Process for production of high-purity diaryl carbonate
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. Moreover, it is particularly preferable if a reactive distillation column and the three distillation columns, each of which has a specified structure, and the three distillation columns are each operated under specified distillation conditions.
1. In a process for the production of a high-purity diaryl carbonate in which a diaryl carbonate is produced by 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 the improvement comprises:
(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B T , a side cut component B S and a column bottom component B B , the high-purity diaryl carbonate being continuously withdrawn as the side cut component B S ; and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 an 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 process according to claim 1 , wherein said column top component C T from said intermediate boiling point material separating column C is continuously fed into said reactive distillation column.
3. The process according to claim 1 or 2 , wherein said column bottom component C B from said intermediate boiling point material separating column C is continuously fed into said high boiling point material separating column A.
4. The process according to claim 1 , wherein said reactive distillation column is a continuous multi-stage distillation column comprising an internal with a number of stages n thereinside, n satisfying 10≦n≦80.
5. The process according to claim 1 , wherein said high boiling point material separating column A is a continuous multistage distillation column comprising an internal with a number of stages n A thereinside, n A satisfying 20≦n≦100.
6. The process according to claim 1 , wherein said diaryl carbonate purifying column B is a continuous multi-stage distillation column comprising an internal with a number of stages n B thereinside n B satisfying 20≦n B ≦70.
7. The process according to claim 1 , wherein said intermediate boiling point material separating column C is a continuous multistage distillation column comprising an internal with a number of stages n C thereinside, n C satisfying 10≦n C ≦50.
8. The process according to claim 1 , wherein a distillation operation of said high boiling point material separating column A is carried out at a column bottom temperature T A in a range of from 185 to 280° C., and a column top pressure P A in a range of from 1000 to 20000 Pa.
9. The process according to claim 1 , wherein a distillation operation of said diaryl carbonate purifying column B is carried out at a column bottom temperature T B in a range of from 185 to 280° C., and a column top pressure P B in a range of from 1000 to 20000 Pa.
10. The process according to claim 1 , wherein a distillation operation of said intermediate boiling point material separating column C is carried out at a column bottom temperature T C in a range of from 150 to 280° C., and a column top pressure P C in a range of from 500 to 18000 Pa.
11. The process according to claim 1 , wherein a reflux ratio for said high boiling point material separating column A is in a range of from 0.01 to 10.
12. The process according to claim 1 , wherein a reflux ratio for said diaryl carbonate purifying column B is in a range of from 0.01 to 10.
13. The process according to claim 1 , wherein a reflux ratio for said intermediate boiling point material separating column C is in a range of from 0.01 to 10.