The method of water desalination in electrodialyzer

 

The invention relates to electrochemical technology and can be used in power, chemical, metallurgical, dairy industries, in water treatment for drinking water. A method of water desalination in electrodialyzer with alternating cation-exchange and anion-exchange membranes forming chamber concentration and desalination, with a periodic change of direction of electric current and simultaneously switching threads cameras desalting and concentration, which is in the process of desalting using two pairs of electrodes, working together to change the direction of the electric current, and the anode of one pair and the cathode of the other of the pair located on one side of the filter presnogo package, anodes made of film-forming metal with a coating of metal oxides as cathodes from non-corroding cast metal. The method provides the possibility of achieving high current densities, which increases the degree of demineralization and performance process. 13 C.p. f-crystals, 1 tab., 1 Il.

The invention relates to electrochemical technology and can be used in which otoke for drinking water.

A known method of purification of aqueous solutions by electrodialysis in electrodialyzer using chemically resistant electrodes of platinized titanium (Smagin Century. N. Water treatment by means of electrodialysis. - M.: stroiizdat, 1986, S. 110).

However, the scarcity of platinum hinder the dissemination of these electrodes.

A known method of purification of an aqueous solution of zinc sulfate by means of electrodialysis using a graphite anode and cathode (patent USSR No. 1837950, CL 01 D 61/44, 1993).

These electrodes are relatively easily damaged, especially in the presence of organic matter, have a low electrical conductivity, dissolved when working with high current densities.

The closest in technical essence is a method of water desalination in electrodialyzer with periodic change of polarity of the electrodes and simultaneously switching threads cameras desalting and concentration (USSR author's certificate No. 982712, CL 01 D 13/02, 1982).

Changing the polarity of the electrodes essentially means changing the direction of electric current. The known method is carried out using graphite electrodes.

These electrodes comparative is, that, in turn, provides a high degree of demineralization and, as a consequence, the productivity of the process is very low.

The technical result of the present invention is the ability to achieve high current densities, which allows to increase the degree of demineralization and increase the productivity of the process.

The invention consists in that the known method of water desalination in electrodialyzer with alternating cation-exchange and anion-exchange membranes forming chamber concentration and desalination, with a periodic change of direction of electric current and simultaneously switching threads cameras desalting and concentration, use two pairs of electrodes, working together to change the direction of the electric current, and the anode of one pair and the cathode of the other of the pair located on one side of the filter presnogo package. Anodes made of film-forming metal with a coating of metal oxides as cathodes from non-corroding cast metal.

Using an anode made of titanium or tantalum, as a coating anodes using ruthenium oxide, cobalt oxide or dioxide, margant the ut to be made of the same or different materials, the anodes from the same or different film-forming metal, and the coating of the anodes from the same or different metal oxides.

As a film-forming metal, preferably titanium or tantalum because of their high chemical resistance, and as a coating to apply the oxides of metals, persistent during electrolysis, such as manganese, cobalt and ruthenium.

The choice of metal oxide applied to the film-forming base, depends on economic considerations and composition of water entering the desalination, for example, in the case of cleaning chloride solutions the advantage of performing coating of ruthenium oxide, because of the resulting electrodes ORTA provide the slope of the polarization curves, equal to 40-45 mV. At the anode mainly highlight the chlorine and the data electrodes is less sensitive to the presence in water of organic compounds.

Anodes with a coating of cobalt oxide of OCT more economical, but also more sensitive to impurities.

Anodes with a coating of manganese dioxide is recommended for cleaning sulfate and phosphate solutions.

As cathodes can be used non-corroding cast metal, because in the process of electrodialysis metal is under canie and easy-to-machine metals.

In the implementation process, the electrodes of the two pairs can be of identical or different materials, for example, both of the anode can be made of titanium or one of titanium and the other of tantalum. You can also use the same coating electrodes, such as cobalt oxide or ruthenium oxide.

Similarly, the cathodes of both pairs can be made from a single material, for example stainless steel, or different from, for example, stainless steel and copper.

