Microstructure evolution characteristics of Shengli lignite during combustion process

The combustion of Shengli lignite demineralized with hydrochloric acid was carried and residues from different reaction conditions were obtained. The microstructural properties of the lignite and residues were examined by FT-IR, XRD, XPS and Raman, respectively. The results indicate that aliphatic functional groups were consumed during combustion, while oxygen-containing groups and aromatic structure were consumed and generated alternatively. The proportion of C-C/C-H structure decreased after increasing, while the content of carbon-oxygen structure was increased following decrease. The aromaticity of residues increased and I_D/I_G increased before decrease, while I_S/I_G decreased before increase. This indicated that graphitization transformation degree of lignite obviously increased during combustion, especially in the late stage of reaction.