A mixed matrix membrane based on symbiotic method, a preparation method thereof and a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system

Abstract

The application provides a mixed matrix membrane based on a symbiotic method and a preparation method thereof and a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system, and belongs to the technical field of gas separation. The application adopts the symbiotic method to prepare a mixed matrix membrane for O2 / N2 separation and CO2 / N2 separation by taking polydimethylsiloxane as a substrate and ZIF-8 as a nano-porous filler. The mixed matrix membrane has excellent O2 / N2 and CO2 / N2 separation effects by combining the selective solution diffusion effect of polydimethylsiloxane and the pore size screening effect of ZIF-8, and when the mixed matrix membrane is applied to a boiler oxygen-enriched combustion system, the energy consumption of an air separation process is greatly reduced, high-purity N2 is prepared, the CO2 concentration in a carbon capture process is greatly improved, and the mixed matrix membrane has great practical significance for realizing the double carbon target.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas separation, in particular to a mixed matrix membrane based on symbiotic method and preparation method thereof and boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system. BACKGROUND

[0002] Global climate change caused by excessive emission of greenhouse gases has brought disastrous consequences to the world. In order to transform economic development to green and low carbon, it is imperative to vigorously develop carbon capture, utilization and storage technology. Coal-fired boilers in power plants are the main places of CO2 emission, so it is of great significance to develop carbon capture technology in coal-fired power plants. Oxygen-enriched combustion refers to the process of producing high-concentration O2 by air separation and burning coal powder with CO2 in the boiler. The core of this technology is the process of preparing high-concentration oxygen.

[0003] Membrane separation is a new generation of efficient gas separation method, which is praised as one of the most potential high-end separation technologies due to its small occupied area, high separation efficiency, simple operation and environmental friendliness. Membrane materials can be divided into inorganic membranes, organic membranes and organic-inorganic composite membranes. Organic membranes have a place in the field of gas separation due to their low cost and easy preparation, but are restricted by the "trade-off" effect, so the separation effect of such membranes cannot meet the industrial requirements. The gas separation performance of inorganic membranes is better than that of polymer membranes, but they are limited in industrial practical application due to their brittleness, high manufacturing cost and other shortcomings. Mixed matrix membranes combine the advantages of traditional organic membranes and inorganic membranes, not only have excellent gas separation performance, but also have the advantages of easy processing and low cost, and can realize the scale-up of membranes, so they have great industrial application potential.

[0004] The mixed matrix membrane is used in the boiler oxygen-enriched combustion system, and its selective permeation to O2 / N2 and CO2 / N2 not only greatly reduces the energy consumption of air separation process and prepares high-purity nitrogen, but also realizes efficient capture of CO2.

[0005] Therefore, how to obtain a mixed matrix membrane with high separation efficiency of O2 / N2 or CO2 / N2 and use it in the boiler oxygen-enriched combustion system is a technical problem to be solved at present. SUMMARY

[0006] The present application aims to provide a mixed matrix membrane based on symbiotic method and preparation method thereof and boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system, so as to solve the technical problem of low separation efficiency of the existing mixed matrix membrane.

[0007] In order to achieve the above-mentioned application purpose, the present application provides the following technical scheme:

[0008] The present application provides a preparation method of a mixed matrix membrane based on symbiotic method, comprising the following steps:

[0009] 1) mixing the polydimethylsiloxane n-hexane solution and the zinc nitrate aqueous solution to obtain a mixed solution 1;

[0010] 2) mixing the mixed solution 1 and the 2-methylimidazole aqueous solution to obtain a mixed solution 2;

[0011] 3) mixing and reacting the mixed solution 2 and the tetraethyl orthosilicate to obtain a film solution, and then performing ultrasonic and drying in sequence to obtain the mixed matrix membrane.

[0012] Further, in the polydimethylsiloxane n-hexane solution, the mass fraction of polydimethylsiloxane is 5-15%; in the zinc nitrate aqueous solution, the molar volume ratio of zinc nitrate to water is 1-1.5 mmol:3 mL.

