Heat-flow Microcalorimetric Study of the Adsorptive Properties of A Slightly Weathered Bituminous Coal

The adsorption of water, methanol and n-hexane on demineralized Colombian coal (fresh and exposed for 20 days to the atmosphere) has been investigated by means of heat-flow microcalorimetry. A sample of graphite has also been studied for comparison. The results have been interpreted considering the different activity of three kinds of regions of the coal surface: (i) inorganic region; (ii) oxidized organic region, containing carboxyl, carbonyl and/or phenol groups; (iii) graphite-like region. In the case of hexane adsorption, due to the weakness of the interaction, the differentiation of the two coals in relation to their slightly different oxidation state is particularly evident. It has been concluded that weathering causes a further slight increase of the oxidation state of the organic part of coal and of microporosity. Moreover, a stronger interaction of the organic part of coal with the residual inorganics after weathering is suggested.