Process for the Treatment of a Recycling Stream from a Plant for the Production of Polyarylene Ether Sulfones

A process is proposed for the treatment of a recycling stream (1) from a plant for the production of polyarylene ether sulfones via polycondensation of aromatic bishalogen compounds and of aromatic bisphenols or their salts in the presence of at least one alkali metal carbonate or ammonium carbonate or alkali metal hydrogencarbonate or ammonium hydrogencarbonate in an N-alkyl-2-pyrrolidone as solvent, comprising from 60 to 90% by weight of water, from 10 to 40% by weight of the N-alkyl-2-pyrrolidone and, as contaminant detrimental to specification, up to 5000 ppm by weight of the N-alkylsuccinimide corresponding to the N-alkyl-2-pyrrolidone and, alongside this, up to 1000 ppm by weight of other substances with higher boiling point than the N-alkyl-2-pyrrolidone, in particular inorganic salts, based in each case on the total weight of the recycling stream (1), where the entirety of the components gives 100% by weight, giving a pure N-alkyl-2-pyrrolidone stream (2) which can be returned to the plant for the production of polyarylene ether sulfones, via a final distillation process in a final column (K), wherein the final distillation is preceded upstream by a preliminary purification via evaporation in one or more evaporator stages for reduction of the content of high boilers compared to N-alkyl-2-pyrrolidone, giving one or more vapor streams (4, 5) which are fed as feed streams to the final column (K), the bottom stream (6) from the last evaporator stage being discharged and a substream (9) of the bottom stream (7) from the final column (K) being discharged and the rest of the bottom stream from the final column (K) being recycled into the last evaporator stage, and the one evaporator stage or the first of the plurality of evaporator stages being a column (WK) which is designed such that the top stream (10) therefrom still comprises a maximum of 200 ppm by weight of the N-alkyl-2-pyrrolidone, based on the total weight of the top stream therefrom, and is discharged, and the vapor streams (4, 5) being supplied to the final column (K) in vaporous form.