A nano-molecular sieve gas separation membrane, preparation method and application in carbon dioxide capture

Abstract

The present invention relates to the field of membrane separation technology, and discloses a gas separation membrane of a nanomolecular sieve, a preparation method and an application in carbon dioxide capture. The preparation method of the gas separation membrane of the nanomolecular sieve comprises the following steps: preparing microporous nano cerium oxide by microwave-assisted solvothermal method; modifying microporous nano cerium oxide to obtain amination microporous nano cerium oxide; treating single-walled carbon nanotubes to obtain carboxylated carbon nanotubes; amination microporous nano cerium oxide reacts with carboxylated carbon nanotubes to obtain modified carbon nanotubes; modified carbon nanotubes are inserted into the sheet of MOF nanosheets to obtain intercalation modified MOF nanosheets; preparing PIM‑1 polymers; intercalation modified MOF nanosheets are used as fillers and mixed with PIM‑1 polymers to prepare the gas separation membrane of the nanomolecular sieve. The gas separation membrane of the nanomolecular sieve of the present invention has a good separation effect on carbon dioxide and is used for the capture of carbon dioxide.

Description

Technical Field

[0001] The present invention relates to the field of membrane separation technology, and in particular to a nano-molecular sieve gas separation membrane, a preparation method and application thereof in carbon dioxide capture. Background Art

[0002] The use of fossil fuels has been powering the progress of human society since the second industrial revolution. However, the surge in carbon dioxide emissions has raised concerns about global warming and its consequences. Membrane separation technologies have become one of the main carbon emission reduction methods because they are less energy intensive and more environmentally friendly than other separation technologies. Compared with pure polymer membranes, mixed matrix membranes that contain both polymer matrices and molecular sieve fillers have received great attention because they combine the advantages of polymers and molecular sieves while offsetting each other's disadvantages. MOFs are considered promising molecular sieves for various separation applications due to their extremely high surface area, adjustable pore / channel size, and customizable functionality. However, inorganic molecular sieve fillers have interfacial compatibility issues with polymer matrices, which adversely affect the separation effect of the membrane. In addition, interfacial problems can also produce non-selective voids, affecting the selectivity of the membrane. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for preparing a gas separation membrane of a nano molecular sieve, comprising the following steps:

[0004] Step (1), preparing microporous nano-cerium oxide by microwave-assisted solvothermal method; modifying the microporous nano-cerium oxide to obtain amino-modified microporous nano-cerium oxide;

[0005] Step (2), treating the single-walled carbon nanotubes to obtain carboxylated carbon nanotubes; reacting the aminated microporous nano-cerium oxide with the carboxylated carbon nanotubes to obtain modified carbon nanotubes;

[0006] Step (3), inserting the modified carbon nanotubes into the MOF nanosheets to obtain intercalated modified MOF nanosheets;

[0007] The method for preparing the MOF nanosheets comprises the following steps:

[0008] Step S1, reacting 3,5-diaminosalicylic acid with 5,10,15,20-tetrakis(4-formylphenyl)porphyrin to obtain a multifunctional porphyrin compound;

[0009] Step S2, using zinc nitrate hexahydrate and a multifunctional porphyrin compound as raw materials to prepare MOF nanosheets;

[0010] Step (4), using 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and tetrafluoroterephthalonitrile as raw materials to prepare PIM-1 polymer;

[0011] Intercalated modified MOF nanosheets were used as fillers and mixed with PIM-1 polymer to prepare nano-molecular sieve gas separation membranes.

[0012] Preferably, in step (1), the preparation method of the microporous nano-cerium oxide is as follows: dissolving cerium (III) nitrate hexahydrate in diethylene glycol, adding hexamethylenetetramine under stirring conditions of 500-700 r / min to obtain a suspension, reacting the suspension in a microwave accelerated reaction system at a pressure of 8-12 bar for 40-80 min, precipitating with acetone, and then centrifuging, washing, and drying; wherein the mass ratio of cerium (III) nitrate hexahydrate, ethanol, and hexamethylenetetramine is (0.4-0.8):(20-50):(0.7-1.4);

[0013] In the above process, diethylene glycol is used as solvent, cerium (III) nitrate hexahydrate is used as precursor, and hexamethylenetetramine is used as precipitant. Under microwave-assisted conditions, nano-cerium oxide particles with an average particle size of about 3 nm and micropores with an average pore size of about 1.2 nm can be obtained.

[0014] Preferably, in step (1), the preparation method of the aminated microporous nano-cerium oxide is as follows: ultrasonically dispersing the microporous nano-cerium oxide in a mixture of ethanol and deionized water, adding diethylenetriaminepropyltrimethoxysilane, keeping warm at 55-60°C for 8-10 hours, filtering, washing, and drying; wherein the mass ratio of microporous nano-cerium oxide, ethanol, deionized water, and diethylenetriaminepropyltrimethoxysilane is (0.5-1):(12-24):(2-4):(1.5-3);

[0015] In the above process, diethylenetriaminopropyltrimethoxysilane is hydrolyzed and grafted onto the surface of microporous nano-cerium oxide, and multiple amino groups are introduced onto the surface of microporous nano-cerium oxide, thereby further reducing the pore size of the microporous nano-cerium oxide.

