Investigation of EPET, EPEI, and EPU pyrolysis characteristics: Thermal decomposition behaviours, pyrolysis products and mechanism

Abstract

Pyrolysis is a promising technology in recycling copper from enamelled wires. Nevertheless, due to the unclear pyrolysis characteristics, the sorting of enamelled wires is deficient in the pyrolysis process. This work systematically investigated the pyrolysis characteristics of polyester enamelled wire (EPET), polyester imine enamelled wire (EPEI) and polyurethane enamelled wire (EPU). The decomposition behaviours showed that the mass loss for EPEI and EPET was around 1.9%, while it was about 1.5% for EPU. The pyrolysis temperature intervals and peaks for both EPEI and EPET appeared in the range of 320 ∼ 500 ℃ and around 420 ℃, while it was in a larger range of 228 ∼ 657 ℃ for EPU, and the peak was about 280 ℃. The average activation energies (E) calculated with Flynn-Wall-Ozawa (FWO) model demonstrated that EPEI and EPET were respectively 275.8 kJ/mol and 296.9 kJ/mol, while it was 194.2 kJ/mol for EPU. TG-FTIR results proved that the -CH, -CO, -CH2, and -OH were the main functional groups in the pyrolysis process for the three enamelled wires. Moreover, Py-GC/MS results indicated that the main pyrolysis product was benzoic acid for EPET and EPEI, while it was not observed for EPU. The pyrolysis mechanism displayed that the kinds of pyrolysis products were directly related to the connected aromatic functional group. The complicated pyrolysis products for EPU were mainly caused by the generation of isocyanate. Accordingly, EPU could be separately pyrolyzed, while EPET and EPEI were suitable for co-pyrolyzed. In consideration of improving pyrolysis efficiency and reducing energy consumption, the classification treatment by this method could be extended.