A gas separation membrane, its preparation method and application

Abstract

This invention relates to the field of gas separation and discloses a method for preparing a gas separation membrane. The method includes: (1) mixing sodium hydride, octafluoropentanol, and organic solvent A to react and obtain sodium octafluoropentanol; (2) mixing sodium octafluoropentanol with a polydichlorophosphazene solution under a protective atmosphere and heating under reflux to react and obtain the product polyoctafluoropentoxyphosphazene; (3) mixing polydichlorophosphazene, n-octylamine, and an acid-binding agent in organic solvent B to react and obtain the product polyn-n-octylaminephosphazene; (4) mixing polyvinylidene fluoride with triethyl phosphate, coating the mixture onto a nonwoven fabric, and then immersing it in water to obtain a polyvinylidene fluoride substrate; (5) mixing polyoctafluoropentoxyphosphazene, polyn-n-octylaminephosphazene, and organic solvent C, and then coating the mixture onto the polyvinylidene fluoride substrate. The gas separation membrane of this invention has excellent high selectivity for CO2 and has broad industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of gas separation, specifically to a gas separation membrane, its preparation method, and its application. Background Technology

[0002] The rapid growth in energy demand and fossil fuel consumption has been a major concern. Biogas, as a renewable and clean energy source, can replace fossil fuels to alleviate the global energy crisis. However, the high CO2 content in biogas can lead to problems such as reduced calorific value, solidification in low-temperature equipment, and corrosion of steel pipes. Membrane separation of CO2 is an emerging natural gas decarbonization technology that offers advantages over traditional separation technologies, including smaller footprint, simpler operation, and lower operating costs.

[0003] Membranes used for CO2 separation are mainly inorganic and polymer membranes. Inorganic membranes offer high gas separation performance, but their high cost and difficult preparation hinder large-scale industrial applications. Polymer membranes, on the other hand, are inexpensive and easy to process, and can combine the advantages of different materials through blending modification to meet diverse industrial needs. To improve the "trade-off" effect and enhance the gas separation performance of polymer membranes, researchers have conducted extensive work on optimizing and modifying membrane materials. The main methods include crosslinking, copolymerization, filling with inorganic particles, and blending, with blending being a simple and effective method.

[0004] Among numerous polymer membranes, polyphosphazene materials have attracted widespread attention due to their controllable synthesis, flexible main chain, high temperature resistance, and high gas separation performance. However, the synthesis of polydichlorophosphazene, an intermediate in polyphosphazene materials, requires extremely high purity of the precursor monomers, and the material itself is prone to cross-linking and difficult to store. Therefore, polyphosphazene materials are currently rarely used for carbon dioxide gas separation. Furthermore, the selection of novel polymer separation membranes is limited. Thus, researching and developing a novel gas separation membrane for separating carbon dioxide from biogas has significant practical implications. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of limited polymer membrane options and poor separation performance in existing technologies, and to provide a gas separation membrane, its preparation method, and its application. The gas separation membrane has a separation layer and a base membrane. The separation layer is obtained by blending polyoctafluoropentoxyphosphazene and polyn-octylaminephosphazene. The blended gas separation membrane is prepared by chemical modification and physical modification methods. Furthermore, the gas separation membrane of this invention has excellent high selectivity for CO2 and has broad prospects for industrial applications.

[0006] To achieve the above objectives, the present invention provides a method for preparing a gas separation membrane, the method comprising the following steps:

[0007] (1) Sodium hydride, octafluoropentanol and organic solvent A are mixed and reacted to obtain sodium octafluoropentanol;

[0008] (2) Under a protective atmosphere, the sodium octafluoropentoxide solution is mixed with polydichlorophosphazene solution and heated under reflux to react and obtain the product polyoctafluoropentoxyphosphazene:

[0009] (3) In a protective atmosphere, polydichlorophosphazene, n-octylamine and acid-binding agent are mixed in organic solvent B and reacted to obtain the product polyn-octylaminephosphazene;

[0010] (4) Mix polyvinylidene fluoride with triethyl phosphate, coat the resulting mixture onto a nonwoven fabric, and then immerse it in water to obtain a polyvinylidene fluoride substrate;

[0011] (5) Mix the polyoctafluoropentoxyphosphazene, the poly(n-octylamine phosphazene) and organic solvent C, and then coat the mixture onto the polyvinylidene fluoride substrate;

[0012] The weight ratio of the polyoctafluoropentoxyphosphazene to the polyn-octylamine phosphazene is 2-4:1.

[0013] Preferably, in step (1), the weight ratio of sodium hydride to octafluoropentanol is 1:1-1.2;

[0014] Preferably, in step (1), the reaction conditions include: a temperature of 60-65°C and a time of 60-72 h;

[0015] Preferably, the organic solvent A is dioxane, benzene, or tetrahydrofuran.

