RU2802630C1 - Method for producing a composite anion exchange membrane - Google Patents

Abstract

FIELD: membrane technology.

SUBSTANCE: present invention relates to a method for producing a composite anion-exchange membrane. The method includes placing the membrane in working solutions, one of which is a monomer solution, the other is a solution of an oxidizing agent, and washing, and an anion-exchange heterogeneous membrane consisting of polyethylene and an anion-exchange resin with positively charged nitrogen-containing fixed groups is used as the initial membrane, whereas the membrane is placed first into an oxidizing agent solution, which is 1 M ammonium persulfate, and kept for 60 minutes, and then into a monomer solution, which is an aqueous 0.1 M solution of 2-aminobenzenesulfonic acid, and kept for 48 hours, and the membrane is washed in deionized water.

EFFECT: increase in electrical conductivity and a decrease in the diffusion permeability of membranes.

2 cl, 1 dwg, 2 tbl, 6 ex

Description

The invention relates to membrane technology, in particular, to methods for producing composite anion-exchange membranes based on anion-exchange membranes and sulfonated polyaniline (SPANI), intended for use in processes of electrodialysis desalting and concentration of electrolyte solutions and separation of multicomponent mixtures.

A composite anion-exchange membrane is known, consisting of a heterogeneous anion-exchange membrane-substrate and a thin homogeneous cation-exchange layer of sulfonated polytetrafluoroethylene containing carbon nanotubes deposited on its surface, and having improved selectivity for the transfer of counterions [RF Patent 195198 B01D 67/00 (2006. 01) B01D 71/36 (2006.01) B82Y 30/00 (2011.01) publ. 01/17/2020 Bulletin. No. 2]. The disadvantage is the possible destruction of the thin homogeneous cation exchange layer of sulfonated polytetrafluoroethylene due to different swelling coefficients of the thin homogeneous cation exchange layer of sulfonated polytetrafluoroethylene and the heterogeneous anion exchange membrane substrate, and lower electrical conductivity compared to the proposed composite anion exchange membrane.

There is a known method for producing anion-exchange membranes made of a polymer containing amino groups of varying degrees of alkylation by immersing them in a 5% aqueous solution of a polymer polyelectrolyte, which is polyquaternium-22. The treatment is carried out for 8 hours at a temperature of 50°C. The invention provides a simple method for modifying anion-exchange membranes, reducing the duration of the modification process and stable membrane characteristics over a longer operating time [RF Patent 2 699646 B01D 71/06 (2019.05); B01D 71/82 (2019.05) publ. 09/06/2019 Bulletin. No. 25]. The disadvantages of the method are the lack of explanation of the action of the modifier and the lack of confirmation of the presence of polyquaternium-22 in the membrane.

An anion exchange membrane is known, consisting of a substrate, which is a membrane containing 35% polyethylene and 65% strong basic anion exchange resin, and a modifier layer located on the profiled surface of the membrane. The layer is made of phosphorylated hyperbranched polymer based on Boltorn H20 and perfluorosulfopolymer MF-4SK in a 1:1 ratio by weight. The technical result is an increase in electrical conductivity while maintaining diffusion permeability, which makes it possible to achieve high current outputs while reducing energy costs [RF Patent 207737 B01D 71/26 (2006.01); B01D 71/82 (2006.01); B01D 69/02 (2006.01); B01D 61/44 (2006.01) publ. 11/12/2021 Bulletin. No. 32]. The electrical conductivity of the anion exchange membrane is 1.4 times higher compared to the original membrane. The disadvantage of this anion-exchange membrane is its lower electrical conductivity compared to that obtained by the proposed method, as well as different swelling coefficients of the membrane taken as a substrate and a modifier layer, which can lead to detachment of the modifier layer or damage to its integrity.

There is a known method for producing a composite anion-exchange membrane modified with polyaniline [RF Patent 2612269 B01D 71/60 (2006.01) publ. 03.03.2017 Bulletin. No. 7], which includes placing an anion exchange membrane with positively charged fixed groups in a two-chamber cell formed by a vertically fixed membrane, one of the chambers of which is filled with water, and the other - sequentially with solutions of ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ , and then 1 M aniline prepared in 1 M HCl, while using 0.5 M ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ prepared in a solution of 1 M HCl, and exposing the membrane to the resulting solution of ammonium persulfate for 10-30 minutes, and then use an aniline solution for 10-30 minutes, while the positively charged fixed groups of the anion exchange membrane are nitrogen-containing. The disadvantage of this method is the low electrical conductivity of the resulting membranes.

