Preparation of highly stable hydrated covalent organic framework membranes and their application in natural gas decarburization

Abstract

The application discloses a kind of high stability hydrated covalent organic framework films, the hydrated covalent organic framework film includes ionic covalent organic framework and self-supporting flexible substrate, and is prepared by vacuum assisted self-assembly method, film thickness is less than 100nm, film aperture is 2±0.2nm;Covalent organic framework is the nanosheet of aldehyde group monomer 1,3,5-tricarbonyl phloroglucinol and amino monomer 4,4'-diamino-3.3'-diphenyl disulfonic acid is polymerized by phase transfer method.The application of the film in natural gas decarburization is that the film is used in wet natural gas purification system, and the CO2 / CH4 separation process has high flux, high selectivity, can tolerate H2S, heavy hydrocarbon (C2H6, C3H8, n-C4H 10 , n-C6H 14 , etc.) and other multi-component conditions and up to 33bar pressure, and also has excellent separation performance for H2S / CH4, and the separation performance of the film does not change significantly in the saturated vapor of C6H 14 , C7H8, C8H 10 (n-hexane partial pressure ≥20kPa).

Description

Technical Field

[0001] This invention relates to the preparation of gas separation membranes, and more particularly to a highly stable hydrated covalent organic framework membrane for use in natural gas decarbonization. Background Technology

[0002] Natural gas refers to a mixture of hydrocarbons (mainly CH4) and non-hydrocarbon substances found in underground strata. Using natural gas for power generation can reduce CO2 emissions by up to 60%, and when used for combustion, its CO2 emissions are approximately 41% and 26% lower than coal and oil, respectively. Globally, about one-quarter of energy is provided by natural gas, and this proportion is expected to continue to grow. In addition to the main component CH4, natural gas feedstock typically contains various impurity gases such as CO2, hydrogen sulfide (H2S), water vapor, and C2-C6 hydrocarbons. CO2 is the main impurity component; its presence reduces the calorific value of natural gas and shortens the lifespan of transportation pipelines, therefore CO2 removal is essential. Currently, industrial CO2 / CH4 separation is achieved through absorption, which requires a two-step process of absorption and desorption, and the desorption process is energy-intensive. The absorption method also faces problems such as equipment corrosion, absorbent passivation, and pre-absorbent leakage, which pollutes the environment. Membrane separation technology for CO2 / CH4 separation has lower energy consumption compared to absorption methods, and it offers continuous operation, smaller footprint, and higher operational flexibility, making it a key technology for CO2 / CH4 separation development.

[0003] Membrane materials are the core of membrane technology. Covalent organic frameworks (COFs), with their long-range ordered channels, high-density tunable functional sites, and rigid, stable framework structure, have shown great potential in natural gas purification. However, most COF channels are generally larger than 1.0 nm, which is larger than the molecular size of CO2 and CH4, making it difficult to achieve separation processes based on mechanisms such as molecular sieving commonly used in porous membranes. How to achieve efficient separation of small molecule mixtures based on the macropores of COFs is a crucial problem that must be solved for their application in gas separation membranes.

[0004] Studies have shown that the solubility difference between CO2 and CH4 in bulk water at room temperature is more than 20 times. In some nanochannels, water can act as an adsorption site for CO2 while reducing the adsorption of inert gases such as CH4. It has been demonstrated that ionic COFs have extremely high ion exchange capacities, and the ionic groups within the channels are orderly distributed. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a highly stable hydrated covalent organic framework membrane, which is used in natural gas decarbonization. The preparation method of the highly stable hydrated covalent organic framework membrane of the present invention is simple and controllable, and the prepared membrane can be used in the CO2 / CH4 separation process, with high separation performance and stability.

[0006] To address the aforementioned technical problems, this invention proposes a highly stable hydrated covalent organic framework membrane, comprising an ionic covalent organic framework and a self-supporting flexible substrate, prepared by a vacuum-assisted self-assembly method. The membrane thickness is less than 22-100 nm, and the pore size is 2 ± 0.2 nm. The ionic covalent organic framework is TpBD-(SO3Na)2, which is a nanosheet polymerized from an aldehyde monomer and an amino monomer via a phase transfer method. The aldehyde monomer is 1,3,5-trimethylaldehyde phloroglucinol, and the amino monomer is 4,4'-diamino-3,3'-biphenyl disulfonic acid.

