Ultraviolet crosslinking type polyethylene oxide multilayer composite film, preparation method and application thereof

Abstract

The application belongs to the technical field of gas separation membranes, and relates to a kind of ultraviolet crosslinking type polyethylene oxide multilayer composite membrane and its preparation method and application. Including base film, polydimethylsiloxane interlayer covered on the base film, and ultraviolet crosslinking type polyethylene oxide separation layer covered on the interlayer. The application solves the problem that the reaction speed is difficult to control in the process of ultraviolet initiated radical polymerization, and successfully prepares soluble UV-cPEO with suitable crosslinking degree. The preparation method is simple and controllable, and the prepared ultraviolet crosslinking type polyethylene oxide multilayer composite membrane can realize efficient separation of CO2 / N2 mixed gas, and has wide application prospect in flue gas system separation of coal-fired power plant.

Description

Technical Field

[0001] This invention belongs to the field of gas separation membrane technology, and relates to an ultraviolet cross-linked polyethylene oxide multilayer composite membrane, its preparation method and application. Background Technology

[0002] Faced with the severe challenges of global climate change, developing efficient carbon capture technologies has become an urgent need to achieve carbon neutrality. Among numerous carbon capture technologies, membrane separation demonstrates enormous application potential due to its outstanding advantages such as relatively low energy consumption, simple operation, high modularity, and environmental friendliness. This technology utilizes the differences in permeation rates of different gases in membrane materials to achieve efficient separation, and its core lies in developing membrane materials that possess high permeability, high selectivity, and long-term stability.

[0003] In recent years, polymer membrane materials have become ideal materials for industrial separation processes due to their low cost, ease of processing, and scale-up capabilities. Among polymer membrane materials used for CO2 separation, cross-linked polyethylene oxide (PEO) is one of the main membrane materials.

[0004] Most current research on cross-linked PEO membranes focuses on homogeneous membranes with thicknesses ranging from tens to hundreds of micrometers. However, excessively thick homogeneous membranes result in low permeation flux, while excessively thin membranes exhibit poor mechanical properties, making them unsuitable for industrial scale-up. Composite membranes, on the other hand, can achieve thinner membrane materials while incorporating a support material to ensure their mechanical properties. However, research on cross-linked PEO composite membranes is extremely limited. This is because the controlled synthesis of soluble cross-linked PEO polymers via free radical polymerization is challenging, making it difficult to prepare composite membranes using industrially mature solution coating methods. While there are reports of synthesizing soluble cross-linked PEO polymers via atom transfer radical polymerization (ATRP), the synthesis conditions are demanding, the process is cumbersome, and it utilizes large amounts of highly toxic organic solvents. Summary of the Invention

[0005] This invention addresses the problems existing in the preparation process of traditional cross-linked polyethylene oxide composite membranes by proposing an ultraviolet cross-linked polyethylene oxide multilayer composite membrane, its preparation method, and its application in the CO2 / N2 separation process.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution: A UV-crosslinked polyethylene oxide multilayer composite membrane includes a base membrane, a polydimethylsiloxane intermediate layer covering the base membrane, and a UV-crosslinked polyethylene oxide separation layer covering the intermediate layer.

[0007] Preferably, the thickness of the UV cross-linked polyethylene oxide separation layer is 20-120 nm, and the thickness of the polydimethylsiloxane interlayer is 100-200 nm.

[0008] The preparation method of the above-mentioned UV crosslinked polyethylene oxide multilayer composite film includes the following steps: (1) Add polydimethylsiloxane precursor, tetraethyl orthosilicate and dibutyltin dilaurate to n-heptane, mix evenly to obtain mixture A, heat mixture A to carry out crosslinking reaction to obtain polydimethylsiloxane casting solution.

[0009] (2) After cooling the polydimethylsiloxane casting solution, it is coated onto the base film, dried and thermally crosslinked to obtain a polydimethylsiloxane composite film.

