A separation membrane, its preparation method and application

Abstract

This invention relates to the field of CO2 capture technology, and more particularly to a separation membrane, its preparation method, and its applications. By controlling the amount of a weak acid reducing agent added, this invention can regulate the degree of reduction of graphene oxide, thereby controlling the interlayer spacing of the graphene oxide sheets within a certain range, thus achieving efficient separation of gas molecules of different diameters (e.g., [missing information]). This not only avoids the problem of poor separation effect due to excessively large interlayer spacing, but also avoids the problem of low separation rate due to excessively small interlayer spacing. Epoxy resin is used for mechanical fixation. The final prepared separation membrane is suitable for CO2 separation in both high-pressure and low-pressure environments.

Description

Technical Field

[0001] This invention relates to the field of CO2 capture technology, and in particular to a separation membrane, its preparation method and application. Background Technology

[0002] According to the generational classification of CO2 capture technologies, the first-generation combustion capture technologies (post-combustion capture, pre-combustion capture, and oxy-fuel combustion) are currently the most mature. These methods have the advantages of high separation performance and large throughput, and have been successfully applied industrially, but they still have problems such as high cost and high energy consumption. Membrane separation, as the second-generation capture technology, has advantages such as high separation efficiency, low investment cost, low energy consumption, simple process flow, no pollution, modular design, and small footprint, and has a promising future in the field of CO2 capture.

[0003] Graphene oxide (GO) membranes are two-dimensional layered membranes composed of ordered stacked monolayers of graphene oxide sheets. By adjusting the spacing between the sheets, molecules of different sizes can be sieved, making them a promising candidate for CO2 separation.

[0004] The interlayer spacing of graphene oxide sheets is related to its oxidation degree; the negatively charged COO₂ within and at the edges of the sheets... - The more functional groups a graphene oxide sheet has, the stronger its interaction forces and the larger its interlayer spacing. Under dry conditions, the interlayer spacing of pure graphene oxide sheets is [value missing]. All higher than The molecular dynamics diameter of GO nanosheets is insufficient for the separation of CO2 / N2, CO2 / CH4, and CO2 / H2 systems. Therefore, some studies have reported using cross-linking methods to modify the pore structure of GO membranes, thereby improving separation efficiency. For example, the Jiang Zhongyi research group at Tianjin University introduced borate as a cross-linking agent and a transport-promoting carrier into the interlayer of GO nanosheets. Due to the reasonable control of the interlayer size and the effect of transport-promoting sites within the membrane, the CO2 permeation rate of the composite membrane reached 650 GPU, and the CO2 / CH4 separation coefficient was 75. This method achieves a high CO2 permeation rate due to the introduction of a carrier that promotes CO2 transport; however, the modification method is complex, and a third type of substance is introduced into the system.

[0005] Furthermore, researchers have prepared graphene oxide-based hybrid matrix membranes by doping graphene oxide with nanomaterials, thereby controlling the gas transport channels and improving separation efficiency. The Jin Wanqin research group at Nanjing University of Technology introduced GO into Pebax polymer to prepare hybrid matrix membranes. The hydrogen bonding interaction between GO and Pebax induced the recombination and regular arrangement of two-dimensional GO. The hybrid matrix membrane exhibited excellent separation performance (CO2 permeability coefficient of 100 Barrer, CO2 / N2 selectivity of 91). While the GO-Pebax hybrid matrix membrane showed good separation performance in CO2 / N2, the CO2 permeation rate was not ideal, and the preparation method of the hybrid matrix membrane was costly and difficult to scale up. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a separation membrane, its preparation method and application, which is applicable to the separation of CO2 in both high-pressure and low-pressure environments.

[0007] This invention provides a method for preparing a separation membrane, comprising the following steps:

[0008] A) Mix the graphene oxide dispersion with a weak acid and carry out a reduction reaction at 50-100℃ to obtain a partially reduced graphene oxide solution.

[0009] B) The partially reduced graphene oxide solution is mixed with water, and the partially reduced graphene oxide is deposited on the surface of the substrate film by vacuum filtration. After drying, a partially reduced graphene oxide film is obtained.

[0010] C) The partially reduced graphene oxide film is immersed in a resin solution, defoamed under vacuum, and then cured to obtain a preform;

[0011] The resin solution includes epoxy resin and a coagulant;

[0012] D) The blank is thinned and polished to obtain a separation membrane.

