CN112090298A

CN112090298A - Full-nano porous MOF/HOF composite membrane, preparation method and application thereof in gas separation

Info

Publication number: CN112090298A
Application number: CN202010959058.4A
Authority: CN
Inventors: 康子曦; 张彩艳; 范黎黎; 王荣明; 孙道峰
Original assignee: China University of Petroleum East China
Current assignee: China University of Petroleum East China
Priority date: 2020-09-14
Filing date: 2020-09-14
Publication date: 2020-12-18

Abstract

A full-nano porous MOF/HOF composite membrane, a preparation method and application of the membrane in gas separation belong to the technical field of membrane materials and separation thereof. According to the invention, porous ZIF-8 particles with the particle size of about 100nm are synthesized by a hydrothermal method, ZIF-8 with different amounts are uniformly dispersed in UPC-HOF-6 casting solution by an ultrasonic method, and then a series of composite membranes with different composition ratios are obtained by a solution pouring-solvent evaporation method, wherein the method comprises three steps of preparation of ZIF-8, preparation of HOF precursor NBP-DAT, preparation of MOF/HOF composite membranes and the like. Scanning electron microscope result displayThe surface of the alloy film was rough and there were particulate matter of varying sizes, presumably incorporated particles of ZIF-8. The comparison of the permeation properties shows that the MOF/HOF composite membranes with different composition ratios are paired with H₂/N₂The ZIF-8 composite membrane has certain selectivity, and the gas permeability is increased and the separation selectivity is reduced along with the increase of the ZIF-8 doping amount, so that the composite membrane can be used for gas separation.

Description

Full-nano porous MOF/HOF composite membrane, preparation method and application thereof in gas separation

Technical Field

The invention belongs to the technical field of membrane materials and separation thereof, and particularly relates to a full-nano porous MOF/HOF composite membrane, a preparation method and application of the membrane in gas separation.

Background

The separation of gas molecules having similar physical or chemical properties is of industrial importance. The separation technique usually employed is cryogenic distillation, which accounts for 90% to 95% of all isolates. However, this technique requires a large amount of energy and is difficult to separate gas molecules having similar compressibility and boiling points. The energy-intensive distillation technology is replaced by a relatively low-energy-consumption process, so that the remarkable energy-saving effect can be achieved. The novel membrane separation technology is researched more and more widely in the field of gas separation by virtue of the advantages of low energy consumption, simple operation, small occupied area, high efficiency and the like, and has great potential in solving the energy and environmental challenges. The permeability and the separation ratio are two most important parameters for measuring the membrane performance, the high membrane separation ratio can save redundant treatment processes, simplify the operation flow, reduce the operation cost, increase the yield corresponding to the permeability, and reduce the use of membrane area and membrane components and energy loss.

The current most widely used commercial membrane material is a polymer membrane, which has low cost and good processability. However, research data show that a trade-off effect exists between permeability and selectivity when a traditional polymer membrane is used for gas separation, which is caused by a separation mechanism of the polymer membrane and the characteristics of wide pore size distribution and lack of orderliness of the membrane, and meanwhile, the thermal stability and chemical stability of most polymers also limit the application of the polymers.

The traditional mixed matrix membrane is a composite membrane material formed by doping high-performance porous material nanoparticles into a polymer matrix which is easy to prepare and low in cost. On one hand, the addition of the inorganic porous filler can overcome the 'trade-off' effect between selectivity and permeability of a pure polymer system, so that the performance of the membrane is improved; on the other hand, the problem that the traditional inorganic filler is limited in application due to the particle state and the problem that the inorganic film is fragile and difficult to expand and prepare is solved by utilizing the easy processability of the polymer to prepare the film. Although the traditional mixed matrix membrane is greatly improved in gas selectivity and permeability, the limitation of the performance of the polymer matrix on the performance of the final mixed matrix membrane is still a problem to be solved in the research of further improving the performance of the mixed matrix membrane, and the stability of the mixed matrix membrane is also influenced by the problems of easy plasticization and aging of the polymer matrix.

