Nanofiber interwoven composite gel membrane for carbon dioxide separation and preparation method of nanofiber interwoven composite gel membrane

Abstract

The invention discloses a nanofiber interwoven composite gel membrane for carbon dioxide separation and a preparation method of the nanofiber interwoven composite gel membrane. The nanofiber interwoven composite gel membrane comprises a nanofiber interwoven framework and a carbon dioxide-philic gel matrix layer, wherein the surface of the nanofiber interwoven framework is coated with the carbon dioxide-philic gel matrix layer; the carbon dioxide-philic gel matrix layer is formed by in-situ polymerization and gelation of a precursor solution containing an oxidizing agent, a cross-linking agent and a functional monomer on the surface of the nanofiber interwoven skeleton. The nanofiber interwoven composite gel membrane provided by the invention has excellent carbon dioxide permeability and selectivity. The invention also discloses an application of the nanofiber interwoven composite gel membrane in separation of carbon dioxide.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, and in particular to a nanofiber interwoven composite gel membrane for carbon dioxide separation and a preparation method thereof. BACKGROUND

[0002] With the rapid increase in the consumption of fossil fuels in modern society, the emission of large amounts of carbon dioxide (CO2) gas into the atmosphere has caused serious environmental problems such as the "greenhouse effect". To solve this problem, researchers have proposed many carbon dioxide capture and separation technologies. At present, among the many carbon capture technologies, membrane separation has the advantages of high efficiency, energy saving, environmental friendliness, simple operation, and easy large-scale application, and has important research significance and application prospects in reducing CO2 emissions.

[0003] Among the many separation membrane materials, mixed matrix membranes have both the excellent processability of polymers and the excellent gas transport channels of nanomaterials, and have become the most promising candidate material for improving the gas separation efficiency of membranes. How to manipulate the spatial distribution of nanomaterials in the polymer matrix to finely form continuous gas fast transport channels is the key to preparing high-performance mixed matrix membranes.

[0004] For example, the Chinese patent document with publication number CN115025631A reports a mixed matrix membrane based on polyethylene glycol metal organic frameworks. The carbon dioxide permeability of the composite membrane is 190.1 Barrer, and the carbon dioxide / nitrogen selectivity is 46.2. Although this performance is already higher than many mixed matrix membranes, it still cannot meet the performance requirements of practical applications. This is because during the preparation of the mixed matrix membrane, nanomaterials will inevitably aggregate in the polymer matrix, and the compatibility between the nanomaterial-polymer interface is poor, so most mixed matrix membranes are prone to form non-selective defects during preparation. In addition, the distribution of nanomaterials in the mixed matrix membrane is often discrete and not connected, which makes it difficult to form a continuous gas transport channel in the membrane and limits the gas separation performance of the membrane.

[0005] One of the most effective ways to construct continuous gas transport channels is to increase the loading content of nanomaterials in the polymer matrix. For example, the Chinese patent document CN114950167A reports a method for preparing an ultra-high loading MOFs-based mixed matrix membrane. The MOFs filler loading in the mixed matrix membrane reaches more than 60 wt.%. Ultra-high loading makes the gas transport channels in the membrane mainly formed by MOFs. However, this strategy is only suitable for a few material systems with matching physical and chemical properties of nanomaterials and polymers. In addition, under high loading content, most nanomaterials will have more obvious agglomeration and deposition, resulting in more serious non-selective defects.

[0006] Therefore, it is of great significance to construct high-efficiency carbon dioxide separation mixed matrix membranes with interconnected gas transport channels for carbon capture and carbon enrichment. SUMMARY

[0007] The present application provides a nanofiber interwoven composite gel membrane for carbon dioxide separation and a preparation method thereof, which has excellent carbon dioxide permeability and selectivity.