[0013] Preferably, the preparation method of the graphene oxide dispersion includes the following steps:

[0014] a) Mix concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder, and react at 75-85°C to obtain graphite preoxide;

[0015] b) Mix the second concentrated sulfuric acid, the graphite preoxide, potassium permanganate and sodium nitrate evenly at 5-20°C, and react at 30-35°C for 1-5 hours; add deionized water to dilute, and continue the reaction at 30-35°C for 1-5 hours; add 30wt%-35wt% hydrogen peroxide to terminate the reaction, and obtain graphite oxide;

[0016] c) The graphite oxide was acid-washed, then washed with water until neutral, and the graphite oxide was ultrasonically dispersed in water and centrifuged to obtain a graphene oxide dispersion.

[0017] The concentration of the graphene oxide dispersion is 1–3 g / L.

[0018] Preferably, in step a), the mass ratio of potassium persulfate, phosphorus pentoxide, and graphite powder is 5-10:5-10:2-10;

[0019] The ratio of the first concentrated sulfuric acid to graphite powder is 20-60 mL: 2-10 g;

[0020] The reaction then includes:

[0021] After cooling to 25–35°C, deionized water was added for dilution, followed by vacuum filtration, washing until neutral, and drying to obtain graphite preoxide.

[0022] Preferably, in step b), the mass ratio of the graphite preoxide, potassium permanganate, and sodium nitrate is 2-10:15-25:2-10;

[0023] The ratio of graphite preoxide to second concentrated sulfuric acid is 2-10 g: 20-250 mL.

[0024] Preferably, in step A), the weak acid includes tannic acid and / or theanine;

[0025] The mass ratio of the weak acid to the graphene oxide dispersion is 0.05 to 3:1.

[0026] Preferably, in step A), the reduction reaction takes 2 to 12 hours.

[0027] In step B), the base membrane is made of cellulose acetate, porous anodic aluminum oxide, or nylon.

[0028] The pore size of the base membrane is 0.22–0.45 μm.

[0029] Preferably, in step C), the volume ratio of the epoxy resin to the coagulant is 1:2 to 3;

[0030] The vacuum degree of the vacuum defoaming is -0.08 to -0.1 MPa;

[0031] The curing time is 12 to 24 hours.

[0032] Preferably, in step D), the thickness of the thinned graphene oxide-resin preform is 0.2–2 μm;

[0033] The polishing includes:

[0034] The upper and lower surfaces of the thinned graphene oxide-resin preform were polished using metallographic sandpaper with a mesh size of 20 million.

[0035] The interlayer spacing of the separation membrane is

[0036] The present invention also provides a separation membrane prepared by the preparation method described above.

[0037] The present invention also provides an application of the separation membrane described above in the field of CO2 separation.

[0038] This invention provides a method for preparing a separation membrane, comprising the following steps: A) mixing a graphene oxide dispersion with a weak acid and carrying out a reduction reaction at 50–100°C to obtain a partially reduced graphene oxide solution; B) mixing the partially reduced graphene oxide solution with water, depositing the partially reduced graphene oxide onto the surface of a substrate membrane using vacuum filtration, and drying to obtain a partially reduced graphene oxide membrane; C) immersing the partially reduced graphene oxide membrane in a resin solution, defoaming under vacuum, and then curing to obtain a preform; the resin solution includes epoxy resin and a coagulant; D) thinning and polishing the preform to obtain the separation membrane. This invention can regulate the degree of reduction of graphene oxide by controlling the amount of the reducing agent (weak acid), and can control the interlayer spacing of graphene oxide within a certain range. Within a certain range, this allows for the realization of gas molecules of different diameters (e.g. This method achieves highly efficient separation of CO2. It avoids both the poor separation effect caused by excessively large interlayer spacing and the low separation rate caused by excessively small interlayer spacing. Epoxy resin is used for mechanical fixation. The final separation membrane is suitable for CO2 separation in both high-pressure and low-pressure environments. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the self-supporting partially reduced graphene oxide film separated from the base film in Embodiment 1 of the present invention.

[0040] Figure 2 This is a schematic diagram of the resin-encapsulated partially reduced graphene oxide film preform prepared in Example 1 of the present invention;

[0041] Figure 3 This is a schematic diagram of the structure of the resin-encapsulated partially reduced graphene oxide film prepared in Example 1 of the present invention.

[0042] Figure 4The XRD characterization diagrams of the separation membranes of the embodiments and comparative examples of the present invention correspond to (1) - Example 1; (2) - Example 2; (3) - Example 3; (4) - Example 4 and; (5) - Example 5; (6) - Example 6; (7) - Comparative Example 1; (8) - Comparative Example 2; (9) - Comparative Example 3; (10) - Comparative Example 4; (11) - Comparative Example 5. Detailed Implementation

[0043] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] This invention provides a method for preparing a separation membrane, comprising the following steps:

[0045] A) Mix the graphene oxide dispersion with a weak acid and carry out a reduction reaction at 50-100℃ to obtain a partially reduced graphene oxide solution.

