Barbara Pilawa1, Andrzej B. Wieckowski2, Mieczyslaw Kozlowski3, Helena Wachowska4
1 Department of Biochemistry and Biophysics, Faculty of Pharmacy, Silesian Medical Academy, Narcyzow 1, 41-200 Sosnowiec, Poland,
2 Institute of Physics, Faculty of Mathematics, Physics and Technology, Pedagogical University, pl. Slowianski 6, 65-069 Zielona Gora, Poland, and - Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17/19, 60-179 Poznan, Poland,
3 Department of Chemical Technology, Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
The lineshape of complex EPR spectra of medium-volatile bituminous coal (85.7 wt% C) was numerically analyzed. The EPR spectrum of the coal was approximated by super position of a broad Gauss (0.87 mT) and two Lorentz lines differing in their linewidths (0.22 mT, 0.06 mT). In the studied coal sample there exist mainly paramagnetic centres incorporated in chemical structures consisting of a few aromatic rings responsible for the Gauss component (66.5% total spectrum). The lower contents of paramagnetic centres of large aromatic structures (two Lorentz components 28.3% and 5.2%) were measured. All the paramagnetic centres actively interact with atmospheric oxygen. The changes in the EPR spectrum of the coal reduction and reductive alkylation were monitored. The protonation and alkylation reduce the amount of paramagnetic centres with Gauss curve. The percentage fraction of the Gauss line in total EPR spectrum of ethylated coal decreases after extraction with CH2Cl2. The obtained EPR results for the studied coal samples were correlated with chemical analysis data.