Chemical Structure and Properties of Heat Treated Coal in the Early State of Carbonization

In a constitution analysis of coal, it is very important to obtain the true density of coal. As for Japanese coal, the density has been measured with water and methanol. Because of their comparatively high molecular weight and polarity, results can hardly be considered as representing the true density of coal. In this experiment, the true densities of Japanese coals are measured with helium and these results are compared with those obtained from foreign coals. Coal samples are chosen according to the coal rank which is based upon the carbon content of coal, from lignite to anthracite and so-called vitrain is employed after the separation by float or sink method.In Japanese coals, the change in density with coal rank is summarized as follows. Tenpoku coal, (72. 7%C) which is the lowest in coal rank among the samples, has the density of 1. 348 and as coal rank increases, density decreases to reach a minimum value of 1. 267 shown by Miike Miyanoura coal (84. 5% C). However, a further increase in coal rank increases density and thus the density of Omine coal (93. 2% C) ammounts to 1. 470. The comparison of these data with those of foreign coals shows that in lower rank coal, the density of Japanese coal is generally smaller than that of foreign coal, but a fairly good agreement is observed for the coal with the carbon content above 86% C.The variation of H/C with coal rank is nearly opposite to the change in density with coal rank, and by comparison with foreign coal, a high value of H/C is noted in the lower rank coal. Thus the difference of density between Japanese and foreign coal can be ascribed to the high hydrogen content of the lower rank Japanese coal . The reciprocal of density is plotted against the hydrogen content of coal and it is found that the points of Japanese coals and foreign coals lie on the same curve. In addition, according to van Krevelen's graphical densimetric method the aromatic carbon fraction (fa) is calculated from the measured density and the relation between fa and coal rank is obtained . Tenpoku coal having a lowest coal rank shows fa of 0. 77 and fa decreases with increasing coal rank. But as coal rank exceeds that of Akabira coal, fa shows a steep increase and in Ohmine coal fa reaches 0. 99. If results are compared with those of foreign coals, in the lower rank coal fa of Japanese coal is generally smaller than foreign coal . However by plotting fa agaist H/C, both are shown to lie on the same curve.In conclusion, the density and fa of coal are greatly affected by its hydrogen content and the graphical plot of density and fa against coal rank shows a clear difference between Japanese and foreign coal. However if they are plotted against hydrogen content, a good agreement is attained. By making use of this relation, density and fa of coal can be determined approximately.