[0016] Preferably, in step (2), the preparation method of the modified carbon nanotubes is:

[0017] Mixing 98% sulfuric acid and 70% nitric acid in a volume ratio of 3:1 to obtain an acidic mixture; adding single-walled carbon nanotubes to the acidic mixture, reflux at 70-90° C. for 3-5 hours, cooling, filtering, washing the filtered product with distilled water until the washing liquid is neutral, and drying to obtain carboxylated carbon nanotubes; wherein the amount ratio of the single-walled carbon nanotubes to the acidic mixture is (1-3) g: (100-200) mL;

[0018] Disperse carboxylated carbon nanotubes in N,N-dimethylformamide, add 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide, stir for 2.5-3.5h, then add aminated microporous nano-cerium oxide, adjust the pH of the reaction system to 5.3-5.7 with a 1 mol / L hydrochloric acid aqueous solution, react for 20-30h in a nitrogen atmosphere at room temperature, filter, wash the obtained solid product with methanol and then dry to obtain modified carbon nanotubes; wherein the mass ratio of carboxylated carbon nanotubes, N,N-dimethylformamide, 1,3-dicyclohexylcarbodiimide, N-hydroxysuccinimide, and aminated microporous nano-cerium oxide is (3-6):(150-250):(3.7-7.4):(2.1-4.2):(3-6);

[0019] In the above process, the carboxyl groups of the carboxylated carbon nanotubes undergo an amidation reaction with the amino groups of the aminated microporous nano-cerium oxide, so that the aminated microporous nano-cerium oxide is grafted onto the surface of the carboxylated carbon nanotubes.

[0020] Preferably, in step (3), the preparation method of the intercalated modified MOF nanosheets comprises: dispersing the modified carbon nanotubes in deionized water to obtain a dispersion A with a concentration of 0.3-0.7 mg / mL; dispersing the MOF nanosheets in deionized water to obtain a dispersion B with a concentration of 0.3-0.7 mg / mL; mixing the dispersion A and the dispersion B in a volume ratio of 1:(2-4), ultrasonically treating for 3-5 hours, centrifuging, washing, and drying;

[0021] In the above process, the amino groups on the MOF nanosheets form hydrogen bonds with the amino and amide groups on the modified carbon nanotubes. At the same time, the negatively charged phenolic hydroxyl groups on the MOF nanosheets combine with the positively charged amino groups on the modified carbon nanotubes through electrostatic action, inserting the modified carbon nanotubes into the sheet structure of the MOF nanosheets, thereby increasing the interlayer spacing of the MOF nanosheets.

[0022] Preferably, in step (3), the preparation method of the MOF nanosheet is:

[0023] Step S1, adding 3,5-diaminosalicylic acid to ethanol, ultrasonically treating for 10-30 minutes, then adding 5,10,15,20-tetrakis(4-formylphenyl)porphyrin, heating to 55-62° C., stirring for reaction for 2.5-3.5 hours, filtering, washing, and drying to obtain a multifunctional porphyrin compound; wherein the mass ratio of 3,5-diaminosalicylic acid, ethanol, and 5,10,15,20-tetrakis(4-formylphenyl)porphyrin is (6-12):(100-200):(7.3-14.6);

[0024] Step S2, ethanol and N,N-dimethylformamide are mixed in a volume ratio of 3:1 to obtain a mixed solution, zinc nitrate hexahydrate and a multifunctional porphyrin compound are added, and the mixture is stirred and mixed at 45-55°C for 40-80 minutes, and then heated in a vacuum environment at 75-85°C for 20-28 hours, and then kept at room temperature for 4-5 hours, centrifuged, washed, and dried to obtain MOF nanosheets; wherein the mass ratio of zinc nitrate hexahydrate, multifunctional porphyrin compound, and mixed solution is (3.6-7.2):(1.8-3.6):(40-60);

[0025] In the above process, the amino group of 3,5-diaminosalicylic acid reacts with the aldehyde group of 5,10,15,20-tetrakis(4-formylphenyl)porphyrin to generate a multifunctional porphyrin compound containing amino, phenolic hydroxyl and carboxyl groups; the multifunctional porphyrin compound acts as a carboxyl ligand and coordinates with zinc nitrate hexahydrate to form MOF nanosheets containing phenolic hydroxyl and amino groups on the surface, and the average pore size of the MOF nanosheets is about 3.4 nm.

