CHARACTERIZATION OF DIFFERENT POSSIBLE SOLVENT-COAL INTERACTION MECHANISMS BY THE RELATIONSHIP BETWEEN THE VOLUMETRIC SWELLING OF COALS ANDHEAT RELEASE IN SWELLING SOLVENT

The heat of mixing a polar or nonpolar swelling solvent with coal was measured by flow microcalorimetry (FMC). Eight coals, having different oxygen contents, were used as the adsorbent, and methanol, THF, tetra lin were used as the adsorbate. We examined a range of swelling solven t concentrations in n-hexane, 2-20 g/L, and found that there are large differences in the adsorption heats for the three solvents. Methanol adsorption heat reaches the maximum at low methanol concentrations and remains constant at higher concentrations, while heats for THF and te tralin adsorption increase with swelling solvent concentrations. The m ethanol adsorption heat maximum is about 2000 mJ/m(2), THF is 70 mJ/m( 2), and tetralin is 40 mJ/m(2) over the concentration range 0-20 g/L. Uptake for swelling solvent was determined by comparing the concentrat ion of swelling solvent in n-hexane before and after adsorption. Metha nol uptake reaches about 80 mmol/g coal, while THF only reaches 0.3 mm ol/g coal. Tetralin uptake is too small to be determined by such a tec hnique. Similar to adsorption heat, methanol uptake reaches its maximu m value at a lower concentration and then remains constant, and THF up take increases with its concentration over the concentration range. We also investigated swelling of the eight coals in such swelling solven ts and found that in contrast to methanol, THF has relatively low adso rption heats but large swelling ratios. This suggests that methanol li kely interacts with specific sites on coal without disrupting coal-coa l cross-links between macromolecular chains in coal, while THF may bre ak such coal-coal cross-links. The low swelling ratios for tetralin su ggest no disruption of coal-coal cross-links, although this solvent do es interact with coal as seen from its moderate adsorption heat values . For coals swollen in a solvent, the heat for swelling Solvent adsorp tion on coal correlates strongly with coal swelling ratio in the solve nt.