Organic-inorganic composite air separation membrane and preparation method thereof

Abstract

The invention relates to a membrane material, in particular to an organic-inorganic composite air separation membrane and a preparation method thereof. According to the invention, the alpha-Al2O3 support body with high stability is adopted as a base material of the PIM-1 polymerization selection layer, so that the problem that the traditional organic support body is corroded by an organic solvent in the preparation process of the selection layer is avoided, and the interface bonding force between the support body and the polymer film layer is enhanced through the modification of the silane coupling agent. In order to solve the problem that the oxygen flux is reduced due to the improvement, high-temperature thermal annealing is abandoned, and a normal-temperature drying mode is adopted to avoid transition crosslinking of the silane coupling agent interface layer and / or the PIM-1 polymer selection layer at high temperature, so that the oxygen flux is remarkably improved, and the method is more suitable for industrial application.

Description

Technical Field

[0001] This invention relates to a membrane material, specifically to an organic-inorganic composite air separation membrane and its preparation method. Background Technology

[0002] With the development of industry and the growth of medical needs, oxygen-enriched air is increasingly widely used in metallurgy, chemical industry, environmental protection, healthcare, and aquaculture. While traditional cryogenic separation and pressure swing adsorption technologies are mature, they suffer from drawbacks such as high equipment investment, high energy consumption, and complex operation. Membrane gas separation technology has become a highly attractive alternative due to its energy-saving, high-efficiency, simple operation, and environmentally friendly advantages. Traditional polymer membrane materials such as poly(1-trimethylsilyl-1-propyne) (PTMSP) possess high permeability, but their selectivity is poor, and they suffer from severe physical aging and rapid performance degradation. In recent years, a class of polymers with inherent microporosity (PIMs), such as PIM-1, have attracted widespread attention because their rigid, twisted main chain structure cannot effectively stack, forming a large number of continuous micropores while simultaneously exhibiting high permeability and high selectivity.

[0003] However, pure PIM-1 membranes also have certain problems: (1) Under high pressure or after long-term operation, the membrane structure will undergo physical aging, resulting in a decrease in free volume and a decrease in permeability; (2) Its mechanical strength is sometimes difficult to meet the requirements of actual membrane modules; (3) Its oxygen-nitrogen selectivity (O2 / N2) still has room for improvement to meet the requirements of more demanding oxygen-rich scenarios; (4) The polymer itself is too brittle. To solve the above problems, the existing technology often adopts the methods of blending, crosslinking or preparing composite membranes. Among them, the composite membrane (Thin-Film Composite, TFC) combines the advantages of the mechanical strength of the porous support layer and the high selectivity of the dense separation layer, and is an ideal solution. However, in the preparation of composite membranes, the use of PIM-1 requires the use of highly corrosive organic solvents such as chloroform or polar solvents such as N,N-dimethylformamide. The use of the above solvents will seriously corrode the organic substrate and thus affect the gas separation performance.

[0004] To address this, the applicant attempted to replace the organic substrate with a highly stable α-Al₂O₃ support to avoid solvent corrosion, and also tried coating the α-Al₂O₃ support with a silane coupling agent to enhance the interfacial bonding between the support and the polymer membrane. However, high-temperature heat treatment is often used in the preparation of PIM-1 membranes to accelerate solvent evaporation and improve crosslinking. The applicant found that this heat annealing resulted in excessively low flux, making it unsuitable for practical production applications. Therefore, how to prepare a high-flux air separation membrane based on an α-Al₂O₃ support modified with a silane coupling agent is a pressing problem to be solved. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides an organic-inorganic composite air separation membrane based on PIM-1. This composite membrane exhibits excellent oxygen and nitrogen selectivity, high oxygen permeation flux, good anti-aging properties, and mechanical strength, making it suitable for efficient and energy-saving air separation to prepare oxygen-enriched air.