[0026] Preferably, in step (4), the preparation method of the PIM-1 polymer is as follows: 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and tetrafluoroterephthalonitrile are mixed, N,N-dimethylformamide is added in an argon atmosphere, and the mixture is stirred at 60-70°C until the mixed system becomes clear, potassium carbonate powder is added, the temperature is kept constant, and the stirring reaction is continued for 65-75 hours, the solid obtained by the reaction is washed with methanol and deionized water, dried, and then dissolved in chloroform and filtered, and the filtrate obtained is added to methanol for recrystallization, filtered, and dried; wherein the mass ratio of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane, tetrafluoroterephthalonitrile, N,N-dimethylformamide, and potassium carbonate is (1.5-2):(0.8-1.2):(30-40):(1-1.5);

[0027] In the above process, the hydroxyl group of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane condenses with the four -Fs of tetrafluoroterephthalonitrile to form a PIM-1 polymer.

[0028] Preferably, in step (4), the preparation method of the gas separation membrane of the nano molecular sieve is as follows: the intercalated modified MOF nanosheets and tetrahydrofuran are mixed in a mass ratio of (0.01-0.03): (10-20), and ultrasonic treatment is performed for 40-80 minutes to obtain a nanosheet suspension; the PIM-1 polymer and tetrahydrofuran are mixed in a mass ratio of (0.3-0.5): (10-20), filtered, and then added to the nanosheet suspension, stirred for 10-16 hours, and ultrasonic treatment is performed for 40-80 minutes to obtain a casting liquid; the casting liquid is poured into a culture dish, evaporated at room temperature for 36-48 hours to form a film, and the film is soaked in methanol for 3-5 hours, and then vacuum dried at 100-120°C for 10-16 hours.

[0029] The gas separation membrane of the nanomolecular sieve is prepared by the method for preparing the gas separation membrane of the nanomolecular sieve.

[0030] The gas separation membrane of the nano molecular sieve is used for carbon dioxide capture.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention uses a multifunctional porphyrin compound as a carboxyl ligand, which is coordinated with zinc nitrate hexahydrate to form a MOF nanosheet containing phenolic hydroxyl groups, amino functional groups and a small mesoporous structure. The two-dimensional nanosheet with a high aspect ratio can have a larger contact area with the PIM-1 polymer matrix, thereby improving its compatibility in the PIM-1 polymer matrix; the inner pores of the MOF nanosheet and the nanochannels between the sheets can exhibit the selectivity and permeability of a molecular sieve, and can be used for the capture and separation of carbon dioxide; further, the phenolic hydroxyl groups and amino functional groups on the MOF nanosheet can form hydrogen bonds with the cyano groups in the PIM-1 polymer, further enhancing the interfacial interaction and improving the dispersibility of the MOF nanosheet. The introduction of the amino group can also provide an alkaline carrier to promote the selective adsorption of carbon dioxide.

[0033] 2. The present invention prepares microporous nano-cerium oxide by microwave-assisted solvothermal method, and then modifies the microporous nano-cerium oxide to obtain amino-modified microporous nano-cerium oxide. The amino-modified microporous nano-cerium oxide is grafted onto the surface of carboxylated carbon nanotubes through amidation reaction to obtain modified carbon nanotubes. The modified carbon nanotubes are then inserted into the sheet structure of MOF nanosheets. The modified carbon nanotubes play a supporting role on the one hand, and the interlayer spacing of MOF nanosheets is further increased compared with the carboxylated carbon nanotubes, and nano-microchannels are formed between the MOF nanosheets to improve the permeability and selectivity of carbon dioxide. On the other hand, the modified carbon nanotubes play a supporting role. Compared with the carboxylated carbon nanotubes, the interlayer spacing of MOF nanosheets is further increased, and nano-microchannels are formed between the MOF nanosheets to improve the permeability and selectivity of carbon dioxide. The nano-cerium oxide on the nanotubes has a strong affinity for carbon dioxide gas. The amination of microporous nano-cerium oxide introduces multiple amino groups on the surface of the microporous nano-cerium oxide, while further reducing the pore size of the microporous nano-cerium oxide, making the amination of microporous nano-cerium oxide more selective for carbon dioxide, thereby giving the membrane excellent gas separation performance. In addition, the amino groups on the surface of the microporous nano-cerium oxide can modify the carbon nanotubes and MOF nanosheets to combine through hydrogen bonds and electrostatic effects, so that the modified carbon nanotubes can be better inserted into the MOF nanosheet layer, thereby making the gas separation membrane have better permeability and selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a process flow chart of the preparation method of the gas separation membrane of the nano molecular sieve of the present invention;

[0035] Figure 2 It is a schematic diagram of the synthesis of the multifunctional porphyrin compound of the present invention;

[0036] Figure 3 It is a schematic diagram of the synthesis of the PIM-1 polymer of the present invention;

[0037] Figure 4 It is a comparison chart of CO2 permeability test of the gas separation membrane of the nano molecular sieve of Example 2-4 of the present invention and Comparative Example 2-5;

[0038] Figure 5 It is a comparison chart of CO2 / N2 selectivity test of the nano molecular sieve gas separation membrane of Example 2-4 of the present invention and Comparative Example 2-5. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] Example 1: This example discloses a method for preparing a MOF nanosheet, comprising the following steps:

[0041] Step S1, adding 9 g of 3,5-diaminosalicylic acid to 150 g of ethanol, ultrasonically treating for 20 min, then adding 11 g of 5,10,15,20-tetrakis(4-formylphenyl)porphyrin, heating to 60° C., stirring for reaction for 3 h, filtering, washing, and drying to obtain a multifunctional porphyrin compound;

[0042] Step S2, mixing ethanol and N,N-dimethylformamide in a volume ratio of 3:1 to obtain a mixed solution, adding zinc nitrate hexahydrate and a multifunctional porphyrin compound, stirring and mixing at 50°C for 60 minutes, first heating in a vacuum environment at 80°C for 24 hours, then keeping at room temperature for 4.5 hours, centrifuging, washing, and drying to obtain MOF nanosheets; wherein the mass ratio of zinc nitrate hexahydrate, the multifunctional porphyrin compound, and the mixed solution is 5.4:2.7:50.

[0043] Example 2: This example discloses a method for preparing a gas separation membrane of a nano molecular sieve, comprising the following steps:

[0044] Step (1), dissolving 0.4 g of cerium (III) nitrate hexahydrate in 20 g of diethylene glycol, adding 0.7 g of hexamethylenetetramine under stirring at 500 r / min to obtain a suspension, reacting the suspension in a microwave accelerated reaction system at a pressure of 8 bar for 80 min, precipitating with acetone, and then centrifuging, washing, and drying to obtain microporous nano-cerium oxide;

[0045] 0.5 g of microporous nano-cerium oxide was ultrasonically dispersed in a mixture of 12 g of ethanol and 2 g of deionized water, 1.5 g of diethylenetriaminopropyltrimethoxysilane was added, and the mixture was kept at 55° C. for 8 h, filtered, washed, and dried to obtain amino-modified microporous nano-cerium oxide;

[0046] Step (2), mixing 98% by volume sulfuric acid and 70% by volume nitric acid in a volume ratio of 3:1 to obtain an acidic mixture; adding 1 g of single-walled carbon nanotubes to 100 mL of the acidic mixture, reflux at 70° C. for 5 h, cooling, filtering, washing the filtered product with distilled water until the washing liquid is neutral, and drying to obtain carboxylated carbon nanotubes;

[0047] 3 g of carboxylated carbon nanotubes were dispersed in 150 g of N,N-dimethylformamide, 3.7 g of 1,3-dicyclohexylcarbodiimide and 2.1 g of N-hydroxysuccinimide were added, and the mixture was stirred for 2.5 h. Then, 3 g of amino-modified microporous nano-cerium oxide was added, and the pH of the reaction system was adjusted to 5.3 with a 1 mol / L aqueous hydrochloric acid solution. The mixture was reacted for 20 h in a nitrogen atmosphere at room temperature, and the solid product was filtered and washed with methanol and then dried to obtain modified carbon nanotubes.

[0048] Step (3), dispersing the modified carbon nanotubes in deionized water to obtain a dispersion A with a concentration of 0.3 mg / mL; dispersing the MOF nanosheets in deionized water to obtain a dispersion B with a concentration of 0.3 mg / mL; mixing the dispersion A and the dispersion B in a volume ratio of 1:2, ultrasonically treating for 3 hours, centrifuging, washing, and drying to obtain intercalated modified MOF nanosheets;

[0049] Step (4), 1.5 g of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and 0.8 g of tetrafluoroterephthalonitrile are mixed, 30 g of N,N-dimethylformamide is added in an argon atmosphere, and the mixture is stirred at 60° C. until the mixture becomes clear, and then 1 g of potassium carbonate powder is added. The temperature is kept constant and the reaction is continued with stirring for 65 hours. The solid obtained by the reaction is washed with methanol and deionized water, dried, and then dissolved in chloroform and filtered. The filtrate obtained is added to methanol for recrystallization, filtered, and dried to obtain a PIM-1 polymer;

[0050] 0.01 g of intercalated modified MOF nanosheets were dispersed in 10 g of tetrahydrofuran, and ultrasonically treated for 40 min to obtain a nanosheet suspension; 0.3 g of PIM-1 polymer was dissolved in 10 g of tetrahydrofuran, filtered, and then added to the nanosheet suspension, stirred for 10 h, and ultrasonically treated for 40 min to obtain a casting liquid; the casting liquid was poured into a culture dish, evaporated at room temperature for 36 h to form a film, the membrane was soaked in methanol for 3 h, and then vacuum dried at 100 ° C for 16 h to obtain a gas separation membrane of a nano molecular sieve.

