Covalently bridged polymethylhydrogenosiloxane and ethyl cellulose film and method for preparing the same

Abstract

This invention discloses a covalently bridged polymethylhydrosiloxane (PHMS) and ethyl cellulose (EC) membrane and its preparation method, relating to the field of gas separation membrane preparation. Using allyl glycidyl ether (AGE) as a reactive bridging agent, and polymethylhydrosiloxane (PHMS) and ethyl cellulose (EC) as matrix materials, the bridged polymer membrane material is prepared via hydrosilylation and epoxy ring-opening reactions, respectively. By constructing a topological microstructure of covalently interpenetrating rigid EC segments and flexible PHMS segments, a synergistic mass transfer channel combining rigid confined sieving and flexible high permeability is formed. The prepared blend membrane exhibits both good mechanical and separation properties, synergistically promoting the dissolution and diffusion mass transfer of CO2. Furthermore, this method is simple to prepare and uses inexpensive and readily available raw materials, providing a new approach for the design and preparation of high-performance gas separation membranes.

Description

Technical Field

[0001] This invention relates to the field of gas separation membrane preparation, and more particularly to a covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane and its preparation method. Background Technology

[0002] With rapid global economic development, the greenhouse effect caused by excessive carbon dioxide emissions has become a major challenge facing the world, leading to frequent extreme weather events that seriously threaten human sustainable development. Against this backdrop, developing efficient carbon capture, utilization, and storage (CFS) technologies is of urgent practical significance. Compared with traditional carbon capture technologies such as adsorption and cryogenic distillation, membrane separation processes do not require phase change or regeneration steps, offering advantages such as ease of operation, small footprint, and low energy consumption, and are considered a highly promising carbon capture technology.

[0003] Gas separation using polymer membranes primarily follows a "dissolution-diffusion" mechanism. Gas molecules first adsorb and dissolve on the upstream side of the membrane, then diffuse through the membrane driven by the concentration gradient, and finally desorb on the downstream side. An ideal membrane material should simultaneously promote the dissolution and diffusion of the target gas (such as CO2). Ethyl cellulose, as a cellulose derivative, has attracted widespread attention due to its wide availability, low cost, good biocompatibility, excellent film-forming properties, and good mechanical properties. The ether-oxygen bonds in its molecular chain can serve as sites for reversible interactions with CO2, helping to improve the solubility selectivity of CO2, thus demonstrating great potential in CO2 separation. However, the intrinsic structure of ethyl cellulose materials also brings significant limitations. Although some hydroxyl groups are ethylated, a strong hydrogen bond network still exists between ethyl cellulose chains. These strong intermolecular forces lead to tight packing of polymer segments, reduced free volume, and easy formation of crystalline regions. Gas molecules have difficulty penetrating the highly ordered crystalline regions, resulting in a tortuous gas diffusion path and severely limiting the permeation rate. Studies have shown that while ethyl cellulose membranes exhibit moderate selectivity for CO2 / N2, their CO2 permeability coefficient is typically low. Furthermore, ethyl cellulose membranes also face the "trade-off" effect common to polymer membranes, where permeability and selectivity are mutually exclusive, significantly limiting their industrial application potential.

[0004] To overcome these bottlenecks, researchers have explored various modification strategies. Among them, blending ethyl cellulose with porous inorganic fillers to prepare hybrid matrix membranes is one of the important ways to overcome the "trade-off" effect of polymer membranes. Although these studies have made significant progress, their industrial application still faces severe challenges. The core difficulties lie in the compatibility issues between multiphase materials and the fact that modification strategies involve complex synthetic steps (such as the synthesis and post-processing of MOFs) or the use of expensive and non-environmentally friendly solvents, which greatly increases production costs and environmental burden, weakens the price advantage of ethyl cellulose itself, and makes process scale-up extremely difficult. Summary of the Invention

[0005] This invention aims to propose a covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane and its preparation method. Using allyl glycidyl ether as a reactive bridging agent, a topological microstructure of covalently interpenetrating rigid segments of ethyl cellulose and flexible segments of polymethylhydrosiloxane is constructed, forming a synergistic mass transfer channel that combines rigid confined sieving with flexible high permeability.

[0006] To achieve the above objectives, the technical solution adopted in this invention is a covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane and its preparation method, the steps of which are as follows:

[0007] (1) Grafting modification of polymethylhydrosiloxane: Add appropriate amounts of polymethylhydrosiloxane and allyl glycidyl ether to isopropanol solvent respectively, add appropriate amount of catalyst and mix thoroughly to obtain allyl glycidyl ether modified polymethylhydrosiloxane (PHMS-AGE).

