Long-range ordered separation membranes, methods of making and using the same

Abstract

This invention relates to the field of CO2 capture technology, and more particularly to a long-range ordered separation membrane, its preparation method, and its applications. This invention employs a wedge-shaped mold with a suitable angle combined with freeze-drying to prepare a long-range (5-6 cm) and continuous layered graphene oxide framework, ensuring the membrane's separation effect. Simultaneously, a controllable hydrothermal reduction method is used, where the reduction temperature is adjusted to precisely control the degree of reduction of the graphene oxide framework, thereby controlling the interlayer spacing and improving the separation effect. Epoxy resin is used for mechanical fixation. Furthermore, the hydrothermal reduction reaction does not require the introduction of additional environmentally harmful reducing agents, making it simple, fast, and environmentally friendly. The final prepared long-range ordered separation membrane is a multi-channel long-range ordered separation membrane suitable for high-pressure and low-pressure environments, and can be used for the separation of CO2 in CO2 / N2 and CO2 / H2.

Description

Technical Field

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

[0002] CO2 emission reduction is one of the major challenges facing countries worldwide. Currently, the most widely used carbon capture methods include absorption, adsorption, and cryogenic separation. Membrane separation, a relatively new technology that has emerged in the last decade or so, shows promising prospects in the field of CO2 capture due to its advantages such as low energy consumption, high selectivity, no phase change, simple and flexible equipment, and no secondary pollution. Membrane separation processes can be used alone or in combination with other separation technologies to further achieve highly efficient CO2 separation.

[0003] Two-dimensional graphene-based separation membrane materials, as a novel type of nano-carbon material, have been active in the field of two-dimensional layered materials for the past decade. Their main types include perfect lattice graphene membranes, nanoporous graphene membranes, and graphene oxide membranes.

[0004] Perfect-lattice graphene membranes, due to their extremely dense delocalized π-electron clouds occupying the pores of the lattice and being impermeable to all molecules and atoms, have limited applications in separation. Researchers typically prepare nanoporous graphene membranes by introducing nano / sub-nanometer pores of varying sizes onto the surface of monolayer graphene membranes, enabling the selective separation of molecules with different particle sizes. The research group of Zhao Yuliang at the Chinese Academy of Sciences designed a series of porous graphene membranes with different pore sizes and shapes to separate H2 / N2 using molecular dynamics simulations. Their research revealed that the selectivity and permeability of the membrane can be achieved by controlling the shape and size of the pores: when the pore size is larger than H2 molecules but smaller than N2 molecules, 100% separation of H2 from N2 can be achieved (gas permeation rate N2:H2 = 0:10); as the pore size continues to increase, separation of N2 from H2 can be achieved (gas permeation rate N2:H2 = 255:39). The Kumar Varoon Agrawal group at the Swiss Federal Institute of Technology in Lausanne (EPFL) has achieved ultrathin (20 nm) polymer-functionalized monolayer graphene films using ion beam bombardment, resulting in ultra-high CO2 / N2 separation performance: a CO2 flux of 6200 GPU and a CO2 / N2 separation factor of 22.5, surpassing the highest performance of non-promoted transport membranes. However, current pore-forming techniques such as high-energy ion beam bombardment and oxygen plasma etching are costly and immature, making it difficult to avoid problems such as irregular pore sizes and stress concentration that significantly reduce the mechanical strength of the film, thus hindering the large-scale production of qualified nanoporous graphene products.

[0005] Graphene oxide (GO) membranes are two-dimensional layered membranes composed of ordered monolayers of graphene oxide sheets. By controlling the spacing between the sheets, molecules of different sizes can be sieved. The preparation method is simple, low-cost, and can be mass-produced, making it a promising candidate for CO2 separation.

[0006] The interlayer spacing of graphene oxide sheets is related to its oxidation degree; the more oxygen-containing functional groups within a sheet, the larger the interlayer spacing. Under dry conditions, the interlayer spacing of pure graphene oxide sheets is [value missing]. Higher than The molecular dynamic diameter of graphene oxide (QDO) is insufficient for the separation of CO2 / N2 and CO2 / H2 systems. Therefore, some studies have reported the use of reduction methods to reduce the interlayer spacing of graphene oxide. For example, hydrazine hydrate or hydroiodic acid is used as a reducing agent to reduce graphene oxide. However, due to the excessively high reducing power of hydrazine hydrate or hydroiodic acid, it is difficult to achieve precise control of the interlayer spacing over a wide range. The resulting graphene oxide membrane with excessively small interlayer spacing significantly reduces the CO2 permeability of the graphene oxide membrane, thereby decreasing the separation rate.

