Preparation method and application of mixed substituted polyphosphazene gas separation membrane

Abstract

The invention discloses a preparation method and application of a mixed substituted polyphosphazene gas separation membrane, and belongs to the technical field of gas separation. The preparation method comprises the following steps: 1) carrying out ring-opening polymerization of phosphonitrilic chloride trimer by a chemical reaction method to obtain an intermediate polydichlorophosphazene, 2) introducing aniline and n-octylamine with different molar contents (X) into the polyphosphazene to synthesize polyaniline-n-octylamine phosphazene (PBAPX / POA (1-X), the range of X being 0.30-0.05), 3) carrying out blade coating on a polytetrafluoroethylene (PVDF) support layer by a blade coating method, and 4) carrying out drying to obtain the polyaniline-n-octylamine phosphazene composite material. And preparing the PBAPX / POA (1-X) / PVDF gas separation composite membrane. The polyphosphazene gas separation membrane prepared by adopting the mixed substitution method is compact and uniform in surface, tight in connection between the supporting layer and the separation layer, free of obvious defects and excellent in separation and membrane forming performance.

Description

Technical Field

[0001] The invention relates to the technical field of gas separation, and in particular to a method for preparing a mixed substituted polyphosphazene gas separation membrane and application thereof. Background Art

[0002] Carbon capture, utilization and storage (CCUS) is an important way to prevent the further intensification of the greenhouse effect. Membrane separation technology has attracted widespread attention due to its advantages such as low energy consumption and high efficiency. The development of a membrane material with high permeability, selectivity and good film-forming properties is a hot topic in the current membrane material research field. In the foreseeable future, membrane separation technology will develop rapidly and gradually replace some traditional separation technologies.

[0003] Gas separation membranes mainly include polymer membranes, inorganic membranes and mixed matrix membranes, and polymer membranes are the most widely used membrane materials. However, due to the limitation of the types of traditional polymer membrane materials, the research on the use of new polymer materials in the field of gas separation is becoming less and less. Therefore, it is of great significance to study a new polymer membrane with high selectivity for CO2. As a polymer material with great research value, polyphosphazene materials are easy to modify after synthesis so that the required functional side groups can be connected after assembling the skeleton. By utilizing the diversity of the side group functions of polyphosphazene, suitable side groups are selected, and polyphosphazene membranes are prepared by chemical modification and physical modification methods, and used for CO2 / CH4 separation. Nowadays, many scholars have studied polyphosphazene membranes with different substituents, which show good permeability and selectivity in the field of gas separation. The addition of rigid substituents makes the material extremely strong, while the flexible side group single-substituted polyphosphazene often makes it difficult to prepare membranes due to the high degree of freedom of the chain segment, and the mechanical properties of the membrane are poor. In addition, the flexible side chain of the single-substituted polyphosphazene membrane is prone to collapse naturally during long-term stable operation, resulting in reduced stability.

[0004] Disubstituted polyphosphazenes can combine the advantages of two single-substituted materials. By introducing two substituents with different effects, the polyphosphazene membrane material has both excellent separation performance and good film-forming performance. However, since polydichlorophosphazene is easy to cross-link and difficult to store, and has extremely high requirements for the purity of the reaction precursor, there are not many literatures or reports on polyphosphazenes in the field of gas separation membranes, and there are relatively few related mixed-substituted polyphosphazene membranes. Summary of the invention

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] Technical Solution 1: PBAP X / POA (1-X)Preparation, (molar contents (X) are 0.30, 0.20, 0.10, and 0.05, respectively).