[0007] The specific steps of the preparation method of the highly stable hydrated covalent organic framework membrane are as follows:

[0008] Step 1) Dissolve 1,3,5-tricarboxymethyl-resorcinol in octanoic acid to prepare an octanoic acid solution with a concentration of 0.01 mmol / mL, denoted as solution A; dissolve 4,4'-diamino-3,3'-biphenyl disulfonic acid and sodium carbonate in deionized water to prepare an aqueous solution of sodium 4,4'-diamino-3,3'-biphenyl disulfonic acid with a concentration of 0.01 mmol / mL, denoted as solution B; using solutions A and B, prepare an ionic nanosheet dispersion with a concentration of 3.0 ± 0.1 mg / mL through a phase transfer polymerization reaction;

[0009] Step 2) Take the ionic nanosheet dispersion prepared in Step 1) and dilute it with deionized water to a concentration of 3.0±0.1mg / L. Then, use a vacuum-assisted self-assembly method to prepare a film on a polyacrylonitrile substrate with a molecular weight cutoff of 100,000.

[0010] Furthermore, in the preparation method described in this invention, wherein:

[0011] Step 1) specifically involves: dissolving 1,3,5-tricarboxaldehyde-resorcinol in octanoic acid at a molar volume ratio of 0.01 mmol / mL, and stirring at 700 rpm for 20 min at 40°C to prepare solution A; dissolving 4,4'-diamino-3,3'-biphenyl disulfonic acid and sodium carbonate in deionized water, wherein the molar volume ratio of 4,4'-diamino-3,3'-biphenyl disulfonic acid to deionized water is 0.01 mmol / mL, and the molar volume ratio of sodium carbonate to deionized water is 0.02 mmol / mL, and stirring at 700 rpm for 20 min at room temperature to prepare solution A. Solution B was obtained; solution B was added to a container, and solution A was added to the liquid surface at a rate of 2 mL / min to form an interface layer, wherein the molar ratio of 1,3,5-tricarboxaldehyde-resorcinol to 4,4'-diamino-3,3'-biphenyl disulfonic acid was 2:3; the reaction system was allowed to stand at 60°C for 30 days; then, the upper octanoic acid phase of the reaction system after standing was removed, and the lower aqueous phase was dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 30,000, with the deionized water being changed every 8 hours; the final orange-yellow nanosheet dispersion was the ionic nanosheet dispersion.

[0012] In step 2), when preparing a film on a polyacrylonitrile substrate with a molecular weight cutoff of 100,000 using a vacuum-assisted self-assembly method, the amount of the diluted ionic nanosheet dispersion is 8.75-875 μg / cm², based on the mass-to-area ratio of nanosheets to film area. 2 count.

[0013] The application of the highly stable hydrated covalent organic framework membrane prepared by the method of this invention in natural gas decarbonization, i.e., in the purification of wet natural gas, includes one or more of the following:

[0014] Scenario 1, by Figure 6 It can be seen that, for the separation of CO2 from the CO2 / CH4 mixed gas system, under the conditions of 25℃, CO2 / CH4 molar ratio of 3 / 7, pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux is 1303 GPU and the selectivity is 36; at 33 bar, the CO2 flux is higher than 800 GPU and the CO2 / CH4 selectivity is higher than 33.

[0015] Scenario 2, by Figure 7It can be seen that for the separation of the H2S / CO2 / CH4 mixed gas system, under the conditions of 25℃, a molar ratio of H2S / CO2 / CH4 of 10 / 20 / 70, a pressure of 2 bar, and 100% relative humidity: the CO2 permeation flux is 1468 GPU, and the CO2 / CH4 selectivity is higher than 34.0; the H2S permeation flux is 3287 GPU, and the H2S / CH4 selectivity is 77.3; under the conditions of 25℃, a molar ratio of H2S / CO2 / CH4 of 10 / 20 / 70, a pressure of 5 bar, and 100% relative humidity: the CO2 permeation flux is 1447 GPU, and the selectivity is 31.

