Kinetics of pyrolysis of cotton stalk using model-fitting and model-free methods

Abstract

With the depletion of fossil fuels, the conversion of biomass to biofuel is increasingly seen as a possible solution. Pyrolysis is one of these biomass-to-biofuel conversion technologies. In the present study, cotton stalk pyrolysis was investigated to determine the intrinsic kinetic parameters to understand the pyrolysis process. Model-fitting and model-free methods are applied to assess the kinetics. Pyrolysis of the cotton stalk was performed at different heating rates (10, 20, 30, and 40 K min−1) using a thermogravimetric analyzer. The obtained data from TGA was used to estimate the key kinetic parameters using various models/methods including Single reaction model, Series reaction model, Kissinger-Akahira-Sunose (KAS) method, and Flynn–Wall–Ozawa (FWO) method. The results of model-fitting kinetics showed that the pyrolysis mechanism could not be explained by the simple reaction models and obtained unrealistic kinetic parameters. Further, model-free methods were investigated to address the complex reaction mechanism. Besides, the predicted activation energy using KAS method values ranged from 223 to 230 kJ mol−1. In the FWO method, activation energy ranges from 213 to 240 kJ mol−1. In both methods, the calculated average activation energy value is in the proximity of 226 kJ mol−1 for fractional conversion value of 0.05 > α > 0.7.