Gas separation membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of gas separation, and discloses a preparation method of a gas separation membrane, which comprises the following steps: (1) mixing sodium hydride, octafluoropentanol and an organic solvent A for reaction to obtain sodium octafluoropentanol; (2) in a protective atmosphere, mixing sodium octafluoropentanol with a polydichlorophosphazene solution, and carrying out heating reflux for a reaction to obtain a product poly (octafluoropentyloxy) phosphazene; (3) mixing the polydichlorophosphazene, n-octylamine and an acid-binding agent in an organic solvent B for a reaction to obtain a product poly (n-octylamine) phosphazene; (4) mixing polyvinylidene fluoride and triethyl phosphate, coating a non-woven fabric with the mixed solution, and soaking the non-woven fabric in water to obtain a polyvinylidene fluoride-based substrate; and (5) mixing poly (octafluoropentyloxy) phosphazene, poly (n-octylamine) phosphazene and an organic solvent C, and then coating the polyvinylidene fluoride base with the mixed solution. The gas separation membrane disclosed by the invention has excellent high selectivity on CO2 and has a wide industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the field of gas separation, and in particular to a gas separation membrane and a preparation method and application thereof. Background Art

[0002] The rapid growth of energy demand and fossil fuel consumption has always attracted great attention. Biogas, as a renewable clean energy, can replace fossil fuels to alleviate the global energy crisis. The large amount of CO2 contained in biogas will lead to problems such as reduced combustion calorific value, solid formation in low-temperature devices and corrosion of steel pipes. Membrane separation of CO2 is an emerging technology for removing carbon dioxide from natural gas. Compared with traditional separation technology, it has the advantages of small footprint, simple process operation and low operating cost.

[0003] The membranes used to separate CO2 mainly include inorganic membranes and polymer membranes. Among them, inorganic membranes have higher gas separation performance, but their high cost and difficulty in preparation make it difficult to achieve large-scale industrial applications. Polymer membranes are inexpensive and easy to process, and can be combined with the advantages of different materials through blending and modification to meet different industrial needs. In order to improve the "trade-off" effect and improve the gas separation performance of polymer membranes, researchers have done a lot of work to optimize and modify membrane materials. The main methods include cross-linking, copolymerization, filling with inorganic particles, blending, etc., among which preparation by blending is a simple and effective method.

[0004] Among the numerous polymer membranes, polyphosphazene materials have attracted extensive attention due to their controllable synthesis, flexible main chain, high temperature resistance and high gas separation performance. However, since the synthesis of polydichlorophosphazene, the intermediate of polyphosphazene materials, requires extremely high purity of the precursor monomer, and it is very easy to cross-link and difficult to store, polyphosphazene materials are rarely used for carbon dioxide gas separation. In addition, there are few new types of polymer separation membranes available. Therefore, it is of great practical significance to study and develop a new type of gas separation membrane for separating carbon dioxide from biogas. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of the prior art, such as the small number of polymer membranes to choose from and the poor separation effect, and to provide a gas separation membrane and a preparation method and application thereof. The gas separation membrane has a separation layer and a base membrane, and the separation layer is obtained by blending polyoctafluoropentyloxyphosphazene and poly-n-octylaminephosphazene. The blended gas separation membrane is prepared by chemical modification and physical modification. The gas separation membrane described in the present invention has excellent high selectivity for CO2 and has broad industrial application prospects.

[0006] In order to achieve the above object, the present invention provides a method for preparing a gas separation membrane, the method comprising the following steps: (1) mixing sodium hydride, octafluoropentanol and an organic solvent A to react to obtain sodium octafluoropentanolate; (2) In a protective atmosphere, the sodium octafluoropentanolate and the polydichlorophosphazene solution are mixed, and the mixture is heated under reflux to react, thereby obtaining the product polyoctafluoropentyloxyphosphazene: (3) In a protective atmosphere, polydichlorophosphazene, n-octylamine and an acid-binding agent are mixed in an organic solvent B for reaction to obtain a product, poly-n-octylaminephosphazene; (4) mixing polyvinylidene fluoride and triethyl phosphate, coating the obtained mixture on a non-woven fabric, and then soaking the mixture in water to obtain a polyvinylidene fluoride substrate; (5) mixing the polyoctafluoropentyloxyphosphazene, the poly-n-octylaminephosphazene and the organic solvent C, and then coating the mixture on the polyvinylidene fluoride substrate; Wherein, the weight ratio of the polyoctafluoropentyloxyphosphazene to the poly-n-octylaminephosphazene is 2-4:1.

