Patent ID: 6268531
Filing Date: 2001-07-31
Classification: A23K,B01J,C07C

Abstract:
A process for the preparation of 2-hydroxy-4-methylthiobutanoic acid or a salt thereof comprising:introducing 2-hydroxy-4-methylthiobutanenitrile and an aqueous mineral acid into an aqueous hydrolysis mixture comprising 2-hydroxy-4-methylthiobutanamide, mineral acid, and unreacted 2-hydroxy-4-methylthiobutanenitrile;hydrolyzing 2-hydroxy-4-methylthiobutanenitrile in said hydrolysis mixture in a continuous nitrile hydrolysis reactor comprising a back-mixed reaction zone and a circulation zone in fluid flow communication with said back-mixed reaction zone, said circulation zone comprising a circulating line;continuously circulating said aqueous hydrolysis mixture in a circulating stream that is withdrawn from said back-mixed reaction zone, passed through said circulation zone and returned to said back-mixed reaction zone, said circulating stream as withdrawn from said back-mixed reaction zone containing unreacted 2-hydroxy-4-methylthiobutanenitrile;removing a portion of said circulating aqueous hydrolysis mixture as a nitrile hydrolysis reactor product stream from a forward flow port in said circulation zone and transferring said nitrile hydrolysis reactor product stream to an amide hydrolysis flow reactor;diluting said nitrile hydrolysis reactor product stream with water at a point downstream of said forward flow port to provide a finishing reaction stream;hydrolyzing 2-hydroxy-4-methylthiobutanamide contained in said finishing reaction stream in said amide hydrolysis flow reactor to produce a finished aqueous hydrolyzate product containing 2-hydroxy-4-methylthiobutanoic acid;the sum of the residence time of said circulating stream in said circulation zone upstream of said forward flow port and the residence time of said nitrile hydrolysis reactor product stream downstream of said forward flow port prior to dilution being sufficient to substantially extinguish residual 2-hydroxy-4-methylthiobutanenitrile prior to the dilution of said nitrile hydrolysis reactor product stream.