Process for recovering n-methylpyrrolidone by plural distillations

Abstract

A process for recovering N-methylpyrrolidone contained in an N-methylpyrrolidone-containing liquid formed in the process for preparing a polyarylene thioether by the dehalogenosulfidation of a dihalogeno-aromatic compound and an alkali metal sulfide in the presence of N-methylpyrrolidone as the polymerization solvent, which comprises (a) subjecting the N-methylpyrrolidone-containing liquid to distillation to distill and recover the majority of contained N-methylpyrrolidone while recovering a distillation residue having such a flowability that flow transferring of the distillation residue is possible, and (b) supplying the distillation residue to an air-tight mixer for a highly-viscous fluid, which has a vent and is provided with a heater, to treat the distillation residue under the conditions of a temperature in the mixer of 190.degree. to 310.degree. C., a pressure in the mixer of 50 to 760 Torr and a residence time in the mixer of 5 minutes to 10 hours, thereby to distill N-methylpyrrolidone contained in the distillation residue through said vent, the distilled N-methylpyrrolidone being collected. According to this process, N-methylpyrrolidone can be recovered at a high recovery without deterioration of the N-methylpyrrolidone.