Silicon network cross-linked polyether block polyamide pervaporation membrane as well as preparation and application thereof

Abstract

The invention discloses a silicon network cross-linked polyether block polyamide pervaporation membrane as well as preparation and application thereof. The preparation method comprises the following steps: firstly preparing an n-butyl alcohol solution of Pebax, then adding siloxane and an alkali solution, carrying out solution crosslinking to obtain a crosslinked Pebax membrane casting solution, spin-coating the surface of a dried polysulfone ultrafiltration membrane with the crosslinked Pebax membrane casting solution, and drying to obtain the silicon network crosslinked polyether block polyamide pervaporation membrane. The preparation method disclosed by the invention is simple, the Pebax membrane which performs silicon network crosslinking through a one-pot method has the characteristics of short operation flow and high controllability, and the prepared silicon network crosslinked polyether block polyamide pervaporation membrane has relatively high permeability and selectivity and has relatively high adaptability to different feed concentrations.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology and relates to a silicon network crosslinked polyether block polyamide pervaporation membrane, its preparation method, and its application in the pervaporation separation of aromatics / alkane. Background Technology

[0002] Membrane separation technology, represented by pervaporation, is green, energy-saving, and efficient. It can be applied to the separation of aromatic systems of different concentrations and is a powerful means to achieve efficient organic solvent separation.

[0003] Polyether-block polyamides, as a type of high-molecular-weight block polymer, consist of rigid polyamide segments and flexible polyether segments, exhibiting excellent resistance to organic solvents. As a polymer material, Pebax possesses excellent film-forming properties and has a solubility parameter relatively close to toluene, endowing it with sufficient aromatic hydrocarbon affinity. However, due to excessive swelling of Pebax in toluene, the film may lose its selectivity for the toluene / n-heptane system.

[0004] Therefore, to limit the swelling of the membrane in toluene / n-heptane and improve the selectivity of the Pebax membrane for toluene, grafting modification is an important method for Pebax modification. This involves introducing a crosslinking agent with multiple reaction sites to covalently crosslink with Pebax, strengthening the inter-segment interactions, and limiting the swelling of Pebax. Commonly used crosslinking agents include toluene diisocyanate and functional siloxanes, but these require the addition of a large amount of additives during use, resulting in complex system composition and preparation processes. Summary of the Invention

[0005] The technical problem to be solved by this invention is the swelling problem of pervaporated organic functional membranes in the separation process of aromatics / non-aromatics and in the separation process of aromatics / non-aromatics in naphtha, while improving the selectivity and flux of organic membranes.

[0006] To address the problems existing in the prior art, this invention provides a silicon network crosslinked polyether block polyamide pervaporation membrane, its preparation and application. The preparation method is simple and controllable, the obtained membrane surface is dense and defect-free, and the overall performance has good repeatability. This membrane is used in the pervaporation separation process of toluene / n-heptane and the naphtha aromatics separation system, and has a high separation factor and good permeation flux, and has good adaptability to systems with different concentrations.

[0007] The method for preparing the silicon network crosslinked polyether block polyamide pervaporation membrane of the present invention includes the following steps:

[0008] Step (1): Add Pebax and n-butanol into the reactor, heat in a water bath and stir until Pebax is completely dissolved to obtain a homogeneous and transparent Pebax solution;

[0009] Step (2): Add siloxane, stir, then add alkaline solution to adjust the pH value of the system, continue stirring, and obtain cross-linked Pebax casting solution;

[0010] Step (3): Spin-coat the crosslinked Pebax casting solution onto the surface of the polysulfone ultrafiltration membrane and dry it to obtain a silicon network crosslinked polyether block polyamide pervaporation membrane.

[0011] Preferably, the siloxane includes at least one of N-[3-(trimethoxysilyl)propyl]aniline, 2-methyl-2-acrylate [3-(trimethoxysilyl)propyl] ester, and γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0012] Preferably, the Pebax is a polyether block polyamide, and its grade is at least one of 1657, 2533, 3533, 4033, and 4533.

[0013] Preferably, in step (2), the alkali includes at least one of ammonia, piperazine, sodium hydroxide, and potassium tert-butoxide.

