Pretreatment of coal by ionic liquids towards coal electrolysis liquefaction

• Coal is pretreated by ionic liquids (ILs).
• [Bmim]Cl exhibits the best performance of coal extraction and swelling.
• The mechanism for pretreatment of coal in IL is proposed.
• IL-pretreated coal is electrolyzed on a Ni–W–B electrode.
• Pretreatment with IL promotes the coal electrolysis liquefaction (CEL) substantially.

Ionic liquids have been employed to pretreat coal to modify its network structure, and thus to improve the electroreduction activity of coal on a Ni–W–B catalytic electrode. Among the pretreatment solvents, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) exhibits the best performance of coal extraction and swelling. The coal sample is pretreated by [Bmim]Cl at optimized temperature (150 °C), then the pretreated coal is analyzed and characterized by scanning electron microscopy, gas chromatograph, infrared spectroscopy and linear sweep voltammetry. The results show that the coal network is fractured, resulting in a loose and porous structure, which facilitates hydrogenation reactions of coal on the catalytic electrode. A liquefaction yield of 57.6% is realized after electrolysis of coal on the catalytic electrode for 24 h at −1.7 V in a NaOH + H2O + tetrabutylammonium bromide mixed electrolyte system, 15% higher compared to the coal without pretreatment (40.3%). The mechanism for the pretreatment of coal in ionic liquids has been proposed.

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