Pyrolysis kinetics of chemically treated and torrefied radiata pine identified through thermogravimetric analysis

Abstract

This study investigates the effects of separate and combined chemical (acid and alkaline pretreatment) and torrefaction pretreatment of radiata pine biomass on the pyrolysis kinetic parameters using thermogravimetric analysis (TGA). Thermal degradation profiles of the treated biomass samples were examined and correlated to changes in proximate and ultimate analyses. The TGA results were then used to determine the activation energies (Ea) and pre-exponential factors (A) in various kinetic models, including Kissinger, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and simplified Distributed Activation Energy Model (DAEM) methods, where the obtained values of Ea for these models ranged between 170.9 and 270.9 kJ mol−1, 170.1–262.3 kJ mol−1, 186.2–259.2 kJ mol−1, and 169.3–266.3 kJ mol−1, respectively, for all of the treated biomass samples. The mean Ea values after pretreatments increased in comparison with that of the Control sample. In general, the Ea values increased over the degree of conversion from 0.2 to 0.8 attributed to the crystallinity and carbonisation effects upon pretreatments. However, the mean Ea values varied with the pretreatment methods, indicating a complex multi-step mechanism of pyrolysis process of the treated biomass. The A values determined for all of the treated biomass samples varied over a broad magnitude ranging from 105 to 1026 s−1 for the adopted kinetic models.