Influence of chemical structure on the fluidity of rapidly heated bituminous vitrinites

When heated rapidly, many coal particles undergo thermoplastic transformations which change the particle size, shape and morphology. In the current work, vitrinites with subtle differences in rank and bulk chemical composition but significant differences in chemical constitution produced chars with different particle size and helium density. The particle size of an Upper Freeport (UF) sample increased by a factor of 2.5, and the helium density increased to 2.1 g/cm³ (daf). In contrast, a Lewiston-Stockton (LS) vitrinite swelled by a factor of 1.8 and the helium density increased slightly then decreased to 1.3 g/cm³. The LS vitrinite had more aliphatic hydrogen than the UF vitrinite, which should promote thermoplasticity. However, less aromatic hydrogen and more oxygen in the LS sample contributed to increased "cross-linking", presumably increasing the lamella size in the thermoplast, thus reducing the extent of thermoplasticity.