A high-temperature-resistant and solvent-resistant vapor permeable organic membrane and a preparation method thereof

Abstract

The application discloses a high-temperature-resistant and solvent-resistant vapor permeation organic membrane and a preparation method thereof. The preparation method adopts alkali soaking and heat treatment of a PAN-based membrane; a hydroxy vinyl silicone oil solution is deeply crosslinked under the action of a crosslinking agent and a catalyst, and then is staggered crosslinked with hydrogen-containing silicone oil under the action of a catalyst to obtain a casting solution; and the casting solution is combined and crosslinked with the PAN-based membrane, thereby obtaining the membrane. The application adopts polyacrylonitrile which has strong resistance to organic solvents as a base film raw material, and carries out annealing and alkali treatment on the base film raw material to improve the high-temperature resistance of the base film raw material. The active layer is prepared by taking hydroxy vinyl silicone oil as a main component, the active layer can be staggered crosslinked by adding hydrogen-containing silicone oil after deep crosslinking, and the solvent resistance of the active layer is improved. The composite membrane has strong high-temperature resistance and solvent resistance, and can adapt to the conditions of high temperature and strong corrosive solvents existing in a vapor permeation process.

Description

Technical Field

[0001] This invention belongs to the field of vapor permeation membrane separation technology, specifically relating to a high-temperature resistant and solvent-resistant vapor permeation organic membrane and its preparation method. Background Technology

[0002] With the development of global industrialization, people have paid increasing attention to the chemical, food, environmental protection, and energy sectors. A contradiction has emerged between the extreme demand for chemicals and the growing awareness of environmental protection. Therefore, people have begun to adopt environmentally friendly separation technologies—membrane separation technology—to produce and separate certain types of organic solvents. In the late 1980s, a new membrane separation technology similar in principle to pervaporation—vapor permeation (VP)—was first proposed by Uragami. Because both sides of the membrane are in a gaseous phase, and the driving force is the pressure difference between the vapor pressure of the feed-side component and the vapor pressure of the permeate-side component, vapor permeation is more economical than pervaporation and has thus attracted widespread attention.

[0003] Currently, commonly used vapor permeation membranes are mainly divided into two categories: organic membranes and inorganic membranes. Inorganic membranes have advantages such as high temperature resistance, corrosion resistance, and high mechanical strength. However, their application is limited by their high manufacturing cost, complex processes, and the instability of membrane flux and performance caused by uneven pore structure and pore size distribution. Organic membranes, on the other hand, have advantages such as low cost, simple preparation, and stable product performance. However, with the gradual development of vapor permeation technology, it has been found that under common high-temperature and strong solvent operating conditions, vapor permeation organic membranes are prone to aging, deformation, and even dissolution, leading to a decline in membrane performance or even failure.

[0004] Therefore, developing a high-temperature resistant and solvent-resistant vapor permeation membrane has become a top priority in the development of vapor permeation technology, which is of great significance for improving the efficiency of vapor permeation and the development of vapor permeation technology. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention uses polyacrylonitrile (PAN), which has extremely strong resistance to organic solvents, as the base membrane raw material. It pre-treats PAN to improve its high-temperature resistance. A deeply cross-linked and cross-linked structure, obtained by the reaction of hydroxyvinyl silicone oil, tetraethoxysilane (TEOS), and hydrogen-containing silicone oil, is used as the active layer. This results in a novel high-temperature and solvent-resistant vapor permeation organic membrane with extremely strong high-temperature and solvent resistance, capable of withstanding the high temperatures and highly corrosive solvents present in vapor permeation processes.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing a high-temperature resistant and solvent-vapor-permeable organic membrane includes the following steps:

[0008] (1) Pretreatment of PAN base film: Immerse the PAN base film in an alkaline solution to generate polar groups on the surface of the PAN base film; then heat treat to obtain a pretreated base film;

[0009] (2) Preparation of deeply cross-linked precast film solution: After uniformly mixing hydroxy vinyl silicone oil solution and cross-linking agent, a catalyst is added and stirred until the viscosity of the mixture reaches 20 mPa·s to obtain deeply cross-linked precast film solution.