[0016] Preferably, in step (2), the temperature of the heating reflux is 60-70°C. o C, the heating reflux time is 65-75 hours;

[0017] Preferably, the molar ratio of sodium octafluoropentoxide to polydichlorophosphazene is 1.0-1.5:1, wherein the molar amount of polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene.

[0018] Preferably, in step (3), the reaction temperature is 50-65°C and the reaction time is 60-75 h;

[0019] Preferably, in step (3), the weight ratio of the amount of n-octylamine to the amount of the acid-binding agent is 1:1.2-1.5;

[0020] Preferably, in step (3), the molar ratio of the polydichlorophosphazene to the n-octylamine is 1:2-3, wherein the molar amount of the polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene;

[0021] Preferably, the organic solvent B is dioxane, benzene, or tetrahydrofuran;

[0022] Preferably, the acid-binding agent is triethylamine.

[0023] Preferably, the specific process of step (2) includes: mixing sodium octafluoropentoxide with a polydichlorophosphazene solution in a protective atmosphere, heating and refluxing to react, purifying the reacted material to obtain the product polyoctafluoropentoxyphosphazene.

[0024] Preferably, the purification process includes:

[0025] S1 adjusts the pH of the reacted material to 6.5-7.5, filters it, then rotary evaporates the filtrate, mixes the rotary evaporated material with n-hexane, filters it to obtain filter residue, washes it with water and dries it.

[0026] S2 mixes the dried product with tetrahydrofuran, then filters it. The resulting filtrate is then mixed with petroleum ether, filtered again to obtain a filter residue, and the residue is dried to obtain the product polyoctafluoropentoxyphosphazene.

[0027] Preferably, the specific process of step (3) includes: in a protective atmosphere, mixing polydichlorophosphazene, n-octylamine and an acid-binding agent in organic solvent B to react, purifying the reacted material to obtain the product polyn-octylaminephosphazene;

[0028] Preferably, the purification process includes: concentrating the material obtained from the reaction, then mixing the concentrated product with water, filtering to obtain a filter residue, mixing the obtained filter residue with tetrahydrofuran, filtering again, and drying the obtained filter residue to obtain the product poly(n-octylaminophosphazene).

[0029] Preferably, in step (4), the weight ratio of polyvinylidene fluoride to triethyl phosphate is 20:1-2;

[0030] Preferably, the organic solvent C is tetrahydrofuran, benzene, or ethyl acetate;

[0031] Preferably, in step (5), the coating thickness is 3-5 μm;

[0032] Preferably, in step (5), the solid content in the mixture is 9-11 wt%.

[0033] A second aspect of the present invention provides a gas separation membrane prepared by the above method.

[0034] A third aspect of the present invention provides the application of the gas separation membrane in the process of separating carbon dioxide from a mixed gas;

[0035] Preferably, the gas mixture contains methane and carbon dioxide.

[0036] Preferably, the separation conditions include a temperature of 25-45°C and a mixing gas flow rate of 35-45 ml / min.

[0037] In the preparation method described in this invention, a fluorinated polyphosphazene material, polyoctafluoropentoxyphosphazene, with higher bond energy, better thermal stability, and stronger affinity for CO2, was synthesized through chemical modification. The polyoctafluoropentoxyphosphazene was then blended with poly(n-octylamine phosphazene) to prepare a composite membrane. The method described in this invention, by introducing CF bonds with affinity for CO2 and appropriately increasing the free volume porosity of the membrane, effectively solves the drawback of low selectivity for CO2 / CH4 in current polymer membranes. Gas separation performance tests revealed that the gas separation membrane prepared by this invention overcomes the "trade-off" effect, enabling rapid separation of carbon dioxide from biogas and possessing broad industrial application prospects. Attached Figure Description

[0038] Figure 1 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Example 1;

[0039] Figure 2 This is a surface morphology diagram of the gas separation membrane prepared in Example 1;

[0040] Figure 3 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Comparative Example 1;

[0041] Figure 4 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Comparative Example 2;

[0042] Figure 5 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Comparative Example 3;

[0043] Figure 6 This is a surface morphology diagram of the gas separation membrane prepared in Comparative Example 1;

[0044] Figure 7 This is a surface morphology diagram of the gas separation membrane prepared in Comparative Example 2;

[0045] Figure 8 This is a surface morphology diagram of the gas separation membrane prepared in Comparative Example 3. Detailed Implementation

[0046] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0047] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0048] This invention provides a method for preparing a gas separation membrane, the method comprising the following steps:

[0049] (1) Sodium hydride, octafluoropentanol and organic solvent A are mixed and reacted to obtain sodium octafluoropentanol;