[0013] Further, in the step 1), the mass ratio of the polydimethylsiloxane n-hexane solution to the zinc nitrate aqueous solution is 20-25:0.2-0.5;

[0014] The mixing speed is 500-700 rpm, the mixing time is 1-2 h, and the mixing temperature is 20-30°C.

[0015] Further, in the step 2), in the 2-methylimidazole aqueous solution, the molar volume ratio of 2-methylimidazole to water is 0.06-0.09 mol:10 mL;

[0016] The mixing speed is 500-700 rpm, the mixing time is 3-5 h, and the mixing temperature is 20-30°C.

[0017] Further, the mass ratio of the polydimethylsiloxane n-hexane solution to the 2-methylimidazole aqueous solution is 20-25:4-10;

[0018] The addition amount of the tetraethyl orthosilicate is 5-15% of the polydimethylsiloxane.

[0019] Further, in the step 3), the mixing speed is 700-1200 rpm, the mixing time is 2-4 h, and the mixing temperature is 30-40°C.

[0020] Further, in the step 3), the ultrasonic frequency is 30-50 kHz, and the ultrasonic time is 1-3 h; the drying is in sequence of normal temperature drying, air blowing drying and vacuum drying, the normal temperature drying time is 10-14 h; the air blowing drying temperature is 80-90°C, and the time is 10-14 h; the vacuum drying temperature is 110-135°C, the time is 18-24 h, and the vacuum degree is 0.09-0.095 MPa.

[0021] The application provides a mixed matrix membrane obtained by the preparation method, and the mixed matrix membrane comprises polydimethylsiloxane and ZIF-8 material, the polydimethylsiloxane is a substrate, and the ZIF-8 material is a nanoporous filler.

[0022] The application provides a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system.

[0023] The air separation membrane system 1 and the CO2 / N2 separation membrane system 6 both comprise a mixed matrix membrane.

[0024] Further, the air separation membrane system 1 adopts a three-stage mixed matrix membrane series connection structure.

[0025] The application has the following beneficial effects:

[0026] The application improves the traditional synthesis steps, improves the MOF dispersity and interface compatibility, and improves the O2 / N2 and CO2 / N2 gas separation performance compared with the traditional separation membrane. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The application provides a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system.

[0028] Figure 2 The application provides a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system.

[0029] Figure 3 Preparation flow chart of the mixed matrix membrane by the symbiotic method of the present application;

[0030] Figure 4 Preparation flow chart of the mixed matrix membrane by the traditional method of the present application;

[0031] Figure 5 Comparison chart of O2 / N2 separation effect of Example 1 and the comparative example of the present application;

[0032] Figure 6 Comparison chart of CO2 / N2 separation effect of Example 2 and the comparative example of the present application;

[0033] Figure 7 Schematic diagram of the experimental device for testing the O2 / N2 and CO2 / N2 separation performance of the mixed matrix membrane of the present application. DETAILED DESCRIPTION

[0034] The present application provides a preparation method of a mixed matrix membrane based on a symbiotic method, comprising the following steps:

[0035] 1) mixing a n-hexane solution of polydimethylsiloxane and a zinc nitrate aqueous solution to obtain a mixed solution 1;

[0036] 2) mixing the mixed solution 1 and a 2-methylimidazole aqueous solution to obtain a mixed solution 2;

[0037] 3) mixing the mixed solution 2 and tetraethyl orthosilicate and then reacting to obtain a membrane solution, and then sequentially performing ultrasonic treatment and drying to obtain the mixed matrix membrane.

[0038] In the present application, the mass fraction of polydimethylsiloxane in the n-hexane solution of polydimethylsiloxane is 5-15%, preferably 8-12%, and further preferably 10%; the molar volume ratio of zinc nitrate to water in the zinc nitrate aqueous solution is 1-1.5 mmol: 3 mL, preferably 1.1-1.4 mmol: 3 mL, and further preferably 1.2-1.3 mmol: 3 mL.

