GB667075A - An improved process for the manufacture of lactams - Google Patents

Abstract

Lactams are separated from the mixture obtained by Beckmann's re-arrangement of cyclic oximes with strong sulphuric acid by continuously mixing said mixture with the required amount of a neutralizing agent and with at least the same amount of a neutral salt solution obtained in a previous neutralization process and continuously drawing off the separated lactam. The components should be intimately mixed and their residence time in the neutralization zone should be as short as possible, e.g. not exceeding 3-10 minutes. Cooling with brine is not necessary and the salt solution may be used in its precooled state after removal of lactam. The neutralizing agents are preferably those which yield readily soluble sulphates, i.e. from highly concentrated solutions. Preferably the salt solutions used are nearly or totally saturated. The preferred neutralizing agent is aqueous ammonia solution containing 13-15 per cent of ammonia and 20-25 per cent sodium or potassium hydroxide solutions are also specified. The pH of the neutralization mixture should be between 3 and 8, preferably at about 6. Lactams containing 6-11 carbon atoms are preferred, those specified being caprolactam, oenatholactam, o -aminooctylic acid lactam, o -aminononylic acid lactam, o -aminodecylic acid lactam and o -amino-undecylic acid lactam. In examples: (1) the product obtained by the reaction of cyclohexanone oxime with oleum together with 14.5 per cent aqueous ammonia solution and saturated ammonium sulphate solution obtained in a prior neutralization stage flows to a neutralization vessel whose effective volume is decreased by means of a siphon overflow and then to a separator at 75 DEG C and pH6 the sulphate solution being extracted with an organic solvent; (2) is as (1) the temperature of the components being respectively 50 DEG , 20 DEG and 30 DEG C., mixing being effected in a continuous fashion through a high-speed mixer, the product is separated at 80 DEG C. and pH7 and part of the ammonium sulphate fed back, and (3) product from the reaction of suberone oxime with oleum, 15 per cent aqueous ammonium and recycled ammonium sulphate are intimately mixed as in (2) to yield a mixture which on separation has pH 6.5 and is at 90 DEG C. oenantholactam being obtained.