[0046] B) The partially reduced graphene oxide solution is mixed with water, and the partially reduced graphene oxide is deposited on the surface of the substrate film by vacuum filtration. After drying, a partially reduced graphene oxide film is obtained.

[0047] C) The partially reduced graphene oxide film is immersed in a resin solution, defoamed under vacuum, and then cured to obtain a preform;

[0048] The resin solution includes epoxy resin and a coagulant;

[0049] D) The blank is thinned and polished to obtain a separation membrane.

[0050] In step A):

[0051] A graphene oxide dispersion was mixed with a weak acid and subjected to a reduction reaction at 50–100 °C to obtain a partially reduced graphene oxide solution.

[0052] In some embodiments of the present invention, the preparation method of the graphene oxide dispersion includes the following steps:

[0053] a) Mix concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder, and react at 75-85°C to obtain graphite preoxide;

[0054] b) Mix the second concentrated sulfuric acid, the graphite preoxide, potassium permanganate and sodium nitrate evenly at 5-20°C, and react at 30-35°C for 1-5 hours; add deionized water to dilute, and continue the reaction at 30-35°C for 1-5 hours; add 30wt%-35wt% hydrogen peroxide to terminate the reaction, and obtain graphite oxide;

[0055] c) The graphite oxide was acid-washed and then washed with water until neutral. The graphite oxide was ultrasonically dispersed in water and centrifuged to obtain a graphene oxide dispersion.

[0056] In step a):

[0057] The first concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder are mixed and reacted at 75-85℃ to obtain graphite preoxide.

[0058] Specifically, including:

[0059] After mixing concentrated sulfuric acid, potassium persulfate and phosphorus pentoxide, a clear solution was obtained by stirring. Then, the solution was heated to 75-85°C, graphite powder was added, and the reaction was carried out at 75-85°C to obtain graphite preoxide.

[0060] The stirring speed for obtaining a clear solution is 300–800 rpm, for example, 500 rpm.

[0061] The method of raising the temperature is by water bath heating.

[0062] The mass ratio of potassium persulfate, phosphorus pentoxide, and graphite powder is 5-10:5-10:2-10.

[0063] The ratio of the first concentrated sulfuric acid to graphite powder is 20-60 mL: 2-10 g. The mass concentration of the first concentrated sulfuric acid is 97%-98%. The graphite powder is natural graphite powder with a particle size of 200 mesh.

[0064] The reaction time is 3 to 10 hours at 75 to 85°C.

[0065] The reaction then includes:

[0066] After cooling to 25–35°C, deionized water is added for dilution, followed by vacuum filtration, washing until neutral, and drying to obtain graphite preoxide. This invention does not impose any special limitations on the amount of deionized water used; in some embodiments, the amount of deionized water is 100–400 mL.

[0067] The drying temperature is 40–70℃, for example, 60℃; the drying time is 12–24 hours, for example, 12 hours.

[0068] In step b):

[0069] The second concentrated sulfuric acid, the graphite preoxide, potassium permanganate, and sodium nitrate are mixed evenly at 5–20°C and reacted at 30–35°C for 1–5 hours. Deionized water is added for dilution, and the reaction is continued at 30–35°C for 1–5 hours. The reaction is terminated by adding hydrogen peroxide with a mass concentration of 30%–35%, yielding graphite oxide.

[0070] Specifically, including:

[0071] At 5–20°C, graphite preoxide, potassium permanganate, and sodium nitrate are added sequentially to a stirred second concentrated sulfuric acid solution, and the reaction is carried out at 30–35°C for 1–5 hours. Deionized water is added for dilution, and the reaction is continued at 30–35°C for 1–5 hours. The reaction is terminated by adding hydrogen peroxide with a mass concentration of 30%–35%, yielding graphite oxide.

[0072] The mass ratio of the graphite preoxide, potassium permanganate, and sodium nitrate is 2-10:15-25:2-10.

[0073] The ratio of graphite preoxide to second concentrated sulfuric acid is 2–10 g : 20–250 mL. The mass concentration of the second concentrated sulfuric acid is 97%–98%.

[0074] The present invention does not impose any special restrictions on the amount of deionized water used. In some embodiments, the amount of deionized water used is 200-400 mL.

[0075] The reaction was carried out under water bath heating conditions.

[0076] After adding hydrogen peroxide with a mass concentration of 30%–35%, the brown reaction solution abruptly turns bright yellow, thus obtaining graphite oxide. In some embodiments, the amount of hydrogen peroxide used is 5–20 mL.

