The swelling behavior of six typical solvents on low-rank coal at 150 ℃ and their influence on the pyrolysis characteristics of coal

Solvent swelling, which can adjust the molecular and chemical structure of coal, serves as an important technique for studying its structure, pyrolysis behavior, and the mechanisms of product control. This study employed high-temperature swelling of demineralized low-rank coal (Shendong coal, RD) using six solvents (tetrahydrofuran, ethanol, benzene, acetic acid, acetone, and n -heptane) at 150 °C. This enhanced solvent-coal interaction was combined with multi-step pyrolysis using a fast pyrolysis–gas chromatography/mass spectrometry (PY-GC/MS) instrument (50–150 °C, 150–200 °C, 250–250 °C, 250–650 °C) to capture residual solvents and solvent-leached substances during swelling, thereby elucidating the specific role of solvent swelling. Calculations of pyrolysis kinetics for the high-temperature-swelling coal samples revealed that, based on changes in activation energy required for different pyrolysis stages of the swollen samples, the solvents could be approximately grouped into three sets: G1 (tetrahydrofuran and ethanol), G2 (acetone and benzene), and G3 (acetic acid and n -heptane), with corresponding E a of G1 (110 kJ·mol −1 ) > G2 (100 kJ·mol −1 ) > RD = G3 (89 kJ·mol −1 ). This indicates that the swelling effects of different solvents occur in distinct pyrolysis stages during high-temperature swelling. The substantial products detected in the 50–150 °C pyrolysis segment serve as direct evidence of solvent-coal interactions. This study elucidates the synergistic effects between different solvents and high temperature, providing theoretical support for the high-temperature swelling and pyrolysis characteristics of low-rank coal. It also offers important references for direct coal liquefaction and coal-oil co-processing.