Patent EA-000239-B1 (EA)
Title: Process for combined electrochemical production of sodium peroxide disulphate and soda lye
Inventor: THIELE WOLFGANG
IPC: C25B1/28
Filed: 1996-08-14
Abstract: 1. Process for combined production of sodium peroxide disulphate and soda lye from sodium sulphate using electrolysis, characterized in that electrolysis is carried out in at least one two-chamber electrolysis cell with cathode and anode chambers separated by a cation-exchanger membrane, the electrolysis temperature is set at between 30 and 70 degree C, a sodium sulphate solution which is at least 75 % saturated at this temperature is introduced into the anode chamber, the sodium ion concentrations are maintained in the range of between 4.5 and 6.0 mol/l and soda lye is extracted from the cathode chamber. 2. Process as claimed in Claim 1, characterized in that maintaining of sodium ion concentration is carried out by an additional solution of sodium sulphate or/and by water evaporation. 3. Process as claimed in Claim 1 or 2, characterized in that 10-40% soda lye is extracted from the cathode chamber, by adding a predetermined amount of water, if necessary. 4. Process as claimed in one of the preceding Claims, characterized in that electrolysis is carried out in one or several steps. 5. Process as claimed in one of the preceding Claims, characterized in that a sodium sulphate solution which is at least 90 % saturated is introduced into the anode chamber. 6. Process as claimed in Claim 1, characterized in that crystalline sodium sulphate is suspended in electrolysis in such amount which is used during electrolysis thus by an additional dissolving the process is carried out in the saturation zone. 7. Process as claimed in one of the preceding Claims, characterized in that in two-step process at first stage of electrolysis anolyte is carried out in a closed cycle through a chamber intended for sodium sulphate solution and above anode chambers of the electrolysis cell, while in a steady return electrolyte the predetermined amount of water, or crystalline sodium sulphate are added and, if necessary, crystallizers containing sodium sulphate and sodium peroxide disulphate or mother liquor are also added wherein containing saturated sodium peroxide and containing to 250 g/l disulphate comprising saturated sodium sulphate anolyte is introduced into the anode chamber of next electrolysis step. 8. Process as claimed in one of the preceding Claims, characterized in that the electrolysis is carried out at temperatures from 40 to 60 degree C. 9. Process as claimed in one of the preceding Claims, characterized in that in a closed anolyte cycle a return of soda lye, appearing on the cathode, is used to obtain on the cathode pH value, equal to 0.5 and 2. 10. Process as claimed in one of the preceding Claims, characterized in that in the obtained solution of sodium peroxide by cooling to 10-25 degree C most part of excess sodium sulphate as, Glauber's salt, is sent for crystallization, separated and further returned into electrolysis process. 11. Process as claimed in one of the preceding Claims, characterized in that to obtain alkali solution of sodium peroxide disulphate approximately having stoichiometric composition anolyte solution before or after preliminary enrichment with sodium sulphate is mixed with catolyte solution. 12. Process as claimed in one of the preceding Claims, characterized in that to obtain crystalline sodium peroxide disulphate, an anolyte solution obtained at 40-60 degree C and saturated with sodium peroxide disulphate, if necessary, when using from 100 to 200 g/l of solid sodium sulphate, settled in crystals sodium peroxide disulphate is separated, and mother liquid is again introduced to electrolysis. 13. Process as claimed in one of the preceding Claims, characterized in that to obtain crystalline sodium peroxide disulphate, a solution obtained at 40-60 degree C and containing sodium peroxide disulphate and sodium sulphate after cooling to 15-25 degree C then freed from main amount of excess sodium sulphate after which is evaporated by 90-30% of initial volume and at temperatures from 25 to 35 degree C part of sodium peroxide disulphate is crystallezed and treated by known methods, while the mother liquid is again introduced to the process after electrolysis. 14. Process as claimed in one of the preceding Claims, characterized in that  heat loses during electrolysis are used for concentration of peroxide disulphate solution. 15. Process as claimed in one of the preceding Claims, characterized in that a solution, obtained at temperatures from 40 to 60 degree C and containing sodium peroxide disulphate and sodium sulphate are treated till full water evaporation, in particular, by a spraying drying or in a fluidized layer to obtain a granulated oxidant or a bleach based on sodium peroxide disulphate. 16. Process as claimed in one of the preceding Claims, characterized in that a solution, obtained at temperatures from 40 to 60 degree C and containing sodium peroxide disulphate and sodium sulphate to obtain solid mixture of active substances is spray-coated on the base during water evaporation. 17. Process as claimed in Claim 16, characterized in that the base is presented in a granulated form. 18. Process as claimed in Claim 16 or 17, characterized in that the base is in said fluidized layer. 19. Process as claimed in one of the preceding 16-18 Claims, characterized in that the base present in said granulated form comprises sodium carbonate. 20. Process as claimed in one of the preceding 16-18 Claims, characterized in that the granulated base comprises sodium percarbonate. 21. Process as claimed in one of the preceding Claims, characterized in that settled on the cathode soda lye is introduced in an exchange reaction in cathode chamber with added or settled on the cathode by the reaction members with forming derived products. 22. Process as claimed in Claim 21, characterized in that settled on the cathode soda lye is introduced into reaction of exchange by introducing of carbon dioxide into catalytes forming derived products of sodium carbonate or sodium bicarbonate. 23. Process as claimed in Claim 21, characterized in that by oxygen introduction and its reduction on the cathode producing hydrogen peroxide producing soda lyeas a derived product alkali bleaching solution of sodium peroxide is produced.