[0010] (3) Preparation of casting solution: After uniformly mixing the pre-casting solution with hydrogen-containing silicone oil, add platinum-based catalyst and stir until the viscosity of the mixture reaches 30 mPa·s to complete cross-linking and obtain casting solution.

[0011] (4) Preparation of vapor permeation membrane: The casting solution obtained in step (4) is coated on the surface of the pretreated base membrane obtained in step (1), and crosslinked at 120-140℃ for 4-6 hours to obtain the high temperature resistant and solvent resistant vapor permeation organic membrane.

[0012] Preferably, the PAN-based film in step (1) is prepared by the following method:

[0013] The PAN solution is coated onto a nonwoven fabric, which is then immediately immersed in water to complete the phase transformation, thus obtaining the PAN base film.

[0014] Preferably, the coating thickness is 150–170 μm.

[0015] Preferably, the solvent of the PAN solution is one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) or N-methylpyrrolidone (NMP).

[0016] Preferably, in the PAN solution, the mass ratio of PAN to solvent is 20-25:75-80.

[0017] Preferably, the PAN solution has undergone degassing treatment.

[0018] Preferably, the PAN molecular weight of the PAN base film is 400,000 to 500,000.

[0019] Preferably, the alkaline solution in step (1) is a NaOH solution with a concentration of 0.3 to 1 M.

[0020] Preferably, the PAN base film is immersed in the alkaline solution for 1 to 12 hours in step (1).

[0021] Preferably, the heat treatment in step (1) is as follows: after unfolding the PAN base film, it is treated at 120-180°C for 10-30 minutes, and then naturally cooled. This process is repeated 3 times.

[0022] Preferably, the solvent for the hydroxyvinyl silicone oil solution in step (2) is n-heptane.

[0023] Preferably, in step (2), the mass ratio of hydroxyvinyl silicone oil to n-heptane in the hydroxyvinyl silicone oil solution is 6-12:88-94.

[0024] Preferably, the crosslinking agent in step (2) is tetraethoxysilane (TEOS).

[0025] Preferably, the mass ratio of the crosslinking agent to the hydroxyvinyl silicone oil solution in step (2) is 1-3:7-9.

[0026] Preferably, the catalyst in step (2) is tetrabutyltin.

[0027] Preferably, the mass of the catalyst in step (2) is 0.01 to 1% of the mass of the hydroxyvinyl silicone oil solution.

[0028] Preferably, the mass of the hydrogen-containing silicone oil in step (3) is 0.5 to 2% of the mass of the hydroxyvinyl silicone oil solution.

[0029] Preferably, the platinum-based catalyst in step (3) is Castel PT5000-TMDVDS600.

[0030] Preferably, the mass of the platinum-based catalyst in step (3) is 0.1 to 0.3% of the hydrogen-containing silicone oil.

[0031] Preferably, the coating thickness in step (4) is 60–90 μm.

[0032] The present invention also provides a high-temperature resistant and solvent vapor permeation resistant organic membrane prepared by the above preparation method.

[0033] The beneficial effects of this invention are as follows:

[0034] The novel high-temperature and solvent-resistant vapor permeation organic membrane prepared by this invention uses polyacrylonitrile (PAN) as the base membrane material. Because it has extremely strong solvent resistance, PAN with a relatively high molecular weight of 400,000 to 500,000 can be used to prepare a PAN base membrane with high crystallinity. Considering the high temperature of the vapor permeation process, alkali treatment and high-temperature annealing are further adopted to maximize the crystallinity and orientation of the high molecular weight PAN, thereby enhancing the high-temperature resistance of the base membrane.

[0035] Furthermore, the present invention uses hydroxyl vinyl silicone oil as the main component to prepare the active layer, which provides active hydroxyl groups that can be deeply crosslinked with TEOS under catalytic conditions. After deep crosslinking, hydrogen-containing silicone oil is added, and under catalytic conditions, the vinyl groups of the hydroxyl vinyl silicone oil and the hydrogen-containing silicone oil undergo crosslinking, completing the dual crosslinking of the active layer coating liquid, thereby improving the solvent resistance of the active layer.