[0039] In the present application, in step 1), the mass ratio of the n-hexane solution of polydimethylsiloxane to the zinc nitrate aqueous solution is 20-25: 0.2-0.5, preferably 22-24: 0.3-0.4, and further preferably 23: 0.3.

[0040] In the present application, in step 1), the rotation speed of the mixing is 500-700 rpm, preferably 600 rpm; the mixing time is 1-2 h, preferably 1.5 h; and the mixing temperature is 20-30℃, preferably 25℃.

[0041] In the present application, in step 2), the molar volume ratio of 2-methylimidazole to water in the 2-methylimidazole aqueous solution is 0.06-0.09 mol: 10 mL, preferably 0.07-0.08 mol: 10 mL, and further preferably 0.075 mol: 10 mL.

[0042] In the present application, in step 2), the rotation speed of mixing is 500-700 rpm, preferably 600 rpm; the mixing time is 3-5 h, preferably 4 h; and the mixing temperature is 20-30℃, preferably 25℃.

[0043] In the present application, the mass ratio of the n-hexane solution of polydimethylsiloxane to the 2-methylimidazole aqueous solution is 20-25: 4-10, preferably 22-24: 5-8, and further preferably 23: 6-7.

[0044] In the present application, the addition amount of the tetraethyl orthosilicate is 5-15% of the polydimethylsiloxane, preferably 6-12%, and further preferably 8-10%.

[0045] In the present application, in step 3), the rotation speed of mixing is 700-1200 rpm, preferably 800-1000 rpm, and further preferably 900 rpm; the mixing time is 2-4 h, preferably 3 h; and the mixing temperature is 30-40℃, preferably 32-38℃, and further preferably 35℃.

[0046] In the present application, in step 3), the ultrasonic frequency is 30-50 kHz, preferably 35-45 kHz, and further preferably 40 kHz; and the ultrasonic time is 1-3 h, preferably 2 h.

[0047] In the present application, the drying sequence is normal temperature drying, air blowing drying, and vacuum drying; the normal temperature drying time is 10-14 h, preferably 11-13 h, and further preferably 12 h; the air blowing drying temperature is 80-90℃, preferably 85℃; and the time is 10-14 h, preferably 11-13 h, and further preferably 12 h.

[0048] In the present application, the vacuum drying temperature is 110-135℃, preferably 115-130℃, and preferably 120-125℃; the time is 18-24 h, preferably 20-22 h, and further preferably 21 h; and the vacuum degree is 0.09-0.095 MPa, preferably 0.093 MPa.

[0049] The present application provides a mixed matrix membrane obtained by the above preparation method, comprising polydimethylsiloxane and ZIF-8 material, wherein the polydimethylsiloxane is a substrate, and the ZIF-8 material is a nanoporous filler.

[0050] The application provides a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system, wherein the boiler oxygen-enriched combustion system comprises an air separation membrane system 1, an oxygen-enriched boiler 2, a gas heat exchanger 3, a dust remover 4, a desulfurization tower 5, a CO2 / N2 separation membrane system 6, a flue gas condenser 7, a compressor 8, a CO2 purification treatment system 9, a coal mill 10, a primary flue gas recirculation pipeline 11 and a secondary flue gas recirculation pipeline 12.

[0051] The air separation membrane system 1 and the CO2 / N2 separation membrane system 6 both comprise a mixed matrix membrane.

[0052] In the application, the air separation membrane system 1 adopts a three-stage mixed matrix membrane series structure.

