Preparation of high-stability hydrated covalent organic framework membrane and application of high-stability hydrated covalent organic framework membrane in natural gas decarburization

Abstract

The invention discloses a high-stability hydrated covalent organic framework membrane which comprises an ionic covalent organic framework and a self-supporting flexible substrate and is prepared by a vacuum-assisted self-assembly method, the thickness of the membrane is less than 100nm, and the pore size of the membrane is 2 + / -0.2 nm; the covalent organic framework is a nanosheet formed by polymerizing an aldehyde monomer 1, 3, 5-triformyl phloroglucinol and an amino monomer 4, 4 '-diamino-3. 3'-biphenyl disulfonic acid through a phase transfer method. According to the application of the membrane in natural gas decarburization, the membrane is applied to a wet natural gas purification system, has high flux and high selectivity in a CO2 / CH4 separation process, can tolerate multi-component conditions such as H2S, heavy hydrocarbons (C2H6, C3H8, n-C4H10, n-C6H14 and the like) and pressure as high as 33 bar, also has excellent separation performance on H2S / CH4, and has excellent separation performance in saturated steam of C6H14, C7H8 and C8H10 (hexane partial pressure is greater than or equal to 20 kPa). And the membrane separation performance is not obviously changed.

Description

Technical Field

[0001] The present invention relates to the preparation of gas separation membranes, and in particular to a high-stability hydrated covalent organic framework membrane used in natural gas decarbonization. Background Art

[0002] Natural gas refers to a mixture of hydrocarbons (primarily CH4) and non-hydrocarbons found in underground formations. Using natural gas for power generation can reduce CO2 emissions by up to 60%. When burned, its CO2 emissions are approximately 41% and 26% lower than those of coal and oil, respectively. Natural gas provides approximately a quarter of global energy, and this proportion is expected to continue to grow. In addition to its primary component, CH4, natural gas feedstock typically contains various impurities, such as CO2, hydrogen sulfide (H2S), water vapor, and C2-C6 hydrocarbons. CO2 is the primary impurity, and its presence reduces the calorific value of natural gas and shortens the life of transportation pipelines, making it essential for CO2 removal. Currently, CO2 / CH4 separation is achieved industrially through absorption, a two-step process involving absorption and desorption, with the desorption process being energy-intensive. Absorption also faces challenges such as equipment corrosion, absorbent passivation, and environmental pollution from pre-absorbent leakage. The use of membrane separation technology to separate CO2 / CH4 has lower energy consumption than absorption methods, and is characterized by continuous operation, small footprint, and high operational flexibility. It is a key development technology for CO2 / CH4 separation.

[0003] Membrane materials are the core of membrane technology. Covalent organic frameworks (COFs) have long-range ordered channels, high-density adjustable functional sites, and a rigid and stable framework structure, showing great potential in natural gas purification. However, the channel size of most COFs is generally larger than 1.0nm, 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 large pores of COFs is an important issue that must be addressed for their use in gas separation membranes.

[0004] Research has shown that at room temperature, the solubility of bulk water for CO₂ and CH₄ differs by more than 20 times. In some nanochannels, water can act as adsorption sites for CO₂ while simultaneously reducing the adsorption of inert gases like CH₄. Ionic COFs have been shown to possess extremely high ion exchange capacities, with orderly distribution of ionic groups within the channels. Summary of the Invention

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

[0006] In order to solve the above technical problems, the present invention proposes a high-stability hydrated covalent organic framework membrane, which includes an ionic covalent organic framework and a self-supporting flexible substrate, and is prepared by a vacuum-assisted self-assembly method. The membrane thickness is less than 22-100 nm and the membrane pore size is 2±0.2 nm; the ionic covalent organic framework is TpBD-(SO3Na)2, and is a nanosheet polymerized by an aldehyde monomer and an amino monomer through a phase transfer method; the aldehyde monomer is 1,3,5-triformaldehyde phloroglucinol; and the amino monomer is 4,4'-diamino-3.3'-biphenyldisulfonic acid.

