to prepare a defect-free covalent organic framework membrane. The construction of the gel-liquid interface is expected to utilize the solid-state properties of the gel to construct an interface that is not easily disturbed. The defect-free preparation of a high permeability flux covalent organic framework membrane is achieved, and it is used in the catalytic cracking diesel separation process with a high cyclohexane flux. So far, there are no literature reports on the regulation of MOF gel as a catalyst and the aqueous phase for interfacial polymerization during the membrane preparation process; the method for MOF gel-induced preparation of COF membranes is simple and controllable, and is used for the first time for interface regulation in COF interfacial polymerization; the prepared covalent organic framework membrane is used for the effective separation of aromatic hydrocarbons and aliphatic hydrocarbons, and the full liquid phase separation of alkane / aromatic hydrocarbon mixtures is achieved.

[0006] In order to solve the above technical problems, the present invention proposes a method for preparing a covalent organic framework membrane by MOF gel induction. First, a MOF gel material with good morphology is prepared. The MOF gel has a unique nanoscale radial size and a three-dimensional cross-linked gel network structure. This structure gives the MOF gel uniform dispersion ability in the solvent, high viscosity and weak fluidity; then a gel-liquid interface is constructed, so that a defect-free covalent organic framework membrane is generated by reaction at the interface of the two phases; finally, the membrane prepared by MOF gel-liquid interfacial polymerization is placed on a base film and dried at room temperature to further study the hydrocarbon permeability of common alkanes and aromatics. This is achieved by the following steps:

[0007] Step 1: Preparation of MOF gel-liquid interface system: Disperse MOF gel in aqueous solution at a mass concentration of 0.5%-2% by ultrasonic dispersion and magnetic stirring for 2 hours. The resulting solution is recorded as solution A; at a concentration of 0.3-0.5mmol L -1 1,3,5-tris(aminophenyl)benzene and a concentration of 0.6-0.75mmol L -1 2,5-Dihexyloxyterephthalaldehyde was dissolved in an organic solvent and ultrasonically dispersed for 0.5 h. The resulting solution was designated as solution B.

[0008] Step 2: Preparation of MOF gel-induced covalent organic framework membrane: Solution A is slowly dripped onto the surface of solution B according to equal volume. After sealing, it is allowed to react at room temperature for 24-72 hours. After the reaction is completed, a membrane is formed. The membrane is washed with acetone and ethanol respectively, removed and placed on a base film and dried at room temperature for 24 hours. The resulting MOF gel-induced interfacial assembly covalent organic framework membrane is recorded as TAPB-TPOC6 COF.

[0009] In the method of the present invention, in step 1: the MOF gel can be any one of UiO-66, ZIF-8, and ZIF-67 gels, preferably UiO-66 gel.

[0010] The organic solvent is one of dichloromethane, o-dichlorobenzene, mesitylene, dioxane, preferably dichloromethane.

[0011] The concentration of the solution B is 0.3-0.9mmol / L. -1 .

[0012] In the method, the interfacial polymerization time in step two is 24-72 hours.

[0013] The base film is a commercially available solvent-resistant base film; the commercially available solvent-resistant base film is a polyacrylonitrile, polytetrafluoroethylene, polyethylene terephthalate nanopore membrane or polyvinylidene fluoride membrane.

[0014] The application of the covalent organic framework film prepared from the MOF gel is used for the separation of alkanes and aromatic hydrocarbons.

[0015] The operating temperature is 35℃, and the operating pressure is 40bar, so that the aromatic hydrocarbons and alkanes are separated; the aromatic hydrocarbons are any one of C7, C8, C 12 , and the alkanes are any one of toluene, xylene and mesitylene, preferably C 12 and toluene.

[0016] Compared with the prior art, in the method for preparing the covalent organic framework film, the MOF gel is used as a catalyst and a water phase interface for the first time, and a gel-liquid interface polymerization method is constructed, so that the obtained film has high crystallinity, can be easily transferred to the surface of any base film, has certain mechanical strength and flexibility, and the film surface is smooth, dense and defect-free. The MOF gel prepared by the method is used for the separation of alkanes and aromatic hydrocarbons, and excellent separation performance is exhibited. Small-sized aromatic hydrocarbons can pass through the membrane, and large-sized alkanes slowly permeate through the membrane. The permeation flux of the aromatic hydrocarbons is 0.053-0.05kg m - 2 h -1 bar -1 , and the permeation flux of the alkanes is 0.049-0.009kg m -2 h -1 bar -1 . BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the XRD pattern of the film of Example 1;

[0018] Figure 2 is the gel surface scanning electron microscope image of the film 1 of Example 1;

[0019] Figure 3 is the organic surface scanning electron microscope image of the film 1 of Example 1;

[0020] Figure 4 is a gel area scan electron microscope image of Example 2 film 2;

[0021] Figure 5 is an organic area scan electron microscope image of Example 2 film 2;

[0022] Figure 6 is a gel area scan electron microscope image of Example 3 film 3;

[0023] Figure 7 is an organic area scan electron microscope image of Example 3 film 3;

[0024] Figure 8 is a water area scan electron microscope image of Comparative Example film 4;

[0025] Figure 9 is an organic area scan electron microscope image of Comparative Example film 4;

[0026] Figure 10 is a permeation flux comparison chart of aromatic and alkane pure solvents of films 1-4;

[0027] Figure 11 is a preparation schematic diagram of MOF gel induced preparation of covalent organic framework film. DETAILED DESCRIPTION

[0028] The present application will be further described below in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means limiting to the present application.

