A homogeneous anion-selective exchange membrane and a method for preparing the same

Abstract

This application discloses a homogeneous anion-selective exchange membrane and its preparation method, belonging to the field of exchange membrane technology. The preparation method includes: adding a branching agent to an aqueous caprolactam solution, heating to a fixed temperature, undergoing a hydrolysis ring-opening polymerization reaction, and post-treatment to obtain a hyperbranched nylon resin-based membrane resin; extruding and stretching the hyperbranched nylon resin-based membrane resin into a film to obtain a homogeneous anion-selective exchange membrane; wherein the branching agent is one or a mixture of several of the following in any proportion: an amino-terminated derivative of trimethylolpropane tripropylene glycol ether, melamine cyanurate, etc. The homogeneous anion exchange membrane obtained in this application exhibits excellent selective adsorption and migration exchange capabilities, demonstrating excellent rapid kinetics during ion exchange.

Description

Technical Field

[0001] This application belongs to the field of exchange membrane technology, and specifically relates to a homogeneous anion selective exchange membrane and its preparation method. Background Technology

[0002] Ion exchange membranes are crucial ion separation tools in the purification or treatment of water, food, beverages, chemicals, and wastewater, as well as in equipment used for fractionation, migration, and electroregeneration, particularly in electrodialysis (EDI) units. They are key materials in energy and environmental technologies such as fuel cells, flow batteries, and electrodialysis. Ion exchange membrane materials primarily function to isolate gases and conduct ions. Their main roles include: enhancing the sealing performance of the membrane electrode assembly (MEA) and improving its ion conduction; enhancing the mechanical properties of the MEA; preventing excessive compression of the gas diffusion layer; reducing the risk of leakage; reducing freezing damage; reducing equipment size; and achieving the highest possible encapsulation density. Ion exchange membranes can be classified into heterogeneous membranes, semi-homogeneous membranes, and homogeneous membranes. Considering ion exchange efficiency and overall performance, homogeneous membranes represent the future direction of industry development. Membrane exchange materials not only need to maintain physical stability but also good chemical stability. Furthermore, they must prevent chain segmentation of the polymer backbone and minimal degradation of anionic groups in alkaline environments. The membrane exchange materials also require good ionic conductivity to further enhance the transport of water and ions. The preparation process of homogeneous ion exchange membrane materials is complex. Traditional homogeneous ion exchange membranes (such as those containing quaternary ammonium salts) suffer from high cost, poor mechanical properties, and low selectivity. The research and development of homogeneous membrane materials is challenging, making the development of novel high-performance ion exchange membrane materials of great significance. The goal is to prepare ion exchange membranes with suitable thicknesses that not only possess appropriate sheet resistivity but also avoid high gas permeability. Preparing ion exchange membrane materials with excellent comprehensive performance has always been a significant challenge.

[0003] Currently, there are many materials that can be used as membrane electrolytes, including polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyetherimide (PEI), polyimide (PI), and polyethylene terephthalate (PET). These membrane materials are generally transformed into functionalized polymer membrane materials through post-polymerization functionalization. Post-polymerization functionalization includes polymerization (electrophilic reagent) and polymerization (nucleophilic reagent), which mainly involves attaching anionic functional groups to a pre-formed polymer backbone. The advantage of this method is that the backbone polymer is usually commercially available or easily synthesized, and the anionic groups can be easily diversified. The disadvantage is that the degree of functionalization is greatly limited by the solubility of the starting material and the polymer of the functionalized product. In some cases, multiple steps are required to bind anions, and side reactions may occur. These reactions are difficult to control and detect, and the bonds to the anionic active functional groups are easily activated and decomposed. Furthermore, the ion transference numbers of homogeneous anion selective exchange membranes currently being prepared are not high enough, while the sheet resistance is relatively high, and their performance in terms of temperature resistance, oxidation resistance, and dimensional stability is not ideal. Summary of the Invention

[0004] To address the above problems, this application provides a homogeneous anion-selective exchange membrane and its preparation method.