[0010] (3) Polyethylene glycol diacrylate, polyethylene glycol methacrylate and 1-hydroxycyclohexylphenyl ketone were added to ethanol and mixed evenly to obtain mixture B. Crosslinking reaction was carried out under intermittent nitrogen purging and ultraviolet irradiation to obtain ultraviolet crosslinked polyethylene oxide casting solution.

[0011] (4) The polydimethylsiloxane composite membrane was treated in an ultraviolet ozone cleaner to obtain a hydrophilic membrane.

[0012] (5) The UV cross-linked polyethylene oxide casting solution is coated onto the hydrophilic membrane and dried under vacuum to obtain the composite membrane.

[0013] Preferably, in step (1), the relative molecular weight of the polydimethylsiloxane precursor is 50,000-100,000, the mass ratio of polydimethylsiloxane precursor: tetraethyl orthosilicate: dibutyltin dilaurate is (10-1):1:0.1, the mass fraction of polydimethylsiloxane in mixture A is 1-10%, the crosslinking reaction temperature is 50-80℃, and the crosslinking reaction time is 1-5h.

[0014] Preferably, the drying and thermal crosslinking temperature in step (2) is 40-70℃ and the time is 6-18h.

[0015] Preferably, in step (3), the relative molecular weight of polyethylene glycol diacrylate is 500-1000, the molecular weight of polyethylene glycol methacrylate is 500-1000, and the mass ratio of polyethylene glycol diacrylate to polyethylene glycol methacrylate is (0.1-9):1; the total mass fraction of polyethylene glycol diacrylate and polyethylene glycol methacrylate in mixture B is 5-20%, and the mass fraction of 1-hydroxycyclohexylphenyl ketone in mixture B is 0.2-2.5%; the intermittent nitrogen purging and ultraviolet irradiation treatment process is as follows: under the conditions of ultraviolet irradiation wavelength of 300-400nm and nitrogen purging flow rate of 20-100mL / min, the treatment is repeated for 1-2min, intermittently for 0.3-0.6min, and the total treatment time is 6-10min.

[0016] Preferably, the ultraviolet ozone treatment temperature in step (4) is 25-30℃ and the treatment time is 60-180s.

[0017] Preferably, in steps (2) and (5), the coating is performed using a wire bar coater with a wire bar specification of 10-60 μm; in step (5), the mass fraction of the UV crosslinking polyethylene oxide casting solution is 0.1-2%, the vacuum drying temperature is 30-40℃, and the drying time is 11-13h.

[0018] This invention proposes the application of the ultraviolet cross-linked polyethylene oxide multilayer composite membrane prepared by the above method in carbon dioxide / nitrogen separation.

[0019] This invention achieves controllable regulation of the free radical polymerization reaction of PEO monomers through an intermittent ultraviolet irradiation / nitrogen purging strategy, successfully preparing soluble ultraviolet-crosslinked polyethylene oxide (hereinafter referred to as UV-cPEO) with different degrees of crosslinking. A challenge in traditional composite membrane preparation lies in the difficulty of controlling the viscosity of UV-clinked PEO, making it difficult to form composite membranes. This invention, however, optimizes the concentration and viscosity of the casting solution to achieve the coating of an ultrathin UV-cPEO separation layer, ultimately obtaining a UV-cPEO / PDMS / PAN multilayer composite membrane. Intermittent ultraviolet irradiation helps to slow down the generation rate of primary free radicals, while intermittent nitrogen purging quenches some free radicals during the reaction, thereby reducing the free radical reaction rate and achieving controllable regulation of the reaction process to obtain a soluble crosslinked PEO polymer with a suitable degree of crosslinking. The synthesized polymer has good solution processability, making it easy to prepare an ultrathin separation layer through solution coating, thus obtaining a multilayer composite membrane suitable for practical CO2 / N2 separation processes.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. This invention solves the problem of difficult-to-control reaction rate in UV-initiated free radical polymerization by using an intermittent UV irradiation / nitrogen purging strategy, and successfully prepares soluble UV-cPEO with suitable crosslinking degree.