[0006] First, this invention provides a method for preparing an organic-inorganic composite air separation membrane, which includes the following steps: S1: Provides a porous ceramic support; S2: Coat the surface of the porous ceramic support with a silane coupling agent solution and dry it to form a silane coupling agent interface layer; S3: Dissolve PIM-1 polymer in an organic solvent to prepare a coating solution with a concentration of 1-8 wt.%; S4: Apply the coating liquid to the surface of the silane coupling agent interface layer; S5: The coated porous ceramic support is left to stand at room temperature to evaporate the solvent, forming a dense and defect-free polymer selective layer, thus obtaining the organic-inorganic composite air separation membrane.

[0007] Preferably, in step S1, the porous ceramic support is an α-Al2O3 hollow fiber carrier with a pore size of 50-100 nm.

[0008] Preferably, in step S2, the silane coupling agent is one of γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane.

[0009] Preferably, in step S4, the coating liquid is applied to the surface of the porous ceramic support using an immersion-lift method, with the immersion time controlled to be 5-40 seconds and the lifting speed controlled to be 40-60 mm / min.

[0010] Preferably, in step S3, the PIM-1 has the following repeating units: , where m and n are any integers between 1 and 20.

[0011] Preferably, in step S5, the time for standing at room temperature is 8-24 hours.

[0012] Preferably, the synthesis steps of PIM-1 are as follows: S3-1: K2CO3, TTSBI and DCTB are added to an organic solvent under inert gas protection and reacted at 330-350K for 12-36h; S3-2: Pour the reaction solution into water, stir vigorously to obtain a yellow precipitate, and dry it to obtain PIM-1.

[0013] Secondly, the present invention also provides an organic-inorganic composite air separation membrane prepared according to the above preparation method, comprising a porous ceramic support and a polymer selective layer, wherein the thickness of the polymer selective layer is 1-12 μm.

[0014] Preferably, air is separated under the conditions of a feed pressure of 0.2 MPa ~ 1.6 MPa and a feed temperature of 25 °C, so that oxygen preferentially permeates through the separation membrane, and oxygen-enriched air with an oxygen concentration of not less than 35% is obtained on the permeation side.

[0015] Compared with the prior art, the present invention has the following advantages: This invention employs a highly stable α-Al₂O₃ support as the substrate for the PIM-1 polymer selective layer, avoiding the corrosion problem of organic solvents during the selective layer preparation process of traditional organic supports. Furthermore, the interfacial bonding between the support and the polymer film is enhanced through modification with a silane coupling agent. To address the issue of decreased oxygen flux resulting from these improvements, this invention abandons high-temperature thermal annealing and uses room-temperature drying to prevent excessive cross-linking of the silane coupling agent interfacial layer and / or the PIM-1 polymer selective layer at high temperatures, thereby significantly improving oxygen flux and making it more suitable for industrial applications. The PIM-1 / α-Al₂O₃ composite membrane prepared by this invention separates air under conditions of a feed pressure of 0.2 MPa ~ 1.6 MPa and a feed temperature of 25 °C, allowing oxygen to preferentially permeate through the separation membrane, resulting in oxygen-enriched air with an oxygen concentration of not less than 35% on the permeate side. Attached Figure Description

[0016] Figure 1 These are the 1H-NMR data of the PIM-1 membrane synthesized in Example 1 of this invention; Figure 2 This is an energy dispersive spectroscopy (EDS) spectrum of the porous ceramic support coated with silane coupling agent (KH550) in Example 1 of the present invention; Figure 3 These are scanning electron microscope (SEM) images of the PIM-1 / α-Al2O3 composite film, where (a) is a cross-sectional view of the film and (b) is a surface view of the film. Figure 4 This is a graph showing the long-term stability test results of the composite membrane under repeated start-stop cycles. Detailed Implementation

[0017] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the essence of the invention are within the scope of the present invention.

