Hydrolytic degradation of monomer casting nylon in subcritical water

In contrast with the conventional physical methods, sub- and supercritical hydrolysis is not only a more environmentally friendly method to recycle the monomer casting nylon (MC nylon) wastes, but also a more feasible way to produce the corresponding monomer. In subcritical water, MC nylon was decomposed completely into water-soluble oligomers within 45 min at 345 °C and 9 MPa. Fourier transform infrared spectroscopy and X-ray diffraction were employed to characterize the chemical composition and crystalline form changes of the solid products obtained within 30 min of the degradation. Qualitative and quantitative analyses of liquid phase product were performed by liquid chromatography mass spectrometry and high performance liquid chromatography. The yield of the main degradation product ε-caprolactam largely depended on the hydrolysis temperature and reaction time. The maximum yield value reached 89.0% when the reaction time was 75 min. A hydrolytic degradation mechanism of MC nylon in subcritical water is proposed as well.