[0036] After the active layer and the base membrane are bonded together, the resulting composite membrane has extremely strong high temperature resistance and solvent resistance, and can adapt to the high temperature and highly corrosive solvent conditions present in the vapor permeation process. Attached Figure Description

[0037] Figure 1 These are the appearance images of the steam-permeable organic membrane before and after boiling in Example 5.

[0038] Figure 2 These are images showing the appearance of the vapor-permeable organic membrane before and after immersion in tetrahydrofuran in Example 5. Detailed Implementation

[0039] The present invention will be further explained below with reference to the embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0040] Example 1

[0041] Polyacrylonitrile (PAN) was dissolved in DMAc at 70°C. The molecular weight of PAN was 400,000, and the mass ratio of PAN to solvent was 20:80. After complete dissolution, the solution was allowed to stand and cool to remove bubbles. The solution was then uniformly coated onto a nonwoven fabric with a coating thickness of 150 μm. Immediately after coating, the solution was immersed in pure water to complete the phase transformation process of the base film, resulting in a PAN base film, which was then stored in pure water.

[0042] The PAN base film is completely immersed in a 0.3M NaOH solution for 1 hour. This process is an alkaline treatment of the PAN base film, which generates polar groups such as carboxyl and hydroxyl groups on its surface, thereby enhancing its polar affinity.

[0043] The alkali-treated PAN base film is laid flat and placed in an oven for heat treatment at 120°C for 10 minutes. After the time is up, it is removed and allowed to cool naturally to room temperature. This process is repeated 3 times to obtain a high-temperature resistant PAN base film.

[0044] Hydroxyvinyl silicone oil was dissolved in n-heptane at room temperature, with a mass ratio of 6:94 between hydroxyvinyl silicone oil and n-heptane, to obtain a homogeneous hydroxyvinyl silicone oil solution.

[0045] The crosslinking agent tetraethoxysilane (TEOS) was added to the hydroxyvinyl silicone oil solution at a mass ratio of 1:9, and stirred until homogeneous at room temperature. Then, the catalyst tetrabutyltin was added at 0.01% of the weight of the hydroxyvinyl silicone oil solution. After addition, the mixture was stirred at room temperature until the viscosity of the mixed solution reached 20 mPa·s, at which point stirring was stopped, thus completing the first step: deep crosslinking of the active layer coating solution.

[0046] Hydrogen-containing silicone oil was added to the deeply cross-linked hydroxyvinyl silicone oil mixture. The amount of hydrogen-containing silicone oil added was 0.5% of the total amount of hydroxyvinyl silicone oil solution. After the addition was completed, the mixture was stirred evenly. Then, Castel PT5000-TMDVDS600 platinum-based catalyst was added to catalyze the cross-linking of hydrogen-containing silicone oil and deeply cross-linked hydroxyvinyl silicone oil. The amount of platinum-based catalyst added was 0.1% of the amount of hydrogen-containing silicone oil added. After the addition, the mixture was stirred at room temperature until the final viscosity of the mixed silicone oil solution reached 30 mPa·s, which indicates that the active layer coating solution has completed deep cross-linking and cross-linking.

[0047] A mixed silicone oil solution with deeply cross-linked and cross-linked active layers was applied to a high-temperature resistant PAN base film, with a coating thickness of 60 μm. After coating, the film was placed in an oven at 120°C for 4 hours for cross-linking. The high-temperature cross-linking process yielded a high-temperature resistant and solvent vapor permeable organic membrane.

[0048] Example 2

[0049] Polyacrylonitrile (PAN) was dissolved in DMF at 80°C. The molecular weight of PAN was 500,000, and the mass ratio of PAN to solvent was 22:78. After complete dissolution, the mixture was allowed to stand and cool to remove bubbles. It was then uniformly coated onto a nonwoven fabric with a coating thickness of 160 μm. Immediately after coating, the film was immersed in pure water to complete the phase transformation process of the base film, resulting in a PAN base film, which was then stored in pure water.

