Procédé de récupération d'une lactame

A process for recovering a lactam from a mixture thereof with sulphuric acid comprises treating the mixture at a temperature in the range of 20 DEG to 60 DEG C. with ammonia in the presence of concentrated liquid aqueous lactam, the weight of lactam in solution being at least 2 1/3 times the weight of water, separating from the resulting mixture a solid ammonium sulphate phase and a lactam rich liquid phase, washing the solid ammonium sulphate phase with concentrated aqueous ammonium sulphate liquid, mixing the washings with the lactam-rich liquid phase and separating from the resulting mixture a lactam-rich liquid phase, and a concentrated aqueous ammonium sulphate phase, and recycling a part of the last-mentioned lactam-rich liquid phase to the treating step to provide the desired concentration. The ammonium sulphate phase may be recycled to the washing step. The concentrations in the treatment stage are preferably regulated to give a solid ammonium sulphate phase which is 20 to 35% of the weight of the total mixture. The lactam may be caprolactam and water may be added in the treatment step to give a mixture containing as liquids about 68% by weight of lactam, 28% of water and 4% solutes, the solids being 43 parts by weight per 133 parts of liquid mixture. C4- 11 lactams are preferred.