Product distribution and free radical reaction behavior during coal liquefaction in solvents with different hydrogen donor indexes

In this manuscript, the products distribution was studied in solvents with different proton donor quality index (PDQIs), and the reaction behavior of radicals was investigated using ESR. Besides, the correlation between products distribution and characteristics of radical's reaction was investigated. The results showed that increasing temperature and PDQI had a significant promoting effect on coal conversion. When the PDQI of solvent was 30, yields of oil-gas were always maintained at maximum value compared to other solvents, which was up to 42.70 wt% at 450 °C. The free radical's concentration (CR) of residue and asphaltene (AS) decreased gradually with increasing PDQI, and the difference of C_R of residue at different temperatures also reduced. The g value of residue increased significantly as PDQI increased from 10 to 20, while g value of residue (2.0033–2.0037) decreased significantly at the PDQI of 30, which may be due to that heteroatom in residue combined with more active hydrogen. A high correlation existed between the amount of hydrogen supplied by THN (N_H) and C_R of residue with increasing temperature, and the correlation could be enhanced as PDQI increased. However, the C_R in asphaltene was less correlated with N_H. Besides, the C_R of residue was significantly correlated with coal conversion and oil-gas yield.