[0007] Preferably, in step (1), the weight ratio of sodium hydride to octafluoropentanol is 1:1-1.2; Preferably, in step (1), the reaction conditions include: temperature of 60-65°C and time of 60-72h; Preferably, the organic solvent A is dioxane, benzene or tetrahydrofuran.

[0008] Preferably, in step (2), the heating reflux temperature is 60-70 o C, the heating reflux time is 65-75h; Preferably, the molar ratio of sodium octafluoropentanolate to polydichlorophosphazene is 1.0-1.5:1, wherein the molar amount of the polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene.

[0009] Preferably, in step (3), the reaction temperature is 50-65°C and the reaction time is 60-75h; Preferably, in step (3), the weight ratio of the n-octylamine to the acid binding agent is 1:1.2-1.5; 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; Preferably, the organic solvent B is dioxane, benzene or tetrahydrofuran; Preferably, the acid binding agent is triethylamine.

[0010] Preferably, the specific process of step (2) comprises: mixing the sodium octafluoropentanolate with the polydichlorophosphazene solution in a protective atmosphere, heating under reflux for reaction, and purifying the material obtained by the reaction to obtain the product polyoctafluoropentyloxyphosphazene: Preferably, the purification process comprises: S1: adjusting the pH value of the reacted material to 6.5-7.5, filtering, and then rotary evaporating the obtained filtrate, and then mixing the rotary evaporated material with n-hexane, filtering to obtain a filter residue, washing with water, and drying; S2: Mix the dried product with tetrahydrofuran, filter, mix the obtained filtrate with petroleum ether, filter to obtain filter residue, and dry the filter residue to obtain the product polyoctafluoropentyloxyphosphazene.

[0011] Preferably, the specific process of step (3) comprises: mixing polydichlorophosphazene, n-octylamine and an acid-binding agent in an organic solvent B for reaction in a protective atmosphere, purifying the material obtained by the reaction to obtain the product poly-n-octylaminephosphazene; Preferably, the purification process comprises: concentrating the material obtained by the reaction, then mixing the concentrated product with water, filtering to obtain a filter residue, mixing the obtained filter residue with tetrahydrofuran, then filtering, and drying the obtained filter residue to obtain the product poly-n-octylamine phosphazene.

[0012] Preferably, in step (4), the weight ratio of polyvinylidene fluoride to triethyl phosphate is 20:1-2; Preferably, the organic solvent C is tetrahydrofuran, benzene or ethyl acetate; Preferably, in step (5), the coating thickness is 3-5 μm; Preferably, in step (5), the solid content in the mixed solution is 9-11 wt %.

[0013] The second aspect of the present invention provides a gas separation membrane prepared by the above method.

[0014] A third aspect of the present invention provides an application of the gas separation membrane in a process of separating carbon dioxide from a mixed gas; Preferably, the mixed gas contains methane and carbon dioxide.

[0015] Preferably, the separation conditions include: a temperature of 25-45° C. and a mixed gas flow rate of 35-45 ml / min.

[0016] In the preparation method described in the present invention, a fluorine-containing polyphosphazene material polyoctafluoropentyloxyphosphazene with higher bond energy, better thermal stability and stronger affinity with CO2 is prepared and synthesized by a chemical modification method, and polyoctafluoropentyloxyphosphazene is blended with poly-n-octylaminephosphazene to prepare a composite membrane. The method described in the present invention solves the disadvantage of low selectivity of polymer membranes for CO2 / CH4 in current technology by introducing CF bonds with affinity for CO2 and appropriately increasing the free volume pores of the membrane. Through gas separation performance testing, it is found that the gas separation membrane prepared by the present invention breaks through the "trade-off" effect, can quickly separate carbon dioxide from biogas, and has broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a cross-sectional morphology diagram of the gas separation membrane prepared in Example 1; Figure 2 is a surface morphology image of the gas separation membrane prepared in Example 1; Figure 3 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Comparative Example 1; Figure 4 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Comparative Example 2; Figure 5 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Comparative Example 3; Figure 6 This is a surface morphology of the gas separation membrane prepared in Comparative Example 1; Figure 7 This is a surface morphology of the gas separation membrane prepared in Comparative Example 2; Figure 8 This is the surface morphology of the gas separation membrane prepared in Comparative Example 3. DETAILED DESCRIPTION