[0016] Scenario 3, by Figure 8 It can be seen that it is used for different heavy hydrocarbon components containing 2% C2H6, C3H8, and n-C4H 10 Under conditions of 25℃, a CO2 / CH4 molar ratio of 3 / 7, a pressure of 2 bar, and a relative humidity of 100%, the membrane CO2 permeation flux exceeded 1250 GPU, the selectivity exceeded 34.6%, and the separation performance showed no significant decline, with a decline percentage of less than 8%. Figure 9 It can be seen that in C6H 14 C7H8, C8H 10 In saturated vapor with hexane partial pressure ≥20 kPa, at 25°C, with a CO2 / CH4 molar ratio of 3 / 7, a pressure of 2 bar, and a relative humidity of 100%, the membrane CO2 permeation flux exceeded 1290 GPU, the selectivity exceeded 36, and the separation performance showed no significant decline, with a decline percentage of less than 3.4%.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] Compared to absorption technology, membrane technology for natural gas decarbonization consumes less energy and causes less environmental pollution. Among existing membrane technologies, polymer membranes based on dissolution-diffusion mechanisms suffer from a trade-off effect between permeability and selectivity, making it difficult to achieve high performance. Furthermore, most polymer membranes experience a significant performance decline under high pressure due to plasticization, an effect exacerbated by the presence of H2S. Polymer membranes based on transport-enhancing mechanisms exhibit excellent performance at low pressures, but their performance drops sharply with increasing pressure. Inorganic membranes such as zeolite membranes and CMS membranes possess high separation performance and remain stable at higher pressures, but when the separated system contains impurities such as heavy hydrocarbons and water vapor, the inorganic membrane mass transfer channels become clogged, leading to a significant performance degradation. Moreover, the rigid structure of inorganic membranes makes large-area, defect-free fabrication difficult, limiting their further application. Blending inorganic fillers with polymers to prepare mixed-matrix membranes can balance processability and separation performance, but currently prepared mixed-matrix membranes are all self-supporting thick membranes of tens of micrometers, rather than ultrathin composite membranes at the submicron level. Even after being fabricated into ultrathin composite membranes, hybrid matrix membranes still face problems such as decreased separation performance and processing defects.

[0019] In comparison, the highly stable hydrated covalent organic framework membrane prepared by this invention possesses both high permeability and high selectivity, while maintaining stable high performance under complex and harsh conditions such as high pressure and the presence of heavy hydrocarbons, water vapor, and H2S. It can also achieve efficient H2S / CH4 separation simultaneously and can be fabricated into different types such as flat sheet membranes and hollow fiber membranes. Therefore, the highly stable hydrated covalent organic framework membrane of this invention combines high separation performance, strong stability, and ease of processing. Attached Figure Description

[0020] Figure 1-1 and Figure 1-2 This is a schematic diagram of the structure of the aldehyde monomer and amino monomer used to prepare ionic covalent organic frameworks;

[0021] Figure 2 This is an electron microscope image of the surface of film 1;

[0022] Figure 3 This is a cross-sectional electron microscope image of membrane 1;

[0023] Figure 4 This is a diagram showing the channel size distribution of membrane 1;

[0024] Figure 5 This is a comparison chart of CO2 permeation flux and CO2 / CH4 selectivity performance between membrane 1 and comparison membranes 1-3;

[0025] Figure 6 This is a comparison chart of CO2 permeation flux and CO2 / CH4 selectivity of membrane 1 at 25℃ and 2 to 33 bar.

[0026] Figure 7 The permeation fluxes of membrane 1 at 25°C, 2 to 5 bar, and feed gas ratios of H2S / CO2 / CH4 (10 / 20 / 70 mol%) are H2S and CO2 permeation fluxes, as well as H2S / CH4 and CO2 / CH4 selectivity.

[0027] Figure 8 Membrane 1 is at 25°C and 2 bar, in C2H6, C3H8, and n-C4H 10 CO2 / CH4 separation performance in the presence of heavy hydrocarbons.

[0028] Figure 9 Membrane 1 was subjected to a temperature of 25°C and 2 bar at C6H. 14 C7H8, C8H 10 CO2 / CH4 separation performance in the presence of saturated vapor of heavy hydrocarbons (hexane partial pressure ≥20kPa). Detailed Implementation