[0014] Preferably, in step (3), the molecular weight cutoff of the polysulfone ultrafiltration membrane is 20,000-100,000.

[0015] Preferably, in step (1), the mass concentration of Pebax is 3 wt% to 13 wt% of the total reactor solution volume.

[0016] Preferably, in step (2), the amount of siloxane added is 10wt% to 50wt% of the mass of Pebax; the amount of alkaline solution added does not exceed 35 vol% of the volume of butanol.

[0017] Preferably, in step (1), the temperature of the water bath is 40℃~80℃, and the stirring time is 2~6h.

[0018] Preferably, in step (2), the pH value is 9 to 10, and the stirring time is 4 to 8 hours.

[0019] Preferably, in step (3), the drying time is 24 to 48 hours.

[0020] The present invention also provides a silicon network crosslinked polyether block polyamide pervaporation membrane obtained by the above preparation method.

[0021] The present invention further provides an application of the silicon network crosslinked polyether block polyamide pervaporation membrane obtained by the above preparation method in the separation of organic solvents.

[0022] Preferably, the silicon network crosslinked polyether block polyamide pervaporation membrane is used for the separation of aromatic hydrocarbons and alkanes via pervaporation.

[0023] Preferably, the silicon network crosslinked polyether block polyamide pervaporation membrane is used for the separation of toluene and n-heptane; the pervaporation separation process of toluene and n-heptane is tested at a temperature of 30–70°C and a toluene concentration of 10 wt%–50 wt%.

[0024] This invention uses siloxane as a crosslinking agent to achieve the simple and effective preparation of polyether block polyamide crosslinked membranes through a one-pot method. Utilizing the dual crosslinking process between siloxane and Pebax, and between siloxanes themselves, intermolecular condensation of end groups and intersegmental entanglement occur simultaneously, forming an interpenetrating network between Pebax and siloxane. This restricts the swelling of Pebax in toluene / n-heptane solutions while introducing functional groups, such as aniline, into the system. Through the π-interaction between the introduced functional groups and toluene, the membrane's selectivity for toluene is further enhanced, resulting in an aromatic / alkane separation membrane with both high permeability and high selectivity.

[0025] This invention constructs an interpenetrating network within the membrane through covalent cross-linking between siloxanes and polyether-block polyamides, and physical entanglement between the polymer segments of the polyether-block polyamides. This strengthens the interactions between segments, restricts polymer segment movement, and effectively inhibits membrane swelling in aromatic / alkane systems. While sacrificing some permeability, it significantly improves membrane selectivity. The functional groups, represented by aniline, in siloxanes can generate π-π interactions with toluene, providing more transport sites within the cross-linked membrane and synergistically enhancing the selectivity and permeability of the cross-linked membrane for aromatic components. The one-pot preparation of Pebax membranes via solution cross-linking is simple, controllable, and has a certain degree of universality for methods using trimethoxysilanes with different functional groups. Applied to the pervaporation separation of aromatics and alkanes, it exhibits high permeability and toluene separation selectivity, maintaining a high separation factor under different feed concentrations, demonstrating good applicability. The silicon-network crosslinked polyether block polyamide pervaporation membrane prepared in this invention was applied to the pervaporation separation of aromatics / alkanes. Under the conditions of 40°C and a 50 / 50 wt% toluene / n-heptane mixture, the permeation flux was 914–1873 g m³. -2 h -1 The separation factor ranged from 2.19 to 5.12, and it maintained a high separation factor under different toluene concentration systems. Attached Figure Description

[0026] Figure 1 This is a surface electron microscope image of membrane 1 obtained in Example 1.

[0027] Figure 2 This is a cross-sectional electron microscope image of membrane 1 obtained in Example 1.

[0028] Figure 3 This is a surface electron microscope image of membrane 2 obtained in Example 2.

[0029] Figure 4 This is a cross-sectional electron microscope image of membrane 2 obtained in Example 2.

[0030] Figure 5 This is a surface electron microscope image of film 3 obtained in Example 3.

[0031] Figure 6 This is a cross-sectional electron microscope image of membrane 3 obtained in Example 3.