[0018] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0019] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0020] The present invention provides a method for preparing a gas separation membrane, the preparation method comprising the following steps: (1) mixing sodium hydride, octafluoropentanol and an organic solvent A to react to obtain sodium octafluoropentanolate; (2) In a protective atmosphere, the sodium octafluoropentanolate and the polydichlorophosphazene solution are mixed, and the mixture is heated under reflux to react, thereby obtaining the product polyoctafluoropentyloxyphosphazene: (3) In a protective atmosphere, polydichlorophosphazene, n-octylamine and an acid-binding agent are mixed in an organic solvent B for reaction to obtain a product, poly-n-octylaminephosphazene; (4) mixing polyvinylidene fluoride and triethyl phosphate, coating the obtained mixture on a non-woven fabric, and then soaking the mixture in water to obtain a polyvinylidene fluoride substrate; (5) The polyoctafluoropentyloxyphosphazene, the poly-n-octylaminephosphazene and the organic solvent C are mixed, and then the mixed solution is coated on the polyvinylidene fluoride substrate.

[0021] In the method of the present invention, in step (1), since sodium hydride is active and reacts violently with water, the organic solvent A used in step (1) needs to remove the water contained therein in advance. Specifically, the method for removing water from the organic solvent A comprises: using benzophenone as an indicator, adding sodium wire to the 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 standby use. In a preferred embodiment, the organic solvent A is one of dioxane, benzene or tetrahydrofuran, and more preferably tetrahydrofuran.

[0022] 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.

[0023] In a preferred embodiment, in step (1), the reaction conditions include: a temperature of 60-65°C and a reaction time of 60-72 hours. Specifically, the reaction temperature may be 60°C, 61°C, 62°C, 63°C, 64°C or 65°C; and the reaction time may be 60 hours, 65 hours, 70 hours or 72 hours.

[0024] In a specific embodiment, in step (2), the polydichlorophosphazene solution is obtained by dissolving polydichlorophosphazene in a common organic solvent, and the organic solvent may be tetrahydrofuran. Specifically, the polydichlorophosphazene may be prepared according to a common method in the art.

[0025] More preferably, the preparation method of the polydichlorophosphazene used in the method of the present invention comprises: in a vacuum environment, the purified hexachlorocyclotriphosphazene is subjected to a melt polymerization method to obtain the polydichlorophosphazene. The reaction conditions of the melt polymerization method include: a temperature of 240-260°C and a time of 16-36h. The temperature of the melt polymerization method may be 240°C, 250°C or 260°C; the time of the melt polymerization method may be 16h, 20h, 25h, 30h or 36h. Specifically, after the reaction is completed, the material will become viscous and difficult to flow.

[0026] In a specific embodiment, the purification process of the hexachlorocyclotriphosphazene comprises: dissolving the crude hexachlorocyclotriphosphazene in an n-heptane solvent, heating and refluxing at 75-80° C. to fully dissolve it, filtering to remove insoluble impurities, cooling the obtained filtrate for recrystallization, and vacuum drying the precipitated crystals. After repeating this purification process 3-5 times, the obtained product is sublimated at 80-90° C. to constant weight to obtain the purified hexachlorocyclotriphosphazene.

[0027] In a preferred embodiment, in step (2), the heating reflux temperature is 60-70 o C, and the heating reflux time is 65-75h. Specifically, in step (2), the heating reflux temperature is the temperature of the reaction in step (2), and the heating reflux time is the time of the reaction in step (2). Specifically, the heating reflux temperature can be 60 o C. 65 o C or 70 o C; the heating reflux time can be 65h, 70h, 72h or 75h.

[0028] In a preferred embodiment, the molar ratio of sodium octafluoropentanolate to polydichlorophosphazene is 1.0-1.5:1, more preferably 1-1.2:1, more preferably 1.2:1, wherein the molar amount of the polydichlorophosphazene is based on the molar amount of hexachlorocyclotriphosphazene. Specifically, the molar ratio of sodium octafluoropentanolate to polydichlorophosphazene can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1.