[0051] Example 3: This example discloses a method for preparing a gas separation membrane of a nano molecular sieve, comprising the following steps:

[0052] Step (1), dissolving 0.8 g of cerium (III) nitrate hexahydrate in 50 g of ethanol, adding 1.4 g of hexamethylenetetramine under stirring at 700 r / min to obtain a suspension, reacting the suspension in a microwave accelerated reaction system at a pressure of 12 bar for 40 min, precipitating with acetone, and then centrifuging, washing, and drying to obtain microporous nano-cerium oxide;

[0053] 1 g of microporous nano-cerium oxide was ultrasonically dispersed in a mixture of 24 g of ethanol and 4 g of deionized water, 3 g of diethylenetriaminopropyltrimethoxysilane was added, and the mixture was kept at 60° C. for 8 h, filtered, washed, and dried to obtain amino-modified microporous nano-cerium oxide;

[0054] Step (2), mixing 98% by volume sulfuric acid and 70% by volume nitric acid in a volume ratio of 3:1 to obtain an acidic mixture; adding 3 g of single-walled carbon nanotubes to 200 mL of the acidic mixture, reflux at 90° C. for 3 h, cooling, filtering, washing the filtered product with distilled water until the washing liquid is neutral, and drying to obtain carboxylated carbon nanotubes;

[0055] 6 g of carboxylated carbon nanotubes were dispersed in 250 g of N,N-dimethylformamide, 7.4 g of 1,3-dicyclohexylcarbodiimide and 4.2 g of N-hydroxysuccinimide were added, and the mixture was stirred for 3.5 h. Then, 6 g of amino-modified microporous nano-cerium oxide was added, and the pH of the reaction system was adjusted to 5.7 with a 1 mol / L aqueous hydrochloric acid solution. The mixture was reacted for 30 h in a nitrogen atmosphere at room temperature, and the solid product was filtered and washed with methanol and then dried to obtain modified carbon nanotubes.

[0056] Step (3), dispersing the modified carbon nanotubes in deionized water to obtain a dispersion A with a concentration of 0.7 mg / mL; dispersing the MOF nanosheets in deionized water to obtain a dispersion B with a concentration of 0.7 mg / mL; mixing the dispersion A and the dispersion B in a volume ratio of 1:4, ultrasonically treating for 5 hours, centrifuging, washing, and drying to obtain intercalated modified MOF nanosheets;

[0057] Step (4), 2 g of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and 1.2 g of tetrafluoroterephthalonitrile are mixed, 40 g of N,N-dimethylformamide is added in an argon atmosphere, and the mixture is stirred at 70° C. until the mixture becomes clear, and then 1.5 g of potassium carbonate powder is added. The temperature is kept constant and the reaction is continued with stirring for 75 hours. The solid obtained by the reaction is washed with methanol and deionized water, dried, and then dissolved in chloroform and filtered. The filtrate obtained is added to methanol for recrystallization, filtered, and dried to obtain a PIM-1 polymer;

[0058] 0.03 g of intercalated modified MOF nanosheets were dispersed in 20 g of tetrahydrofuran, and ultrasonically treated for 80 min to obtain a nanosheet suspension; 0.5 g of PIM-1 polymer was dissolved in 20 g of tetrahydrofuran, filtered, and then added to the nanosheet suspension, stirred for 10-16 h, and ultrasonically treated for 80 min to obtain a casting liquid; the casting liquid was poured into a culture dish, evaporated at room temperature for 48 h to form a film, the film was immersed in methanol for 5 h, and then vacuum dried at 120 ° C for 10 h to obtain a gas separation membrane of a nano molecular sieve.

[0059] Example 4: This example discloses a method for preparing a gas separation membrane of a nano molecular sieve, comprising the following steps:

[0060] Step (1), dissolving 0.6 g of cerium (III) nitrate hexahydrate in 35 g of ethanol, adding 1.1 g of hexamethylenetetramine under stirring at 600 r / min to obtain a suspension, reacting the suspension in a microwave accelerated reaction system at a pressure of 10 bar for 60 min, precipitating with acetone, and then centrifuging, washing, and drying to obtain microporous nano-cerium oxide;

[0061] 0.8 g of microporous nano-cerium oxide was ultrasonically dispersed in a mixture of 18 g of ethanol and 3 g of deionized water, 2.2 g of diethylenetriaminopropyltrimethoxysilane was added, and the mixture was kept at 58° C. for 9 h, filtered, washed, and dried to obtain amino-modified microporous nano-cerium oxide;

[0062] Step (2), mixing 98% by volume sulfuric acid and 70% by volume nitric acid in a volume ratio of 3:1 to obtain an acidic mixture; adding 2 g of single-walled carbon nanotubes to 150 mL of the acidic mixture, reflux at 80° C. for 4 h, cooling, filtering, washing the filtered product with distilled water until the washing liquid is neutral, and drying to obtain carboxylated carbon nanotubes;

[0063] 4.5 g of carboxylated carbon nanotubes were dispersed in 200 g of N,N-dimethylformamide, 5.6 g of 1,3-dicyclohexylcarbodiimide and 3.2 g of N-hydroxysuccinimide were added, and the mixture was stirred for 3 h. Then, 4.5 g of amino-modified microporous nano-cerium oxide was added, and the pH of the reaction system was adjusted to 5.5 with a 1 mol / L aqueous hydrochloric acid solution. The mixture was reacted for 25 h in a nitrogen atmosphere at room temperature, and the solid product was filtered and washed with methanol and then dried to obtain modified carbon nanotubes.