[0007] The specific steps of the preparation method of the high-stability hydrated covalent organic framework membrane are as follows:

[0008] Step 1) dissolving 1,3,5-triformaldehyde phloroglucinol in n-octanoic acid to prepare a 0.01 mmol / mL 1,3,5-triformaldehyde phloroglucinol n-octanoic acid solution, recorded as solution A; dissolving 4,4'-diamino-3,3'-biphenyldisulfonic acid and sodium carbonate in deionized water to prepare a 0.01 mmol / mL aqueous solution of sodium 4,4'-diamino-3,3'-biphenyldisulfonate, recorded as solution B; using solution A and solution B, a phase transfer polymerization reaction was used to prepare an ionic nanosheet dispersion with a concentration of 3.0±0.1 mg / mL;

[0009] Step 2) The ionic nanosheet dispersion prepared in step 1) was diluted with deionized water to a concentration of 3.0±0.1 mg / L, and a film was prepared on a polyacrylonitrile substrate with a molecular weight cut-off of 100,000 using a vacuum-assisted self-assembly method.

[0010] Furthermore, the preparation method of the present invention, wherein:

[0011] The specific content of step 1) is: dissolving 1,3,5-triformaldehyde phloroglucinol in n-octanoic acid at a molar volume ratio of 0.01 mmol / mL, stirring at 700 rpm for 20 min at 40°C to prepare the solution A; dissolving 4,4'-diamino-3.3'-biphenyldisulfonic acid and sodium carbonate in deionized water, wherein the molar volume ratio of 4,4'-diamino-3.3'-biphenyldisulfonic 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, stirring at 700 rpm for 20 min at room temperature to prepare Obtain the solution B; add solution B into a container, and add solution A to the liquid surface at a rate of 2 mL / min to form an interface layer, wherein the molar ratio of the 1,3,5-triformaldehyde phloroglucinol to 4,4'-diamino-3,3'-biphenyldisulfonic acid is 2:3; the reaction system is allowed to stand for reaction at 60° C. for 30 days; then, the upper octanoic acid phase of the reaction system after the standing reaction is removed, and the lower aqueous phase is dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 30,000, and the deionized water is replaced every 8 hours; the orange-yellow nanosheet dispersion finally obtained is the ionic nanosheet dispersion.

[0012] In step 2), when a film is prepared on a polyacrylonitrile substrate with a molecular weight cut-off of 100,000 by vacuum assisted self-assembly, the amount of the diluted ionic nanosheet dispersion is 8.75-875 μg / cm according to the mass area ratio of the nanosheets to the film area. 2 count.

[0013] The application of the high-stability hydrated covalent organic framework membrane prepared by the preparation method of the present invention in natural gas decarbonization, i.e., in the wet natural gas purification process, includes one or more of the following situations:

[0014] Scenario 1: Figure 6 It can be seen that for CO2 separation in a CO2 / CH4 mixed gas system, at 25°C, a molar ratio of 3 / 7 in the raw gas CO2 / CH4, a pressure of 2 bar, and a relative humidity of 100%, 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: Figure 7It can be seen that for the separation of the H2S / CO2 / CH4 mixed gas system, at 25°C, the molar ratio of the raw gas H2S / CO2 / CH4 is 10 / 20 / 70, the pressure is 2 bar, and the relative humidity is 100%: 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; at 25°C, the molar ratio of the raw gas H2S / CO2 / CH4 is 10 / 20 / 70, the pressure is 5 bar, and the relative humidity is 100%: the CO2 permeation flux is 1447 GPU, and the selectivity is 31.

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

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] Membrane technology for natural gas decarbonization offers lower energy consumption and less environmental pollution than absorption technologies. Among existing membrane technologies, polymer membranes based on a solution-diffusion mechanism are constrained by a trade-off between permeability and selectivity, making it difficult to achieve high performance. Furthermore, most polymer membranes experience significant performance degradation at high pressures due to plasticization, an effect exacerbated by the presence of H₂S. Polymer membranes based on a facilitated transfer mechanism offer excellent performance at low pressures, but their performance decreases sharply with increasing pressure. Inorganic membrane channels, such as zeolite and CMS membranes, offer high separation performance and remain stable at higher pressures. However, when the separation system contains impurities such as heavy hydrocarbons and water vapor, the inorganic membrane mass transfer channels become clogged by the impurities, leading to a significant performance degradation. Furthermore, the structural rigidity of inorganic membranes makes them difficult to fabricate defect-free over large areas, limiting their further application. Mixed-matrix membranes, prepared by blending inorganic fillers with polymers, offer a balance between processability and separation performance, but currently prepared mixed-matrix membranes are typically self-supporting thick membranes measuring tens of microns, rather than ultrathin submicron composite membranes. After being made into ultra-thin composite membranes, mixed matrix membranes also face the problems of decreased separation performance and processing defects.

