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2 Polish Geological Institute Special Papers

2 2002

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Petrological studies of low temperature oxidation of lignites

Markova K., Stefanova Y., Boneva M.

Polish Geological Institute Special Papers

2002

Vol. 7

159-168

The low temperature oxidation processes which has taken place in lignites and their lithotypes (xylain, humovitrain, semifusain, fusain and liptain) from the East Maritza basin have been studied. The changes occurring in the coals/lithotypes composition and structure during their oxidation have been followed by examining reflectance, microhardness, proximate, ultimate, functional, and increment analyses. The main kinetic parameters such as duration of the induction period, maximum and stationary rates and the apparent activation energies were evaluated. The complex investigation provides a detailed information for the behaviour of low rank coals and their lithotypes towards the action of atmospheric oxygen. Thus some suggestions concerning the mechanisms of their oxidation reactions can be made. The individual way of the genesis of each one of the lithotypes and the resulting physicochemical structure predetermine the basic mechanism of these reactions. However, it has been found that in spite of the similar genesis the lithotypes differ in the mechanism of their oxidation. For xylain the oxidation takes place mainly via aryl radicals yielding tertiary peroxide and carbonyl groups. The oxidation of humovitrain is characterised by the dominant participation of aroxyl radicals resulting in accumulation of primary hydroperoxide and phenol groups. The oxidation of semifusain leads mainly to the formation of molecular products. The oxidation of fusain is found to be essentially different from that of other lithotypes. It is characterised by the formation of carbonyl groups attached to biphenyl aromatic structures. The peculiar petrographic composition and structure of liptain account for the occurrence of oxidation processes accompanied by destruction reactions at relatively lower temperatures. It has been established that the intensity of the oxidation processes varies from one lithotype to an other. Xylain and humovitrain oxidise most intensively. The intensity drops off from the first towards the second member of the corresponding genetic series, i.e. from xylain to humovitrain and from semifusain to fusain.

Molecular indicators for coal-forming palaeoplant community. "Katrishte" Coal deposit

Stefanova M., Markova K., Marinov S.

Polish Geological Institute Special Papers

2002

Vol. 7

245-252

Coal deposit "Katrishte" located in south-western Bulgaria, Ro = 0.34%, was subjected to geochemical study. By chromatographic and spectral methods, a variety of coal biomarkers in bitumen extract has been revealed. n-Alkane distribution pattern indicated at least two possible sources, lacustrine and terrestrial ones. The aliphatic fraction was strongly dominated by 16a(H)-kaurane and 16a(H)-phyllocladane, a proof for the presence of Pinales in coal-forming palaeoplant community. The kaurane prevalence over phyllocladane could indicate the herbaceous flowering plant contribution. The combination of sesquiterpenoids/diterpenoids pointed to Pinaceae and Araucariceae.As a biomarker assemblage peculiarity, the lack of isoprenoids, tricyclic diterpenoids, and pentacyclic triterpenoids could be indicated.Our data gave us ground to assume existence of bush moor with the presence of herbaceous flowering plants, and subordinate contributions of conifers and sedge-reeds to coal forming plant taxa of "Katrishte"