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The concept of a mobile or molecular phase within the macromolecular network of coals: A debate

1986; Elsevier BV; Volume: 65; Issue: 2 Linguagem: Inglês

10.1016/0016-2361(86)90001-3

1873-7153

P.H. Given, Anna Marzec, Wesley A. Barton, Leo J. Lynch, B. C. Gerstein,

Thermodynamic properties of mixtures

The question addressed here is whether coals contain a substantial fraction of relatively small molecules clathrated within the macromolecular network and requiring long time or extra thermal energy for release. The debate primarily hinges on the interpretation of 1H n.m.r. data, but some other relevant findings reported in the literature are recapitulated. Cases are made out by the original authors for two different interpretations of the n.m.r. data (it should be emphasized that there is no dispute about the actual data, only about its interpretation). It appears that there are two (or possibly three) populations of protons in coals, which exhibit appreciably different free induction decay times and hence have quite different levels of rotational mobility. This is a fact of considerable interest in its own right, but the possession of high mobility does not necessarily mean that the mobile protons must be in relatively small molecules which are free to tumble in cages within the macromolecular network. Taking into account evidence from extractability and other experiments, it is possible to draw the conclusion that the content of relatively small molecules held within coal is larger than has been supposed and is essentially equal to the content of substances containing highly mobile protons, though a substantial proportion of these substances can probably be extracted only under various special conditions. However, it should be stated that there is disagreement between the authors on the admissibility of evidence from solvent extraction experiments. There is certainly evidence that the very high extractability of lignites with ethylenediamine is due to chemical reaction, and it is argued that this may be true also of higher-rank coals.