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.