Method for preparing alpha-hydroxycarboxylic acid esters in which ammonia is recycled
The present invention relates to a process for preparing alpha-hydroxycarboxylic esters proceeding from hydrogen cyanide, wherein the ammonia formed in the step of alcoholysis of the corresponding alpha-hydroxycarboxamide is recycled into a hydrogen cyanide preparation process after a purification step.
1. A process for preparing an alpha-hydroxycarboxylic ester, comprising:
preparing hydrogen cyanide,
alcoholysis of an alpha-hydroxycarboxamide to obtain said alpha-hydroxycarboxylic ester,
wherein ammonia and at least one alkylamine formed in the alcoholysis of the alpha-hydroxycarboxamide, after a purification step, are recycled into the hydrogen cyanide preparation process still comprising at least one alkylamine
wherein the hydrogen cyanide preparation is according to an Andrussow process of reaction of methane with ammonia.
2. The process according to claim 1 , wherein a concentration of a total amount of the alkylamines based on ammonia is 1-100 000 ppm.
3. The process according to claim 1 , wherein the alpha-hydroxycarboxylic ester is methyl 2-hydroxyisobutyrate.
4. The process according to claim 1 , wherein the alkylamine is trimethylamine.
5. The process according to claim 1 , wherein the ammonia is purified by an absorbent by passage through a solid.
6. The process according to claim 1 , wherein the ammonia is purified in a continuously operated adsorber bed.
7. The process according to claim 1 , wherein the ammonia is purified by activated carbon.
8. The process according to claim 1 , wherein the alcoholysis reaction of the alpha-hydroxycarboxamide is effected in a liquid phase or in a gas phase.
9. The process according to claim 1 , wherein the purification is effected within a temperature range from 0° C. to 150° C.
10. The process according to claim 1 wherein the purification is effected within a pressure range from 0.05 to 5 bar.
11. The process according to claim 1 , comprising:
a) feeding a reactant stream comprising the alpha-hydroxycarboxamide and an alcohol into a pressure reactor containing a catalyst, to obtain a reaction mixture,
b) converting the reaction mixture in the pressure reactor at a pressure in the range of 0.1-100 bar, to obtain a product mixture,
c) depleting the product mixture of alcohol and ammonia that arises from b),
d) separating alcohol and ammonia containing at least trimethylamine and
e) purifying ammonia containing at least trimethylamine by activated carbon before said ammonia into the hydrogen cyanide preparation process.