In order to investigate a relationship between chemical structure of coking coals and their thermoplasticity during their carbonizationn, evaluation of both hydrogen transfer reaction and heat treatment coupled with SEM observation was conducted along with measurement of SPE/ MAS 13 C NMR of virgin coals. The hydrogen transfer reaction from coal to hydrogen acceptor was carried out at 420 °C for 5 min. In the case using anthracene as acceptor, 0.6-1.1 mg of H 2 was transferred from 1 g of daf coal to the acceptor. A correlation between the weight of hydrogen transferred and % carbon of each coal (coal rank) showed a similar tendency to that between Gieseler fluidity and coal rank. This result suggests that the quantities of donatable hydrogen could be correlated strongly with the development of plasticity. To obtain the insight into the amounts of functional groups involved in releasing hydrogen, solid state 13 C NMR of sample coals was measured, the results indicating the presence of somewhat correlation between the concentrations of bridge methylene groups linking two aromatic moieties and maximum fluidities. Heat treatment of the coals up to their softening temperature, resolidification temperature, and 1000 °C was also conducted, the combination of crystallite parameters of the resulting chars and their SEM observation suggesting that lamellar structures of coal became disordered upon heating and then turned to the ordered structures as the heating proceeds. On the basis of the above results, chemical structural changes during carbonization process are discussed.

The development of aromatic cluster size in heat-treated coals by heating above 500 °C is discussed. Heat treatment of coal was performed at 500, 600, and 700 °C to obtain semicoke samples. The temperature range was above the resolidification temperature of the coal samples. For comparison, a strongly coking coal, Australian Goonyella coal, and a slightly coking coal, Chinese Enshu coal, were used as the sample coals. Analysis of the virgin coals and the semicoke samples with solid-state 13C NMR indicated that the strongly coking coal tended to develop the aromatic ring size to a greater degree than the slightly coking coal as the heat-treatment temperature increased. To examine this tendency, a ruthenium ion catalyzed oxidation reaction was applied to the semicoke samples to obtain information concerning the distribution of the aromatic ring size. The products from this reaction also implied that the semicoke samples obtained from the strongly coking coal had an aromatic ring of larger size on average. A schematic representation of the behavior of molecules in the two coal samples during heating was established.

A new method was developed to study the preliminary surface textural change of a single coal particle heated rapidly to 500 °C with well-characterized CO2 laser under nitrogen at atmospheric pressure. The SEM observable changes of surface texture were not observed up to 485 °C with heating rates above 6300 °C s-1, even with coking coal. However, the changes were observed at about 440 °C at heating rates of ≤1800 °C s-1 even with weak-coking coal. These results suggest that the effect of heating rate on softening and melting (plasticity) of the coal particles shows that there are limited and optimum ranges of heating rate for the increase of plasticity. In addition, at heating rates of 50−240 °C s-1 for two kinds of coal, the change of surface texture (initial structural relaxation) begins around 240−260 °C, the initial softening (first melting phase) begins around 290−310 °C, the second melting phase appears around 400−410 °C, and the uniformly melting temperature is around 420−440 °C. The heating rate (<240 °C s-1) seems to have little effect on the temperature range at which the initial structural relaxation and initial softening occur for two kinds of coal.