Ethane guest response gating film as well as preparation method and application thereof

Abstract

The invention discloses an ethane guest response gating film as well as a preparation method and application thereof. According to the ethane guest response gating membrane, a specific membrane structure is designed, and ethane is used as a guest molecule to trigger a gating effect, so that precise separation of ethylene and ethane is realized. A series of S-COF membranes with different numbers of hydroxyl groups are grown on the upper side of AAO in situ to prepare the composite membrane. The membrane can selectively allow ethane to penetrate through in ethylene and ethane mixed gas, effectively intercept ethylene, and is high in separation efficiency and good in stability. Besides, the invention further relates to application of the ethane guest response gating membrane in ethylene and ethane separation, the C2H6 / C2H4 selectivity of the S-COF3 membrane reaches 18.2, and the wide prospect of the S-COF3 membrane in the field of industrial separation is shown. The ethane guest response gating membrane provides a new technical path for efficient separation of ethylene and ethane.

Description

Technical Field

[0001] The present invention relates to an ethane guest responsive gated membrane, a preparation method thereof and application in ethylene-ethane separation, and belongs to the technical field of membrane separation. Background Art

[0002] As a core raw material in the petrochemical industry, ethylene is widely used in the synthesis of polypropylene, plastics, and high-value-added chemicals. Its purity directly affects the performance of downstream products. However, small amounts of ethane are often mixed into the ethylene production process. Even trace amounts of residues can seriously hinder the polymerization reaction of ethylene. Therefore, there is an urgent need to develop efficient separation technologies to obtain high-purity ethylene. Currently, the industry mainly relies on low-temperature and high-pressure distillation. However, because ethylene and ethane have similar boiling points and highly similar molecular dynamic diameters, multi-stage compression and condensation are required, and energy consumption accounts for 0.3% of the world's total industrial energy consumption, and the economic and environmental costs remain high. Membrane separation technology is considered a potential alternative due to its advantages such as low energy consumption and simple operation. Its core lies in the use of material pore size or adsorption differences to achieve molecular screening. However, traditional polymer membranes (such as polyimide and polysulfone) are limited by the "permeability-selectivity trade-off effect", making it difficult to achieve both high flux and high retention rate (selectivity is often less than 4). Carbon molecular sieve membranes have a microporous structure regulated by high-temperature carbonization, but their uneven pore size distribution leads to fluctuations in separation efficiency (selectivity <10), and the harsh carbonization conditions limit large-scale preparation.

[0003] The dynamic separation mechanism of flexible porous materials offers new insights into intelligent separation. Inspired by natural membrane systems, pore conformational changes can be triggered by stimuli such as light and pressure, bypassing the need for precise pore size control through the "gating effect." However, existing research has focused primarily on highly polar molecules (such as C2H2 and CO2), while the response mechanism for inert ethane is scarce. Furthermore, dynamic separation performance relies heavily on precise pore size matching, making it difficult to adapt to the complex and variable mixing ratios used in industry. Covalent organic framework (COF) membranes exhibit high stability due to their rigid backbones connected by strong covalent bonds and their functionalizable pores. Although their potential for gas separation is widely recognized, their application still faces significant challenges: existing research focuses on static pore size screening and lacks exploration of dynamic gating effects. Furthermore, the synthesis and regulation mechanisms of flexible COF membranes are immature, making it difficult to precisely balance framework flexibility and rigidity through molecular design. Crucially, there are currently no reports on the manipulation of COF membrane flexibility through functional groups to achieve ethane-specific induced separation, and there is a lack of systematic research on the correlation between flexibility and separation performance. Summary of the Invention

[0004] Objectives of the invention: The first objective of the present invention is to provide an ethane guest-responsive gated covalent organic framework membrane based on a covalent organic framework. The second objective of the present invention is to provide a method for preparing the ethane guest-responsive gated covalent organic framework membrane, which is simple to operate and easy to implement. The third objective of the present invention is to provide the use of the ethane guest-responsive gated covalent organic framework membrane in ethylene-ethane separation. The membrane can be used to separate ethylene-ethane and maintains excellent separation selectivity over a wide range of complex ethylene-ethane mixing ratios.

[0005] Technical solution: The ethane guest-responsive gating membrane described in the present invention includes a gated covalent organic framework (S-COF) membrane with functional groups and a macroporous anodic aluminum oxide membrane. The S-COF membrane material with functional groups is adjusted in flexibility by introducing functionalized functional groups and forming intramolecular hydrogen bonds, thereby realizing a gated separation mechanism under the induction of ethane.