Compared with the high polymer material, the ordered porous membrane material has more uniform pore structure and pore distribution and excellent pore size sieving performance. Taking different ordered nano-porous materials as the dispersed phase and the continuous phase of the mixed matrix membrane simultaneously provides a new research idea for solving the problem of the limitation of the polymer matrix on the performance of the mixed matrix membrane, and the obtained results show that the membrane material can surpass the performance of other similar membrane materials taking macromolecules as the matrix (Rashidi F, Leisen J, Kim S J, et al, all-nanoporous membranes: refining upper limits on molecular separation properties [ J ]. Angewandte chemical International Edition,2019,131(1): 242-245.). Meanwhile, UPC-HOF-6 has the same solution processability as a polymer as a novel ordered porous membrane material (Feng S, Shang Y, Wang Z, et al, "Fabrication of a hydrogen bonded organic frame membrane through solution processing for compressed regulated gas separation [ J ]. Angewandte chemical International Edition, 2020.).

Disclosure of Invention

The invention aims to provide a full-nano porous MOF/HOF composite membrane, a preparation method and application of the membrane in gas separation.

According to the invention, porous ZIF-8 particles with the particle size of about 100nm are synthesized by a hydrothermal method, ZIF-8 with different amounts is uniformly dispersed in UPC-HOF-6 casting solution by an ultrasonic method, and a series of composite membranes with different composition ratios are obtained by a solution pouring-solvent evaporation method, wherein the method comprises the following steps:

(1) preparation of ZIF-8: according to the mass ratio of 1: (10-30) weighing zinc nitrate (Zn (NO)₃)₂) Respectively ultrasonically dissolving the above-mentioned materials and 2-methylimidazole (2-HmIm) to obtain aqueous solution; adding Zn (NO)₃)₂Rapidly mixing the aqueous solution and the 2-HmIm aqueous solution, magnetically stirring for 5-15 minutes at room temperature, centrifuging (6500-10000 rpm, 10-30 min), collecting a reaction product, and washing with deionized water; finally, drying for 6-12 hours at the temperature of 60-100 ℃ to obtain dried and activated ZIF-8 particles;

(2) preparation of HOF precursor NBP-DAT: respectively mixing 6-10 g of tri (4-bromophenyl) amine and the tri (4-bromophenyl) amine in a mass ratio of (0.5-5): 1 and (10-100): 1, 4-cyanophenylboronic acid and anhydrous N, N-Dimethylformamide (DMF) are mixed, then nitrogen is introduced in a sealed manner to exhaust air, and 10-100 mL and 0.1-0.5 g/mL are added after 10-30 minutes^-1K of₂CO₃Continuously introducing nitrogen into the aqueous solution and 10-100 mL of deionized water for protection; adding 1-3 g of tetrakis (triphenylphosphine) palladium after 10-30 minutes, heating to 80-120 ℃, and reacting for 36-72 hours; after the reaction is finished, the reaction mixture is cooled to room temperature and CH is used₂Cl₂Extracting with saturated NaCl water solution, and drying the organic phase with anhydrous magnesium sulfate overnight; the organic phase was filtered and the bulk of the CH was removed by rotary evaporation₂Cl₂Slowly adding 100-300 mL of methanol, standing for 1-3 days, and performing suction filtration to obtain tris (4-cyanophenyl) aniline; mixing 3 to 4g of tris (4-cyanophenyl) aniline and tris (4-cyanophenyl) aniline in a mass ratio of (0.5 to 5): 1 and (50-100): 1, mixing dicyandiamide and ethylene glycol monomethyl ether, sealing and introducing nitrogen to exhaust air, adding 0.1-1 g of KOH after 10-30 minutes, continuously introducing nitrogen for 10-30 minutes, raising the temperature to 90-125 ℃, reacting for 12-36 hours, cooling to room temperature after the reaction is finished, performing suction filtration to obtain a faint yellow solid product, and leaching for 2-3 times respectively by using deionized water and methanol to obtain the productTo pure 4,4, 4-tris (2, 4-diamino-1, 3, 5-triazinylphenyl) aniline, i.e. the HOF precursor NBP-DAT;

