Co-Pyrolysis of Corn Cob-Husk Blends: Kinetics, Reaction Mechanism, and Products Using TG and Py-GC/MS Analysis

Abstract

A comparative study on the pyrolysis of untreated (SA) and NaOH-treated (SB) corn cob-husk blends (1:1, wt%) was conducted to elucidate their kinetic, thermodynamic, and mechanistic characteristics. The NaOH treatment was performed using 10 wt% NaOH solution for 2 h. Thermogravimetric analysis (TGA) was carried out over a temperature range of 50 to 600 °C, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was performed at 550 °C. The Kissinger-Akahira-Sunose (KAS) and Friedman (FR) isoconversional methods were used to evaluate the activation energies and thermodynamic parameters (pre-exponential factor, Gibbs free energy, enthalpy, and entropy). The minor discrepancies between activation energy (E_α) and enthalpy change (ΔH) (< 6 kJ/mol) for both SA and SB suggest a high potential for biomass energy utilization. Notably, the NaOH treatment resulted in a downward shift in pyrolysis temperature and a lower average activation energy for SB, indicating a thermodynamically more favorable pathway. Mechanistically, the Criado method confirmed that SA follows a three-dimensional diffusion model (D3) initially (Zone I), transitioning to a random nucleation model (F1) beyond approximately 325 °C (Zone II), while SB consistently adheres to the D3 model. Additionally, Py-GC/MS analysis revealed that NaOH treatment, despite reducing bio-oil yield, noticeably enhanced biochar formation.