Evolution of carbon structure and functional group during Shenmu lump coal pyrolysis

Abstract

An in-depth study on the chemical structure evolution during the pyrolysis of lump coal is of great significance for revealing the pyrolysis mechanism in fixed-bed gasifier. In this paper, the pyrolysis chars with different residence time were prepared, and then the evolutions of chemical structure at particle surface and particle center during lump coal pyrolysis were explored by Raman spectroscopy and FTIR. Results indicated that during the pyrolysis of lump coal, there were obvious differences in aromatic ring structures and cross-linking density between particle surface and particle center, and these differences were significantly affected by pyrolysis temperature. At a certain stage of the pyrolysis process, aromatic ring structures and cross-linking density at surface and center had different change trends. Additionally, the change trend of aromatic ring structures and cross-linking density at surface was sometimes even completely opposite to that at center. The evolutions of functional group at surface and center were quite different only at 1000 °C. In the first 2 min of pyrolysis, the aliphatic C-H structure at center changed little, but the aliphatic C-H structure at surface was almost completely decomposed. Furthermore, the low-substituted aromatic ring structure at surface would decompose gradually in this stage, and the (2H) aromatic structure at center would be converted to (1H) aromatic structure. When the pyrolysis time increased from 0.5 min to 2 min, the content of (1H) aromatic structure at particle center increased from 23.6% to 40.9%, while (2H) aromatic structure decreased from 43.1% to 25.9%.