[0018] Example 1 The preparation route of the PIM-1 composite membrane in this embodiment is as follows:

[0019] The specific preparation process is as follows: 1. Polymer Synthesis PIM-1 was synthesized using a one-step method, detailed as follows: Step 1: 200 ml of DMF was added to a dried three-necked round-bottom flask. Under nitrogen protection, K₂CO₃ (60 mmol), TTSBI (30 mmol), and DCTB (30 mmol) were added separately to the three-necked flask. After complete dissolution, the flask was placed in a preheated oil bath and reacted at 343 K for 24 h to synthesize the PIM-1 microporous polymer. Step 2: The reaction solution was poured into deionized water and stirred vigorously to obtain a yellow precipitate. Finally, the washed polymer was dried in a vacuum oven at 333 K for 48 h to obtain the desired polymer.

[0020] 2. Preparation of polymer solutions and pretreatment of the carrier PIM-1 polymer was dissolved in CHCl3 and stirred vigorously for 24 h to form a homogeneous solution of 1-8 wt.%. The α-Al2O3 support was removed, and a 1-5 wt.% KH550 solution was prepared. The KH550 solution was coated for 20 s using a dip-coating machine, and then the solution was dried in an oven at 100 °C for 6 h until the solvent was completely evaporated. Finally, the polymer solution was coated onto the support using a dip-coating machine. α The surface of the hollow fiber carrier is impregnated with Al2O3 for 5-40 seconds. Before impregnation, both ends of the hollow fiber carrier are sealed with PTFE tape to prevent the polymer solution from entering. The impregnation and lifting speeds of the dip-coating machine are uniformly set to 50 mm / min, and the coating time is 5 seconds.

[0021] 3. Post-processing The obtained composite membrane was then placed in a fume hood for 0.5 hours to defoam and avoid defects. It was then covered with a petri dish and left overnight (12 hours) at room temperature. The next day, the membrane (denoted as M1) was removed for gas separation testing.

[0022] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the post-processing is as follows: the obtained composite membrane is placed in a preheated vacuum oven and vacuum dried at 323 K for 12 hours, and then the membrane (denoted as M2) is taken out for gas separation test.

[0023] Comparative Example 2 The only difference between Comparative Example 1 and Example 1 is that the post-treatment is as follows: the prepared composite membrane is directly immersed in a methanol solution and left overnight, and then allowed to evaporate naturally at room temperature for one day to obtain the methanol-treated composite membrane (denoted as M3).

[0024] Characterization Figure 1 These are the 1H-NMR data of the PIM-1 membrane synthesized in Example 1, obtained using a 600 MHz Bruker NMR spectrometer with deuterated chloroform (CDCl3) as the solvent. The signal peaks are broad, consistent with the characteristics of polymer materials, and the signal-to-noise ratio is good. The spectral signal is small in number and clearly assigned, perfectly matching the designed polymer repeating unit structure. The absence of redundant peaks indicates that the starting materials (especially the phenolic hydroxyl and fluorine atoms) have reacted completely. Peak d confirms that the aliphatic bridged ring structure has been fully incorporated into the polymer backbone. Peak c confirms the formation of the ether bond (-O-), a hallmark of polymerization. Peaks a / b confirm the presence of the aromatic ring structure, and its chemical shift is consistent with the expected substituted aromatic ring.

[0025] Figure 2 This is an energy dispersive spectroscopy (EDS) spectrum of the porous ceramic support coated with silane coupling agent (KH550) in Example 1, used to show the distribution of silicon on the support surface, confirming that the interface layer has been successfully modified. Figure 3 The image shows a scanning electron microscope (SEM) image of the PIM-1 / α-Al2O3 composite membrane prepared in Example 1. The membrane surface is smooth and no defects were found. The selective layer of the membrane material has a thickness of 3 μm and is tightly bonded to the α-Al2O3 support. No interface defects were observed.

[0026] The membrane samples prepared in Example 1 and Comparative Examples 1-2 were subjected to gas separation tests at 25 °C and a feed pressure of 2 bar, with a feed flow rate of 200 ml / min and air as the feed gas. High-pressure separation tests were also performed, and the results are shown in Table 1. Table 1 Gas separation performance of composite membranes with different post-treatment methods

[0027] As can be seen from the table above, compared with other drying methods, the drying method of the present invention can significantly increase the O2 permeation flux while ensuring that the selectivity is not reduced by much.

