RU2366616C1 - Method for electrochemical treatment of water salt solutions and device thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: treatment of water solutions in diaphragm electrolyser is carried out at specific electricity quantity not less than 12000 C/l and current density not less than 4000 A/m² up to redox potential of catholyte more than 1000 mV and anolyte more than 1300 mV. The device is designed as diaphragm electrolyser containing the tank separated with ion-permeable membrane to two chambers (cathode and anode) where the corresponding electrodes are vertically mounted. The tank walls and diaphragm are corrugate; solution feeding is carried out with ejector nozzles. The diaphragm can be made planar and electrodes tubular or rod-shaped. The diaphragm can be cylindrical and located in the tank centre forming thus the inner chamber in which centre the tubular or rod-shaped electrode is positioned, the second electrode is cylindrical and mounted coaxially to the diaphragm in the outer chamber.

EFFECT: quality enhancing of obtained production.

4 cl, 4 dwg, 1 tbl

Description

The invention relates to the electrochemical treatment of aqueous solutions. It can be used mainly for the treatment of salt solutions for the industrial production of metal hydroxides (alkalis) and acids from them.

Known methods for the electrochemical activation of aqueous solutions in a diaphragm electrolyzer, in which the final product of a given quality is achieved by providing a given value of the redox potential eh of catholyte and anolyte, in which for activating the aqueous solution the eh value is not more than 850 mV (RF patent No. 2221753, C02F 1/46, 2004) (1).

This method is applicable for the activation of aqueous solutions and does not provide complete cleavage of the solution molecules (electrolysis), and therefore cannot be used to obtain alkalis and acids from salts, i.e. in fact, is not an analogue of the invention.

A known method of electrochemical processing of salt solutions in a diaphragm electrolyzer with obtaining acid in the anode chamber and alkali in the cathode. In this method, electrolysis is carried out at a specific amount of electricity of 3000-4500 C / l (according to the applicant's claims), in which the eh of catholyte is - (910-940) mV, and the eh of anolyte + (1250-1260) mV at a current density of 156.25 A / m ² (RF patent No. 2236893, B01D 53/34, 2003) - prototype (2).

The disadvantages of this method are the insufficient quality of the products obtained, as well as the low productivity due to the low values of the specific amount of electricity and current density and, as a result, the values of the redox potential of eh catholyte and anolyte are not high enough.

So, the purity of the products obtained by the prototype method is not more than 90%, while, for example, according to GOST 2263 "Sodium hydroxide" should be at least 94.0 wt.% Sodium hydroxide for grade I and 98.5% - for higher, according to GOST 2184 “Sulfuric acid” not less than 92.5 wt.% sulfuric acid for grades I and II and 92.5-94.0 for improved.

Known devices for the electrochemical treatment of aqueous solutions in the form of a diaphragm electrolyzer containing a container divided by an ion-permeable diaphragm into two chambers, each of which has at least one electrode connected to the corresponding pole of a direct current source (for example, RF patent No. 2177454 , C02F 1/46, 2001) (3).

The disadvantages of these devices are inadequate performance at high energy costs, as well as insufficient quality of the finished product due to uneven processing throughout the fluid volume and the formation of stagnant zones.

Closest to the proposed one is a device for electrochemical activation of a liquid in the form of a diaphragm electrolyzer, in which, in addition to the mentioned features (3), the electrodes in the chambers are placed vertically, which somewhat improves the conditions for interaction with the treated solution, and there are also liquid flow distributors made in the form perforated pipes connected to the pump (RF patent No. 2221753).

The disadvantages of this solution are the insufficient uniformity of the distribution of eh over the volume of liquid, because electrodes are placed on the periphery of the chamber, as well as the complexity and cost of the structure due to the presence of additional flow distributors with its own pump.

The technical task of the proposed method is to improve the quality of the finished product (acids and alkalis) by providing deep electrolysis of the initial salt solutions.

The technical task of the device for implementing this method is to increase the efficiency of electrolysis by increasing the uniformity of the distribution of eh over the volume of liquid while simplifying and cheapening the design.

The stated technical problem is solved in that in the method for the electrochemical treatment of aqueous solutions of salts in a diaphragm electrolyzer, the treatment is carried out with a specific amount of electricity of at least 12,000 C / l and a current density of at least 4000 A / m ² , with a numerical value of the redox potential of catholyte - not less than 1000 mV and anolyte - at least 1300 mV.

With such parameters of electrochemical treatment, deep electrolysis of water-soluble salts occurs, i.e. complete decomposition of the starting reagents into an acidic component (acids) and an alkaline (alkali, alkaline-earth or transition metal hydroxides), as a result of which a finished product of high purity is obtained in accordance with the requirements of state standards.

The stated technical problem is also solved by the fact that in the device for implementing this method, made in the form of a diaphragm electrolyzer, containing a capacitance divided by an ion-permeable diaphragm into two chambers, anode and cathode, in which the corresponding electrodes are vertically mounted, and there are also means for supplying chambers of the initial solution, new is that to ensure uniform processing by distributing eh over the entire volume of the treated solution and eliminating stagnant zones with Enki container and diaphragm are corrugated, the means for supplying solution formed as the ejector nozzles and the electrodes are mounted in the central zone of chambers.

In this case, the diaphragm can be made planar, and the electrodes tubular or rod.

