Process for separating and recovering residual monomers from aqueous suspensions of acrylonitrile polymers

Claim 1

A process for the separation and recovery of unreacted acrylonitrile and comonomers with a boiling point below 99°C under normal conditions from an aqueous polymer dispersion of a filament-forming acrylonitrile polymer, wherein a filterable polymer dispersion, the liquid phase of which may contain up to 7% by weight of residual monomer, is subjected continuously and uniformly to straightforward distillation in a thin-layer evaporator, the pressure prevailing inside the thin-layer evaporator being regulated so that the temperature of the evaporating liquid phase of the polymer dispersion does not exceed 95°C, the average residence time of the polymer dispersion in the evaporator does not exceed 5 minutes, and the evaporation rate of the liquid phase amounts to up to 30% by weight, wherein the vapours given off during evaporation are condensed in a condenser initially under substantially the same pressure which prevails in the thin-layer evaporator and at temperatures above 0°C, after which the vapours which have not been condensed in the condenser are compressed to a pressure higher than that prevailing in the condenser, and wherein the monomer-rich phases obtained, following separation of the aqueous phases, are returned to the polymerisation process.