Based on the orthogonal microscopic image analysis system, we have examined the swelling behavior of the three kinds of pretreated Taiheiyo coal, such as acetylated, pyridine-preextracted, and HCl-washed ones, along with virgin coal, to obtain an insight into the effects of the non-covalent bonding interactions on the swelling behavior of coal particles. The acetylated sample showed the fastest rate for swelling with pyridine, this indicating that hydrogen bonds in coal play an meaningful role during its solvent swelling.