[0029] The design concept of the MOF gel induced preparation of covalent organic framework film proposed by the present application is: the adjustable concentration and weak flowability of the MOF gel can provide a stable and not easily disturbed interface for interfacial polymerization; secondly, the three-dimensional network structure of the MOF gel can expose more metal sites as Lewis acid catalysts to catalyze the COF interfacial polymerization reaction. Based on the gel-liquid interface construction, the reaction zone is limited to provide a suitable environment for the formation and crystal structure of the covalent organic framework film, and the covalent organic framework film is endowed with a dense, continuous and stable structure. The preparation process can control the MOF gel concentration, reaction monomer concentration and reaction time and other conditions to adjust the structure of the covalent organic framework film, and obtain a dense and defect-free self-supporting covalent organic framework film. The prepared covalent organic framework film uses the interlaced disturbance of the multi-alkyl chain of the pore channel, and the smaller size aromatic hydrocarbon can pass through the film, and the larger size alkane slowly penetrates the film, wherein the permeation flux of the aromatic hydrocarbon is 0.053-0.05 kg m -2 h -1 bar -1 , and the permeation flux of the alkane is 0.049-0.009 kg m -2 h -1 bar -1 .

[0030] The technical solutions of the present application will be further described in detail below in combination with the drawings and specific examples. The specific examples described are only used to explain and illustrate the present application, and do not limit the present application.

[0031] Example 1

[0032] The MOF gel induces the preparation of a covalent organic framework film, and the steps are as follows:

[0033] Step 1, preparation of a MOF gel-liquid interface system: 0.7 mg of UiO-66 gel is weighed and dispersed in an aqueous solution by ultrasonic dispersion, and is magnetically stirred for 2 hours. The obtained 0.7% UiO-66 gel solution is recorded as solution A;

[0034] According to the concentration of 0.3-0.5 mmol L-1 1,3,5-tris(aminophenyl)benzene and the concentration of 0.6-0.75 mmol L-1 2,5-dihexyloxy terephthaldehyde, the solution is ultrasonically dispersed for 0.5 hours, and the obtained solution is recorded as solution B;

[0035] Step 2, preparation of a MOF gel induced covalent organic framework film:

[0036] According to the same volume, solution A is slowly dropped onto the surface of solution B, sealed, and placed at room temperature for 24 hours after reaction. After the reaction is completed, a film is formed, which is sequentially washed with acetone and ethanol, and then taken out and placed on a base film to dry at room temperature for 24 hours. The obtained MOF gel induced interface assembled covalent organic framework film is recorded as film 1. Figure 1 is a powder X-ray diffraction spectrum (PXRD) of film 1, Figure 2 is a gel face scanning electron micrograph of film 1, Figure 3 is an organic face scanning electron micrograph of film 1.

[0037] The film 1 is subjected to aromatic and alkane permeation experiments: a dead-end filtration device is used, and aromatic and alkane pure solvents are selected. The aromatic permeation flux of film 1 is 0.053 kg m -2 h -1 bar -1 , and the alkane permeation flux is 0.033 kg m -2 h -1 bar -1 .

[0038] Example 2, a MOF gel induced preparation of a covalent organic framework film, the steps of example 2 are basically the same as those of example 1, except that the reaction time in step 2) is changed from 24 hours to 48 hours. Finally, a MOF gel induced covalent organic framework film is obtained, which is recorded as film 2. Figure 4 is a gel face scanning electron micrograph of film 2, Figure 5 is an organic face scanning electron micrograph of film 2.

[0039] Membrane 2 was subjected to catalytic cracking diesel separation experiment: using dead-end filtration device, using dead-end filtration device, selecting aromatic pure solvent and alkane pure solvent, the aromatic permeation flux of membrane 2 was 0.051 kg m -2 h -1 bar -1 , the alkane permeation flux was 0.014 kg m -2 h -1 bar -1 .

[0040] Example 3, preparation of a MOF gel induced covalent organic framework membrane, the steps of example 3 and example 1 are basically the same, only the reaction time in step 2) is changed from 24 hours to 72 hours, finally a MOF gel induced covalent organic framework membrane is obtained, which is recorded as membrane 3. Figure 6 is the gel face scanning electron micrograph of membrane 3, Figure 7 is the organic face scanning electron micrograph of membrane 3.

[0041] Membrane 3 was subjected to catalytic cracking diesel separation experiment: using dead-end filtration device, selecting aromatic pure solvent and alkane pure solvent, the aromatic permeation flux of membrane 3 was 0.050 kg m -2 h -1 bar -1 , the alkane permeation flux was 0.009 kg m -2 h -1 bar -1 .

