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

Abstract

Infrared spectra of coals in different ranks have been measured, as described in the previous paper, by the KBr technique as quantitatively as possible. The specific extinction coefficients, K (l/g·cm), at 1, 600, 1, 450, 1, 380, 1, 260, 870, 820 and 750cm-1 were calculated and their relations with the elementary composition were discussed.1. Base-lineThree methods that could be taken up in the technical means were examined; in A method the maximum value of transmission at near 1, 850cm-1 was taken as the base; in B method the base-line according to R.A . Friedel, and in C method the line between the shoulder at near 1, 800cm-1 and that at near 700cm-1 was used respectively . For the absorption band at 1, 380cm-1, however, the base-line according to R .A. Friedel was used.For each absorption band between 1, 600cm-1 and 900cm-1 the corresponding K values calculated by above mentioned methods are quite near, but for the absorption bands under 900cm-1 K values obtained by A method namely differ from that by other two methods.2. Absorption band at 1, 600cm-1The assignment of the absorption band near 1, 600cm-1 is still undefinite at present, but in general the band have been assumed to be due to hydrogen bonded carbonyl groups as well as aromatic C=C structures . When K values of the band are plotted against the carbon content of coal, a straight line is formed which declines toward high carbons. On the other hand, a straight line declines toward low oxygens when the relations between oxygen content of coal and K is considered.3. Absorption bands at 1, 450 and 1, 380cm-1These absorption bands at 1, 450 and 1, 380cm-1 are assignd to aliphatic and hydroaromatic CH hydrogen. The K value at 1, 450cm-1 decreases gradually as the carbon content of coal increases. So far as Japanese coals are regarded, the K value at 1, 380cm-1 increases with increasing carbon content until Yabari coal (86 .2% C), and then decreases beyond this point.4. Absorption band at 1, 260cm-1The K value at 1, 260cm-1 which is assigned to phenolic C-O- and aromatic ether decreases nearly linearly with increasing carbon content of coal or with decreasing oxygen content.5. Absorption bands at 870, 820 and 750cm-1These absorption bands at 870, 820 and 750cm-1 have been assumed to be due to out-of-plane CH vibration in benzene and condensed aromatic ring system. The K values calculated according to B and C methods increase with increasing coal rank, especially the K value at 750cm-1 increases rapidly beyond Moura coal (87.6% C).