He Li,Shisheng Liang,Yucui Hou,Yupeng Wang,Shuhang Ren,Weize Wu
Direct coal liquefaction (DCL) is not only for fuel but also for chemicals, which shows high efficiencies in atom utilization and energy. The study on coal structure is important to select coal for direct liquefaction . Naomaohu coal is a kind of subbituminous coal and a typical coal for direct liquefaction . In this work, the structure of Naomaohu coal was investigated via alkali‑oxygen oxidation , ruthenium ion catalyzed oxidation and physical analyses and a representative structural model with a model size of 128,755 amu was constructed. The structural characteristics show that the ratio of single-, double-, triple-, and quadruple-aromatic rings is 149:164:102:63. The triple- and quadruple-rings aromatic structures are mainly connected by C C bonds of 2–4 carbon atoms. The single- or double-ring is connected on the triple- and quadruple-rings aromatic structures through ether or ester bonds , which can be broken easily under mild conditions. Long alkyl side chains with carbon atoms from 13 to 25 accounting for 0.91 wt%. The high H/C, high oxygen content (mainly weak bonds such as ether and ester bonds between aromatic clusters), abundant single-, double-, triple, and quadruple-aromatic rings, and alkyl bridge bonds of 2–4 carbon atoms are beneficial to the mild liquefaction of Naomaohu coal
Xizhuang Qin,Qingya Liu,Jiachen Yu,Lei Shi,Zhenyu Liu
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.
Three coal samples with different density (d < 1.35, 1.35 < d < 1.40 and d > 1.40 g cm −3 ) which were separated using ZnCl 2 specific gravity liquid from Naomaohu (NMH) coal were investigated to understand the difference in their physicochemical and thermal properties. Fourier transform infrared spectrometry (FTIR), Raman, X-ray diffraction (XRD), solid-state 13 C Nuclear Magnetic Resonance ( 13 C NMR) and scanning electron microscopy (SEM) methods were used to determine the physicochemical characteristics of the coal sample. In addition, a TG-FTIR analyzer was used to investigate the key thermal conversion characteristics and volatile emissions of the three coal samples. Typical volatile contents including CO 2 , CO, CH 4, and Aromatic C C were analyzed. Results showed that the density has great effect on functional groups and crystalline structure on coal sample. Four distinct peaks are showed in DTG curves, indicating that four reaction stages, namely, drying, desorption, pyrolysis , and polycondensation , were involved in the pyrolysis process of NMH coal. The TG/DTG curves of the three densities indicate that the low-density coal assumes the highest weight loss rate at the pyrolysis stage and the trend becomes weaker at the polycondensation stage. Two obvious emission peaks vividly showed that light gases such as CO 2 , CO, and CH 4 can be separated into two stages at the pyrolysis and polycondensation stage.
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