[0032] Figure 7 This is a comparison graph of the permeation flux and separation factor of the membranes obtained in Examples 1-3 and Comparative Example 1.

[0033] Figure 8 This is a comparison graph of the permeation flux and separation factor of the membranes obtained in Examples 2, 4, 5 and Comparative Example 1. Detailed Implementation

[0034] The design concept of the silicon network crosslinked polyether block polyamide perevaporation membrane of this invention is as follows: Utilizing the characteristic that siloxanes have multiple silanol reaction sites after hydrolysis, they crosslink with the terminal hydroxyl groups of Pebax. Furthermore, the siloxanes can undergo condensation polymerization, connecting different Pebax segments. Combined with the physical entanglement between Pebax segments, an interpenetrating network structure of functional siloxanes and Pebax is constructed within the membrane. This strengthens the interaction between Pebax segments, restricts the mobility of polymer chains, reduces swelling in toluene / n-heptane, and improves the membrane's selectivity for toluene. Simultaneously, the functional groups on the siloxanes can generate π-π interactions with aromatic components such as toluene, enhancing the adsorption and transport of aromatics within the membrane. The preparation steps are as follows: First, a n-butanol solution of Pebax is prepared. Then, siloxanes and an alkaline solution are added. After crosslinking, a crosslinked Pebax casting solution is obtained. This crosslinked Pebax casting solution is spin-coated onto the surface of a dry polysulfone ultrafiltration membrane and dried to obtain the silicon network crosslinked polyether block polyamide perevaporation membrane. The preparation method of this invention is simple. The Pebax membrane, which is cross-linked with silicon network in a one-pot process, has the characteristics of short operation process and high controllability. The prepared silicon network cross-linked polyether block polyamide pervaporation membrane has high permeability and selectivity and high adaptability to different feed concentrations.

[0035] The present invention will be further described below through specific embodiments and comparative examples. The present invention is not limited to the following embodiments. Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional reagents, which can be purchased commercially or synthesized according to conventional methods in the art; the experimental methods, unless otherwise specified, are all conventional methods.

[0036] Example 1:

[0037] This embodiment provides a method for preparing a silicon network crosslinked polyether block polyamide pervaporation membrane, the steps of which are as follows:

[0038] (1) Put Pebax 2533 and n-butanol into a three-necked flask and seal it. The mass concentration of Pebax is 10wt% of the total solution volume. Place the sealed three-necked flask in an 80°C water bath and stir for 2 hours until Pebax is completely dissolved to obtain a homogeneous and transparent Pebax solution.

[0039] (2) Add N-[3-(trimethoxysilyl)propyl]aniline to a three-necked flask, stir for 5 min, then add ammonia water. The amount of ammonia water added is 20 vol% of the volume of butanol. Adjust the pH of the system to 9-10, and continue stirring at 80℃ for 4 h. The amount of siloxane added is 20 wt% of the mass of Pebax. After the reaction, let the three-necked flask stand for 30 min to remove bubbles and obtain the crosslinked Pebax casting solution.

[0040] (3) The degassed crosslinked Pebax casting solution was filtered through gauze and spin-coated onto the surface of a polysulfone ultrafiltration membrane. The polysulfone ultrafiltration membrane had a molecular weight cutoff of 20,000. After drying at room temperature for 24 hours, a silicon network crosslinked polyether block polyamide pervaporation membrane (denoted as membrane 1) was obtained. The surface electron microscope image and cross-sectional electron microscope image of membrane 1 are shown below. Figure 1 , Figure 2 As shown.

[0041] Membrane 1 was used for pervaporation separation of toluene / n-heptane. Under conditions of 40°C and a 50 / 50 wt% toluene / n-heptane mixture, the permeation flux was 1873 g·m⁻¹. -2 ·h -1 The separation factor is 2.19, such as Figure 7 As shown.

