Earlier research has shown that coals hydrogenated in the absence of solvent and in the presence of a dispersed Mo catalyst become progressively more fluid. The present studies were undertaken to examine the relationships between the catalytically generated coal liquids and thermoplastic behavior. Five coals of rank varying from subbituminous to low-volatile bituminous and exhibiting little or no fluidity were hydrogenated by using an impregnated molybdenum catalyst and without vehicle for various times at temperatures up to 400 °C. Except for the low-volatile bituminous coal, the fluid behavior of the hydrogenated coals, as measured by Gieseler plastometry and microdilatometry, was greatly improved compared to that of the untreated coals. The development of fluid behavior displayed by the hydrogenated coals is attributed to the generation of relatively small, solvent-soluble, molecular fragments. The structure of the low-volatile bituminous coal is considered to contain a large proportion of strong covalent bonds, which inhibit degradation of the coal structure. Air oxidation of a high-volatile A bituminous coal substantially reduced its fluid properties. Following catalytic hydrogenation, the hydrogenated coal became even more fluid than the original untreated coal. Microdilatometry measurements on mixtures of a high-volatile A bituminous coal with chloroform-soluble extracts, obtained from the same coal after hydrogenation, showed a progressive enhancement in swelling and lowering in softening temperature as the proportion of the extract in the mixture was increased. However, neither mixing a hydrogenated high-volatile A bituminous coal with its unhydrogenated parent coal nor mixing with the chloroform-soluble extract from a hydrogenated subbituminous coal improved the dilatation properties.
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