WO2014102306A3 - Method for purifying a recycling flow from a plant for producing polyarylene ether sulfones - Google Patents

Abstract

The invention relates to a method for purifying a recycling flow (1) from a plant for producing polyarylene ether sulfones by polycondensing aromatic bis-halogen compounds and aromatic bisphenols or salts thereof in the presence of at least one alkali-metal carbonate or hydrogencarbonate or ammonium carbonate or hydrogencarbonate in an N-alkyl-2-pyrrolidone as a solvent, containing 60 to 90 wt% of water, 10 to 40 wt% of N-alkyl-2-pyrrolidone, and, as a specification-impairing contaminant, up to 5000 ppm by weight of the alkyl succinimide corresponding to the N-alkyl-2-pyrrolidone and in addition thereto up to 1000 ppm by weight of additional high boilers in relation to N-alkyl-2-pyrrolidone, in particular inorganic salts, in each case with respect to the total weight of the recycling flow (1), the sum of the components equaling 100 wt%, so as to obtain a pure N-alkyl-2-pyrrolidone flow (2), which can be fed back into the plant for producing polyarylene ether sulfones, by means of purification by distillation in a purification column (K), the method being characterized in that a pre-purification by evaporation in one or more evaporator stages in order to reduce the content of inorganic salts is performed before the purification by distillation, one or more vapor flows (3, 4, 5) being obtained, which are fed to the purification column (K) as feed flows, and the bottom flow from the last evaporator stage being discharged and the bottom flow from the purification column (K) being completely recycled into the last evaporator stage.