[0064] Step (3), dispersing the modified carbon nanotubes in deionized water to obtain a dispersion A with a concentration of 0.5 mg / mL; dispersing the MOF nanosheets in deionized water to obtain a dispersion B with a concentration of 0.5 mg / mL; mixing the dispersion A and the dispersion B in a volume ratio of 1:3, ultrasonically treating for 4 hours, centrifuging, washing, and drying to obtain intercalated modified MOF nanosheets;

[0065] Step (4), 1.8 g of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and 1 g of tetrafluoroterephthalonitrile (TFTPN) were mixed, 35 g of N,N-dimethylformamide was added in an argon atmosphere, and the mixture was stirred at 65° C. until the mixture became clear, and then 1.2 g of potassium carbonate powder was added. The temperature was kept constant and the reaction was continued with stirring for 70 h. The solid obtained by the reaction was washed with methanol and deionized water, dried, and then dissolved in chloroform and filtered. The filtrate obtained was added to methanol for recrystallization, filtered, and dried to obtain a PIM-1 polymer;

[0066] 0.02 g of intercalated modified MOF nanosheets were dispersed in 15 g of tetrahydrofuran, and ultrasonically treated for 60 min to obtain a nanosheet suspension; 0.4 g of PIM-1 polymer was dissolved in 15 g of tetrahydrofuran, filtered, and then added to the nanosheet suspension, stirred for 14 h, and ultrasonically treated for 60 min to obtain a casting liquid; the casting liquid was poured into a culture dish, evaporated at room temperature for 40 h to form a film, the membrane was soaked in methanol for 4 h, and then vacuum dried at 110°C for 13 h to obtain a gas separation membrane of a nanomolecular sieve.

[0067] The MOF nanosheets used in the above Examples 2-4 are the MOF nanosheets prepared in Example 1.

[0068] Comparative Example 1

[0069] Comparative Example 1 Compared with Example 1, in the process of preparing MOF nanosheets in Comparative Example 1, 5,10,15,20-tetrakis(4-formylphenyl)porphyrin is used instead of the multifunctional porphyrin compound, and other conditions remain unchanged.

[0070] Comparative Example 2

[0071] Comparative Example 2 Compared with Example 4, Comparative Example 2 uses the MOF nanosheets prepared in Comparative Example 1, and other conditions remain unchanged.

[0072] Comparative Example 3

[0073] Comparative Example 3 Compared with Example 4, in the process of preparing modified carbon nanotubes in Comparative Example 3, microporous nano-cerium oxide is used instead of amino-treated microporous nano-cerium oxide, and other conditions remain unchanged.

[0074] Comparative Example 4

[0075] Comparative Example 4 Compared with Example 4, in the process of preparing the intercalated modified MOF nanosheets, carboxylated carbon nanotubes were used instead of modified carbon nanotubes, and other conditions remained unchanged.

[0076] Comparative Example 5

[0077] Comparative Example 5 Compared with Example 4, in the process of preparing the gas separation membrane of nano molecular sieve, the MOF nanosheets are used instead of the intercalated modified MOF nanosheets, and other conditions remain unchanged.

[0078] In the above embodiments and comparative examples, the single-walled carbon nanotubes, with a diameter of 0.8-1.2 nanometers and a length of about 100-1000 nanometers, are from Shanghai Ziyi Reagent Factory. The product number is 101715 and the brand is Kramar.

[0079] Experimental example

[0080] The performance of the gas separation membranes of the nano molecular sieves in Examples 2-4 and Comparative Examples 2-5 was tested.

[0081] The mixed gas separation performance was tested by a constant pressure variable volume (CPVV) device. A CO2 / N2 (20 / 80 vol%) mixed gas was used to simulate the composition of flue gas or natural gas. A pure N2 flow was used as an upstream sweep gas (20 SCCM) to eliminate the concentration polarization effect, and the feed pressure for all tests was maintained at 2 bar. The downstream permeate composition was analyzed by a gas chromatograph (Shimadzu GC-2030). In order to accurately evaluate the separation performance, each test took at least 1 hour to reach a steady state, and all membrane tests were repeated three times.

[0082] The permeability is calculated by the following formula:

[0083] Among them, P i is the gas permeability (1Barrer=10 -10 cm 3 (STP)cm / cm -2 s -1 cmHg), Q i is the volume flow rate (cm 3 s -1 , STP), L is the membrane thickness (cm), A is the membrane effective area (cm 2 ), Δp i is the pressure difference between upstream and downstream of the membrane (cmHg).

[0084] The formula for calculating the selectivity of mixed gas is:

[0085] where x i / x j and i / y j are the volume fractions of feed gas and permeate gas, respectively. For the permeation tests at different pressures, all other conditions were kept constant except the upstream pressure (ranging from 2 to 50 bar).