[0077] In step c):

[0078] The graphite oxide was acid-washed and then washed with water until neutral. The graphite oxide was then ultrasonically dispersed in water and centrifuged to obtain a graphene oxide dispersion.

[0079] The pickling reagent used is dilute hydrochloric acid with a volume concentration of 5% to 15%, for example, 10%. In some embodiments of the present invention, the amount of reagent used for pickling can be 100 to 200 mL. Pickling is carried out under stirring conditions.

[0080] Deionized water is used for washing.

[0081] The ultrasonic dispersion of graphite oxides in water includes:

[0082] Add graphite oxide to deionized water, stir for 20–40 min, and then ultrasonically disperse for 0.5–2.5 h.

[0083] The centrifugation speed is 3800–4200 rpm, for example, 4000 rpm; the time is 8–12 min, for example, 10 min. The centrifugation is used to remove unreacted graphite sheets.

[0084] The concentration of the graphene oxide dispersion is 1–3 g / L, for example, 1 g / L.

[0085] After obtaining the graphene oxide dispersion, the graphene oxide dispersion was mixed with a weak acid and a reduction reaction was carried out at 50-100℃ to obtain a partially reduced graphene oxide solution.

[0086] The weak acids include tannic acid and / or theanine.

[0087] The mass ratio of the weak acid to the graphene oxide dispersion is 0.05–3:1, for example, 0.05:1, 1:1, or 2:1. This invention allows for the control of the reduction degree of graphene oxide by adjusting the amount of the weak acid added as a reducing agent. Furthermore, the reducing agent used is a weak reducing agent such as tannic acid or theanine, which not only enables precise control of the reduction degree of graphene oxide but is also environmentally friendly and will not cause harm to the environment.

[0088] The reduction reaction is carried out at a temperature of 70°C for 2–12 hours, for example, 10 hours. The reduction reaction is a water bath reaction.

[0089] In some embodiments of the present invention, the reduction reaction is further performed by diluting with water. The dilution factor is 5 to 10 times.

[0090] In step B):

[0091] The partially reduced graphene oxide solution was mixed with water, and the partially reduced graphene oxide was deposited on the surface of a substrate film using a vacuum filtration method. After drying, a partially reduced graphene oxide film was obtained.

[0092] The water is deionized water. The purpose of the water is to dilute the partially reduced graphene oxide solution by a factor of 5 to 10.

[0093] The base membrane is made of cellulose acetate, porous anodized aluminum oxide (AAO), or nylon; the pore size of the base membrane is 0.22–0.45 μm, for example, 0.22 μm.

[0094] The drying temperature is 20–30°C, for example, 25°C; the drying time is 45–55 hours, for example, 48 hours.

[0095] In some embodiments of the present invention, after drying, the process further includes:

[0096] The partially reduced graphene oxide film is separated from the base film.

[0097] In some embodiments of the present invention, the separation process further includes cutting. The material can be cut into small strips of 2mm × 8mm.

[0098] In step C):

[0099] The partially reduced graphene oxide film is immersed in a resin solution, defoamed under vacuum, and then cured to obtain a preform.

[0100] The resin solution includes epoxy resin and a coagulant.

[0101] In some embodiments of the present invention, immersing the partially reduced graphene oxide film in a resin solution includes:

[0102] The partially reduced graphene oxide film after being cut was immersed in the resin solution at a 90° angle to form a 2×3 array.

[0103] In some embodiments of the present invention, the resin solution is placed in a mold. The mold is made of polyethylene.

[0104] The resin solution comprises epoxy resin and a coagulant. Epoxy resin is used for mechanical fixing.

[0105] The volume ratio of the epoxy resin to the coagulant is 1:2 to 3, for example, 1:2.

[0106] The vacuum degree of the vacuum defoaming is -0.08 to -0.1 MPa.

[0107] The curing time is 12 to 24 hours.

[0108] After curing, the process also includes removing the blank from the mold.

[0109] In step D):

[0110] The blank is thinned and polished to obtain a separation membrane.

[0111] The thinning process is performed using a grinding and polishing machine.

[0112] The thickness of the thinned blank is 0.2 to 2 μm, for example, 0.2 μm.

[0113] The polishing includes:

[0114] The upper and lower surfaces of the thinned preform were polished using metallographic sandpaper with a mesh size of 20 million. This process was used to fully expose the sides of the partially reduced graphene oxide film.

[0115] The interlayer spacing d of the separation membrane is for example Effective interlayer spacing μ (μ==d-3.4, where (where the electron cloud thickness of a single layer of graphene is) for example 2.8 Thus, gas molecules of different diameters can be achieved. This method achieves highly efficient separation. It not only avoids the problem of poor separation effect caused by excessively large interlayer spacing, but also avoids the problem of low separation rate caused by excessively small interlayer spacing.

