Non-isothermal kinetic study by TGA analysis of printed circuit boards and cotton stalk

Abstract

Waste electrical and electronic equipment (WEEE) consisting of Printed circuit boards (PCBs) is a very hazardous materials with a complex chemical composition, making it difficult to reuse and recycle. Pyrolysis has thus far been demonstrated to be a viable alternative for energy and material recovery in the form of gas, solid char and especially liquid oil. In this study, the pyrolysis of PCB, CS (Cotton Stalk) and its different compositions are examined by thermogravimetric analysis (TGA) using a non-isothermal technique. The thermal degradation was carried out for the temperature range 25–700 °C, in the presence of N2 atmosphere, with 50 ml/min flow rate using three different heating rates 5, 10 and 15° 30 C/min. The kinetic parameters such as apparent activation energy (Eα and lnA)were calculated using the Flynn Wall Ozawa (FWO) model-free method and the degradation mechanism was investigated by the Criado method, using a range from reaction order n = 1 to n = 3 for different samples. Within the two pyrolysis zones, the first zone of CS:PCB composition, showed slower reactions and better thermal stability of char compared to individual samples; whereas, in the second zone decreased activation energy is an indication of a faster reaction rate due to the presence of lignin in CS and alkali metals from the PCB. The experiment was carried out in a lab scale fixed bed reactor and the produced oil has been analysed using gas chromatography-mass spectrometry. Co-pyrolysis facilitated the suppressed phenol, and phenolic compounds and the fixing of bromine in char by almost twice as much.