(3) preparing an MOF/HOF composite membrane: weighing 4.8-14.4 mg of ZIF-8 particles dried and activated in the step (1), adding the particles into 0.5-1 mL of anhydrous dimethyl sulfoxide (DMSO), performing ultrasonic treatment for 30-60 minutes to uniformly disperse the ZIF-8, adding 80-150 mg of HOF precursor NBP-DAT prepared in the step (2), and completely dissolving the NBP-DAT at 50-150 ℃ to obtain a composite membrane casting solution; preheating a porous alpha-alumina substrate at 60-80 ℃ for 30-60 minutes, transferring 80-150 mu L of composite membrane casting liquid, uniformly dripping the composite membrane casting liquid on the preheated porous alpha-alumina substrate, evaporating the solvent at 60-100 ℃ for 1-3 hours, and obtaining a homogeneous full-nano porous MOF/HOF composite membrane on the porous alpha-alumina substrate, wherein the thickness of the composite membrane is 4-11 mu m.

Drawings

FIG. 1: SEM image of ZIF-8 particles in example 1;

FIG. 2: XRD patterns of MOF/HOF composite film samples of examples 1-3 and comparative example;

FIG. 3: SEM images of MOF/HOF composite film samples of examples 1-3 and comparative example;

FIG. 4: examples 1-3 comparative graph of gas separation performance;

FIG. 1 is an SEM image of ZIF-8 particles of examples 1-3, showing that the resulting ZIF-8 particles had a particle size of about 100 nm.

FIG. 2 is an XRD spectrum of different types of MOF/HOF composite films prepared in examples 1-3, by comparing different types of films with simulated XRD diffraction spectra, the composite films have characteristic peaks identical to those of single-phase HOF and MOF, and we can speculate that the ZIF-8 particles are successfully loaded in the HOF crystal film, the intensity of the ZIF-8 characteristic peak increases with the increase of doping concentration, and the crystal structure of ZIF-8 is not damaged in the film forming process.

FIG. 3 is a front scanning electron micrograph of a pure HOF film in a comparative example and different types of composite films prepared in examples 1-3. From the images we can see that the composite membrane surface is rough with different size particulate matter, presumably the incorporated ZIF-8 particles. Fig. 3(a) is a comparative example, fig. 3(b) is example 1, fig. 3(c) is example 2, and fig. 3(d) is example 3.

FIG. 4 is a graph of H vs. normal temperature and pressure for different types of composite films prepared in examples 1-3₂/N₂Comparative permeation performance of (c). From the figure, it can be seen that different MOF/HOF composite membrane pairs H₂/N₂There is a certain selectivity. With the increase of the amount of ZIF-8 doped, the gas permeability increases and the separation selectivity decreases.

In order to determine the doping amount of ZIF-8 in the composite membrane, the prepared composite membrane can show more excellent H₂/N₂Separating property, pure HOF membranes, UPC-HOF-6/ZIF-8-4, UPC-HOF-6/ZIF-8-8, UPC-HOF-6/ZIF-8-12, which do not contain or contain 4%, 8% and 12% of ZIF-8 doping amount respectively are prepared according to the conditions in the table 1, the film forming temperature is 80 ℃, and the film forming time is 2 hours.

Table 1: composition conditions and film-making conditions of different composite films

Example 1:

(1) preparation of ZIF-8: 1.17g of zinc nitrate (Zn (NO) was weighed out separately₃)₂) This was dissolved with 22.7g of 2-methylimidazole (2-HmIm) in two beakers by sonication to prepare an aqueous solution. Dissolving Zn (NO)₃)₂Rapidly mixing the solution with 2-HmIm solution, magnetically stirring at room temperature for 5 min, centrifuging (6500rpm, 30min) to collect the product, and washing with deionized water; finally, dried at 60 ℃ for 10 hours to obtain dry activated ZIF-8 granules.

