A high-volatile bituminous coal was extracted at room temperature by various organic solvents. The yields of the extracts ranged from 4.5 wt% daf (ethanol/benzene extract) to 38 wt% daf (pyridine/ethylenediamine extract). The extracts were analysed by FI mass spectrometry; the volatile part (75-80 wt%) was composed of substances of molecular weight in the range 70-800 amu, but the compounds in the 200-600 amu range predominated. Over 300 compounds were identified by high-resolution mass soectrometry. The results indicate that compounds ~800 amu constitute at least 30 wt% daf of the analysed coal.
Coal extraction experiments' -6, carried out at temperatures sufficiently to prevent thermal cleavage of chemical bonds, lead to the conclusion that the contents of extractable substances in high-volatile bituminous coals can be quite high: extract yields up to 4&50 wt y0 have been reported. Therefore, a study of the mechanism of coal extraction, as well as identification of extractable substances, may contribute to the elucidation of significant elements of coal structure.
The key to the understanding of the extraction mechanism is inherent in a correlation between solvent properties and their effectiveness in coal extraction, and in the chemical nature of extractable substances.
Several years ago, Gutmann'-" established a method for the quantitative determination of electron-donor and electron-acceptor properties of solvents. We have carried out experiments" on the extraction of high-volatile bituminous coal at ambient temperature (18-22Β°C) with 18 solvents, their donor and acceptor numbers having been determined according to Gutmann, which were then correlated with the extract yields. On this basis, a model for coal extraction has been established". The elements of the model are:
(1) electron-donor-acceptor (e-d-a) bonds occur in coal and are responsible for binding together the coal macromolecular network and the extractable substances;
(2) extraction is, in principle, a substitution reaction: extractable substances are replaced by solvent molecules in those e-d-a bonds;
(3) substitution capabilities of the solvents, manifested as extract yields, depend on solvent electron-donor as well as electron-acceptor numbers.
Further information on the extraction has now been obtained by obtaining field ionization and highresolution mass spectrometry analyses of some extracts of a coal. EXTRACTION