The authors have recently proposed an upgrading method of low-rank coals in which low-rank coals are treated in a non-polar solvent at around 350℃ to produce upgraded coals containing a large amount of low-molecular-weight compounds with less oxygen content. In this study the solvent treatment method was applied to various types of low-grade carbonaceous resources such as biomass waste, peat, brown coal, and sub-bituminous coal. The method was effective for any of the low-grade resources, and the carbon contents of the upgraded products all converged on around 80% (daf). To further upgrade the coals, heat-treatments at around 400℃ under either mechanical or gaseous pressure were investigated. It was found that heat-treatment under mechanical pressure could alter the structural and thermal properties of a sub-bituminous coal (C: 79.6%-daf) to the properties which were close to coking coals'.
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