[0007] Alternatively, graphene oxide can be doped to prepare graphene oxide-based hybrid matrix membranes, thereby modifying the separation membrane and improving the separation effect. 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) and operational stability (>6000 min). Professor Zhang Yatao of Zhengzhou University used a strategy of mild reduction and etching of GO to prepare Pebax-GO hybrid matrix membranes, which exhibited excellent separation performance: CO2 permeability coefficient of 119 Barrer and CO2 / N2 selectivity of 104. Literature reports that graphene-based hybrid matrix membranes have good separation effects in CO2 / N2, but the preparation methods of hybrid matrix membranes are relatively complex, costly, and difficult to scale up, and are difficult to use for CO2 / N2 separation under high pressure conditions. Summary of the Invention

[0008] In view of this, the technical problem to be solved by the present invention is to provide a long-range ordered separation membrane, its preparation method and application, which is suitable for the separation of CO2 in both high-pressure and low-pressure environments.

[0009] This invention provides a method for preparing a long-range ordered separation membrane, comprising the following steps:

[0010] A) Pour the graphene oxide dispersion into a wedge mold with an angle of 15-30°, freeze it, and then vacuum dry it to obtain a layered graphene oxide framework.

[0011] B) The layered graphene oxide framework is subjected to a hydrothermal reaction at 100-175°C to obtain a reduced layered graphene oxide framework.

[0012] C) The reduced layered graphene oxide framework is immersed in a resin solution, defoamed under vacuum, and then cured to obtain a graphene oxide-resin preform.

[0013] The resin solution includes epoxy resin and a coagulant;

[0014] D) The graphene oxide-resin preform is thinned and polished to obtain a long-range ordered separation membrane.

[0015] Preferably, the preparation method of the graphene oxide dispersion includes the following steps:

[0016] a) Mix concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder, and react at 75-85°C to obtain graphite preoxide;

[0017] 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;

[0018] 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.

[0019] The concentration of the graphene oxide dispersion is 1–3 g / L.

[0020] Preferably, in step a), the mass ratio of potassium persulfate, phosphorus pentoxide, and graphite powder is 5-10:5-10:2-10;

[0021] The ratio of the first concentrated sulfuric acid to graphite powder is 20-60 mL: 2-10 g;

[0022] The reaction then includes:

[0023] After cooling to room temperature, deionized water was added for dilution, followed by vacuum filtration, washing until neutral, and drying to obtain graphite preoxide.

[0024] Preferably, in step b), the mass ratio of the graphite preoxide, potassium permanganate, and sodium nitrate is 2-10:15-25:2-10;

[0025] The ratio of graphite preoxide to second concentrated sulfuric acid is 2-10 g: 20-250 mL.

[0026] Preferably, the method for preparing the wedge-shaped mold includes the following steps:

[0027] A square copper sheet or plate is used as the freezing surface, and a Teflon square tube is glued to the freezing surface as a freezing container. The container is placed on an inclined platform with a slope of 15 to 30 degrees, and a mixture including polydimethylsiloxane and curing agent is poured into the freezing container until it just covers the freezing surface. After curing, a wedge mold with an angle of 15 to 30 degrees is obtained.

[0028] The mass ratio of polydimethylsiloxane to curing agent is 8-10:1-2.

[0029] Preferably, in step A), the freezing temperature is -20 to -70°C, and the freezing time is 0.5 to 2 hours;

[0030] The vacuum drying temperature is -60 to -80°C, and the time is 12 to 48 hours.

[0031] Preferably, in step C), the volume ratio of the epoxy resin to the coagulant is 1:2 to 3;

[0032] The vacuum degree of the vacuum defoaming is -0.08 to -0.1 MPa;

[0033] The curing time is 12 to 24 hours.

[0034] Preferably, in step D), the thickness of the thinned graphene oxide-resin preform is 0.2–2 μm;

[0035] The polishing includes:

[0036] The upper and lower surfaces of the thinned graphene oxide-resin preform were polished using metallographic sandpaper with a mesh size of 40 million.