[0019] In comparison, the high-stability hydrated covalent organic framework membrane prepared by the present invention combines 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 and can be manufactured into different types, such as flat membranes and hollow fiber membranes. Therefore, the high-stability hydrated covalent organic framework membrane described in the present invention combines high separation performance, strong stability, and easy processing. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] Figure 2 is the surface electron micrograph of membrane 1;

[0022] Figure 3 is a cross-sectional electron micrograph of membrane 1;

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

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

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

[0026] Figure 7 are the H2S and CO2 permeation fluxes, and H2S / CH4 and CO2 / CH4 selectivities of membrane 1 at 25°C, 2 to 5 bar, and a feed gas ratio of H2S / CO2 / CH4 (10 / 20 / 70 mol%);

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

[0028] Figure 9 Membrane 1 at 25°C, 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). DETAILED DESCRIPTION

[0029] The present invention proposes a highly stable hydrated covalent organic framework membrane for use in natural gas decarbonization, specifically in the natural gas separation process. The ionic covalent organic framework membrane has an extremely high ion exchange capacity, and the ionic groups in the channels are orderly distributed. It can adsorb water vapor in wet natural gas to form hydrated channels within the membrane, thereby achieving the effective construction of a hydrated covalent organic framework membrane. By changing the monomer type, the channel size and ionic group type of the covalent organic framework membrane are changed, and the optimized monomer types are Tp (1,3,5-triformaldehyde phloroglucinol) and BD-(SO3H)2 (4,4'-diamino-3.3'-biphenyldisulfonic acid), thereby regulating the hydrated channel structure and thus affecting CO2 mass transfer. Due to the large channel size, the water in the channel can be used as a mass transfer medium for gas molecules, and an efficient CO2 / CH4 separation process is achieved based on the difference in solubility and diffusion of gas molecules in the bound water network. Based on the fully organic structure of the hydrated covalent organic framework, the membrane can remain stable in the presence of H2S and can efficiently separate H2S / CH4. The bound water network has strong polarity and is very sensitive to C2H6, C3H8, n-C4H 10 、n-C6H 14 The membrane does not adsorb heavy hydrocarbons, so its performance does not significantly decrease in the presence of heavy hydrocarbons. The membrane's separation performance also remains unchanged in saturated vapors of hexane, toluene, and p-xylene (hexane partial pressure ≥ 20 kPa). Due to the rigid structure and stable bound water network of the highly stable hydrated covalent organic framework membrane, the membrane exhibits strong stability under high pressure.

[0030] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. The described specific implementation examples are only used to explain the present invention and are not intended to limit the present invention.

[0031] Example:

[0032] Prepare TpBD-(SO3Na)2 membrane as follows:

[0033] Step 1) Tp (its structure is as follows Figure 1-1 As shown) and BD-(SO3H)2 (whose structure is as Figure 1-2 As shown in FIG, 4,4'-diamino-3,3'-biphenyl disulfonic acid sodium nanosheets (TpBD-(SO3Na)2) are prepared by phase transfer polymerization of monomers, and the steps are as follows:

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

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

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

[0037] After the reaction mixture settled, the upper octanoic acid phase was removed, and the lower aqueous phase was dialyzed against deionized water using a 30,000 molecular weight cutoff dialysis bag for three days, with the deionized water replaced every eight hours. This resulted in an orange-yellow dispersion of TpBD-(SO3Na)2 nanosheets. The nanosheets were dried and the residual solids were weighed to determine a TpBD-(SO3Na)2 nanosheet concentration of approximately 3.1 mg / mL.

