Abstract
The proposal that low rank coals consist of a two-component molecular structure has been investigated by in situ 1H n.m.r. measurements during heating (to 875 K) of a suite of Australian and New Zealand brown coals, a set of Morwell brown coal lithotypes, and extracts and extract residues of some of these coals. The variation in behaviour of the coals during heating and pyrolysis, although significant, was not particularly sensitive to lithotype ranking, but showed a strong correlation with atomic H/C ratio. The extracts were found to be fully mobilized in the temperature range 470–700 K whereas the residues essentially remained rigid molecular lattices throughout heating and pyrolysis. This behaviour was independent of the lithotype and H/C ratio of the source coal. The higher H/C ratios of the extracts compared with the residue materials allow these observations to be explained (to a first approximation) in terms of the host/guest hypothesis whereby the coals are composed of extract (guest) and residue (host) materials in differing proportions.
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