Cattle manure pyrolysis process: Kinetic and thermodynamic analysis with isoconversional methods

The kinetic and thermodynamic behaviors of the pyrolysis process of cattle manure are greatly important for the understanding of its prolysis mechanism and the design of pyrolysis reactors. In this research, the thermogravimetric analysis (TGA) experiments of cattle manure were firstly implemented with six different heating rates, e.g. 10, 20, 30, 40, 60 and 80 °C min−1. And then, the activation energies (E) during the pyrolysis process were calculated with four isoconversional methods (e.g., Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink methods); the thermodynamic behavior was addressed by considering the thermodynamic parameters including pre-exponential factor (A), as well as the changes of enthalpy (ΔH), free Gibbs energy (ΔG), and entropy (ΔS). Results demonstrates that the pyrolysis process is constituted by a multi-stage reaction and can be roughly divided into three stages with the increase of conversion degrees (α): Stage I (α = 0.05-0.35) represents the dominating reaction zone of the extractives and hemicellulose component, stage II (α = 0.35-0.55) cellulose and lignin components, and stage III (α = 0.55-0.85) lignin and mineral components. The decomposition processes of each component have no clear boundaries and interact with each other. The complex mechanism of cattle manure pyrolysis is also revealed with the thermodynamic analysis.