Effect of reduction and butylation on coal: Application of microwave saturation of two-component EPR spectra

Abstract

Changes in individual groups of paramagnetic centers after reduction and reductive butylation of Polish flame coal (70.8 wt.% C) were studied by electron paramagnetic resonance (EPR) spectroscopy. The modero method of reductive butylation of coal in a potassium-liquid ammonia system was used. This process increases the solubility of coal in organic solvents. Microwave saturation of EPR spectra was applied to test the spin-lattice relaxation in coal. The measured EPR spectra were a superposition of broad (ABpp, 0.424).49 mT) and narrow (ABpp, 0.09-0.13 toT) Lorentz lines. Paramagnetic centers located in simple and multiring aromatic structures were responsible for the broad and narrow lines, respectively. Microwave saturation indicates that slow and fast spin-lattice relaxation processes are characteristic for these two types of structures in the original coal. A decrease of the microwave power saturation of the broad Lorentz line after a single reduction of coal was observed. It inereased for both 4 times reduced coal and reductively butylated coal. As the result of multiple reduction and butylation, spin-lattice relaxation processes in simple coal aromatic units were fastened. The narrow Lorentz lines of both 4 times reduced and reductively butylated coal were saturated and the spin-lattiee relaxation time increased.

Groups of Paramagnetic Centres in Reduced and Methylated Low Rank Coal

“…The multicomponent character of the EPR spectrum is visible for low microwave power. This eect was also seen earlier for other coals [7,12] (Table II). g-factor for Lorentzian 2 lines is smaller (2.00282.0030) ( Table II).…”

“…The linewidths of 0.070.09 mT were measured for the narrow Lorentzian 2 lines. The narrowing of EPR component lines is caused by exchange (and superexchange) and the broadening of EPR lines is a result of dipole dipole interactions in the system of paramagnetic centres [6,7,11]. Paramagnetic centres belonging to coal units consisting of a few aromatic rings are responsible for the broad lines.…”

“…The intensity of component lines depends on the type of coal (low, medium and high rank coal) [3,4], on chemical treatment (e.g. demineralization) [6,7]. The intensity of EPR signal is proportional to the concentration of paramagnetic centres.…”

“…The intensity of EPR signal is proportional to the concentration of paramagnetic centres. The relaxation processes (spinspin, spinlattice) were studied by EPR method for dierent groups of paramagnetic centres in coal [3,4,6,7]. Relaxation processes are responsible for saturation (or not saturation) of component lines with microwave power used during EPR experiments.…”

Size effects in the conduction electron spin resonance of anthracite and higher anthraxolite

“…Different physical properties of anthracite have recently been studied. This includes the following: structural analysis, DC conductivity of the order 10 1 –10 −4 S m −1 for different anthracite samples(our sample 10 −4 to 100 S m −1 ; Table ), and CESR analysis …”