Some Physical Chemical Concepts Relevant to Coal Science

摘要

This report discusses approaches to understanding certain physical and physical chemical properties of low-rank coals from a molecular perspective. Dielectric relaxation measurements are described which have identified two distinct modes of water incorporation in lignite. The theoretical aspects of dielectric relaxation are presented along with the experimental details. The need for performing vapor pressure measurements on lignite-water vapor equilibrium systems is examined. In recent years, many researchers have attempted to understand the macromolecular network in coal by means of techniques useful for studying bulk polymers. Here, the underlying theoretical ideas are presented for dynamic mechanical relaxation and rubber elasticity. Researchers have drawn inferences, from the measurement of viscoelastic properties of coals, about the molecular nature of the crosslinking in the organic network. Their conclusions are critically examined and suggestions are made as to how the experimental procedures might be improved. The interpretation of the temperature dependence of slag viscosity is a particularly vexing problem. Here, it is suggested that the theoretical methods used to describe the viscosity of molten glasses may be useful as a point of departure in characterizing slag viscosities. Finally, a brief outline of the Hildebrand theory of liquid-liquid miscibility is presented; the ideas relevent to understanding supercritical solvent extraction of coals in terms of the Hildebrand solubility parameter are discussed. 28 references, 22 figures. (ERA citation 09:047313)