Characterization of four hydrophilic sites in bituminous coal by ionic thermal current measurements

Abstract

Ionic thermal current (ITC) techniques were used to study the behaviour of water in two low-rank coals of < 5 wt% as-received moisture content. Four relaxation peaks were precisely characterized by means of narrow Gaussian activation energy distributions and the results were compared with the much simpler spectrum obtained by different relaxation techniques. Drying and rehydration treatments show that the thermally stimulated depolarization peaks are due to physisorbed moisture. The Guasare (Venezuela) coal of 39 wt% C shows a much greater water affinity than the Bucaramanga (Colombia) coal of ~ 76 wt% C. The ITC relaxations are attributed to water dipoles bound to hydroxyl and carboxyl functional groups of the macromolecular structure of the coal.