[0008] (2) Grafting modification of ethyl cellulose: Add an appropriate amount of ethyl cellulose to the isopropanol solvent and mix thoroughly to dissolve. Then add an appropriate amount of allyl glycidyl ether modified polymethyl hydrosiloxane isopropanol solution from (1) to the ethyl cellulose isopropanol solution and mix thoroughly to obtain the casting solution.

[0009] (3) Polymer membrane preparation: The casting solution obtained in (2) is subjected to ultrasonic degassing and static treatment, and then placed in a mold. It is fully reacted and the solvent is removed under appropriate temperature conditions. It is then placed in a vacuum oven to dry, and an allyl glycidyl ether covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane is obtained.

[0010] Further, in step (1), the mass ratio of polymethylhydrosiloxane, allyl glycidyl ether, and isopropanol is 1:(0.5-5):(10-30), the amount of Karstedt catalyst added is 0.0039-0.0294 g, the mixing temperature is 50-80 ℃, and the mixing time is 1-6 h. In step (2), the mass ratio of ethyl cellulose to isopropanol is 1:(10-40), the mixing temperature is 20-80 ℃, and the mixing time is 0.5-6 h. The mass ratio of grafted modified polymethylhydrosiloxane solution to ethyl cellulose solution is 1:(0.857-7.752). In step (3), the ultrasonic degassing time of the casting solution is 0.1-0.5 h, the standing time is 0.1-0.5 h, the reaction temperature in the glass mold is 25 ℃, the reaction time is 24-36 h, and the solvent removal time in the vacuum oven at room temperature is 1-24 h.

[0011] Furthermore, the isopropanol mentioned in steps (1) and (2) can be replaced by one or more solvent mixtures in the isobutanol solvent.

[0012] Furthermore, the hydrosilylation reaction described in step (1) is prone to side reactions, and the reaction needs to be carried out under a nitrogen atmosphere to reduce the occurrence of side reactions.

[0013] Furthermore, the gas separation membrane described in step (3) achieves a separation performance comparable to CO2 permeation performance (P). CO2 The range is 100-800 Barrer, and the CO2 / N2 selectivity is 18-35.

[0014] The purpose of this invention is to develop a covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane and its preparation method. This method uses allyl glycidyl ether as a reactive bridging agent to construct a topological microstructure of covalently interpenetrating rigid segments of ethyl cellulose and flexible segments of polymethylhydrosiloxane, forming a synergistic mass transfer channel that combines rigid confined sieving with flexible high permeability. By synergistically disrupting the hydrogen bond network of ethyl cellulose through "hydrogen bond dilution" and "steric hindrance," crystallization is inhibited, free volume is significantly increased, and CO2 dissolution and diffusion mass transfer are synergistically promoted, successfully breaking the "trade-off" effect. The bridging effect of allyl glycidyl ether not only aims to fundamentally solve the compatibility difference problem between nonpolar polymethylhydrosiloxane and polar ethyl cellulose, enabling good blending preparation of gas separation membranes in an environmentally friendly isopropanol solvent system, but also enhances the stability and mechanical properties of the membrane by forming a strong covalent bond network. Attached Figure Description

[0015] Figure 1 A schematic diagram of the reaction route of allyl glycidyl ether bridging polymethylhydrosiloxane and ethyl cellulose;

[0016] Figure 2SEM and EDS images of the gas separation membranes prepared in Examples 1-3 and Comparative Example 1;

[0017] Figure 3 The following are FTIR images of allyl glycidyl ether modified polymethylhydrosiloxane and ethyl cellulose in Examples 1-3 and Comparative Example 1;

[0018] Figure 4 The mechanical properties of the gas separation membranes prepared in Examples 1-3 and Comparative Example 1 are shown in the diagram. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] Example 1:

[0021] (1) 2.5 g of polymethylhydrosiloxane, 2.5 g of allyl glycidyl ether, and 45 g of isobutanol were thoroughly mixed to form a clear and transparent liquid. This mixture was then added to a three-necked flask, and 0.0492 g of Karstedt catalyst was added while stirring under a nitrogen atmosphere. The mixture was stirred at 70 °C and 300 rpm / min for 4 h until no more bubbles appeared, yielding a 10 wt.% PHMS-AGE isobutanol solution.