[0007] S1. synthesizing the intermediate polydichlorophosphazene (PDCP) from the purified hexachlorocyclotriphosphazene (HCCP) monomer by melt polymerization;

[0008] S2. Add a certain amount of tetrahydrofuran into a three-necked flask, and gradually add shredded sodium into tetrahydrofuran, stir the system at 70°C for 15-20h, then add benzophenone and distill it at 85°C after the system turns blue to obtain anhydrous tetrahydrofuran, seal it with a sealing film and place it in a drying oven for later use;

[0009] S3. The polydichlorophosphazene synthesized in S1, a slightly excess amount of aniline, n-octylamine, and triethylamine for dehydration are dissolved in tetrahydrofuran, and added to the dissolved polydichlorophosphazene by a one-time feeding method under nitrogen protection to make the reaction complete, thereby obtaining PBAP. X / POA (1-X) Crude product;

[0010] S4. In PBAP X / POA (1-X) Add solvent to the crude product, wash and dry, repeat 2-3 times to obtain PBAP X / POA (1-X) of pure product;

[0011] S5. The obtained pure PBAP X / POA (1-X) Dissolve in organic solvent to obtain PBAP with a solid content of 5-20% X / POA (1-X) Casting liquid;

[0012] S6. The polyaniline-n-octylamine phosphazene casting solution is coated on the polyvinylidene fluoride (PVDF) porous base membrane to obtain PBAP X / POA (1-X) / PVDF gas separation composite membrane.

[0013] Preferably, the purification treatment described in S1 comprises the following steps: dissolving the crude hexachlorocyclotriphosphazene in n-heptane of 80% of its own mass, refluxing at 80°C to fully dissolve it, filtering it while hot to remove impurities, sealing the filtrate and placing it in a refrigerator to recrystallize the hexachlorocyclotriphosphazene and then vacuum drying it, and repeating this operation three times. The recrystallized hexachlorocyclotriphosphazene is placed in a sublimation device and heated for vacuum sublimation.

[0014] Preferably, the reaction conditions of the melt polymerization method in S1 are: reacting in an anhydrous and oxygen-free environment at a temperature of 250-260°C for 17-37 hours. If the temperature is too high and the time is too long, cross-linking is easy to occur. If the temperature is too low and the time is too short, the molecular weight is low and the polymerization is incomplete.

[0015] Preferably, the commercially available analytically pure tetrahydrofuran in S2 contains a trace amount of water, and tetrahydrofuran is easily miscible with water molecules in the air, so the tetrahydrofuran must be dehydrated to prevent the reaction between water and polydichlorophosphazene.

[0016] Preferably, the acid binding agent in S3 is trimethylamine or triethylamine, and the molar ratio of aniline and triethylamine to the acid binding agent is 1:1; and the molar ratio of the polydichlorophosphazene to the aniline is 1:4.

[0017] Preferably, the washing in S4 specifically comprises: concentrating the crude polyaniline-n-octylamine phosphazene, pouring it into water, ethanol or methanol to wash the salt substances in the reaction product, and then stirring and precipitating it in n-heptane or petroleum ether, and washing the oligomers in the reaction product.

[0018] Preferably, the organic solvent in S5 is selected from tetrahydrofuran, dioxane and benzene; the pure polyaniline-n-octylamine phosphazene is heated in the organic solvent at 70° C. and refluxed for 2-4 hours.

[0019] Technical Solution 2: (PBAP X / POA (1-X) ) / PVDF composite membrane.

[0020] S1. Preparing a polyvinylidene fluoride (PVDF) base film;

[0021] S2. PBAP X / POA (1-X) The casting solution was coated on the PVDF porous substrate to obtain (PBAP X / POA (1-X) ) / PVDF gas separation composite membrane;

[0022] Preparation process of polyvinylidene fluoride base film in S1: a certain amount of polymer (polyvinylidene fluoride) is added to triethyl phosphate solvent after vacuum drying, heated and stirred with a constant temperature magnetic stirrer to make it fully dissolved for 24 hours, placed in a vacuum drying oven for 1 hour for degassing, and then the prepared polyvinylidene fluoride solution is evenly scraped on the non-woven fabric, which is quickly immersed in ultrapure water solution, and the water is changed every 2 hours. After one day, it is taken out and dried at room temperature to obtain the polyvinylidene fluoride base film.

[0023] Technical Solution 3: PBAP X / POA (1-X) Application of gas separation composite membrane in CO2 / CH4 gas separation.

[0024] Preferably, CO2 / N2 gas separation is performed at a temperature of 17-40°C, a pressure difference of 2-6 bar, a carrier gas flow rate of 40 mL / min, and a gas flow rate of 100 mL / min.