[0028] In practical industrial applications of gas separation membranes, separation units often need to be started and stopped according to production needs, such as during process peak shaving, equipment maintenance, or load adjustments. This repeated pressurization and depressurization process generates periodic mechanical stress and chemical environmental impact on the membrane material, potentially leading to membrane delamination, interface failure, or performance degradation. Therefore, examining the long-term stability of the membrane under repeated start-stop conditions is a crucial step in evaluating its feasibility for industrial application. To verify the durability of the composite membrane of this invention, we conducted accelerated aging tests on it at 1.6 MPa. Figure 4 As shown, the entire process from operation to complete shutdown and restart was simulated in 12 consecutive start-stop cycles. Throughout the entire cycle, the composite membrane's separation performance remained highly stable, with virtually no significant performance degradation. This result fully demonstrates that the composite membrane prepared by the method of this invention possesses excellent bonding strength between its separation layer and support layer, maintains a complete membrane structure, and can effectively resist physical stress and chemical atmosphere changes caused by frequent start-stop cycles. This superior cycle stability ensures that the composite membrane maintains highly efficient and reliable separation performance even in real, discontinuous operating environments, providing a solid guarantee for its large-scale industrial application.

[0029] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. However, the above description is merely a specific embodiment of the present invention, and the technical features of the present invention are not limited thereto. Any other embodiments derived by those skilled in the art without departing from the technical solution of the present invention should be covered within the patent scope of the present invention.

Claims

1. A method for preparing an organic-inorganic composite air separation membrane, characterized by, The method comprises the following steps: S1: providing a porous ceramic support; S2: coating a silane coupling agent solution on the surface of the porous ceramic support and drying to form a silane coupling agent interface layer; S3: dissolving PIM-1 polymer in an organic solvent to prepare a coating solution with a concentration of 1-8 wt.%; S4: coating the coating solution on the surface of the silane coupling agent interface layer; S5: placing the coated porous ceramic support at room temperature to volatilize the solvent, forming a dense and defect-free polymer selection layer, and obtaining the organic-inorganic composite air separation membrane.

2. The production method according to claim 1, characterized by, In step S1, the porous ceramic support is an α-Al2O3 hollow fiber carrier with a pore size of 50-100 nm.

3. The preparation method according to claim 1, characterized in that, In step S2, the silane coupling agent is one of γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane.

4. The method of claim 1, wherein, In step S4, the coating solution is coated on the surface of the porous ceramic support by dip coating, and the dip time is controlled to be 5-40 seconds, and the pulling speed is controlled to be 40-60 mm / min.

5. The method of claim 1, wherein, In step S3, the PIM-1 has the following repeat unit: where m and n are taken from any integer between 1 and 20.

6. The method of claim 1, wherein, In step S5, the time for standing at room temperature is 8-24 h.

7. The preparation method according to claim 1, characterized in that, The synthesis steps of the PIM-1 are as follows: S3-1: adding K2CO3, TTSBI and DCTB into an organic solvent under inert gas protection, and reacting at 330-350 K for 12-36 h; S3-2: pouring the reaction solution into water, stirring vigorously to obtain a yellow precipitate, and drying to obtain the PIM-1.

8. An organic-inorganic composite air separation membrane prepared according to the production method of claim 1, characterized by, The method comprises a porous ceramic support and a polymer selection layer, and the thickness of the polymer selection layer is 1-12 μm.

9. The air separation membrane of claim 8, wherein, Under the conditions of a feed pressure of 0.2 MPa-1.6 MPa and a feed temperature of 25 ℃, air is separated, oxygen preferentially permeates through the separation membrane, and oxygen air with an oxygen concentration of not less than 35% is obtained on the permeation side.

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