[0022] (2) Weigh 48.5 g of isobutanol and add it to a round-bottom flask. Stir and heat to 70 °C, then add 1.5 g of ethyl cellulose to the round-bottom flask. Under reflux cooling with a condenser, stir at 75 °C and 300 rpm / min for 4 h to completely dissolve it, and obtain a 3 wt.% ethyl cellulose isobutanol solution. Weigh 4.667 g of PHMS-AGE solution and 6.667 g of ethyl cellulose solution, mix the two solutions evenly, stir at 400 rpm / min for 0.4 h, disperse, sonicate for 0.25 h, and let stand for 0.25 h to obtain the casting solution for the blended membrane.

[0023] (3) Pour the casting solution into a clean glass dish, place it in an oven at 25 °C for 36 h, remove it from the glass dish, place it in a vacuum oven to remove the solvent for another 12 h, and obtain an ethyl cellulose blend membrane containing 70 wt.% PHMS-AGE.

[0024] like Figure 1As shown, PHMS-AGE is synthesized by hydrosilylation reaction of polymethylhydrosiloxane and allyl glycidyl ether via silane-hydrogen bonds and carbon-carbon double bonds, thereby increasing the polarity of polymethylhydrosiloxane. This, in turn, improves the compatibility of the matrix material polymethylhydrosiloxane with ethyl cellulose, and a homogeneous membrane is obtained through ring-opening addition reactions of epoxy groups and hydroxyl groups and solution casting.

[0025] like Figure 2 As shown, compared with the SEM image of the membrane surface of Comparative Example 1a, the surface of the PHMS-AGE and ethyl cellulose blend membrane did not show large-sized pores, cracks or obvious two-phase protrusions caused by severe phase separation. In the cross-sectional EDS image of Example 1b, the Si element is uniformly dispersed in the ethyl cellulose matrix, proving that PHMS-AGE and ethyl cellulose are well miscible and uniformly distributed.

[0026] like Figure 3 As shown, compared to the FTIR spectrum of Comparative Example 1, the FTIR spectrum of Example 1 at 1158 cm⁻¹... -1 The presence of Si-CH3 peaks and a significantly weakened -OH peak further confirms that the modification reaction reduced the number of hydrophilic groups. PHMS-AGE and ethyl cellulose are well miscible and evenly distributed.

[0027] like Figure 4 As shown in the mechanical property diagram of Example 1 compared to Comparative Example 1, the tensile strength of the PHMS-AGE and ethyl cellulose blend film decreased while the tensile elongation increased to 51.47%. This indicates that after the flexible polymethylhydrosiloxane segments are covalently bridged into the rigid network of ethyl cellulose, they effectively disrupt its brittle hydrogen bond network ("hydrogen bond dilution effect"), providing space for the movement of molecular chains and improving the mechanical properties of the film.

[0028] The CO2 permeation performance (P0.05) of the above-mentioned blend membrane was tested under conditions of 0.8 MPa and 25 ℃. CO2 The value was 703.78 Barrer, and the CO2 / N2 selectivity was 25.11.

[0029] Example 2:

[0030] (1) 2.0 g of polymethylhydrosiloxane, 2.0 g of allyl glycidyl ether, and 36 g of isopropanol were thoroughly mixed. After mixing, a clear and transparent liquid was obtained. The mixture was added to a three-necked flask and 0.03936 g of Karstedt catalyst was added while stirring under a nitrogen atmosphere. The mixture was stirred at 70 °C and 300 rpm / min for 4 h until no more bubbles appeared, yielding a 10 wt.% PHMS-AGE isopropanol solution.

[0031] (2) Weigh 47.5 g of isopropanol and add it to a round-bottom flask. Stir and heat to 70 °C. Then add 2.5 g of ethyl cellulose to the round-bottom flask. Under reflux cooling with a condenser, stir at 70 °C and 300 rpm / min for 3 h to completely dissolve the ethyl cellulose and obtain a 5 wt.% ethyl cellulose isopropanol solution. Weigh 2 g of PHMS-AGE solution and 4 g of ethyl cellulose solution. Mix the two solutions evenly and disperse them. Stir at 400 rpm / min for 0.4 h. After dispersion, sonicate for 0.25 h and let stand for 0.25 h to obtain the casting solution for the blended membrane.

[0032] (3) Pour the casting solution into a glass dish, place it in an oven at 25 °C for 24 h, remove it from the glass dish, place it in a vacuum oven and continue to remove the solvent for 12 h to obtain an ethyl cellulose blend membrane containing 50 wt.% PHMS-AGE.

