PROCESS FOR THE PRODUCTION OF DIARYL CARBONATES AND TREATMENT OF ALKALICHLORIDE SOLUTIONS RESULTING THEREFROM

• US 20080053836A1
• Filed: 09/04/2007
• Published: 03/06/2008
• Est. Priority Date: 09/02/2006
• Status: Abandoned Application

• Current Assignee: Bayer Materialscience AG (Covestro AG)
• Original Assignee: Bayer Materialscience AG (Covestro AG)
• Inventors: Weber, Rainer, Bulan, Andreas, Ooms, Pieter, Rechner, Johann, Buts, Marc, Vanden Eynde, Johan
• Application Number:
  US11/849,542
• Publication Number:
  US 20080053836A1
• Time in Patent Office: Days
• US Class Current: 205/338
• CPC Class Codes: C01D 3/04 Chlorides
• CPC Class Codes: C01D 3/06 Preparation by working up brines; seawater or spent lyes
• CPC Class Codes: C07C 68/02 from phosgene or haloformates
• CPC Class Codes: C07C 69/96 Esters of carbonic or haloformic acids
• CPC Class Codes: C25B 1/34 Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
• CPC Class Codes: C25B 1/46 in diaphragm cells
• CPC Class Codes: C25B 15/08 Supplying or removing reactants or electrolytes; Regeneration of electrolytes

Abstract

Processes comprising: (a) reacting phosgene and a monohydroxyl aryl compound in the presence of a suitable catalyst to form a diaryl carbonate and a solution comprising an alkali chloride; (b) separating the diaryl carbonate from the solution; (c) adjusting the pH of the solution to a value of less than or equal to 8 to form a pH-adjusted solution; (d) treating the pH-adjusted solution with an adsorbent to form a treated solution; (e) subjecting at least a portion of the treated solution to electrochemical oxidation to form chlorine and an alkali hydroxide solution; and (f) recycling at least a portion of one or both of the chlorine and the alkali hydroxide solution.

Claims

1. A process comprising:

(a) reacting phosgene and a monohydroxyl aryl compound in the presence of a suitable catalyst to form a diaryl carbonate and a solution comprising an alkali chloride;

(b) separating the diaryl carbonate from the solution;

(c) adjusting the pH of the solution to a value of less than or equal to 8 to form a pH-adjusted solution;

(d) treating the pH-adjusted solution with an adsorbent to form a treated solution;

(e) subjecting at least a portion of the treated solution to electrochemical oxidation to form chlorine and an alkali hydroxide solution; and

(f) recycling at least a portion of one or both of the chlorine and the alkali hydroxide solution.

2. The process according to claim 1, wherein recycling at least a portion of the chlorine comprises feeding the portion to a reaction with carbon monoxide to form at least a portion of the phosgene reacted with the monohydroxyl aryl compound.

3. The process according to claim 1, wherein recycling at least a portion of the alkali hydroxide solution comprises feeding the portion to the reaction of the phosgene and the monohydroxyl aryl compound.

4. The process according to claim 1, further comprising subjecting one or more of the solution, the pH-adjusted solution and the treated solution to a separation to remove an amount of residual solvent.

5. The process according to claim 4, wherein the separation comprises steam stripping.

6. The process according to claim 1, wherein the electrochemical oxidation is carried out with a cathode comprising a gas diffusion electrode.

7. The process according to claim 1, further comprising feeding a portion of the treated solution to a brine circuit of a membrane electrolysis process.

8. The process according to claim 1, further comprising adding additional alkali chloride to the electrochemical oxidation.

9. The process according to claim 1, wherein the pH of the solution is adjusted to a value of less than or equal to 7.

10. The process according to claim 1, wherein adjusting the pH of the solution comprises adding hydrogen chloride.

11. The process according to claim 1, wherein the treated solution prior to electrochemical oxidation has an alkali chloride concentration of 100 to 280 g/L.

12. The process according to claim 1, wherein the alkali hydroxide solution has an alkali hydroxide concentration of 13 to 33 wt. %.

13. The process according to claim 1, wherein separating the diaryl carbonate from the solution comprises:

(i) separating a diaryl carbonate-containing organic phase and an aqueous alkali chloride-containing waste water solution; and

(ii) washing the diaryl carbonate-containing organic phase at least once and separating the wash liquid.

14. The process according to claim 1, wherein the electrochemical oxidation is carried out using an ion exchange membrane having a water transport value greater than 4 moles H₂O per mole of alkali chloride.

15. The process according to claim 1, wherein the electrochemical oxidation is carried out using an ion exchange membrane having a water transport value of 5.5 to 6.5 moles H₂O per mole of alkali chloride.

16. The process according to claim 1, wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m² of membrane.

17. The process according to claim 15, wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m² of membrane.

18. The process according to claim 1, wherein the electrochemical oxidation is carried out at a temperature of 70 to 100°

C.

19. The process according to claim 1, wherein the electrochemical oxidation is carried out at an absolute pressure of 1.0 to 1.4 bar.

20. The process according to claim 1, wherein the electrochemical oxidation is carried out at a differential pressure between an anode compartment and a cathode compartment of 20 to 150 mbar.

21. The process according to claim 1, wherein the electrochemical oxidation is carried out using an anode having a coating comprising ruthenium oxide and a compound of an element selected from the group consisting of Group 4 elements, Group 7 elements, Group 8 elements, and combinations thereof.

22. The process according to claim 1, wherein the electrochemical oxidation is carried out using an electrolysis cell having an anode and a membrane, and wherein the anode has a surface area greater than a surface area of the membrane.

23. The process according to claim 1, wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m² of membrane;

a temperature of 70 to 100°

C.;

an absolute pressure of 1.0 to 1.4 bar; and

a differential pressure between an anode compartment and a cathode compartment of 20 to 150 mbar.

24. The process according to claim 1, wherein the monohydroxyl aryl compound comprises a phenol compound of the general formula (I):

25. A process comprising:

(a) reacting phosgene and a phenol compound of the general formula (I) in the presence of a suitable catalyst to form a diaryl carbonate and a solution comprising an alkali chloride;

wherein each R independently represents a substituent selected from the group consisting of hydrogen, halogens, C_1-9 alkyl groups, C_1-9 alkoxy groups, C_1-9 carbonyl groups, and C_1-9 alkoxycarbonyl groups; and

n represents an integer of 0 to 5;

(b) separating the diaryl carbonate from the solution;

(c) adjusting the pH of the solution with hydrogen chloride to a value of less than or equal to 7 to form a pH-adjusted solution;

(d) treating the pH-adjusted solution with an adsorbent to form a treated solution;

(e) subjecting at least a portion of the treated solution to electrochemical oxidation to form chlorine and an alkali hydroxide solution; and

(f) recycling at least a portion of one or both of the chlorine and the alkali hydroxide solution;

wherein recycling at least a portion of the chlorine comprises feeding the portion to a reaction with carbon monoxide to form at least a portion of the phosgene reacted with the monohydroxyl aryl compound;

wherein recycling at least a portion of the alkali hydroxide solution comprises feeding the portion to the reaction of the phosgene and the monohydroxyl aryl compound; and

wherein the electrochemical oxidation is carried out at a current density of 2 to 6 kA per m² of membrane;

a temperature of 70 to 100°

C.;

an absolute pressure of 1.0 to 1.4 bar; and

a differential pressure between an anode compartment and a cathode compartment of 20 to 150 mbar.