Patent ID: 8882984

Claim:
A process for preparing diaryl carbonate comprising: a) preparing phosgene by reacting chlorine with carbon monoxide; b) reacting the phosgene formed in step a) with at least one monophenol in the presence of an aqueous alkali metal-containing base and, optionally, a nitrogen catalyst, to form a diaryl carbonate and a reaction wastewater solution comprising alkali metal chloride; c) separating and working-up the diaryl carbonate formed in step b); d) separating solvent residues and, optionally, catalyst residues from said reaction wastewater solution comprising alkali metal chloride remaining after step c) and subsequently feeding the solution to an osmotic membrane distillation in step e); e) increasing concentration of at least part of said reaction wastewater solution comprising alkali metal chloride from step d) by means of osmotic membrane distillation using an alkali metal hydroxide solution as water acceptor; f) electrochemically oxidizing at least part of said reaction wastewater solution comprising alkali metal chloride from e) to form chlorine, alkali metal hydroxide, and, optionally, hydrogen.