RU2566415C1 - Method to change characteristics of electrodialyser with alternating cation- and anion-exchange membranes - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is referred to membrane technique and technology, and namely to electrodialysis. The method to change characteristics of electrodialyser with alternating cation- and anion-exchange membranes includes delivery to the electrodialyser electrode chambers of sulphuric acid solution with concentration of 0.025 M, to desalting cells - 0.005-0.01 M of solution of aniline in mineral acid with concentration of hydrogen ions of 0.05 M, an to concentrate compartment - salt solution with concentration of 0.0005-0.015 M wherein anion of acid residue is the oxidiser in mineral acid with concentration of hydrogen ions of 0.05 M at current density equal to 100-400 A/m² during 60-120 minutes, with further washing of the electrodialyser chambers and cells with distilled water, thereafter the electrodialyser is withhold under current with density of 100 A/m² during 60 minutes with delivery of 0.025 M sulphuric acid solution to all chambers and cells.

EFFECT: reduced power consumption at usage of the electrodialyser.

3 cl, 1 tbl, 2 dwg

Description

The invention relates to membrane technology and technology, namely the technique of electrodialysis.

The properties of electrodialyzers are determined by the features of ion-exchange membranes, which are used in its manufacture. At present, for electrodialysis desalination and concentration of electrolyte solutions, heterogeneous ion-exchange membranes are most often used, which are relatively cheap and at the same time possess the necessary set of physicochemical and electric transport properties. However, depending on the technological task performed by the electrodialyzer, ion-exchange membranes with a specific set of properties may be required. So, to increase the efficiency of electrodialysis concentration of electrolyte solutions, ion-exchange membranes with reduced electroosmotic permeability are required [RF patent No. 2411070, B01D 071/60 (2006.01) Composite ion-exchange membrane / Shkirskaya SA, Sycheva A.A.-R., Berezina N. P., Timofeev S.V., Krishtopa M.V .; FSBEI HPE “Kuban State University”. - No. 20091314/05.].

However, the choice of ion-exchange membranes is limited to commercially available membranes. Therefore, there is a need to develop methods for modifying existing industrial ion-exchange membranes in order to give them the necessary properties. The process of modifying ion-exchange membranes becomes in this case a separate technological stage in the production of the electrodialyzer, prior to its assembly, and requires additional equipment, for example, baths with solutions of modifying agents. Thus, a separate preliminary stage is added to the assembly stages of the electrodialyzer, associated with the production of modified membranes with the necessary properties, which leads to an increase in the manufacturing time and cost of the electrodialyzer.

Known methods that allow you to change the characteristics of a single membrane. So there is a known method of producing a cation exchange composite membrane with simultaneous exposure to the membrane of gradient concentration and electric fields in two stages [RF patent No. 2487145, IPC C08J 5/22 (2006.01), B01D 69/12 (2006.01), B01D 71/32 (2006.01) , H01M 4/94 (2006.01), C08J 5/20 (2006.01), B01D 67/00 (2006.01)]. In this case, the cation exchange membrane separates the cell chambers with solutions of various compositions and concentrations. At both stages, a solution of a 0.005 M solution of sulfuric acid is fed into the chamber from the side of a negatively charged electrode. At the first stage, a 0.01-0.001 M aniline solution is fed into the cell chamber from the side of the positively charged electrode against a background of a 0.005 M sulfuric acid solution. In this case, the membrane is saturated with phenylammonium ions for 15-180 minutes. At the second stage, a 0.01 M solution of iron (III) chloride against a background of a 0.005 M solution of sulfuric acid. Polymerization of aniline in the membrane in the presence of an oxidizing agent (iron (III) chloride) occurs within 60-180 minutes. The process is carried out by passing a constant electric current with a density of 40-100 A / m ² . The disadvantages of this method is that the obtained composite materials are volume-modified, that is, they have a uniform distribution of the modifying component of polyaniline over the volume of the polymer matrix. The use of iron (III) chloride as an oxidizing agent can cause the formation of an iron (III) hydroxide precipitate on the surface of the cation exchange membrane, which will lead to the need for complete disassembly of the electrodialyzer to clean the membranes. In addition, volume-modified composites do not possess the necessary set of properties for a significant change in the characteristics of the electrodialyzer, namely, their diffusion and electroosmotic permeabilities slightly differ from the characteristics of the initial cation-exchange membranes.

A method for changing the characteristics of a finished (assembled) electrodialyzer with alternating cation exchange and anion exchange membranes is not known from the prior art.

The technical task of the invention is the development of a method for changing the characteristics of the finished (assembled) electrodialyzer depending on the intended purpose, for example, as a deionizer or concentrator.