[0053] In the application, air enters the compressor 8 from 1-1, and then enters the air separation membrane system 1 composed of a three-stage mixed matrix membrane series structure. Since the mixed matrix membrane prepared based on the symbiotic method has excellent O2 / N2 separation performance, high-purity O2 enters the oxygen-enriched boiler 2 from 1-3 in turn through the three-stage mixed matrix membrane, and the remaining high-purity N2 is discharged from the outlet 1-2 and stored for use. The raw coal is transported into the oxygen-enriched boiler 2 after being ground by the coal mill 10, and the coal powder is combusted together with high-concentration O2 and CO2 obtained through the primary flue gas recirculation pipeline 11 and the secondary flue gas recirculation pipeline 12. The flue gas product with high-concentration CO2 discharged from the tail of the boiler is purified through the gas heat exchanger 3, the dust remover 4 and the desulfurization tower 5, and then enters the CO2 / N2 separation membrane system 6 from 6-1. Since the mixed matrix membrane prepared based on the symbiotic method has excellent CO2 / N2 separation performance, high-concentration CO2 enters the flue gas condenser 7 from 6-3 through the mixed matrix membrane, and the remaining high-purity N2 is discharged from the outlet 6-2 and stored for use. The high-concentration CO2 entering the flue gas condenser 7 is partially recirculated 11, and the remaining CO2 enters the compressor 8, and finally high-purity liquid CO2 is obtained in the CO2 treatment and purification system 9 for storage and use.

[0054] The technical solutions provided by the application will be described in detail below in combination with the embodiments, but they should not be understood as limitations to the protection scope of the application.

[0055] Example 1

[0056] 1) 2g of polydimethylsiloxane was dissolved in 20g of n-hexane, and the mixture was stirred at 25℃ at a stirring rate of 600rpm for 2h to obtain a polydimethylsiloxane n-hexane solution.

[0057] 2) Dissolve 0.298 g (0.001 mol) Zn(NO3)2·6H2O in 3 mL of deionized water, then pour it into the hexane solution of polydimethylsiloxane prepared in step 1). Stir thoroughly at 25 °C at a stirring rate of 600 rpm for 1.5 h. After complete dissolution, pour the homogeneous solution into 10 mL of deionized water containing 4.93 g (0.06 mol) 2-methylimidazole. Stir vigorously at 25 °C until completely dissolved for 4 h at a stirring rate of 1000 rpm.

[0058] 3) Add 0.2g of tetraethyl orthosilicate to the homogeneous solution and stir thoroughly at 35℃ for 3 hours at a stirring speed of 1000 rpm. Then, sonicate at 40Hz for 2 hours. Cast the sonicated membrane solution onto the membrane mold and dry at room temperature for 12 hours. After curing into a membrane, place it under a forced-air drying at 85℃ for 12 hours. Then, peel off the membrane and continue to dry it in a vacuum drying oven at 120℃ and a vacuum degree of 0.093MPa for 12 hours to obtain a mixed matrix membrane.

[0059] like Figure 5 As shown, the maximum O2 permeability is 736 Barrer, and the maximum O2 / N2 selectivity is 2.5. Compared to hybrid matrix membranes prepared by conventional methods, hybrid matrix membranes prepared by the symbiotic method exhibit superior O2 / N2 separation performance.

[0060] Example 2

[0061] 1) Dissolve 2g of polydimethylsiloxane in 20g of n-hexane, stir thoroughly at 25°C at a stirring speed of 600rpm for 2h, and obtain a n-hexane solution of polydimethylsiloxane after thorough dissolution.

[0062] 2) Dissolve 0.446 g (0.0015 mol) Zn(NO3)2·6H2O in 3 ml of deionized water, then pour it into the hexane solution of polydimethylsiloxane prepared in step 1). Stir thoroughly at 25°C at a stirring rate of 600 rpm for 1.5 h. After complete dissolution, pour the homogeneous solution into 10 ml of deionized water containing 7.39 g (0.09 mol) 2-methylimidazole. Stir vigorously at 25°C until completely dissolved for 4 h at a stirring rate of 1000 rpm.