[0050] (2) Under a protective atmosphere, the sodium octafluoropentoxide solution is mixed with polydichlorophosphazene solution and heated under reflux to react and obtain the product polyoctafluoropentoxyphosphazene:

[0051] (3) In a protective atmosphere, polydichlorophosphazene, n-octylamine and acid-binding agent are mixed in organic solvent B and reacted to obtain the product polyn-octylaminephosphazene;

[0052] (4) Mix polyvinylidene fluoride with triethyl phosphate, coat the resulting mixture onto a nonwoven fabric, and then immerse it in water to obtain a polyvinylidene fluoride substrate;

[0053] (5) Mix the polyoctafluoropentoxyphosphazene, the polyn-octylamine phosphazene and organic solvent C, and then coat the mixture onto the polyvinylidene fluoride substrate.

[0054] In the method described in this invention, in step (1), because sodium hydride is highly reactive and reacts violently with water, the organic solvent A used in step (1) needs to have its water content removed beforehand. Specifically, the method for removing water from organic solvent A includes: using benzophenone as an indicator, adding sodium wire to organic solvent A at 60-80°C and stirring until the reaction system turns blue, then stopping the addition of sodium wire, and then distilling the obtained material at 80-90°C to obtain anhydrous organic solvent A for later use. In a preferred embodiment, the organic solvent A is one of dioxane, benzene, or tetrahydrofuran, more preferably tetrahydrofuran.

[0055] In a preferred embodiment, in step (1), the weight ratio of sodium hydride to octafluoropentanol is 1:1-1.2. Specifically, the weight ratio of sodium hydride to octafluoropentanol can be 1:1, 1:1.1 or 1:1.2.

[0056] In a preferred embodiment, in step (1), the reaction conditions include a temperature of 60-65°C and a time of 60-72 hours. Specifically, the reaction temperature can be 60°C, 61°C, 62°C, 63°C, 64°C, or 65°C; and the reaction time can be 60 hours, 65 hours, 70 hours, or 72 hours.

[0057] In a specific embodiment, in step (2), the polydichlorophosphazene solution is obtained by dissolving polydichlorophosphazene in a common organic solvent, which may be tetrahydrofuran. Specifically, the polydichlorophosphazene can be prepared according to methods commonly used in the art.

[0058] More preferably, the preparation method of polydichlorophosphazene used in the method of the present invention includes: obtaining polydichlorophosphazene by melt polymerization of purified hexachlorocyclotriphosphazene in a vacuum environment. The reaction conditions for the melt polymerization include: a temperature of 240-260℃ and a time of 16-36 h. Specifically, the temperature of the melt polymerization can be 240℃, 250℃, or 260℃; the time of the melt polymerization can be 16 h, 20 h, 25 h, 30 h, or 36 h. After the reaction, the material will become viscous and difficult to flow.

[0059] In a specific embodiment, the purification process of the hexachlorocyclotriphosphazene includes: dissolving crude hexachlorocyclotriphosphazene in n-heptane solvent, heating and refluxing at 75-80°C to ensure complete dissolution, then filtering to remove insoluble impurities, cooling and recrystallizing the obtained filtrate, and vacuum drying the precipitated crystals. This purification process is repeated 3-5 times, and the resulting product is sublimated to constant weight at 80-90°C to obtain purified hexachlorocyclotriphosphazene.

[0060] In a preferred embodiment, in step (2), the temperature of the heating reflux is 60-70°C. o C, the reflux heating time is 65-75 hours. Specifically, in step (2), the reflux heating temperature is the same as the reaction temperature in step (2), and the reflux heating time is the same as the reaction time in step (2). Specifically, the reflux heating temperature can be 60°C. o C, 65 o C or 70 o C; The heating reflux time can be 65h, 70h, 72h or 75h.

[0061] In a preferred embodiment, the molar ratio of sodium octafluoropentoxide to polydichlorophosphazene is 1.0-1.5:1, more preferably 1-1.2:1, and even more preferably 1.2:1, wherein the molar amount of polydichlorophosphazene is calculated as the molar amount of hexachlorocyclotriphosphazene. Specifically, the molar ratio of sodium octafluoropentoxide to polydichlorophosphazene can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1.

[0062] In a specific implementation, in step (2), the protective atmosphere can be one of nitrogen atmosphere, argon atmosphere or helium atmosphere.

