Method of preparing ester-substituted diaryl carbonates

1. In a method of making an ester-substituted diaryl carbonate by reacting phosgene with a recycle stream of ester-substituted phenol from a reaction process using a tetraalkyl phosphonium hydroxide, a tetraalkyl ammonium hydroxide, or both, as a catalyst, the improvement comprising:

treating the recycle stream to reduce a catalyst degradation product concentration, if catalyst degradation product is present, prior to the reaction with phosgene,

wherein the catalyst degradation product comprises a trialkyl phosphine, a trialkyl amine, or both, and

wherein at least one alkyl group of the tetraalkyl phosphonium hydroxide or the tetraalkyl ammonium hydroxide is a methyl group.

2. The improvement of claim 1 , wherein catalyst degradation product is initially present and is reduced to a concentration of less than 1.00 ppm in the recycle stream.

3. The improvement of claim 1 , wherein reducing catalyst degradation product concentration in the recycle stream-is accomplished by washing the recycle stream with an aqueous solution.

4. The improvement of claim 3 , wherein the aqueous solution is water.

5. The improvement of claim 3 , wherein the aqueous solution is acidic.

6. The improvement of claim 1 , wherein reducing catalyst degradation product concentration in the recycle stream is accomplished by mixing the recycle stream with an ester-substituted phenol stream containing a lower concentration of the catalyst degradation product than the recycle stream.

7. The improvement of claim 1 , wherein:

the tetraalkyl phosphonium hydroxide comprises tetramethyl phosphonium hydroxide, diethyldimethyl phosphonium hydroxide, or both, and

the tetraalkyl ammonium hydroxide comprises tetramethyl ammonium hydroxide, diethyldimethyl ammonium hydroxide, or both.

8. The improvement of claim 1 , wherein the catalyst degradation product is trimethyl phosphine, diethylmethyl phosphine, dimethylethyl phosphine, trimethyl amine, diethylmethyl amine, dimethylethyl amine, or any combination thereof.

9. In a method of making a polycarbonate using a carbonate source comprising an ester-substituted diaryl carbonate prepared by reacting phosgene with a recycle stream of ester-substituted phenol from a reaction process using a tetraalkyl phosphonium hydroxide, a tetraalkyl ammonium hydroxide, or both, as a catalyst the improvement comprising:

treating the recycle stream to reduce a catalyst degradation product concentration, if catalyst degradation product is present, prior to the reaction with phosgene,

wherein the catalyst degradation product comprises a trialkyl phosphine, a trialkyl amine, or both, and

wherein at least one alkyl group of the tetraalkyl phosphonium hydroxide or the tetraalkyl ammonium hydroxide is a methyl group.

10. The improvement of claim 9 , wherein the catalyst degradation product is present and is reduced to a concentration of less than 1.00 ppm in the recycle stream.

11. The improvement of claim 9 , wherein reducing the catalyst degradation product concentration in the recycle stream is accomplished by washing the recycle stream with an aqueous solution.

12. The improvement of claim 11 , wherein the aqueous solution is water.

13. The improvement of claim 11 , wherein the aqueous solution is acidic.

14. The improvement of claim 9 , wherein reducing the catalyst degradation product concentration in the recycle stream is accomplished by mixing the recycle stream with an ester-substituted phenol stream containing a lower concentration of catalyst degradation product than the recycle stream.

15. The improvement of claim 9 , wherein:

the tetraalkyl phosphonium hydroxide comprises tetramethyl phosphonium hydroxide, diethyldimethyl phosphonium hydroxide, or both, and

the tetraalkyl ammonium hydroxide comprises tetramethyl ammonium hydroxide, diethyldimethyl ammonium hydroxide, or both.

16. The improvement of claim 9 , wherein the catalyst degradation product is trimethyl phosphine, diethylmethyl phosphine, dimethylethyl phosphine, trimethyl amine, diethylmethyl amine, dimethylethyl amine, or any combination thereof.

17. A facility for making polycarbonate comprising:

(i) a melt polymerization reactor system comprising a reaction vessel containing a reaction mixture, said reaction mixture comprising a dihydroxy compound, an ester-substituted diaryl carbonate, and a catalyst, wherein the catalyst comprises a tetraalkyl ammonium hydroxide, a tetraalkyl phosphonium hydroxide, or both,

wherein at least one alkyl group of the tetraalkyl phosphonium hydroxide or the tetraalkyl ammonium hydroxide is a methyl group,

(ii) an ester-substituted diaryl carbonate reactor system comprising a reaction vessel containing an ester-substituted phenol and phosgene,

(iii) a recycle ester-substituted phenol line, connected to both the melt polymerization reactor system and to the ester-substituted diaryl carbonate reactor system, the recycle line containing a recycle stream of an ester-substituted phenol and a catalyst degradation product, wherein the catalyst degradation product comprises a trialkyl amine, a trialkyl phosphine, or both, and

(iv) an aqueous extraction tower for reducing catalyst degradation product concentration in the recycle ester-substituted phenol line, connected to the recycle ester-substituted phenol line between the melt polymerization reactor system to the ester-substituted diaryl carbonate reactor system.

18. The facility of claim 17 , further comprising:

(v) an ester-substituted diaryl carbonate line, connected to both the melt polymerization reactor and to the ester-substituted diaryl carbonate reactor system, the ester-substituted diaryl carbonate line containing an ester-substituted diaryl carbonate formed in the ester-substituted diaryl carbonate reactor system.

19. A facility for making polycarbonate comprising:

(i) a melt polymerization reactor system comprising a reaction vessel containing a reaction mixture, said reaction mixture comprising a dihydroxy compound, an ester-substituted diaryl carbonate, and a catalyst, wherein the catalyst comprises a tetraalkyl ammonium hydroxide, a tetraalkyl phosphonium hydroxide, or both,

wherein at least one alkyl group of the tetraalkyl phosphonium hydroxide or the tetraalkyl ammonium hydroxide is a methyl group,

(ii) an ester-substituted diaryl carbonate reactor system comprising a reaction vessel containing an ester-substituted phenol and phosgene,

(iii) a recycle ester-substituted phenol line, connected to both the melt polymerization reactor system and to the ester-substituted diaryl carbonate reactor system, the recycle line containing a recycle stream of an ester-substituted phenol and a catalyst degradation product, wherein the catalyst degradation product comprises a trialkyl amine, a trialkyl phosphine, or both, and

(iv) a distillation column for reducing catalyst degradation product concentration in the recycle ester-substituted phenol line, connected to the recycle ester-substituted phenol line between the melt polymerization reactor system to the ester-substituted diaryl carbonate reactor system.

20. The facility of claim 19 , further comprising:

(v) an ester-substituted diaryl carbonate line, connected to both the melt polymerization reactor and to the ester-substituted diaryl carbonate reactor system, the ester-substituted diaryl carbonate line containing an ester-substituted diaryl carbonate formed in the ester-substituted diaryl carbonate reactor system.

21. The improvement of claim 1 , wherein the recycle stream of ester-substituted phenol comes from a melt polymerization reaction that produces polycarbonate.

22. The improvement of claim 9 , wherein the recycle stream of ester-substituted phenol comes from a melt polymerization reaction that produces polycarbonate.