Process for preparing dialkyl carbonate and alkanediol

1. Process for the preparation of a dialkyl carbonate and an alkanediol, comprising:

(a) reacting an alkylene carbonate and an alkanol to obtain a product mixture containing unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, alkanediol and an ether alkanol impurity;

(b) separating unconverted alkylene carbonate and alkanediol from the product mixture to obtain a top stream containing unconverted alkanol, dialkyl carbonate and the ether alkanol impurity;

(c) recovering the alkanediol;

(d) separating unconverted alkanol from the top stream obtained in step (b) to obtain a bottom stream containing dialkyl carbonate and the ether alkanol impurity; and

(e) subjecting the bottom stream obtained in step (d) to extractive distillation using an extraction solvent to obtain a top stream comprising dialkyl carbonate and a bottom stream comprising the ether alkanol impurity and the extraction solvent, wherein the extraction solvent is an organic compound containing one or more ester moieties and/or ether moieties which organic compound does not contain a hydroxyl group; and

(f) removing the ether alkanol impurity from the bottom stream obtained in step (e) and recycling the extraction solvent to step (e).

2. Process according to claim 1 , wherein the alkylene carbonate is a C 2 -C 6 alkylene carbonate, and the alkanol is a C 1 -C 4 alkanol.

3. Process according to claim 2 , wherein the alkylene carbonate is ethylene carbonate or propylene carbonate, the alkanol is ethanol and the dialkyl carbonate is diethyl carbonate.

4. Process according to claim 1 , wherein the extraction solvent is an ester of formula R 1 X(C—O)OR 2 wherein X is absent or is an oxygen atom and wherein R 1 and R 2 comprise a total of 2 to 20 carbon atoms and do not contain a hydroxyl group.

5. Process according to claim 4 , wherein the ester of formula R 1 X(C═O)OR 2 is:

an ester wherein X is absent which originates from reacting an alkanol of formula R 2 OH containing 1 or more hydroxyl groups with a carboxylic acid of formula R 1 (C═O)OH, wherein all of the 1 or more hydroxyl groups of the alkanol are esterified; or

an alkylene carbonate wherein X is an oxygen atom and R 1 and R 2 are connected to form a ring; or a carbonate wherein X is an oxygen atom and R 1 and R 2 are not connected to form a ring.

6. Process according to claim 5 , wherein the alkylene carbonate used as extraction solvent in step (e) is identical to the alkylene carbonate used as reactant in step (a).

7. Process according to claim 1 , wherein the extraction solvent is an ether of formula R 4 —O—R 5 wherein R 4 and R 5 comprise a total of 2 to 20 carbon atoms and do not contain a hydroxyl group.

8. Process according to claim 7 , wherein the ether of formula R 4 —O—R 5 is:

an ether of a polyalkylene glycol wherein the polyalkylene glycol contains two hydroxyl groups which are both etherified with an alkanol; or

an ether of an alkanol of formula R 4 OH containing 1 or more hydroxyl groups and an alkanol of formula R 5 OH containing 1 or more hydroxyl groups, wherein all of the hydroxyl groups of said alkanols are etherified; or

an acetal or a ketal.

9. Process for removing an ether alkanol impurity from a stream containing a dialkyl carbonate and the ether alkanol impurity, comprising:

(e) subjecting the stream containing a dialkyl carbonate and the ether alkanol impurity to extractive distillation using an extraction solvent to obtain a top stream comprising dialkyl carbonate and a bottom stream comprising the ether alkanol impurity and the extraction solvent, wherein the extraction solvent is an organic compound containing one or more ester moieties and/or ether moieties which organic compound does not contain a hydroxyl group; and

(f) removing the ether alkanol impurity from the bottom stream obtained in step (e) and recycling the extraction solvent to step (e).

10. Process for making a diaryl carbonate, comprising removing an ether alkanol impurity from a stream containing a dialkyl carbonate and the ether alkanol impurity in accordance with the process of claim 1 , and then contacting, in the presence of a transesterification catalyst, an aryl alcohol with the stream containing the dialkyl carbonate.

11. The process according to claim 5 , wherein the ester of formula R 1 X(C═O)OR 2 is an alkylene carbonate wherein X is an oxygen atom and R 1 and R 2 are connected to form a ring, which alkylene carbonate is ethylene carbonate or propylene carbonate.