Physical characterization of coal

Abstract

On both microscopic and macroscopic scales, coal is a complex heterogeneous material. The organic fraction of coal is composed of microcrystalline and amorphous materials, and exists as small condensed aromatic layers. The packing of layers improves with rank. Coals. have an extensive porosity; pores vary in size from micron to molecular dimensions. Most of the coal surface area, however, is enclosed in micropores < 2 nm in size. Significant results on densities, surface area and pore volume distribution have been discussed. All of these parameters show some dependence on coal rank. Pore structure of coal has a large influence on its behavior during mining, preparation, and utilization. The mechanism of water adsorption on coal, and its dependence on rank are different from that of non-polar molecules. The nature of coal surface rather than its surface area determines its moisture sorption capacity. Exchangeable cations present in the carboxylate groups of low-rank coals also have a major effect on water adsorption. Water adsorption-desorption isotherms on coals show hysteresis. © 1984.