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 (TS d 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/Al 2 O 3 catalyst under the same conditions. After hydrogenation for 72 h, the aromaticity of the hydrogenated TS d fraction (H-TS d fraction), f a , 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 TS d fraction was greatly enhanced as a result of the hydrogenation, and 96 wt % of the H-TS d 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.

Uncovering Structure–Reactivity Relationships in Pyrolysis and Gasification of Biomass with Varying Severity of Torrefaction

“…The results were in accord with those from the literature. Takagi and co-workers declared that there was a relationship between the H/C ratio and aromaticity of biochar or coal. , As mentioned above, the H/C and O/C molar ratio of pine declined with increasing torrefaction severity. Pine mainly underwent dehydration and aromatization reactions during torrefaction, thus causing the decreases in H/C molar ratio and the increases in aromaticity of pine.…”

“…However, there is a lack of quantitative information on the structural transformations of biomass during torrefaction and their influences on subsequent pyrolysis and gasification reactivity. Previous studies demonstrated that the pyrolysis and gasification reactivity of coal were related to its aromaticity or H/C molar ratio. , Hence, in the present study, the H/C molar ratio or aromaticity of biomass is attempted as an indicator of structural alteration of biomass during torrefaction, aiming to predict reactivity of torrefied biomass during pyrolysis/gasification. As shown in Figure , under different torrefaction conditions, biomass will proceed various reactions (such as dehydration, decarboxylation, and decarbonylation) with different severity to form cross-linking and charring biomass with varying H/C molar ratio and aromaticity, thus leading to the alterations in the pyrolysis/gasification reactivity of torrefied biomass.…”

An experimental study on the evolution of aggregate structure in coals of different ranks by in situ X-ray diffractometry

“…15 In the past couple of decades, teams of researchers have proposed several structural parameters for evaluating the molecular structure of coal and other less-crystalline carbonaceous materials by the use of XRD. For example, the XRD proles of carbonaceous materials with low-crystallinity has been statistically interpreted by Hirsch 16 and Diamond; 17 Fujimoto and Shiraishi 18 modied the Diamond's method for estimating carbon-layer sizes; and Takagi 19 and Mennelia 20 used a standard analysis of the carbon stacking structure to understand the stacking structure of coal and other less-crystalline carbonaceous materials. Lu et al 21 conducted a systematic study on the evolution of L a of different types of coal, which proved that the development of L a was more dependent on coal rank.…”

Aromatic hydrogenation of benzyl alcohol and its derivatives using compressed CO2/water as the solvent

“…In addition, it is speculated that protonation of the hydroxyl group could occur in the weak acidic environment (in our case, pH around 3). 18 The protonated hydroxyl group could manipulate the electron density of the total compound causing a lowering of activation energy for the aromatic ring hydrogenation. Moreover, lowering the pH value of the system may promote the hydrogenolysis reaction since the elimination of the functional group could be catalyzed by acid.…”