[0033] like Figure 2 As shown, compared with the SEM image of the membrane surface of Comparative Example 1a, the surface of the PHMS-AGE and ethyl cellulose blend membrane in Example 2a did not show large-sized pores, cracks or obvious two-phase protrusions caused by severe phase separation. In the cross-sectional EDS image of Example 2b, the Si element is uniformly dispersed in the ethyl cellulose matrix, proving that PHMS-AGE and ethyl cellulose are well miscible and uniformly distributed.

[0034] like Figure 3 As shown, compared to the FTIR spectrum of Comparative Example 1, Example 2's FTIR spectrum at 1158 cm⁻¹... -1 The presence of Si-CH3 peaks and a significantly weakened -OH peak further confirms that the modification reaction reduced the number of hydrophilic groups, and that PHMS-AGE and ethyl cellulose are well miscible and evenly distributed.

[0035] like Figure 4 As shown, Example 2 showed a decrease in tensile strength but an increase in tensile elongation to 50.23% compared to Comparative Example 1. This indicates that after the flexible polymethylhydrosiloxane segments were covalently bridged into the rigid ethyl cellulose network, they effectively disrupted the brittle hydrogen bond network (“hydrogen bond dilution effect”), providing space for the movement of molecular chains and improving the mechanical properties of the membrane.

[0036] The CO2 permeation performance (P0.05) of the above-mentioned blend membrane was tested under conditions of 0.8 MPa and 25 ℃. CO2 The value was 394.78 Barrer, and the CO2 / N2 selectivity was 25.74.

[0037] Example 3:

[0038] (1) 2.5 g of polymethylhydrosiloxane, 2.5 g of allyl glycidyl ether, and 45 g of isopropanol were thoroughly mixed. After mixing, a clear and transparent liquid was obtained. The mixture was added to a three-necked flask and 0.04952 g of Karstedt catalyst was added while stirring under a nitrogen atmosphere. The mixture was stirred at 70 °C and 300 rpm / min for 4 h until no more bubbles appeared, yielding a 10 wt.% PHMS-AGE isopropanol solution.

[0039] (2) Weigh 47.5 g of isopropanol and add it to a round-bottom flask. Stir and heat to 70 °C, then add 2.5 g of ethyl cellulose to the round-bottom flask. Under reflux cooling with a condenser, stir at 70 °C and 300 rpm / min for 3 h to completely dissolve the ethyl cellulose and obtain a 5 wt.% ethyl cellulose isopropanol solution. Weigh 0.8571 g of PHMS-AGE solution and 4 g of ethyl cellulose solution. Mix the two solutions evenly and disperse them. Stir at 400 rpm / min for 0.4 h, sonicate for 0.25 h after dispersion, and let stand for 0.25 h to obtain the casting solution for the blended membrane.

[0040] (3) Pour the casting solution into a clean glass dish, place it in an oven at 25 °C for 24 h, remove it from the glass dish, place it in a vacuum oven to remove the solvent for another 12 h, and obtain an ethyl cellulose blend membrane containing 30 wt.% PHMS-AGE.

[0041] like Figure 2 As shown, compared with the SEM image of the membrane surface of Comparative Example 1a, the surface of the PHMS-AGE and ethyl cellulose blend membrane of Example 3a did not show large-sized pores, cracks or obvious two-phase protrusions caused by severe phase separation; the cross-sectional EDS image of Example 3b shows that the Si element is uniformly dispersed in ethyl cellulose, proving that PHMS-AGE and ethyl cellulose are well miscible and uniformly distributed.

[0042] like Figure 3 As shown, compared to the FTIR spectrum of Comparative Example 1, Example 3 has a higher FTIR spectrum at 1158 cm⁻¹. -1 The presence of Si-CH3 peaks and a significantly weakened -OH peak further confirms that the modification reaction reduced the number of hydrophilic groups, and that PHMS-AGE and ethyl cellulose are well miscible and evenly distributed.

[0043] like Figure 4 As shown, Example 3 exhibits a lower tensile strength compared to Comparative Example 1, but its tensile elongation increases to 35.21%. This indicates that the flexible polymethylhydrosiloxane segments, after being covalently bridged into the rigid ethyl cellulose network, effectively disrupt its brittle hydrogen bond network (“hydrogen bond dilution effect”), providing space for molecular chain movement and improving the mechanical properties of the membrane.

[0044] The CO2 permeation performance (P0.05) of the above-mentioned blend membrane was tested under conditions of 0.8 MPa and 25 ℃. CO2 The value was 171.46 Barrer, and the CO2 / N2 selectivity was 22.69.