[0005] The first objective of this application is to provide a method for preparing a homogeneous anion-selective exchange membrane, comprising: The branching agent was added to an aqueous solution of caprolactam, heated to a fixed temperature, and subjected to a hydrolysis ring-opening polymerization reaction. After post-treatment, hyperbranched nylon resin-based film resin was obtained. Hyperbranched nylon resin-based membranes are extruded and stretched into films to obtain homogeneous anion selective exchange membranes. The branching agent is one or a mixture of several of the following in any proportion: an amino-terminated derivative of trimethylolpropane tripropylene glycol ether and melamine cyanurate. The molecular structure of the amino-terminated derivative of the trimethylolpropane tripropylene glycol ether is shown in Formula I: I In Equation I, the sum of x, y, and z is 5-6.

[0006] Furthermore, the amino-terminated derivative of the trimethylolpropane tripropylene glycol ether is prepared by hydrogen-catalyzed amination of trimethylolpropane tripropylene glycol and polyamine under the conditions of reaction temperature of 190~210℃ and reaction time of 8~12h.

[0007] Furthermore, the polyamine is one or a mixture of several of the following in any proportion: ethylenediamine, propylenediamine, butanediamine, and m-phenylenediamine.

[0008] Furthermore, the trimethylolpropane tripropylene glycol and the polyamine are mixed at a molar ratio of hydroxyl and amino functional groups of 1:1-1.5.

[0009] Furthermore, the mass of the branching agent added is 4-10% of the mass of caprolactam added.

[0010] Furthermore, in the hydrolytic ring-opening polymerization reaction, the amount of water used is 5-8% of the mass of caprolactam.

[0011] Furthermore, the fixed temperature is 240~255℃, and the hydrolysis ring-opening polymerization reaction time is 8~12h.

[0012] Furthermore, the hydrolysis ring-opening polymerization reaction is carried out under a nitrogen atmosphere.

[0013] Further, the post-processing includes: The reaction solution obtained from the polymerization reaction was boiled in water at 90~100℃ for 12~24h and then vacuum dried at 80~120℃ for 12~24h.

[0014] Furthermore, during the extrusion stretching process, the extrusion temperature is 230~250℃ and the extrusion speed is 0.5~0.8m / min.

[0015] The second objective of this application is to provide a homogeneous anion selective exchange membrane, which is prepared by the aforementioned method for preparing a homogeneous anion selective exchange membrane.

[0016] Furthermore, the number-average molecular weight of the hyperbranched nylon resin-based film is 15,000 to 25,000.

[0017] Compared with the prior art, this application has the following advantages: This application discloses a homogeneous anion-selective exchange membrane and its preparation method. A branching agent containing terminal amino groups (such as an amino-terminated derivative of trimethylolpropane tripropylene glycol ether and / or melamine cyanurate) is added to the hydrolytic ring-opening polymerization reaction of caprolactam to form an amino-containing hyperbranched nylon resin-based membrane. Utilizing the ion exchange properties of amino groups under certain conditions, the membrane can serve as an anion-selective exchange membrane. The resulting homogeneous anion exchange membrane exhibits excellent selective adsorption and migration exchange capabilities, demonstrating superior rapid kinetics during ion exchange.

[0018] The resulting hyperbranched nylon resin-based membrane not only possesses excellent flowability, thermal stability, and chemical stability, but also exhibits temperature resistance, oxidation resistance, and dimensional stability due to the use of nylon resin matrix as a carrier. It demonstrates good gas separation and water treatment performance and has broad application prospects.

[0019] The homogeneous anion-selective exchange membrane obtained in this application has a thickness of 25 μm-80 μm, an ion mobility number >85%, and a sheet resistivity <10 Ω·cm. 2 With its superior properties such as temperature resistance, oxidation resistance, and high strength, it is a membrane material with even better performance in engineering applications.

[0020] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The synthetic route 1 for hyperbranched nylon resin-based film resin according to certain embodiments of this application is shown; Figure 2 The synthetic route 2 of hyperbranched nylon resin-based film resin according to certain embodiments of this application is shown. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] like Figure 1 As shown, the synthetic route 1 of the hyperbranched nylon resin-based film resin according to certain embodiments of this application is a route for synthesizing the hyperbranched nylon resin-based film resin from an amino-terminated derivative of trimethylolpropane tripropylene glycol ether and caprolactam.

[0025] like Figure 2 As shown, the synthesis route 2 of the hyperbranched nylon resin-based membrane resin according to certain embodiments of this application is a route for synthesizing hyperbranched nylon resin-based membrane resin from melamine cyanurate (MCA) and caprolactam, which mainly utilizes the active hydrogen on the amino group in MCA as the active exchange site.

