XPS analysis and combustibility of residues from two coals extraction with sub- and supercritical water

Two kinds of residues, obtained from the extraction of a weakly reductive coal, Shenfu-Dongsheng coal (SD), and a reductive coal, Pingshuo coal (PS), with sub- and supercritical water on a semi-continuous apparatus, were characterized by calorific value analysis and X-ray photoelectron spectroscopy analysis, and the combustion behaviors of residues were investigated by thermogravimetric analysis. The results show that the residues have higher calorific value than raw coal samples, and SD residue has higher calorific value than PS residue. C—C, C—O, and pyridinic nitrogen and pyrrolic nitrogen are the dominant form of C, O, and N on the surface of raw coal samples and their extraction residues. The combustion behaviors of extraction residues show that the SD residue is more reactive and more easily burned than PS residue.