Process for preparing alkanediol and dialkyl carbonate

1. A process for the preparation of an alkanediol and a dialkyl carbonate comprising:

(a) reacting an alkylene carbonate and an alkanol in the presence of a transesterification catalyst to obtain a reaction mixture comprising dialkyl carbonate, unconverted alkanol, alkanediol, unconverted alkylene carbonate and an alkoxy alkanol impurity;

(b) subjecting the reaction mixture to distillation in a first distillation column to obtain a top stream comprising dialkyl carbonate, alkanol and alkoxy alkanol impurity and a bottom stream comprising alkanediol and alkylene carbonate;

(c) subjecting the bottom stream from the first distillation column to distillation in a second distillation column to obtain a top stream comprising alkanediol and a bottom stream comprising alkylene carbonate;

(d) subjecting the top stream from the first distillation column to distillation in a third distillation column in the presence of a catalyst to effect reaction of the alkoxy alkanol impurity with the dialkyl carbonate into a carbonate ether impurity, to obtain a top stream comprising alkanol and a bottom stream comprising dialkyl carbonate and carbonate ether impurity; and

(e) subjecting the bottom stream from the third distillation column to distillation in a fourth distillation column to obtain a top stream comprising dialkyl carbonate and a bottom stream comprising dialkyl carbonate and carbonate ether impurity; and

(f) recycling the bottom stream from the fourth distillation column to the first distillation column.

2. A process according to claim 1 , wherein the dialkyl carbonate is a di(C 1 -C 5 )alkyl carbonate.

3. A process according to claim 1 , wherein the catalyst in step (d) is a heterogeneous catalyst.

4. A process according to claim 1 , wherein the alkylene carbonate is ethylene carbonate, the unconverted alkanol is ethanol, the dialkyl carbonate is diethyl carbonate, the alkanediol is monoethylene glycol and the alkoxy alkanol impurity is 2-ethoxyethanol.

5. A process for making a diaryl carbonate, comprising

(a) reacting an alkylene carbonate and an alkanol in the presence of a transesterification catalyst to obtain a reaction mixture comprising dialkyl carbonate, unconverted alkanol, alkanediol, unconverted alkylene carbonate and an alkoxy alkanol impurity;

(b) subjecting the reaction mixture to distillation in a first distillation column to obtain a top stream comprising dialkyl carbonate, alkanol and alkoxy alkanol impurity and a bottom stream comprising alkanediol and alkylene carbonate;

(c) subjecting the bottom stream from the first distillation column to distillation in a second distillation column to obtain a top stream comprising alkanediol and a bottom stream comprising alkylene carbonate;

(d) subjecting the top stream from the first distillation column to distillation in a third distillation column in the presence of a catalyst to effect reaction of the alkoxy alkanol impurity with the dialkyl carbonate into a carbonate ether impurity, to obtain a top stream comprising alkanol and a bottom stream comprising dialkyl carbonate and carbonate ether impurity; and

(e) subjecting the bottom stream from the third distillation column to distillation in a fourth distillation column to obtain a top stream comprising dialkyl carbonate and a bottom stream comprising dialkyl carbonate and carbonate ether impurity; and

(f) recycling the bottom stream from the fourth distillation column to the first distillation column;

and additionally comprising: (h) contacting, in the presence of a transesterification catalyst, an aryl alcohol with the top stream comprising dialkyl carbonate from the fourth distillation column.

6. A process according to claim 5 , wherein the diaryl carbonate is diphenyl carbonate and the aryl alcohol is phenol.