[0026] In some embodiments of this application, the number-average molecular weight of the hyperbranched nylon resin-based film resin is 15,000 to 25,000.

[0027] In some embodiments of this application, the preparation of the amino-terminated derivative of trimethylolpropane tripropylene glycol ether includes: using trimethylolpropane tripropylene glycol as a raw material, and a polyamine (propylenediamine) at a molar ratio of 1:1 of the active groups of the two materials, under the conditions of a reaction temperature of 190~210℃ and a reaction time of 8~12h, the hydroxyl groups at the end of the polyether are prepared by hydrogenation catalytic amination in the presence of a catalyst (such as a noble metal supported catalyst, such as palladium supported on activated carbon). Its molecular structure is shown in Formula I, where the sum of x, y, and z is 5.3.

[0028] In the above embodiments, trifunctional polyetheramines are used to ensure that the amino-terminated derivatives of trimethylolpropane tripropylene glycol ether contain as many nitrogen ions as possible, thus providing more active sites for anion exchange groups. Its unique molecular structure also endows the hyperbranched nylon resin with excellent overall properties.

[0029] In some embodiments of this application, the polycyanuric acid cyanate is commercially available MCA, which is a material well known in the art, and this application does not specifically limit it.

[0030] The following are specific embodiments of the homogeneous anion-selective exchange membrane of this application: Example 1 Preparation of homogeneous anion-selective exchange membranes: The first step involves adding the amino-terminated derivative of the prepared trimethylolpropane tripropylene glycol ether to a caprolactam aqueous solution at a dosage of 5% of the caprolactam mass. After thorough mixing, the mixture is transferred to a high-pressure reactor, and the feed port is closed. High-purity nitrogen is then introduced until the reactor pressure reaches 0.3 MPa, followed by slow evacuation to reduce the reactor pressure to -0.05 to -0.08 MPa. The process was repeated 3 times, with high-purity nitrogen gas being introduced until the pressure inside the reactor was at atmospheric pressure. The reactor was heated until the reaction temperature was reached, and then stirred for 10 hours. The exhaust valve was opened to allow the pressure inside the reactor to slowly decrease to atmospheric pressure, and then a vacuum was applied for 4 hours. High-purity nitrogen gas was introduced until the pressure inside the reactor was at positive pressure, and after standing and equilibrating for 3 hours, the exhaust valve was opened to allow the pressure inside the reactor to decrease to atmospheric pressure. Inert gas was then introduced into the reactor until the pressure was 0.4 MPa, and then a vacuum was applied until the pressure was -0.06 MPa. This process of introducing inert gas and applying a vacuum was repeated 4 times. The reactor was then adjusted to atmospheric pressure. The temperature was raised to 250°C under atmospheric pressure, and the reaction was stirred for 10 hours. After the reaction was completed, a vacuum was applied for 2 hours. Then, the bottom valve of the reactor was opened to discharge the material. The obtained material was extracted in boiling water for 24 hours and then vacuum dried at 80°C for 12 hours to prepare an amino-containing hyperbranched nylon resin-based film resin. The second step involves extruding and stretching an amino-containing hyperbranched nylon resin base into a film using a twin-screw extruder to obtain a homogeneous anion selective exchange membrane. The extrusion temperature is 230~240℃ and the extrusion speed is 0.5m / min. The membrane surface is then subjected to gloss treatment and biaxial stretching treatment.

[0031] Example 2 The amino-terminated derivative of the prepared trimethylolpropane tripropylene glycol ether was added to an aqueous caprolactam solution at an amount equal to 8% of the caprolactam mass, with all steps identical to those in Example 1. An anion exchange membrane material using hyperbranched nylon resin containing terminal amino groups as the matrix resin was prepared.

[0032] Example 3 Melamine cyanurate (MCA) was added to an aqueous caprolactam solution at a concentration of 6% of the mass of caprolactam. All steps were the same as in Example 1. An anion exchange membrane material with hyperbranched nylon resin as matrix resin and melamine cyanurate (MCA) as branching agent was prepared, and a homogeneous anion selective exchange membrane material was prepared.

[0033] Example 4 Melamine cyanurate (MCA) was added to an aqueous caprolactam solution at a dosage of 8% of the mass of caprolactam. All steps were the same as in Example 1. An anion exchange membrane material with hyperbranched nylon 6 resin as matrix resin and melamine cyanurate (MCA) as branching agent was prepared, and a homogeneous anion selective exchange membrane material was prepared.

