TEMPERATURE-DEPENDENCE OF SOLVENT SWELLING AND DIFFUSION-PROCESSES INCOALS

The rates of solvent swelling of the Argonne Premium Sample coals have been measured in various organic solvents at various temperatures. Th e results show that the extents of swelling, when experiments are carr ied out in liquid solvents, are independent of the temperature, within the temperature range studied here (10-60 degrees C). Thermodynamical ly, this requires that equilibrium swelling should occur with a near-z ero enthalpy, as generally required for absence of a temperature effec t on equilibrium. This conclusion is consistent with a number of other recently published results. The rates of swelling of the coals do not correlate with rank. The nature of the swelling process varies from r elaxation controlled to Fickian diffusion controlled. The activation e nergies for the kinetics of swelling are consistent with other recentl y published values, but again, a correlation with rank could not be su bstantiated. The activation energies all fall in the range from 20 to 60 kJ/mol, suggesting that the activation barrier may be associated wi th the breakage of internal electron donor-acceptor (e.g., hydrogen bo nding) interactions. Thermal pretreatment of some of the coals to 350 degrees C had significant effects on their swelling behaviors. The eff ect was generally to increase the rate of swelling, and in some cases, the extent of swelling. The activation energies for swelling were, ho wever, unaffected. This is interpreted as consistent with the hypothes is that the activation energy barrier is determined by donor-acceptor interactions which are unaffected by pretreatment but that other therm ally dissociable coal-coal interactions may serve to stiffen its struc ture.