[0021] 2. The excellent solution processability of UV-cPEO solves the problem that cross-linked PEO polymers prepared by conventional methods are difficult to coat into films. Ultra-thin separation layers can be obtained through industrially mature coating methods such as spin coating and blade coating, which is conducive to the practical application and scale-up preparation of this type of membrane material.

[0022] 3. The preparation method of this invention is simple and controllable. The prepared ultraviolet cross-linked polyethylene oxide multilayer composite membrane can achieve efficient separation of CO2 / N2 mixed gas, with CO2 permeability exceeding 2500 GPU and CO2 / N2 selectivity exceeding 34. Moreover, the membrane has excellent stability and has broad application prospects in the separation of flue gas systems in coal-fired power plants. Attached Figure Description

[0023] Figure 1 This is a photograph of the UV-crosslinked polyethylene oxide casting solution with uneven viscosity obtained in Comparative Example 1 of this invention. Detailed Implementation

[0024] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0025] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification. Example 1

[0026] This embodiment provides a method for preparing a UV-crosslinked polyethylene oxide multilayer composite membrane. The polydimethylsiloxane precursor was purchased from Shanghai Rubber Factory, with a molecular weight of 60,000 g / mol. Dibutyltin dilaurate was purchased from Aladdin Reagent (Shanghai) Co., Ltd. The oligomers polyethylene glycol diacrylate (PEGDA) and polyethylene glycol methacrylate (PEGMEA) were both purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.; the molecular weight of PEGDA was 700 g / mol, product code 102915242; and the molecular weight of PEGMEA was 480 g / mol, product code 003856419. 1-Hydroxycyclohexylbenzophenone (HCPK) was purchased from Adamas Beta (Shanghai) Chemical Reagent Co., Ltd., with a molecular weight of 204.26 g / mol. The base membrane was polyacrylonitrile, purchased from Shandong Lanjing Membrane Technology Co., Ltd., China, with a pore size of approximately 20 nm. All reagents mentioned above, and other reagents in this embodiment unless otherwise specified, are of analytical grade.

[0027] Take 1g of polydimethylsiloxane, 1g of tetraethyl orthosilicate, and 0.1g of dibutyltin dilaurate and add them to 98g of n-heptane. Mix them thoroughly to obtain mixture A. Then place mixture A at 60°C. o The crosslinking reaction was carried out for 3 hours under C water bath conditions to obtain polydimethylsiloxane casting solution.

[0028] The above-mentioned polydimethylsiloxane casting solution was allowed to cool naturally to room temperature. Then, a 10 μm doctor blade was used to evenly coat the polydimethylsiloxane casting solution onto the base film to obtain a polydimethylsiloxane wet film. The wet film was then placed in a forced-air drying oven and dried continuously at 60°C for 12 hours to obtain a polydimethylsiloxane composite film.

[0029] Take 2.1g of oligomeric polyethylene glycol diacrylate and 0.9g of oligomeric polyethylene glycol methacrylate and add them to 27g of ethanol. Stir manually with a glass rod for 2min. Then add 0.15g of 1-hydroxycyclohexyl benzophenone and continue stirring for 2min to obtain mixture B.

[0030] The above mixture B was placed in an ultraviolet (UV) irradiator, and nitrogen gas was introduced at a flow rate of 100 mL / min. Simultaneously, a 365 nm UV lamp was used for irradiation for 1.5 min. Afterward, the nitrogen gas valve and UV lamp were closed, and the process was allowed to proceed for 0.5 min, which was counted as one intermittent irradiation / purging cycle. This process was repeated continuously until the total operation time reached 8 min, i.e., four intermittent irradiation / purging cycles, yielding a UV-crosslinked polyethylene oxide casting solution. The viscosity of the casting solution at this point was measured to be 30 mPa·s.

