Chemical Structure of Bituminous Coals

Abstract

Problems of chemical structure of bituminous coals are summarized. The concept of coal as an aggregate of coal macromolecules or oligomer molecules linked by non-covalent bonds is discussed. For low-rank coals, a two-phase model is accepted, for high-rank coals, a one-phase model can be considered. Aromaticity and related parameters as well as oxygen, nitrogen and sulfur functionalities are quantified, compared with other data and their role in coal structure is expressed. Finally, structural features of bituminous coals are listed: the cluster size is 3 - 5 rings, ether and hydroxy oxygens predominate over carbonyl oxygen, pyrrole and pyridine nitrogen are main forms of the nitrogen content, diaryl sulfides, dibenzothiophene and higher-fused thiophenes are prevailing forms of organic sulfur, whereas dialkyl sulfides are minority components.