E.p.r. studies of interactions between paramagnetic centres of exinite, vitrinite and inertinite during thermal decomposition

Abstract

Electron paramagnetic resonance in the X-band (9.3 GHz) was used for investigations of petrographically complex coal samples (densities 1.24–1.28 and 1.30–1.36 g cm −3) from Polish medium-rank coal (85.6 wt% C) heated in an inert atmosphere at 300–650°C. A strong increase in total concentration of paramagnetic centres in the sample of lower density at 300–350 and 450–550°C was measured. Relatively smaller changes in the total amount of paramagnetic centres in the heavier sample at 300–650°C were observed. There are three different types of paramagnetic centres in both samples, and their e.p.r. spectra are a superposition of one broad Gauss and two Lorentz (broad and narrow) lines. The most active group in the thermal decomposition of the two coal samples is formed by paramagnetic centres responsible for the broad Lorentz lines. Mainly dipolar interactions of unpaired electrons influence the linewidths of the e.p.r. signals. The microwave saturation power of all the e.p.r. lines detected increases with temperature. According to the e.p.r. results for pure macerals and the complex coal samples, the hypothesis of independent progress of reactions in individual macerals during the thermal decomposition of coal can be rejected.