Processes for purifying diaryl carbonates

1. A process comprising:

transesterifying (i) a dialkyl carbonate of the general formula (II):

wherein R 1 and R 2 each independently represents a substituent selected from the group consisting of linear or branched, optionally substituted C 1 -C 34 -alkyl groups,

and (ii) an aromatic hydroxyl compound of the general formula (III):

wherein R, R′ andR″ each independantly represents a substituent selected from the group consisting of hydrogen, linear or branched, optionally substituted C 1 -C 34 -alkyl groups, a C 1 -C 34 -alkoxy groups, C 5 -C 34 -cycloalkyl groups, C 7 -C 34 -alkylaryl groups, C 6 - 34 -aryl groups, halogen radicals, and —COO—R′″ wherein each R′″ independently represents a substituent selected from the group consisting of hydrogen, linear or branched C 1 -C 34 alkyl, C 1 -C 34 -alkoxy, C 5 -C 34 -cycloalkyl, C 7 -C 34 -alkylaryl and C 6 -C 34 -aryl,

in the presence of a transesterification catalyst to provide a diaryl carbonate product comprising the transesterification catalyst as an impurity, wherein the diaryl carbonate product comprises a diaryl carbonate of the general formula (I):

wherein each R, R′ and R″ is independently defined as above;

subjecting the diaryl carbonate product to distillation in a first dividing wall distillation column having an upper part and a lower part, wherein the upper part comprises a rectifying section and the lower part comprises a stripping section; and

withdrawing a first sidestream from the first distillation column, wherein the first sidestream comprises a purified diaryl carbonate.

2. The process according to claim 1 , further comprising subjecting the purified diaryl carbonate to an additional distillation in a second distillation column.

3. The process according to claim 2 , wherein the second distillation column has no stripping section.

4. The process according to claim 2 , wherein the second distillation column is integrated into the first distillation column.

5. The process according to claim 1 , wherein the first sidestream is withdrawn from the first distillation column as a vapor.

6. The process according to claim 1 , wherein the diaryl carbonate product further comprises an alkyl aryl carbonate transesterification by-product and an additional compound having a boiling point between that of the diaryl carbonate and the alkyl aryl carbonate; and the process further comprises withdrawing a second sidestream comprising the additional compound from the first distillation column.

7. The process according to claim 6 , wherein the second sidestream is withdrawn from the first distillation column above the first sidestream.

8. The process according to claim 1 , wherein the stripping section comprises an upper stripping section and a lower stripping section.

9. The process according to claim 1 , wherein the rectifying section comprises an upper rectifying section and a lower rectifying section.

10. The process according to claim 1 , wherein the dividing wall column comprises a dividing wall section having a dividing wall, a feed side and a withdrawal side; wherein the feed side comprises an upper feed side section and a lower feed side section, and the withdrawal side comprises an upper withdrawal side section and a lower withdrawal side section; and wherein the diaryl carbonate product is fed to the first distillation column between the upper and lower feed side sections and the first sidestream is withdrawn from the first distillation column between the upper and lower withdrawal sections.

11. The process according to claim 10 , further comprising subjecting the purified diaryl carbonate to an additional distillation in a second distillation column.

12. The process according to claim 1 , wherein the first distillation column has a diameter D 1 and further comprises a top condenser integrated into the first distillation column and a vapor line from the first distillation column to the top condenser, the vapor line having a diameter d 1 , and wherein a ratio d 1 /D 1 is 0.2 to 1.

13. The process according to claim 2 , wherein the second distillation column has a diameter D 2 and further comprises a top condenser integrated into the second distillation column and a vapor line from the second distillation column to the top condenser, the vapor line having a diameter d 2 , and wherein a ratio d 2 /D 2 is 0.2 to 1.

14. The process according to claim 1 , wherein a bottom product is withdrawn from a bottom of the first distillation column, and wherein the process further comprises recycling at least 50% of the bottom product back into the transesterification of the diallyl carbonate and the aromatic hydroxyl compound.

15. The process according to claim 14 , wherein an unrecycled portion of the bottom product is concentrated and subjected to catalyst recovery.

16. The process according to claim 14 , wherein the dividing wall column comprises a dividing wall section having a dividing wall, a feed side and a withdrawal side; wherein the feed side comprises an upper feed side section and a lower feed side section, and the withdrawal side comprises an upper withdrawal side section and a lower withdrawal side section; and wherein the diaryl carbonate product is fed to the first distillation column between the upper and lower feed side sections and the first sidestream is withdrawn from the first distillation column between the upper and lower withdrawal sections.

17. The process according to claim 16 , further comprising subjecting the purified diaryl carbonate to an additional distillation in a second distillation column.

18. The process according to claim 14 , wherein an unrecycled portion of the bottom product is concentrated and subjected to catalyst recovery.