[0008] The technical solutions of the present application are as follows: A nanofiber interwoven composite gel membrane for carbon dioxide separation, comprising a nanofiber interwoven skeleton and a carbon dioxide-philic gel matrix layer coated on the surface of the nanofiber interwoven skeleton. The carbon dioxide-philic gel matrix layer is formed by in-situ polymerization and gelation of a precursor solution containing an oxidizing agent, a crosslinking agent and a functional monomer on the surface of the nanofiber interwoven skeleton.

[0009] The present application also provides a preparation method of a nanofiber interwoven composite gel membrane for carbon dioxide separation, comprising the following steps: (1) The suspension of nanofibers is suction filtered onto a porous support membrane, dried, and a porous membrane loaded with a nanofiber interwoven skeleton is obtained. (2) The precursor solution containing an oxidizing agent, a crosslinking agent and a functional monomer is coated onto the porous membrane loaded with the nanofiber interwoven skeleton, and reacted at 40-90℃ for 0.5-20 min to obtain the nanofiber interwoven composite gel membrane.

[0010] The present application forms a nanofiber interwoven skeleton on a porous membrane support membrane by negative pressure suction filtration method, then fills a precursor solution containing an oxidizing agent, a crosslinking agent and a functional monomer in the nanofiber interwoven skeleton, and finally forms a nanofiber interwoven composite gel functional layer on the porous support membrane by in-situ thermal initiation polymerization gelation, thereby obtaining a nanofiber interwoven composite gel membrane. In the nanofiber interwoven composite gel membrane, the nanofiber interwoven skeleton not only can serve as a rapid gas molecule transmission channel to improve the carbon dioxide permeability, but also can destroy the stacking of polymer chains in the gel network, thereby improving the flowability of the polymer chains, increasing the free volume, and further promoting the diffusion and permeation of carbon dioxide; the in-situ thermal initiation polymerization method does not involve a phase change process, so that the carbon dioxide-permeable gel matrix formed has good interfacial compatibility with the nanofiber interwoven skeleton, defects in the membrane can be avoided, and the abundant polar ether bonds in the polyethylene glycol gel promote the dissolution of carbon dioxide molecules and repel nitrogen molecules, thereby ensuring that the nanofiber interwoven composite gel membrane has excellent carbon dioxide permeability and selectivity.

[0011] The porous support membrane is one of polysulfone ultrafiltration membrane, polyether sulfone ultrafiltration membrane, cellulose acetate ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polypropylene microfiltration membrane, polyvinylidene fluoride microfiltration membrane, polytetrafluoroethylene microfiltration membrane, polyether sulfone microfiltration membrane and nylon microfiltration membrane.

[0012] Preferably, the porous support membrane is a nylon microfiltration membrane.

[0013] Preferably, the nanofiber is at least one of nanocrystalline cellulose, carbon nanotube, silicon nanowire and silver nanowire.

[0014] Preferably, the loading amount of nanofiber on the porous membrane support membrane is 0.1-30 g / m 2 .

[0015] The loading amount of nanofiber on the porous membrane affects the morphology, thickness of the composite gel functional layer and the carbon dioxide flux of the composite gel membrane. When the loading amount of nanofiber is too low, the gel precursor solution will seep from the nanofiber interwoven skeleton into the porous support membrane, generating a pure gel layer with low carbon dioxide diffusion rate and reducing the carbon dioxide flux of the composite membrane; when the loading amount of nanofiber is too high, the generated composite gel functional layer is too thick, which will also increase the resistance of carbon dioxide molecules to cross the membrane and reduce the flux of the composite membrane.

[0016] Further preferably, the loading amount of nanofiber on the porous membrane support membrane is 0.5-10 g / m 2 .

[0017] The loading amount of nanofiber is 0.5-10 g / m 2The prepared composite gel functional layer has a thickness of 0.05-20 μm, and the content of the nanofiber is 35-70%, so that the prepared nanofiber interwoven composite gel film has good carbon dioxide flux and selectivity.

[0018] Further preferably, the loading amount of the nanofiber on the porous membrane support film is 1-5 g / m 2 .