[0042] Example 2:

[0043] This embodiment provides a method for preparing a silicon network crosslinked polyether block polyamide pervaporation membrane, the steps of which are as follows:

[0044] The preparation process is basically the same as in Example 1, except that in step (1), the amount of Pebax added is changed from 2533 to 1657, the mass concentration is changed from 10wt% to 3wt%, the water bath temperature is changed from 80℃ to 60℃, and the stirring time is changed from 2h to 4h; in step (2), the mass of N-[3-(trimethoxysilyl)propyl]aniline added is changed from 20wt% to 50wt%, that is, the amount of siloxane added is 50wt% of the mass of Pebax, and the crosslinking time is changed from 4h to 6h; in step (3), the molecular weight cutoff of the polysulfone ultrafiltration membrane is 60000; a silicon network crosslinked polyether block polyamide pervaporation membrane (denoted as membrane 2) is obtained. The surface electron microscope image and cross-sectional electron microscope image of membrane 2 are shown below. Figure 3 , Figure 4 As shown.

[0045] Membrane 2 was used for pervaporation separation of toluene / n-heptane. Under conditions of 30°C and a 50 / 50 wt% toluene / n-heptane mixture, the permeation flux was 1086 g·m⁻¹. -2 ·h -1 The separation factor is 5.12, such as Figure 7 As shown.

[0046] Example 3:

[0047] This embodiment provides a method for preparing a silicon network crosslinked polyether block polyamide pervaporation membrane, the steps of which are as follows:

[0048] The preparation process is basically the same as in Example 1, except that in step (1), the mass concentration of Pebax added is changed to 13wt%, the ammonia added is changed to piperazine, the water bath temperature is changed from 80℃ to 40℃, and the stirring time is changed from 2h to 6h; in step (2), the mass of N-[3-(trimethoxysilyl)propyl]aniline added is changed from 20wt% to 10wt%, that is, the amount of siloxane added is 10wt% of the mass of Pebax, and the crosslinking time is changed from 6h to 8h; in step (3), the molecular weight cutoff of the polysulfone ultrafiltration membrane is 100,000; a silicon network crosslinked polyether block polyamide pervaporation membrane (denoted as membrane 3) is obtained. The surface electron microscope image and cross-sectional electron microscope image of membrane 3 are shown below. Figure 5 , Figure 6 As shown.

[0049] Membrane 3 was used for pervaporation separation of toluene / n-heptane. Under conditions of 70°C and a 10 / 90 wt% toluene / n-heptane mixture, the permeation flux was 780 g·m⁻¹. -2 ·h -1 The separation factor is 5.45, such as Figure 7 As shown.

[0050] Example 4:

[0051] This embodiment provides a method for preparing a silicon network crosslinked polyether block polyamide pervaporation membrane, the steps of which are as follows:

[0052] The preparation process is basically the same as that in Example 2, except that in step (2), the added N-[3-(trimethoxysilyl)propyl]aniline is replaced with 2-methyl-2-acrylate [3-(trimethoxysilyl)propyl] ester, and a silicon network crosslinked polyether block polyamide pervaporation membrane (denoted as membrane 4) is obtained.

[0053] Membrane 4 was used for pervaporation separation of toluene / n-heptane. Under conditions of 70°C and a 40 / 60 wt% toluene / n-heptane mixture, the permeation flux was 5013 g·m⁻¹. -2 ·h -1 The separation factor is 1.21, such as Figure 8 As shown.

[0054] Example 5:

[0055] This embodiment provides a method for preparing a silicon network crosslinked polyether block polyamide pervaporation membrane, the steps of which are as follows:

[0056] The preparation process is basically the same as that in Example 2, except that in step (2), the added N-[3-(trimethoxysilyl)propyl]aniline is replaced with γ-(2,3-epoxypropoxy)propyltrimethoxysilane to obtain a silicon network crosslinked polyether block polyamide pervaporation membrane (denoted as membrane 5).

[0057] Membrane 5 was used for pervaporation separation of toluene / n-heptane. Under conditions of 50°C and a 50 / 50 wt% toluene / n-heptane mixture, the permeation flux was 2311 g m³. -2 h -1 The separation factor is 2.08, such as Figure 8 As shown.

