Effect of temperature on Shenfu coal pyrolysis process related to its chemical structure transformation.

Revealing the pyrolysis reaction pathway related to coal structure evolution under different temperatures is important for the industry to design reactors and process operations. In this study, all the pyrolysis products obtained under different pyrolysis temperatures were comprehensively analyzed by multiple techniques. The results showed that the aromatic nucleus were inclined to react with methyl radicals, forming char with abundant methyl substitution aromatic structure at low pyrolysis temperature. At medium pyrolysis temperature, dramatically condensation reaction occurred, resulting in the formation of aromatic protonated carbon and abundant polycyclic aromatic hydrocarbons (PAHs) containing benzenoid rings joined by a carbon‑carbon single bond remaining in char. The concentration of aliphatic hydrocarbons in light tar decreased dramatically and converted into light hydrocarbon gas compounds (especially H 2 and CH 4). At high pyrolysis temperature, severe carbonation of char led to the formation of abundant PAHs with reduced aliphatic side chain in light tar. Tar precursors preferred to form larger PAHs due to occurrence of drastic secondary reaction. The contents and diversity of oxygen−/nitrogen-containing heteroatom compounds in heavy tar were significantly reduced with the increase of temperature. Finally, the devolatilization mechanism responsible for the evolution of chemical structure of Shenfu coal pyrolyzed at elevated temperatures was proposed. Unlabelled Image • Low temperature leads to char with abundant methyl substitution aromatic structure. • Medium temperature results in aromatic protonated carbon and single-bond PAHs in char. • Tar precursors prefer to form larger PAHs at high pyrolysis temperature. • Contents and diversity of heteroatom compounds in heavy tar decreased with elevated temperature. • Evolution pathways of coal chemical structure at elevated temperature was proposed. [ABSTRACT FROM AUTHOR]