Method for preparing functionalized covalent organic framework membranes and application in gas separation

Abstract

The present application belongs to the technical field of gas separation membrane material, and relates to a selective gas separation membrane and a preparation method thereof. A separation layer is prepared by a spin coating method from a casting solution containing a covalent organic framework material and an ionic liquid, the organic framework material is a nanosheet synthesized based on a Schiff base reaction by reaction of an aldehyde group-containing monomer and an amino group-containing monomer; there is electrostatic interaction between the organic framework material and the ionic liquid in the separation layer, and the thickness of the separation layer is 40-100 nm. The membrane material used in the present application has a simple preparation process, raw materials are easy to obtain, and the structure of the membrane is stable. The technical index of the membrane material meets the technical index of industrialized separation of CO2 gas, continuous operation can be realized, and a new path is provided for the covalent organic framework membrane to realize gas separation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gas separation membrane materials, and relates to a preparation method of a functionalized covalent organic framework membrane and application thereof, in particular to a preparation of an ionic liquid functionalized covalent organic framework membrane and application thereof in carbon dioxide / nitrogen separation. BACKGROUND

[0002] Excessive CO2 emission leads to global warming effect, thereby causing sea level rise, frequent extreme weather, etc. Compared with traditional absorption technology, membrane technology has the advantages of simple operation, low energy consumption, green environmental protection, etc. Traditional high polymer materials are difficult to simultaneously realize high selectivity and high permeability, that is, are restricted by trade-off effect, and have aging and plasticization effect, which limits the separation efficiency. Developing high-performance membrane materials that break through the trade-off effect of traditional high polymers is a key technology for realizing industrial development of carbon dioxide membrane separation technology.

[0003] Covalent organic framework materials (COFs) are considered to be disruptive materials in the field of gas separation due to their permanent porosity, high specific surface area, rich modifiable sites, excellent chemical stability, etc. Especially, the long-range ordered pore structure makes the gas permeation rate of COF materials much higher than that of traditional high polymer materials. However, the intrinsic pore size of the existing COF materials is greater than 0.6 nm, which is greater than the kinetic diameter of common gases, and it is difficult to realize physical screening of gas molecules by relying on the intrinsic pore size.

[0004] Ionic liquids are considered to have the potential to replace organic amines for CO2 absorption due to their excellent thermal stability, processability and high CO2 solubility. However, ionic liquids have the disadvantages of high viscosity and poor mass transfer, and cannot be directly used as CO2 absorbents. Moreover, ionic liquids as liquid phase are not conducive to transportation and pressure bearing, and thus it is difficult to realize their large-scale application in CO2 capture.

[0005] Since the amount of carbon dioxide to be separated in industry is huge, under the premise of meeting the requirement of selectivity, the size of the flux of the separation membrane becomes the focus of research and development. In addition, gas separation often faces high pressure environment, and therefore the strength and stability of the membrane are also very important. At present, there is no ideal membrane suitable for industrial carbon dioxide / nitrogen system separation reported. SUMMARY

[0006] The application proposes a new type of selective gas separation membrane and a preparation method thereof aiming at the problems existing in the traditional CO2 / N2 system separation.

[0007] In order to achieve the above purpose, the application is realized by adopting the following technical scheme:

[0008] A functionalized covalent organic framework membrane, comprising a base membrane and a separation layer, the separation layer is prepared by spin coating method from a casting solution containing covalent organic framework material and ionic liquid, the organic framework material is nanosheet synthesized based on Schiff base reaction by reaction of aldehyde group-containing monomer and amino group-containing monomer; there is electrostatic interaction between the organic framework material and the ionic liquid in the separation layer, and the thickness of the separation layer is 30-100 nm.

[0009] As preferred, the aldehyde group monomer includes 1,3,5-triformylphloroglucinol; the amino monomer includes 1,4-phenylenediamine-2-sulfonic acid, ethidium bromide; the ionic liquid includes any one or several of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium glycine.

[0010] As preferred, the base membrane is any one of polyacrylonitrile ultrafiltration membrane, polyether sulfone membrane, anodic aluminum oxide membrane.