[0116] This invention provides a controllable reduction method to prepare a separation membrane with controllable interlayer spacing. This membrane is suitable for CO2 separation in both high-pressure and low-pressure environments.

[0117] The present invention also provides a separation membrane prepared by the method described above. The separation membrane is suitable for separating CO2 in both high-pressure and low-pressure environments.

[0118] This invention also provides an application of the separation membrane described above in the field of CO2 separation. Specifically, it provides an application of the separation membrane for CO2 separation.

[0119] This invention uses a separation membrane performance evaluation device (MGPT-Ⅰ type separation membrane performance evaluation device from Dalian Karibona Technology Co., Ltd.) to test the performance of the separation membrane.

[0120] The feed gas is first humidified to saturation in a humidification tank before entering the membrane cell for testing. The feed gas can be a CO2 / N2 mixture with a pressure range of 0.1–5.0 MPa, while the permeate-side pressure is atmospheric pressure. The purge gas is helium or argon. The permeate-side gas enters a gas chromatograph, and the peak areas are analyzed to obtain the gas composition and separation coefficient of the permeate. Simultaneously, the permeate-side gas flow rate is measured by an electronic soap membrane flow meter to obtain the gas permeation rate.

[0121] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0122] To further illustrate the present invention, the following detailed description of a separation membrane, its preparation method, and its application, in conjunction with embodiments, is provided by the present invention, but should not be construed as limiting the scope of protection of the present invention.

[0123] Example 1

[0124] 1) Preparation of graphene oxide dispersion:

[0125] 1-1) 50 mL of concentrated sulfuric acid, 8.0 g of potassium persulfate, and 8.0 g of phosphorus pentoxide were added sequentially to a round-bottom flask and stirred to obtain a clear solution. After heating to 80 °C in a water bath, 4.0 g of natural graphite powder with a particle size of 200 mesh was added, and the mixture was reacted at 80 °C for 5 h. After the reaction was completed, the mixture was cooled to 25 °C, diluted with 200 mL of deionized water, filtered, washed until neutral, and dried at 60 °C for 12 h to obtain graphite preoxide.

[0126] 1-2) Weigh 140 mL of concentrated sulfuric acid and add it to a round-bottom flask. At 20 °C, add 3.0 g of the graphite preoxide, 18.0 g of potassium permanganate, and 3.0 g of sodium nitrate in sequence under stirring. React in a water bath at 35 °C for 2 h. After diluting with 300 mL of deionized water, continue the reaction in a water bath at 35 °C for 2 h. Add 10 mL of 35% hydrogen peroxide. When the brown reaction solution suddenly turns bright yellow, the graphite oxide is obtained.

[0127] 1-3) Add 100 mL of 10% dilute hydrochloric acid to the graphite oxide, stir and acid wash, then wash with deionized water until neutral to obtain GO product; add the GO product to 300 mL of deionized water, stir for 30 min, ultrasonically disperse for 2 h, and then centrifuge at 4000 rpm for 10 min to obtain a stable GO dispersion with a concentration of 1 g / L.

[0128] 2) Reduction of GO dispersion:

[0129] Add 1.5 mg of tannic acid to 30 mL of 1 g / L graphene oxide dispersion, then dilute with 200 mL of water 7.7 times, and react in a water bath at 70 °C for 10 h to obtain a partially reduced graphene oxide solution.

[0130] 3) Preparation of partially reduced graphene oxide films:

[0131] The partially reduced graphene oxide solution (10 mL) was diluted twice with water, and then the reduced graphene oxide was deposited onto a 0.22 μm cellulose acetate substrate membrane using vacuum filtration. The membrane was dried at 25°C for 48 h, and then the partially reduced graphene oxide membrane was separated from the substrate membrane. Figure 1 As shown, cut it into small strips of 2mm × 8mm. Figure 1 This is a schematic diagram of the self-supporting partially reduced graphene oxide film separated from the base film in Embodiment 1 of the present invention.