[0034] Comparative Example 1: Compared with Examples 1-4, no branching agent was added, and nylon polymerization was carried out directly. Caprolactam was added to 6% by mass of deionized water, mixed evenly, and then transferred to a high-pressure reactor. The synthesis steps were the same as in Example 1, and nylon 6 resin material without terminal amine groups was prepared and film material was prepared, which was used as a comparative analysis of ion exchange resins.

[0035] Comparative Example 2: Compared with Examples 1-4, a branching agent (hexa(2,4-diaminophenoxy)cyclotriphosphazene) was added during the direct polymerization process. The amount added was 1.5% by mass of caprolactam. Preparation method: Same as the hydrolysis ring-opening polymerization reaction operation in Example 1. Membrane material preparation: Same as the membrane preparation method in Example 1.

[0036] The homogeneous anion selective exchange membranes obtained in Examples 1-4 can be applied to electrodialysis EDI equipment. The homogeneous anion selective exchange membranes obtained in Examples 1-4 are compared with the membrane materials obtained in Comparative Examples 1-2, and their exchange performance is tested. The test results are shown in Table 1.

[0037] Table 1

[0038] As can be seen from the data in Table 1, the nylon resin material with terminal amino hyperbranched containing multifunctional groups has a certain ion selective migration and exchange capacity, indicating that the branching agent used in Examples 1-4 has good film-forming properties for the resin material and also has good ion selective exchange capacity.

[0039] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a homogeneous anion-selective exchange membrane, characterized in that, include: The branching agent was added to an aqueous solution of caprolactam, heated to a fixed temperature, and subjected to a hydrolysis ring-opening polymerization reaction. After post-treatment, hyperbranched nylon resin-based film resin was obtained. Hyperbranched nylon resin-based membranes are extruded and stretched into films to obtain homogeneous anion selective exchange membranes. The branching agent is one of the amino-terminated derivatives of trimethylolpropane tripropylene glycol ether and melamine cyanurate. The molecular structure of the amino-terminated derivative of the trimethylolpropane tripropylene glycol ether is shown below: The sum of x, y, and z is 5-6.

2. The method for preparing a homogeneous anion-selective exchange membrane according to claim 1, characterized in that, The amino-terminated derivative of the trimethylolpropane tripropylene glycol ether is prepared by hydrogenation catalytic amination of trimethylolpropane tripropylene glycol and polyamine under the conditions of reaction temperature of 190~210℃ and reaction time of 8~12h.

3. The method for preparing a homogeneous anion-selective exchange membrane according to claim 2, characterized in that, The polyamine is one or a mixture of several of the following in any proportion: ethylenediamine, propylenediamine, butanediamine, and m-phenylenediamine.

4. The method for preparing a homogeneous anion-selective exchange membrane according to claim 1, characterized in that, The mass of the branching agent added is 4-10% of the mass of caprolactam added.

5. The method for preparing a homogeneous anion-selective exchange membrane according to claim 1, characterized in that, In the hydrolytic ring-opening polymerization reaction, the amount of water used is 5-8% of the mass of caprolactam.

6. The method for preparing a homogeneous anion-selective exchange membrane according to claim 1, characterized in that, The fixed temperature is 240~255℃, and the hydrolysis ring-opening polymerization reaction time is 8~12h.

7. The method for preparing a homogeneous anion-selective exchange membrane according to claim 1, characterized in that, The hydrolysis ring-opening polymerization reaction was carried out under a nitrogen atmosphere.

8. The method for preparing a homogeneous anion-selective exchange membrane according to claim 1, characterized in that, The post-processing includes: The reaction solution obtained from the polymerization reaction was boiled in water at 90~100℃ for 12~24h and then vacuum dried at 80~120℃ for 12~24h.

9. A method for preparing a homogeneous anion-selective exchange membrane according to any one of claims 1-8, characterized in that, During the extrusion stretching process, the extrusion temperature is 230~250℃ and the extrusion speed is 0.5~0.8m / min.

10. A homogeneous anion-selective exchange membrane, characterized in that, It is prepared by the method for preparing a homogeneous anion selective exchange membrane according to any one of claims 1-9.

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