[0050] The PAN base film was completely immersed in a 0.8M NaOH solution for 10 hours. This process is an alkaline treatment of the PAN base film, which generates polar groups such as carboxyl and hydroxyl groups on its surface, thereby enhancing its polar affinity.

[0051] The alkali-treated PAN base film is laid flat and placed in an oven for heat treatment at 160℃ for 25 minutes. After the time is up, it is removed and allowed to cool naturally to room temperature. This process is repeated 3 times to obtain a high-temperature resistant PAN base film.

[0052] Hydroxyvinyl silicone oil was dissolved in n-heptane at room temperature, with a mass ratio of hydroxyvinyl silicone oil to n-heptane of 10:90, to obtain a homogeneous hydroxyvinyl silicone oil solution.

[0053] The crosslinking agent tetraethoxysilane (TEOS) was added to the hydroxyvinyl silicone oil solution at a mass ratio of 2:8, and stirred until homogeneous at room temperature. Then, the catalyst tetrabutyltin was added at a mass ratio of 0.8% of the hydroxyvinyl silicone oil solution weight. After addition, the mixture was stirred at room temperature until the viscosity of the mixed solution reached 20 mPa·s, at which point stirring was stopped, thus completing the first step: deep crosslinking of the active layer coating solution.

[0054] Hydrogen-containing silicone oil was added to the deeply cross-linked hydroxyvinyl silicone oil mixture. The amount of hydrogen-containing silicone oil added was 1.5% of the total amount of hydroxyvinyl silicone oil solution. After the addition was completed, the mixture was stirred evenly. Then, Castel PT5000-TMDVDS600 platinum-based catalyst was added to catalyze the cross-linking of hydrogen-containing silicone oil and deeply cross-linked hydroxyvinyl silicone oil. The amount of platinum-based catalyst added was 0.2% of the amount of hydrogen-containing silicone oil added. After the addition, the mixture was stirred at room temperature until the final viscosity of the mixed silicone oil solution reached 30 mPa·s, which indicates that the active layer coating solution has completed deep cross-linking and cross-linking.

[0055] A mixed silicone oil solution with deeply cross-linked and cross-linked active layers was applied to a high-temperature resistant PAN base film, with a coating thickness of 80 μm. After coating, the film was placed in an oven at 130°C for 5 hours for cross-linking. The high-temperature cross-linking process yielded a high-temperature resistant and solvent vapor permeable organic membrane.

[0056] Example 3

[0057] Polyacrylonitrile (PAN) was dissolved in NMP at 90°C. The molecular weight of PAN was 500,000, and the mass ratio of PAN to solvent was 25:75. After complete dissolution, the solution was allowed to stand and cool to remove bubbles. The solution was then uniformly coated onto a nonwoven fabric with a coating thickness of 170 μm. Immediately after coating, the solution was immersed in pure water to complete the phase inversion process of the base film, resulting in a PAN base film, which was then stored in pure water.

[0058] The PAN base film was completely immersed in a 1M NaOH solution for 12 hours. This process is an alkaline treatment of the PAN base film, which generates polar groups such as carboxyl and hydroxyl groups on its surface, thereby enhancing its polar affinity.

[0059] The alkali-treated PAN base film is laid flat and placed in an oven for heat treatment at 180°C for 30 minutes. After the time is up, it is removed and allowed to cool naturally to room temperature. This process is repeated 3 times to obtain a high-temperature resistant PAN base film.

[0060] Hydroxyvinyl silicone oil was dissolved in n-heptane at room temperature, with a mass ratio of hydroxyvinyl silicone oil to n-heptane of 12:88, to obtain a homogeneous hydroxyvinyl silicone oil solution.

[0061] The crosslinking agent tetraethoxysilane (TEOS) was added to the hydroxyvinyl silicone oil solution at a mass ratio of 3:7, and stirred until homogeneous at room temperature. Then, the catalyst tetrabutyltin was added at 1% of the weight of the hydroxyvinyl silicone oil solution. After addition, the mixture was stirred at room temperature until the viscosity of the mixed solution reached 20 mPa·s, at which point stirring was stopped, thus completing the first step: deep crosslinking of the active layer coating solution.

