Kinetics and Thermodynamic Studies of Depolymerization of Nylon Waste by Hydrolysis Reaction

Depolymerization reaction of nylon waste was carried out by hydrolysis reaction. Yield of depolymerization products was up to 72.20% for a two-hour reaction time. The products obtained were characterized by melting point and FTIR spectra. The values obtained for dibenzoyl derivative of hexamethylenediamine (DBHMD) agreed with those of the pure substance. Chemical kinetics of this reaction shows that it is a first-order reaction with respect to hexamethylenediamine (HMD) concentration with velocity constant ？min？1. The energy of activation and Arrhenius constant obtained by Arrhenius plot were 87.22？KJg？1 and 0.129, respectively. The other thermodynamic parameters such as enthalpy of activation () and entropy of activation () and free energy of activation were 5975.85？J and ？270.86？J·K？1·mol？1 and 101.59？KJ·mol？1, respectively. 1. Introduction There are many types of industrial waste; among them waste of polymer industry is important because of its resistance to biodegradation. The interest in recycling of nylon waste is continuously increasing because of environmental and economic factors and as a process for generating valuable products [1]. Polyamide such as nylon is one of the plastics that are widely used in our life. Its depolymerization was explored over 30 years and many efforts have been made so far [2]. The consumption of nylon is small as compared to other polymers. It has high melting point and low solubility, providing nylon with advantageous properties such as thermal, mechanical, and chemical resistance. Thus, nylon is used in extremely broad range of applications and its production and consumption have recently increased. Nylon recycling has focused on hydrolysis, aminolysis, and pyrolysis. Nylon-6,6 can be depolymerized to corresponding oligomers and monomer [3], while nylon-6 in the presence of phosphoric acid provides a mixture of ethylene glycol derivative and -caprolactam and linear oligomers [4]. Duch and Allgeier [5] reported that nylon-6,6 can be recycled via combination of ammonolysis, dehydration, and nitrate hydrogenation in the presence of Raney catalyst to predominantly produce hexamethylenediamine (HMD). Goto and coworkers [6–8] investigated hydrolysis of nylon-6 and found aminocaproic acid as first product which underwent cyclodehydration to -caprolactam. Their findings were consistent with the depolymerization [9] of nylon-6,6. Relatively less work has been reported on depolymerization of nylon-6,6. In the present work depolymerization of nylon-6,6 waste by hydrothermal hydrolysis has been investigated. The kinetics of