RU2612269C1 - Method of producing composite anion-exchange membrane - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing anion-exchange membranes with improved electrotransport characteristics used in the electrodialysis apparatus for processing of various technological solutions. The method of producing an anion-exchange membrane comprises placing of the anion-exchange membrane with positively charged fixed groups in a two-compartment cell formed by vertically fixed membrane, one of its chambers is filled with water, the other one is filled consecutively with (NH₄)₂S₂O₈ ammonium persulfate solution, then with 1 M aniline solution prepared at 1 M HCl, characterized by using 0.5 M (NH₄)₂S₂O₈ ammonium persulfate made with 1 M HCl solution, and the membrane is being reacted by the resulting ammonium persulfate solution for 10-30 minutes, then the aniline solution is used for 10-30 minutes, wherein the positively charged fixed groups of anion-exchange membrane are nitrogen-containing.

EFFECT: invention reduces the time of producing anion-exchange composite membrane with a layer of polyaniline showing high conductivity.

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Description

The invention relates to a method for producing anion-exchange membranes with improved electrical transport characteristics used in electrodialysis apparatus for processing various technological solutions.

A known method of producing a composite ion-exchange membrane modified by polyaniline [patent for the invention of the Russian Federation No. 2411070 Composite ion-exchange membrane MPK Β01D 71/60 (2006.01) / Shkirskaya SA, Sycheva A.A.-R., Berezina NP, Timofeev S.V., Krishtopa M.V. - No. 2009131427/05; Claim 08/18/2009; Publ. 02/10/2011]. The perfluorinated sulfonic cation-ion exchange membrane MF-4SK was preliminarily kept in an HCl solution for conversion to the H ⁺ form, and then vertically fixed between the chambers of the two-chamber cell, a 1 M solution of protonated aniline (C ₆ H ₅ NH ₃ ⁺ ) was poured into one of its chambers, and distilled water into another. For an hour, the matrix was saturated with protonated aniline ions by the mechanism of exchange and non-exchange sorption. Then, the protonated aniline solution was replaced by a polymerizing solution, which was taken as an aqueous solution of 0.1 M ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ . The contact time with the polymerizing solution ranged from 1 to 3 hours. The polyaniline barrier layer was obtained by sequential diffusion of solutions of protonated aniline and ammonium persulfate through a membrane into water.

In cation-exchange membranes, both on a perfluorinated and on a polystyrene matrix, the phenylammonium ion monomer (An ⁺ ) is a counterion, therefore this method is not applicable for modification of the anion-exchange membrane.

The closest analogue to the claimed method is a method for producing a composite anion-exchange membrane with polyaniline, namely, that a membrane based on styrene copolymer crosslinked with divinylbenzene is successively exposed to an aqueous solution of 1 M ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ for 1 hour, and then 10% aniline in 1M HCl for 1 or 2, or 3, or 4 hours in a two-chamber cell [RK Nagarale, GS Gohil, VK Shahi, GS Trivedi, R. Rangarajan Preparation and electrochemical characterization of cation- and anion-exchange / polyaniline composite membranes // J. Colloid and Interface Science 2004. V. 277. P. 162-171]. The disadvantages of the method include the length of the production process and the fact that such a production method does not lead to a significant increase in the electrical conductivity of the obtained composite membrane. So with a 5-hour modification, an increase in membrane conductivity by 10% is achieved.

The technical result of the claimed invention is to reduce the time to obtain an anion-exchange composite membrane with a polyaniline layer having high electrical conductivity.

To achieve a technical result, anion-exchange membranes with nitrogen-containing positively charged fixed groups, for example, MA-40 or MA-41 membranes, can be taken vertically in a two-chamber cell, one of the chambers of which is filled with water and the other with solutions of various compositions and concentrations. First, 0.5 M ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ prepared on 1 M HCl is used as a solution and exposed for 10-30 minutes, and then a solution of 1 M aniline on 1 M HCl for 10-30 minutes.

Distinctive features of the proposed method in comparison with the prototype are:

- halving the concentration of a solution of ammonium persulfate and the use of hydrochloric acid for its preparation,

- reducing the time taken to obtain the membrane, 2-5 times.