[0063] In the method described in this invention, step (2) specifically includes: mixing sodium octafluoropentoxide with a polydichlorophosphazene solution under a protective atmosphere, heating and refluxing to react, purifying the reacted material to obtain the product polyoctafluoropentoxyphosphazene. To further improve the purity of the prepared product polyoctafluoropentoxyphosphazene, thereby improving the selectivity of the prepared gas separation membrane, the purification step of the reacted material includes:

[0064] S1 adjusts the pH of the reacted material to 6.5-7.5, filters it, then rotary evaporates the filtrate, mixes the rotary evaporated material with n-hexane, filters it to obtain filter residue, washes it with water and dries it.

[0065] S2 mixes the dried product with tetrahydrofuran, then filters it. The resulting filtrate is then mixed with petroleum ether, filtered again to obtain a filter residue, and the residue is dried to obtain the product polyoctafluoropentoxyphosphazene.

[0066] Specifically, in step S1, most of the solvent is removed by rotary evaporation, and then crystals are precipitated by hexane precipitation. After filtration, the obtained crystals are washed with water and dried to obtain crude polyoctafluoropentoxyphosphazene product. The obtained crude polyoctafluoropentoxyphosphazene product is then dissolved in tetrahydrofuran solution, and insoluble polymers and impurities are removed by centrifugation. The liquid obtained by centrifugation is then precipitated with petroleum ether 3-4 times to remove unreacted monomers and oligomers from the product. The obtained solid phase is then dried to obtain the product polyoctafluoropentoxyphosphazene.

[0067] In a preferred embodiment, in step (3), the reaction temperature is 50-65°C and the reaction time is 60-75h. Specifically, the reaction temperature can be 50°C, 52°C, 55°C, 60°C, 62°C or 65°C; and the reaction time can be 60h, 65h, 72h or 75h.

[0068] In a preferred embodiment, in step (3), the weight ratio of n-octylamine to the acid-binding agent is 1:1.2-1.5. Specifically, the weight ratio of n-octylamine to the acid-binding agent can be 1:1.2, 1:1.3, 1:1.4, or 1:1.5.

[0069] In a preferred embodiment, in step (3), the molar ratio of the polydichlorophosphazene to the n-octylamine is 1:2-3, wherein the molar amount of the polydichlorophosphazene is expressed as the molar amount of hexachlorocyclotriphosphazene. Specifically, the molar ratio of the polydichlorophosphazene to the n-octylamine can be 1:2, 1:2.5, 1:2.8, or 1:3.

[0070] In a preferred embodiment, the organic solvent B is selected from tetrahydrofuran, dioxane, or benzene, more preferably tetrahydrofuran.

[0071] In a more preferred embodiment, the organic solvent A is the same as the organic solvent B. For example, when the organic solvent A is tetrahydrofuran, the organic solvent B is tetrahydrofuran.

[0072] In a preferred embodiment, the acid-binding agent is triethylamine.

[0073] In the method described in this invention, step (3) specifically includes: reacting polydichlorophosphazene, n-octylamine, and an acid-binding agent in organic solvent B under a protective atmosphere; purifying the reacted material to obtain the product poly(n-octylaminephosphazene). In a preferred embodiment, the purification process includes: concentrating the reacted material; mixing the concentrated product with water; filtering to obtain a filter residue; mixing the obtained filter residue with tetrahydrofuran; filtering again; and drying the obtained filter residue to obtain the product poly(n-octylaminephosphazene).

[0074] Specifically, in the purification process of step (3), the reaction material is concentrated using a rotary evaporator, and then the concentrated product is precipitated in water. The precipitated material is filtered, and the resulting filter residue is dissolved in tetrahydrofuran to remove undissolved impurities. The filtrate is then cooled and recrystallized, and dried to obtain the product poly(n-octylamine phosphazene). To further improve the purity of the product, the recrystallized product can be repeatedly dissolved and recrystallized in tetrahydrofuran multiple times.

[0075] In a specific implementation, in step (3), the protective atmosphere can be one of nitrogen atmosphere, argon atmosphere or helium atmosphere.

[0076] In the method described in this invention, a more porous polyvinylidene fluoride substrate can be prepared through the operation of step (4), which further improves the performance of the prepared gas separation membrane.

[0077] In a preferred embodiment, in step (4), the weight ratio of polyvinylidene fluoride to triethyl phosphate is 20:1-2. Specifically, the weight ratio of polyvinylidene fluoride to triethyl phosphate can be 20:1, 20:1.5, or 20:2.

[0078] In one specific embodiment, in step (4), after the slurry of polyvinylidene fluoride and triethyl phosphate is coated onto the nonwoven fabric, it is immediately immersed in water for 20-24 hours, and the water used for immersion is changed every 2 hours. After immersion, it is taken out and dried to obtain the polyvinylidene fluoride substrate.

[0079] In a preferred embodiment, the organic solvent C is tetrahydrofuran, benzene, or ethyl acetate, preferably tetrahydrofuran.