[0011] The preparation method of the above-mentioned functionalized covalent organic framework membrane, the steps are as follows:

[0012] (1) The covalent organic framework material is prepared by any one of the following methods:

[0013] Method one, 1,3,5-triformylphloroglucinol is added to octanoic acid and mixed uniformly to obtain solution A, 1,4-phenylenediamine-2-sulfonic acid is added to deionized water and mixed uniformly to obtain solution B, solution A is slowly added to solution B, and the reaction is placed for 4-6 days, the top octanoic acid phase is removed, the bottom water phase is collected and dialyzed with deionized water for 2-4 days to obtain TpPa-SO3H nanosheet dispersion;

[0014] Method two, 1,3,5-triformylphloroglucinol is uniformly dispersed in dichloromethane, deionized water is slowly added to the surface as a buffer layer, ethidium bromide and p-toluenesulfonic acid are uniformly dispersed in deionized water to obtain solution C, and solution C is slowly added to the buffer layer, and the reaction is placed for 9-11 days, the reaction solution is divided into two phases, the mixed liquid at the interface of the two phases is collected and dialyzed with deionized water for 2-4 days to obtain TpEbr nanosheet dispersion;

[0015] (2) Preparation of casting solution

[0016] The ionic liquid is added to ethanol and mixed uniformly to obtain ionic liquid dispersion, the ionic liquid dispersion, TpPa-SO3H nanosheet dispersion or TpEbr nanosheet dispersion is added to ethanol solution D and mixed uniformly to obtain the casting solution;

[0017] (3) Preparation of gas separation membrane

[0018] The casting solution is spin-coated on a polyacrylonitrile ultrafiltration membrane substrate, dried at room temperature, and then repeated spin-coating and drying for several times until the thickness of the separation layer reaches 40-100 nm.

[0019] Preferably, in mode one of step (1), the concentrations of solution A and solution B are both 1-10 mmol / L, and the concentrations of the two are the same, and the volume ratio of octanoic acid in solution A to deionized water in solution B is 2:3.

[0020] Preferably, in mode two of step (1), the molar ratio of 1,3,5-triformylphloroglucinol, ethidium bromide and p-toluenesulfonic acid is 1:(1.4-1.6):(2.5-3.5); the volume ratio of dichloromethane, buffer layer (deionized water) and deionized water in solution C is 1:(0.5-0.7):1, and the concentration of 1,3,5-triformylphloroglucinol in dichloromethane is 0.6-0.8 mmol / L.

[0021] Preferably, in step (2), the concentration of the ionic liquid in the casting solution is 0.01-0.2 mg / mL, and the concentration of TpPa-SO3H nanosheets or TpEbr nanosheets in the casting solution is 0.1-0.2 mg / mL.

[0022] Preferably, in step (3), the spin-coating is performed 2-5 times, the spin-coating amount is 90-110 μL each time, the spin-coating speed is 1000-2000 rpm, the spin-coating time is 25-35 s, and the drying time at room temperature after each spin-coating is at least 1 h, so as to obtain an ultra-thin film with a thickness of 30-100 nm.

[0023] The application provides application of the functionalized covalent organic framework film prepared by the above method in CO2 / N2 separation.

[0024] The ionic liquid functionalized covalent organic framework film obtained by the application is used for separating CO2 from a CO2 / N2 mixed gas system, under the conditions of 20℃, raw gas pressure of 2 bar and 100% relative humidity, the CO2 flux is 200-1100 GPU, the CO2 / N2 selectivity is 20-85; after 100 hours, the flux and selectivity of the film remain stable, and when the raw gas pressure is increased to 10 bar, the film still has certain separation performance.

[0025] The ion liquid functionalized covalent organic framework membrane provided by the application has simple and controllable preparation method, and the prepared membrane has high permeability and stability when used for CO2 / N2 system separation. The composite membrane is assembled by ion liquid and covalent organic framework nanosheet, is prepared by spin coating mixed solution of ion liquid and covalent organic framework nanosheet on a polyacrylonitrile ultrafiltration membrane, and is assembled by electrostatic interaction between the charged groups on the surface of the ion type COFs material and the ion liquid. On the one hand, the ion liquid introduced in the COF membrane can repair defects in the membrane and improve the CO2 solubility of the membrane. On the other hand, the electrostatic interaction between the charged groups of the COF side chain and the IL can fix the IL in the channel, avoiding loss under high pressure conditions and in a wet environment.