[0058] Comparative Example 1:

[0059] This comparative example provides a method for preparing a polyether block polyamide film, the steps of which are as follows:

[0060] (1) Put Pebax 2533 and n-butanol into a three-necked flask and seal it. The mass concentration of Pebax is 10wt% of the total solution volume. Place the sealed three-necked flask in an 80°C water bath and stir for 2 hours until Pebax is completely dissolved to obtain a homogeneous and transparent Pebax solution.

[0061] (2) The casting solution was filtered through gauze and spin-coated onto the surface of a polysulfone ultrafiltration membrane. The molecular weight cutoff of the polysulfone ultrafiltration membrane was 20,000. The membrane was dried at room temperature for 24 hours to obtain a Pebax pure membrane (referred to as control membrane 1).

[0062] Comparative membrane 1 was used for pervaporation separation of toluene / n-heptane. Under conditions of 40°C and a 50 / 50 wt% toluene / n-heptane mixture, the permeation flux was 14315 g·m⁻¹. -2 ·h -1 The separation factor is 0.81, such as Figure 7 , Figure 8 As shown.

[0063] The comparison between Comparative Example 1 and Examples 1-5 shows that the introduction of siloxane and the construction of Pebax interpenetrating network can effectively limit the swelling of Pebax segments in toluene / n-heptane mixture, improve the membrane's selectivity for toluene separation, and the membrane performance will change significantly with the change of the type and amount of siloxane selected. It can be seen that the silicon network crosslinked polyether block polyamide pervaporation membrane proposed in this invention has extremely broad application and promotion potential.

[0064] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention, and these modifications are all within the protection scope of the present invention.

Claims

1. A method for preparing a silicon network crosslinked polyether block polyamide pervaporation membrane, characterized in that, Includes the following steps: Step (1): Add Pebax and n-butanol into the reactor, heat in a water bath and stir until Pebax is completely dissolved to obtain a homogeneous and transparent Pebax solution; Step (2): Add siloxane, stir, then add alkaline solution to adjust the pH value of the system, continue stirring, and obtain cross-linked Pebax casting solution; Step (3): Spin-coat the crosslinked Pebax casting solution onto the surface of the polysulfone ultrafiltration membrane and dry it to obtain a silicon network crosslinked polyether block polyamide pervaporation membrane.

2. The preparation method according to claim 1, characterized in that, The siloxane includes at least one of N-[3-(trimethoxysilyl)propyl]aniline, 2-methyl-2-acrylate [3-(trimethoxysilyl)propyl] ester, and γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

3. The preparation method according to claim 1, characterized in that, The Pebax brand name is at least one of 1657, 2533, 3533, 4033, and 4533; In step (2), the alkali includes at least one of ammonia, piperazine, sodium hydroxide, and potassium tert-butoxide.

4. The preparation method according to claim 1, characterized in that, In step (3), the molecular weight cutoff of the polysulfone ultrafiltration membrane is 20,000-100,000.

5. The preparation method according to claim 1, characterized in that, In step (1), the mass concentration of Pebax is 3 wt% to 13 wt% of the total reactor solution volume; In step (2), the amount of siloxane added is 10wt% to 50wt% of the mass of Pebax; the amount of alkaline solution added does not exceed 35 vol% of the volume of butanol.

6. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the water bath is 40℃~80℃, and the stirring time is 2~6h; In step (2), the pH value is 9-10, and the stirring time is 4-8 hours. In step (3), the drying time is 24 to 48 hours.

7. A silicon network crosslinked polyether block polyamide pervaporation membrane obtained by the preparation method according to any one of claims 1-6.

8. The application of a silicon network crosslinked polyether block polyamide pervaporation membrane obtained by the preparation method according to any one of claims 1-6 in the separation of organic solvents.

9. The application according to claim 8, characterized in that, The silicon network crosslinked polyether block polyamide pervaporation membrane is used for the separation of aromatic hydrocarbons and alkanes by pervaporation.

10. The application according to claim 8, characterized in that, The silicon network crosslinked polyether block polyamide pervaporation membrane is used for the separation of toluene and n-heptane; the pervaporation separation process of toluene and n-heptane is tested at a temperature of 30–70°C and a toluene concentration of 10 wt%–50 wt%.

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