[0037] The interlayer spacing of long-range ordered separation membranes is

[0038] The present invention also provides a long-range ordered separation membrane prepared by the preparation method described above.

[0039] The present invention also provides an application of the long-range ordered separation membrane described above in the field of CO2 separation.

[0040] This invention provides a method for preparing a long-range ordered separation membrane, comprising the following steps: A) pouring a graphene oxide dispersion into a wedge mold with an angle of 15-30°, freezing, and then vacuum drying to obtain a layered graphene oxide framework; B) subjecting the layered graphene oxide framework to a hydrothermal reaction at 100-175°C to obtain a reduced layered graphene oxide framework; C) immersing the reduced layered graphene oxide framework in a resin solution, defoaming under vacuum, and then curing to obtain a graphene oxide-resin preform; the resin solution includes epoxy resin and a coagulant; D) thinning and polishing the graphene oxide-resin preform to obtain a resin-graphene oxide separation membrane, which is the long-range ordered separation membrane. This invention employs a wedge-shaped mold with a suitable angle combined with freeze-drying to prepare a long-range (5-6 cm) and continuous layered graphene oxide framework, ensuring the membrane's separation effect. Simultaneously, a controllable hydrothermal reduction method is used, where the reduction temperature is adjusted to precisely control the degree of reduction of the graphene oxide framework, thereby controlling the interlayer spacing and improving the separation effect. Epoxy resin is used for mechanical fixation. Furthermore, the hydrothermal reduction reaction does not require the introduction of additional environmentally harmful reducing agents, making it simple, fast, and environmentally friendly. The final prepared long-range ordered separation membrane is a multi-channel long-range ordered separation membrane suitable for high-pressure and low-pressure environments, and can be used for the separation of CO2 in CO2 / N2 and CO2 / H2. Attached Figure Description

[0041] Figure 1 A wedge-shaped mold and its manufacturing schematic diagram are provided for one embodiment of the present invention;

[0042] Figure 2 A flowchart illustrating the preparation of a long-range ordered separation membrane according to an embodiment of the present invention;

[0043] Figure 3 This is a SEM image of the side surface of the layered graphene oxide framework prepared in Example 1 of the present invention;

[0044] Figure 4 This is a SEM image of a single sheet within the layered graphene oxide framework prepared in Example 1 of the present invention.

[0045] Figure 5 This is a schematic diagram of the structure of the long-range ordered separation membrane prepared in Example 1 of the present invention.

[0046] Figure 6 The XRD characterization diagrams of the separation membranes in the embodiments and comparative examples of the present invention correspond to (1) - Example 1; (2) - Example 2; (3) - Example 3; (4) - Example 4 and Example 6; (5) - Example 5; (6) - Comparative Example 1; (7) - Comparative Example 2; (8) - Comparative Example 3. Detailed Implementation

[0047] 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.

[0048] This invention provides a method for preparing a long-range ordered separation membrane, comprising the following steps:

[0049] A) Pour the graphene oxide dispersion into a wedge mold, freeze it, and then vacuum dry it to obtain a layered graphene oxide framework.

[0050] B) The layered graphene oxide framework is subjected to a hydrothermal reaction at 100-175°C to obtain a reduced layered graphene oxide framework.

[0051] C) The reduced layered graphene oxide framework is immersed in a resin solution, defoamed under vacuum, and then cured to obtain a graphene oxide-resin preform.

[0052] The resin solution includes epoxy resin and a coagulant;

[0053] D) The graphene oxide-resin preform is thinned and polished to obtain a resin-graphene oxide separation membrane, which is a long-range ordered separation membrane.

[0054] In step A):

[0055] The graphene oxide dispersion was poured into a wedge mold, frozen, and then vacuum dried to obtain a layered graphene oxide framework.

[0056] In some embodiments of the present invention, the preparation method of the graphene oxide dispersion includes the following steps:

[0057] a) Mix concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder, and react at 75-85°C to obtain graphite preoxide;

[0058] 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;

[0059] 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.

[0060] In step a):

[0061] The first concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder are mixed and reacted at 75-85℃ to obtain graphite preoxide.

[0062] Specifically, including:

[0063] 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.

[0064] The stirring speed for obtaining a clear solution is 300–800 rpm, for example, 500 rpm.

