Relation between char structures and formation of volatiles during the pyrolysis of Shenfu coal: Further understanding on the effects of mobile phase and fixed phase

Abstract

The formation of resultant volatiles is closely related with chemical structure of char during the pyrolysis process. In this study, all-components, that are semi-char, tar and gas product obtained by Shenfu coal pyrolyzed under various residence time at 435 °C were comprehensively analyzed at molecular level, aiming to reveal the reaction pathways responsible for the evolution of chemical structure of coal/char. The results showed that CO2 and CO were the predominant pyrolysis gas product which inferred high content of organic oxygen species in low-rank Shenfu coal. At the initial stage of pyrolysis, cracking of bridged bonds, especially heteroatom bridged bonds, such as O, N and S, would produce relatively stable radicals in semi-char. Phase change of light components and decomposition of asphaltene in mobile phase can be strongly related with light tar aliphatic compounds formation. At the middle and later stage of pyrolysis, thermal cracking of polar radicals and decomposition of solvent extracted metaplast materials made predominant contribution to tar formation. In addition, the cracking of peripheral aromatic structures of coal/char skeleton structure, through which secondary reaction (such as methylation and dehydrogenation reaction) took place, would result in tar (light tar and heavy tar) and H2 formation.