[0045] Comparative Example 1:

[0046] (1) Weigh 47.5 g of isopropanol and add it to a round-bottom flask. Stir and heat to 70 °C, then add 2.5 g of ethyl cellulose to the round-bottom flask. Under reflux cooling conditions, stir at 70 °C and 300 rpm / min for 3 h to completely dissolve the polymer matrix solution.

[0047] (2) Take 10 g of ethyl cellulose solution and stir at 400 rpm / min for 0.4 h. After dispersion, sonicate for 0.25 h and let stand for 0.25 h to obtain casting solution.

[0048] (3) Pour the casting solution into a clean glass dish, place it in an oven at 25 °C for 24 h, remove it from the glass dish, place it in a vacuum oven to remove the solvent for another 12 h, and obtain an ethyl cellulose membrane.

[0049] like Figure 2 As shown, there is no significant difference in surface morphology between Comparative Example 1a and Examples 1a-3a. The cross-sectional view in Comparative Example 1b is uniformly black, indicating that the ethyl cellulose membrane does not contain Si, providing a direct contrast with the Si-containing matrix material, polymethylhydrosiloxane, and ethyl cellulose blend membrane.

[0050] like Figure 3 As shown, Comparative Example 1 is at 3480 cm. -1 The presence of a characteristic -OH peak at 1158 cm⁻¹ reflects its strong hydrophilicity; while at 1158 cm⁻¹... -1 The absence of Si-CH3 characteristic peaks indicates that PHMS-AGE was not introduced, resulting in a fundamental structural difference from Examples 1-3.

[0051] like Figure 4 As shown, the ethyl cellulose membrane in Comparative Example 1 exhibited the highest tensile strength but the lowest elongation at 4.49%. In contrast, the blend membrane prepared by covalently bridging polymethylhydrosiloxane and ethyl cellulose with allyl glycidyl ether significantly improved the balance between rigidity and toughness: Elongation of Example 1 was 51.47%, Elongation of Example 2 was 50.23%, Elongation of Example 3 was 35.21%, and Elongation of Comparative Example 1 was 4.49%.

[0052] The CO2 permeation performance (P0.05) of the above-mentioned blend membrane was tested under conditions of 0.8 MPa and 25 ℃. CO2 The value was 105.25 Barrer, and the CO2 / N2 selectivity was 22.29.

Claims

1. A method for preparing a covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane, characterized in that, Includes the following steps: (1) Grafting modification of polymethylhydrosiloxane: Polymethylhydrosiloxane and allyl glycidyl ether were added to the first solvent respectively, and a hydrosilylation reaction was carried out under the action of a catalyst to obtain an allyl glycidyl ether modified polymethylhydrosiloxane solution. (2) Preparation of casting solution: Ethyl cellulose is mixed and dissolved with a second solvent to obtain an ethyl cellulose solution; the allyl glycidyl ether modified polymethyl hydrosiloxane solution obtained in step (1) is mixed with the ethyl cellulose solution and stirred evenly to obtain a casting solution; (3) Polymer membrane preparation: After degassing and standing, the casting solution obtained in (2) is placed in a clean container, reacted and heated to remove the solvent to form a membrane, and then placed in a vacuum oven to dry, thus obtaining an allyl glycidyl ether covalently bridged polymethyl hydrosiloxane and ethyl cellulose membrane. In step (1), the first solvent is a mixture of one or more solvents, namely isopropanol or isobutanol; in step (2), the second solvent is a mixture of one or more solvents, namely isopropanol or isobutanol.

2. The method for preparing a covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane according to claim 1, characterized in that, In step (1), the mass ratio of polymethylhydrosiloxane, allyl glycidyl ether, and the first solvent is 1:(0.5-5):(10-30). The catalyst is a Karstedt catalyst, and its addition amount is 0.0039-0.0294 g per gram of polymethylhydrosiloxane. The hydrosilylation reaction is carried out at 50-80 °C for 1-6 h. In step (2), the mass ratio of ethyl cellulose to the second solvent is 1:(10-40), the dissolution is carried out at 20-80 °C, and the dissolution time is 0.5-6 h; the mass ratio of the allyl glycidyl ether modified polymethylhydrosiloxane solution to the ethyl cellulose solution is 1:(0.857-7.752). In step (3), the degassing is performed by ultrasonic treatment for 0.1-0.5 h; the settling time is 0.1-0.5 h.

3. The method for preparing a covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane according to claim 1 or 2, characterized in that, In step (1), the hydrosilylation reaction is carried out under a nitrogen atmosphere.

4. A covalently bridged polymethylhydrosiloxane and ethyl cellulose membrane, characterized in that, It is prepared by the preparation method described in any one of claims 1-3.

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