Study on the transformation characteristic of heteroatoms during liquefaction of Naomaohu coal

In this work, Naomaohu coal was used for direct liquefaction. The conversion and oil yield as a function of hydrogenating temperature were investigated, and the transformation characteristics of heteroatoms in raw coal and liquefaction products were clarified. The results showed that Naomaohu coal presented high liquefaction performance even under lower initial pressure of 2 MPa. The conversion and oil yield could reach 69.6% and 55.3%, respectively, at a pressure of 2 MPa and 400 ℃. Gas chromatography-mass spectrometry and gas chromatography-atomic emission spectrometry were combined to analyze the products. It was found that the weak bond structure containing heteroatoms was easier hydrogenated to fracture and removed in the form of H₂S, NH₃, H₂O, etc. The sulfur-containing compounds in liquefied products were mainly thiophene and thiophene homologues. The content of nitrogen-containing compounds was trace and mainly consisted of nitrogen heterocyclic compounds. The oxygen-containing compounds in liquefied oil were dominantly phenols and their homologues. The heteroatoms in the aromatic structure would generate more stable heteroatom-containing compounds in the liquefaction residue via the free radical polycondensation reaction.