[0029] In a specific embodiment, in step (2), the protective atmosphere can be one of a nitrogen atmosphere, an argon atmosphere or a helium atmosphere.

[0030] In the method of the present invention, the specific process of step (2) includes: mixing the sodium octafluoropentanolate with the polydichlorophosphazene solution in a protective atmosphere, heating and refluxing to react, purifying the material obtained by the reaction to obtain the product polyoctafluoropentyloxyphosphazene. In order to further improve the purity of the prepared product polyoctafluoropentyloxyphosphazene, thereby improving the selectivity of the prepared gas separation membrane, the purification step of the material after the reaction includes: S1: adjusting the pH value of the reacted material to 6.5-7.5, filtering, and then rotary evaporating the obtained filtrate, and then mixing the rotary evaporated material with n-hexane, filtering to obtain a filter residue, washing with water, and drying; S2: Mix the dried product with tetrahydrofuran, filter, mix the obtained filtrate with petroleum ether, filter to obtain filter residue, and dry the filter residue to obtain the product polyoctafluoropentyloxyphosphazene.

[0031] Specifically, in step S1, most of the solvent is removed by rotary evaporation, and then crystals are precipitated by n-hexane precipitation, and the obtained crystals are washed with water and dried after filtration to obtain a crude polyoctafluoropentyloxyphosphazene product. The obtained crude polyoctafluoropentyloxyphosphazene product is then dissolved in a tetrahydrofuran solution, and then insoluble polymers and impurities are removed by centrifugation, and then the liquid obtained by centrifugation is precipitated 3-4 times with petroleum ether to remove unreacted monomers and oligomers in the product, and then the obtained solid phase is dried to obtain the product polyoctafluoropentyloxyphosphazene.

[0032] 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 may be 50°C, 52°C, 55°C, 60°C, 62°C or 65°C; the reaction time may be 60h, 65h, 72h or 75h.

[0033] In a preferred embodiment, in step (3), the weight ratio of the n-octylamine to the acid binding agent is 1:1.2-1.5. Specifically, the weight ratio of the n-octylamine to the acid binding agent can be 1:1.2, 1:1.3, 1:1.4 or 1:1.5.

[0034] In a preferred embodiment, in step (3), the molar ratio of the amount of the polydichlorophosphazene to the amount of the n-octylamine is 1:2-3, wherein the molar amount of the polydichlorophosphazene is calculated based on the molar amount of hexachlorocyclotriphosphazene. Specifically, the molar ratio of the amount of the polydichlorophosphazene to the amount of the n-octylamine can be 1:2, 1:2.5, 1:2.8 or 1:3.

[0035] In a preferred embodiment, the organic solvent B is selected from tetrahydrofuran, dioxane or benzene, more preferably tetrahydrofuran.

[0036] 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.

[0037] In a preferred embodiment, the acid binding agent is triethylamine.

[0038] In the method of the present invention, the specific process of step (3) comprises: in a protective atmosphere, mixing polydichlorophosphazene, n-octylamine and an acid-binding agent in an organic solvent B for reaction, purifying the material obtained by the reaction to obtain the product poly-n-octylaminephosphazene. In a preferred embodiment, the purification process comprises: concentrating the material obtained by the reaction, then mixing the concentrated product with water, filtering to obtain a filter residue, mixing the obtained filter residue with tetrahydrofuran, then filtering, and drying the obtained filter residue to obtain the product poly-n-octylaminephosphazene.

[0039] Specifically, in the purification process of step (3), the material after the reaction is concentrated by a rotary evaporator, and then the concentrated product is precipitated in water, the precipitated material is filtered, and then the filter residue is dissolved in tetrahydrofuran, undissolved impurities are removed, and the filtrate is obtained by filtering, and then the temperature is reduced for recrystallization, and the product poly-n-octylamine phosphazene is obtained after drying. In order to further improve the purity of the product, the recrystallized product can be repeatedly placed in tetrahydrofuran for multiple dissolution-recrystallization operations.

[0040] In a specific embodiment, in step (3), the protective atmosphere can be one of a nitrogen atmosphere, an argon atmosphere or a helium atmosphere.

[0041] In the method described in the present invention, by the operation of step (4), a more loose and porous polyvinylidene fluoride substrate can be prepared, thereby further improving the performance of the prepared gas separation membrane.

