Publisher Summary It is the geoscience of coals, that is, their geochemistry of origin and postburial geological history, that suggests that coals are a very diverse set of materials. This chapter discusses the relations between the chemistry of coal macerals and reviews the biochemistry of their precursors and the biological markers in coals that are indicative of their origins. The content of carboxyl groups in coals is commonly determined by an ion-exchange reaction with barium acetate. Values of 1–4 milliequivalents per gram have been found for lignites and lower-rank subbituminous coals—decreasing with increasing rank and essentially zero for coals of higher rank—except that HVC coals of the Rocky Mountain province may contain some carboxyl. The cations in the carboxylates of low-rank coals can give rise to calcite deposits in liquefaction reactors, can promote liquefaction, and can give rise to catalysts for the gasification of lignite chars.

An Essay on the Organic Geochemistry of Coal

Asphaltenes, the key intermediates in the liquefaction of bituminous coals, consist of hydrogen bonded complexes which can be separated into their acidic and basic components. The acidic components contain all, while the basic components contain none, of the exchangeable protons present. The significance of these findings with respect to coal structure and coal solubilization is discussed.

Acid-base structure of coal-derived asphaltenes.

Fourier transform infrared spectroscopy has been used to characterize the oxidation of a coking coal. The results demonstrate that the most important initial products of oxidation are carbonyl and carboxylic acid groups. Bands associated with carbon-oxygen single bonds, as in ethers or phenols, do not become prominent until the later stages of the oxidative process. Upon reaction with potassium in tetrahydrofuran a number of changes in the spectrum of both the oxidized and unoxidized coal become apparent. This reagent cannot be considered specific for cleavage of ether bonds, but can also lead to products usually associated with air oxidation.

C.L. Delle Donne

Papers

Solubilization of an lvb coal by reductive alkylation

Similarity between the electrochemical elimination of sulfur from coal and from dibenzothiophehe