Depolymerization of polyamide 6 in hydrophilic ionic liquids

Polyamide 6 underwent an efficient depolymerization in hydrophilic ionic liquids under microwave irradiation at 300 degrees C. The depolymerization completed within 60 min. Caprolactam was readily separated by simple extraction procedure and the ionic liquids were recovered and reused for several times. Addition of catalytic amounts of DMAP (N,N-dimethylaminopyridine) promoted the depolymerization effectively. The present improved procedure provides a method to avoid direct distillation procedure, which consumes energy for the separation of caprolactam from ionic liquids. Although some contamination of ionic liquids was observed, the present procedure provides a new possibility for the use of ionic liquids for plastic chemical recycling from the viewpoint of development of an energy-saving methodology. Use of solubility switchable ionic liquids is also examined to explore a possibility for better separation although depolymerization did not work well. (C) 2019, Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V.