[0038] Step 2): Prepare TpBD-(SO3Na)2 film by vacuum-assisted self-assembly method.

[0039] Take 20 μL of the TpBD-(SO3Na)2 nanosheet dispersion prepared in step 1) and dilute it to 20 mL with deionized water. Use vacuum-assisted self-assembly to prepare a film on a polyacrylonitrile substrate with a molecular weight cutoff of 100,000 and a diameter of approximately 1.5 cm to obtain a yellow TpBD-(SO3Na)2 film, which is recorded as film 1. Figure 2 and Figure 3 The surface and cross-sectional electron micrographs of membrane 1 are shown respectively, and it can be seen that the thickness of membrane 1 is 22 nm. The pore size obtained from the gas adsorption data is about 2.2 nm. Figure 4 shown.

[0040] Membrane 1 was used in the 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 805GPU and the selectivity is 33, as shown Figure 6 As shown, the membrane has the potential to withstand high pressure. At the same time, due to strong covalent bonding, the covalent organic framework membrane can remain stable in natural gas containing hydrogen sulfide. Using H2S / CO2 / CH4 (10 / 20 / 70 mol%) mixed gas as the feed gas at 100% relative humidity, the TpBD-(SO3Na)2 membrane has a CO2 permeation flux of 1468 GPU at 2 bar and a CO2 / CH4 selectivity of more than 34.0. Figure 7 As shown. The bound water network has strong polarity and is very sensitive to C2H6, C3H8, n-C4H 10 、n-C6H 14 Heavy hydrocarbons are not adsorbed, so the performance of the membrane does not significantly decrease in the presence of heavy hydrocarbons, e.g. Figure 8 shown. Figure 9 The results show that the membrane 1 was heated 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] Preparation of TpPa-(SO3Na)2 membrane. The preparation of comparative example 1 is basically the same as that of example 1, with the only difference being: in step 1), 0.1mmol Tp is dissolved in 20mL of n-octanoic acid, and stirred at 40°C for 20min to prepare an octanoic acid solution of Tp with a concentration of 0.005mmol / mL; 0.15mmol of 2,5-diamino-1,4-benzenedisulfonic acid Pa-(SO3H)2 and 0.6mmol Na2CO3 are dissolved in 30mL of deionized water, and stirred at room temperature for 20min to prepare an aqueous solution of 2,5-diamino-1,4-benzenedisulfonic acid sodium (Pa-(SO3Na)2) with a concentration of 0.005mmol / mL; the finally obtained ionic covalent organic framework Pa-(SO3Na)2 membrane is recorded as comparative membrane 1.

[0043] Comparative membrane 1 was used in the 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 shown.

[0044] Comparative Example 2:

[0045] The TpBD-(COONa)2 membrane was prepared. The preparation of Comparative Example 2 was basically the same as that of Example 1, with the only difference being 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 a 0.01 mmol / mL aqueous solution of the amino monomer BD-(COONa)2 (sodium 4,4'-diaminobiphenyl-2,2'-dicarboxylate). The final ionic covalent organic framework TpBD-(COONa)2 membrane was recorded as Comparative Membrane 2.

[0046] Comparative membrane 2 was used in the 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 shown.

[0047] Comparative Example 3:

[0048] Preparation of TpDS-(SO3H)2 membrane. The preparation of comparative example 3 is basically the same as that of example 1, except that: in step 1-1), 0.1mmol Tp is dissolved in 20mL of n-octanoic acid and stirred at 40°C for 20min to prepare a 0.005mmol / mL Tp octanoic acid solution; 0.15mmol DS-(SO3H)2 (4,4'-diaminostilbene-2,2'-disulfonic acid) and 0.6mmol Na2CO3 are dissolved in 30mL of deionized water and stirred at room temperature for 20min to prepare a 0.005mmol / mL DS-(SO3Na)2 (sodium 4,4'-diaminostilbene-2,2'-disulfonic acid) aqueous solution. The final ionic covalent organic framework TpDS-(SO3H)2 membrane is recorded as comparative membrane 3.