[0132] 4) Resin-encapsulated partially reduced graphene oxide film:

[0133] A resin solution was prepared by mixing epoxy resin (TDE-85 type epoxy resin from Guangzhou Qian'an Chemical Co., Ltd.) and coagulant at a volume ratio of 1:2. The solution was poured into a polyethylene mold with a diameter of 8 cm. The partially reduced graphene oxide film was then immersed in the resin solution at a 90° angle to form a 2×3 array. After vacuum defoaming at 0.08 MPa, the resin solidified for 12 hours, and the preform was removed from the mold. Figure 2 This is a schematic diagram of the resin-encapsulated partially reduced graphene oxide film preform prepared in Example 1 of the present invention;

[0134] The preform was thinned to 0.2 μm using a polishing machine. Then, the upper and lower surfaces of the thinned preform were polished with 20 million grit metallographic sandpaper to fully expose the sides of the partially reduced graphene oxide film, thus obtaining a resin-encapsulated partially reduced graphene oxide separation membrane with an interlayer spacing of [missing information]. Figure 3 This is a schematic diagram of the structure of the resin-encapsulated partially reduced graphene oxide film prepared in Example 1 of the present invention. Figure 3 (a) in the diagram is a schematic diagram of gas transport in a traditional graphene oxide membrane. Figure 3 (b) in the diagram is a schematic diagram of gas transport in a partially reduced graphene oxide film fixed with epoxy resin. From... Figure 3 As can be seen, this invention uses epoxy resin to mechanically fix the partially reduced graphene oxide membrane, achieving vertical fixation of the separation membrane. After vertical fixation, the transport channel of the graphene oxide membrane changes from the original "S" shape to a straight line, greatly shortening the transport path and improving the gas transport rate. Simultaneously, the epoxy resin significantly improves the mechanical strength of the separation membrane, making it suitable for high-pressure CO2 separation applications.

[0135] 5) Application of the separation membrane prepared in Example 1 in the field of CO2 separation:

[0136] Specifically, the steps for separating CO2 using a membrane separation device include:

[0137] Performance tests were conducted using a membrane performance evaluation device (MGPT-Ⅰ type, Dalian Karibona Technology Co., Ltd.). The feed gas was a CO2 / N2 mixture, the purge gas was helium, and the pressure was 0.1 MPa. The permeate side pressure was atmospheric pressure. The permeate gas entered a gas chromatograph, and the peak area was analyzed to obtain the separation coefficient. The gas permeation rate was measured by an electronic soap membrane flow meter. The test results are shown in Table 1.

[0138] Example 2

[0139] The difference from Example 1 is as follows:

[0140] In step 2), 1.5 mg of tannic acid was added to 15 mL of 1 g / L graphene oxide dispersion.

[0141] The final interlayer spacing of the separation membrane is

[0142] CO2 was separated according to the method in Example 1.

[0143] Example 3

[0144] The difference from Example 1 is as follows:

[0145] In step 2), 1.5 mg of tannic acid was added to 10 mL of 1 g / L graphene oxide dispersion.

[0146] The final interlayer spacing of the separation membrane is

[0147] CO2 was separated according to the method in Example 1.

[0148] Example 4

[0149] The difference from Example 1 is as follows:

[0150] In step 2), 1.5 mg of tannic acid was added to 7.5 mL of 1 g / L graphene oxide dispersion.

[0151] The final interlayer spacing of the separation membrane is

[0152] CO2 was separated according to the method in Example 1.

[0153] Example 5

[0154] The difference from Example 1 is as follows:

[0155] In step 2), 1.5 mg of tannic acid was added to 5 mL of 1 g / L graphene oxide dispersion.

[0156] The final interlayer spacing of the separation membrane is

[0157] CO2 was separated according to the method in Example 1.

[0158] Example 6

[0159] The difference from Example 1 is as follows:

[0160] In step 2), 1.5 mg of tannic acid was added to 3 mL of 1 g / L graphene oxide dispersion.

[0161] The final interlayer spacing of the separation membrane is

[0162] CO2 was separated according to the method in Example 1.

[0163] Example 7

[0164] The difference from Example 1 is as follows:

[0165] In step 2), 1.5 mg of tannic acid was added to 1.5 mL of 1 g / L graphene oxide dispersion.

[0166] The final interlayer spacing of the separation membrane is

[0167] CO2 was separated according to the method in Example 1.

[0168] Example 8

[0169] The difference from Example 1 is as follows:

[0170] In step 2), 3 mg of tannic acid was added to 1.5 mL of 1 g / L graphene oxide dispersion.

[0171] The final interlayer spacing of the separation membrane is

[0172] CO2 was separated according to the method in Example 1.

[0173] Comparative Example 1

[0174] The difference from Example 1 is as follows:

[0175] (Does not contain step 2);

[0176] In step 3), the GO dispersion prepared in step 1) is used directly.

[0177] The final interlayer spacing of the separation membrane is

[0178] CO2 was separated according to the method in Example 1.

