Abstract
To understand the main reactions in direct coal liquefaction and to find out the temperature at which condensation reactions become significant, the liquefaction of a vitrinite-rich coal, Naomaohu (NMH), is studied at 380–460 °C in tetrahydronaphthalene (THN). The main focuses are on the trends of products yield and evolution of solid residues’ composition and structure. It is found that NMH is very active at 420 °C with a conversion of >90 wt% and an oil-plus-water yield of 39 wt% in 40 min. The reaction, especially the condensation behaviors at temperatures lower than 420 °C are different from those at higher temperatures as indicated by the trends in products yield and in the residue’s morphology and properties. The residues obtained at 440–460 °C contain mesophase pitch spherules. The changes in residues’ volatiles content, H/C and O/C ratios, FTIR and Raman spectra, and ESR parameters are slow at 380–420 °C but much fast at 440–460 °C. These different trends are clearly evidenced by plotting the residues’ characterization parameters against the decreasing residue yield during the reaction.
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