The size of polyaromatic layer of coal char estimated from elemental analysis data

The structure of coal char was investigated based on elemental composition of char. Char used in this study were prepared at 800 °C from four demineralized Argonne Premium Coals. Elemental analysis was made using the conventional ultimate analysis method, and hydrogen content was determined by the temperature programmed oxidation method. This method is more reliable for hydrogen analysis than the conventional method. The H/C atomic ratio was evaluated at 0.16–0.18 for these chars. It is impossible to determine the char structure only with elemental analysis data. However, it becomes possible to deduce the layer size, if making some assumptions about the peripheral structure of polyaromatic layer of coal char. If the presence of four bridges per each cluster is assumed, then the polyaromatic layer size of these chars was calculated to be from 1.7 to 2.2 nm. These values were compared with those obtained using other methods like X-ray diffraction, nuclear magnetic resonance technique, and others.