Observation of hydroxyl hydrogen in coal by in-situ FTIR difference spectroscopy

Abstract

Direct studies of the chemical and thermal reactivity of complex materials such as coal are difficult due to their high optical density and chemical heterogeneity. To overcome these difficulties, highly sensitive semi-micro in-situ techniques have been developed which employ Fourier transform i.r. difference spectroscopy of optically thin sections of coal. These novel techniques are illustrated in studies of the intrinsic Bronsted type hydrogen bonding in coal at room temperature. Hydroxyl groups in coal are isotopically labelled with deuterium by exposure to gaseous D 2O. The difference spectrum obtained by comparing the deuterium labelled coal to the unlabelled coal provides a ‘fingerprint’ of Bronsted type hydrogen bonding. The exchanged hydroxyls are spectroscopically identified as hydrogen bonded phenolic-OH (5 per 100 carbon atoms) and 0.03% tightly bound water. The high intrinsic sensitivity of in-situ i.r. difference spectroscopy combined with the spectral simplification resulting from isotopic substitution provides a rapid and direct method for the study of the effects of chemical and thermal treatment of coal.