[0029] This invention proposes a highly stable hydrated covalent organic framework membrane for application in natural gas decarbonization, specifically in the natural gas separation process. The ionic covalent organic framework membrane possesses extremely high ion exchange capacity, and the ionic groups within the channels are orderly distributed, enabling the adsorption of water vapor from wet natural gas to form hydrated channels within the membrane, thus achieving effective construction of the hydrated covalent organic framework membrane. By changing the monomer type to modify the channel size and ionic group types of the covalent organic framework membrane, the optimal monomer types are Tp (1,3,5-tricarboxaldehyde-resorcinol) and BD-(SO3H)2 (4,4'-diamino-3,3'-biphenyl disulfonic acid), thereby regulating the hydrated channel structure and influencing CO2 mass transfer. Due to its large channel size, the water within the channel can serve as a mass transfer medium for gas molecules, enabling efficient CO2 / CH4 separation based on the differences in dissolution and diffusion of gas molecules within the bound water network. Based on its fully organic structure within a hydrated covalent organic framework, the membrane remains stable in the presence of H2S and can efficiently separate H2S / CH4. The bound water network exhibits strong polarity, readily separating C2H6, C3H8, and n-C4H4 molecules. 10 n-C6H 14 Heavy hydrocarbons are not adsorbed, therefore the membrane performance does not significantly decrease in the presence of heavy hydrocarbons; the membrane separation performance also does not change significantly in saturated vapors of hexane, toluene, and p-xylene (hexane partial pressure ≥20 kPa). Based on the rigid structure of the highly stable hydrated covalent organic framework membrane and the stable bound water network, the membrane exhibits strong stability under high pressure.

[0030] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The specific implementation examples described are only for explanation and illustration of the present invention and are not intended to limit the present invention.

[0031] Example:

[0032] The steps for preparing the TpBD-(SO3Na)2 membrane are as follows:

[0033] Step 1) Using Tp (whose structure is as follows) Figure 1-1 (as shown) and BD-(SO3H)2 (whose structure is as shown) Figure 1-2 The above describes the preparation of a 4,4'-diamino-3,3'-biphenyl disulfonate sodium nanosheet (TpBD-(SO3Na)2) dispersion via phase transfer polymerization of monomers. The steps are as follows:

[0034] 0.2 mmol Tp was dissolved in 20 mL of octanoic acid and stirred at 700 rpm for 20 min at 40 °C to prepare an octanoic acid solution with a concentration of 0.01 mmol / mL Tp.

[0035] 0.3 mmol of BD-(SO3H)2 and 0.6 mmol of Na2CO3 were dissolved in 30 mL of deionized water and stirred at room temperature for 20 min to prepare an aqueous solution of BD-(SO3Na)2 with a concentration of 0.01 mmol / mL.

[0036] Add 30 mL of BD-(SO3Na)2 aqueous solution to a 100 mL beaker, and slowly add 20 mL of Tp octanoic acid solution to the surface of the liquid at a rate of 2 mL / min to form an interface layer; let the reaction system stand at 60 °C for 30 days.

[0037] After standing, the upper octanoic acid phase of the reaction system was removed, and the lower aqueous phase was dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 30,000, with the deionized water being changed every 8 hours. Finally, an orange-yellow TpBD-(SO3Na)2 nanosheet dispersion was obtained. By drying the nanosheets and weighing the residual solids, the concentration of TpBD-(SO3Na)2 nanosheets was found to be approximately 3.1 mg / mL.

[0038] Step 2): TpBD-(SO3Na)2 membrane was prepared by vacuum-assisted self-assembly.

[0039] Take 20 μL of the TpBD-(SO3Na)2 nanosheet dispersion prepared in step 1) and dilute it to 20 mL with deionized water. Then, prepare a film on a polyacrylonitrile substrate with a molecular weight cutoff of 100,000 and a diameter of about 1.5 cm by vacuum-assisted self-assembly to obtain a yellow TpBD-(SO3Na)2 film, which is denoted as film 1. Figure 2 and Figure 3 Electron microscopy images of the surface and cross-section of membrane 1 are shown, revealing a thickness of 22 nm. The pore size, obtained from gas adsorption data, is approximately 2.2 nm. Figure 4 As shown.