[0042] 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.

[0043] In a specific embodiment, in step (4), after the slurry of polyvinylidene fluoride and triethyl phosphate is coated on the non-woven fabric, it is immediately immersed in water for 20-24 hours, and the water used for immersion is changed every 2 hours. After the immersion is completed, it is taken out and dried to obtain the polyvinylidene fluoride substrate.

[0044] In a preferred embodiment, the organic solvent C is tetrahydrofuran, benzene or ethyl acetate, preferably tetrahydrofuran.

[0045] In a preferred embodiment, in step (5), the coating thickness of the mixed solution obtained by mixing polyoctafluoropentyloxyphosphazene and poly-n-octylaminephosphazene on the polyvinylidene fluoride substrate is 3-5 μm. Specifically, the coating thickness can be 3 μm, 4 μm or 5 μm.

[0046] In a preferred embodiment, in step (5), the solid content in the mixed liquid has a great influence on the performance of the prepared gas separation membrane. The solid content in the mixed liquid is 9-11 wt %, preferably 9.5-10.5 wt %, and more preferably 10 wt %.

[0047] In the method described in the present invention, a blended gas separation membrane is prepared by mixing the prepared polyoctafluoropentyloxyphosphazene and poly-n-octylaminephosphazene. The mixed 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.

[0048] More importantly, in the present invention, there is a direct correlation between the amount relationship of polyoctafluoropentyloxyphosphazene and poly-n-octylaminephosphazene and the separation performance of the prepared gas separation membrane. When the amount relationship between the two is not within the range defined by the present invention, it will have an adverse effect on the performance of the prepared gas separation membrane and affect the selectivity of the gas separation membrane. It is further defined that the weight ratio of the amount of the polyoctafluoropentyloxyphosphazene and the poly-n-octylaminephosphazene is 2-4:1, preferably 2.5-3.5:1. Specifically, the weight ratio of the polyoctafluoropentyloxyphosphazene and the poly-n-octylaminephosphazene can be 2:1, 3:1 or 4:1.

[0049] The present invention also provides a gas separation membrane prepared by the above method, which has a high affinity for carbon dioxide and appropriately increases the free volume pores of the membrane, thereby effectively solving the problem of the "trade-off" effect existing in the gas separation membrane in the prior art, has excellent selectivity, and can quickly achieve the separation of carbon dioxide and methane.

[0050] 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.

[0051] In a preferred embodiment, the separation conditions when the gas separation membrane is used to separate carbon dioxide from a mixed gas include: a temperature of 25-45° C. and a mixed gas flow rate of 35-45 ml / min.