[0063] 3) 0.2 g of tetraethyl orthosilicate was added to the homogeneous solution, and stirred at 35°C at a stirring rate of 1000 rpm for 3 h, then ultrasonically oscillated at a frequency of 40 Hz for 2 h, the membrane liquid after ultrasonic oscillation was cast on a membrane support, dried at room temperature for 12 h, and then placed in a vacuum drying oven at a temperature of 120°C and a vacuum value of 0.093 MPa for 12 h to obtain a mixed matrix membrane.

[0064] As shown in Figure 6 , the maximum permeability of CO2 was 1840 Barrer, and the maximum selectivity of CO2 / N2 was 5.2. Compared with the mixed matrix membrane prepared by the conventional method, the mixed matrix membrane prepared by the symbiotic method has excellent CO2 / N2 separation effect.

[0065] Example 3

[0066] The mixed matrix membrane prepared in Example 1 was used in a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system, specifically used in an air separation membrane system 1 and a CO2 / N2 separation membrane system 6 (as shown in Figure 2 , the operating steps of the boiler oxygen-enriched combustion system are as follows:

[0067] Air enters the compressor 8 from 1-1, and then enters the air separation membrane system 1 composed of a three-stage mixed matrix membrane in series. Since the mixed matrix membrane prepared based on the symbiotic method has excellent O2 / N2 separation performance, high-purity O2 penetrates the three-stage mixed matrix membrane from 1-3 into the oxygen-enriched boiler 2 in turn, and the remaining high-purity N2 is discharged from the outlet 1-2 and stored for use. The raw coal is transported to the oxygen-enriched boiler 2 after being ground by the coal mill 10, and the high-concentration O2 and the CO2 obtained through the primary flue gas recirculation pipeline 11 and the secondary flue gas recirculation pipeline 12 are used to burn the pulverized coal. The flue gas product with high concentration of CO2 discharged from the tail of the boiler is purified by the gas heat exchanger 3, the dust remover 4 and the desulfurization tower 5, and then enters the CO2 / N2 separation membrane system 6 from 6-1. Since the mixed matrix membrane prepared based on the symbiotic method has excellent CO2 / N2 separation performance, high-concentration CO2 penetrates the mixed matrix membrane from 6-3 into the flue gas condenser 7, and the remaining high-purity N2 is discharged from the outlet 6-2 and stored for use. The high-concentration CO2 entering the flue gas condenser 7 is partially recirculated 11, and the remaining CO2 enters the compressor 8, and finally high-purity liquid CO2 is obtained in the CO2 treatment and purification system 9 for storage and use.

[0068] Comparative Example

[0069] 1) Dissolve 2g of polydimethylsiloxane in 20g of n-hexane, stir thoroughly at 25°C at a stirring speed of 600rpm for 2h, and obtain a n-hexane solution of polydimethylsiloxane after thorough dissolution.

[0070] 2) Dissolve 0.298 g (0.001 mol) Zn(NO3)2·6H2O in 3 ml of deionized water and stir thoroughly at 25°C at a stirring speed of 600 rpm for 1.5 h; dissolve 4.93 g (0.06 mol) 2-methylimidazole in 10 ml of deionized water and stir thoroughly at 25°C at a stirring speed of 600 rpm for 1.5 h; then pour 3 ml of the Zn(NO3)2·6H2O deionized water solution into 10 ml of the 2-methylimidazole deionized water solution and stir vigorously at 25°C for 3 h at a stirring speed of 1000 rpm; collect the product by centrifugation for 15 min at a centrifugation speed of 4000 rpm and wash three times with methanol; place the product in a vacuum drying oven at 120°C and a vacuum value of 0.093 MPa and dry for 12 h to obtain ZIF-8 particles.

[0071] 3) Dissolve the prepared ZIF-8 particles in 10g of n-hexane and subject them to ultrasonic oscillation at a frequency of 40kHz for 1.5h to obtain a filling solution.

