Methods for producing alkyl(meth)acrylates

1. A process for preparing an alkyl (meth)acrylate, comprising:

transesterifying an alkyl α-hydroxycarboxylate with a (meth)acrylic acid to obtain the alkyl (meth)acrylate and an α-hydroxycarboxylic acid, and

dehydrating the α-hydroxycarboxylic acid to obtain a (meth)acrylic acid,

wherein the transesterification comprises from 0.1 to 50% water by weight relative to the alkyl α-hydroxycarboxylate, and

the (meth)acrylic acid obtained by dehydration of the α-hydroxycarboxylic acid is the same as or different from the (meth)acrylic acid transesterified with the alkyl α-hydroxycarboxylate.

2. The process according to claim 1 , wherein the alkyl α-hydroxycarboxylate is obtained by alcoholysis of a hydroxycarboxamide.

3. The process according to claim 2 , wherein the hydroxycarboxamide is obtained by a hydrolysis of a cyanohydrin.

4. The process according to claim 3 , wherein the cyanohydrin is acetone cyanohydrin.

5. The process according to claim 3 wherein a catalyst is used for the hydrolysis.

6. The process according to claim 5 , wherein the catalyst comprises manganese oxide, sulphuric acid or an enzyme.

7. The process according to claim 2 , wherein the alcohol used for the alcoholysis of the hydroxycarboxamide comprises 1 to 10 carbon atoms.

8. The process according to claim 7 , wherein the alcohol is methanol and/or ethanol.

9. The process according to claim 2 , wherein the alcoholysis is carried out at a temperature in the range of 160-240° C.

10. The process according to claim 2 , wherein the alcoholysis is carried out at a pressure in the range from 5 to 30 bar.

11. The process according to claim 2 , wherein at least one basic catalyst is used for the alcoholysis.

12. The process according to claim 1 , wherein the transesterification of the alkyl α-hydroxycarboxylate with (meth)acrylic acid is catalysed by an acid.

13. The process according to claim 12 , wherein the acid is an ion exchanger.

14. The process according to claim 12 , wherein the transesterification is carried out in a still.

15. The process according to claim 1 , wherein the transesterification of the alkyl α-hydroxycarboxylate with (meth)acrylic acid is carried out at a pressure in the range from 100 mbar to 3 bar.

16. The process according to claim 1 , wherein the transesterification of the alkyl α-hydroxycarboxylate with (meth)acrylic acid is carried out at a temperature in the range from 70 to 130° C.

17. The process according to claim 1 , wherein a molar ratio of water to the alkyl α-hydroxycarboxylate is from 0.2 to 1.00.

18. The process according to claim 1 , wherein the molar ratio of alkyl α-hydroxycarboxylate to (meth)acrylic acid in the transesterification of the alkyl α-hydroxycarboxylate with (meth)acrylic acid is in the range from 3:1 to 1:3.

19. The process according to claim 1 , wherein the reaction time in the transesterification of the alkyl α-hydroxycarboxylate with (meth)acrylic acid is in the range from 5 minutes to 5 hours.

20. The process according to claim 1 , wherein the dehydration of the α-hydroxycarboxylic acid and the transesterification of the alkyl α-hydroxycarboxylate with (meth)acrylic acid is carried out at the same pressure.

21. The process according to claim 1 , wherein the (meth)acrylic acid obtained in gaseous form by the dehydration of the α-hydroxycarboxylic acid is passed to the transesterification without condensation and reevaporation.

22. A process for preparing alkyl (meth)acrylates, comprising

transesterifying an alkyl α-hydroxycarboxylate with (meth)acrylic acid to obtain alkyl (meth)acrylates and α-hydroxycarboxylic acid, and

dehydrating the α-hydroxycarboxylic acid to obtain (meth)acrylic acid,

wherein

the transesterification comprises from 0.1 to 50% water by weight relative to the alkyl α-hydroxycarboxylate, and

the alkyl α-hydroxycarboxylate is obtained by alcoholysis of a hydroxycarboxamide.