In fig. 1 shows the kinetics of changes in the conductivity of a solution in a chamber with water during the diffusion of an aqueous solution of 1 M (NH ₄ ) ₂ S ₂ O ₈ ; in fig. 2 - kinetics of changes in the conductivity of a solution in a chamber with water during the diffusion of a 1M solution of aniline hydrochloride; in fig. 3 - concentration dependences of the electrical conductivity of the MA-41 membranes (curve 1) and the MA-41 / PAn membrane (curve 2) obtained in Example 1 in a solution of sodium chloride; in fig. 4 - kinetics of changes in the conductivity of solutions in a chamber with water during the diffusion of an aqueous solution of 0.3 M (NH ₄ ) ₂ S ₂ O ₈ , Fig. 4a) and 0.5 M aniline hydrochloride, Fig. 4b); in fig. 5 - concentration dependence of the electrical conductivity of the membranes MA-41 (curve 1) and MA-41 / PAn (curve 2) obtained in example 2 in a solution of sodium chloride; in fig. 6 - kinetics of changes in the conductivity of a solution in a chamber with water during the diffusion of a solution of 0.5 M (NH ₄ ) ₂ S ₂ O ₈ + 1 M HCl, Fig. 6a) and 1 MC ₆ H ₅ NH ₂ + 1 M HC1, Fig. 6b) through the MA-41 membrane; in fig. 7 - kinetics of changes in the conductivity of a solution in a chamber with water during the diffusion of a solution of 0.5 M (NH ₄ ) ₂ S ₂ O ₈ + 1 M HCl, Fig. 7a) and 1 MC ₆ H ₅ NH ₂ +1 M HCl, Fig. 7b) through the MA-40 membrane; in fig. 8 - concentration dependence of the electrical conductivity of the original membrane (curve 1) and the composite with polyaniline based on it (curve 2) in a solution of sodium chloride: Fig. 8a) MA-41 and MA-41 / PAn, Fig. 8b) MA-40 and MA-40 / PAn; in fig. 9 - concentration dependences of the water transfer numbers of the studied membranes MA-40 (curve 1), MA-40 / PAn (curve 2) obtained according to example 4 in NaCl solutions. In Figures 3, 5, 8, 9, curves 1 refer to the data for the original membranes, and curves 2 to the data for the modified membranes.

Example 1

The heterogeneous anion-exchange membrane MA-41 was used as the initial membrane. The original membrane separates the cells of the non-flowing cell, in one of which is distilled water, and in the other we pour the solutions sequentially. First, pour a 1 M aqueous solution of ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) into the cell chamber, which is an oxidizing agent for the aniline polymerization process. The diffusion process takes place with stirring for an hour. The kinetics of changes in the conductivity of solutions in a chamber with water was measured. Moreover, in fig. 1 shows the change in the slope of the curve after 35 minutes. This means that at first the diffusion of the (NH ₄ ) ₂ S ₂ O ₈ solution is 1.7 times slower. This can be explained by the fact that within 35 minutes the ion exchange process between the chlorine counterions and persulfate ions diffusing through the membrane occurs, therefore, the diffusion of the solution (NH ₄ ) ₂ S ₂ O _{8 is} inhibited.

Then the usual process of diffusion of the S ₂ O ₈ ^2– ion proceeds, without additional inhibitory effects, as a result of which the speed of the diffusion process into the chamber with water increases.

Then the solution is replaced with a solution of 1 M aniline prepared in 1 M HCl (aniline hydrochloride). The process lasts for an hour. We observe the change in conductivity in a chamber with water by measuring the resistance of water conductometric (Fig. 2). As can be seen from fig. 2, the diffusion process of the aniline hydrochloride solution proceeds with a change in speed. First, the exchange of persulfate counterions to chlorine ions occurs, accompanied by non-exchange sorption of phenylammonium coions (the first section on the curve). Further, after 20 minutes, the process speed drops sharply as a result of the formation of polyaniline on the surface of the MA-41 heterogeneous membrane, which exhibits blocking properties for ion transfer.