[0072] 4) Mix the filler solution with the hexane solution of polydimethylsiloxane, then add 0.2g of tetraethyl orthosilicate, stir thoroughly at 35℃ at a stirring speed of 1000rpm for 4h, then sonicate at 40kHz for 2h, cast the ultrasonically treated membrane solution onto a mold, dry at room temperature for 12h, and after curing into a film, place it under a forced-air drying at 85℃ for 12h. Then peel off the film and place it in a vacuum drying oven at 120℃ and a vacuum value of 0.093MPa for 12h to obtain a mixed matrix membrane.

[0073] like Figure 6 As shown, the maximum O2 permeability of the hybrid matrix membrane prepared by the conventional method is 167 Barrer, the maximum O2 / N2 selectivity is 1.7, the maximum CO2 permeability is 1097 Barrer, and the maximum CO2 / N2 selectivity is 4.2. Compared with the hybrid matrix membrane prepared by the symbiotic method, the gas separation performance of the hybrid matrix membrane prepared by the conventional method is poor.

[0074] The testing method is as follows:

[0075] Gas separation performance experiment

[0076] The mixed matrix membrane based on the symbiotic method of Example 1 and the mixed matrix membrane based on the traditional synthesis method of Comparative Example 1 were subjected to O2 / N2, CO2 / N2 gas separation performance experiments, and the experimental device is shown in Figure 7 The operation steps are as follows:

[0077] 1) The mixed matrix membrane was loaded into the gas separation performance test body device, and then placed in a constant temperature tank for experiment at 25°C.

[0078] 2) Open valves F3 and F4, and keep the remaining valves closed. Open the vacuum pump to vacuum the upper and lower cavities of the body to an absolute pressure of less than 3 kPa, and close the vacuum pump.

[0079] 3) Close valves F3 and F4, open valve F1, and adjust the pressure gauge to make the mixed gas pressure reach the measured working point, then wait for 3 min. The slope value of the pressure change of the lower cavity with time is obtained from the pressure sensor of the lower cavity.

[0080] 4) Open valve F2, adjust the flow control meter of the sweep gas Ar to a flow rate of 15 sccm, sweep the lower cavity to a positive pressure, and then continue to reduce the Ar flow rate to 1.6 sccm and open valve F5. The chromatographic column in the gas chromatograph on the permeation side was swept for 5 min, valve F5 was closed, and the detection switch of the gas chromatograph was opened to detect the gas composition of the permeation.

[0081] 5) The selectivity and permeability of the mixed matrix membrane to O2 / N2 and CO2 / N2 can be calculated using the gas composition detection results of the gas chromatograph, the pressure values of the upper and lower gas paths, the slope value of the pressure change of the lower cavity with time, and the area and thickness values of the membrane. The permeability and selectivity calculation formulas are as follows:

[0082] The permeability calculation formula of the separation membrane is:

[0083]

[0084] In the formula, V is the effective volume of the lower cavity, in cm 3 ; L is the thickness of the membrane, in μm; A is the effective area of the membrane, in cm 2 ; p i is the pressure difference of gas component i on the upper and lower sides, in cmHg -1 ; dp / dt is the slope of the downstream pressure change with time, in pa / s; x i is the volume fraction of the gas component i on the permeation side. In order to simplify the unit, Barrer is introduced as the permeability unit, and the unit conversion is:

[0085] 1 Barrer = 10 -10 cm3 (STP) cm cm -2 · s -1 cmHg -1 (STP is standard condition, i.e. 273.15K, 76cmHg).

[0086] The calculation formula of the selectivity of the separation membrane is:

[0087] In the formula, P A , P B respectively represent the permeation amount of the gas components A and B.