The closest to the claimed is the method of producing a composite cation exchange membrane [RF Patent 2700530 publ. B01D 67/00 (2006.01) B01D 71/06 (2006.01)09/17/2019 Bulletin. No. 26], characterized by the fact that the cation-exchange homogeneous perfluorinated membrane is placed in a solution of an equivalent mixture of aniline with a concentration of 0.01-0.001 M and sulfuric acid for 30 minutes to saturate it with aniline, then the cation-exchange homogeneous perfluorinated membrane is placed in a solution of the oxidizing agent ferric chloride (III ) in sulfuric acid with a concentration of 0.005 M to form polyaniline under the influence of an oxidizing agent for a period of 30 minutes, after which the membrane is thoroughly washed with distilled water and placed in a solution of sulfuric acid with a concentration of 0.5 M.

The disadvantage of this method is the low electrical conductivity and high diffusion permeability of the resulting membranes.

The objective of the invention is to improve the method for producing a composite anion-exchange membrane, which makes it possible to improve the performance characteristics of the resulting membranes.

The technical result of the proposed invention is to increase electrical conductivity and decrease the diffusion permeability of membranes.

The technical result is achieved by placing an anion exchange membrane consisting of polyethylene and an anion exchange resin with positively charged nitrogen-containing fixed groups in a container with an oxidizing solution containing ammonium persulfate with a concentration of 1 M for 60 minutes, and then replacing the oxidizing solution with an aqueous solution of the monomer 2-aminobenzenesulfonic acids with a concentration of 0.1 M for 48 hours, after which the composite anion exchange membrane is washed with deionized water; an anion exchange membrane with positively charged fixed groups is placed in a two-chamber cell formed by a vertically fixed membrane, one of the chambers of which is filled with water, and the other - successively with solutions of the oxidizing agent ammonium persulfate, and then with an aqueous solution of 2-aminobenzenesulfonic acid monomer, then the composite anion exchange membrane is washed with deionized water.

According to the proposed method, SPANI is formed directly in the anion-exchange membrane as a result of oxidative polymerization of the monomer 2-aminobenzenesulfonic acid, which is a derivative of aniline, under the action of the oxidizing agent ammonium persulfate. The use of 2-aminobenzenesulfonic acid as a monomer instead of aniline makes it possible to obtain SPANI, which has cation exchange properties due to the presence of sulfonic groups. In this case, the resulting polymers, polyaniline and SPANI, have the same linear “head-tail” structure, distinguished by the presence of a sulfo group substituent in the polymer chain [S. Shimizu, T. Saitoh, M. Uzawa at all. Synthesis and applications of sulfonated polyaniline // Synth. Metals. 1997. V. 85. P. 1337-1338].

Distinctive features of the proposed method are:

- the use of an anion exchange membrane consisting of polyethylene and an anion exchange resin with positively charged nitrogen-containing fixed groups;

- using a working solution of the oxidizer ammonium persulfate at the first stage to treat the membrane, and at the second stage a working solution of 2-aminobenzenesulfonic acid monomer.

Thus, the combination of the proposed essential features makes it possible to obtain a composite anion-exchange membrane with an electrical conductivity 3 times higher and a diffusion permeability 15% lower than that of the original membrane.

In fig. Figure 1 shows the infrared spectra of attenuated total internal reflection (IR ATR spectra) of the original membrane (curve 0) and composite anion-exchange membranes (curves 1 - 4). Let's look at examples of specific implementation.

Example 1

An anion-exchange heterogeneous membrane consisting of polyethylene and an anion-exchange resin with positively charged nitrogen-containing fixed groups was used as the starting membrane. A sample of the original membrane weighing about 1 g was placed in 20 ml of a solution containing the oxidizing agent ammonium persulfate with a concentration of 0.125 M (NH ₄ ) ₂ S ₂ O ₈ and the monomer 2-aminobenzenesulfonic acid with a concentration of 0.1 M for 48 hours. The time for the sample color to appear is indicated in Table 1. After this, the composite anion exchange membrane was washed with deionized water. The ATR IR spectrum is shown in Fig. 1, curve 1.

Example 2

A sample similar to Example 1 was used as the starting membrane. At the first stage, a sample of the starting membrane was placed in 20 ml of an aqueous solution of 0.1 M 2-aminobenzenesulfonic acid monomer for 24 hours. The sample was then placed in 20 ml of 0.125 M ammonium persulfate oxidizing solution for 48 hours. The time for the color appearance of sample 2 is indicated in Table 1. After this, the composite anion-exchange membrane (sample 2 in Table 1) was washed with deionized water. The ATR IR spectrum is shown in Fig. 1, curve 2.