[0179] Comparative Example 2

[0180] The difference from Example 1 is as follows:

[0181] The graphene oxide is reduced using hydrazine hydrate. Specifically, steps 2), 3), and 4) are replaced with:

[0182] 2) Take 30 mL of graphene oxide dispersion, adjust the pH to 9 with NaOH, add 1 mL of 85% hydrazine hydrate to the dispersion, and stir the mixture in a 95°C water bath for 1 h. Filter the product, wash it with anhydrous ethanol, then wash it with deionized water, and dry it at 25°C for 48 h to obtain reduced graphene oxide.

[0183] 3) Subsequently, the reduced graphene oxide was deposited on a cellulose acetate substrate membrane with a pore size of 0.22 μm by vacuum filtration and dried at 25 °C for 48 h. Then, the reduced graphene oxide membrane was separated from the substrate membrane and cut into small strips of 2 mm × 8 mm.

[0184] 4) Prepare a resin solution by mixing epoxy resin and coagulant at a volume ratio of 1:2, and pour it into a polyethylene mold with a diameter of 8 cm. Immerse the cut and reduced graphene oxide film at a 90° angle into the resin solution, forming a 2×3 array. After vacuum defoaming at 0.08 MPa, allow the resin to solidify for 12 hours, and then remove the preform from the mold. Thin the preform to 0.2 μm using a polishing machine, and then polish the upper and lower surfaces of the thinned preform with 20 million grit metallographic sandpaper to obtain the separation membrane.

[0185] The final interlayer spacing of the separation membrane is

[0186] CO2 was separated according to the method in Example 1.

[0187] Comparative Example 3

[0188] The difference from Example 1 is as follows:

[0189] The graphene oxide is reduced using hydroiodic acid; specifically, steps 2), 3), and 4) are replaced with:

[0190] 2) Add 3 mL of hydroiodic acid to 30 mL of graphene oxide dispersion and stir in a 100 °C water bath for 1 h. Filter the product, wash with anhydrous ethanol, then wash with deionized water, and dry at 25 °C for 48 h to obtain reduced graphene oxide.

[0191] 3) Subsequently, the reduced graphene oxide was deposited on a cellulose acetate substrate membrane with a pore size of 0.22 μm by vacuum filtration and dried at 25 °C for 48 h. Then, the partially reduced graphene oxide membrane was separated from the substrate membrane and cut into small strips of 2 mm × 8 mm.

[0192] 4) Prepare a resin solution by mixing epoxy resin and coagulant at a volume ratio of 1:2, pour it into a polyethylene mold with a diameter of 8cm, immerse the partially reduced graphene oxide film at 90° into the resin solution to form a 2×3 array, perform vacuum defoaming under 0.08MPa conditions, wait 12h for the resin to solidify, and then remove the preform from the mold.

[0193] The final interlayer spacing of the separation membrane is

[0194] CO2 was separated according to the method in Example 1.

[0195] Figure 4 The XRD characterization diagrams of the separation membranes of the embodiments and comparative examples of the present invention correspond to (1) - Example 1; (2) - Example 2; (3) - Example 3; (4) - Example 4 and; (5) - Example 5; (6) - Example 6; (7) - Comparative Example 1; (8) - Comparative Example 2; (9) - Comparative Example 3; (10) - Comparative Example 4; (11) - Comparative Example 5.

[0196] The separation performance test results of the separation membranes prepared in Examples 1-8 and Comparative Examples 1-3 are shown in Tables 1 and 2.

[0197] Table 1. Evaluation results of the separation performance of the separation membranes in Examples 1-8

[0198]

[0199] Table 2 shows the separation performance evaluation results of the separation membranes in Comparative Examples 1-3.

[0200]

[0201]

[0202] The graphene oxide in Examples 1-8 was partially reduced.

[0203] Tables 1 and 2 show that controlled reduction of graphene oxide can be achieved by adjusting the amount of tannic acid (a weak acid). When the amount of tannic acid increases to a certain level, all oxygen-containing functional groups on the surface of graphene oxide are reduced. The interlayer spacing of partially reduced graphene oxide is larger than that of fully reduced graphene oxide. However, a small amount of hydrazine hydrate and hydroiodic acid can completely reduce the oxygen-containing functional groups on the surface of graphene oxide. Therefore, tannic acid can achieve controlled reduction of graphene oxide, and graphene oxide with different interlayer spacings exhibits different sieving effects. However, a small amount of hydrazine hydrate (a strong acid) can completely reduce graphene oxide. This demonstrates that tannic acid can achieve controlled reduction of graphene oxide, and graphene oxide with different interlayer spacings can be obtained by controlling the degree of reduction, thereby optimizing the sieving effect.