[0026] Compared with the prior art, the application has the advantages and positive effects that:

[0027] The membrane material used in the application has simple preparation process, easily available raw materials and stable structure. The covalent organic framework material is composed of all-organic units, and the rich types, long-range ordered channel structure and strong designability of the covalent organic framework material make the membrane of the application have higher flux than the traditional polymer membrane, and can meet the technical index of industrialized separation of CO2 gas. Compared with direct use of ion liquid as absorbent for separation, the amount of ion liquid used in the supported ion liquid membrane is very small and continuous operation can be realized, and the method can be popularized to other ion type COFs materials and other types of ion liquid. By replacing different types of ion liquid, the screening function of other types of gas mixture can be realized, and the method has strong universality. The method provides a new path for realizing gas separation of the covalent organic framework membrane. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The cross-section electron microscope image of the separation membrane prepared in Example 1.

[0029] Figure 2 The cross-section electron microscope image of the separation membrane prepared in Example 2.

[0030] Figure 3 The detection result of the performance change of the separation membrane with pressure.

[0031] Figure 4 The stability test result of the separation membrane. DETAILED DESCRIPTION

[0032] In order to more clearly understand the above-mentioned purposes, features and advantages of the application, the application will be further described below in combination with specific examples. It should be noted that the examples and features in the examples of the application can be combined with each other without conflict.

[0033] Many specific details are set forth in the following description in order to provide a thorough understanding of the present application. However, the present application can be practiced according to other embodiments that can not be described in detail herein, and the present application is not limited to the specific embodiments described in this disclosure.

[0034] Example 1

[0035] In the preparation process of the functionalized covalent organic framework membrane of the present embodiment, the nanosheet dispersion liquid adopts TpPa-SO3H.

[0036] 0.1 mmol of 1,3,5-triformylphloroglucinol (Tp) was uniformly dispersed in 20 ml of octanoic acid solution, 0.15 mmol of 1,4-phenylenediamine-2-sulfonic acid (Pa-SO3H) was uniformly dispersed in 30 ml of deionized water, the Tp solution was slowly added to the surface of the Pa-SO3H solution, the total drop time was controlled in 5-15 min, after the drop was completed, the system was reacted at 25℃ without disturbance (standing) for 5 days, at this time the system was divided into two phases, the top octanoic acid phase was removed, the bottom water phase solution was collected and dialyzed with deionized water for 3 days, to obtain TpPa-SO3H nanosheet dispersion liquid, and the concentration of the dispersion liquid was 1.5 mg / mL.

[0037] 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) was mixed with ethanol at a mass ratio of 1:1 to obtain an ionic liquid dispersion liquid, which was uniformly mixed by ultrasonic for 10 min. 6 mL of ethanol and 9 mL of deionized water were mixed to obtain an ethanol solution, 1 mL of TpPa-SO3H nanosheet dispersion liquid and 0.25 mL of ionic liquid dispersion liquid were added, which were uniformly mixed by ultrasonic for 2 min to obtain a spin-coating casting solution.

[0038] The casting solution was spin-coated on a 2 cm x 2 cm polyacrylonitrile ultrafiltration membrane (Shandong Tai'an Lanjing Business and Trade Co., Ltd., molecular weight cut-off 100000) substrate by a spin-coating method, 100 μL was spin-coated each time, the spin-coating speed was set to 1500 rpm, the spin-coating time was set to 30 s, and the spin-coating was performed twice, and after each spin-coating, the membrane was dried at room temperature for 1 hour to form an ionic liquid functionalized covalent organic framework membrane. After spin-coating, a circular separation layer with a diameter of 2 cm was obtained on the surface of the base membrane, and the separation layer was an ultra-thin membrane with a thickness of 32 nm. The cross-sectional electron microscope image of the separation membrane is as shown in Figure 1 , Figure 1 It can be seen that the obtained membrane is dense and defect-free, and has no pore penetration phenomenon.