[0042] Comparative example 1, preparation of covalent organic framework membrane catalyzed by acetic acid, the steps are as follows:

[0043] Step one, preparation of water-liquid interface system: prepare 3M acetic acid mixed aqueous solution by ultrasonic dispersion, which is recorded as solution A;

[0044] According to the concentration of 0.3-0.5 mmol L -1 1,3,5-tris(aminophenyl)benzene and the concentration of 0.6-0.75 mmol L -1 2,5-dihexyloxy terephthaldehyde is dissolved in organic solvent and ultrasonic dispersed for 0.5 hours, the obtained solution is recorded as solution B;

[0045] Step two: preparation of covalent organic framework membrane catalyzed by acetic acid:

[0046] According to equal volume, solution A is slowly dropped to the surface of solution B, after sealing, it is placed at room temperature for 24 hours, after the reaction is completed, the membrane is formed, which is washed with acetone and ethanol in turn, and then taken out and placed on the base film to dry at room temperature for 24 hours, the obtained MOF gel induced interface assembled covalent organic framework membrane is recorded as membrane 4. Figure 8is a water surface scanning electron micrograph of film 4, Figure 9 is an organic surface scanning electron micrograph of film 4.

[0047] The film 4 was subjected to catalytic cracking diesel separation experiment: using dead-end filtration device, selecting aromatic pure solvent and alkane pure solvent, the aromatic permeation flux of film 3 was 0.051 kg m -2 h -1 bar -1 , the alkane permeation flux was 0.049 kg m -2 h -1 bar -1 .

[0048] It can be seen by comparing the examples and the comparative examples that the surface of the covalent organic framework film prepared by the MOF gel induction of the application is dense and defect-free, the MOF gel has a unique nanoscale radial size and three-dimensional cross-linked gel network structure, and not only serves as a catalyst but also as a phase in the interfacial polymerization, giving the gel an interfacial slow diffusion feature; compared with acetic acid as a catalyst, the surface of the covalent organic framework film prepared by the MOF gel induction is smoother, and the separation performance is significantly improved. Figure 10 is a comparison diagram of aromatic and alkane pure solvent permeation of films 1-4.

[0049] Although the application has been described in conjunction with the accompanying drawings, the application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative rather than limiting, and a person of ordinary skill in the art can make many modifications under the inspiration of the application without departing from the purpose of the application, and these all belong to the protection of the application.

Claims

1. A method for preparing a covalent organic framework membrane by MOF gel induction, characterized in that: The method comprises constructing a liquid-liquid interface system using an MOF gel aqueous solution and an organic solvent, distributing reactive monomers of a covalent organic framework material in the organic solvent, and controlling the diffusion rate of the reactive monomers and the polymerization reaction at the phase interface by changing the concentration of the MOF gel to assemble a covalent organic framework membrane having a smooth and dense surface. The membrane is prepared according to the following steps: Step 1: Preparation of MOF gel-liquid interface system: The MOF gel was dispersed in an aqueous solution at a mass concentration of 0.5%-2% by ultrasonic dispersion and magnetic stirring for 2 hours. The resulting solution was recorded as solution A. According to the concentration of 0.3-0.5 mmol·L -1 1,3,5-Tris(4-aminophenyl)benzene and concentration of 0.6-0.75 mmol·L -1 2,5-Dihexyloxyterephthalaldehyde was dissolved in an organic solvent and ultrasonically dispersed for 0.5 h. The resulting solution was designated as solution B. Step 2: A method for preparing a covalent organic framework membrane by inducing MOF gel: Solution A was slowly dripped onto the surface of solution B according to equal volume. After sealing, the solution was allowed to stand at room temperature for 24-72 hours for interfacial polymerization reaction. After the reaction, a film was formed. The film was washed with acetone and ethanol respectively, removed and placed on the base film and dried at room temperature for 24 hours. The obtained MOF gel-induced interfacial assembly covalent organic framework film was recorded as TAPB-TPOC6 COF.

2. The method for preparing a covalent organic framework membrane by MOF gel induction according to claim 1, characterized in that: In step 1, the MOF gel is any one of UiO-66, ZIF-8, and ZIF-67 gels.

3. The method for preparing a covalent organic framework membrane by MOF gel induction according to claim 1, characterized in that: In step 1, the organic solvent is one of dichloromethane, o-dichlorobenzene, mesitylene, and dioxane solvents.

4. The method for preparing a covalent organic framework membrane by MOF gel induction according to claim 1, characterized in that: In step 2, the base film is a commercially available solvent-resistant base film, and the film material is any one of polyacrylonitrile, polytetrafluoroethylene, and polyvinylidene fluoride.

5. Use of a covalent organic framework membrane prepared by MOF gel induction according to the method according to any one of claims 1 to 4 for separating aromatic hydrocarbons from alkanes.

6. The use according to claim 5, wherein the operating temperature is 35 ° C and the operating pressure is 40 bar, to achieve separation of aromatic hydrocarbons and alkanes; the aromatic hydrocarbons are C7, C8, C 12 Any one of; alkane is any one of toluene, xylene, and mesitylene.

7. According to the use of claim 6, the aromatic hydrocarbon is C 12 , the alkane is toluene.

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