[0019] The thermal initiation in-situ polymerization gelation is a reaction in which an oxidizing agent generates free radicals under thermal initiation, and induces in-situ polymerization of a crosslinking agent and a functional monomer to form a gel.

[0020] In the present application, the oxidizing agent is at least one of azobisisobutyronitrile, ammonium persulfate, sodium persulfate and potassium persulfate.

[0021] Preferably, the concentration of the oxidizing agent in the precursor solution is 1-30 mg / mL.

[0022] The crosslinking agent is at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate.

[0023] The average molecular weight of the polyethylene glycol diacrylate is 200-600.

[0024] Preferably, the concentration of the crosslinking agent in the precursor solution is 1-30 mg / mL.

[0025] The functional monomer is at least one of polyethylene glycol diacrylate (average molecular weight 200-600) and polyethylene glycol methacrylate (average molecular weight 300-1000).

[0026] Preferably, the concentration of the functional monomer in the precursor solution is 200-1000 mg / mL.

[0027] Preferably, the oxidizing agent is ammonium persulfate, the crosslinking agent is polyethylene glycol diacrylate, and the functional monomer is polyethylene glycol diacrylate; The concentration of the oxidizing agent in the precursor solution is 5-15 mg / mL, and the total concentration of the crosslinking agent and the functional monomer is 600-1000 mg / mL.

[0028] Preferably, in step (2), the reaction time is 1-10 min.

[0029] Further preferably, in step (2), the reaction time is 2-8 min.

[0030] The prepared nanofiber interwoven composite gel membrane maintains the interwoven nanofiber network as an ultrafast transmission channel for improving the carbon dioxide permeability. In the traditional mixed matrix membrane, the nanomaterials are often dispersed in the matrix, and even agglomerate, so that a continuous distribution through the thickness direction of the membrane cannot be formed, which limits the carbon dioxide separation performance of the traditional mixed matrix membrane. The thermal initiation in-situ polymerization gelation method can form a dense and defect-free selective carbon dioxide gel layer in the nanofiber interwoven skeleton for the gel precursor solution, and the phase separation process used in the preparation process of the traditional mixed matrix membrane cannot achieve this effect.

[0031] The application further provides application of the nanofiber interwoven composite gel membrane in separating carbon dioxide.

[0032] Compared with the prior art, the application has the following beneficial effects: (1) The prepared nanofiber interwoven composite gel membrane has an interwoven nanofiber network as a fast gas molecule transmission channel to improve the carbon dioxide permeability, and can also destroy the stacking of polymer chains in the gel network, so as to improve the flowability of the polymer chains, increase the free volume of the gel matrix to facilitate the rapid transmission of gas molecules, so that the prepared nanofiber interwoven composite gel membrane has excellent carbon dioxide permeability; (2) The thermal initiation in-situ polymerization method used in the application does not involve a phase change process, so that the carbon dioxide gel matrix formed has good interfacial compatibility with the nanofiber skeleton, defects in the membrane can be avoided, and the rich polar ether bonds in the polyethylene glycol gel promote the dissolution of carbon dioxide molecules and repel nitrogen molecules, so that the prepared nanofiber interwoven composite gel membrane has excellent carbon dioxide selectivity; (3) The prepared nanofiber interwoven composite gel membrane can use the high-strength rigid nanofiber interwoven skeleton to form topological chain entanglement and multiple interactions with the polymer gel matrix, so as to anchor the polymer gel matrix and realize excellent structural and performance stability. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A scanning electron microscope image of the nanofiber interwoven composite gel membrane prepared in Example 1; Figure 2 A transmission electron microscope image of the cross section of the nanofiber interwoven composite gel membrane prepared in Example 1. DETAILED DESCRIPTION

[0034] The application will be further described in detail below in combination with the drawings and examples, and it should be pointed out that the following examples are intended to facilitate the understanding of the application and do not limit the application in any way.