[0062] Hydrogen-containing silicone oil was added to the deeply cross-linked hydroxyvinyl silicone oil mixture solution. The amount of hydrogen-containing silicone oil added was 2% of the total amount of hydroxyvinyl silicone oil solution. After the addition was completed, the mixture was stirred evenly. Then, Castel PT5000-TMDVDS600 platinum-based catalyst was added to catalyze the cross-linking of hydrogen-containing silicone oil and deeply cross-linked hydroxyvinyl silicone oil. The amount of platinum-based catalyst added was 0.3% of the amount of hydrogen-containing silicone oil added. After the addition, the mixture was stirred at room temperature until the final viscosity of the mixed silicone oil solution reached 30 mPa·s, which indicates that the active layer coating solution has completed deep cross-linking and cross-linking.

[0063] A mixed silicone oil solution with deeply cross-linked and cross-linked active layers was applied to a high-temperature resistant PAN base film, with a coating thickness of 90 μm. After coating, the film was placed in an oven at 140°C for 6 hours for cross-linking. The high-temperature cross-linking process yielded a high-temperature resistant and solvent vapor permeable organic membrane.

[0064] Example 4

[0065] Polyetherimide (PEI) was dissolved in DMF at 90°C with a PEI to solvent mass ratio of 25:75. After complete dissolution, the mixture was allowed to stand and cool to remove bubbles. It was then uniformly coated onto a nonwoven fabric with a coating thickness of 170 μm. Immediately after coating, the film was immersed in pure water to complete the phase transformation process of the base film, resulting in a PEI base film, which was then stored in pure water.

[0066] Hydroxyvinyl silicone oil was dissolved in n-heptane at room temperature, with a mass ratio of hydroxyvinyl silicone oil to n-heptane of 12:88, to obtain a homogeneous hydroxyvinyl silicone oil solution.

[0067] A crosslinking agent, tetraethoxysilane (TEOS), was added to a hydroxyvinyl silicone oil solution at a mass ratio of 3:7. The mixture was stirred until homogeneous at room temperature. Then, a catalyst, tetrabutyltin, was added at 1% of the weight of the hydroxyvinyl silicone oil solution. After addition, the mixture was stirred at room temperature until the viscosity of the catalyst-added solution reached 20 mPa·s. The solution was then coated onto a PEI substrate with a thickness of 90 μm. After coating, the membrane was placed in an oven at 140 °C for 6 hours for crosslinking. The PEI vapor permeation organic membrane was obtained after high-temperature crosslinking.

[0068] Example 5

[0069] (1) High-temperature boiling test and small-scale permeation vaporization test after high-temperature boiling:

[0070] The high-temperature and solvent-resistant vapor-permeable organic membranes prepared in Examples 1-3 and the ordinary PEI vapor-permeable organic membrane prepared in Example 4 were boiled in water and kept for 6 hours. The separation performance of the vapor-permeable organic membranes before and after boiling was tested on a self-designed pervaporation experimental platform. The separation performance test used 5% ethanol-water as raw material, the experimental temperature was 40℃, and the vacuum degree was 2000 Pa. The experimental results are shown in Table 1.

[0071] Table 1 Summary of Experimental Performance Data

[0072]

[0073] Experiments show that the high-temperature resistant and solvent-resistant vapor permeation membrane prepared by this invention has strong high-temperature resistance, such as... Figure 1 As shown, no obvious damage or shrinkage was observed on the membrane surface after high-temperature boiling. The small-scale pervaporation test results after high-temperature boiling demonstrated that the membrane's separation performance was not affected, thus proving that this type of membrane has extremely strong high-temperature resistance. While ordinary PEI vapor permeate organic membranes also did not show obvious damage or shrinkage after high-temperature boiling, the membrane flux increased significantly and the separation factor decreased significantly, indicating a decline in membrane separation performance. Therefore, it can be concluded that ordinary PEI vapor permeate organic membranes are affected by high-temperature conditions and cannot maintain excellent separation performance for extended periods under high-temperature conditions.