[0031] The polydimethylsiloxane composite membrane was placed in a UV ozone cleaner. The instrument was started and preheated to 25°C. Then, the UV ozone treatment device (PCE-22, purchased from Hefei Kejing Instrument Co., Ltd.) was turned on. The treatment time was 120 seconds. At this time, the surface of the polydimethylsiloxane composite membrane changed from hydrophobic to hydrophilic, and finally a hydrophilic polydimethylsiloxane composite membrane was obtained.

[0032] Take 2g of UV-crosslinked polyethylene oxide casting solution, add 18g of ethanol to dilute to a 1% (w / w) casting solution, and then use a 10μm doctor blade to evenly coat the diluted casting solution onto a hydrophilic polydimethylsiloxane composite membrane to obtain a UV-crosslinked polyethylene oxide wet membrane. Then place the wet membrane in a vacuum drying oven and vacuum dry at 35℃ for 12h to obtain a UV-crosslinked polyethylene oxide multilayer composite membrane.

[0033] The polydimethylsiloxane composite membrane and the UV-crosslinked polyethylene oxide multilayer composite membrane prepared in this embodiment were subjected to XPS etching to characterize the thickness of the polydimethylsiloxane membrane layer and the polyethylene oxide separation layer, respectively. The thickness of the PDMS membrane layer was found to be approximately 120 nm, while the thickness of the UV-cPEO separation layer was less than 60 nm. Separation performance verification showed that the membrane achieved highly efficient separation of the CO2 / N2 (15 / 85, v / v%) system at 25 °C and 0.2 MPa, with a CO2 permeation flux of 2510 GPU and a CO2 / N2 selectivity of 34.8. Example 2

[0034] This embodiment provides a method for preparing an ultraviolet cross-linked polyethylene oxide multilayer composite film. Unless otherwise specified, this embodiment and the following embodiments are consistent with Embodiment 1. 1g of polydimethylsiloxane, 1g of tetraethyl orthosilicate, and 0.1g of dibutyltin dilaurate are added to 98g of n-heptane and mixed thoroughly to obtain mixture A; then mixture A is placed at 60°C. o The crosslinking reaction was carried out under water bath heating for 3 hours to obtain a polydimethylsiloxane casting solution. The polydimethylsiloxane casting solution was allowed to cool naturally to room temperature, and then a 10 μm doctor blade was used to evenly coat the polydimethylsiloxane casting solution onto the base film to obtain a polydimethylsiloxane wet film. The wet film was then placed in a forced-air drying oven and dried continuously at 60°C for 12 hours to obtain a polydimethylsiloxane composite film. 2.1 g of oligomer polyethylene glycol diacrylate and 0.9 g of oligomer polyethylene glycol methacrylate were added to 27 g of ethanol and mixed thoroughly. Then, 0.15 g of 1-hydroxycyclohexyl benzophenone was added, and the mixture was stirred and mixed thoroughly to obtain mixture B. Mixture B was placed in an ultraviolet (UV) irradiator, and nitrogen gas was introduced at a flow rate of 100 mL / min. Simultaneously, a 365 nm UV lamp was used for irradiation for 1.5 min. Afterward, the nitrogen gas valve and UV lamp were simultaneously closed, and the process was allowed to proceed for 0.5 min, counted as one intermittent irradiation / purging cycle. This intermittent irradiation / purging cycle was repeated three times to obtain a UV-crosslinked polyethylene oxide (PEO) casting solution. At this point, the viscosity of the casting solution reached 20 mPa·s. The PEO composite membrane was placed in a UV ozone cleaner, and the instrument was preheated to 25°C. The UV ozone treatment device was then turned on and treated for 120 s to obtain a hydrophilic PEO composite membrane. 2 g of the UV-crosslinked PEO casting solution was diluted with 18 g of ethanol, and then a 10 μm doctor blade was used to evenly coat the diluted casting solution onto the hydrophilic PEO composite membrane to obtain a UV-crosslinked PEO wet membrane. The wet film was then placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain an ultraviolet cross-linked polyethylene oxide multilayer composite film.