[0035] The nanofiber interwoven composite gel membrane prepared by the application is used for carbon dioxide separation. The gas permeation test is carried out at room temperature (298 K) using a self-made permeation device by using the constant pressure variable volume method. In the case of no humidification, pure gases such as N2 and CO2 are used for continuous test. The carbon dioxide flux and selectivity are two important parameters for evaluating the composite gel membrane.

[0036] wherein the carbon dioxide flux (GPU) is defined as: P

[0037] wherein, V the volume of gas permeated through the membrane (cm 3 ), Δh the permeation time, S the effective separation area of the membrane (cm 2 ), Δp the pressure difference between the feed end and the permeation end of the membrane (100 kPa).

[0038] The carbon dioxide / nitrogen ideal selectivity of the composite membrane is determined by the following formula:

[0039] wherein, the carbon dioxide flux (GPU) of the composite membrane, the nitrogen flux (GPU) of the composite membrane.

[0040] The nanofiber interwoven composite gel membrane for efficient carbon dioxide separation and the preparation method thereof of the application are further described in detail by the following examples.

[0041] Example 1 (1) The nylon microfiltration membrane is laid in the sand core funnel, and the carbon nanotube suspension is poured into the nylon microfiltration membrane to stack the carbon nanotubes with a bulk density of 0.2 mg / cm 2 on the nylon microfiltration membrane, and the membrane is completely dried in a vacuum drying oven at 60℃ to obtain a carbon nanotube interwoven skeleton.

[0042] (2) The gel precursor solution is prepared: 9.5 g of polyethylene glycol diacrylate (average molecular weight 200), 0.095 g of ammonium persulfate and 0.5 g of water are stirred into a uniform solution at room temperature.

[0043] (3) The gel precursor is coated on the prepared carbon nanotube interwoven skeleton, and the excess precursor solution on the surface of the membrane is removed by centrifugal spin coating at 3600 revolutions. Finally, the above liquid membrane is placed in an oven at 70℃ for 3 minutes to obtain a nanofiber interwoven composite gel membrane.

[0044] ​The scanning electron microscope images and cross-section transmission electron microscope images of the nanofiber interwoven composite gel membrane prepared in Example 1 are shown in Figure 1 and Figure 2 .

[0045] Examples 2-4 On the basis of Example 1, the carbon nanotube draw density was adjusted, and the other conditions were the same as in Example 1. See Table 1 for details.

[0046] Examples 5-8 On the basis of Example 1, the thermal initiation polymerization time was adjusted, and the other conditions were the same as in Example 1. See Table 1 for details.

[0047] Test Example 1 The nanofiber interwoven composite gel membranes prepared in Examples 1-8 were tested for carbon dioxide permeation flux and carbon dioxide / nitrogen separation selectivity. The gas permeation test was performed at room temperature (298 K) using the constant pressure variable volume method. During the test, the temperature was 25°C, the test gas purity was 99.99%, and the test gas pressure was 100 kPa. The results are shown in Table 1.

[0048] Table 1

[0049] As can be seen from the data in Table 1, the carbon dioxide permeation flux and carbon dioxide / nitrogen separation selectivity of the nanofiber interwoven composite gel membranes prepared in the present application are both high. As the carbon nanotube draw density decreases, the composite gel layer thickness decreases, the carbon dioxide flux of the composite membrane significantly increases, and the carbon dioxide / nitrogen selectivity always remains above 100. As the thermal initiation polymerization time is extended, the gel crosslinking network gradually becomes dense, the polymer molecular chain movement is difficult, and the carbon dioxide flux of the composite membrane gradually decreases.