[0006] Furthermore, the functional groups in the S-COF membrane with functional groups are hydroxyl groups. The macroporous anodic aluminum oxide membrane is an aminated anodic aluminum oxide membrane. The layer thickness of the S-COF membrane with functional groups is 180 to 280 nm, preferably 240 nm. The pore size of the S-COF membrane with functional groups is 0.3 to 0.4 nm, preferably 0.37 nm. The pore diameter of the macroporous anodic aluminum oxide membrane material is 50 to 80 nm, preferably 70 nm.

[0007] The method for preparing the ethane guest-responsive gated membrane of the present invention comprises the following steps:

[0008] (1) placing an amine-functionalized anodic aluminum oxide at the bottom of a reaction bottle, adding a 4,4'-biphenyldicarboxaldehyde derivative solution, adding a catalyst, and reacting with a Schiff base to obtain a CHO-OH / AAO membrane;

[0009] (2) adding the CHO-OH / AAO membrane to a tetrakis(4-aminophenyl)methane solution and adding a catalyst, and then reacting with a Schiff base to obtain a S-COF / AAO membrane;

[0010] (3) The S-COF / AAO membrane is taken out, washed with a solvent, and vacuum dried to obtain an ethane guest-responsive gated membrane.

[0011] Furthermore, in step (1), the 4,4'-biphenyldicarboxaldehyde derivative solution is a 5-(4-formylphenyl)-2-hydroxybenzaldehyde solution or a 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde solution, the 5-(4-formylphenyl)-2-hydroxybenzaldehyde solution is prepared using a solvent 1,4-dioxane solution, and the concentration of the 5-(4-formylphenyl)-2-hydroxybenzaldehyde solution is 0.08 to 0.10 mmol / mL, preferably 0.095 mmol / mL. In step (2), the tetrakis(4-aminophenyl)methane solution is prepared using a solvent 1,4-dioxane solution, and the concentration of the tetrakis(4-aminophenyl)methane solution is 0.04 to 0.06 mmol / mL, preferably 0.053 mmol / mL. In steps (1) and (2), the catalyst is acetic acid, and the temperature of the Schiff base reaction is 50 to 70°C, preferably 65°C. In step (1), the Schiff base reaction time is 0.5 to 2 hours, preferably 1 hour. In step (2), the Schiff base reaction time is 3 to 7 days, preferably 6 days. In step (3), the solvent is tetrahydrofuran, the vacuum drying temperature is 40 to 65° C., preferably 50° C., and the vacuum drying time is 1 to 4 days, preferably 3 days.

[0012] The invention relates to the application of the ethane guest responsive gated membrane in ethylene-ethane separation.

[0013] Furthermore, during application, different numbers of hydroxyl functional groups are introduced to form intramolecular hydrogen bonds to adjust its flexibility, and the separation of ethylene and ethane is achieved through the gating effect.

[0014] Furthermore, during the application process, a mixed gas containing ethylene and ethane is passed through the ethane guest-responsive gated membrane of the present invention, and the specific interaction between ethane and the membrane material is utilized to achieve ethane-induced gated separation, thereby obtaining high-purity ethylene.

[0015] Furthermore, the pressure ratio of ethane to ethane is (0.1-0.8):1.

[0016] The present invention first adopts an in-situ growth method to grow S-COF membranes on the upper side of AAO. The ethane guest responsive gating membrane uses ethane as a guest molecule to trigger the gating effect by designing a specific membrane structure, thereby achieving precise separation of ethylene and ethane. It is prepared by in-situ growing a series of S-COF membranes with different numbers of hydroxyl groups on the upper side of AAO. In the ethylene and ethane mixed gas, the membrane can selectively allow ethane to pass through, while effectively intercepting ethylene, with high separation efficiency and good stability. In addition, the present invention also relates to the application of the ethane guest responsive gating membrane in the separation of ethylene and ethane, with a C2H6 / C2H4 selectivity of up to 18.2, demonstrating its broad prospects in the field of industrial separation. The ethane guest responsive gating membrane of the present invention provides a new technical path for the efficient separation of ethylene and ethane.

