Pyrolysis Kinetic Analysis of Sequential Extract Residues from Hefeng Subbituminous Coal Based on the Coats-Redfern Method

[Image: see text] Sequential extract residues (R(i), i = 1, 2, 3, 4, and 5) were obtained from Hefeng acid-washing coal (HF(AC)) by petroleum ether, carbon disulfide, methanol, acetone, and isometric carbon disulfide/acetone mixture, sequentially. Pyrolysis behavior of the residues was determined using thermogravimetry analysis. The Coats–Redfern method with different reaction orders was used to analyze the pyrolysis kinetic of each sample, and the kinetic parameters, including correlation coefficient (R(2)), activation energy (E), and pre-exponential factor (A), were calculated. Results showed that the weight loss of extract residues was higher than HF(AC), and pyrolysis behavior varies greatly for residues, which is related to the unstable structure after extraction. From conversion–temperature (α–T) curves, the pyrolysis process was divided into three stages: low-temperature stage (150–350 °C), medium-temperature stage (350–550 °C), and high-temperature stage (550–950 °C). The medium-temperature stage made great contribution to the process of pyrolysis, which was dominated by depolymerization and decomposition reaction. The relationship between kinetic parameters and reaction order showed that the swelling effect is an important reason for the discrepancy of E for each sample in the process of pyrolysis.