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

Abstract

Nine vitrains (72. 7-90.7%C) were carbonized up to the temperatures between 320 and 600°C in a step of 20°C. The temperature was rised at the rate of 3°C/min. and the final temperature was kept for 10 minutes. The chars thus obtained were examined by X-band ESR spectrometer. ESR spectra were observed in vacuum (10-4-10-5 torr.), in air, in ethylene diamine after heating with it at 180°C and in air after washing with methanol and hydrochloric acid. Spin concentration (No.of spin/g of char) increased with rising temperature and it was noticed that the increase in spin concentration took place considerably even at temperatures as low as 320-380°C where no appreciable weight loss was observed by thermogravimetry. All of the chars, excepting these obtained at temperatures above 540°C, decreased their spin concentration when they were heated with ethylene diamine and the ΔHmsl observed in ethylene diamine kept constant value for each individual vitrains while the ΔHmsl observed in vacuum varied considerably. By washing the chars heated with ethylene diamine the spin concentration was recovered almost quantitatively for the chars obtained at temperature above 460°C, but not quantitatively for the other chars. It was observed that the recovery of spin concentration seemed difficult for some of chars which were obtained at temperatures between 400 and 440°C.It was assumed that the increase in spin concentration which was observed at low temperatures took place as a result of coming loose of the low molecular materials, on the analogy of the fact that chloroform-extract increases at the temperature. The spin centres which form and exist at temperatures below 500°C were considered to be similar to those exist in original coal in nature although as temperature gets near 500°C they vary gradually. It would be concluded that the spin centres of coal, especially of bituminos coal, are aliphatic or alicyclic in natue at temperatures below 500°C and above 500°C they become aromatic in nature.