[0049] Comparative membrane 3 was used in the 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 shown.

[0050] In summary, by changing the monomer type to change the channel size and ionic group type of the covalent organic framework membrane, in the preparation method of the present invention, the monomer types are optimized to be Tp and BD-(SO3H)2, thereby regulating the hydrated channel structure and affecting the mass transfer of CO2. The ionic covalent organic framework membrane has an extremely high ion exchange capacity, and the ionic groups in the channel are orderly distributed. By adsorbing water vapor in wet natural gas to form hydration channels in the membrane, the effective construction of the hydrated covalent organic framework membrane is achieved. Due to the larger channel size, the water in the channel can be used as a mass transfer medium for gas molecules, and the solubility difference between CO2 and CH4 is used for separation. And the high-stability hydrated covalent organic framework membrane has good separation stability.

[0051] The high-stability hydrated covalent organic framework membrane prepared by the present invention has a large channel size. The water in the channel can be used as a transfer medium for gas molecules. It is expected to adsorb water vapor in wet natural gas to form hydrated channels in the membrane, and then achieve separation based on the difference in their solubility for CO2 and CH4. Under a pressure of 1-50 bar, the solubility difference multiples of CO2 and CH4 in water remain almost unchanged. Combined with the rigid channel structure, this separation strategy is expected to withstand high-pressure conditions; at the same time, the formation of hydrated channels will also hinder non-polar heavy hydrocarbon molecules from entering the channel, avoiding channel blockage and performance degradation. The high-stability hydrated covalent organic framework membrane prepared by the present invention is used in a natural gas purification system, which has high throughput and high selectivity for the CO2 / CH4 separation process, and can tolerate H2S, heavy hydrocarbons (C2H6, C3H8, n-C4H 10 、n-C6H 14 etc.) and pressure up to 33 bar, and has excellent separation performance for H2S / CH4. 14 、C7H8、C8H 10 In the saturated steam (hexane partial pressure ≥ 20kPa), the membrane separation performance has no significant change. In the natural gas purification process, under 2 bar pressure, the CO2 permeation flux exceeds 1300GPU, CO2 / CH4 selectivity is higher than 36; H2S flux exceeds 3000GPU, H2S / CH4 selectivity is higher than 75; in C2H6, C3H8, n-C4H 10 、n-C6H 14 In the presence of impurities, the separation performance does not show significant degradation. At 33 bar, the CO2 flux is higher than 800 GPU and the CO2 / CH4 selectivity is 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 above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many modifications without departing from the purpose of the present invention, such as: the ionic covalent organic framework has a high density of ionic groups, and the ionic groups include but are 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, filter press, spin coating, doctor blade coating, dip coating or solvent volatilization; the prepared membrane form includes but is not limited to flat composite membranes, hollow fiber composite membranes, etc.; different covalent organic framework membranes can also be prepared according to the guidance of the technical solution of the present invention for use in gas separation or other molecular separation fields, all of which are within the protection of the present invention.

Claims

1. A high-stability hydrated covalent organic framework membrane, characterized in that: The hydrated covalent organic framework membrane includes an ionic covalent organic framework and a self-supporting flexible substrate, and is prepared by a vacuum-assisted self-assembly method. The membrane thickness is 22-100 nm and the membrane pore size is 2±0.2 nm. The covalent organic framework is TpBD-(SO3Na)2, and is a nanosheet polymerized by an aldehyde monomer and an amino monomer through a phase transfer method. The aldehyde monomer is 1,3,5-triformaldehyde phloroglucinol; and the amino monomer is 4,4'-diamino-3.3'-biphenyldisulfonic acid.

