In a process for the production of acrylic fibers by the emulsion polymerization of acrylonitrile, the unreacted monomer is recovered from water by distillation. Acrylonitrile forms an zoetrope with water and the overhead product from the column contains around 5 mol% water. The overheads are condensed and the recovered acrylonitrile separated from the water in a decanter. The decanter operating temperature will be 20 °C. Size a suitable decanter for a feed rate of 3000 kg/h.