EFFECT: reduced energy consumption of an electrodialyzer with alternating cation exchange and anion exchange membranes when using it.

To achieve the stated result, a 0.005-0.01 M solution of aniline in mineral acid with a concentration of hydrogen ions of 0.05 M is fed to the electrodialyzer with the initial alternating cation-exchange and anion-exchange membranes in the desalination (KO) chambers, and potassium dichromate, potassium permanganate, to the concentration chambers (CC), ammonium persulfate or another salt solution in which the anion of the acid residue acts as an oxidizing agent, with a concentration of 0.0005-0.015 M in sulfuric, hydrochloric or other mineral acid with a concentration of hydrogen ions of 0.05 M, and pass a constant electric current with a density of 80-500 A / m ² for 10-120 minutes. A 0.025 M solution of sulfuric or any other mineral acid is fed into the electrode chambers. Then, the electrodialyzer is washed with distilled water to remove aniline and an oxidizing agent from the chambers. Next, all the electrodialyzer chambers are fed with a solution of mineral acid with a concentration of at least 0.05 M and kept at a current density of 80-150 A / m ² for 1 hour to completely remove aniline and oxidizing agent from the membranes.

The method is suitable for electrodialyzers, consisting of alternating anionic and cation-exchange membranes having flowing concentration and desalination chambers, as well as for electrodialyzers with non-flowing chambers, in which flow through the process of polyaniline synthesis on one of the surfaces of cation-exchange membranes can be arranged. The method allows to reduce energy consumption and increase the current efficiency of the electrodialyzer in the processes of electrodialysis concentration or demineralization of acid solutions.

Upon dissolution of aniline in a solution containing hydrogen cations, for example, in an acid solution, it protonates to form phenylammonium cations. Phenylammonium cations in accordance with the direction of the electric current are transferred to the concentration chamber through a cation exchange membrane. At the same time, the oxidizing anions under the influence of a constant field are transferred to the surface of the cation exchange membrane in CC where they are found with phenylammonium cations. As a result, the synthesis of polyaniline occurs on the surface of the cation exchange membrane facing the concentration chamber.

The figure 1 shows the connection diagram of the electrodialyzer with alternating anion-exchange and cation-exchange membranes. The figure 2 shows the dependence of the current efficiency on the current density on the electrodialyzer in the process of demineralization of a solution of sulfuric acid: a - when the voltage drops on the pair chamber formed by the desalination and concentration chamber, 1V, b - when the voltage drops on the pair chamber 10V, while I the curves corresponding to the initial electrodialyzer are indicated, II - the curves corresponding to the electrodialyzer with MK-40 / PAn composite anisotropic membranes when oriented with a polyaniline layer in KO, III - the curves corresponding to the electrodes an analyzer with composite anisotropic membranes MK-40 / PAn with the orientation of a polyaniline layer in CC.

The proposed method for changing the characteristics of the electrodialyzer was applied to a frame electrodialyzer with internal collectors (Fig. 1) containing polarizing electrodes made of platinum titanium - 1. The electrodialyzer included five cation exchange membranes - 2, six anion exchange membranes MA-41 (JSC Shchekinoazot, Russia) - 3. A grid-separator was placed between the electrodes and membranes, as well as between each pair of membranes. 4. The electrode chambers 5 were separated by anion-exchange membranes 3. Cation-exchange 2 and anion-exchange 3 membrane membranes there were five paired chambers, each of which consisted of a concentration chamber 6 and a desalination chamber 7. Each type of chambers was fed with an electrolyte solution from a separate container: 8 — a container with a solution for electrode chambers 5; 9 - a container with a solution for KO 7; 10 — a container with a solution for CC 6. A solution of sulfuric acid with a concentration of 0.025 M was fed into the electrode chambers 5 from a container 8. The working area of one membrane was 1 dm ² , the intermembrane distance was 0.9 mm, and the electrolyte solution circulated at a linear velocity of 0.02 m / s , which was provided by a multi-channel peristaltic pump (not shown in the diagram). A constant electric current was supplied to the polarizing electrodes 1 by a pulsed DC power source B5-50 - 11. To control the direct current strength, an ammeter was connected in series to the electric circuit, and a voltmeter was connected in parallel to control the voltage drop across the electrodialyzer.

