Process for production of high-purity diaryl carbonate
A high-purity diphenyl carbonate, wherein the diphenyl carbonate is unsubstituted or substituted with a lower hydrocarbon, and has a halogen content of not more than 0.1 ppm, a content of an intermediate boiling point material of not more than 100 ppm, and a content of by-products having a higher boiling point than that of said diphenyl carbonate of not more than 100 ppm. A specific industrially useful process for the production of a high-purity diaryl carbonate in which a diaryl carbonate having low contents of intermediate boiling point and high boiling point impurities is produced is disclosed. As a starting material, a reaction mixture containing an alkyl aryl carbonate obtained through a transesterification reaction between a dialkyl carbonate and an aromatic monohydroxy compound is used. The process in which separation by distillation is carried out uses three distillation columns in a specified order.
1. A high-purity diphenyl carbonate, wherein the diphenyl carbonate is unsubstituted or substituted with a lower hydrocarbon, and has a halogen content of not more than 1 ppb, a content of an intermediate boiling point material of not more than 100 ppm, and a content of by-products having a higher boiling point than that of said diphenyl carbonate of not more than 100 ppm; and
wherein the high-purity diphenyl carbonate is prepared by a process that comprises taking as a starting material a reaction mixture containing an alkyl aryl carbonate that has been obtained through a transesterification reaction between a dialkyl carbonate and an aromatic monohydroxy compound, continuously feeding the starting material into a reactive distillation column comprising a continuous multi-stage distillation column in which a homogeneous catalyst is present, carrying out a transesterification reaction and distillation simultaneously in said column, continuously withdrawing a low boiling point reaction mixture containing a produced dialkyl carbonate from an upper portion of the column in a gaseous form, and continuously withdrawing a high boiling point reaction mixture containing a diaryl carbonate from a lower portion of the column in a liquid form, wherein:
(a) said high boiling point reaction mixture is continuously introduced into a high boiling point material separating column A, and continuously subjected to separation by distillation into a column top component A T containing the diaryl carbonate and a column bottom component A B containing the catalyst and a high boiling point material,
(b) said column top component A T is continuously introduced into a diaryl carbonate purifying column B having a side cut outlet, and continuously subjected to separation by distillation into a column top component B T , a side cut component B S and a column bottom component B B , the high-purity diaryl carbonate being continuously withdrawn as the side cut component B S , and
(c) said column top component B T is continuously introduced into an intermediate boiling point material separating column C having a side cut outlet, and continuously subjected to separation by distillation into a column top component C T having said alkyl aryl carbonate as a main component thereof, a side cut component C S having as a main component thereof said intermediate boiling point material having a boiling point between that of said alkyl aryl carbonate and that of said diaryl carbonate, and a column bottom component C B having said diaryl carbonate as a main component thereof.
2. The high-purity diphenyl carbonate according to claim 1 , wherein said diphenyl carbonate is unsubstituted diphenyl carbonate, the content of said intermediate boiling point material is not more than 30 ppm, and the content of each of phenyl salicylate, xanthone, phenyl methoxybenzoate, and 1-phenoxycarbonyl-2-phenoxycarboxy-phenylene, which are by-products having a higher boiling point than that of said diphenyl carbonate, is not more than 30 ppm.
3. The high-purity diphenyl carbonate according to claim 2 , wherein the content of said intermediate boiling point material is not more than 10 ppm, and the content of the by-products having a higher boiling point than that of said diphenyl carbonate is not more than 50 ppm.
4. The high-purity diphenyl carbonate according to claim 3 , wherein the content of the by-products having a higher boiling point than that of said diphenyl carbonate is not more than 10 ppm.