Process for the production of diaryl carbonates and treatment of alkalichloride solutions resulting therefrom

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.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates, in general, to a combined process for the production of diaryl carbonate and electrolysis of alkali chloride-containing process wastewater. The invention also relates, more particularly, to processes for the treatment of alkali chloride-containing waste solutions for further use in a diaryl carbonate production process, and even more particularly, a diphenyl carbonate production process (“DPC process”). [0002] The production of diaryl carbonates, and more particularly diphenyl carbonates, generally takes place by a continuous process, by the production or introduction of phosgene and subsequent reaction of monophenols and phosgene in an inert solvent in the presence of alkali and a nitrogen catalyst at the reaction interface, according to the following general reaction scheme: [0003] The production of diaryl carbonates, e.g., by interfacial polycondensation, is described in various literature sources, e.g., in “Chemistry and...

AI Technical Summary

Benefits of technology

[0013] It has been found that the alkali chloride-containing wastewater solutions forming during the continuous production of diaryl carbonates, such as by reaction of monophenols and phosgene in an inert solvent in the presence of alkali and amine catalyst at the interface, can be fed directly into an electrochemical oxidation of the alkali chloride obtained to form chlorine, alkali hydroxide solution and optionally hydrogen without costly purification. It has been found that this can be accomplished by introduction of the wastewater solution into an electrochemical oxidation after adjustment of the pH of the solution to a value less than or equal to 8 and simple treatment with an adsorbent, such as activated carbon. The chlorine obtained from the electrochemical oxidation can be recycled into the production of phosgene. Moreover, the alkali hydroxide solution can be recycled into the diaryl carbonate production reaction as basic catalyst.

Problems solved by technology

In such known processes, however a high residual phenol value in the wastewater, which can pollute the environment and confront the sewage works with increased wastewater problems, makes costly purification operations necessary.

A disadvantage of ozonolysis is that such processes can be very cost-intensive.

A disadvantage of such processes is that the water has to be completely evaporated, and so the processes cannot be carried out economically.

However, only a maximum of 26% of the sodium chloride is known to be recoverable from the wastewater from DPC production by such processes, since if greater quantities were recovered, the water introduced into the electrolysis with the wastewater would bring the water balance of the sodium chloride electrolysis out of equilibrium.

Thus, the sodium chloride present in the solutions can never be completely recovered by known processes.

No complete recycling of the sodium chloride-containing solution has become known.

However, the evaporation is energy-intensive and costly.

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