(2) Preparation of HOF precursor NBP-DAT: a three-necked reaction flask was charged with 8.16g of tris (4-bromophenyl) amine, 10.43g of 4-cyanophenylboronic acid and 284.61g of anhydrous N, N-Dimethylformamide (DMF), sealed and purged with nitrogen to remove air. After 30 minutes, 48mL, 0.275 g/mL were added^-1K of₂CO₃The aqueous solution and 48mL of deionized water are continuously introduced with nitrogen for protection. After 30 minutes 1.56g of tetrakis (triphenylphosphine) palladium were added and the reaction was carried out for 48 hours after heating to 90 ℃. After the reaction is finished, the reaction mixture is cooled to room temperature and CH is used₂Cl₂Extracting with saturated NaCl solution, drying the organic phase with anhydrous magnesium sulfate overnight, filtering to obtain organic phase, and removing large amount of CH by rotary evaporation₂Cl₂To the remaining small amount of organic solution, 200mL of methanol was slowly added, allowed to stand for two days, and filtered with suction to give tris (4-cyanophenyl) aniline. A three-necked reaction flask was charged with 3.4g of tris (4-cyanophenyl) aniline, 2.3g of dicyandiamide and 289.5g of ethylene glycol methyl ether, sealed and purged with nitrogen to remove air. Adding 0.4g of KOH after 30 minutes, continuously introducing nitrogen for 30 minutes, raising the temperature to 125 ℃, reacting for 24 hours, cooling to room temperature after the reaction is finished, carrying out suction filtration to obtain a light yellow solid product, eluting with deionized water and methanol twice respectively to obtain pure 4,4, 4-tris (2, 4-diamino-1, 3, 5-triazinylphenyl) aniline (NBP-DAT), placing in an oven, drying, and weighing 3.14 g of pure 4,4, 4-tris (2, 4-diamino-1, 3, 5-triazinylphenyl) aniline (NBP-DAT).

(3) Preparing an MOF/HOF composite membrane: weighing 4.8mg of activated ZIF-8 particles, placing the particles in a 10mL glass bottle, transferring 1mL of anhydrous dimethyl sulfoxide (DMSO) into the glass bottle, performing ultrasonic treatment for 30 minutes to uniformly disperse the ZIF-8 particles in a DMSO solution, accurately weighing 120mg of HOF precursor NBP-DAT, dissolving the HOF precursor NBP-DAT in the DMSO solution, and completely dissolving the HOF precursor NBP-DAT at 150 ℃ to obtain a composite membrane casting solution. Preheating a porous alpha-alumina substrate for 30 minutes at 80 ℃, transferring 100 mu L of composite membrane casting solution, uniformly dripping the composite membrane casting solution on the preheated substrate, evaporating the solvent at 80 ℃, and obtaining a homogeneous MOF/HOF composite membrane which is marked as UPC-HOF-6/ZIF-8-4 after 2 hours, wherein the thickness of the membrane is 4.87 mu m.

(4) Characterization of the membrane: and (3) performing X-ray diffraction spectrum characterization, scanning electron microscope characterization and gas separation test on the composite membrane. When a gas separation test is carried out, the prepared porous alpha-alumina substrate loaded with the MOF/HOF composite membrane is placed in a mold of a gas chromatography membrane separation device, and a carrier gas (Ar) and a gas to be tested (H) are introduced₂、N₂) Testing is carried out, and the permeability P of the composite membrane to two testing gases is obtained after the testing is finished_H2、P_N2The separation factor is the ratio of the permeability of the composite membrane to the two gases (P)_H2/P _N2) The test results are shown in table 1.

Table 1: h₂/N₂Separation factor and H₂Coefficient of permeability

	H₂Permeability (GPU)	Separation factor
			H₂/N₂	37.42	6.68

Permeability is the amount of gas molecules that pass through a unit of membrane area per unit time.