[0074] (2) Solvent resistance immersion test (immersion in tetrahydrofuran):

[0075] The high-temperature resistant and solvent-resistant vapor-permeable organic membranes prepared in Examples 1-3 and the ordinary PEI vapor-permeable organic membrane prepared in Example 4 were immersed in tetrahydrofuran for 1 month, and the hydrophobic properties of the vapor-permeable organic membranes before and after immersion were examined.

[0076] like Figure 2As shown, after soaking in tetrahydrofuran for one month, the membrane remained intact, and the membrane surface still exhibited hydrophobicity. This indicates that both the base membrane and the active layer of the membrane have extremely strong solvent resistance, and the membrane surface remained undamaged, thus proving that this type of membrane has extremely strong solvent resistance. Ordinary PEI vapor permeation membranes showed separation of the active layer from the base membrane, and the base membrane exhibited partial dissolution, indicating that ordinary PEI vapor permeation membranes cannot withstand tetrahydrofuran solvent, meaning that ordinary PEI vapor permeation membranes have extremely poor solvent resistance.

[0077] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, any substitutions or obvious modifications made without departing from the inventive concept, provided that the performance or application remains the same, should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant and solvent vapor permeation resistant organic membrane, characterized in that, Includes the following steps: (1) Pretreatment of PAN base film: Immerse the PAN base film in an alkaline solution to generate polar groups on the surface of the PAN base film; then heat treat to obtain a pretreated base film; (2) Preparation of deeply cross-linked precast film liquid: After uniformly mixing hydroxy vinyl silicone oil solution and cross-linking agent, a catalyst is added and stirred until the viscosity of the mixture reaches 20 mPa•s to obtain deeply cross-linked precast film liquid; the cross-linking agent is tetraethoxysilane and the catalyst is tetrabutyltin. (3) Preparation of casting solution: After uniformly mixing the pre-casting solution with hydrogen-containing silicone oil, add platinum-based catalyst and stir until the viscosity of the mixture reaches 30 mPa•s to complete cross-linking and obtain casting solution; (4) Preparation of vapor permeation membrane: The casting solution obtained in step (4) is coated on the surface of the pretreated base membrane obtained in step (1), and crosslinked at 120~140℃ for 4~6h to obtain the high temperature resistant and solvent resistant vapor permeation organic membrane.

2. The preparation method according to claim 1, characterized in that, The PAN molecular weight of the PAN-based film is 400,000 to 500,000.

3. The preparation method according to claim 1, characterized in that, In step (1), the PAN base film is immersed in the alkaline solution for 1 to 12 hours.

4. The preparation method according to claim 1, characterized in that, The heat treatment described in step (1) is as follows: after unfolding the PAN base film, it is treated at 120~180℃ for 10~30min, and then naturally cooled. This process is repeated 3 times.

5. The preparation method according to claim 1, characterized in that, The solvent for the hydroxyvinyl silicone oil solution in step (2) is n-heptane.

6. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of hydroxyvinyl silicone oil to n-heptane in the hydroxyvinyl silicone oil solution is 6~12:88~94; the mass ratio of crosslinking agent to the hydroxyvinyl silicone oil solution is 1~3:7~9; and the mass of catalyst is 0.01~1% of the mass of the hydroxyvinyl silicone oil solution.

7. The preparation method according to claim 1, characterized in that, In step (3), the mass of the hydrogen-containing silicone oil is 0.5 to 2% of the mass of the hydroxyvinyl silicone oil solution; the mass of the platinum-based catalyst is 0.1 to 0.3% of the mass of the hydrogen-containing silicone oil.

8. The preparation method according to claim 1, characterized in that, The platinum-based catalyst mentioned in step (3) is Castel PT5000-TMDVDS600.

9. A high-temperature resistant and solvent vapor permeation resistant organic membrane prepared by any one of the preparation methods described in claims 1-8.

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