[0050] As Figure 1 and Figure 2As shown, the functional skin layer of the nanofiber-interwoven composite gel membrane prepared in Example 1 is dense and defect-free, and has a thickness of about 4 microns and an interwoven and stacked nanofiber skeleton in the skin layer. The interwoven nanofiber network serves as a fast gas molecule transport channel to improve the carbon dioxide permeability, and can also break the stacking of polymer chains in the gel network, thereby improving the flowability of the polymer chains, increasing the free volume of the gel matrix to facilitate the rapid transport of gas molecules, so that the prepared nanofiber-interwoven composite gel membrane has excellent carbon dioxide permeability; the thermally induced in-situ polymerization method does not involve a phase change process, so the carbon dioxide-selective gel matrix formed has good interfacial compatibility with the nanofiber skeleton, which can avoid defects in the membrane, and at the same time, the abundant polar ether bonds in the polyethylene glycol gel promote the dissolution of carbon dioxide and repel nitrogen molecules, thereby ensuring that the prepared nanofiber-interwoven composite gel membrane has excellent carbon dioxide selectivity.

[0051] The above-described embodiments illustrate the technical solutions and beneficial effects of the present application in detail. It should be understood that the above-described embodiments are only specific embodiments of the present application and are not intended to limit the present application. Any modifications, supplements, and equivalent replacements made within the principle range of the present application shall be included in the protection scope of the present application.

Claims

1. A nanofiber interwoven composite gel membrane for carbon dioxide separation, characterized in that: It includes a nanofiber interwoven skeleton and a carbon dioxide-philic gel matrix layer coated on the surface of the nanofiber interwoven skeleton; The carbon dioxide-philic gel matrix layer is formed by in-situ polymerization and gelation of a precursor solution containing an oxidant, a cross-linking agent and a functional monomer on the surface of the nanofiber interwoven skeleton.

2. A method for preparing the nanofiber interwoven composite gel membrane according to claim 1, characterized in that: The following steps are involved: (1) Filtering the nanofiber suspension onto a porous support membrane and drying it to obtain a porous membrane loaded with a nanofiber interwoven skeleton; (2) A precursor solution containing an oxidant, a cross-linking agent, and a functional monomer is coated onto a porous membrane loaded with a nanofiber interwoven skeleton, and reacted at 40-90°C for 0.5-20 min to obtain a nanofiber interwoven composite gel membrane.

3. The method for preparing the nanofiber interwoven composite gel membrane according to claim 1, characterized in that: The porous support membrane is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, cellulose acetate ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polypropylene microfiltration membrane, polyvinylidene fluoride microfiltration membrane, polytetrafluoroethylene microfiltration membrane, polyethersulfone microfiltration membrane, and nylon microfiltration membrane.

4. The method for preparing the nanofiber interwoven composite gel membrane according to claim 1, characterized in that: The nanofiber is at least one of nanocrystalline cellulose, carbon nanotubes, silicon nanowires, and silver nanowires.

5. The method for preparing the nanofiber interwoven composite gel membrane according to claim 1 or 4, characterized in that: The loading amount of nanofibers on the porous membrane support is 0.1~30 g / m 2 .

6. The method for preparing the nanofiber interwoven composite gel membrane according to claim 1, characterized in that: The oxidant is at least one of azobisisobutyronitrile, ammonium persulfate, sodium persulfate, and potassium persulfate; and the concentration of the oxidant in the precursor solution is 1-30 mg / mL.

7. The method for preparing the nanofiber interwoven composite gel membrane according to claim 1, characterized in that: The cross-linking agent is at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate; and the concentration of the cross-linking agent in the precursor solution is 1-30 mg / mL.

8. The method for preparing the nanofiber interwoven composite gel membrane according to claim 1, characterized in that: The functional monomer is at least one of polyethylene glycol diacrylate and polyethylene glycol methacrylate; and the concentration of the functional monomer in the precursor solution is 200-1000 mg / mL.

9. The method for preparing the nanofiber interwoven composite gel membrane according to claim 1, characterized in that: The oxidant is ammonium persulfate, the cross-linking agent is polyethylene glycol diacrylate, and the functional monomer is polyethylene glycol diacrylate; In the precursor solution, the concentration of the oxidant is 5-15 mg / mL, and the total concentration of the cross-linking agent and the functional monomer is 600-1000 mg / mL.

10. Use of the nanofiber interwoven composite gel membrane according to claim 1 in separating carbon dioxide.

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