Oxygen in Coals and Coal-Derived Liquids

The oxygen present in dry coal can be divided into organic oxygen and inorganic oxygen, which is closely related to the inorganic matter in coal, such as silicates, sulfides, sulfates, carbonates, and oxides. Their nonvolatile decomposition and combustion products formed during the proximate analysis are termed “coal ash.” Oxygen is the only major constituent of coal that is not always determined during routine ultimate coal analysis. The analysis of chemical functionality of coal is important because the reactions of coal can be described as those of functional groups. Furthermore, the oxygen functionalities dictate the oxygen compound composition of coal-derived liquids. For example, the pyridine extraction process may begin with unblocking of the coal structure through dissolution of hydrogen-bonded phenolic structures. This chapter describes two categories in which coal-derived liquids can be divided. The first includes those obtained in relatively low yield by solvent extraction at low temperatures, which are substances removed mainly by dissolution of soluble coal constituents. The second includes those obtained by a higher-temperature depolymerization of coal. Higher liquid yields are achieved by means of a number of processes in commercial applications, such as solvent refining and catalytic hydrogenation.