[0040] Membrane 1 was used in a CO2 / CH4 separation system. At 25°C and a feed gas pressure of 2 bar, the CO2 permeation flux was 1303 GPU, and the selectivity was 36. Figure 5 As shown. At 33 bar, the CO2 permeation flux is 805 GPUs, and the selectivity is 33, as... Figure 6 As shown, this demonstrates the membrane's potential for high-pressure resistance. Furthermore, due to strong covalent bonding, the covalent organic framework membrane remains stable in natural gas containing hydrogen sulfide. Using a H2S / CO2 / CH4 (10 / 20 / 70 mol%) mixture as feed gas, tests were conducted at 100% relative humidity. At 2 bar, the TpBD-(SO3Na)2 membrane exhibited a CO2 permeation flux of 1468 GPU and a CO2 / CH4 selectivity higher than 34.0. Figure 7 As shown. The bound water network exhibits strong polarity, acting on C2H6, C3H8, and n-C4H... 10 n-C6H 14 Heavy hydrocarbons are not adsorbed; therefore, the membrane performance does not significantly degrade in the presence of heavy hydrocarbons, such as... Figure 8 As shown. Figure 9 This shows the membrane 1 at 25°C and 2 bar in C6H. 14 C7H8, C8H 10 CO2 / CH4 separation performance in the presence of saturated vapor of heavy hydrocarbons (hexane partial pressure ≥20kPa).

[0041] Comparative Example 1:

[0042] The preparation of the TpPa-(SO3Na)2 membrane was basically the same as that of Example 1, except that in step 1), 0.1 mmol of Tp was dissolved in 20 mL of octanoic acid and stirred at 40 °C for 20 min to prepare an octanoic acid solution with a concentration of 0.005 mmol / mL of Tp; 0.15 mmol of 2,5-diamino-1,4-benzenedisulfonic acid Pa-(SO3H)2 and 0.6 mmol of Na2CO3 were dissolved in 30 mL of deionized water and stirred at room temperature for 20 min to prepare an aqueous solution of sodium 2,5-diamino-1,4-benzenedisulfonic acid (Pa-(SO3Na)2) with a concentration of 0.005 mmol / mL; the final ionic covalent organic framework Pa-(SO3Na)2 membrane was designated as control membrane 1.

[0043] When control membrane 1 was used in a CO2 / CH4 separation system at 25°C and a feed gas pressure of 2 bar, the CO2 permeation flux was 178 GPU and the selectivity was 63.8. Figure 5 As shown.

[0044] Comparative Example 2:

[0045] The preparation of TpBD-(COONa)2 membrane was basically the same as that of Example 1, except that in step 1), 0.3 mmol of BD-(COOH)2 (4,4'-diaminobiphenyl-2,2'-dicarboxylic acid) and 0.6 mmol of NaOH were dissolved in 30 mL of deionized water and stirred at room temperature for 20 min to prepare an aqueous solution of 0.01 mmol / mL amino monomer BD-(COONa)2 (sodium 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid). The resulting ionic covalent organic framework TpBD-(COONa)2 membrane was designated as control membrane 2.

[0046] When the control membrane 2 was used in a CO2 / CH4 separation system at 25°C and a feed gas pressure of 2 bar, the CO2 permeation flux was 2273 GPU and the selectivity was 3.3. Figure 5 As shown.

[0047] Comparative Example 3:

[0048] The preparation of the TpDS-(SO3H)2 membrane was basically the same as that of Example 1, except that in step 1-1), 0.1 mmol of Tp was dissolved in 20 mL of octanoic acid and stirred at 40 °C for 20 min to prepare an octanoic acid solution with a Tp concentration of 0.005 mmol / mL; 0.15 mmol of DS-(SO3H)2 (4,4'-diaminostilbene-2,2'-disulfonic acid) and 0.6 mmol of Na2CO3 were dissolved in 30 mL of deionized water and stirred at room temperature for 20 min to prepare an aqueous solution of DS-(SO3Na)2 (4,4'-diaminostilbene-2,2'-disulfonic acid sodium salt). The resulting ionic covalent organic framework TpDS-(SO3H)2 membrane was designated as control membrane 3.

[0049] When the control membrane 3 was used in a CO2 / CH4 separation system at 25°C and a feed gas pressure of 2 bar, the CO2 permeation flux was 2751 GPU and the selectivity was 3.1. Figure 5 As shown.

[0050] In summary, by changing the monomer type to alter the channel size and ionic group types of the covalent organic framework membrane, the preparation method of this invention optimizes the monomer types to Tp and BD-(SO3H)2, thereby regulating the hydration channel structure and influencing CO2 mass transfer. Ionic covalent organic framework membranes possess extremely high ion exchange capacity, and the ionic groups within the channels are orderly distributed. The effective construction of the hydrated covalent organic framework membrane is achieved by adsorbing water vapor from wet natural gas to form hydration channels within the membrane. Due to the large channel size, the water within the channels can serve as a mass transfer medium for gas molecules, utilizing the difference in solubility between CO2 and CH4 for separation. Furthermore, this highly stable hydrated covalent organic framework membrane exhibits excellent separation stability.

