Classification of water sorbed in coal on the basis of congelation characteristics

Water sorbed in eight coals of different ranks was analyzed by differential scanning calorimetry (DSC) over a temperature range from 123 to 293 K. On the basis of its congelation characteristics, the water was classified into three types: free water that is identical with bulk water, bound water that freezes at a lower temperature than free water, and nonfreezable water that never freezes in the present temperature range. The contents of the free and bound waters were experimentally determined from their respective heats of congelation, and the nonfreezable water was then calculated by difference. The congelation of the freezable water was also observed using proton nuclear magnetic resonance (¹H NMR) as the conversion of the slowly decaying into Gaussian components at 213-273 K. The fraction of freezable water as determined by ¹H NMR was in good agreement with that by DSC. The nonfreezable water was also found to have some mobility and thus gave exponential decays even at 213 K.