Method for the continuous preparation of methionine or methionine derivatives

摘要

PCT No. PCT/EP93/02838 Sec. 371 Date May 23, 1995 Sec. 102(e) Date May 23, 1995 PCT Filed Oct. 14, 1993 PCT Pub. No. WO94/08957 PCT Pub. Date Apr. 28, 1994The direct saponification of methionine nitrile obtained from methylmercaptopropionaldehyde, prussic acid and ammonia gives low yields, catalyst and educt losses and unwanted side-products. The aim of the invention is therefore to provide a method which can be carried out without isolating the intermediate products, in particular continuously, and with low losses. The ketone used is recovered in high yields after amide saponification since this liberates the ketone from side-products. In order to recover the ammonia, it is necessary for the ammonia to be substantially freed of ketone, the mixture of ammonia, ketone and water obtained being separated under pressure in a separation column. When the amide is saponified at >/=160 DEG C., amide concentrations of less than 25% by wt. are preferred. Methionine nitrile is produced by treatment with at least 4 equivalents of >/=50% by wt. ammonia at between 40 DEG and 80 DEG C./or between 5 and 60 min. Cyanide residues are destroyed by heating to over 150 DEG C. Methionine is of particular use as a feedstuff, in particular in aqueous solution.