The essence of the method is illustrated by a drawing, which schematically shows electrodialyzer.

Electrodialyzer contains the first pair of electrodes 1 and 2, the second pair of electrodes 3 and 4, 5 cation exchange and anion-exchange 6 of the membrane, the working frame 7 camera 8 and 13, the holes 9-12 to enter salt water and conclusion diluate and brine.

The electrodes 1 and 2 and 3 and 4 are used for alternating sum of the direct electric current to electrodialyzer, and the electrode 1 is the anode, 2 - cathode 3 - anode, 4 - anode. The anodes 1 and 4 is made of titanium coated with ruthenium oxide, and the cathode 2 and 3 is made of copper.

The method of water desalination is carried out in electrodialyzer, which operates in the synchronous reverse hydrodynamic flow and electric current. The reverse is clucene line desalting and concentration, moreover, the switching is carried out after a certain period of time, such as 15 minutes.

During the first cycle of the source water through the holes 9 and 10 is supplied to the working chamber formed by the membranes 5 and 6 and the working frame 7. By static field created by the electrodes 1 and 2, the cations and anions migrate to the surface oninoelectrical 6 and nationalaction 5 membranes. Water, gradually purifying, sequentially passes through a number of similar working chambers. Through holes 11 to output diluate from the anode chamber 8 (camera demineralization) and the holes 12 for the withdrawal of brine from the near-cathode chamber 13 (camera concentration) purified water is removed from device.

To prevent salt deposits on the membranes 5 and 6 after a certain period of time, the electrodes 1 and 2 are disconnected simultaneously stops the flow of salt water in electrodialyzer. This insoluble salts and traces of contaminants are washed from the membranes 5 and 6.

After switching the electric current to the electrodes 3 and 4 during the second cycle salty water is supplied through the holes 11 and 12. Demineralization diluate and concentration of brine is due to the migration of unlike ions of salts through the IO is s), and dilut - through hole 10 of the anode chamber 13 (camera demineralization).

After 15 minutes of electrodialyzer again carry out a reverse electric current, repeating the first cycle. Then after 15 minutes is repeated in the second cycle.

The cyclical nature of the process ensures long-term operation of membranes, at the same time, the use of two pairs of electrodes allows virtually no limit voltage and current, which is conducted process.

Simultaneous change in the direction of the electric current and hydraulic flow contributes to a significant lengthening of the service life of the membranes by preventing deposits in the pores of the calcium sulfate.

Example 1 (prototype)

The solution absoluut standard electrodialysis installation with perforated graphite electrodes. The area of the electrodes 0.03 m2. The voltage at the device 170 C. the Initial current density on the electrodes 233 a/m2. The reverse direction of the current and hydraulic flows carry out every 15 minutes the performance of the device 30 l/h Final salinity diluate 3.2 g/L. the Amount of the missed solution of 150 l for 5 hours

Example 2 (the proposed method)

The solution containing 28,0 g/l salt NaCl, absoluut in the well side chamber of electrodialyzer, and the anode is made of titanium with a thickness of 2 mm with a coating of ruthenium oxide ORT, and the cathode is stainless steel. The area of the anodes and cathodes of 0.032. The voltage at the device 300 C. the Initial current density on the electrodes 900 a/m2. The performance of the device 30 l/h of the working surface of the ion exchange membranes of 0.07 m2.

The number of membrane pairs in a package of 100 pieces. The reverse direction of the current and electrical currents carry out every 15 minutes Final salinity diluate 0.52 g/L.

Example 3

Analogously to example 2, using only the anode of tantalum. The final salinity diluate 0.65 g/L.

Example 4

Analogously to example 2, only with the use of anodes with a coating of cobalt oxide (OCT). The final salinity diluate 0.55 g/L.

Example 5

Analogously to example 2, only with the use of anodes with a coating of manganese dioxide. The final salinity diluate 0.52 g/L.

Example 6

Analogously to example 2, only with the use of cathode copper. The final salinity diluate 0.50 g/L.