[0017] The ethane guest-responsive gated membrane designed by the present invention achieves high selectivity. Compared with traditional porous membranes, it can achieve precise control of the permeability of gas molecules. At the same time, combined with guest-specific adsorption and flexible design of the internal structure, a unique functional separation membrane can be created to achieve gas separation without precise control of the pore size. In addition, by introducing functional groups to adjust the flexibility of the material, the ethane guest-responsive gated membrane has a high degree of flexibility. Both ethane and ethylene can open the gate, and the separation selectivity is low. The hydroxyl groups of the S-COF membrane can form intramolecular hydrogen bonds, and the structure becomes rigid, which can preferentially adsorb ethane and open pores for ethane, forming a gated channel that allows ethane to pass through but not ethylene, achieving a highly selective separation effect. And it still maintains excellent separation selectivity under a very wide and complex ethylene-ethane mixing ratio.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) The ethane guest responsive gated membrane of the present invention is in situ grown, including an upper layer of in situ grown S-COF membrane and a lower layer of an anodic aluminum oxide membrane material (AAO) with a macroporous structure. The preparation method is simple and convenient, and the reaction conditions are easy to achieve.

[0020] (2) The application of the ethane guest-responsive gated covalent organic framework membrane of the present invention in ethane and ethylene separation has obvious advantages:

[0021] First, the ethane guest-responsive gated membrane of the present invention demonstrates exceptional separation efficiency in the ethane-ethylene separation process. Its unique gating mechanism accurately identifies and preferentially transmits ethane molecules while effectively blocking ethylene molecules, thereby achieving highly efficient ethane-ethylene separation. This not only improves the purity of the separation process but also significantly reduces energy consumption and costs.

[0022] Secondly, the ethane guest-responsive gated membrane of the present invention exhibits exceptional stability and durability, maintaining excellent separation performance over extended periods of use. Its covalent organic framework structure imparts excellent chemical and thermal stability to the membrane material, ensuring sustained, efficient, and stable ethane-ethylene separation.

[0023] At the same time, the membrane material preparation process of the present invention is simple and easy to mass produce and apply. By optimizing the synthesis conditions and membrane preparation process, a membrane material with excellent separation performance can be obtained, providing reliable technical support for ethane and ethylene separation.

[0024] Finally, the ethane guest-responsive gated membrane of the present invention exhibits excellent environmental performance. During the ethane-ethylene separation process, no harmful substances or pollutants are generated, making it environmentally friendly. Furthermore, the recyclability and reusability of the membrane material reduce waste generation, aligning with the concept of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation process of the ethane guest responsive gated covalent organic framework membrane prepared in Example 1;

[0026] Figure 2 Schematic diagram of the preparation process of the AAO membrane prepared in Example 1;

[0027] Figure 3 This is a scanning electron micrograph of the amine-functionalized AAO membrane prepared in Example 1;

[0028] Figure 4 Scanning electron micrographs of different ethane guest-responsive gated covalent organic framework films prepared in Example 1;

[0029] Figure 5 Schematic diagram of the ethane ethylene membrane separation device in Example 2;

[0030] Figure 6 This is the selectivity diagram of ethylene and ethane separation of the AAO membrane prepared in Example 1 at different ethane partial pressures;

[0031] Figure 7 Graph showing the selectivity of ethylene-ethane separation for ethane guest-responsive gated covalent organic framework membranes with different degrees of flexibility prepared in Example 1 at different ethane partial pressures;

[0032] Figure 8 This is a comparison chart of the selectivity of the ethane guest responsive gating membrane with different degrees of flexibility prepared in Example 1 and the existing membrane material in Comparative Example 1. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0034] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0035] Example 1 Preparation of Ethane Guest-Responsive Gated Covalent Organic Framework Film

[0036] (1) Preparation of anodic aluminum oxide (AAO) film:

[0037] First, the aluminum foil needs to be ultrasonically cleaned with anhydrous ethanol and 1 mol / L KOH solution for 15 minutes respectively, and then deionized water is used to thoroughly rinse off the residual liquid on the surface of the aluminum foil. The initial anodizing process uses 0.3 mol / L oxalic acid as the electrolyte and lasts for 30 minutes at a constant voltage of 40V and 25°C. Next, the oxide layer formed on the surface of the aluminum foil after the initial anodizing is cleaned at 60°C for 40 minutes using an acidic solution mixed with 5wt% phosphoric acid and 1.5wt% oxalic acid. After that, a second anodizing is carried out for 6 hours, and the other conditions remain the same as the initial anodizing. Subsequently, a saturated SnCl2 solution is used to remove the aluminum substrate. Next, the AAO membrane is treated with a 5wt% phosphoric acid solution for 60 minutes to remove the barrier layer on the top of the anodized aluminum membrane. The entire preparation process is as follows. Figure 2 shown.

