Process for production of diaryl carbonate

Abstract

The invention relates to a process for production of diaryl carbonate combined with the electrolysis of the resultant alkali metal chloride-containing process wastewater. The process according to the invention makes possible, inter alia, improved utilization in electrolysis of the alkali metal chloride-containing solution obtained in the production of diaryl carbonate.

1 . A process for producing diaryl carbonate and the processing of at least a part of the 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 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 said alkali-metal-chloride-containing solution has an alkali metal chloride content in the range of from 18 to 25% by weight based on the total weight of said alkali-metal-chloride-containing solution and/or at least a part of said 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 it 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 1 , wherein said base in b) is an alkali-metal-containing base. 
   
   
       5 . The process of  claim 4 , 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 sodium phenolate content of the resultant solution of said alkali-metal-containing base and said monophenol is in the range of from 31 to 40% by weight sodium phenolate, based on the total weight of the solution. 
   
   
       6 . The process of  claim 1 , wherein up to 80% by weight of said alkali-metal-chloride-containing solution from d) is recycled to b). 
   
   
       7 . The process of  claim 6 , wherein up to 50% by weight of said alkali-metal-chloride-containing solution from d) is recycled to b). 
   
   
       8 . The process of  claim 1 , wherein a gas diffusion electrode as cathode is used to achieve said electrochemical oxidation. 
   
   
       9 . The process of  claim 1 , wherein at least a part of the purified alkali-metal-chloride-containing solution from d) is added to the brine circuit of a membrane electrolysis for producing chlorine, sodium hydroxide solution and optionally hydrogen. 
   
   
       10 . The process of  claim 1 , wherein additional alkali metal chloride is added to the alkali-metal-chloride-containing solution in e) so as to elevate the alkali metal chloride concentration. 
   
   
       11 . 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. 
   
   
       12 . The process of  claim 11 , wherein the pH of said alkali-metal-chloride-containing solution is adjusted with hydrochloric acid or hydrogen chloride. 
   
   
       13 . The process of  claim 1 , wherein ion-exchange membranes are used in e), wherein the water transport per mole of sodium is 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.