Studies on individual pyrolysis and co-pyrolysis of corn cob and polyethylene: Thermal degradation behavior, possible synergism, kinetics, and thermodynamic analysis

Abstract

The knowledge on thermo-kinetics, synergistic effect, and reaction mechanism of pyrolysis/co-pyrolysis of biomass with plastics is crucial for designing efficient reactor system and subsequently the pyrolysis/co-pyrolysis process. The present work explores thermal response, kinetics, reaction mechanism and thermodynamic analysis of pyrolysis and co-pyrolysis of individual corn cob (CC) and polyethylene (PE), and their blend in the ratio of 3:1 (w/w). Thermogravimetric analysis (TGA) data was obtained under inert atmosphere at various heating rates of 10, 20, and 30 °C/min and synergistic effect in the co-pyrolysis of CC and PE is discussed. The obtained TGA data was processed using various model-free isoconversional methods like KAS, FWO, Friedman, Starink, and Vyazovkin for determination of kinetics of pyrolysis/co-pyrolysis process of CC and PE. Average activation energy for CC pyrolysis was estimated to be 240 ± 51.25 kJ/mol, 240 ± 51.51 kJ/mol, 237 ± 49.67 kJ/mol, and 245 ± 52.10 kJ/mol according to KAS, Starink, FWO, and Vyazovkin models, respectively. Statistical analysis showed that the variation in reported values of activation energy was not significantly different (p = 0.994). Similar statistically insignificant difference was also observed for pyrolysis of PE and co-pyrolysis of CC and PE. Results showed that co-pyrolysis (CC + PE) requires 10% less activation energy than pyrolysis of CC alone. For the co-pyrolysis process, the extent of synergistic effect was discussed by difference in mass loss (ΔW). Investigation also revealed that residue left for co-pyrolysis of CC and PE is 50% less than pyrolysis of CC alone showing synergistic effect during co-pyrolysis. Thermodynamic parameters were calculated to illustrate complex mechanism of the process. Third order reaction, 3D diffusion Jander, and Ginstling–Brounshtein (D4) models were found to be best fitted for CC pyrolysis, PE pyrolysis, and co-pyrolysis, respectively. Results obtained are expected to be useful in the design of corn cob and waste polyethylene co-pyrolysis systems.