[0035] The UV crosslinked polyethylene oxide multilayer composite membrane prepared in this embodiment achieved efficient separation of the CO2 / N2 (15 / 85, v / v%) system under the conditions of 25℃ and 0.2MPa. The CO2 permeation flux reached 3012 GPU, while the CO2 / N2 selectivity reached 25.6. Example 3

[0036] Take 1g of polydimethylsiloxane, 1g of tetraethyl orthosilicate, and 0.1g of dibutyltin dilaurate and add them to 98g of n-heptane. Mix them thoroughly to obtain mixture A. Place mixture A at 60°C. oThe crosslinking reaction was carried out under water bath heating for 3 hours to obtain a polydimethylsiloxane casting solution. The polydimethylsiloxane casting solution was allowed to cool naturally to room temperature, and then a 10 μm doctor blade was used to evenly coat the polydimethylsiloxane casting solution onto the base film to obtain a polydimethylsiloxane wet film. The wet film was then placed in a forced-air drying oven and continuously dried at 60°C for 12 hours to obtain a polydimethylsiloxane composite film. 1.5 g of oligomer polyethylene glycol diacrylate and 1.5 g of oligomer polyethylene glycol methacrylate were added to 27 g of ethanol and mixed thoroughly. Then, 0.15 g of 1-hydroxycyclohexylbenzophenone was added, and the mixture was further mixed thoroughly to obtain mixture B. Mixture B was placed in an ultraviolet (UV) irradiator, and nitrogen gas was introduced at a flow rate of 100 mL / min. Simultaneously, a 365 nm UV lamp was used for irradiation for 1.5 min. Afterward, the nitrogen gas valve and UV lamp were simultaneously closed, and the process was allowed to proceed for 0.5 min, counted as one intermittent irradiation / purging cycle. This intermittent irradiation / purging cycle was repeated four times to obtain a UV-crosslinked polyethylene oxide (PEO) casting solution. At this point, the viscosity of the casting solution reached 30 mPa·s. The polydimethylsiloxane (PDMS) composite membrane was placed in a UV ozone cleaner, and the instrument was preheated to 25°C. The UV ozone treatment device was then turned on, and the treatment lasted for 120 s to obtain a hydrophilic PMO composite membrane. 2 g of the UV-crosslinked PMO casting solution was diluted with 18 g of ethanol. Then, a 10 μm doctor blade was used to evenly coat the diluted casting solution onto the hydrophilic PMO composite membrane to obtain a UV-crosslinked PMO wet membrane. The wet film was then placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain an ultraviolet cross-linked polyethylene oxide multilayer composite film.

[0037] The UV crosslinked polyethylene oxide multilayer composite membrane prepared in this embodiment was tested and found to achieve efficient separation of CO2 / N2 (15 / 85, v / v%) system under the conditions of 25℃ and 0.2MPa. The CO2 permeation flux reached 3552 GPU, and the CO2 / N2 selectivity reached 15.2.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that the UV irradiation and nitrogen purging process of the polyethylene oxide casting solution was changed to a continuous process, while the other conditions remained the same as in Example 1. The results showed that after 2 minutes of treatment, some of the casting solution exhibited over-crosslinking, even though the viscosity of the casting solution had not yet reached its optimal level. Figure 1 As shown, the uneven viscosity of the casting solution prevents the successful coating of polyethylene oxide films.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that the UV irradiation and nitrogen purging process of the polyethylene oxide casting solution was changed to not introducing nitrogen gas, and only the UV lamp was intermittently switched on and off; all other conditions remained the same as in Example 1. Verification showed that this comparative example exhibited uneven cross-linking of the casting solution, making coating impossible.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A UV cross-linked polyethylene oxide multilayer composite film, characterized in that, It includes a base film, a polydimethylsiloxane intermediate layer covering the base film, and an ultraviolet cross-linked polyethylene oxide separation layer covering the intermediate layer.

