The rates of solvent swelling of a suite of low rank US coals have bee
n measured in various organic solvents at various temperatures. The eq
uilibrium extents of swelling are independent of temperature within th
e temperature range studied (25-70 degrees C). The rate of the swellin
g process was generally relaxation-controlled. The activation energies
for the kinetics of swelling are consistent with other recently publi
shed values, and support the hypothesis that the activation barrier is
associated with the breakage of internal electron donor-acceptor (e.g
. hydrogen bonding) interactions. Thermal pretreatment of a lignite at
various temperatures up to 395 degrees C decreased the activation ene
rgy barrier and the rate of swelling. Swelling rates of the same ligni
te in different solvents suggest that the activation energy can exceed
the value for breaking single hydrogen bonds, possibly because the tr
ue barrier involves cleaving more than one of those bonds at a time. (
C) 1998 Elsevier Science Ltd. All rights reserved.