Method for preparing methionine
The present invention relates to a method for preparing methionine or methionine salts. In particular, the invention describes the step of preparing 2-hydroxy-4-(methylthio)butyronitrile (MMP-CN) from 3-methylthiopropanal (MMP) and hydrogen cyanide (HCN) in the presence of ammonia by bringing a gaseous mixture comprising HCN and ammonia into contact with MMP.
1. A method for preparing 2-hydroxy-4-(methylthio)butyronitrile, the method comprising:
bringing a gas mixture comprising hydrogen cyanide and ammonia into contact with 3-methylmercaptopropionaldehyde, thereby producing a product mixture comprising 2-hydroxy-4-(methylthio)butyronitrile.
2. A method for preparing methionine or a salt of methionine, the method comprising:
bringing a gas mixture comprising hydrogen cyanide and ammonia into contact with 3-methylmercaptopropionaldehyde, thereby producing a product mixture comprising 2-hydroxy-4-(methylthio)butyronitrile.
3. The method of claim 1 , in which a molar ratio of ammonia to hydrogen cyanide in the gas mixture is from 0.06 to 0.99.
4. The method of claim 1 , further comprising, prior to the bringing:
preparing the gas mixture essentially comprising hydrogen cyanide, ammonia, and water according to an Andrussow process from methane, ammonia, and oxygen.
5. The method of claim 1 , further comprising, prior to the bringing:
preparing the gas mixture essentially comprising hydrogen cyanide, ammonia, and hydrogen according to a BMA process from methane and ammonia.
6. The method of claim 1 , further comprising:
separating the product mixture obtained after the bringing in and/or after the bringing into an offgas comprising nitrogen, hydrogen, and/or methane, and a liquid mixture comprising 2-hydroxy-4-(methylthio)butyronitrile, and
optionally purifying the offgas.
7. The method of claim 1 , wherein the product mixture obtained in the bringing further comprises 2-amino-4-(methylthio)butyronitrile and/or 2,2′-bis(2-(methylmercaptoethyl)iminodiacetonitrile.
8. The method of claim 2 , further comprising:
storing the product mixture obtained in the bringing at temperatures no higher than 60° C. and a pH of 2 to 8, before the product mixture is further reacted.
9. The method of claim 2 , further comprising:
first reacting the product mixture obtained in the bringing with ammonia and/or ammonium salts and carbon dioxide and/or carbonic acid salts to give 5-(2-methylmercaptoethyl)hydantoin.
10. The method of claim 9 , further comprising:
second reacting the 5-(2-methylmercaptoethyl)hydantoin under basic conditions, thereby forming carbon dioxide and ammonia, to give at least one methionine salt.
11. The method of claim 10 , further comprising:
at least partially recycling the ammonia and the carbon dioxide from the second reacting to the first reacting.
12. The method of claim 10 , further comprising:
at least partially recycling the ammonia obtained in the second reacting to the preparing.
13. The method of claim 10 , further comprising:
at least partially disposing of the ammonia obtained in the second reacting.
14. The method of claim 2 , further comprising:
purifying the product mixture from the bringing by distillation by removing at least a part of water.
15. The method of claim 12 , further comprising:
freeing the ammonia obtained after the second reacting from sulfur-containing compounds and optionally from CO 2 before it is recycled to the preparing.
16. The method of claim 10 , further comprising:
reacting the at least one methionine salt with an acid to give methionine.
17. A method for preparing a dipeptide of methionine, the method comprising:
carrying out the method of claim 1 , and then, in any order, aminating and hydrolyzing the 2-hydroxy-4-(methylthio)butyronitrile with acid or base to obtain a carboxylic acid;
optionally esterifying the carboxylic acid, to obtain an ester; and
condensing the carboxylic acid and/or the ester to form the dipeptide.
18. A method for preparing 3,6-bis(2′-methylmercaptoethyl)-2,5-diketopiperazine, the method comprising:
carrying out the method of claim 1 , and then, in any order, aminating and hydrolyzing the 2-hydroxy-4-(methylthio)butyronitrile with acid or base to obtain a carboxylic acid;
optionally esterifying the carboxylic acid, to obtain an ester; and
condensing the carboxylic acid and/or the ester to form the 3,6-bis(2′-methylmercaptoethyl)-2,5-diketopiperazine.
19. The method of claim 2 , in which a molar ratio of ammonia to hydrogen cyanide in the gas mixture is from 0.06 to 0.99.
20. The method of claim 2 , further comprising, prior to the bringing:
preparing the gas mixture essentially comprising hydrogen cyanide, ammonia, and water according to an Andrussow process from methane, ammonia, and oxygen.