[0025] Compared with the prior art, the (PBAP) prepared by mixed substitution X / POA (1-X) ) / PVDF gas separation composite membrane, its surface is dense and uniform, the support layer and the separation layer are tightly connected, and there are no obvious defects. Rigid side groups and flexible side groups are introduced into the main chain of polyphosphazene, and amine compounds with the function of promoting CO2 transport are selected as substituents. By introducing functional side groups in different proportions, the targeting function of polymer separation is increased, the separation and film-forming properties of polyphosphazene and the practical application value of polyphosphazene membrane are improved. It has a complete set of preparation process flow and huge development potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0027] like Figure 1 The PBAP prepared in Example 4 is shown. 0.05 / POA 0.95 Electron micrograph of the surface of gas separation composite membrane;

[0028] like Figure 2 Shown are cross-sectional electron micrographs of the PBAPX / POA (1-X) gas separation composite membrane prepared in Example 1;

[0029] like Figure 3 Shown are cross-sectional electron micrographs of the PBAPX / POA (1-X) gas separation composite membrane prepared in Example 2;

[0030] like Figure 4 Shown are cross-sectional electron micrographs of the PBAPX / POA (1-X) gas separation composite membrane prepared in Example 3. DETAILED DESCRIPTION

[0033] Embodiment 1:

[0034] S1. Dissolve the crude hexachlorocyclotriphosphazene in n-heptane (80% of its weight), reflux at 80°C to fully dissolve it, filter it while hot to remove impurities, seal the filtrate, cool it, and then vacuum dry it. Repeat this operation several times. The recrystallized HCCP is placed in a sublimation device, heated to 90°C for vacuum sublimation, and white crystalline hexachlorocyclotriphosphazene is obtained;

[0035] S2. The hexachlorocyclotriphosphazene obtained in step S1 is quickly transferred into an ampoule, connected to a double-row tube, filled with nitrogen, and evacuated for 3-5 times to completely replace the air, then evacuated for 30 minutes and sealed, and then placed in a muffle furnace at 250°C for 36 hours until the system becomes viscous, thereby obtaining a completely reacted polydichlorophosphazene (PDCP);

[0036] S3. Add a certain amount of tetrahydrofuran into a three-necked flask, and gradually add shredded sodium into the tetrahydrofuran, and then stir the system at 70°C for 15-20 hours. After adding benzophenone, the system turns blue and is distilled. Seal it with a sealing film and place it in a drying oven for later use.

[0037] S4. The polydichlorophosphazene (PDCP) obtained in step S2 is dissolved in 200 ml of tetrahydrofuran, and aniline, n-octylamine and slightly excess triethylamine are dissolved in 150 ml of tetrahydrofuran. Under nitrogen protection, the mixture is dripped into the dissolved polydichlorophosphazene (PDCP) drop by drop in a constant pressure funnel using a one-time feeding method, refluxed and stirred for reaction for 48 hours under nitrogen protection (the molar ratio of polydichlorophosphazene to aniline is 1:4, and the molar ratio of aniline, n-octylamine and triethylamine is 0.3:0.7:1). After filtering with a sand core funnel, the reaction mixture is concentrated under reduced pressure, and the residual complex amine salt is first washed with ethanol and water (1:9) for multiple times to remove the residual complex amine salt, and the polymer is purified by precipitation with petroleum ether or n-heptane 3 times after being dissolved in tetrahydrofuran, and then placed in a 60°C oven for drying to obtain PBAP. 0.3 / POA 0.7 ;

[0038] S5. Configure 10w.% PBAP 0.3 / POA 0.7 The tetrahydrofuran solution was centrifuged and the supernatant was evenly scraped on the surface of the porous PVDF base membrane with a glass rod. 0.3 / POA 0.7 The PVDF base film coated with tetrahydrofuran liquid evaporates a large amount of solvent at room temperature, and then is placed in a 60°C oven for continuous drying for 24 hours to evaporate the remaining solvent, thereby obtaining PBAP. 0.3 / POA 0.7 The composite films were stored in a desiccating dish for further characterization.

