Effects of Imidazole Ionic Liquids with Different Chain Lengths on Caking Property of Shenhua Long-Flame Coal

Abstract—To upgrading the caking property of Shenhua long-flame coal (SH), imidazole ionic liquids (IILs) were used. SH and the treated samples were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy to reveal the upgrading mechanism. The results showed that IILs treatment could improve the caking property of SH. When exploring the effects of IILs with different chain lengths on the caking property of SH, it was found that the caking index of the treated samples first increased and then decreased with increasing chain length, and [C₅MIM]Cl treatment exhibited the best modification effect among all IILs used. Additionally, an upgrading mechanism of caking property of SH using IILs is proposed. IILs treatment could increase the content of small aromatics with 3–5 rings and decreased the length of side chain alkanes and oxygen content, which could increase the caking property of SH.