GB996322A - Simultaneous recovery of pure ammonium sulphate and pure lactams from rearrangement mixtures of alicyclic ketoximes - Google Patents

Abstract

A process for continuously recovering pure ammonium sulphate in the preparation of lactams (see Division C2) by Beckmann rearrangement of a cycloalkanone oxime having 6 to 10 ring carbon atoms with 98 to 100% wt. sulphuric acid or oleum containing up to 35% wt. of free sulphur trioxide, which reaction mixture contains 30 to 50% wt. lactam, followed by neutralizing said reaction mixture by contact with ammonia in the presence of 5 to 50 times the amount (with reference to the weight of reaction mixture) of 25 to 45% wt. ammonium sulphate solution, comprises separating the resulting lactam and ammonium sulphate phases, evaporating the ammonium sulphate phase until ammonium sulphate has been precipitated in an amount corresponding to the sulphuric acid in the rearrangement mixture, diluting the mother liquor with such an amount of water as is necessary to restore the ammonium sulphate solution to its original concentration, and returning the diluted mother liquor to the neutralization zone. Concentration of the ammonium sulphate fraction may be effected by evaporation under reduced pressure. Preferably 5 to 50 times the weight of mother liquor (with reference to the weight of rearrangement mixture) is returned to the neutralization zone.ALSO:A process for the recovery of pure lactams and pure ammonium sulphate from reaction mixtures obtained by Beckmann re-arrangement of a cycloalkanone oxime having 6 to 10 ring carbon atoms with 98 to 100% wt. sulphuric acid or oleum containing up to 35% wt. of free sulphur trioxide, which reaction mixture contains 30 to 50% wt. of lactam, comprises neutralizing said reaction mixtures by contact with ammonia in the presence of 5 to 50 times the amount (with reference to the weight of the reaction mixture) of 25 to 45% wt. ammonium sulphate solution, separating the resulting lactam and ammonium sulphate phases, evaporating the ammonium sulphate phase until ammonium sulphate has been precipitated in an amount corresponding to the sulphuric acid in the re-arrangement mixture, diluting the mother liquor with such an amount of water as is necessary to restore the ammonium sulphate solution to its original concentration, returning the diluted mother liquor to the neutralization zone, extracting the lactam phase with at least three times its weight of benzene, toluene or xylene, and distilling to obtain the lactam. Preferably 5 to 50 times the amount of mother liquor (with reference to the weight of re-arrangement mixture) is returned to the neutralization zone. Concentration of the ammonium sulphate solution may be effected by evaporation under reduced pressure. The lactam may be extracted by a countercurrent extraction in a one-stage or multi-stage process. In specific examples caprolactam and caprylolactam are produced from cyclohexanone oxine and cyclooctanone oxine respectively.