[0065] The method of raising the temperature is by water bath heating.

[0066] The mass ratio of potassium persulfate, phosphorus pentoxide, and graphite powder is 5-10:5-10:2-10.

[0067] 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.

[0068] The reaction time is 3 to 10 hours at 75 to 85°C.

[0069] The reaction then includes:

[0070] After cooling to room temperature, the solution is diluted with deionized water, filtered, washed until neutral, and dried 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.

[0071] The drying temperature is 40–70℃, for example, 60℃; the drying time is 12–24 hours, for example, 12 hours.

[0072] In step b):

[0073] 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.

[0074] Specifically, including:

[0075] 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.

[0076] The mass ratio of the graphite preoxide, potassium permanganate, and sodium nitrate is 2-10:15-25:2-10.

[0077] 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%.

[0078] 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.

[0079] The reaction was carried out under water bath heating conditions.

[0080] 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.

[0081] In step c):

[0082] 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.

[0083] 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.

[0084] Deionized water is used for washing.

[0085] The ultrasonic dispersion of graphite oxides in water includes:

[0086] Add graphite oxide to deionized water, stir for 20–40 min, and then ultrasonically disperse for 0.5–2.5 h.

[0087] 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.

[0088] The concentration of the graphene oxide dispersion is 1–3 g / L, for example, 2 g / L.

[0089] After obtaining the graphene oxide dispersion, the graphene oxide dispersion was poured into a wedge mold, frozen, and then vacuum dried to obtain a layered graphene oxide framework.

[0090] The angle of the wedge mold is 15 to 30°, for example, 20°.

[0091] The method for preparing the wedge-shaped mold includes the following steps:

[0092] A square copper sheet (or plate) is used as the freezing surface, and a Teflon square tube is glued to the freezing surface to serve as a freezing container. Placed on an inclined platform with a slope of 15–30°, a mixture including polydimethylsiloxane (PDMS) and a curing agent is poured into the freezing container until it just covers the freezing surface. After curing, a PDMS wedge mold with an angle of 15–30° is obtained. Figure 1 As shown. Figure 1 A wedge mold and its manufacturing process are shown in a schematic diagram according to an embodiment of the present invention.

[0093] The dimensions of the square copper sheet are: side length 50mm, thickness 2mm.

[0094] The Teflon square tube is a square hollow tube with a wall thickness of 3mm. Each side of the Teflon square tube is the same size as the copper sheet.

[0095] Specifically, the dimensions of the Teflon square tube are: 50mm side length, 20mm height, and 3mm thickness.

[0096] The mass ratio of polydimethylsiloxane (PDMS) to curing agent is 8–10:1–2, for example, 10:2. This invention does not impose any special limitations on the composition of the curing agent; it can be a commercially available PDMS standard curing agent. The PDMS can be Dow Corning Sylgard 184.

[0097] The curing time is 10 to 14 hours, for example, 12 hours.

[0098] After obtaining the wedge mold, the graphene oxide dispersion was poured into the wedge mold, frozen, and then vacuum dried to obtain the layered graphene oxide framework.

[0099] The freezing temperature is -20 to -70°C, for example -40°C; the freezing time is 0.5 to 2 hours, for example 0.5 hours. The freezing method is as follows: a wedge mold containing graphene oxide dispersion is placed above an ice-ethanol cold source at -20 to -70°C for freezing.

[0100] The vacuum drying temperature is -60 to -80°C, for example -70°C; the time is 12 to 48 hours. The vacuum drying is carried out in a freeze drying oven.

[0101] This invention uses a freeze-drying method to prepare long-range and continuous layered graphene oxide frameworks. The length of the layered graphene oxide framework is 1–4 cm.

[0102] In step B):

[0103] The layered graphene oxide framework was subjected to a hydrothermal reaction at 100–175 °C to obtain a reduced layered graphene oxide framework.

[0104] Specifically, including:

[0105] Deionized water was added to the polytetrafluoroethylene liner of the hydrothermal reactor, a polytetrafluoroethylene circular substrate was placed inside, the layered graphene oxide framework was placed on the substrate, the hydrothermal reactor was sealed, and a hydrothermal reaction was carried out at 100-175°C to obtain a partially reduced layered graphene oxide framework, that is, the graphene oxide was partially reduced.

[0106] The volume of the hydrothermal reactor is 200 mL.