[0088] From the above examples, the application provides a mixed matrix membrane based on symbiotic method and a preparation method thereof and a boiler oxygen-enriched combustion, nitrogen production and carbon capture coupling system. The application uses polydimethylsiloxane as a substrate and ZIF-8 as a nano-porous filler to prepare a mixed matrix membrane for O2 / N2 separation and CO2 / N2 separation by using a symbiotic method. The mixed matrix membrane combines the selective solution diffusion effect of polydimethylsiloxane and the pore size screening effect of ZIF-8 and has excellent O2 / N2 and CO2 / N2 separation effect. When the mixed matrix membrane is applied to a boiler oxygen-enriched combustion system, the energy consumption of an air separation process is greatly reduced, high-purity N2 is prepared, and the CO2 concentration in a carbon capture process is greatly improved.

[0089] The above only describes the preferred embodiments of the application, and it should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A method for preparing a mixed matrix membrane based on the coacervation method, characterized in that, The method comprises the following steps: 1) mixing a polydimethylsiloxane n-hexane solution and a zinc nitrate aqueous solution to obtain a mixed solution 1; 2) mixing the mixed solution 1 and a 2-methylimidazole aqueous solution to obtain a mixed solution 2; 3) mixing and reacting the mixed solution 2 and tetraethyl orthosilicate to obtain a film solution, and then performing ultrasonic treatment and drying in sequence to obtain a mixed matrix membrane. In the polydimethylsiloxane n-hexane solution, the mass fraction of polydimethylsiloxane is 5-15%; in the zinc nitrate aqueous solution, the molar volume ratio of zinc nitrate to water is 1-1.5 mmol:3 mL. In step 1), the mass ratio of the polydimethylsiloxane n-hexane solution to the zinc nitrate aqueous solution is 20-25:0.2-0.

5. The mixing speed is 500-700 rpm, the mixing time is 1-2 h, and the mixing temperature is 20-30°C.

2. The production method according to claim 1, characterized by, In step 2), in the 2-methylimidazole aqueous solution, the molar volume ratio of 2-methylimidazole to water is 0.06-0.09 mol:10 mL. The mixing speed is 500-700 rpm, the mixing time is 3-5 h, and the mixing temperature is 20-30°C.

3. The production method according to claim 1 or 2, characterized by, The mass ratio of the polydimethylsiloxane n-hexane solution to the 2-methylimidazole aqueous solution is 20-25:4-10. The addition amount of the tetraethyl orthosilicate is 5-15% of polydimethylsiloxane.

4. The production method according to claim 3, characterized by, In step 3), the mixing speed is 700-1200 rpm, the mixing time is 2-4 h, and the mixing temperature is 30-40°C.

5. The production method according to claim 1 or 2 or 4, characterized by, In step 3), the ultrasonic frequency is 30-50 kHz, and the ultrasonic time is 1-3 h; the drying is performed in sequence at room temperature, by air blowing, and by vacuum drying; the room temperature drying time is 10-14 h; the air blowing drying temperature is 80-90°C, and the time is 10-14 h; the vacuum drying temperature is 110-135°C, the time is 18-24 h, and the vacuum degree is 0.09-0.095 MPa.

6. The mixed matrix membrane prepared according to the method of any one of claims 1-5, characterized by, The method comprises polydimethylsiloxane and ZIF-8 material, the polydimethylsiloxane is a substrate, and the ZIF-8 material is a nanoporous filler.

7. A boiler oxycombustion, nitrogen production and carbon capture coupling system, characterized in that, The boiler oxygen-enriched combustion system comprises an air separation membrane system (1), an oxygen-enriched boiler (2), a gas heat exchanger (3), a dust remover (4), a desulfurization tower (5), a CO2 / N2 separation membrane system (6), a flue gas condenser (7), a compressor (8), a CO2 purification treatment system (9), a coal mill (10), a primary flue gas recirculation pipeline (11), and a secondary flue gas recirculation pipeline (12). The air separation membrane system (1) and the CO2 / N2 separation membrane system (6) each comprise the mixed matrix membrane of claim 6.

8. The boiler oxycombustion, nitrogen production, and carbon capture coupling system of claim 7, wherein, The air separation membrane system (1) adopts a three-stage mixed matrix membrane series connection structure.

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