[0052] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0053] In the present invention, the experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0054] Example 1 (1) The crude hexachlorocyclotriphosphazene was dissolved in n-heptane solvent at a solid-liquid ratio of 0.5 g:1 mL, heated under reflux at 80° C. for 0.5 h, and then filtered. The filtrate was cooled to 25° C. to precipitate white crystals. The precipitated crystals were vacuum dried, and the dried product was sublimated at 85° C. to constant weight to obtain purified hexachlorocyclotriphosphazene; (2) In a nitrogen atmosphere, 5 g of purified hexachlorocyclotriphosphazene was placed in a glass ampoule, which was connected to a double-row tube and evacuated with nitrogen for three times, and 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. When the hexachlorocyclotriphosphazene in the tube became viscous and no longer flowed, heating was stopped, and the glass ampoule was taken out of the oven and placed at room temperature for standby use; (3) Put tetrahydrofuran in a three-necked flask and use benzophenone as an indicator. Add metallic sodium wire to tetrahydrofuran in an ice-water bath. Then heat the reaction system to 70°C and stir the reaction for 18 hours until the reaction system turns blue. Then stop adding sodium wire. Then distill the obtained material at 85°C to obtain anhydrous tetrahydrofuran. (4) Sodium hydride (NaH, 60% stored in mineral oil) is dissolved in the anhydrous tetrahydrofuran, and nitrogen is passed through the double-row tube to evacuate 2-3 times to replace the air in the three-necked flask. Under nitrogen protection, octafluoropentanol is placed in a syringe and dripped dropwise into the anhydrous tetrahydrofuran solution containing NaH (the molar ratio of octafluoropentanol to NaH is 1:1), and the system temperature is maintained at 0°C with an ice bath. After the octafluoropentanol is added, the system is moved into a 60°C oil bath for reaction for 60 hours to obtain sodium octafluoropentanolate; (5) directly adding the polydichlorophosphazene obtained in step (2) to the anhydrous tetrahydrofuran solution, and then adding the anhydrous tetrahydrofuran solution of sodium octafluoropentanolate obtained in step (4), and reacting under reflux stirring at 65° C. for 72 hours in a nitrogen atmosphere (the molar ratio of sodium octafluoropentanolate to polydichlorophosphazene is 1.2:1, and the molar amount of polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene); after the reaction, neutralizing the obtained reaction material with 3M HCl to make the pH value of the material 7, filtering and rotary evaporating the obtained filtrate, and the rotary evaporation temperature is 45 oC, then dissolving the material obtained by rotary evaporation in n-hexane, filtering to remove insoluble matter, then cooling the obtained filtrate to precipitate crystals, then washing the precipitated crystals with water to remove residual salt and then drying them in an oven for 24 hours; then dissolving the dried product in tetrahydrofuran solution, centrifuging to remove insoluble polymers and impurities, washing the obtained solution with petroleum ether for 3 times, and then drying at 60°C to obtain polyoctafluoropentyloxyphosphazene (POFP); (6) Pour the polydichlorophosphazene obtained in step (2) into a 250 mL three-necked flask, then disperse n-octylamine and an 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 based on hexachlorocyclotriphosphazene; the molar ratio of n-octylamine to triethylamine is 5:6), and slowly add the mixture dropwise to the three-necked flask containing the polydichlorophosphazene under nitrogen protection. After the addition is completed, reflux reaction is carried out at 60° C. for 72 h. After the reaction is completed, the material obtained after the reaction is concentrated by a rotary evaporator, and the concentrated product is precipitated in ultrapure water. The obtained filter residue is filtered and dissolved in tetrahydrofuran, then filtered, the obtained filtrate is cooled and crystallized, and then placed in an oven at 60° C. for 24 h to obtain poly-n-octylaminephosphazene (POA); (7) Add the vacuum-dried polyvinylidene fluoride into 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. o C and stirred for 24 hours to fully dissolve it, then placed in a vacuum drying oven and dried for 1 hour, then the prepared PVDF solution was evenly scraped onto the non-woven fabric, and then quickly placed in an ultrapure water solution and soaked for 24 hours, during which the water was changed every 2 hours, and after the soaking was completed, the non-woven fabric was taken out and dried at room temperature to obtain a polyvinylidene fluoride (PVDF) substrate; (8) The poly(n-octylamine phosphazene) (POA) and the poly(octafluoropentyloxyphosphazene) (POFP) were mixed in a weight ratio of 25:75 and added to a tetrahydrofuran solvent. The mixture was heated and stirred, and ultrasonicated for 30 min to uniformly disperse the mixture to obtain a slurry (in the slurry, the mass fraction of poly(octafluoropentyloxyphosphazene) and poly(n-octylamine phosphazene) was 10 wt %, i.e., the solid content in the slurry was 10 wt %); the obtained slurry was scraped onto the polyvinylidene fluoride substrate to form a film with a coating thickness of 4 μm, and the film was allowed to stand at 25° C. and then dried at 60° C. for 24 h to obtain a gas separation membrane Blend1 / PVDF.

[0055] Example 2 The method of Example 1 is used for implementation, except that the poly-n-octylamine phosphazene (POA) and the poly-octafluoropentyloxyphosphazene (POFP) are mixed in a weight ratio of 30:70 for preparation.

[0056] Comparative Example 1 The method of Example 1 is followed, except that in step (8), the weight ratio of poly-n-octylamine phosphazene (POA) to poly-octafluoropentyloxyphosphazene (POFP) is 50:50.

[0057] Comparative Example 2 The method of Example 1 is used for implementation, except that in step (8), the weight ratio of poly-n-octylamine phosphazene (POA) to poly-octafluoropentyloxyphosphazene (POFP) is 75:25.

[0058] Comparative Example 3 The method of Example 1 is used, except that no poly-n-octylamine phosphazene is added to the gas separation membrane, that is, in step (8), no poly-n-octylamine phosphazene (POA) is added for mixing. Specifically, poly-octafluoropentyloxyphosphazene is added to a tetrahydrofuran solution to obtain a slurry, and the mass fraction of poly-octafluoropentyloxyphosphazene in the slurry is 10 wt %.

