Subcritical water hydrolysis of nylon 6 extract concentrate

Nylon 6 extract concentrate, namely, wastewater produced from industrial nylon 6 extraction unit, was hydrolyzed in subcritical water to efficiently decrease the cyclic dimer (CD) content. The CD equilibrium conversion reached a maximum when the initial water content ranged from 0.40 to 0.45 g/g; specifically, a CD conversion of 94.3 % was achieved at the hydrolysis temperature of 543 K and an initial water content of 0.40 g/g. A kinetic model including both acid- and base-catalyzed mechanisms was developed. The model predictions were in good agreement with the experimental results. The hydrolysis reaction constants increased significantly with increasing subcritical water content. By considering the effects of subcritical water on the individual reaction constants, the kinetic model could reproduce the experimental results over a wide range of initial water contents. Hopefully, the developed kinetic model will be applied in the design of a novel nylon 6 extract liquor recycling process.