[0080] In a preferred embodiment, in step (5), the coating thickness of the mixture obtained by mixing polyoctafluoropentoxyphosphazene and polyn-octylaminephosphazene on the polyvinylidene fluoride substrate is 3-5 μm. Specifically, the coating thickness can be 3 μm, 4 μm, or 5 μm.

[0081] In a preferred embodiment, in step (5), the solid content in the mixture has a significant impact on the performance of the prepared gas separation membrane. The solid content in the mixture is 9-11 wt%, preferably 9.5-10.5 wt%, and more preferably 10 wt%.

[0082] In the method described in this invention, a blended gas separation membrane is prepared by mixing the prepared polyoctafluoropentoxyphosphazene and polyn-octylaminephosphazene. The use of the two polyphosphazene materials can significantly improve the selectivity of the prepared gas separation membrane and greatly improve the separation efficiency of carbon dioxide.

[0083] More importantly, in this invention, the ratio of polyoctafluoropentoxyphosphazene to poly(n-octylamine phosphazene) is directly related to the separation performance of the prepared gas separation membrane. When the ratio of their amounts is outside the range defined in this invention, it will adversely affect the performance of the prepared gas separation membrane and affect its selectivity. The weight ratio of polyoctafluoropentoxyphosphazene to poly(n-octylamine phosphazene) is further defined as 2-4:1, preferably 2.5-3.5:1. Specifically, the weight ratio of polyoctafluoropentoxyphosphazene to poly(n-octylamine phosphazene) can be 2:1, 3:1, or 4:1.

[0084] The present invention also provides a gas separation membrane prepared by the above method. The gas separation membrane has a high affinity for carbon dioxide and appropriately increases the free volume porosity of the membrane, which effectively solves the problem of the "trade-off" effect existing in the prior art gas separation membrane. It has excellent selectivity and can quickly separate carbon dioxide and methane.

[0085] The present invention also provides an application of the gas separation membrane in the process of separating carbon dioxide from a mixed gas. Preferably, the mixed gas contains methane and carbon dioxide.

[0086] In a preferred embodiment, the separation conditions for separating carbon dioxide from the mixed gas using the gas separation membrane include: a temperature of 25-45°C and a mixed gas flow rate of 35-45 ml / min.

[0087] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0088] In this invention, the experimental methods in the following embodiments are conventional methods in the art unless otherwise specified. The experimental materials used in the following embodiments are commercially available unless otherwise specified.

[0089] Example 1

[0090] (1) The crude hexachlorocyclotriphosphazene was dissolved in n-heptane solvent at a solid-liquid ratio of 0.5g:1mL, heated under reflux at 80℃ for 0.5h, then filtered, and the filtrate was cooled to 25℃ to precipitate white crystals. The precipitated crystals were dried under vacuum, and the dried product was sublimated to constant weight at 85℃ to obtain purified hexachlorocyclotriphosphazene.

[0091] (2) In a nitrogen atmosphere, 5g of purified hexachlorocyclotriphosphazene was placed in a glass ampoule, connected to a double-row tube, and evacuated three times with nitrogen gas. The tube was then sealed at high temperature under vacuum conditions. The sealed glass ampoule was placed in an oven and rotated at 260°C for 25 hours. The hexachlorocyclotriphosphazene in the tube became viscous and stopped flowing. Heating was stopped, and the glass ampoule was removed from the oven and placed at room temperature for later use.

[0092] (3) Place tetrahydrofuran in a three-necked flask and use benzophenone as an indicator. Add sodium wire to the tetrahydrofuran in an ice-water bath. Then heat the reaction system to 70°C and stir for 18 hours until the reaction system turns blue. Stop adding sodium wire and then distill the obtained material at 85°C to obtain anhydrous tetrahydrofuran.

[0093] (4) Dissolve sodium hydride (NaH, 60% stored in mineral oil) in the anhydrous tetrahydrofuran, and evacuate the three-necked flask 2-3 times by passing nitrogen gas through a double-row tube to replace the air in the flask. Under nitrogen protection, place octafluoropentanol in a syringe and add it dropwise to the anhydrous tetrahydrofuran solution containing NaH (the molar ratio of octafluoropentanol to NaH is 1:1). Maintain the system temperature at 0°C with an ice bath. After the octafluoropentanol is added, transfer the flask to a 60°C oil bath and react for 60 hours to obtain sodium octafluoropentanol.

