Experimental investigation on physicochemical characteristics of coal treated with synthetic sodium salicylate–imidazole ionic liquids

Abstract

Interactions between three types of novel sodium salicylate (NaSal)–imidazole ionic liquids (ILs) and coal were studied at the macro, micro, and micro levels. The experimental results show that the three synthetic ILs effectively dissolved coal and reduced the coal particle size, whereby IL 3 had the strongest ability to dissolve coal and the particle size of most coal samples obtained by dissolution was <10 μm. IL 3 finally adsorbed the small particles of dissolved coal in the form of a neural network-like structure, which had a high fluidity and was conducive to displacement, while the other two ILs involved sedimentation stacking. The treatment of coal samples with the ILs effectively destroyed the hydrogen bonds between the coal molecules, reduced the oxygen content of coal, improved the calorific value, and increased the efficiency of coal conversion. The simulation results show that among the three synthetic ILs, the radial distribution function (RDF) of water molecules in the interaction between IL 3 and coal was the smallest, with a first peak value of 64.70. The RDF of the coal molecules was the largest, with the first peak value of 13.67. These findings reveal that IL 3 had the most powerful interaction function with coal; it decreased the water molecular cohesion energy, enhanced the wettability of solution, strengthened the solution activity, increased the coal molecular cohesion energy, and had the best contact reaction with coal. Thus, we provide a feasible method and theoretical guidance for improving coal production efficiency and safety.