Aliphatic biomarkers from Miocene lignites desulphurization

Lignites of the Thracian basin, the main coal potential of Bulgaria have be en subjected to an extensive study, as their high sulphur content (3-7%) cr eates ecological problems during combustion. The aim of the present study w as to examine the effect of desulphurization (three techniques, i.e. hydrot hermal, t-BuONa and n-BuLi/TMEDA treatments) on biomarkers assemblage, as s ulphur bridge cleavage could release covalently attached species or trapped molecules. Results of the chromatographic analysis of the aliphatic portions of the ch loroform extracts from initial and treated lignites have pointed out that d uring desulphurization treatments coal organic matter was rearranged and sm aller fragments became soluble. Some peculiarities were registered: alkane fraction of Maritza-Iztok treated by t-BuONa was strongly dominated by "eve n" carbon numbered n-alkanes, n-C-16, n-C-18 and n-C-20; in products of Elh ovo lignite desulphurized by n-BuLi/TMEDA alkyl cyclopentanes were tentativ ely identified. After n-BuLi/TMEDA desulphurization, hopane distribution was largely affect ed in the case of the Maritza-Iztok sample: the higher homologues and pp do minance from C-29 to C-31 hopanes have disappeared; "geo hopanes" prevailan ce was registered;-18 alpha(H)-oleanane, 25-nor-17 alpha(H)21 beta(H)-hopan e, C-29 and a suite of "non-hopanoid" C-30 triterpanes were observed. Our data have demonstrated the negligible steric protection of macromolecul ar structure in the case of low rank coals as far as covalently-bound speci es were characterized by higher degree of maturation compared to the easily extractable species. (C) 1999 Elsevier Science Ltd. All rights reserved.