Example 3

A sample similar to Example 1 was used as a starting membrane. At the first stage, a sample of the starting membrane was placed in 20 ml of an aqueous solution of 0.1 M 2-aminobenzenesulfonic acid for 24 hours according to Example 2. Then the sample was placed in 20 ml of a solution containing (NH ₄ ) ₂ S ₂ O ₈ with a concentration of 0.125 M and 2-aminobenzenesulfonic acid with a concentration of 0.1 M for 48 hours. The time for the color appearance of sample 3 is indicated in Table 1. After this, the composite anion-exchange membrane (sample 3 in Table 1) was washed with distilled water. The ATR IR spectrum is shown in Fig. 1, curve 3.

Example 4

A sample similar to Example 1 was used as a starting membrane. At the first stage, a sample of the starting membrane was placed in 20 ml of an aqueous solution of 0.1 M 2-aminobenzenesulfonic acid for 24 hours according to Example 2. Then the sample was placed in 20 ml of a solution containing (NH ₄ ) ₂ S ₂ O ₈ with a concentration of 1 M and 2-aminobenzenesulfonic acid with a concentration of 0.1 M for 48 hours. The time for the color appearance of sample 4 is indicated in Table 1. After this, the composite anion exchange membrane (sample 4 in Table 1) was washed with deionized water. The ATR IR spectrum is shown in Fig. 1, curve 4.

Example 5

A sample similar to Example 1 was used as the starting membrane. A sample measuring 10 cm by 10 cm was placed vertically in a two-chamber cell formed by a vertically fixed membrane. Each cell chamber has a volume of 100 ml. One of the chambers of the cell was filled with deionized water, and the other at the first stage was filled with a solution of 1 M ammonium persulfate and left for 60 minutes. After this, the ammonium persulfate solution was replaced with a 0.1 M solution of 2-aminobenzenesulfonic acid and left for 48 hours. The time for the color appearance of sample 5 is indicated in Table 1. After this, the composite anion exchange membrane (sample 5 in Table 1) was washed with deionized water. The exchange capacity (Q, mmol/g), moisture content (W, %), thickness (l, µm), specific electrical conductivity (k, S/m) and diffusion permeability (P, m ² /s) of the resulting sample 5 are given in the table 2.

Example 6

A sample similar to Example 1 was used as the starting membrane. At the first stage, a sample of the starting membrane measuring 10 cm by 10 cm was placed in 100 ml of 1 M ammonium persulfate and left for 60 minutes, and then in 100 ml of a 0.1 M solution of 2-aminobenzenesulfonic acid for 48 hours according to example 5. The time for the color appearance of sample 6 is indicated in Table 1. After this, the composite anion exchange membrane (sample 6 in Table 1) was washed with deionized water. The exchange capacity, moisture content and thickness of the resulting sample 6 are given in Table 2.

Table 1 - Conditions for obtaining composite anion-exchange membranes Sample No. Stage 1 Stage 2 Time of appearance of membrane staining Composition of the working solution Contact time of the membrane with the working solution Composition of the working solution Contact time of the membrane with the working solution 1 - - 0.1 M 2-aminobenzenesulfonic acid + 0.125 M ammonium persulfate 48 hours >30 min 2 0.1 M solution of 2-aminobenzenesulfonic acid 24 hours 0.125 M (NH ₄ ) ₂ S ₂ O ₈ 48 hours >30 min 3 0.1 M solution of 2-aminobenzenesulfonic acid 24 hours 0.1 M 2-aminobenzenesulfonic acid + 0.125 M ammonium persulfate 48 hours >4 h 4 0.1 M solution of 2-aminobenzenesulfonic acid 24 hours 0.1 M 2-aminobenzenesulfonic acid + 1 M ammonium persulfate 48 hours >30 min 5 1 M (NH ₄ ) ₂ S ₂ O ₈ solution 60 min 0.1 M C ₆ H ₇ NSO ₃ 48 hours 15-30 min 6 1 M (NH ₄ ) ₂ S ₂ O ₈ solution 60 min 0.1 M C ₆ H ₇ NSO ₃ 48 hours 15-30 min

Table 2 - Physico-chemical and electrical transport properties of the original anion-exchange membrane and the composite anion-exchange membrane obtained by the proposed method Sample Q, mmol/g W, % l, µm k, S/m P, m ² /s Initial membrane 2.15 37 520±4 0.20 8.62⋅10 ^-12 5 0.96 42 524±4 0.67 7.74⋅10 ^-12 6 0.97 43 524±4 0.68 7.05⋅10 ^-12

The SPANI modifier is colored, so you can visually estimate the minimum time required for the appearance of SPANI in the membrane. A comparison of the time for the appearance of coloring of samples 1-6, shown in Table 1, shows that placing the initial membrane at the first stage in a solution of ammonium persulfate leads to a significant acceleration of the polymerization reaction of 2-aminobenzenesulfonic acid. The presence of ammonium persulfate in the solution at the second stage has virtually no effect on the time of appearance of the membrane color.

