Patent ID: 7635787

Claim:
A process for producing methionine comprising the step of: reacting methyl mercaptane with acrolein to obtain 3-methylmercaptopropionaldehyde, subjecting 3-methylmercaptopropionaldehyde to cyanhydrination with hydrogen cyanide to obtain 3 -methylmercaptopropioncyanhydrin, subjecting 3 -methylmercaptopropioncyanhydrin to hydantoination using carbon dioxide and ammonia to obtain 5-(β-methvlmercaptoethyl)-hydantoin, and hydrolyzing 5-(β-methylmercaptoethyl)hydantoin in the presence of an alkali, wherein a concentration of hydrogen sulfide is lowered to 5 ppm or less in a solution used for hydrolysis comprising 5-(β-methylmercaptoethyl)hydantoin and the alkali by at least one of the following methods: 1) distillation or rectification of the solution comprising 5-(β-methylmercaptoethyl)hydantoin and the alkali; 2) use of an excessive amount of acrolein relative to methyl mercaptane during the reaction of methyl mercaptane with acrolein; 3) addition of a substance for removing hydrogen sulfide.