[0039] Embodiment 2:

[0040] The same as Example 1, except that the polydichlorophosphazene (PDCP) prepared in step S2 is dissolved in 200 mL of tetrahydrofuran, and aniline, n-octylamine and a slightly excess of triethylamine are dissolved in 150 mL of tetrahydrofuran, and the molar ratio of aniline, n-octylamine and triethylamine is 0.2:0.8:1, to prepare PBAP with a mass fraction of 10% 0.2 / POA 0.8 of tetrahydrofuran solution.

[0041] Embodiment 3:

[0042] The same as Example 1, except that the dichlorophosphazene (PDCP) prepared in step S2 is dissolved in 200 mL of tetrahydrofuran, and aniline, n-octylamine and a slightly excess of triethylamine are dissolved in 150 mL of tetrahydrofuran, and the molar ratio of aniline, n-octylamine and triethylamine is 0.1:0.9:1, to prepare PBAP with a mass fraction of 10% 0.1 / POA 0.9 of tetrahydrofuran solution.

[0043] Embodiment 4:

[0044] The same as Example 1, except that the dichlorophosphazene (PDCP) prepared in step S2 is dissolved in 200 mL of tetrahydrofuran, and aniline, n-octylamine and a slightly excess of triethylamine are dissolved in 150 mL of tetrahydrofuran, and the molar ratio of aniline, n-octylamine and triethylamine is 0.05:0.95:1, to prepare PBAP with a mass fraction of 10%. 0.05 / POA 0.95 of tetrahydrofuran solution.

[0045] Comparative Example 1:

[0046] The polydichlorophosphazene (PDCP) prepared in step S2 was dissolved in 200 ml of tetrahydrofuran, and a slightly excessive amount of aniline (10.00 g, 0.1074 mol) and dehydrated triethylamine (10.90 g, 0.1018 mol) were dissolved in 150 ml of tetrahydrofuran, and the mixture was dripped into the dissolved polydichlorophosphazene in a constant pressure funnel under nitrogen protection. The mixture was refluxed and reacted under nitrogen protection for 96 hours to completely replace the mixture. After filtration, the reaction mixture was concentrated under reduced pressure to obtain a reaction mixture, which was first washed with ethanol and water (1:9) for multiple times to remove the residual complex amine salt, and then the polymer was further purified by dissolving it in tetrahydrofuran for multiple times and precipitating it, and then placed in a 60°C oven to dry for 24 hours.

[0047] Test Example 1

[0048] Under the conditions of feed pressure of 2 bar and test temperature of 17-40°C, H2 was used as carrier gas, CO2 and CH4 were used as test gas, carrier gas flow rate was 40 mL / min, and test gas flow rate was 100 mL / min. 0.05 / POA 0.95 The performance of the PPA / PVDF gas separation composite membrane was tested, and the results are shown in Table 1:

[0049]

[0050] Test Example 2

[0051] Under the conditions of test temperature of 17-40°C and feed pressure of 2 bar, H2 was used as carrier gas, CO2 and CH4 were used as test gas, carrier gas flow rate was 40 mL / min, and test gas flow rate was 100 mL / min, the (PBAP) prepared in Example 4 was 0.05 / POA 0.95 ) / PVDF gas separation composite membrane was tested for performance, and the results are shown in Table 2:

[0052] Table 2 Gas separation performance of composite membranes at different temperatures

[0053]

[0054] Test Example 3

[0055] Under the conditions of test pressure of 2.0-6.0 bar and test temperature of 17°C, H2 was used as carrier gas, CO2 and CH4 were used as test gas, the carrier gas flow rate was 40 mL / min, and the test gas flow rate was 100 mL / min. 0.05 / POA 0.95 ) / PVDF membrane was tested for performance, and the results are shown in Table 3:

[0056] Table 3 Gas separation performance of composite membranes at different pressures

[0057]

[0058]

[0059] The present invention uses a chemical reaction method to react a polymer intermediate polydichlorophosphazene (PDCP) with aniline and n-octylamine in different proportions to generate polyaniline-n-octylaminephosphazene (PBAP). x / POA (1-X) ), which is coated on the support layer PVDF by blade coating to make PBAP X / POA (1-X) / PVDF gas separation composite membrane, prepared (PBAP X / POA (1-X)) The surface of the / PVDF composite membrane is dense and uniform, the support layer and the separation layer are tightly connected, and there are no obvious defects at the interface. The separation membrane prepared by this method has high permeability and relatively high selectivity to CO2. The preparation process is simple and the substitution conditions are mild, so it is expected to be industrialized.