Thus, the optimal mode for obtaining a composite anion exchange membrane has been determined, which consists of sequentially placing the original membrane in a solution of ammonium persulfate for 1 hour, and then in a solution of 2-aminobenzenesulfonic acid for 48 hours. In this case, at the first stage, ion exchange occurs between the anion-exchange membrane and the solution, and the anion-exchange membrane passes into the ionic form of persulfate anions. At the second stage, oxidative polymerization of 2-aminobenzenesulfonic acid occurs under the action of persulfate anions and the polymer SPANI is formed. In the case when the membrane is processed in a container with working solutions, the formation of SPANI occurs on both surfaces of the membrane. In the case when the membrane is processed in a two-chamber cell formed by a vertically fixed membrane, one of the chambers of which is filled with deionized water, and the other - successively with a solution of the oxidizing agent ammonium persulfate, and then with a solution of the monomer 2-aminobenzenesulfonic acid, SPAN is formed on the surface of the membrane facing the chamber with solutions of ammonium persulfate and 2-aminobenzenesulfonic acid. Evidence of the formation of SPANI is provided by visual observations of the change in membrane color from yellow (the color of the original membrane) to brown, as well as the ATR IR spectra of the surface of composite anion exchange membranes, which are shown in Fig. 1.

The composition of the original membrane does not contain sulfo groups, which are present in SPANI. The IR ATR spectra of samples 1-4 of composite anion-exchange membranes (curves 1-4 in Fig. 1) contain absorption bands at 612 cm ^-1 and 1084 cm ^-1 , which are caused by symmetric and asymmetric vibrations of CS and O=S=O bonds, which are absent in the spectrum of the original membrane (curve 0 in Fig. 1), which confirms the presence of sulfo groups in composite anion-exchange membranes. The absorption band at 1650 cm ^-1 , which is present in the spectra of composite anion-exchange membranes (curves 1-4 in Fig. 1), is due to vibrations of the quinoid fragments of C=N bonds in SPANI, which are absent in the original membrane. This also confirms the formation of a modifier in the membrane.

To assess the effect of SPAN on the basic physicochemical and electrical transport properties of membranes, the exchange capacity, total moisture content, membrane thickness, specific electrical conductivity and diffusion permeability of the original and composite anion exchange membrane obtained by the proposed method were determined (Table 2). Specific electrical conductivity and diffusion permeability were determined in a 0.5 M sodium chloride solution. The detected decrease in the exchange capacity of the composite anion exchange membrane compared to the original membrane can be explained by the fact that the negatively charged sulfo groups of SPANI compensate for the positively charged amino groups in the composite anion exchange membrane, which as a result cease to participate in ion exchange, which is expressed in an apparent decrease in the exchange capacity. In this case, a significant, 3-fold increase in the specific electrical conductivity of the composite anion-exchange membrane is observed compared to the original anion-exchange membrane. The diffusion permeability of the composite anion exchange membrane is 10% lower compared to the original membrane. The specific electrical conductivity of membranes and their diffusion permeability are the main properties that influence the efficiency of membrane processes for separating and concentrating electrolyte solutions. The higher the specific electrical conductivity, the lower the energy consumption for electrodialysis processes for processing electrolyte solutions. An increase in diffusion permeability has a negative effect on electrodialysis desalting and concentration of solutions due to reverse diffusion of the electrolyte, which has the opposite direction to migration, that is, the lower the diffusion permeability of the membranes, the more effective electrodialysis will be.

Thus, the claimed technical solution meets the patentability criteria, since it has an inventive step, novelty and industrial applicability.

Claims (2)

1. A method for producing a composite anion-exchange membrane, including placing the membrane in working solutions, one of which is a monomer solution, the other is an oxidizing solution, and washing, characterized in that an anion-exchange heterogeneous membrane consisting of polyethylene and an anion-exchange resin with a positive charged nitrogen-containing fixed groups, while the membrane is first placed in an oxidizing solution, which is 1 M ammonium persulfate, and kept for 60 minutes, and then in a monomer solution, which is an aqueous 0.1 M solution of 2-aminobenzenesulfonic acid, and kept for 48 hours, and the membrane is washed in deionized water. 2. The method according to claim 1, characterized in that the membrane is treated in a two-chamber cell formed by a vertically fixed membrane, one of the chambers of which is filled with deionized water, and the other - sequentially with a solution of the oxidizing agent ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ , and then use a solution of 2-aminobenzenesulfonic acid monomer or in a container with working solutions.