[0094] (5) The polydichlorophosphazene obtained in step (2) is directly added to the anhydrous tetrahydrofuran solution, and then the anhydrous tetrahydrofuran solution of sodium octafluoropentoxide obtained in step (4) is added. The mixture is refluxed and stirred at 65°C for 72 hours under a nitrogen atmosphere (the molar ratio of sodium octafluoropentoxide to polydichlorophosphazene is 1.2:1, and the molar amount of polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene). After the reaction is completed, the resulting reactants are neutralized with 3M HCl to make the pH of the reactants 7. The filtrate is then filtered and rotary evaporated at a temperature of 45°C. o C. The material obtained by rotary evaporation is then dissolved in n-hexane, filtered to remove insoluble matter, and the filtrate is cooled to precipitate crystals. The precipitated crystals are then washed with water to remove residual salts and dried in an oven for 24 hours. The dried product is then dissolved in tetrahydrofuran solution, centrifuged to remove insoluble polymers and impurities, and the resulting solution is washed three times with petroleum ether and then dried at 60°C to obtain polyoctafluoropentoxyphosphazene (POFP).

[0095] (6) Pour the polydichlorophosphazene obtained in step (2) into a 250 mL three-necked flask, then disperse n-octylamine and acid-binding agent (triethylamine) in a tetrahydrofuran solution (wherein, the molar ratio of polydichlorophosphazene to n-octylamine is 1:2, the molar amount of polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene; the molar ratio of n-octylamine to triethylamine is 5:6), and slowly add it dropwise to the three-necked flask containing polydichlorophosphazene under nitrogen protection. After the dropwise addition is completed, reflux the reaction at 60 °C for 72 h. After the reaction is completed, concentrate the material obtained after the reaction using a rotary evaporator, precipitate the concentrated product in ultrapure water, filter and dissolve the obtained filter residue in tetrahydrofuran, then filter, cool the obtained filtrate to crystallize, and then dry it in a 60 °C oven for 24 h to obtain poly(n-octylamine phosphazene) (POA).

[0096] (7) Add the vacuum-dried polyvinylidene fluoride to triethyl phosphate solvent (the weight ratio of polyvinylidene fluoride to triethyl phosphate is 20:1.5), and heat to 110°C using a constant-temperature magnetic stirrer. oStir for 24 hours to fully dissolve the PVDF solution, then dry it in a vacuum drying oven for 1 hour. Next, evenly coat the prepared PVDF solution onto the nonwoven fabric, and then quickly immerse it in an ultrapure aqueous solution for 24 hours. Change the water every 2 hours during the immersion period. After the immersion is completed, take it out and air dry it at room temperature to obtain the polyvinylidene fluoride (PVDF) substrate.

[0097] (8) The poly(n-octylamine phosphazene) (POA) and poly(octafluoropentoxyphosphazene) (POFP) are mixed in a weight ratio of 25:75 and added to a tetrahydrofuran solvent. The mixture is heated and stirred, and ultrasonically dispersed for 30 min to obtain a slurry (the mass fraction of poly(octafluoropentoxyphosphazene) and poly(n-octylamine phosphazene) in the slurry is 10 wt%, that is, the solid content in the slurry is 10 wt%). The obtained slurry is coated onto the polyvinylidene fluoride substrate to form a film with a coating thickness of 4 μm. The film is allowed to stand at 25 °C and then dried at 60 °C for 24 h to obtain the gas separation membrane Blend1 / PVDF.

[0098] Example 2

[0099] The method described in Example 1 was implemented, except that the poly(n-octylamine phosphazene) (POA) and the poly(octafluoropentoxyphosphazene) (POFP) were mixed in a weight ratio of 30:70 before preparation.

[0100] Comparative Example 1

[0101] The method of Example 1 was implemented, except that in step (8), the weight ratio of poly(n-octylamine phosphazene) (POA) and poly(octafluoropentoxyphosphazene) (POFP) was 50:50.

[0102] Comparative Example 2

[0103] The method of Example 1 was implemented, except that in step (8), the weight ratio of poly(n-octylamine phosphazene) (POA) to poly(octafluoropentoxyphosphazene) (POFP) was 75:25.

[0104] Comparative Example 3

[0105] The method of Example 1 is implemented, except that poly(n-octylamine phosphazene) is not added to the gas separation membrane, that is, in step (8), poly(n-octylamine phosphazene) (POA) is not added for mixing. Specifically, poly(octafluoropentoxyphosphazene) is added to a tetrahydrofuran solution to obtain a slurry, and the mass fraction of poly(octafluoropentoxyphosphazene) in the slurry is 10 wt%.

[0106] Comparative Example 4

[0107] The method of Example 1 is implemented, except that polyoctafluoropentoxyphosphazene is not added to the gas separation membrane, that is, in step (8), polyoctafluoropentoxyphosphazene is not added for mixing. Specifically, poly(n-octylamine phosphazene) is added to a tetrahydrofuran solution to obtain a slurry, and the mass fraction of poly(n-octylamine phosphazene) in the slurry is 10 wt%.