A method for changing the characteristics of an electrodialyzer with alternating cation exchange and anion exchange membranes was carried out in the galvanostatic mode at a polarizing current density in the range from 100 to 400 A / m ² , which was supported by a DC power source 11 for a predetermined time from 60 to 120 minutes. Capacity 8 was filled with a solution of 0.025 M sulfuric acid, from where the solution was supplied to the electrode chambers 5. Capacity 10 was filled with a 0.002 M solution of potassium dichromate in 0.025 M sulfuric acid, from where the solution was supplied in KK 6. Capacity 9 was filled with a 0.01 M solution of aniline in 0.025 M sulfuric acid where the solution was supplied to KO 7. At the end of the specified time of direct current exposure, all containers and the electrodialyzer were washed with distilled water. Then, containers 8, 9 and 10 were filled with a 0.025 M solution of sulfuric acid, which circulated through all electrodialyzer chambers for 1 hour at a polarizing current density of 100 A / m ² to completely remove aniline and potassium dichromate from membranes and electrodialyzer chambers.

Tests of the electrodialyzer before and after changing its characteristics in the mode of demineralization of a solution of sulfuric acid were performed in a potentiostatic mode with a voltage drop on the pair chamber (U _c.p. ) 1, 2, 5, and 10 V. Every 30 minutes, the concentration of sulfuric acid solutions at the inlet and outlet of the concentration and desalination chambers was determined by the conductometric method. The initial concentration of the sulfuric acid solution was 0.01 mol / L.

Tests of the electrodialyzer in the mode of concentration of sulfuric acid were carried out in the absence of flow through the concentration chamber 6. The filling of KK 6 was carried out as a result of the electro-mass transfer of hydrogen cations and sulfate ions through cation and anion exchange membranes, respectively, under the influence of direct electric current. The tests were performed in the galvanostatic mode at polarizing current densities of 0.2, 0.4, 0.7, 1.0, 1.5, 2.0 A / dm ² . During the tests of the electrodialyzer, the volume of the formed sulfuric acid concentrate in KK 6 and its concentration were controlled. The concentration of sulfuric acid in the concentration chamber 6 was determined by acid-base titration with a solution of sodium hydroxide using phenolphthalein as an indicator. In flowing desalination chambers, a constant concentration of sulfuric acid solution of 0.02 mol / L was maintained.

Tests of improved electrodialyzers were carried out when composite anisotropic cation-exchange membranes 2 were installed with a layer of polyaniline in desalination chamber 7 (PAn in KO) and concentration 6 (PAn in KK).

Case Study 1

We take an electrodialyzer containing 2 heterogeneous sulfocationite membranes MK-40 as cation exchange (Shchekinoazot OJSC, Russia). To change the characteristics of an electrodialyzer with alternating cation-exchange 2 and anion-exchange 3 membranes, we maintain a constant polarizing current density of 400 A / m ² on the polarizing electrodes for the first 10 minutes and 100 A / m ² for the next 110 minutes. The total time of exposure to a direct current electrodialyzer to change its characteristics was 120 minutes to obtain a polyaniline layer on the surface of MK-40 cation exchange membranes 2 from the side of the concentration chamber 6, and then for 60 minutes to remove phenylammonium and potassium cations and dichromate anions from ion-exchange membranes 2, 3 and chambers 6, 7 of the electrodialyzer.

Tests of the initial electrodialyzer were carried out in the mode of demineralization and concentration of sulfuric acid solutions until its characteristics changed. In the same modes, tests of the electrodialyzer with changed characteristics were carried out.

Evaluation of energy costs for electrodialysis demineralization of sulfuric acid from 0.01 to 0.001 mol / l showed that this value depends on the operating voltage on the electrodialyzer (Table 1). At low values of the voltage drop across the pair chamber (U _cc = 1 and 2V), the energy consumption is almost the same for the initial electrodialyzer and electrodialyzer with altered characteristics when installing MK-40 / PAn 2 cation-exchange membranes with a polyaniline layer in CC 6. When installing cation-exchange membranes MK-40 / PAN 2 with a layer of polyaniline in KO 7 energy consumption is 1.27 times higher compared to the original electrodialyzer. Further increase in U _p.k. leads to a reduction in energy consumption for an electrodialyzer with changed characteristics compared to the original electrodialyzer, regardless of the installation of cation exchange membranes 2. Thus, at U _c.p. = 10V, energy consumption decreases after changing the characteristics of the electrodialyzer compared to the original 1.4-1.6 times.

The current efficiency (ŋ) in the process of demineralization of sulfuric acid is different for the initial electrodialyzer and electrodialyzer with changed characteristics. So at low values of the voltage drop across the pair chamber (U _pk = 1V and U _pk = 2V), the current efficiency for both electrodialyzers is almost the same (Fig. 2, a). With an increase in U _sc up to 5V current output for an electrodialyzer with changed characteristics slightly exceeds the current output of the original electrodialyzer. When the voltage to the pair chamber is increased to 10 V, the current output for the electrodialyzer with changed characteristics increases approximately 2 times compared to the original electrodialyzer (Fig. 2, b).

