Condensation of residue during direct liquefaction of a high-vitrinite coal

To understand the formation of residues and its relation with the vitrinite structure and the products yield in direct coal liquefaction (DCL), a high vitrinite low-rank coal, Naomaohu (NMH), is studied at 380-460 degrees C in the presence of tetrahydronaphthalene and absence of a catalyst. The structures of coal and residues are charac-terized by the proximate and ultimate analyses, 13C nuclear magnetic resonance, and the electron spin resonance. Beside the frequently seen coal conversion and products yield at various temperatures and time, the products yield and the residues structure parameters are correlated with the residues yield (YRes) and the quantity of hydrogen donated from tetrahydronaphthalene (QH). It is found that the DCL can be roughly defined into two regions demarcated by 420 degrees C, with limited condensation at 380-400 degrees C and intensive condensation at 440-460 degrees C, for example. These two-region behaviors can be clearly evidenced by the different trends in products yield and the residues parameters, such as those relevant to the cleavage of bridge bonds (fal, Cn, delta-C and delta-O) and those relevant to the residues' condensation (far, Xb, RD and H/C), against YRes and QH. The two-region behavior is important for optimization of DCL conditions and its processing scheme.