[0051] The highly stable hydrated covalent organic framework membrane prepared by this invention has a large channel size, and the water in the channels can serve as a transfer medium for gas molecules. It is expected to adsorb water vapor from wet natural gas to form hydrated channels within the membrane, thereby achieving separation based on the difference in solubility of CO2 and CH4. Under pressures of 1-50 bar, the difference in solubility between CO2 and CH4 in water remains almost constant. Combined with the rigid channel structure, this separation strategy is expected to withstand high-pressure conditions. Simultaneously, the formation of hydrated channels also hinders the entry of nonpolar heavy hydrocarbon molecules, preventing channel blockage and performance degradation. When the highly stable hydrated covalent organic framework membrane prepared by this invention is used in a natural gas purification system, it exhibits high throughput and high selectivity in the CO2 / CH4 separation process, while also being resistant to H2S and heavy hydrocarbons (C2H6, C3H8, n-C4H). 10 n-C6H 14 It can withstand multi-component conditions (such as [etc.]) and pressures up to 33 bar, and also exhibits excellent separation performance for H2S / CH4, in C6H [etc.]. 14 C7H8, C8H 10 In saturated vapor (hexane partial pressure ≥20 kPa), the membrane separation performance showed no significant change. Used in natural gas purification processes, at 2 bar pressure, the CO2 permeation flux exceeded 1300 GPU, with a CO2 / CH4 selectivity higher than 36; the H2S flux exceeded 3000 GPU, with an H2S / CH4 selectivity higher than 75; and in C2H6, C3H8, and n-C4H... 10 n-C6H 14 Even in the presence of impurities, the separation performance showed no significant degradation. At 33 bar, the CO2 flux was higher than 800 GPUs, and the CO2 / CH4 selectivity was higher than 33.

[0052] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention. For example, the ionic covalent organic framework has a high density of ionic groups, including but not limited to sulfonate groups, carboxylate groups, phosphate groups, etc., and the counter ions of its ionic groups include but are not limited to sodium ions, potassium ions, hydrogen ions, etc.; the substrate material used includes but is not limited to various organic and inorganic materials such as polyacrylonitrile, polyethersulfone, and alumina; the membrane preparation method used includes but is not limited to vacuum-assisted self-assembly, pressure filtration, spin coating, blade coating, dip coating, or solvent evaporation; the membrane form prepared includes but is not limited to flat sheet composite membranes, hollow fiber composite membranes, etc. Different covalent organic framework membranes can also be prepared according to the technical solution of the present invention for gas separation or other molecular separation fields, and these are all within the protection scope of the present invention.

Claims

1. The application of a hydrated covalent organic framework membrane in the purification process of wet natural gas, wherein the hydrated covalent organic framework membrane comprises an ionic covalent organic framework and a self-supporting flexible substrate, and is prepared by vacuum-assisted self-assembly, with a membrane thickness of 22-100 nm and a membrane pore size of 2±0.2 nm; the covalent organic framework is TpBD-(SO3Na)2, and is a nanosheet polymerized from an aldehyde monomer and an amino monomer by a phase transfer method; the aldehyde monomer is 1,3,5-trimethylaldehyde phloroglucinol; the amino monomer is 4,4'-diamino-3,3'-biphenyl disulfonic acid; characterized in that, Under wet natural gas purification conditions, the hydrated covalent organic framework membrane can adsorb water vapor in the wet natural gas to form hydration channels within the membrane; the wet natural gas purification process includes one of the following scenarios: Scenario 1: The hydrated covalent organic framework membrane is used to separate CO2 in a CO2 / CH4 mixed gas system. At 25°C, with a CO2 / CH4 molar ratio of 3 / 7, a pressure of 2 bar, and 100% relative humidity, the membrane CO2 permeation flux is 1303 GPU and the selectivity is 36; at 33 bar, the membrane CO2 permeation flux is higher than 800 GPU and the CO2 / CH4 selectivity is higher than 33. Scenario 2: The hydrated covalent organic framework membrane is used for the separation of an H2S / CO2 / CH4 mixed gas system, including: At 25℃, with a molar ratio of H2S / CO2 / CH4 of 10 / 20 / 70, a pressure of 2 bar, and 100% relative humidity: the membrane CO2 permeation flux is 1468 GPU, and the CO2 / CH4 selectivity is higher than 34.0; the membrane H2S permeation flux is 3287 GPU, and the H2S / CH4 selectivity is 77.