Tests of electrodialyzers in the mode of concentration of sulfuric acid showed that energy consumption decreases after applying the proposed method of changing the characteristics of the electrodialyzer. So at a current density of 2 A / dm ^{2, the} energy consumption for the release of 1 mol of sulfuric acid from a 0.025 M solution is 0.73 kWh / mol for the initial electrodialyzer, for the electrodialyzer with altered characteristics when MK-40 / PAN 2 cation-exchange membranes are installed with a layer of polyaniline in KO 7 and KK 6 - 0.68 and 0.56 kWh / mol, respectively. The content of sulfuric acid in the concentrate at high current densities is approximately the same before and after changing the characteristics of the electrodialyzer and reaches about 1 mol / l at a current density of 2 A / dm ² .

Table 1 Energy consumption for demineralization of 1 m ³ sulfuric acid solution from an initial concentration of 0.01 mol / l to 0.001 mol / l U _s.c. , B W, kW · h / m ³ Source Electrodialyzer Electrodialyzer with anisotropic composite cation exchange membranes MK-40 / PAn PAN in KO PAn in QC one 0.85 1.08 0.87 2 1.66 2.10 1.57 5 4.62 3.84 3.61 10 16.72 12.10 10.70

Case Study 2

An electrodialyzer was used as the initial electrodialyzer, containing 2 sulfocationiconite homogeneous perfluorinated MF-4SK membranes (Plastpolymer OJSC, Russia) as cation exchange membranes, which are similar to Nafion membranes (DuPont, USA). These membranes possess higher chemical resistance in comparison with MK-40 heterogeneous electrodialysis membranes (JSC Shchekinoazot, Russia), therefore they are more suitable for use in electrodialysis processing of acid solutions. A method for changing the characteristics of an electrodialyzer with alternating cation-exchange and anion-exchange membranes was implemented while maintaining a constant polarizing current density of 400 A / m ² on the polarizing electrodes 1 for the first 10 minutes and 100 A / m ² for the next 50 minutes. The total time of exposure to a direct current electrodialyzer to change its characteristics was 60 minutes to obtain a polyaniline layer on the surface of cation exchange membranes 2 MF-4SK from the side of the concentration chamber 6, and then 60 minutes to remove phenylammonium and potassium cations and dichromate anions from ion exchange membranes 2, 3 and chambers 6, 7 of the electrodialyzer.

Tests of the initial electrodialyzer were carried out in the mode of demineralization and concentration of sulfuric acid solutions until its characteristics changed. In the same modes, tests of the electrodialyzer with changed characteristics were carried out.

Tests of the electrodialyzer with changed characteristics in the mode of demineralization of a solution of sulfuric acid showed that when installing cation-exchange membranes MF-4SK / PAN 2 with a polyaniline layer in KK 6 at values of U _bp = 5B and U _sc = 10B there is a decrease in energy consumption by about 1.2 times compared with the original electrodialyzer. However, when installing MF-4SK / PAN 2 cation-exchange membranes with a polyaniline layer in KO 7, the demineralization efficiency is very low and the process in this mode is not practical.

As a result of studying the mass transfer and energy characteristics of the electrodialyzer when operating in the mode of concentration of a solution of sulfuric acid, it was found that the application of the proposed method for changing the characteristics of the electrodialyzer led to an increase in the content of H ₂ SO ₄ in the concentrate by an average of 35% compared with the concentrate obtained using the original electrodialyzer while reducing energy costs by 10%.

Based on the foregoing, it can be argued that the claimed technical solution is industrially applicable, is new, has an inventive step, i.e. is an invention.

Claims (3)

1. A method for changing the characteristics of an electrodialyzer with alternating cation-exchange and anion-exchange membranes, comprising supplying a solution of sulfuric acid with a concentration of 0.025 M to the electrode chambers of the electrodialyzer, and a 0.005-0.01 M solution of aniline in mineral acid with a concentration of hydrogen ions of 0.05 M in the desalination chambers and in the concentration chamber - a salt solution with a concentration of 0.0005-0.015 M, in which the anion of the acid residue is an oxidizing agent, in mineral acid with a concentration of hydrogen ions of 0.05 M, at a current density of 100-400 A / m ² for 60-120 minutes, followed by washing the containers and chambers of the electrodialyzer with distilled water, after which the electrodialyzer is kept at a current density of 100 A / m ² for 60 minutes when a 0.025 M sulfuric solution is supplied to all chambers of the electrodialyzer acids. 2. The method according to p. 1, characterized in that as the cation exchange membranes, the electrodialyzer contains heterogeneous sulfocationite membranes MK-40. 3. The method according to p. 1, characterized in that, as cation exchange membranes, the electrodialyzer contains homogeneous sulfocationite perfluorinated membranes MF-4SK.

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