INFRARED-SPECTROSCOPY OF COAL MACERAL CONCENTRATES AT ELEVATED-TEMPERATURES

Resinite, vitrinite and inertinite from three Chinese and one Australian coal were pyrolysed under nitrogen at temperatures up to 625-degrees-C in a Fourier transform infrared (FT-i.r.) spectrometer. During pyrolysis the infrared spectra were obtained at increments of 25-degrees-C. For the resinites, the main changes in chemical structure were the loss of protonated aliphatic carbon and a change in the distribution of carboxyl functional groups. Pyrolysis of vitrinite produced increased absorption from protonated aromatic carbon, particularly in the 700-900 cm-1 region, but a steady decrease in intensity of the 1600 cm-1 band. Formation of carbon dioxide was evident at temperatures as low as 150-degrees-C and is postulated to arise from the potassium catalysed decomposition of carboxylic acids formed during pyrolysis. Inertinite showed no appreciable change in its i.r. spectrum until 300-degrees-C. Above this temperature, increased absorption in the carbonyl region showed that some oxidation had occurred.