Process for obtaining mixtures containing methionine and potassium hydrogencarbonate

A process for producing methionine, comprising:

• (1) hydrolyzing 5-[2-(methylthio)ethyl]imidazolidin-2,4-dione in the presence of a basic potassium compound to obtain a hydrolysate comprising potassium, methioninate, and potassium methionyl methioninate;
• (2) introducing carbon dioxide in a first carbonation into the hydrolyzate to obtain a suspension comprising methionine, methionyl-methionine, and potassium hydrogencarbonate and a methionine precipitate, then separating the suspension into a methionine-containing first precipitate and a methionyl-methionine-containing first mother liquor;
• (3) concentrating the first mother liquor obtained in (2) in a first concentration to obtain a concentrated first mother liquor,
• (4) recycling a first portion of the concentrated first mother liquor obtained in (3) into (1),
• (5) introducing carbon dioxide into a second portion of the concentrated first mother liquor (3) in a second carbonation to obtain a suspension comprising a methionine and a potassium hydrogencarbonate precipitate, then separating the suspension into a second precipitate and a second mother liquor,
• (6) concentrating the second mother liquor, then introducing carbon dioxide into the concentrated second mother liquor to obtain a suspension comprising a methionine and a potassium hydrogencarbonate precipitate, then separating the suspension into a third precipitate comprising a mixture of methionine and potassium hydrogencarbonate and a third mother liquor comprising methionyl-methionine,
• wherein the third precipitate comprises 6.5% by weight or less of met-met.