[0059] Comparative Example 4 The method of Example 1 is followed, except that polyoctafluoropentyloxyphosphazene is not added to the gas separation membrane, that is, in step (8), polyoctafluoropentyloxyphosphazene is not added for mixing. Specifically, poly-n-octylaminephosphazene is added to tetrahydrofuran solution to obtain a slurry, and the mass fraction of poly-n-octylaminephosphazene in the slurry is 10 wt %.

[0060] Comparative Example 5 The method of Example 1 is used for implementation, except that the poly-n-octylamine phosphazene (POA) and the poly-octafluoropentyloxyphosphazene (POFP) are mixed in a weight ratio of 40:60 for preparation.

[0061] Test Case Test Example 1 The surface morphology and cross-sectional morphology of the gas separation membrane prepared in Example 1 were tested by SEM, wherein the cross-sectional morphology of the cross section was as follows: Figure 1 The surface morphology results are shown in Figure 2 As shown; The surface morphology and cross-sectional morphology of the separation membranes prepared in Comparative Examples 1, 2 and 3 were tested by SEM. The cross-sectional morphology of the separation membranes prepared in Comparative Examples 1, 2 and 3 are as follows: Figure 3 , Figure 4 and Figure 5 As shown; the surface morphology of the separation membranes prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 3 are as follows: Figure 6 , Figure 7 and Figure 8 shown.

[0062] As can be seen from the figure, the gas separation membrane prepared by the method described in the present invention has a dense surface separation layer and a porous support layer, and the separation layer is tightly combined with the base membrane without defects.

[0063] Test Example 2 The gas separation membranes prepared in Examples 1-2 and Comparative Examples 1-5 were tested for separation performance of gaseous carbon dioxide, and the test method was as follows: Under the conditions of test temperature of 25°C and pressure difference of 0.2MPa before and after the membrane, the test was carried out with H2 as carrier gas and a mixture of CO2 and CH4 as 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.

[0064] Table 1

[0065] It can be seen from the results in Table 1 that the gas separation membrane prepared by the method described in the present invention has a higher affinity for carbon dioxide in the mixed gas, and at the same time has a higher selectivity for separating carbon dioxide from the mixed gas, and a better 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 repeated here.

[0066] Test Example 2 The gas separation membrane prepared in Test Example 1 was tested for separation performance of gas carbon dioxide at different separation temperatures, and the test method was as follows: Under the conditions of feed pressure of 2 bar, test temperatures of 25°C, 30°C, 35°C, 40°C and 45°C, H2 as carrier gas, CO2 and CH4 as test gas, carrier gas flow rate of 40 mL / min, test gas flow rate of 20 mL / min, the test results are shown in Table 2: Table 2

[0067] Test Example 3 The gas separation membrane prepared in Test Example 1 was tested for separation performance of gas carbon dioxide at different separation pressures, and the test method was as follows: Under the conditions of feed pressure of 2 bar, 3 bar, 4 bar, 5 bar and 6 bar, test temperature of 25 ° C, H2 as carrier gas, CO2 and CH4 as test gas, carrier gas flow rate of 40 mL / min, test gas flow rate of 20 mL / min, the test results are shown in Table 3: Table 3

[0068] According to the data in Table 2 and Table 3, as the POFP content in the blended composite membrane increases, the permeability of CO2 increases, and the gas separation membrane prepared in the present application can be processed in a wide temperature range and has a good separation effect. The performance of the gas separation membrane prepared in Example 2 and Example 3 is similar to that in Example 1, and will not be repeated here.

[0069] The mixed gas separation membrane prepared by the method described in the present invention has a simple preparation process, mild substitution conditions, and excellent gas separation performance. Compared with a single polymer-based membrane, the CO2 permeability performance is significantly improved, and it exhibits good separation performance in the field of CO2 / CH4 system separation, and has excellent application prospects.