Example 2:

(1) ZIF-8 granules were prepared as in example 1, step 1;

(2) prepare NBP-DAT precursor as in example 1, step 2;

(3) preparing an MOF/HOF composite membrane: weighing 9.6mg of activated ZIF-8 particles, placing the particles in a 10mL glass bottle, transferring 1mL of anhydrous dimethyl sulfoxide (DMSO) into the glass bottle, performing ultrasonic treatment for 30 minutes to uniformly disperse the ZIF-8 particles in a DMSO solution, accurately weighing 120mg of HOF precursor NBP-DAT, dissolving the HOF precursor NBP-DAT in the DMSO solution, and completely dissolving the HOF precursor NBP-DAT at 150 ℃ to obtain a composite membrane casting solution. Preheating a porous alpha-alumina substrate for 30 minutes at 80 ℃, transferring 100 mu L of composite membrane casting solution, uniformly dripping the composite membrane casting solution on the preheated substrate, evaporating the solvent at 80 ℃, and obtaining a homogeneous MOF/HOF composite membrane which is marked as UPC-HOF-6/ZIF-8-8 after 2 hours, wherein the thickness of the membrane is 7.88 mu m.

(4) Characterization of the membrane: and (3) performing X-ray diffraction spectrum characterization, scanning electron microscope characterization and gas separation test on the composite membrane. When a gas separation test is carried out, the prepared porous alpha loaded with the MOF/HOF composite membrane-placing the alumina substrate in a mould of a gas chromatography membrane separation device and introducing a carrier gas (Ar) and a gas to be measured (H)₂、N₂) Testing is carried out, and the permeability P of the composite membrane to two testing gases is obtained after the testing is finished_H2、P_N2The separation factor is the ratio of the permeability of the composite membrane to the two gases (P)_H2/P _N2) The test results are shown in Table 2.

Table 2: h₂/N₂Separation factor and H₂Coefficient of permeability

	H₂Permeability (GPU)	Separation factor
			H₂/N₂	65.54	5.98

Example 3:

(1) ZIF-8 granules were prepared as in example 1, step 1;

(2) prepare NBP-DAT precursor as in example 1, step 2;

(3) preparing an MOF/HOF composite membrane: weighing 14.4mg of activated ZIF-8 particles, placing the particles in a 10mL glass bottle, transferring 1mL of anhydrous dimethyl sulfoxide (DMSO) into the glass bottle, performing ultrasonic treatment for 30 minutes to uniformly disperse the ZIF-8 particles in a DMSO solution, accurately weighing 120mg of HOF precursor NBP-DAT, dissolving the HOF precursor NBP-DAT in the DMSO solution, and completely dissolving the HOF precursor NBP-DAT at 150 ℃ to obtain a composite membrane casting solution. Preheating a porous alpha-alumina substrate for 30 minutes at 80 ℃, transferring 100 mu L of composite membrane casting solution, uniformly dripping the composite membrane casting solution on the preheated substrate, evaporating the solvent at 80 ℃, and obtaining a homogeneous MOF/HOF composite membrane which is marked as UPC-HOF-6/ZIF-8-12 after 2 hours, wherein the thickness of the membrane is 10.77 mu m.

(4) Characterization of the membrane: and (3) performing X-ray diffraction spectrum characterization, scanning electron microscope characterization and gas separation test on the composite membrane. When a gas separation test is carried out, the prepared porous alpha-alumina substrate loaded with the MOF/HOF composite membrane is placed in a mold of a gas chromatography membrane separation device, and a carrier gas (Ar) and a gas to be tested (H) are introduced₂、N₂) Testing is carried out, and the permeability P of the composite membrane to two testing gases is obtained after the testing is finished_H2、P_N2The separation factor is the ratio of the permeability of the composite membrane to the two gases (P)_H2/P _N2) The test results are shown in Table 3.

Table 3: h₂/N₂Separation factor and H₂Coefficient of permeability

	H₂Permeability (GPU)	Separation factor
			H₂/N₂	331.54	4.57

Comparative example:

120mg of the HOF precursor NBP-DAT was dissolved in 1mL of DMSO and dissolved completely at 150 ℃ to prepare a film casting solution. Preheating a porous alpha-alumina substrate at 80 ℃ for 30 minutes, transferring 100 mu L of membrane casting liquid, uniformly dripping the membrane casting liquid on the preheated substrate, evaporating the solvent at 80 ℃ for 2 hours to obtain a pure HOF membrane which is marked as UPC-HOF-6/ZIF-8-0.