[0086] The test results are shown in Table 1:

[0087] Table 1

[0088] <![CDATA[CO2 permeability / barrer]]> <![CDATA[CO2 / N2 selectivity]]> Example 2 18938.25 38.51 Example 3 19386.14 40.22 Example 4 19215.66 39.49 Comparative Example 2 18749.33 36.32 Comparative Example 3 18772.45 36.67 Comparative Example 4 17359.97 33.94 Comparative Example 5 15106.74 30.15

[0089] From the test results in Table 1, it can be seen that the gas separation membrane of the nanomolecular sieve prepared in Examples 2-4 of the present invention has good permeability and selectivity to carbon dioxide. From the comparison between Comparative Example 2 and Example 4, it can be seen that the multifunctional porphyrin compound obtained by modifying 5,10,15,20-tetrakis(4-formylphenyl)porphyrin is used as a carboxyl ligand to form a MOF nanosheet containing phenolic hydroxyl groups, amino functional groups and a small mesoporous structure. The phenolic hydroxyl groups and amino functional groups on the nanosheet can form hydrogen bonds with the cyano groups in the PIM-1 polymer, further enhancing the interfacial interaction and improving the dispersibility of the MOF nanosheet. The introduction of the amino group can also provide an alkaline carrier, thereby improving the permeability and selectivity of the gas separation membrane; from the comparison between Comparative Examples 3-4 and Example 4, it can be seen that the microporous nano-cerium oxide has a strong affinity for carbon dioxide gas. The microporous structure also has good selectivity for carbon dioxide. Furthermore, the microporous nano-cerium oxide is aminated to make it more selective for carbon dioxide, thereby giving the membrane excellent gas separation performance, and enabling the modified carbon nanotubes to be better inserted into the MOF nanosheet layer, so that the gas separation membrane has better permeability and selectivity; from the comparison between Comparative Example 5 and Example 4, it can be seen that the modified carbon nanotubes are inserted into the sheet structure of the MOF nanosheet, so that the interlayer spacing of the MOF nanosheet is further increased, the permeability of carbon dioxide is improved, and the grafting of the aminated microporous nano-cerium oxide on the modified carbon nanotubes greatly improves the permeability and selectivity of the gas separation membrane.

[0090] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a gas separation membrane of a nano molecular sieve, characterized in that: The following steps are involved: Step (1), preparing microporous nano-cerium oxide by microwave-assisted solvothermal method; Modifying microporous nano-cerium oxide to obtain amino-modified microporous nano-cerium oxide; Step (2), treating the single-walled carbon nanotubes to obtain carboxylated carbon nanotubes; reacting the aminated microporous nano-cerium oxide with the carboxylated carbon nanotubes to obtain modified carbon nanotubes; Step (3), inserting the modified carbon nanotubes into the MOF nanosheets to obtain intercalated modified MOF nanosheets; The method for preparing the MOF nanosheets comprises the following steps: Step S1, reacting 3,5-diaminosalicylic acid with 5,10,15,20-tetrakis(4-formylphenyl)porphyrin to obtain a multifunctional porphyrin compound; Step S2, using zinc nitrate hexahydrate and a multifunctional porphyrin compound as raw materials to prepare MOF nanosheets; Step (4), using 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and tetrafluoroterephthalonitrile as raw materials to prepare PIM-1 polymer; Intercalated modified MOF nanosheets were used as fillers and mixed with PIM-1 polymer to prepare nano-molecular sieve gas separation membranes.

2. The method for preparing a gas separation membrane of a nano molecular sieve according to claim 1, characterized in that: In the step (1), the preparation method of the microporous nano-cerium oxide is as follows: cerium (III) nitrate hexahydrate is dissolved in diethylene glycol, and hexamethylenetetramine is added under stirring conditions of 500-700 r / min to obtain a suspension, and the suspension is reacted in a microwave accelerated reaction system at a pressure of 8-12 bar for 40-80 minutes, and then precipitated with acetone, and then centrifuged, washed, and dried; wherein the mass ratio of cerium (III) nitrate hexahydrate, ethanol, and hexamethylenetetramine is (0.4-0.8):(20-50):(0.7-1.4).

3. The method for preparing a gas separation membrane of a nano molecular sieve according to claim 1, characterized in that: In the step (1), the preparation method of the amino-modified microporous nano-cerium oxide is as follows: microporous nano-cerium oxide is ultrasonically dispersed in a mixture of ethanol and deionized water, diethylenetriaminopropyltrimethoxysilane is added, and the mixture is kept warm at 55-60°C for 8-10 hours, filtered, washed, and dried; wherein the mass ratio of microporous nano-cerium oxide, ethanol, deionized water, and diethylenetriaminopropyltrimethoxysilane is (0.5-1):(12-24):(2-4):(1.5-3).

