Process for production of diaryl carbonate

1. A process for producing diaryl carbonate and processing of at least a part of a resulting alkali-metal-chloride-containing solution in a downstream alkali metal chloride electrolysis comprising:

a) producing phosgene by reacting chlorine with carbon monoxide;

b) reacting said phosgene with at least one monophenol in the presence of a base and optionally basic catalyst to form a diaryl carbonate and an alkali-metal-chloride-containing solution;

c) separating off and working up said diaryl carbonate;

d) separating off said alkali-metal-chloride-containing solution from solvent residues and optionally catalyst residues;

e) electrochemically oxidizing at least a part of said separated alkali-metal-chloride-containing solution to form chlorine, alkali solution, and optionally hydrogen;

f) recycling at least a part of said chlorine to a); and/or

g) recycling at least a part of said alkali solution to b);

wherein at least a part of said separated alkali-metal-chloride-containing solution is recycled to b).

2. The process of claim 1 , wherein said separation in d) is achieved by stripping said alkali-metal-chloride-containing solution with steam and treating said alkali-metal-chloride-containing solution with an adsorbent, wherein said alkali-metal-chloride-containing solution is adjusted to a pH less than or equal to 8 before the treatment with said adsorbent.

3. The process of claim 2 , wherein said absorbent is activated carbon.

4. The process of claim 2 , wherein said alkali-metal-chloride-containing solution is adjusted to a pH of less than 7 before the treatment with said adsorbent.

5. The process of claim 4 , wherein the pH of said alkali-metal-chloride-containing solution is adjusted with hydrochloric acid or hydrogen chloride.

6. The process of claim 1 , wherein said base in b) is an alkali-metal-containing base.

7. The process of claim 6 , wherein said alkali-metal-containing base is a sodium containing base and said alkali-metal-containing base and said monophenol are used in amounts such that the formed alkali-metal-chloride-containing solution has a sodium phenolate content in the range of from 31 to 40% by weight sodium phenolate, based on the total weight of the alkali-metal-chloride-containing solution.

8. The process of claim 1 , wherein up to 80% by weight of said separated alkali-metal-chloride-containing solution from d) is recycled to b).

9. The process of claim 8 , wherein up to 50% by weight of said separated alkali-metal-chloride-containing solution from d) is recycled to b).

10. The process of claim 1 , wherein a gas diffusion electrode as cathode is used to achieve said electrochemical oxidation.

11. The process of claim 1 , wherein the electrochemical oxidation of step e) is carried out by way of a membrane electrolysis with a brine circuit and at least a part of the separated alkali-metal-chloride-containing solution from d) is added to the brine circuit of the membrane electrolysis.

12. The process of claim 1 , wherein alkali metal chloride is added to the alkali-metal-chloride-containing solution in e) so as to elevate the alkali metal chloride concentration.

13. The process of claim 1 , wherein ion-exchange membranes are used in e), wherein the ion-exchange membranes exhibit a water transport per mole of sodium greater than 4 mol of H 2 O/mole of sodium.

14. The process of claim 13 , wherein the water transport per mole of sodium is in the range of from 5.5 to 6.5 mol of H 2 O/mole of sodium.

15. The process of claim 1 , wherein said monophenol is phenol, a C 1 -C 9 -alkylphenol, or a halophenol.

16. The process of claim 15 , wherein said C 1 -C 9 -alkylphenol is selected from the group consisting of cresols, p-tert-butylphenol, p-cumylphenol, p-n-octylphenol, p-isooctylphenol, p-n-nonylphenol, and p-isononylphenol.

17. The process of claim 15 , wherein said halophenol is selected from the group consisting of p-chlorophenol, 2,4-dichlorophenol, p-bromophenol, and 2,4,6-tribromophenol.

18. The process of claim 15 , wherein said monophenol is phenol.

19. The process of claim 1 , wherein cells are used in e) which comprise anodes and membranes, wherein said anodes have a higher surface area than that of said membranes.