[0038] Next, the prepared AAO membrane was immersed in a 30% hydrogen peroxide solution and boiled at a constant temperature of 95°C for 30 minutes to modify the channel surface with abundant hydroxyl groups. 2mL APTES (1800μL ethanol and 200μL APTES) was placed on the AAO membrane at 4°C overnight, and then washed three times with deionized water to modify the channel surface with abundant amino groups. Finally, the amino-functionalized AAO membrane was soaked in deionized water overnight and dried. By adjusting the voltage during the anodization process, the pore size of the anodized aluminum oxide membrane nanochannel can be effectively controlled. Scanning electron microscopy analysis of the amino-functionalized AAO membrane showed that its pore size was 70nm and the pores were evenly distributed, as shown in Figure 2. Figure 3 shown.

[0039] (2) Preparation of ethane guest-responsive gated membranes with different degrees of flexibility:

[0040] The amino-functionalized anodic aluminum oxide film prepared in step (1) was placed at the bottom of a reaction bottle, and 0.5 mL of 0.095 mmol / mL 4,4'-biphenyldicarboxaldehyde solution (CAS No.: 66-98-8), 5-(4-formylphenyl)-2-hydroxybenzaldehyde solution (CAS No.: 1261930-12-4) and 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde solution (CAS No.: 14969-32-5) were added to the bottle respectively, and 95 uL of 0.3 mol / L acetic acid solution was added as a catalyst. After Schiff base reaction (65 ° C for 1 h), CHO membrane, CHO-OH1 membrane and CHO-OH2 membrane were obtained respectively; then 1.0 mL of 0.053 mmol / mL tetrakis(4-aminophenyl)methane solution and 0.46 mL of 0.3 mol / L acetic acid solution was used as catalyst and Schiff base reaction (65℃ for 7 days) was performed to obtain S-COF1 membrane, S-COF2 membrane and S-COF3 membrane respectively;

[0041] The above-mentioned S-COF1 film, S-COF2 film and S-COF3 film were taken out respectively, washed with tetrahydrofuran solvent, and vacuum dried at 50°C for 3 days to obtain ethane guest responsive gated films with different degrees of flexibility, which were respectively recorded as S-COF1 film, S-COF2 film and S-COF3 film. The preparation process is as follows Figure 1 shown.

[0042] The ethane guest responsive gate films S-COF1, S-COF2 and S-COF3 prepared in this example with different degrees of flexibility were analyzed by scanning electron microscopy. Figure 4 shown. Figure 4 The scanning electron microscope images of ethane guest-responsive gating films with different degrees of flexibility prepared in Example 1, wherein (A) is the plane and cross-sectional images of the S-COF1 film. (B) is the plane and cross-sectional images of the S-COF2 film. (C) is the plane and cross-sectional images of the S-COF3 film. Figure 4 It can be seen that all three films have dense and defect-free S-COF films, and the thickness of the S-COF films is about 200 nm.

[0043] Example 2 Application of Ethane Guest Responsive Gated Membrane in Ethane and Ethylene Gas Separation

[0044] The AAO membrane prepared in Example 1 and ethane guest response gate membranes with different degrees of flexibility are used to separate ethane and ethylene gases. The gas separation device is as follows: Figure 5As shown, a homemade membrane separation device was connected by a gas pipe, and argon was introduced as a purge gas at a flow rate of 10 mL / min. Ethylene and ethane mixed gas was introduced, and the total volume flow rate was maintained at 60 mL / min (ethylene / ethane was 54 / 6 mL / min). It can be divided into a feed gas side and a permeate gas side, and the permeate gas was transported to an online gas chromatograph (Panna). The results are shown in Figure 6-7 shown.

[0045] Figure 6 This is the ethane and ethylene separation selectivity diagram of the AAO membrane prepared in Example 1. Figure 6 visible. Figure 7 The ethylene-ethane separation selectivity diagram of the ethane guest-responsive gated membrane with different degrees of flexibility prepared in Example 1 at different ethane partial pressures is shown in FIG. Figure 7 It can be seen that at 25°C, the S-COF2 membrane modified with one hydroxyl group and the S-COF3 membrane modified with two hydroxyl groups have better separation selectivity than the S-COF1 membrane without hydroxyl groups, especially the ethane-ethylene separation selectivity of the S-COF3 membrane reaches 18.2.