[0204] As shown in Examples 1-3, with the increase of the degree of reduction of graphene oxide, the interlayer spacing of the partially reduced graphene oxide separation membrane gradually decreases, the CO2 permeation rate gradually decreases, while the CO2 / N2 separation coefficient gradually increases. When the interlayer spacing of the graphene oxide membrane is adjusted to... Its effective interlayer spacing is in The electron cloud thickness of a single layer of graphene is given by the fact that the interlayer spacing is greater than the molecular dynamic diameter of N2. Slightly smaller and smaller than the molecular dynamic diameter of CO2 Larger tannins provide optimal separation performance. Examples 4-6 show that as the reduction degree of graphene oxide continues to increase, the interlayer spacing decreases further, and the CO2 permeation rate drops rapidly. At this point, the interlayer spacing of the partially reduced graphene oxide membrane is smaller than the molecular dynamic diameters of N2 and CO2, resulting in a loss of sieving effect. Examples 7-8 show that after all graphene oxide is reduced, further increasing the amount of tannic acid does not change the separation effect or permeation performance. Similarly, in Comparative Examples 2-3, when all graphene oxide is reduced by hydrazine hydrate and hydroiodic acid, the permeation rate of the graphene oxide membrane drops sharply, and the sieving performance is poor. Partially reduced graphene oxide can achieve both good separation and permeation performance; among them, the partially reduced graphene oxide membrane provided in Example 3 exhibits the best combination of separation and permeation performance.

[0205] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Use of a separation membrane for CO2 / N2 separation; The preparation method of the separation membrane comprises the following steps: A) mixing graphene oxide dispersion liquid and weak acid, and performing reduction reaction at 50-100 ℃ to obtain partially reduced graphene oxide solution; The weak acid is tannic acid; the mass ratio of the weak acid to the graphene oxide dispersion liquid is 0.05-0.2:1; B) mixing the partially reduced graphene oxide solution with water, and depositing the partially reduced graphene oxide on the surface of a base membrane by vacuum filtration, and drying to obtain a partially reduced graphene oxide membrane; C) immersing the partially reduced graphene oxide membrane in a resin solution, vacuum defoaming, and curing to obtain a green body; The resin solution comprises epoxy resin and a solidifying agent; D) thinning the green body, and polishing to obtain a separation membrane.

2. Use according to claim 1, characterized in that, The preparation method of the graphene oxide dispersion liquid comprises the following steps: a) mixing first concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder, and performing reaction at 75-85 ℃ to obtain graphite pre-oxidant; b) uniformly mixing second concentrated sulfuric acid, the graphite pre-oxidant, potassium permanganate and sodium nitrate at 5-20 ℃, and performing reaction at 30-35 ℃ for 1-5 h; diluting by adding deionized water, and continuously performing reaction at 30-35 ℃ for 1-5 h; adding 30 wt%-35 wt% hydrogen peroxide to terminate the reaction to obtain graphite oxide; c) performing acid washing on the graphite oxide, and then washing with water until neutral, and ultrasonic dispersion of the graphite oxide in water, and centrifugation to obtain graphene oxide dispersion liquid; The concentration of the graphene oxide dispersion liquid is 1-3 g / L.

3. Use according to claim 2, characterized in that, In step a), the mass ratio of the potassium persulfate, the phosphorus pentoxide and the graphite powder is 5-10:5-10:2-10; The use amount ratio of the first concentrated sulfuric acid to the graphite powder is 20-60 mL:2-10 g; After the reaction, the following steps are further included: cooling to 25-35 ℃, diluting by adding deionized water, performing vacuum filtration, washing until neutral, drying to obtain the graphite pre-oxidant.

4. Use according to claim 2, characterized in that, In step b), the mass ratio of the graphite pre-oxidant, the potassium permanganate and the sodium nitrate is 2-10:15-25:2-10; The use amount ratio of the graphite pre-oxidant to the second concentrated sulfuric acid is 2-10 g:20-250 mL.

5. The use according to claim 1, characterized in that, In step A), the time of the reduction reaction is 2-12 h; In step B), the material of the base membrane is cellulose acetate, porous anodic aluminum oxide or nylon; The pore size of the base membrane is 0.22-0.45 μm.

6. Use according to claim 1, characterized in that, In step C), the volume ratio of the epoxy resin to the solidifying agent is 1:2-3; The vacuum degree of the vacuum defoaming is -0.08--0.1 MPa; The time of the curing is 12-24 h.

7. Use according to claim 1, characterized in that, In step D), the thickness of the thinned graphene oxide-resin green body is 0.2-2 μm; The polishing comprises: polishing the upper and lower surfaces of the thinned graphene oxide-resin green body by using metallographic sandpaper with a mesh number of 20 million; The interlayer spacing of the separation membrane is 6.2-7.8 Å.

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