Thermogravimetric analysis and pyrolysis kinetics of typical crop straws

Using corn stalks, rapeseed stalks, and cotton stalks as raw materials, the pyrolysis characteristics and kinetic parameters in a nitrogen atmosphere were analyzed from a kinetic perspective through thermogravimetric (TG) and differential thermogravimetric (DTG) curves at four different heating rates of 10, 20, 30, and 40°C/min. Three model-free methods—Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink —were employed to calculate the apparent activation energy and pre-exponential factor. Combining the Coats-Redfern (CR) model method with 17 mechanistic models, the optimal reaction mechanism model was ultimately obtained. Research findings indicate that the pyrolytic weight loss process of straw can be divided into three stages: drying and dehydration, pyrolysis of organic compounds such as cellulose/hemicellulose/lignin, and carbonization. The apparent activation energies calculated for corn straw using the FWO method, KAS method, and Starink method were 85.16 kJ mol
-1
, 75 kJ mol
-1
, and 75.41 kJ mol
-1
, respectively; for rapeseed straw: 99.7 kJ mol
-1
, 89.71 kJ mol
-1
, and 90 kJ mol
-1
; for cotton straw: 90.17 kJ mol
-1
, 79.62 kJ mol
-1
, and 80.04 kJ mol
-1
. The CR method revealed that the mechanism equations for pyrolysis of all three straw types conform to the F3 model. Additionally, under N₂ atmosphere, the thermodynamic properties of the reaction—specifically ΔH, ΔG, and ΔS—were significantly higher for rapeseed straw than for corn and cotton straw, confirming the greater complexity of its reaction. These findings contribute to a deeper understanding of straw pyrolysis mechanisms and provide a theoretical foundation for the resource utilization of solid waste.