Inertinite radical densities

Figure 9. Vitrinite radical densities decrease roughly line-arily with increasing H/C. Inertinite radical densities increase dramatically for H/C below 0.6.

Free Radicals in Macerals. Electron spin resonance (ESR) has been used to study carbon free radicals in coals, and to some extent, separated macerals. The technique provides information on radical density and the environment of the radicals. The resonance position, termed the g-value, is dependent on the structure of the molecule which contains the free electron. The line width is also sensitive to the environment of the unpaired electron. In an early study, Kroger (71) reported that the spin concentration varied between maceral groups with liptinite < vitrinite inertinite. For this limited set of samples the spin concentration increases with rank for liptinites and vitrinites and decreases for the micrinite samples. On the other hand, van Krevelen (72) found the same general results except... 

Inertinite radicals have very uniform g values, the magnitude of which suggests association with aromatic molecules. Radical densities can be extremely high (up to 25 x the levels seen in exinites). The linewidths are much narrower than in other maceral types ( l-2 Gauss vs 7 G for exinites and vitrinites), and both widths and shapes depend sensitively on the maceral "history", as reflected in atomic H/C ratios and the density. 

ESR observations were conducted at 9.5 GHz, using a Varian E-line ESR spectrometer with variable temperature capabilities from 90K-300K. The g value was determined using a Varian pitch standard with a g-value of 2.00302 + 0.00005. The integrated intensity was also calibrated to a Varian pitch standard. The parameters g, AH u, AH-p and the radical density were determined for each sample. Saturation measurements were made on a selected subset of samples. Low temperature runs at 125 K were made for all inertinite samples, as well as for selected samples of the other maceral types. Little temperature variation in g value, linewidth, or lineshape, was seen in any sample. The integrated intensity varied approximately as 1/T, suggesting Boltzmann polarization of the spins at lower temperatures. 

Figure 5. Linewidth increases with radical density for vitri-nites but not for inertinites.

There have been a large number of electron spin resonance (ESR) studies of coal and coal products,(1J but a microscopic interpretation of the resulting data has been hampered by the chemical heterogeneity of the coal samples examined. While several surveys of specially selected macerals have appeared, 3), the recent evolution of maceral separation techniques - now allows detailed ESR observations to be made on coals systematically fractionated in which coal rank, maceral type, and maceral density are simultaneously distinguished. The present report surveys the behavior of a variety of ESR properties of carbon radicals in exinite, vitrinite, and inertinite macerals in a variety of coals of different rank. These data... 

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