In this study, relation between the amount of transferable hydrogen of coal tar pitch (CP) and fluidity of the slightly caking coal adding CP was discussed in order to enhance fluidity of the slightly caking coal. In particular, additive effects of two constituents (toluene soluble but hexane insoluble; TSHI and pyridine soluble but toluene insoluble; PSTI) separated from solvent extraction of CP were estimated. As a result, an amount of transferable hydrogen of these constituents increased slightly by high temperature (360–420°C) hydrogenation. Fluidity of Enshu coal (slightly caking coal) increased by addition of these hydrogenated constituents (TSHI and PSTI). Because retrogressive reaction among the molecules in Enshu coal was suppressed by hydrogen donation from the increased transferable hydrogen in TSHI or PSTI to the molecules in Enshu coal. Further, additive effect of fluoranthene (FL) was estimated. For all tested coals, maximum fluidity of coal adding hydrogenated FL (HFL) was larger than that adding FL. The difference was large for coals containing much of oxygen. Accordingly, retrogressive reaction among the oxygen containing groups in the coal molecules was suppressed by hydrogen donation from the transferable hydrogen in HFL. Estimating from the polarizing micrographs of cokes from coal adding HFL, it was clarified that thermal plasticity of coal was enhanced by addition of HFL, not by thermal plasticity of HFL itself.