[0070] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a gas separation membrane, characterized in that: The preparation method comprises the following steps: (1) mixing sodium hydride, octafluoropentanol and an organic solvent A to react to obtain sodium octafluoropentanolate; (2) In a protective atmosphere, the sodium octafluoropentanolate and the polydichlorophosphazene solution are mixed, and the mixture is heated under reflux to react, thereby obtaining the product polyoctafluoropentyloxyphosphazene: (3) reacting polydichlorophosphazene, n-octylamine and an acid-binding agent in an organic solvent B in a protective atmosphere to obtain a product, poly-n-octylaminephosphazene; (4) mixing polyvinylidene fluoride and triethyl phosphate, coating the obtained mixture on a non-woven fabric, and then soaking the mixture in water to obtain a polyvinylidene fluoride substrate; (5) mixing the polyoctafluoropentyloxyphosphazene, the poly-n-octylaminephosphazene and the organic solvent C, and then coating the mixture on the polyvinylidene fluoride substrate; Wherein, the weight ratio of the polyoctafluoropentyloxyphosphazene to the poly-n-octylaminephosphazene is 2-4:

1.

2. The method for preparing a gas separation membrane according to claim 1, characterized in that: In step (1), the weight ratio of the sodium hydride to the octafluoropentanol is 1:1-1.2; Preferably, in step (1), the reaction conditions include: temperature of 60-65°C and time of 60-72h; Preferably, the organic solvent A is dioxane, benzene or tetrahydrofuran.

3. The method for preparing a gas separation membrane according to claim 1, characterized in that: In step (2), the heating reflux temperature is 60-70 o C, the heating reflux time is 65-75h; Preferably, the molar ratio of the sodium octafluoropentanolate to the polydichlorophosphazene is 1.0-1.5:1, wherein the molar amount of the polydichlorophosphazene is calculated as hexachlorocyclotriphosphazene.

4. The method for preparing a gas separation membrane according to claim 1, characterized in that: In step (3), the reaction temperature is 50-65°C and the reaction time is 60-75h; Preferably, in step (3), the weight ratio of the n-octylamine to the acid binding agent is 1:1.2-1.5; 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; Preferably, the organic solvent B is tetrahydrofuran, dioxane or benzene; Preferably, the acid binding agent is triethylamine.

5. The method for preparing a gas separation membrane according to claim 1, characterized in that: The specific process of step (2) includes: mixing the sodium octafluoropentanolate with the polydichlorophosphazene solution in a protective atmosphere, heating under reflux for reaction, and purifying the material obtained by the reaction to obtain the product polyoctafluoropentyloxyphosphazene: Preferably, the purification process comprises: S1: adjusting the pH value of the reacted material to 6.5-7.5, filtering, and then rotary evaporating the obtained filtrate, and then mixing the rotary evaporated material with n-hexane, filtering to obtain a filter residue, washing with water, and drying; S2: Mix the dried product with tetrahydrofuran, filter, mix the obtained filtrate with petroleum ether, filter to obtain filter residue, and dry the filter residue to obtain the product polyoctafluoropentyloxyphosphazene.

6. The method for preparing a gas separation membrane according to claim 1, characterized in that: The specific process of step (3) comprises: in a protective atmosphere, mixing polydichlorophosphazene, n-octylamine and an acid-binding agent in an organic solvent B for reaction, purifying the material obtained by the reaction to obtain a product, poly-n-octylaminephosphazene; Preferably, the purification process comprises: concentrating the material obtained by the reaction, then mixing the concentrated product with water, filtering to obtain a filter residue, mixing the obtained filter residue with tetrahydrofuran, then filtering, and drying the obtained filter residue to obtain the product poly-n-octylamine phosphazene.

7. The method for preparing a gas separation membrane according to claim 1, characterized in that: In step (4), the weight ratio of the polyvinylidene fluoride to the triethyl phosphate is 20:1-2; Preferably, the organic solvent C is tetrahydrofuran, benzene or ethyl acetate; Preferably, in step (5), the coating thickness is 3-5 μm; Preferably, in step (5), the solid content in the mixed solution is 9-11 wt %.

8. A gas separation membrane prepared according to the method for preparing a gas separation membrane according to any one of claims 1 to 7.

9. Use of the gas separation membrane according to claim 8 in a process of separating carbon dioxide from a mixed gas; Preferably, the mixed gas contains methane and carbon dioxide.

10. The use according to claim 9, characterized in that: The separation conditions include: temperature of 25-45°C and mixed gas flow rate of 35-45 ml / min.

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