[0108] Comparative Example 5

[0109] The method described in Example 1 was followed, except that the poly(n-octylamine phosphazene) (POA) and the poly(octafluoropentoxyphosphazene) (POFP) were mixed in a weight ratio of 40:60 before preparation.

[0110] Test case

[0111] Test Example 1

[0112] The surface morphology and cross-sectional morphology of the gas separation membrane prepared in Example 1 were tested using SEM. The results of the cross-sectional morphology are shown below. Figure 1 As shown, the surface morphology results are as follows Figure 2 As shown;

[0113] The surface morphology and cross-sectional morphology of the separation membranes prepared in Comparative Examples 1, 2, and 3 were measured using SEM. The cross-sectional morphologies of the separation membranes prepared in Comparative Examples 1, 2, and 3 are shown below, in order. Figure 3 , Figure 4 and Figure 5 As shown; the surface morphologies of the separation membranes prepared in Comparative Examples 1, 2, and 3 are as follows: Figure 6 , Figure 7 and Figure 8 As shown.

[0114] As shown in the figure, the gas separation membrane prepared by the method of the present invention has a dense separation layer and a porous support layer on its cross section, and the separation layer is tightly bonded to the base membrane without defects.

[0115] Test Example 2

[0116] The gas separation membranes prepared in Examples 1-2 and Comparative Examples 1-5 were tested for their separation performance against carbon dioxide gas. The test methods are as follows:

[0117] Under the conditions of a test temperature of 25℃ and a pressure difference of 0.2MPa across the membrane, H2 was used as the carrier gas and a mixture of CO2 and CH4 was used as the test gas. The flow rate of the carrier gas was 40mL / min and the flow rate of the test gas was 20mL / min. The test results are shown in Table 1.

[0118] Table 1

[0119]

[0120] As can be seen from the results in Table 1, the gas separation membrane prepared by the method described in this invention has a higher affinity for carbon dioxide in the mixed gas and a higher selectivity for separating carbon dioxide from the mixed gas, resulting in superior separation efficiency for carbon dioxide gas. The performance of the gas separation membranes prepared in Examples 2 and 3 is similar to that in Example 1, and will not be described further here.

[0121] Test Example 2

[0122] The gas separation membrane prepared in Example 1 was tested to assess its separation performance against carbon dioxide at different separation temperatures. The test method is as follows:

[0123] Under the conditions of a feed pressure of 2 bar and test temperatures of 25℃, 30℃, 35℃, 40℃ and 45℃ respectively, H2 was used as the carrier gas, and CO2 and CH4 were used as the test gases. The carrier gas flow rate was 40 mL / min, and the test gas flow rate was 20 mL / min. The test results are shown in Table 2.

[0124] Table 2

[0125]

[0126] Test Example 3

[0127] The gas separation membrane prepared in Example 1 was tested to assess its separation performance against carbon dioxide gas under different separation pressures. The test method is as follows:

[0128] Under the conditions of feed pressures of 2 bar, 3 bar, 4 bar, 5 bar and 6 bar, and a test temperature of 25℃, H2 was used as the carrier gas, and CO2 and CH4 were used as the test gases. The carrier gas flow rate was 40 mL / min, and the test gas flow rate was 20 mL / min. The test results are shown in Table 3.

[0129] Table 3

[0130]

[0131] As shown in Tables 2 and 3, the CO2 permeability increases with the increase of POFP content in the blended composite membrane. Furthermore, the gas separation membrane prepared in this application can be processed over a wide temperature range while maintaining good separation performance. The performance of the gas separation membranes prepared in Examples 2 and 3 is similar to that in Example 1, and will not be repeated here.

[0132] The blended gas separation membrane prepared by the method described in this invention has a simple preparation process, mild substitution conditions, and excellent gas separation performance. Compared with a single polymer-based membrane, it has significantly improved CO2 permeation performance and exhibits good separation performance in the field of CO2 / CH4 system separation, showing excellent application prospects.

[0133] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a gas separation membrane, characterized in that, The preparation method includes the following steps: (1) Sodium hydride, octafluoropentanol and organic solvent A are mixed and reacted to obtain sodium octafluoropentanol; (2) Under a protective atmosphere, the sodium octafluoropentoxide solution is mixed with polydichlorophosphazene solution and heated under reflux to react and obtain the product polyoctafluoropentoxyphosphazene: (3) In a protective atmosphere, polydichlorophosphazene, n-octylamine and acid-binding agent are reacted in organic solvent B to obtain the product polyn-octylaminephosphazene; (4) Mix polyvinylidene fluoride with triethyl phosphate, coat the resulting mixture onto a nonwoven fabric, and then immerse it in water to obtain a polyvinylidene fluoride substrate; (5) Mix the polyoctafluoropentoxyphosphazene, the poly(n-octylamine phosphazene) and organic solvent C, and then coat the mixture onto the polyvinylidene fluoride substrate; The weight ratio of the polyoctafluoropentoxyphosphazene to the polyn-octylamine phosphazene is 2-4:

1.