[0039] It was detected that the separation membrane prepared in the present embodiment was used for CO2 / N2 system separation, under the conditions of 20℃, raw gas pressure 2 bar, and 100% relative humidity, the CO2 permeation rate was 1116 GPU, and the CO2 / N2 selectivity was 20.3.

[0040] Example 2

[0041] The nanosheet dispersion liquid in the preparation process of the separation membrane of the present embodiment uses TpEbr nanosheets.

[0042] 0.1 mmol of 1,3,5-tricarboxaldehyde-based phloroglucinol (Tp) was uniformly dispersed in 130 ml of dichloromethane, 80 ml of deionized water was slowly added to the surface of the Tp solution as a buffer layer, 0.15 mmol of ethidium bromide (Ebr) and 0.3 mmol of p-toluenesulfonic acid were uniformly dispersed in 130 ml of deionized water, and were slowly added to the top of the water phase buffer layer, the system was left undisturbed at 25°C for 10 days, the system naturally formed two phases, the solution at the interface of the two phases was collected and dialyzed with deionized water for 3 days, to obtain a TpEbr nanosheet dispersion liquid with a concentration of 0.2 mg / mL.

[0043] 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl) imide ([EMIM][TF2N]) was mixed with ethanol at a mass ratio of 1:1 to obtain an ionic liquid dispersion liquid, which was ultrasonically stirred for 10 min to obtain a uniform dispersion liquid. 0.8 mL of ethanol was uniformly mixed with 1.2 mL of deionized water, 1.0 mL of the TpEbr nanosheet dispersion liquid, and 0.25 mL of the ionic liquid dispersion liquid were added, and ultrasonically stirred for 2 min to obtain a casting solution.

[0044] The casting solution was spin-coated on a polyacrylonitrile ultrafiltration membrane substrate by a spin coating method, 100 μL was spin-coated each time, the spin coating speed was set to 1500 rpm, the spin coating time was set to 30 s, and the spin coating was performed twice with an interval of 1 hour between each spin coating to form an ionic liquid functionalized covalent organic framework membrane, which was then dried at room temperature to obtain an ultra-thin membrane with a separation layer membrane thickness of 89 nm. The cross-sectional electron microscope image of the separation membrane is as shown in Figure 2 , Figure 2 It can be seen that the obtained membrane is dense and defect-free, and has no pore penetration phenomenon.

[0045] For CO2 / N2 system separation, under the conditions of 20°C, raw gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation rate was 1018 GPU, and the CO2 / N2 selectivity was 22.4.

[0046] Example 3

[0047] The difference between the present embodiment and Example 2 is that the ionic liquid is replaced by 1-ethyl-3-methylimidazolium glycine ([EMIM][Gly]), and the rest of the preparation process is consistent with Example 2, to obtain a composite membrane with a separation layer membrane thickness of 90 nm.

[0048] The composite membrane obtained in the embodiment is detected to have a CO2 permeation rate of 218 GPU and a CO2 / N2 selectivity of 89 in a CO2 / N2 system separation at 20°C and under a raw gas pressure of 2 bar.

[0049] Example 4

[0050] The embodiment differs from Example 1 in that the number of spin coating times is increased to 4, and the rest of the preparation process is consistent with Example 1, to obtain a composite membrane with a separation layer film thickness of 61 nm.

[0051] The composite membrane obtained in the embodiment is detected to have a CO2 permeation rate of 468 GPU and a CO2 / N2 selectivity of 18 in a CO2 / N2 system separation at 20°C and under a raw gas pressure of 10 bar, and the performance of the composite membrane varies with pressure as shown in Figure 3 It can be seen from Figure 3 that the separation performance is not lost when the pressure is increased to 10 bar. With the increase of pressure, the CO2 / N2 selectivity and the CO2 permeation rate of the membrane are gradually reduced, indicating that the dissolution of IL to CO2 approaches saturation in the separation process, and the increase of N2 flux in the pressure increase process leads to the decrease of the selectivity of the membrane. When the pressure is increased to 10 bar, the membrane still has certain separation performance. When the pressure is returned to 2 bar, the membrane restores the original CO2 separation performance, indicating that the membrane has good pressure resistance and can maintain the relative stability of the structure during operation.