[0046] Comparative Example 1

[0047] We synthesized the existing publicly reported membranes with similar structures to ours, namely ZIF-8 (see R. Wei, X. Liu, Z. Zhou, C. Chen, Y. Yuan, Z. Li, X. Li, X. Dong, D. Lu, Y. Han, Z. Lai, Sci. Adv. 2022, 8, eabm6741.), Co-gallate (see Y. Sun, T. Ji, Y. Gao, J. Yan, Y. He, G. Xu, F. Yan, Q. Bian, Y. Liu, ACS Mater. Lett. 2023, 5, 558.), Cu@ORI-MIL -M (see Y.Sun, S.Hu, J.Yan, T.Ji, L.Liu, M.Wu, X.Guo, Y.Liu, Angew.Chem.Int.Ed.2023,62,e202311336.) and Ag@GO-34 (see L.Cheng, Y.Guo, Q.Liu, G.Liu, R.Li, X.Chen, H.Zeng, G.Liu, W.Jin, Adv.Mater.2022,34,2206349.) The ethane-ethylene selectivity of Ag@GO-34 was compared with the performance of different flexible ethane guest-responsive gated membranes prepared in Example 1. The results are shown in FIG. Figure 8 and as shown in Table 1. Figure 8 This is a comparison chart of the selectivity of ethane guest responsive gating membranes with different degrees of flexibility prepared in Example 1 and the existing membrane materials in Comparative Example 1. Figure 8The comparison results show that the ethane guest responsive gated covalent organic framework membrane prepared in Example 1 has much higher ethane and ethylene separation performance than other membranes, especially after being modified with hydroxyl groups, because it can achieve a voiding effect, thereby further improving its separation selectivity.

[0048] Table 1 Comparison of selectivity of ethane guest responsive gated membranes with different degrees of flexibility prepared in Example 1 and existing membrane materials in Comparative Example 1

[0049]

Claims

1. An ethane guest-responsive gating membrane, characterized in that: It includes a gated covalent organic framework S-COF membrane with functional groups and a macroporous anodic aluminum oxide membrane. The S-COF membrane material with functional groups adjusts its flexibility by introducing functional groups and forms intramolecular hydrogen bonds, thereby realizing a gated separation mechanism under the induction of ethane.

2. The ethane guest responsive gating membrane according to claim 1, characterized in that The functional groups in the S-COF membrane with functional groups are hydroxyl groups, and the anodic aluminum oxide membrane with a macroporous structure is an amino-type anodic aluminum oxide membrane.

3. The ethane guest responsive gating membrane according to claim 1, characterized in that The layer thickness of the S-COF membrane with functional groups is 180-280 nm, the pore size of the S-COF membrane with functional groups is 0.3-0.4 nm, and the pore diameter of the macroporous anodic aluminum oxide membrane material is 50-80 nm.

4. The ethane guest responsive gating membrane according to claim 1, wherein: The gated covalent organic framework S-COF membrane with functional groups has one or more functional groups.

5. The method for preparing the ethane guest responsive gated membrane according to any one of claims 1 to 4, characterized in that: The steps include: (1) An amine-functionalized anodic aluminum oxide (AAO) was placed at the bottom of a reaction bottle, and a 4,4'-biphenyldicarboxaldehyde derivative solution was added. A catalyst was added, and a Schiff base reaction was performed to obtain a CHO-OH / AAO membrane. (2) adding the CHO-OH / AAO membrane to a tetrakis(4-aminophenyl)methane solution and adding a catalyst, and then reacting with a Schiff base to obtain a S-COF / AAO membrane; (3) The S-COF / AAO membrane is taken out, washed with a solvent, and vacuum dried to obtain an ethane guest-responsive gated covalent organic framework membrane.

6. The preparation method according to claim 5, characterized in that In step (1), the 4,4'-biphenyldicarboxaldehyde derivative solution is a 5-(4-formylphenyl)-2-hydroxybenzaldehyde solution or a 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde solution, and the 4,4'-biphenyldicarboxaldehyde derivative solution is prepared using a solvent 1,4-dioxane solution. The concentration of the 4,4'-biphenyldicarboxaldehyde derivative solution is 0.08 to 0.10 mmol / mL.

7. The preparation method according to claim 5, characterized in that In step (2), the tetrakis(4-aminophenyl)methane solution is prepared using a solvent 1,4-dioxane solution, and the concentration of the tetrakis(4-aminophenyl)methane solution is 0.04 to 0.06 mmol / mL.

8. The preparation method according to claim 5, characterized in that In step (1) and step (2), the catalyst is an acetic acid aqueous solution, the concentration of the acetic acid aqueous solution is 2 to 4 mol / L, the temperature of the Schiff base reaction is 50 to 70° C., the time of the Schiff base reaction in step (1) is 0.5 to 2 hours, and the time of the Schiff base reaction in step (2) is 7 days.

9. The preparation method according to claim 5, characterized in that In step (3), the solvent is tetrahydrofuran, the vacuum drying temperature is 40 to 65° C., and the vacuum drying time is 1 to 4 days.

10. Use of the ethane guest-responsive gated membrane according to any one of claims 1 to 4 in ethylene-ethane separation.

Images