Undivided electrolytic cell and use of the same
The invention relates to a method for producing an ammonium peroxydisulfate or alkali metal peroxydisulfate, to an undivided electrolytic cell which is composed of individual components, and to an electrolytic device composed of a plurality of said electrolytic cells.
1. A process for the preparation of an ammonium or alkali metal peroxydisulphate, comprising:
anodic oxidation of an aqueous electrolyte comprising a salt chosen from ammonium sulphate, alkali metal sulphate and/or the corresponding hydrogen sulphate in a tubular electrolytic cell comprising at least one anode and one cathode wherein a diamond layer arranged on a conductive carrier and doped with a tri- or pentavalent element is used as the anode,
the tubular electrolytic cell comprises an undivided electrolyte chamber between the anode and the cathode, and
the aqueous electrolyte comprises no promoter for increasing the decomposition voltage of water to oxygen and has a total solids content of from about 0.5 to about 650 g/l.
2. The process of claim 1 , wherein the alkali metal sulphate and/or the corresponding hydrogen sulphate is selected from the group consisting of sodium sulphate, potassium sulphate, sodium hydrogen sulphate, potassium hydrogen sulphate and mixtures thereof.
3. The process of claim 1 , wherein the anode carrier material is selected from the group consisting of silicon, germanium, titanium, zirconium, niobium, tantalum, molybdenum, tungsten, carbides of these elements, aluminium and mixtures thereof.
4. The process of claim 1 , wherein a boron-doped and/or phosphorus-doped diamond layer is used.
5. The process of claim 4 , wherein the boron-doped and/or phosphorus-doped diamond layer is doped up to an extent of 10,000 ppm in the crystal structure.
6. The process of claim 1 , wherein the diamond layer has a film thickness of from about 0.5 μm to about 5.0 μm.
7. The process of claim 1 , wherein a boron-doped diamond layer on a niobium or titanium carrier is used as the anode.
8. The process of claim 1 , wherein the cathode is formed from lead, carbon, tin, platinum, nickel, alloys of these elements, zirconium and/or acid-resistant high-grade steels.
9. The process of claim 1 , wherein multiple electrolytic cells are combined.
10. The process of claim 9 , wherein the multiple electrolytic cells are combined in the form of a double tube package or two-dimensionally.
11. The process of claim 1 , wherein the electrolyte has an acidic or neutral pH.
12. The process of claim 1 , wherein the electrolyte is moved in circulation through the electrolytic cell during the process.
13. The process of claim 12 , further comprising a sluicing out of electrolyte solution from the electrolyte circulation.
14. The process of claim 12 , further comprising a procedure in which the peroxydisulphates produced are obtained by crystallisation and separating off of the crystals from the electrolyte solution to form an electrolyte mother liquor.
15. The process of claim 14 , further comprising a recirculation of the electrolyte mother liquor, to increase the content of acid, sulphate and/or hydrogen sulphate in the electrolytic cell.
16. The process of claim 4 , wherein the anodic oxidation is carried out at an anodic current density of from about 50 to about 1,500 mA/cm 2 .
17. The process of claim 1 , wherein the electrolyte comprises about 100 to about 500 g/ 1 of persulphate.
18. The process of claim 1 , wherein the electrolyte comprises about 0.1 to about 3.5 mol of sulphuric acid per 1 of electrolyte solution.
19. The process of claim 1 , wherein the diamond layer has a film thickness of from about 0.8 μm to about 2.0 μm.
20. The process of claim 1 , wherein the diamond layer has a film thickness of about 1.0 μm.
21. The process of claim 1 , wherein the anodic oxidation is carried out at an anodic current density of from about 250 to about 1,350 mA/cm 2 .
22. The process of claim 1 , wherein the anodic oxidation is carried out at an anodic current density of from about 400 to about 1200 mA/cm 2 .