To increase the efficiency of electrolysis by increasing the area of contact of the liquid with the electrodes, the diaphragm can be made in the form of a cylinder placed in the center of the tank with the formation of an inner chamber, in the center of which there is a tubular or rod electrode, and the second electrode is cylindrical and mounted coaxially with the diaphragm in the outer chamber .

The proposed device is schematically shown in the drawing, where:

figure 1 - is a General view, a longitudinal section, option I;

figure 2 is a section aa in figure 1;

figure 3 is a General view, a longitudinal section, option II;

figure 4 is a section bB in figure 3.

The proposed method is carried out in a diaphragm electrolyzer, both chambers of which, cathodic and anodic, are filled with an initial aqueous solution of inorganic or organic metal salts: alkaline (Na, K), alkaline-earth (Ca, Mg), transition (Fe). The process is conducted with a specific amount of electricity of at least 12,000 C / l and a current density of at least 4000 A / m ² , with a numerical value eh of catholyte - from 1000 mV, and anolyte - from 1300 mV. This ensures complete decomposition (electrolysis) of the initial solution into acidic and alkaline components and the formation of acids in the anode zone (H ₂ SO ₄ , HNO ₃ , CH ₃ COOH, etc.), and in the cathode zone, hydroxides (for example, NaOH, KOH , Ca (OH) ₂ , Mg (OH) ₂ , etc.) according to chemical reactions 1-5 on the example of sodium salts:

Table 1 shows the results of a study of the effectiveness of electrolysis of saline solution depending on the process parameters.

Table 1 The dependence of the efficiency of electrolysis on process parameters Current strength, I, A Current density, d, A / m ² Specific amount of electricity q, C / l Redox potential, eh, mV The electrolysis efficiency of the product yield,% Catholyte Anolyte 6000 3000 9000 -950 +1250 74 7000 3500 10500 -970 +1280 82 7500 3750 11250 -980 +1290 91 8000 4000 12000 -1000 +1300 94 9000 4500 13500 -1010 +1320 96 10,000 5000 15,000 -1020 +1350 99

A device for implementing this method is a diaphragm electrolyzer containing in the first embodiment (Fig. 1-2) a rectangular container 1 of a dielectric material with corrugated walls 2, divided by an ion-permeable planar diaphragm 3 into two chambers 4 and 5. In the center of each chamber vertically mounted, at least one electrode 6 and 7 of a tubular or rod shape, electrically connected to the opposite poles of a direct current source (not shown), resulting in one of electrodes, in particular 6, is positively charged, i.e., anode, and electrode 7 is negatively charged, i.e. cathode, with the possibility, if necessary, of changing their polarity.

In the lower part of the tank there is a means for feeding the source solution into the chambers, made in the form of a collector 8, with ejector nozzles 9 with suction nozzles 10 located in the chambers 4 and 5. In the upper part of the tank 1 there are nozzles 11 for outputting the finished product.

In the second embodiment (Figs. 3-4), the diaphragm 3 is made in the form of a cylinder with a corrugated surface mounted vertically in the center of the container 1, while one of the chambers 4 is located in the inner cavity of the diaphragm, and the second 5 is outside. A tubular or rod electrode 6 is vertically placed in the center of the chamber 4, and an electrode 7 made in the form of a cylinder is mounted coaxially to the diaphragm 3 in the chamber 5. In this case, the container 1 may be rectangular or round (preferable).

The first variant of the device (Fig.1-2) is easier to manufacture, however, the second variant (Fig.3-4) is more effective due to the increase in the contact area of the treated solution with the electrodes and a more uniform distribution of eh throughout the liquid volume.

The device operates as follows.

The processed salt solution is fed into the chambers 4 and 5 through the ejector nozzles 9, which ensure the vortex formation of fluid flows, the interaction of which with the corrugated walls 2 of the vessel and the corrugated diaphragm 3 enhances this vortex formation. This prevents the formation of stagnant zones and contributes to a more uniform mixing of the layers and, therefore, more efficient processing of the entire mass of liquid in the chambers. The placement of electrodes in the center of the chamber also contributes to this.

An electric current is supplied from the current source to the electrodes with the specified parameters given in the description of the “Method”, which provides the specified eh values of catholyte and anolyte, as a result of which acid is formed in the anode chamber and hydroxides are formed in the cathode chamber, which are removed from the outlet pipes 11 from apparatus. The cycle is repeated.

Claims (4)

1. The method of electrochemical treatment of aqueous solutions of salts in a diaphragm electrolyzer, characterized in that the treatment is carried out at a specific amount of electricity of at least 12,000 C / l and a current density of at least 4000 A / m ² until the numerical value of the redox potential of catholyte is at least 1000 mV and anolyte not less than 1300 mV. 2. Device for the electrochemical treatment of aqueous solutions of salts, made in the form of a diaphragm electrolyzer, containing a container divided by an ion-permeable diaphragm into two chambers, in each of which at least one electrode is vertically mounted, means for supplying the source solution to the chambers, characterized the fact that the walls of the tank and the diaphragm are corrugated, the means for supplying the solution is made in the form of an ejector nozzle, and the electrodes are placed in the central zone of the chambers. 3. The device according to claim 2, characterized in that the diaphragm is made planar, and the electrodes are tubular or rod. 4. The device according to claim 2, characterized in that the diaphragm is made cylindrical and installed in the center of the vessel with the formation of an inner chamber, in the center of which a tubular or rod electrode is placed, and the second electrode is made cylindrical and mounted in the outer chamber coaxially with the diaphragm.

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