3. At 25℃, with a feed gas molar ratio of H2S / CO2 / CH4 of 10 / 20 / 70, a pressure of 5 bar, and 100% relative humidity: the membrane CO2 permeation flux is 1447 GPU, and the selectivity is 31. Scenario 3: The hydrated covalent organic framework membrane is used for applications containing 2% of different heavy hydrocarbon components C2H6, C3H8, and n-C4H. 10 n-C6H 14 Under the conditions of 25℃, CO2 / CH4 molar ratio of feed gas of 3 / 7, pressure of 2 bar, and relative humidity of 100%, the membrane CO2 permeation flux exceeded 1250 GPU, the selectivity exceeded 34.6, the separation performance showed no significant decline, and the decline percentage was less than 8%.

2. The application of a hydrated covalent organic framework membrane according to claim 1 in the purification process of wet natural gas, characterized in that, The method for preparing the hydrated covalent organic framework membrane includes: Step 1) Dissolve 1,3,5-tricarboxymethyl-resorcinol in octanoic acid to prepare an octanoic acid solution with a concentration of 0.01 mmol / mL, denoted as solution A; dissolve 4,4'-diamino-3,3'-biphenyl disulfonic acid and sodium carbonate in deionized water to prepare an aqueous solution of sodium 4,4'-diamino-3,3'-biphenyl disulfonic acid with a concentration of 0.01 mmol / mL, denoted as solution B; using solutions A and B, prepare an ionic nanosheet dispersion with a concentration of 3.0 ± 0.1 mg / mL through a phase transfer polymerization reaction; Step 2) Take the ionic nanosheet dispersion prepared in Step 1) and dilute it with deionized water to a concentration of 3.0±0.1mg / L. Then, use a vacuum-assisted self-assembly method to prepare a film on a polyacrylonitrile substrate with a molecular weight cutoff of 100,000.

3. The application of a hydrated covalent organic framework membrane according to claim 2 in the purification process of wet natural gas, characterized in that, The specific details of step 1) of the method for preparing the hydrated covalent organic framework membrane are as follows: 1-1) Dissolve 1,3,5-tricarboxymethylphloroglucinol in octanoic acid at a molar volume ratio of 0.01 mmol / mL, and stir at 700 rpm for 20 min at 40 °C to prepare the solution A. 1-2) Dissolve 4,4'-diamino-3,3'-biphenyl disulfonic acid and sodium carbonate in deionized water, wherein the molar volume ratio of 4,4'-diamino-3,3'-biphenyl disulfonic acid to deionized water is 0.01 mmol / mL and the molar volume ratio of sodium carbonate to deionized water is 0.02 mmol / mL. Stir at 700 rpm for 20 min at room temperature to prepare solution B. 1-3) Add solution B obtained in step 1-2) to the container, and add solution A obtained in step 1-1) to the liquid surface at a rate of 2 mL / min to form an interface layer, wherein the molar ratio of 1,3,5-tricarboxaldehyde-resorcinol to 4,4'-diamino-3,3'-biphenyl disulfonic acid is 2:3; let the reaction system stand at 60 °C for 30 days. 1-4) Remove the upper octanoic acid phase of the reaction system after the static reaction in steps 1-3), and dialyze the lower aqueous phase in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 30,000, changing the deionized water every 8 hours; the final orange-yellow nanosheet dispersion is the ionic nanosheet dispersion.

4. The application of a hydrated covalent organic framework membrane according to claim 2 in the purification process of wet natural gas, characterized in that, In step 2) of the method for preparing the hydrated covalent organic framework membrane, when preparing the membrane on a polyacrylonitrile substrate with a molecular weight cutoff of 100,000 using a vacuum-assisted self-assembly method, the amount of diluted ionic nanosheet dispersion used is 8.75-875 ug / cm² based on the mass-to-area ratio of nanosheets to the membrane surface area. 2 count.

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