[0107] 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 10 to 30 mL.

[0108] The hydrothermal reaction is carried out at temperatures of 100℃, 140℃, 150℃, 160℃, and 170℃, for a duration of 1.5 to 2 hours, for example, 2 hours.

[0109] The hydrothermal reaction does not require the introduction of a reducing agent.

[0110] The hydrothermal reaction also includes:

[0111] The hydrothermal reactor was cooled with room temperature water, and the reacted framework material was removed and dried at room temperature to obtain the reduced layered graphene oxide framework.

[0112] The drying time is 24 to 48 hours, for example, 48 hours.

[0113] In step C):

[0114] The reduced layered graphene oxide framework is immersed in a resin solution, defoamed under vacuum, and then cured to obtain a graphene oxide-resin preform.

[0115] In some embodiments of the present invention, the resin solution is placed in a mold. The mold is made of polyethylene.

[0116] The resin solution comprises epoxy resin and a coagulant. The epoxy resin is used for mechanical fixing. In some embodiments of the present invention, the epoxy resin is TDE-85 type epoxy resin, sourced from Guangzhou Qian'an Chemical Co., Ltd. The coagulant is a polyamide curing agent, such as polyamide 650 or polyamide 651.

[0117] The volume ratio of the epoxy resin to the coagulant is 1:2 to 3, for example, 1:2.

[0118] The vacuum degree of the vacuum defoaming is -0.08 to -0.1 MPa, specifically 0.08 MPa.

[0119] The curing time is 12 to 24 hours.

[0120] After curing, the process further includes removing the graphene oxide-resin preform from the mold.

[0121] In step D):

[0122] The graphene oxide-resin preform is thinned and polished to obtain a resin-graphene oxide separation membrane, which is a long-range ordered separation membrane.

[0123] The thinning process is performed using a grinding and polishing machine.

[0124] The thickness of the thinned graphene oxide-resin preform is 0.2–2 μm, for example, 0.2 μm.

[0125] The polishing includes:

[0126] The upper and lower surfaces of the thinned graphene oxide-resin preform were polished using 40 million grit metallographic sandpaper. This process was used to fully expose the sides of the reduced graphene oxide film.

[0127] The resin-graphene oxide separation membrane prepared by this invention can maintain its order over a relatively long length range (1-4 cm), which is a long-range ordered separation membrane.

[0128] The interlayer spacing d of the resin-graphene oxide 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) 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. In addition, the hydrothermal reduction reaction does not require the introduction of additional reducing agents that are harmful to the environment, making it simple, fast, green and environmentally friendly, and also enabling precise control of the degree of graphene oxide reduction.

[0129] Figure 2 A flowchart illustrating the preparation of a long-range ordered separation membrane according to an embodiment of the present invention.

[0130] This invention also provides a long-range ordered separation membrane prepared by the method described above. The long-range ordered separation membrane is a multi-channel (each layer in the framework is a channel) long-range ordered separation membrane, suitable for high-pressure and low-pressure environments, and can be used for the separation of CO2 in CO2 / N2 and CO2 in CO2 / H2. In some embodiments of this invention, the long-range ordered separation membrane can perform separation at 0.1–2 MPa, specifically at 2 MPa and 0.1 MPa.

[0131] This invention also provides an application of the long-range ordered separation membrane described above in the field of CO2 separation. Specifically, it provides an application of the long-range ordered separation membrane for CO2 separation.

[0132] 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.

[0133] 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 or a CO2 / H2 mixture, with a pressure range of 0.1–5.0 MPa, such as 0.1 MPa or 2 MPa. The permeate-side pressure is atmospheric pressure, and the purge gas is helium or argon. When the feed gas is a CO2 / N2 mixture, the purge gas is helium; when the feed gas is a CO2 / H2 mixture, the purge gas is 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.

[0134] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0135] To further illustrate the present invention, the following detailed description of a long-range ordered 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.

[0136] Example 1

[0137] 1) Preparation of graphene oxide dispersion:

[0138] 1-1) 50 mL of concentrated sulfuric acid (98% by mass), 8.0 g of potassium persulfate, and 8.0 g of phosphorus pentoxide were added sequentially to a round-bottom flask and stirred (500 rpm) to obtain a clear solution. After heating to 80 °C in a water bath, 4.0 g of natural graphite powder (200 mesh) was added and reacted at 80 °C for 5 h. After the reaction was completed, the solution was cooled to room temperature, diluted with 200 mL of deionized water, filtered, washed until neutral, and dried at 60 °C for 12 h to obtain graphite preoxide.