[0060] like Figure 1 As shown, it can be seen that the surface of the composite film is dense and uniform without any defects;

[0061] from Figure 2-4 It can be seen that a uniform PBAP layer is formed on the surface of the PVDF base film.X / POA (1-X) The dense layer shows PBAP X / POA (1-X) Adhering to the surface of the support layer, the separation layer of the composite membrane is tightly bonded to the support layer PVDF, there is no obvious defect at the interface, and the thickness of the separation layer is between 2.29-2.45μm.

Claims

1. A method for preparing a mixed substituted polyphosphazene gas separation composite membrane and its application, characterized in that: The steps include: S1. The hexachlorocyclotriphosphazene product is dissolved in an organic solvent, heated under reflux until it is completely dissolved and filtered while hot, the solution is cooled to precipitate crystals and then vacuum dried, the above operation is repeated 3-5 times, and then placed in a sublimation device at a certain temperature to sublimate to obtain high-purity hexachlorocyclotriphosphazene; S2. isolating the hexachlorocyclotriphosphazene obtained in S1 from air at a certain temperature, heating and ring-opening polymerization to obtain an intermediate polydichlorophosphazene; S3. The polydichlorophosphazene obtained in S2 is dissolved in an organic solvent, aniline, n-octylamine and an acid binding agent are added sequentially, and the substitution reaction is carried out by heating, and then the reaction product is repeatedly washed in a solvent and dried to obtain a pure polyaniline - n-octylamine phosphazene product; S4. The pure polyaniline-n-octylamine phosphazene obtained in S3 is dissolved in an organic solvent to obtain a polyaniline-n-octylamine phosphazene casting solution with a solid content of 5-20%; the casting solution is scraped onto a PVDF porous base membrane to obtain a polyaniline-n-octylamine phosphazene gas separation composite membrane.

2. The use according to claim 1, characterized in that: The organic solvent described in S2 is one or more of n-heptane, n-octane, and toluene, and the heating temperature is 70-90°C.

3. The use according to claim 1, characterized in that: The reaction conditions of the melt polymerization method described in S2 are: reaction in an anhydrous and oxygen-free environment, a temperature of 230-270° C., and a time of 17-37 hours.

4. The use according to claim 1, characterized in that: S3 The organic solvent is selected from tetrahydrofuran, dioxane and benzene; the acid binding agent is trimethylamine or triethylamine, and pure polyaniline-n-octylamine phosphazene is heated in an organic solvent at 70° C. and refluxed for 2-4 hours.

5. The use according to claim 1, characterized in that: S2: The molar ratio of the aniline and n-octylamine as a whole to the acid binding agent is 1-2:1; the molar ratio of the polydichlorophosphazene to the aniline is 1:2-4.

6. The use according to claim 1, characterized in that: The washing in S3 is specifically to concentrate the crude polyaniline-n-octylamine phosphazene and wash it with ethanol and water (1:6-9) for multiple times to remove the residual complex amine salt, dissolve it in tetrahydrofuran and precipitate it with petroleum ether or n-heptane for 2-4 times to purify the polymer.

7. The use according to claim 1, characterized in that: The organic solvent in S4 is one of tetrahydrofuran, chloroform and dioxane.

8. The use according to claim 1, characterized in that: The composite membrane described in S4 has polyaniline-n-octylamine phosphazene as a separation layer and a polyvinylidene fluoride (PVDF) porous bottom membrane as a support layer. The thickness of the separation layer is 2-4 μm, and the thickness of the support layer is 20-50 μm.

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