Process for producing methionine

摘要

The present invention provides a process for producing methionine which is advantageous from the viewpoints of cost and wastewater disposal, and which comprises the following steps (1) to (5):
(1) a reaction step comprising hydrolysis of 5-[2-(methylthio)ethyl]imidazolidine-2,4-dione in the presence of a basic potassium compound;
(2) a first crystallization step comprising introduction of carbon dioxide into the reaction solution obtained in step (1) to precipitate methionine, and separation of the resultant slurry into a precipitate and a mother liquor;
(3) a second crystallization step comprising concentration of the mother liquor obtained in step (2), mixing with a lower alcohol, introduction of carbon dioxide into the mixture to precipitate methionine and potassium hydrogen carbonate, and separation of the resultant slurry into a precipitate and a mother liquor;
(4) a heating step comprising concentration of the mother liquor obtained in step (3) followed by a heating treatment at 150 to 200°C; and
(5) a third crystallization step comprising introduction of carbon dioxide into the heated mother liquor obtained in step (4) to precipitate methionine and potassium hydrogen carbonate, and separation of the resultant slurry into a precipitate and a mother liquor.