After that, the solutions are drained and the membrane is washed from the solutions with water, and then placed in a solution of 1 M HCl to convert polyaniline to the conductive form of emeraldine salt. The resulting composite membrane has a dark green color on the one hand, and on the other remains yellowish, like the original one. Then the membrane was balanced with NaCl solutions of various concentrations for conducting experiments to determine electrical conductivity. From fig. It can be seen from Fig. 3 that, when passing from the initial membrane to the modified one, the conductivity decreases by about 25%.

Example 2

Studies have been conducted to obtain a composite based on MA-41 using lower concentrations of solutions, but with an increase in synthesis time. As solutions, a 0.3 M aqueous solution of (NH ₄ ) ₂ S ₂ O _{8 was used} , which was passed through the membrane for 1 hour, and then a solution of 0.5 M aniline against 0.5 M HCl for 1 hour. From fig. Figure 4a shows that the change in water conductivity as a function of diffusion time of an aqueous solution of 0.3 M (NH ₄ ) ₂ S ₂ O ₈ through the membrane is linear, i.e. during the entire experiment, an ion exchange takes place between the chlorine counterions and persulfate ions diffusing through the membrane. The change in the slope of the curve in Fig. 4b indicates that the diffusion of 0.5 M aniline hydrochloride proceeds with a change in the process rate. First, a faster process of exchange of persulfate counterions to chlorine ions occurs, accompanied by non-exchange sorption of phenylammonium coions. Then the speed of the process decreases by about half. This suggests that a layer of polyaniline has formed on the surface of the membrane, which makes it difficult to transfer the solution through the membrane.

The study of the electrical conductivity of the obtained MA-41 / PAn composite showed a decrease in this characteristic in comparison with the initial MA-41 membrane. From fig. 5 it is seen that the conductivity values for the samples obtained in example 2 are reduced by 50% compared with the original membrane. From literary sources [S. Tan, D. Be'langer Characterization and Transport Properties of Nafion / Polyaniline Composite Membranes // J. Phys. Chem. B. 2005. V. 109. P. 23480-23490.] It is known that a decrease in the concentration of solutions used to modify cation-exchange membranes leads to the formation of longer polyaniline chains and higher electrical conductivity, but a decrease in electrical conductivity occurs on anion-exchange membranes.

Analyzing the kinetics of the transfer of solutions during the synthesis, it can be concluded that the polyaniline layer using the synthesis of example 1 or 2 is formed 20-25 minutes after the start of transfer of aniline monomer.

Example 3

The heterogeneous anion-exchange membrane MA-41 was used as the initial membrane. The original membrane separates the cells of the non-flowing cell, in one of which is distilled water, and the solutions are successively poured into the other. First, a 0.5 M solution of ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) prepared in a 1 M HCl solution for 30 minutes is poured into the cell’s working chamber. Then the solutions are drained and 1 M aniline hydrochloride (1 MC ₆ H ₅ NH ₂ + 1 M HCl) is poured into the chamber as a working solution for 30 minutes. The diffusion transfer of solutions takes place with stirring.

A study of the kinetics of aniline polymerization by changing the conductivity in a chamber with water showed the nature of the dependences, similar to that in Example 1 (Figs. 1, 2), but the processes proceed more rapidly due to the presence of acid in a solution of ammonium persulfate (Fig. 6a). A change in the slope of the curve by about 2 times (Fig. 6b) indicates that the process of diffusion of the aniline hydrochloride solution proceeds with a change in speed. First, the exchange of persulfate counterions to chlorine ions occurs, accompanied by non-exchange sorption of phenylammonium coions (the first section on the curve). Further, 10 minutes after the start of the diffusion process of aniline hydrochloride, the process speed drops sharply as a result of the formation of polyaniline on the surface of the heterogeneous MA-41 membrane, which exhibits blocking properties for ion transfer. To terminate the aniline polymerization process, the solution is drained and the membrane is washed from the working solution with water, and then placed in 1 M HCl to convert polyaniline to the conductive form of emeraldine salt. The resulting composite membrane has a dark green color on the one hand, and on the other remains yellowish, like the original one.

