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There has been copious research exploring the interactions between coal and various solvents either for coal structural investigations using coal swelling or industrial consideration exploring extraction yields. Here the literature is reviewed for Illinois no. 6 coal. This is the most well studied coal in existence and so offers an opportunity to reveal a wealth of information with a wide variety of solvents and extractions. This coal swells extensively (raw) in a good solvent such as pyridine (Q-factors of 2.2) and lesser degrees in benzene (Q-factor of 1.1). However if first extracted the extent of swelling can be greater. The swelling process is typically slow, sometimes taking days with anisotropic swelling being evident on the first exposure but absent from subsequent exposures. Overshoot phenomena, similar to polymer swelling, is also observed for some particles. These behaviors are related to the complex interactions of solvent diffusion and coal "relaxation" that is related to the nature of the solvent and its interactions with coal. Extraction yields are similarly varied with values ~30 wt.% (daf basis) with pyridine although greater values are obtained with two-stage, higher temperature, and exhaustive extractions. With CS 2 /NMP/H 2 O a yield as high as 70% wt.% (daf basis) have been reported at 600 K. Using light cycle oil has yields between 20 and 70 wt.% depending on consitions at 633 K. The swelling evidence supports a cross-linked structure and solvent extraction supports a considerable amount of extractable material. These statements are not necessarily in conflict.

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