Polyaromatic structure in the kerogen from anthracite at Vrška Čuka (Carpatho-Balkan region, Serbia)

Abstract

The Vrška Čuka anthracite shows contents of 16% inorganic compound and 84% organic matter, out of which 82% is kerogen and <2% is bitumen. X-ray diffraction (XRD) indicates the presence of the graphitic structures. The electron spin resonance (ESR) shows a high concentration of polyaromatic paramagnetic structures (PPS; 4.5×10 19 spins g-1). The Fourier transform infrared spectroscopy (FTIR) reveal that the Vrška Čuka kerogen contains predominantly aromatic/polyaromatic structures. Analysis of the aromatic area shows both the absence of aromatic substituents and the presence of aromatic polycondensation (average 3-4 rings; ≥17 carbon atoms). The spectrum also shows considerably reduced absorptions corresponding to the presence of aliphatic groups. Most of the aliphatic carbon is present as CH 3 (probably in short alkyl chains-methyl/methylene attached to polyaromatic structures) as indicated by the CH 3 /CH 2 value 0.7 of the appropriate absorptions. It was suggested that polyaromatic structures were formed by poly-condensation of aromatics during kerogen maturation. Low atomic values of H/C and O/C (0.45 and 0.07) indicate a high degree of genesis (metagenesis). The result of these analyzes are in agreement with each other and show that the maturation of this kerogen led to the formation of polyaromatic structures from aromatic.