Example 4

The heterogeneous anion-exchange membrane MA-40 was used as the initial membrane. The original membrane separates the cells of the non-flowing cell, in one of which is distilled water, and the solutions are successively poured into the other. The diffusion transfer of solutions takes place with stirring. First, a 0.5 M solution of ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) prepared in a 1 M HCl solution for 30 minutes is poured into the cell’s working chamber. Then the solutions are drained and 1 M aniline hydrochloride (1 MC ₆ H ₅ NH ₂ + 1 M HCl) is poured into the chamber as a working solution for 30 minutes. Moreover, in fig. 7a) the change in the slope of the curve is visible after 10 minutes. This means that at first the diffusion of the (NH ₄ ) ₂ S ₂ O ₈ solution proceeds more slowly due to the ion exchange process between the chlorine counterions and persulfate ions diffusing through the membrane; therefore, the diffusion of the (NH ₄ ) ₂ S ₂ O ₈ solution is inhibited. Then the usual process of diffusion of the S ₂ O ₈ ^2– ion proceeds, without additional inhibitory effects, as a result of which the speed of the diffusion process into the chamber with water increases.

A study of the kinetics of aniline polymerization by changing the conductivity in a chamber with water showed (Fig. 7b)) a decrease in the slope of the curve by about 2 times 10 min after the start of the diffusion process of aniline hydrochloride. This indicates that the formation of the polyaniline layer occurs after 10 minutes, and then the epitaxial growth of polyaniline chains occurs after 10-15 minutes and until the termination of the polymerization process. Then the solutions are drained and the membrane is washed from the working solutions with water, and then placed in a solution of 1 M HCl to convert polyaniline to the conductive form of emeraldine salt. The resulting composite membrane has a dark green color on the one hand, and on the other remains yellowish, like the original one.

The membranes made according to examples 3, 4 were balanced with NaCl solutions of various concentrations for conducting experiments to determine the electrical conductivity. The study of the electrical conductivity of composites MA-41 / PAn and MA-40 / PAn showed a significant increase in electrical conductivity by 50% compared to the initial membranes (Fig. 8), which was achieved for the first time. Thus, the use of anion-exchange membranes with a layer of polyaniline in electrodialysis processes will lead to a decrease in energy consumption due to an increase in the conductivity of the electro-membrane system.

It is known that the main characteristics that determine the efficiency of the concentrator electrodialyzer are productivity and salinity. Productivity is determined by current efficiency, and salinity is determined by electroosmotic and osmotic water transfer and the effect of backdiffusion of the concentrate from the concentration chamber to the desalination chamber. In the work [K.V. Protasov, S.A. Shkirskaya, N.P. Berezina, V.I. Zabolotsky // Electrochemistry. 2010. - T. 46, - No. 10. - S. 1209-1218.] It is shown that the electroosmotic transfer of water has a decisive role in the electrodialysis concentration process, while the influence of the diffusion component of the salt stream is negligible. Therefore, to assess the effectiveness of the use of the obtained composites in electrodialysis processes, the electroosmotic permeability was studied, the quantitative characteristic of which is the water transfer numbers. A study of the concentration dependences of the water transfer numbers of the initial MA-40 anion-exchange membranes and composites with MA-40 / PAn polyaniline (Fig. 9) showed that the modification with polyanine led to a slight increase in the numbers of water transfer through the composite membrane. This increase is (10-15)% relative to the original MA-40 membrane in the concentration range from 0.1 M to 0.75 M NaCl. With a further increase in the concentration to 3 M, the differences in the values of the water transfer numbers for the initial and modified membranes do not go beyond the experimental error. Further introduction of polyaniline into the anion exchange membrane is impractical because under the selected conditions for the production of composite membranes, we achieve our goal with the least time and optimal set of their properties.

The specified set of essential features provides a technical result, namely:

- reduction of the manufacturing time of the composite membrane by 2-5 times;

- the resulting membrane has greater electrical conductivity, which makes it promising to use it in electrodialysis machines.

Claims (1)

A method for producing an anion exchange membrane, comprising 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, characterized in that a 0.5 M ammonium persulphate (NH _{4) 2} S ₂ O ₈ solution prepared in 1 M HCl, and act on the membrane with the resulting solution of ammonium persulfate in those ix 10-30 minutes and then used aniline solution over a period of 10-30 minutes while positively charged fixed groups are nitrogen-containing anion exchange membrane.

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