[0139] 1-2) Weigh 140 mL of concentrated sulfuric acid (98% by mass) 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.

[0140] 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 100 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 2 g / L.

[0141] 2) Preparation of long-range ordered layered graphene oxide framework by freeze-drying:

[0142] 2-1) Preparation of wedge mold: A square copper sheet (50mm side length, 2mm thickness) is used as the freezing surface. A Teflon square tube (50mm side length, 20mm height, 3mm thickness) is attached to the copper sheet as a reaction container. The container is placed on an inclined platform with a slope of 20°. A mixture of polydimethylsiloxane (PDMS) and curing agent (the mass ratio of PDMS to curing agent is 10:2) is poured into the reaction container until it just covers the surface of the copper sheet. After curing for 12 hours, a PDMS wedge mold with an angle of 20° is obtained.

[0143] 2-2) Pour the above 2 g / L graphene oxide dispersion (GO dispersion) into the PDMS wedge mold, place it above the -40℃ ice ethanol cold source, freeze for 0.5 h, then transfer the PDMS wedge mold to a freeze dryer and vacuum dry at -70℃ for 24 h to obtain a long-range ordered layered graphene oxide framework.

[0144] Figure 3 This is a SEM image of the side surface of the layered graphene oxide framework prepared in Example 1 of the present invention. Figure 3 It can be seen that each layer inside the skeleton maintains long-range order within the field of view.

[0145] Figure 4 This is a SEM image of a single sheet within the layered graphene oxide framework prepared in Example 1 of the present invention. The sheet is defect-free and has good continuity.

[0146] 3) Preparation of reduced layered graphene oxide framework:

[0147] 10 mL of deionized water was added to the polytetrafluoroethylene (PTFE) liner of a 200 mL hydrothermal reactor. A circular PTFE substrate was then placed inside, and the layered graphene oxide framework was placed on the substrate. The hydrothermal reactor was sealed, and the reaction was carried out at 100 °C for 2 hours. After the reaction was completed, the hydrothermal reactor was cooled with room temperature water. The reacted framework material was then removed and dried at room temperature for 48 hours to obtain the reduced layered graphene oxide framework.

[0148] 4) Resin-encapsulated reduced layered graphene oxide framework:

[0149] A resin solution was prepared by mixing epoxy resin (TDE-85 type epoxy resin from Guangzhou Qian'an Chemical Co., Ltd.) and coagulant (polyamide 650) at a volume ratio of 1:2. The solution was poured into a polyethylene mold with a diameter of 8 cm. The reduced layered graphene oxide skeleton was then immersed in the resin solution. After vacuum defoaming at 0.08 MPa, the resin solidified for 18 hours. The graphene oxide-resin preform was then removed from the mold.

[0150] The graphene oxide-resin preform was thinned to 0.2 μm using a polishing machine. Then, the upper and lower surfaces of the thinned graphene oxide-resin preform were polished with 40 million grit metallographic sandpaper to fully expose the sides of the reduced graphene oxide film, thus obtaining a resin-encapsulated partially reduced graphene oxide separation membrane (resin-graphene oxide separation membrane) with an interlayer spacing of [missing information]. This is a long-range ordered separation membrane.

[0151] Figure 5 This is a schematic diagram of the structure of the long-range ordered separation membrane prepared in Example 1 of the present invention. Figure 5 (a) in the diagram is a schematic diagram of gas transport in a traditional graphene oxide membrane. Figure 5 (b) in the diagram is a schematic diagram of gas transport in a partially reduced graphene oxide film fixed with epoxy resin. From... Figure 5 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.

[0152] 5) Application of the resin-graphene oxide separation membrane prepared in Example 1 in the field of CO2 separation:

[0153] Specifically, the steps for separating CO2 using the resin-graphene oxide separation membrane include:

[0154] Performance testing was conducted using a membrane performance evaluation device (MGPT-Ⅰ type, Dalian Karibona Technology Co., Ltd.). The feed gas was first humidified to saturation in a humidification tank before entering the membrane chamber for testing. The feed gas was either a CO2 / N2 mixture or a CO2 / H2 mixture. When the feed gas was a CO2 / N2 mixture, the purge gas was helium; when the feed gas was a CO2 / H2 mixture, the purge gas was argon. The pressure was 0.1 MPa, and the permeate-side pressure was atmospheric pressure. The permeate-side 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.

