Effects of halogen ionic liquids on structural and pyrolysis characteristics of coal

LI Lin; YANG Beiji; LI Zhihao; WANG Xiaoru; SUN Qianyun; YOU Xiaofang

doi:10.13247/j.cnki.jcumt.20250203

Abstract：Swelling is an effective method for improving coal properties and enhancing its utili-zation efficiency.In recent years,ionic liquids(ILs)have been employed as swelling agents for coal treatment.Although conventional ILs exhibit high stability and environmental friendli-ness,their low polarity limits their swelling efficiency.In contrast,halogen ionic liquids dem-onstrate stronger molecular polarity owing to the high polarity of halogen atoms.Therefore,three halogen-based ionic liquids([Bmim]Cl,[Bmim]Br,and[Bmim]I)were selectedto swell long-flame coal,aiming to investigate their effects on coal structural properties.The re-suits indicate that the swelling efficiency follows the order[Bmim]Cl＞[Bmim]Br＞[Bmim]I.The[Bmim]Cl-treated coal sample exhibited the highest swelling degree(25.07％)after 36 h of treatment at 25 ℃.Furthermore,swelling induced significant structural altera-tions in coal,including an increase in the interlayer spacing of aromatic clusters and a higher a-bundance of small molecular fragments on the coal surface.The oxygen content decreased,with a maximum reduction of 3.63％.Additionally,the weight loss rate of swollen coal sam-ples increased,and the pyrolysis temperature shifted toward lower ranges.Molecular simula-tions reveal that halogen ionic liquids weaken hydrogen bonds associated with oxygen-contai-ning functional groups,converting strong hydrogen bonds into weaker ones,with some bonds even breaking.These findings provide a theoretical foundation for improving coal pyrolysis and liquefaction efficiency,thereby facilitating the high-value utilization of coal resources.