2. The method for preparing the gas separation membrane according to claim 1, characterized in that, In step (1), the weight ratio of sodium hydride to octafluoropentanol is 1:1-1.

2.

3. The method for preparing the gas separation membrane according to claim 1 or 2, characterized in that, In step (1), the reaction conditions include a temperature of 60-65°C and a time of 60-72h.

4. The method for preparing the gas separation membrane according to claim 1 or 2, characterized in that, The organic solvent A is dioxane, benzene, or tetrahydrofuran.

5. The method for preparing the gas separation membrane according to claim 1, characterized in that, In step (2), the temperature of the heating reflux is 60-70°C. o C, the heating and reflux time is 65-75h.

6. The method for preparing the gas separation membrane according to claim 1 or 5, characterized in that, The molar ratio of sodium octafluoropentoxide to polydichlorophosphazene is 1.0-1.5:1, wherein the molar amount of polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene.

7. The method for preparing the gas separation membrane according to claim 1, characterized in that, In step (3), the reaction temperature is 50-65℃ and the reaction time is 60-75h.

8. The method for preparing the gas separation membrane according to claim 1 or 7, characterized in that, In step (3), the weight ratio of the amount of n-octylamine to the amount of the acid-binding agent is 1:1.2-1.

5.

9. The method for preparing the gas separation membrane according to claim 1 or 7, characterized in that, In step (3), the molar ratio of the polydichlorophosphazene to the n-octylamine is 1:2-3, wherein the molar amount of the polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene.

10. The method for preparing the gas separation membrane according to claim 1 or 7, characterized in that, The organic solvent B is tetrahydrofuran, dioxane, or benzene.

11. The method for preparing the gas separation membrane according to claim 1 or 7, characterized in that, The acid-binding agent is triethylamine.

12. The method for preparing the gas separation membrane according to claim 1, characterized in that, The specific process of step (2) includes: mixing sodium octafluoropentoxide with polydichlorophosphazene solution in a protective atmosphere, heating and refluxing to react, purifying the reacted material to obtain the product polyoctafluoropentoxyphosphazene.

13. The method for preparing the gas separation membrane according to claim 12, characterized in that, The purification process includes: S1 adjusts the pH of the reacted material to 6.5-7.5, filters it, then rotary evaporates the filtrate, mixes the rotary evaporated material with n-hexane, filters it to obtain filter residue, washes it with water and dries it. S2 mixes the dried product with tetrahydrofuran, then filters it. The resulting filtrate is then mixed with petroleum ether, filtered again to obtain a filter residue, and the residue is dried to obtain the product polyoctafluoropentoxyphosphazene.

14. The method for preparing the gas separation membrane according to claim 1, characterized in that, The specific process of step (3) includes: in a protective atmosphere, mixing polydichlorophosphazene, n-octylamine and acid-binding agent in organic solvent B to react, purifying the reacted material to obtain the product polyn-octylaminephosphazene.

15. The method for preparing the gas separation membrane according to claim 14, characterized in that, The purification process includes: concentrating the material obtained from the reaction, then mixing the concentrated product with water, filtering to obtain a filter residue, mixing the obtained filter residue with tetrahydrofuran, filtering again, and drying the obtained filter residue to obtain the product poly(n-octylamine phosphazene).

16. The method for preparing the gas separation membrane according to claim 1, characterized in that, In step (4), the weight ratio of the polyvinylidene fluoride and the triethyl phosphate is 20:1-2.

17. The method for preparing a gas separation membrane according to claim 1 or 16, characterized in that, The organic solvent C is tetrahydrofuran, benzene, or ethyl acetate.

18. The method for preparing the gas separation membrane according to claim 1 or 16, characterized in that, In step (5), the coating thickness is 3-5 μm.

19. The method for preparing a gas separation membrane according to claim 1 or 16, characterized in that, In step (5), the solid content in the mixture is 9-11 wt%.

20. A gas separation membrane prepared by the method for preparing a gas separation membrane according to any one of claims 1-19.

21. The application of the gas separation membrane of claim 20 in the process of separating carbon dioxide from a mixed gas.

22. The application according to claim 21, characterized in that, The mixture contains methane and carbon dioxide.

23. The application according to claim 21 or 22, characterized in that, The separation conditions include a temperature of 25-45℃ and a mixed gas flow rate of 35-45 ml / min.

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