| Abstract: | Nylon-6 as an engineering polymer and its starting monomer are both costly. Chemical reutilization offers some economic and environmental benefits. Depolymerization of nylon-6 was carried out by the conventional technique of hydrothermal method using various organo-sulfonic acids such as Methane sulfonic acid (MSA), para-toluene sulfonic acid (p-TSA), benzene sulfonic acid (BSA), and tetra-butyl ammonium bromide (TBAB) as a phase transfer catalyst. Various parameters such as temperature, time, normality of acids, and phase transfer catalyst concentration were varied to optimize its parameters, and characterization techniques such as amine value titrations and Fourier transform infrared spectroscopy were used for quantitative measurements. Solid-state 13C NMR was done for structure confirmation. A chemical kinetics interpretation shows degradation mechanism follows first-order kinetics under various catalysts. MSA has the highest reaction rate of 8.49 × 10?2 h?1 at 90°C; it decreases to 7.72 × 10?2 h?1 at 100°C. At the same time, aromatic Sulfonic acids such as p-TSA and BSA have a higher reaction rate of 8.995 × 10?2 h?1 and 5.582 × 10?2 h?1, respectively. The activation energy was lowered as the acidity of organo-sulfonic acids increased as benzene sulfonic acid has the lowest Ea. Followed by p-TSA, and MSA has the highest Ea. Free energy shows a similar kind of value. A simple theoretical model was used to calculate the activation energy. Thermodynamic parameters such as heat of enthalpy and entropy of reaction were evaluated using the Eryig–Polanyi equation. The combined catalytic effect of organo-sulfonic acids and phase-transfer catalyst provides a better environment-friendly method for depolymerizing nylon-6. |
