Geochemical characteristics of the macromolecular part of crude and biodesulphurised flame coal density fractions

Flame coal (Janina Mine, Poland) was an object of geochemical analyses for changes caused by the process of microbial desulphurisation. Ash content, beryllium, chromium, zinc, cobalt, lithium, manganese, copper, molybdenum, nickel, lead and vanadium concentrations were investigated in coal extracts, its macromolecular part, semi-coke and polar compound fractions of extracts and pyrolysates of crude and biodesulphurised coal density fractions. The macromolecular part of extracted density fractions was pyrolysed giving semi-coke and pyrolysate. These were separated into aliphatic hydrocarbons, aromatic and polar compounds by thin layer chromatography (TLC). Distributions of aliphatic and aromatic hydrocarbons in pyrolysates of the crude and desulphurised coal density fractions were compared by gas chromatography-mass spectrometry (GC-MS). Extracts, extracted density fractions, semi-coke and polar compound fractions were analysed for concentrations of trace elements. In the crude coal their concentrations in the macromolecular part are related only to coke. However, in the desulphurised coal the participation of the particular trace element increases in pyrolysate polar compound fractions. Its values are in the range from 1% (Mn) to 100% (Cr and Mo). These changes are the best seen in the 1.80–2.30×103 kg/m3 density fraction. Very high concentrations of trace elements were found in pyrolysate of desulphurised coal density fraction. This can be explained by the partial decomposition of coal macromolecule resulting from desulphurisation. Significant side-cleavage of peripheral groups and lighter aromatic hydrocarbons is possible. The effects of bacterial influence were manifested by the increase of polar compounds contents both in pyrolysates and extracts of the desulphurised coal and changes in distribution of aliphatic and aromatic hydrocarbon as pyrolytical products. These effects increase with mineral substance contents. Moreover, the increase of trace element concentration in coal organic matter occurs. It is reflected by the increase of participation of coal pyrolysate polar fraction in the total concentration of analysed elements in the macromolecular part of a given density fraction. The presented results are a part of the larger research aimed to find an influence of desulphurisation on chemical and technological properties of coal.