[0052] 1. Stability test

[0053] The separation membrane prepared in Example 1 is continuously tested for 100 h at 20°C, under a raw gas pressure of 2 bar and a relative humidity of 100%, to investigate the stability of the membrane. The results are shown in Figure 4 It can be seen from Figure 4 that the CO2 permeation rate and the CO2 / N2 selectivity of the membrane remain basically stable within 100 h of testing, proving that the membrane has good long-term stability.

[0054] 2. Effect of spin coating times

[0055] The casting solution is spin coated only once, and the rest of the preparation conditions and process are consistent with Example 1. It is detected that the number of spin coating layers of one layer is difficult to shield the holes of the PAN substrate, and the obtained membrane has a permeation rate of more than 30000 GPU and no CO2 / N2 selectivity. The number of spin coating times is increased to 6, and the rest of the preparation conditions and process are consistent with Example 1. It is detected that the CO2 permeation rate is 567 GPU and the CO2 / N2 selectivity is 43. The flux is greatly reduced, which is difficult to meet the needs of large-scale industrial production.

[0056] 3. Spin-coating liquid composition influence

[0057] (1) Without adding ionic liquid, only using nanosheet dispersion liquid to spin-coat, the rest of the conditions are consistent with Example 1, a TpPa-SO3H pure film with a thickness of 43 nm is obtained, and the test shows that the CO2 permeation rate exceeds 30000 GPU, and the CO2 / N2 selectivity is 1, so the film prepared by pure nanosheet dispersion liquid does not have the effect of carbon dioxide separation.

[0058] (2) When preparing the casting solution, the amount of ionic liquid dispersion liquid is changed to 0.05 mL, and the rest of the conditions are consistent with Example 1. The test shows that under the conditions of 20°C, raw material gas pressure 2 bar, 100% relative humidity, the CO2 permeation rate is 1456 GPU, and the CO2 / N2 selectivity is 6.17, so it can be known that too low concentration of ionic liquid in the casting solution will lead to too low selectivity.

[0059] (3) When preparing the casting solution, the amount of ionic liquid dispersion liquid is changed to 1 mL, and the rest of the conditions are consistent with Example 1. The test shows that under the conditions of 20°C, raw material gas pressure 2 bar, 100% relative humidity, the CO2 permeation rate is 275 GPU, and the CO2 / N2 selectivity is 65, so it can be known that too high concentration of ionic liquid in the casting solution will lead to too low CO2 permeation rate and difficult to realize large-scale separation.

[0060] 4. Influence of ionic liquid or nanosheet type

[0061] DhaTG is used instead of TpPa-SO3H nanosheet Cl nanosheet, the preparation method is as follows: 2,5-dihydroxybenzaldehyde (Dha, 0.15 mmol, 24.9 mg) is dissolved in 50 mL dichloromethane and placed in a glass beaker. Then, triaminoguanidine chloride (TG Cl , 0.1 mmol, 14.0 mg) is dissolved in 3M aqueous acetic acid (AcOH, 30 mL) and slowly added to the top of the oil phase. The two-phase system is left to stand at room temperature for 7 d. The water phase becomes a deep yellow transparent solution and is removed using a dropper. The resulting DhaTGCl is dialyzed in DI water using a dialysis membrane tube with a molecular weight cut-off of 30000 for 3 days to obtain DhaTG ClNanosheets. The rest of the preparation process is consistent with Example 1. The obtained casting solution has obvious sedimentation within 1 h, which is due to the fact that the electrostatic interaction between this COF and ionic liquid is too strong to break the electrostatic repulsion between nanosheets, resulting in the aggregation of nanosheets. The test shows that the CO2 permeation rate of the membrane is 265 GPU, and the CO2 / N2 selectivity is only 10, and both the flux and selectivity are quite low, which has no CO2 separation potential. The above results show that appropriate electrostatic interaction can well bind ionic liquid in the COF channel, while too strong electrostatic interaction can affect the structure of COF itself, making the membrane lose the separation performance.

