Relationship between Pyrolysis Reactivity and Aromatic Structure of Coal

Abstract

Illinois No. 6 coal was depolymerized by treatment with trifluoromethanesulfonic acid in methylcyclopentane at 120 °C. The yield of tetrahydrofuran (THF) extract was increased to 89 wt %. This increase was explained by the cleavage of bridges between aromatic units. The extract (TSd fraction) was further hydrogenated using a Ru/carbon catalyst in a mixed solvent of THF and acetic acid at 120 °C for 12−72 h under a hydrogen pressure of 10 MPa. Phenolic resin and polystyrene samples were used as references and were also hydrogenated over Ru/Al2O3 catalyst under the same conditions. After hydrogenation for 72 h, the aromaticity of the hydrogenated TSd fraction (H-TSd fraction), fa, decreased to 0.33 from the original value, 0.6. The pyrolysis reactivity of the treated coals was evaluated using a Curie-point pyrolyzer (CPP) at 500−764 °C in a stream of helium. The reactivity of the TSd fraction was greatly enhanced as a result of the hydrogenation, and 96 wt % of the H-TSd fraction was converted to volatiles during the pyrolysis at 764 °C. A good correlation between the aromaticity and the yield of volatiles was found for both the treated coals and phenolic resins, but not for the polystyrenes. This suggests that pyrolysis reactivity was related to the aromatic structures of the main chains, and that those structures were changed by the hydrogenation.