2. A method for preparing a high-stability hydrated covalent organic framework membrane according to claim 1, characterized in that: The following steps are involved: Step 1) dissolving 1,3,5-triformaldehyde phloroglucinol in n-octanoic acid to prepare a 0.01 mmol / mL 1,3,5-triformaldehyde phloroglucinol n-octanoic acid solution, recorded as solution A; dissolving 4,4'-diamino-3,3'-biphenyldisulfonic acid and sodium carbonate in deionized water to prepare a 0.01 mmol / mL aqueous solution of sodium 4,4'-diamino-3,3'-biphenyldisulfonate, recorded as solution B; using solution A and solution B, a phase transfer polymerization reaction was used to prepare an ionic nanosheet dispersion with a concentration of 3.0±0.1 mg / mL; Step 2) The ionic nanosheet dispersion prepared in step 1) was diluted with deionized water to a concentration of 3.0±0.1 mg / L, and a film was prepared on a polyacrylonitrile substrate with a molecular weight cut-off of 100,000 using a vacuum-assisted self-assembly method.

3. The preparation method according to claim 2, characterized in that The specific contents of step 1) are as follows: 1-1) dissolving 1,3,5-triformaldehyde phloroglucinol in n-octanoic acid at a molar volume ratio of 0.01 mmol / mL, and stirring at 700 rpm for 20 minutes at 40° C. to prepare the solution A; 1-2) dissolving 4,4'-diamino-3,3'-biphenyldisulfonic acid and sodium carbonate in deionized water, wherein the molar volume ratio of 4,4'-diamino-3,3'-biphenyldisulfonic 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 minutes at room temperature to prepare the solution B; 1-3) adding solution B prepared in step 1-2) into a container, and adding solution A prepared in step 1-1) onto the liquid surface at a rate of 2 mL / min to form an interface layer, wherein the molar ratio of 1,3,5-triformaldehyde phloroglucinol to 4,4'-diamino-3,3'-biphenyldisulfonic acid is 2:3; and the reaction system is allowed to react at 60° C. for 30 days; 1-4) The upper octanoic acid phase of the reaction system after the static reaction in step 1-3) was removed, and the lower aqueous phase was dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 30,000 for 3 days, with the deionized water being replaced every 8 hours; the resulting orange-yellow nanosheet dispersion was the ionic nanosheet dispersion.

4. The preparation method according to claim 2, characterized in that In step 2), when a film is prepared on a polyacrylonitrile substrate with a molecular weight cut-off of 100,000 by vacuum assisted self-assembly, the amount of the diluted ionic nanosheet dispersion is 8.75-875 μg / cm according to the mass area ratio of the nanosheets to the film area. 2 count.

5. Use of the high-stability hydrated covalent organic framework membrane prepared by the preparation method according to any one of claims 2 to 4 in natural gas decarbonization.

6. The use of the high-stability hydrated covalent organic framework membrane in natural gas decarbonization according to claim 5, characterized in that: The high-stability hydrated covalent organic framework membrane is used to separate CO2 from a CO2 / CH4 mixed gas system. At 25°C, a molar ratio of 3 / 7 of the raw gas CO2 / CH4, 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.

7. The use of the high-stability hydrated covalent organic framework membrane in natural gas decarbonization according to claim 5, characterized in that: The high-stability hydrated covalent organic framework membrane is used for separation of H2S / CO2 / CH4 mixed gas system. At 25°C, a feed gas H2S / CO2 / CH4 molar ratio of 10 / 20 / 70, a pressure of 2 bar, and a relative humidity of 100%, the membrane CO2 permeation flux was 1468 GPU, and the CO2 / CH4 selectivity was higher than 34.0; the membrane H2S permeation flux was 3287 GPU, and the H2S / CH4 selectivity was 77.3; At 25°C, a molar ratio of H2S / CO2 / CH4 of 10 / 20 / 70 for the raw gas, a pressure of 5 bar, and a relative humidity of 100%, the membrane CO2 permeation flux was 1447 GPU and the selectivity was 31.

8. The use of the high-stability hydrated covalent organic framework membrane in natural gas decarbonization according to claim 5, characterized in that: The high stability hydrated covalent organic framework membrane is used for containing 2% of different heavy hydrocarbon components C2H6, C3H8, n-C4H 10 、n-C6H 14 At 25°C, a molar ratio of CO2 / CH4 of 3 / 7, a pressure of 2 bar, and a relative humidity of 100%, the membrane CO2 permeation flux exceeded 1250GPU, the selectivity exceeded 34.6, and there was no obvious attenuation in the separation performance, with an attenuation percentage of less than 8%.

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