[0155] Example 2

[0156] The difference from Example 1 is as follows:

[0157] In step 3), the reaction temperature is 140℃ and the time is 2h.

[0158] The final partially reduced graphene oxide separation membrane encapsulated in resin (resin-graphene oxide separation membrane) has a layer spacing of [missing information].

[0159] CO2 was separated according to the method in Example 1.

[0160] Example 3

[0161] The difference from Example 1 is as follows:

[0162] In step 3), the reaction temperature is 150℃ and the time is 2h.

[0163] The final partially reduced graphene oxide separation membrane encapsulated in resin (resin-graphene oxide separation membrane) has a layer spacing of [missing information].

[0164] CO2 was separated according to the method in Example 1.

[0165] Example 4

[0166] The difference from Example 1 is as follows:

[0167] In step 3), the reaction temperature is 160℃ and the time is 2h.

[0168] The final partially reduced graphene oxide separation membrane encapsulated in resin (resin-graphene oxide separation membrane) has a layer spacing of [missing information].

[0169] CO2 was separated according to the method in Example 1.

[0170] Example 5

[0171] The difference from Example 1 is as follows:

[0172] In step 3), the reaction temperature is 170℃ and the time is 2h.

[0173] The final partially reduced graphene oxide separation membrane encapsulated in resin (resin-graphene oxide separation membrane) has a layer spacing of [missing information].

[0174] CO2 was separated according to the method in Example 1.

[0175] Example 6

[0176] The difference from Example 4 is as follows:

[0177] The pressure is 2 MPa during CO2 / N2 separation.

[0178] Comparative Example 1

[0179] The difference from Example 1 is as follows:

[0180] In step 3), the reaction temperature is 180℃ and the time is 2h.

[0181] The final partially reduced graphene oxide separation membrane encapsulated in resin (resin-graphene oxide separation membrane) has a layer spacing of [missing information].

[0182] CO2 was separated according to the method in Example 1.

[0183] Comparative Example 2

[0184] The difference from Example 1 is as follows:

[0185] (Does not contain step 3);

[0186] Step 4) The layered graphene oxide framework obtained in step 2) is used directly;

[0187] The final interlayer spacing of the resin-encapsulated separation membrane is

[0188] CO2 was separated according to the method in Example 1.

[0189] Comparative Example 3

[0190] The difference from Example 1 is as follows:

[0191] The graphene oxide is reduced using hydrazine hydrate. Specifically, steps 2) and 3) are replaced with:

[0192] Take 20 mL of graphene oxide dispersion, adjust the pH to 9 with NaOH, add 1 mL of 85% hydrazine hydrate, and stir in a 95°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.

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

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

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

[0196] The separation performance test results of the separation membranes prepared in Examples 1-6 and Comparative Examples 1-3 are shown in Table 1.

[0197] Table 1. Evaluation results of the separation performance of the separation membranes in Examples 1-6 and Comparative Examples 1-3.

[0198]

[0199] From Table 1 and Figure 6 It can be seen that the graphene oxide in Examples 1-5 was partially reduced (see...). Figure 6 XRD characterization was performed, and the diffraction peaks of graphene oxide were known. The interlayer spacing could be calculated using the Bragg equation 2dsinθ=nλ. The graphene oxide in Comparative Example 2 was not reduced, while the graphene oxide in Comparative Example 1 and Comparative Example 3 was completely reduced.

[0200] As shown in Table 1, the controllable reduction of graphene oxide can be achieved by adjusting the temperature of hydrothermal reduction. By controlling the degree of reduction, graphene oxide films with different interlayer spacings can be obtained, thus achieving the optimal sieving effect. However, when the hydrothermal temperature is too high, all the graphene oxide is reduced, and the graphene oxide film loses its sieving effect.

