Thermogravimetric kinetic study of agricultural residue biomass pyrolysis based on combined kinetics

Pyrolytic kinetic of an agricultural residue (AR) feedstock, a mixture of plants (cotton, wheat, rich, corn) stems, was investigated based on combined kinetics. The most suitable mechanism for AR one-step pyrolysis was f(α) = (1 − α)1.1816α−1.8428 with kinetic parameters of: apparent activation energy 221.7 kJ/mol, pre-exponential factor 4.17E16 s−1. Pyrolysis of AR feedstock could not be described by one-step reaction attributes to heterogeneous features of pyrolysis processes. Combined kinetics three-parallel-reaction (CK-TPR) model fitted the pyrolysis experimental data very well. Reaction mechanisms for pseudo hemicelluloses, cellulose, lignin in CK-TPR model was f(α) = (1 − α)1.6244α−0.3371[−ln(1 − α)]−0.0515, f(α) = (1 − α)1.0597α−0.6909[−ln(1 − α)]0.9026 and f(α) = (1 − α)2.9577α−4.7719, respectively. Apparent activation energy of three pseudo components followed the order of Elignin(197.3 kJ/mol) > Ecellulose(176.3 kJ/mol) > Ehemicelluloses (151.1 kJ/mol). Mechanism of hemicelluloses pyrolysis could be further expressed as f(α) = (1 − α)1.4. The pyrolytic mechanism of cellulose met the Nucleation well. However, mechanism of lignin pyrolysis was complex, which possibly was the combined effects of Nucleation, Diffusion, Geometrical contraction, and Power law.