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

Abstract

High vacuum pyrolysis was performed for Japanese original coals and heat treated coals. The molecular weight of resulting distillates was measured by vapour pressure and surface area of residual coal was determined by carbon dioxide according to the theory of Dubinin-Polanyi. The following results were obtained.1. For Yabari coal, the effect of the pyrolysis temperature was studied. The average molecular weight of distillates is about 400, which remains nearly constant at the temperatures of 350, 400, 450 and 500°C. At each temperature, distillates show an approximately same average empirical formula of C29H31O1·3. The results indicate that the substances of distillates are scarcely affected by the temperature of high vacuum pyrolysis. An interesting contrast to this result is shown in the yield of distillates which increases with increase in temperature.The surface area of residual coal increases with increasing temperature of pyrolysis above 400°C, and at 5007deg;C it reaches 167 m2/g, i. e., 50 % increase from the value of original coal.2. The effect of coal rank was examined with various kinds of coals, at the fixed heating temperature (500°C). The molecular weight of distillates increases with increase in coal rank as shown by Taiheiyo coal (329) and Bibai coal (346), reachs maximum (393) at Yabari coal and decreases on further increase in coal rank. However, Takamatsu coal shows an extremely low value (288). This relation bears clear resemblance to the previously reported relation between the yields of distillates and coal rank. When molecular weight of distillates were plotted against C% of distillates, almost all coals were found to lie on the straight line, including Takamatsu coal. This signifies that molecular weight of distillates increases with increasing C%.As for the surface area of residual coal, the youngest Tempoku coal shows the highest surface area (about 300 m2/g), and the surface area tends to decrease with increasing degree of coalification. The difference of the surface areas between original coal and residual coal is large for young coals, and it shows a decreasing tendency with increase in degree of coalification.3. The high vacuum pyrolysis of heat treated coals was performed under the idential condition (500°C) and the effect of heat treatment temperature was investigated. The molecular weight of distillates is generally unaffected when heat treatment temperature is below 400°C, but decrease rapidly at 450°C. This tendency can also be observed for the yields of distillates as reported previously, and combined results suggest that polymerization and decomposition might have been induced to an appreciable extent by the heat treatment at 450°C. The surface area of residual coal tends to increase with increase in heat treatment temperature above 500°C.