Process for preparing methionine
A process is used for preparing methionine. Specifically, the process includes the hydrolysis of 5-(2-methylmercaptoethyl)hydantoin (methionine hydantoin) in an alkaline process solution. Further, the by-products that include formate and other anions of organic acids containing 1 to 5 carbon atoms are removed by electrodialysis of the process solution.
1. A process for preparing methionine, comprising:
conducting alkaline hydrolysis of 5-(2-methylmercaptoethyl)hydantoin in an aqueous process solution containing potassium hydroxide, and/or potassium carbonate, and/or potassium hydrogen carbonate to give a methionine potassium salt,
precipitating methionine from a neutralized aqueous processing solution by neutralization with carbon dioxide,
separating the methionine from the neutralized aqueous process solution,
concentrating the neutralized aqueous process solution from which methionine has been removed, and
recycling the concentrated aqueous process solution to the alkaline hydrolysis of the 5-(2-methylmercaptoethyl)hydantoin step,
wherein by-products, comprising formate and other anions of organic acids containing 1 to 5 carbon atoms, are removed between processing steps and/or during a processing step by electrodialysis in at least one electrodialysis cell,
wherein a larger percentage of methionine and/or potassium salts thereof and potassium hydrogen carbonate remain during said electrodialysis relative to a percentage of formate and other anions of organic acid containing 1 to 5 carbon atoms which remains, and
wherein the electrodialysis cell comprises at least two chambers and one of the at least two chambers is an anode compartment, which is bordered by an anion exchange membrane and an anode, and the pH in the anode compartment is from 5.8 to 8.0.
2. The process according to claim 1 , in which the current density in the electrodialysis cell is in a range from 1.0 to 200 A/m 2 , inclusive.
3. The process according to claim 1 , in which the electrodialysis cell comprises three chambers, wherein one chamber is a cathode compartment which is bordered by a cation exchange membrane and a cathode.
4. The process according to claim 1 , in which the electrodialysis cell comprises two chambers and one of the two chambers is the anode compartment and the other chamber is a cathode compartment, wherein the cathode compartment is bordered by an anion exchange membrane and a cathode.
5. The process according to claim 1 , wherein the electrodialysis is conducted in at least two electrodialysis cells, which are separated from one another by a bipolar electrode.
6. The process according to claim 1 , wherein an aqueous potassium hydroxide solution is formed in a cathode compartment and is partially fed into the anode compartment to adjust the pH to from 5.8 to 8.0.
7. The process according to claim 1 , wherein an aqueous potassium hydroxide solution is formed in a cathode compartment and is partially fed to the aqueous process solution for conducting alkaline hydrolysis.