4. The method for preparing a gas separation membrane of a nano molecular sieve according to claim 1, characterized in that: In the step (2), the preparation method of the modified carbon nanotubes is: Mixing 98% sulfuric acid and 70% nitric acid in a volume ratio of 3:1 to obtain an acidic mixture; adding single-walled carbon nanotubes to the acidic mixture, reflux at 70-90° C. for 3-5 hours, cooling, filtering, washing the filtered product with distilled water until the washing liquid is neutral, and drying to obtain carboxylated carbon nanotubes; wherein the amount ratio of the single-walled carbon nanotubes to the acidic mixture is (1-3) g: (100-200) mL; Disperse carboxylated carbon nanotubes in N,N-dimethylformamide, add 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide, stir for 2.5-3.5h, then add aminated microporous nano-cerium oxide, adjust the pH of the reaction system to 5.3-5.7 with a 1 mol / L aqueous hydrochloric acid solution, react in a nitrogen atmosphere at room temperature for 20-30h, filter, wash the obtained solid product with methanol and then dry to obtain modified carbon nanotubes; wherein the mass ratio of carboxylated carbon nanotubes, N,N-dimethylformamide, 1,3-dicyclohexylcarbodiimide, N-hydroxysuccinimide and aminated microporous nano-cerium oxide is (3-6):(150-250):(3.7-7.4):(2.1-4.2):(3-6).

5. The method for preparing a gas separation membrane of a nano molecular sieve according to claim 1, characterized in that: In the step (3), the preparation method of the intercalated modified MOF nanosheets is as follows: the modified carbon nanotubes are dispersed in deionized water to obtain a dispersion A with a concentration of 0.3-0.7 mg / mL; the MOF nanosheets are dispersed in deionized water to obtain a dispersion B with a concentration of 0.3-0.7 mg / mL; the dispersion A and the dispersion B are mixed in a volume ratio of 1:(2-4), ultrasonically treated for 3-5 hours, centrifuged, washed, and dried.

6. The method for preparing a gas separation membrane of a nano molecular sieve according to claim 1, characterized in that: In the step (3), the preparation method of the MOF nanosheet is: Step S1, adding 3,5-diaminosalicylic acid to ethanol, ultrasonically treating for 10-30 minutes, then adding 5,10,15,20-tetrakis(4-formylphenyl)porphyrin, heating to 55-62° C., stirring for reaction for 2.5-3.5 hours, filtering, washing, and drying to obtain a multifunctional porphyrin compound; wherein the mass ratio of 3,5-diaminosalicylic acid, ethanol, and 5,10,15,20-tetrakis(4-formylphenyl)porphyrin is (6-12):(100-200):(7.3-14.6); Step S2, ethanol and N,N-dimethylformamide are mixed in a volume ratio of 3:1 to obtain a mixed solution, zinc nitrate hexahydrate and a multifunctional porphyrin compound are added, and the mixture is stirred and mixed at 45-55°C for 40-80 minutes, and then heated in a vacuum environment at 75-85°C for 20-28 hours, and then kept at room temperature for 4-5 hours, centrifuged, washed, and dried to obtain MOF nanosheets; wherein the mass ratio of zinc nitrate hexahydrate, the multifunctional porphyrin compound, and the mixed solution is (3.6-7.2):(1.8-3.6):(40-60).

7. The method for preparing a gas separation membrane of a nano molecular sieve according to claim 1, characterized in that: In the step (4), the preparation method of the PIM-1 polymer is as follows: 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and tetrafluoroterephthalonitrile are mixed, N,N-dimethylformamide is added in an argon atmosphere, and the mixture is stirred at 60-70°C until the mixed system becomes clear, potassium carbonate powder is added, the temperature is kept constant, and the stirring reaction is continued for 65-75 hours. The solid obtained by the reaction is washed with methanol and deionized water, dried, dissolved in chloroform, filtered, and the filtrate is added to methanol for recrystallization, filtered, and dried; wherein the mass ratio of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane, tetrafluoroterephthalonitrile, N,N-dimethylformamide, and potassium carbonate is (1.5-2):(0.8-1.2):(30-40):(1-1.5).

8. The method for preparing a gas separation membrane of a nano molecular sieve according to claim 1, characterized in that: In the step (4), the preparation method of the gas separation membrane of the nano molecular sieve is as follows: intercalated modified MOF nanosheets and tetrahydrofuran are mixed in a mass ratio of (0.01-0.03): (10-20), and ultrasonic treatment is performed for 40-80 minutes to obtain a nanosheet suspension; PIM-1 polymer is mixed with tetrahydrofuran in a mass ratio of (0.3-0.5): (10-20), filtered, and then added to the nanosheet suspension, stirred for 10-16 hours, and ultrasonic treatment is performed for 40-80 minutes to obtain a casting liquid; the casting liquid is poured into a culture dish, evaporated at room temperature for 36-48 hours to form a film, and the film is immersed in methanol for 3-5 hours, and then vacuum dried at 100-120°C for 10-16 hours.

9. A nanomolecular sieve gas separation membrane prepared by the method for preparing a nanomolecular sieve gas separation membrane according to any one of claims 1 to 8.

10. Use of the gas separation membrane of the nano molecular sieve according to claim 9 in carbon dioxide capture.

Images