Example 7

Analogously to example 2, with only one anode of titanium coated with ruthenium oxide, and the other anode of tantalum with a coating of ruthenium oxide. End Solana with a coating of ruthenium oxide (ORT), and another from titanium with a coating of cobalt oxide (OCT). The final salinity diluate 0.55 g/L.

Example 9

Analogously to example 2, with only one cathode is stainless steel and the other of copper. The final salinity diluate 0,54 g/L.

Control of the desalting process in electrodialyzer carry out chemical analysis diluate and brine, and measuring the electric current and water flow.

The results of the experiments presented in the table.

In another series of experiments remained the final salt content of 3.2 g/l, and changed the volume of solution subjected to desalting, noise for 5 hours.

Example 10

Analogously to example 3, only differs in that the performance of the device in the desalted solution was 52 l/h and increased in comparison with the prototype on 73,33%. The amount of the missed solution was 260 HP

Example 11

Analogously to example 4, but differs in that the amount of the missed solution was 240 l, and the performance of the device in the desalted solution was 48 l/h and increased in comparison with the prototype of 60.0%.

Example 12

Analogously to example 5, only differs in that it produces is the volume of the missed solution of 253 HP

Example 13

Analogously to example 6, only differs in that the performance of the device in the desalted solution was 53 l/h and increased in comparison with the prototype on 76,66%. The amount of the missed solution 265 HP

From these data suggest that, during the desalting process at high current densities using two pairs of electrodes, the degree of demineralization of the same volume of water increases with 88,57 to 97,68 - being equal to 98.21 per cent. When saving in the experiments the same end salt - 3.2 g/l for the proposed method, the performance of the process is increased by 60.0 - 76,66%.

Claims

1. The method of water desalination in electrodialyzer with alternating cation-exchange and anion-exchange membranes forming chamber concentration and desalination, with a periodic change of direction of electric current and simultaneously switching threads cameras desalting and concentration, characterized in that in the process of desalting using two pairs of electrodes, working together to change the direction of the electric current, and the anode of one pair and the cathode of the other pair are on ml is low, and cathodes from non-corroding cast metal.

2. The method according to p. 1, characterized in that in the process of desalting using an anode made of titanium.

3. The method according to p. 1, characterized in that in the process of desalting using an anode made of tantalum.

4. The method according to p. 1, characterized in that the coating of anodes are used, the oxide of ruthenium.

5. The method according to p. 1, characterized in that the coating of anodes are used, the cobalt oxide.

6. The method according to p. 1, characterized in that the coating of anodes are used manganese dioxide.

7. The method according to p. 1, characterized in that in the process of desalting using a cathode made of stainless steel.

8. The method according to p. 1, characterized in that in the process of desalting using a cathode made of copper.

9. The method according to p. 1, characterized in that the electrodes of the two pairs is made from the same material.

10. The method according to p. 1, characterized in that the electrodes of the two pairs are made from different materials.

11. The method according to p. 1, characterized in that the anodes are made of the same film-forming metal.

12. The method according to p. 1, characterized in that the anodes are made of different film-forming metals.

13. The method according to p. 1, characterized in that the covered is made of different metal oxides.

 

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FIELD: electrochemical engineering.

SUBSTANCE: invention relates to electrochemical treatment of electrolyte solutions and electrodialysis methods, and, in particular, deionization methods. Method of electrodialysis desalting of an electrolyte solution comprises introducing solution into space between ion-selective membranes, applying direct current electric field, and conducting process to final concentration, while simultaneously measuring imposed process parameters, including current and voltage values, followed by calculating therefrom electric resistance of electrodialyzer and adjusting an electrical parameter. The latter is electric resistance of solution, for which part of dialyzate or concentrate is recycled to the process beginning. Direct current electric field originates from rectifier with external feeding voltametric characteristic.

EFFECT: prevented excessive current density above its allowed value, which would lead to concentration polarization and formation of sparingly soluble precipitates on the membrane surfaces; and increased operational reliability.

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