[0062] From the above examples and effect verification experiments, it can be seen that the mixing of ionic liquid with strong CO2 affinity and covalent organic framework can significantly improve the CO2 separation performance of covalent organic framework membrane. The electrostatic interaction between the charged groups of the COF side chain and the ionic liquid can fix the IL in the channel, avoid loss in high pressure conditions and wet environment, and improve the overall stability of the supported ionic liquid membrane.

[0063] The above is only the preferred embodiment of the present application, and is not intended to limit the other forms of the present application. Any skilled person in the art can use the disclosed technical content to make changes or modifications to equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification made on the basis of the technical essence of the present application to the above embodiments shall still fall within the protection scope of the present application.

Claims

1. A method for preparing a functionalized covalent organic framework membrane, characterized in that, It includes a base film and a separation layer, wherein the separation layer is prepared by spin coating of a casting solution containing a covalent organic framework material and an ionic liquid; The preparation steps are as follows: (1) Prepare covalent organic framework materials using any of the following methods: Method 1: Add 1,3,5-tricarboxymethyl-2-pyrogallol to octanoic acid and mix well to obtain solution A. Add 1,4-phenylenediamine-2-sulfonic acid to deionized water and mix well to obtain solution B. Slowly add solution A to solution B and let it stand for 4-6 days. Remove the top octanoic acid phase and collect the bottom aqueous phase. Dialyze it with deionized water for 2-4 days to obtain TpPa-SO3H nanosheet dispersion. Method 2: 1,3,5-tricarboxaldehyde-resorcinol is uniformly dispersed in dichloromethane. Deionized water is slowly added dropwise to the surface as a buffer layer. Ethidium bromide and p-toluenesulfonic acid are uniformly dispersed in deionized water to obtain solution C. Solution C is then slowly added dropwise to the buffer layer and allowed to stand for 9-11 days. The reaction solution separates into two phases. The mixture at the interface of the two phases is collected and dialyzed with deionized water for 2-4 days to obtain a TpEbr nanosheet dispersion. (2) Preparation of casting solution The ionic liquid is added to ethanol and mixed evenly to obtain an ionic liquid dispersion. The ionic liquid dispersion, TpPa-SO3H nanosheet dispersion or TpEbr nanosheet dispersion are added to ethanol solution D and mixed evenly to obtain a casting solution. (3) Preparation of gas separation membrane The casting solution was spin-coated onto a polyacrylonitrile ultrafiltration membrane substrate and dried at room temperature. The spin-coating and drying process was repeated several times until the separation layer thickness reached 30-100 nm. In step (1), the concentration of solution A in method one is 1-10 mmol / L, the volume ratio of octanoic acid in solution A to deionized water in solution B is 2:3, and the molar concentrations of solution A and solution B are the same. In step (1) of method two, the molar ratio of 1,3,5-tricarboxaldehyde-resorcinol:ethidium bromide:p-toluenesulfonic acid is 1:(1.4-1.6):(2.5-3.5); the volume ratio of dichloromethane:buffer layer:deionized water in solution C is 1:(0.5-0.7):1; the concentration of 1,3,5-tricarboxaldehyde-resorcinol in dichloromethane is 0.6-0.8 mmol / L. Step (2) The ionic liquid in the casting solution includes any one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, and 1-ethyl-3-methylimidazolium glycine, and the concentration of the ionic liquid is 0.01-0.2 mg / mL. The concentration of TpPa-SO3H nanosheets or TpEbr nanosheets in the casting solution is 0.1-0.2 mg / mL.

2. The method for preparing the functionalized covalent organic framework membrane according to claim 1, characterized in that, In step (3), the number of spin coatings is 2-5 times, the amount of each spin coating is 90-110 μL, the spin coating speed is 1000-2000 rpm, the spin coating time is 25-35s, and the room temperature drying time after each spin coating is at least 1h.

3. The application of the functionalized covalent organic framework membrane prepared by any one of claims 1-2 in CO2 / N2 separation.

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