Bituminous coal heteroatoms

Coal Hquefaction iavolves raising the atomic hydrogen-to-carbon ratio from approximately 0.8/1.0 for a typical bituminous coal, to 2/1 for Hquid transportation fuels or 4/1 for methane (4). In this process, molecular weight reduction and removal of mineral matter and heteroatoms such as sulfur, oxygen, and nitrogen may need to be effected. 

In thermal processes the formation of asphaltols always precedes other reactions such as major heteroatom rejection and distillate formation. In fact, in the SRC process bituminous coals are actually dissolved by the time the coal slurry exits the preheater (4,11). This has recently been demonstrated at the SRC process development unit (PDU) in Wilsonville, Alabama (11) (see Figure 2). 

A select list of species containing sulfur plus an additional heteroatom is given in Table III. These groups of compounds have been observed in coal derived products from various sources. To be able to make reasonable comparisons only data from bituminous coals are used. Possible structures for the formulae given in Table III are shown in Scheme I. It should be emphasized that further information is necessary to positively assign structures. The viability of these structural assignments will be discussed in the next three sections. 

The fact that the 9.8 G coupling is observed for the subbituminous and high-volatile bituminous coals, which have high heteroatom contents (18.5 wt % and 11.4 wt %, respectively (35)), andmot for the low-volatile bituminous coal, which contains only 3.6% (35), suggests that its assignment to a heteroatomic radical is not unreasonable. 

Heteroatomic Coals, especially low-rank coals that are rich in oxygen, might be expected to contain heteroatomic free radicals. Yen and Sprang (29) showed that the g values of coals as well as those of other bituminous materials showed a systematic trend with their heteroatom content. In particular, they plotted the ESR g values as a function of where X refers to the atom fractions of oxygen, nitrogen, and sulfur in the coals and values are spin-orbit coupling constants of the respective atoms, i.e., 152 cm , 70 cm , and 382 cm . This... 

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