Molecular Structure of Coal

This chapter describes various aspects of coal science. The complexity and heterogeneity of coal is the most persistent problem in discussing any topic in coal science. Coal is a sedimentary rock that is composed principally of two basic classes of materials: inorganic crystalline minerals and organic carbonaceous macerals. The macerals form the combustible part of the coal and are, in turn, divided into three maceral groups—vitrinite, exinite, and inertinite. The macerals are of different origin and differ in chemical composition. The best characterized macerals are the vitrinites. Vitrinites and coals are mixtures of macromolecules. These mixtures are very complex. Each macromolecule is composed of structural units or constituent molecules, which are those units of the macromolecules that survive mild chemical operations on coal. The problem of ascertaining the molecular structure of the organic part of coal is that coal is not structurally dependent on a single molecule but on a complex mixture of molecules that varies according to the type of coal.