2. The UV cross-linked polyethylene oxide multilayer composite film according to claim 1, characterized in that, The thickness of the UV cross-linked polyethylene oxide separation layer is 20-120 nm, and the thickness of the polydimethylsiloxane interlayer is 100-200 nm.

3. The method for preparing the UV crosslinked polyethylene oxide multilayer composite film according to claim 1 or 2, characterized in that, The steps are as follows: (1) Add polydimethylsiloxane precursor, tetraethyl orthosilicate and dibutyltin dilaurate to n-heptane, mix evenly to obtain mixture A, heat mixture A to carry out crosslinking reaction to obtain polydimethylsiloxane casting solution. (2) After cooling the polydimethylsiloxane casting solution, it is coated onto the base film, dried and thermally crosslinked to obtain a polydimethylsiloxane composite film. (3) Polyethylene glycol diacrylate, polyethylene glycol methacrylate and 1-hydroxycyclohexylphenyl ketone were added to ethanol and mixed evenly to obtain mixture B. Crosslinking reaction was carried out under intermittent nitrogen purging and ultraviolet irradiation to obtain ultraviolet crosslinked polyethylene oxide casting solution. (4) The polydimethylsiloxane composite membrane was treated in an ultraviolet ozone cleaner to obtain a hydrophilic membrane; (5) The UV cross-linked polyethylene oxide casting solution is coated onto the hydrophilic membrane and dried under vacuum to obtain the composite membrane.

4. The method for preparing the UV crosslinked polyethylene oxide multilayer composite film according to claim 3, characterized in that, In step (1), the relative molecular weight of the polydimethylsiloxane precursor is 50,000-100,000, the mass ratio of polydimethylsiloxane precursor: tetraethyl orthosilicate: dibutyltin dilaurate is (10-1):1:0.1, the mass fraction of polydimethylsiloxane in mixture A is 1-10%, the crosslinking reaction temperature is 50-80℃, and the crosslinking reaction time is 1-5h.

5. The method for preparing the UV crosslinked polyethylene oxide multilayer composite film according to claim 3, characterized in that, Step (2) Drying and thermal crosslinking temperature is 40-70℃, time is 6-18h.

6. The method for preparing the UV crosslinked polyethylene oxide multilayer composite film according to claim 3, characterized in that, In step (3), the relative molecular weight of polyethylene glycol diacrylate is 500-1000, the molecular weight of polyethylene glycol methacrylate is 500-1000, and the mass ratio of polyethylene glycol diacrylate to polyethylene glycol methacrylate is (0.1-9):1; the total mass fraction of polyethylene glycol diacrylate and polyethylene glycol methacrylate in mixture B is 5-20%, and the mass fraction of 1-hydroxycyclohexylphenyl ketone in mixture B is 0.2-2.5%; the intermittent nitrogen purging and ultraviolet irradiation treatment process is as follows: under the conditions of ultraviolet irradiation wavelength of 300-400nm and nitrogen purging flow rate of 20-100mL / min, the treatment is repeated for 1-2min, intermittently for 0.3-0.6min, and the total treatment time is 6-10min.

7. The method for preparing the UV crosslinked polyethylene oxide multilayer composite film according to claim 3, characterized in that, In step (4), the ultraviolet ozone treatment temperature is 25-30℃ and the treatment time is 60-180s.

8. The method for preparing the UV crosslinked polyethylene oxide multilayer composite film according to claim 3, characterized in that, In both steps (2) and (5), the coating is performed using a wire bar coater with a wire bar size of 10-60 μm. In step (5), the mass fraction of the UV crosslinking polyethylene oxide casting solution is 0.1-2%, the vacuum drying temperature is 30-40℃, and the drying time is 11-13h.

9. The application of the ultraviolet cross-linked polyethylene oxide multilayer composite membrane prepared by any one of claims 4-8 in carbon dioxide / nitrogen separation.

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