[0201] As shown in Examples 1-4, with the increase of hydrothermal temperature, the degree of reduction of graphene oxide increases, 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... (Example 4), its effective interlayer spacing is in The electron cloud thickness of a single layer of graphene is shown in Example 5. Since this interlayer spacing is smaller than that of an N2 molecule but larger than that of a CO2 molecule, it achieves optimal separation. As shown in Example 5, as the hydrothermal temperature continues to increase, the degree of reduction of graphene oxide continues to increase, and the interlayer spacing further decreases. Its effective interlayer spacing is The CO2 permeation rate decreases rapidly. At this point, the interlayer spacing of the partially reduced graphene oxide membrane is smaller than that of N2 and CO2, but larger than that of H2. This results in poor separation of N2 / CO2, but optimal separation performance for CO2 / H2, achieving highly efficient CO2 / H2 separation. As shown in Example 6, compared to Example 4, under 2MPa high pressure, the interlayer spacing is... The graphene oxide membrane also exhibits good CO2 permeation rate and selectivity, but its performance decreases compared to low pressure. Comparative Examples 1 and 3 show that when graphene oxide is completely reduced, the permeation rate of the graphene oxide membrane drops sharply, and its sieving performance is poor. In summary, the partially reduced graphene oxide membrane can achieve both good separation effect and permeation performance. Specifically, the partially reduced graphene oxide membrane provided in Example 4 exhibits the best CO2 / N2 separation performance; the partially reduced graphene oxide membrane provided in Example 5 exhibits the best CO2 / H2 separation performance.

[0202] 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. A method for preparing a long-range ordered separation membrane, comprising the following steps: A) Pour the graphene oxide dispersion into a wedge mold with an angle of 15-30°, freeze it, and then vacuum dry it to obtain a layered graphene oxide framework. B) The layered graphene oxide framework is subjected to a hydrothermal reaction at 100-175°C to obtain a reduced layered graphene oxide framework. C) The reduced layered graphene oxide framework is immersed in a resin solution, defoamed under vacuum, and then cured to obtain a graphene oxide-resin preform. The resin solution includes epoxy resin and a coagulant; D) The graphene oxide-resin preform is thinned and polished to obtain a long-range ordered separation membrane.

2. The preparation method according to claim 1, characterized in that, The preparation method of the graphene oxide dispersion includes the following steps: a) Mix concentrated sulfuric acid, potassium persulfate, phosphorus pentoxide and graphite powder, and react at 75-85°C to obtain graphite preoxide; 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; 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. The concentration of the graphene oxide dispersion is 1–3 g / L.

3. The preparation method according to claim 2, characterized in that, In step a), the mass ratio of potassium persulfate, phosphorus pentoxide, and graphite powder is 5-10:5-10:2-10; The ratio of the first concentrated sulfuric acid to graphite powder is 20-60 mL: 2-10 g; The reaction then includes: After cooling to room temperature, deionized water was added for dilution, followed by vacuum filtration, washing until neutral, and drying to obtain graphite preoxide.

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

5. The preparation method according to claim 1, characterized in that, The method for preparing the wedge-shaped mold includes the following steps: A square copper sheet or plate is used as the freezing surface, and a Teflon square tube is glued to the freezing surface as a freezing container. The container is placed on an inclined platform with a slope of 15 to 30 degrees, and a mixture including polydimethylsiloxane and curing agent is poured into the freezing container until it just covers the freezing surface. After curing, a wedge mold with an angle of 15 to 30 degrees is obtained. The mass ratio of polydimethylsiloxane to curing agent is 8-10:1-2.

6. The preparation method according to claim 1, characterized in that, In step A), the freezing temperature is -20 to -70°C, and the freezing time is 0.5 to 2 hours. The vacuum drying temperature is -60 to -80°C, and the time is 12 to 48 hours.

7. The preparation method according to claim 1, characterized in that, In step C), the volume ratio of the epoxy resin to the coagulant is 1:2 to 3; The vacuum degree of the vacuum defoaming is -0.08 to -0.1 MPa; The curing time is 12 to 24 hours.

8. The preparation method according to claim 1, characterized in that, In step D), the thickness of the thinned graphene oxide-resin preform is 0.2–2 μm; The polishing includes: The upper and lower surfaces of the thinned graphene oxide-resin preform were polished using metallographic sandpaper with a mesh size of 40 million. The interlayer spacing of long-range ordered separation membranes is 9. The long-range ordered separation membrane prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the long-range ordered separation membrane according to claim 9 in the field of CO2 separation.

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