Structure evolution of oxygen functional groups in Dongsheng long flame coal by ¹³C-NMR and FT-IR

Vitrinite was separated and enriched from the 2nd long flame coal seam in Dongsheng coal mine by flotation and centrifugation. Structural parameters of groups were obtained from proximate and ultimate analysis, as well as ¹³C-NMR and FT-IR spectrum. The contents of carboxyl and carbonyl in the vitrain are from 8.91 to 10.90 mol/kg and from 1.61 to 1.79 mol/kg, respectively. Carboxyl is lost rapidly with increasing pyrolysis temperature. Methyl and methylene groups attached in the form of end groups to oxygen in the aliphatic chain or an aliphatic ring structure are removed first, and is basically stable above 350 ℃. The variation in occurrence of oxygen functional groups is the result of competition between aromatic and aliphatic system. Aromatic and aliphatic oxygen in coal pyrolyzed at 510 ℃ are 7.49 and 3.45 mol/kg. The evolution of hydroxyl is closely associated with the occurrence of oxygen. The content of various hydroxyls reduced along with the increasing temperature. Destructive effect on macromolecular network caused by pyrolysis interferes various hydrogen bonds, while the hydroxyl-π effect is enhance. The chemical activity order of oxygen in the coal is COOH > R-O > Ar-O-Ar, Ar-O-C, C-O-C > C=O. The contents of inactive and active ether in the vitrain are 0.68 and 0.48 mol/kg, respectively.