Co-pyrolysis of sewage sludge and low-density polyethylene – A thermogravimetric study of thermo-kinetics and thermodynamic parameters

Abstract This study investigates, for the first time, the thermal behaviors, kinetics and thermodynamics of sewage sludge (SS) and low-density polyethylene (LDPE) and their blends during co-pyrolysis. SS and LDPE co-pyrolysis were examined through thermogravimetric analysis (TGA) using different mixtures and multiple heating rates method. A positive interaction caused by the co-pyrolysis of SS and LDPE has been confirmed by the improved weight loss rate and devolatilization. Discrepancies between theoretical and experimental TGA/DTG curves as a measurement of the extent of synergic effect proved the existence of chemical interactions during the co-pyrolysis between the SS and LDPE blends of 1:1 and 1:2 ratios. The activation energy and reaction order for raw materials and their blends were studied by Coats-Redfern model. SS and LDPE blend of 1:1 ratio was optimal as it decreased the activation energy. Meanwhile, kinetics and thermodynamics were obtained from Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Starink methods. Where the activation energies (76.73–355.83 kJ/mol), Gibbs free energy (116.92–123.04 kJ/mol) and lower difference of enthalpy (ΔH=∼6 kJ/mol) showed a promising potential to convert abundant and low-cost bio-solid wastes into bioenergy. This study provides a theoretical groundwork for co-pyrolysis of SS and LDPE.