Solvent swelling of coal and coal macerals

Selected coals and coal macerals were swollen in organic solvents. A volumetric swelling method was employed using a wide range of solvents. This method was chosen over the gravimetric technique as it is more rapid and does not require corrections for pore-filling. For bituminous coals, swelling decreased in the solvent order, pyridine> THF> acetone> ethanol> CH2CL.2> methanol> toluene> cyclohexane> H2O. A basic thermodynamic study of coal-solvent interactions was performed. The solubility parameter and donor-acceptor theories were applied to correlate swelling behavior. Neither of these theories adequately describes the swelling behavior of coals. Combining the solubility parameter theory and coal-solvent interactions provides a reasonable description of the swelling behavior. The effect of the solvents is to solvate the coal matrix and fill and expand the micropores of the coal. Solvents of suitable polarity cleave secondary hydrogen bonds between the polar groups in the coal, decreasing the crosslink density and increasing the flexibility of the coal macromolecule. Other solvents with good solubility parameters swell the coal without disrupting the secondary bonds.