Table 4: h₂/N₂Separation factor and H₂Coefficient of permeability

	H₂Permeability (GPU)	Separation factor
			H₂/N₂	468.9	11.08

Claims

1. A preparation method of a full-nano porous MOF/HOF composite membrane comprises the following steps:

(1) preparation of ZIF-8: according to the mass ratio of 1: 10-30 weighing zinc nitrate and 2-methylimidazole, and respectively ultrasonically dissolving to prepare an aqueous solution; rapidly mixing a zinc nitrate aqueous solution and a 2-methylimidazole aqueous solution, magnetically stirring for 5-15 minutes at room temperature, centrifuging to collect a reaction product, and washing with deionized water; finally, drying for 6-12 hours at the temperature of 60-100 ℃ to obtain dried and activated ZIF-8 particles;

(2) preparation of HOF precursor NBP-DAT: 6 to 10g of tris (4-bromophenyl) amine, andthe mass ratio of the tri (4-bromophenyl) amine is respectively 0.5-5: 1 and 10 to 100: 1, mixing 4-cyanophenylboronic acid and anhydrous N, N-dimethylformamide, sealing and introducing nitrogen to exhaust air, and adding 10-100 mL and 0.1-0.5 g/mL after 10-30 minutes^-1K of₂CO₃Continuously introducing nitrogen into the aqueous solution and 10-100 mL of deionized water for protection; adding 1-3 g of tetrakis (triphenylphosphine) palladium after 10-30 minutes, heating to 80-120 ℃, and reacting for 36-72 hours; after the reaction is finished, the reaction mixture is cooled to room temperature and CH is used₂Cl₂Extracting with saturated NaCl water solution, and drying the organic phase with anhydrous magnesium sulfate overnight; the organic phase was filtered and the bulk of the CH was removed by rotary evaporation₂Cl₂Slowly adding 100-300 mL of methanol, standing for 1-3 days, and performing suction filtration to obtain tris (4-cyanophenyl) aniline; mixing 3 to 4g of tris (4-cyanophenyl) aniline and tris (4-cyanophenyl) aniline in a mass ratio of 0.5 to 5: 1 and 50 to 100: 1, mixing dicyandiamide and ethylene glycol monomethyl ether, sealing and introducing nitrogen to exhaust air, adding 0.1-1 g of KOH after 10-30 minutes, continuously introducing nitrogen for 10-30 minutes, raising the temperature to 90-125 ℃, reacting for 12-36 hours, cooling to room temperature after the reaction is finished, performing suction filtration to obtain a light yellow solid product, and leaching with deionized water and methanol for 2-3 times respectively to obtain pure 4,4, 4-tris (2, 4-diamino-1, 3, 5-triazinylphenyl) aniline, namely an HOF precursor NBP-DAT;

(3) preparing an MOF/HOF composite membrane: weighing 4.8-14.4 mg of ZIF-8 particles dried and activated in the step (1), adding the particles into 0.5-1 mL of anhydrous dimethyl sulfoxide, performing ultrasonic treatment for 30-60 minutes to uniformly disperse the ZIF-8, adding 80-150 mg of HOF precursor NBP-DAT prepared in the step (2), and completely dissolving the mixture at 50-150 ℃ to obtain a composite membrane casting solution; preheating a porous alpha-alumina substrate at 60-80 ℃ for 30-60 minutes, transferring 80-150 mu L of composite membrane casting liquid, uniformly dripping the composite membrane casting liquid on the preheated porous alpha-alumina substrate, evaporating the solvent at 60-100 ℃, and obtaining a homogeneous full-nano porous MOF/HOF composite membrane on the porous alpha-alumina substrate after 1-3 hours.

2. A full-nanoporous MOF/HOF composite membrane, characterized in that: is prepared by the method of claim 1.

3. Use of the all-nanoporous MOF/HOF composite membrane of claim 2 in gas separation.

4. Use of a full nanoporous MOF/HOF composite membrane according to claim 3 in gas separation wherein: for separating H₂And N₂。