<p>To investigate the effect of swelling temperature on the pyrolysis characteristics of low-rank coal, 1-Butyl-3-methylimidazolium chloride ([Bmim]Cl), 1-Butyl-3-methylimidazolium Bromide ([Bmim]Br), and 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄) were used for the swelling pretreatment of coal at different temperatures. The coal samples were analyzed via swelling degree, X-ray diffraction, and thermogravimetric analyses. The results showed that all ionic liquids could remove oxygen-containing functional groups, disrupt hydrogen bonding, and alter the coal’s crystalline structure, leading to enhanced swelling and volume expansion. The optimal swelling effect of [Bmim]Cl on coal was observed at 25&#xa0;°C, resulting in a 17.39% increase in coal sample swelling degree and an expansion of aromatic interlayer spacing to 3.59&#xa0;Å. Higher temperatures reduced interactions between ionic liquids and coal, increasing carbon–oxygen and hydrogen bond contents, and decreasing mass loss during pyrolysis. Pyrolysis kinetics analysis revealed that [Bmim]Cl-treated coal had the lowest activation energy, which increased with treatment temperature. FT-IR results revealed that the ionic liquid swelling treatment disrupted the oxygen-containing functional groups in coal and broke the hydrogen bonds within its structure, with [Bmim]Cl exhibiting the most pronounced effect on the destruction of oxygen-containing functional groups.</p> Graphical Abstract <p></p>