In this paper, the effects of sulfur on liquefaction performances of coal and the transformation behaviors of γ-Fe 2 O 3 at the S/Fe atomic ratio of 0-1.3 under mild conditions were investigated. Compared with traditional liquefaction processes, the oil yield and coal conversion were insensitive to the addition of sulfur under mild conditions (temperature of 430°C, reaction pressure of 8.5-13.8 MPa). The optimum S/Fe atomic ratios at the initial H 2 pressures of 4.0 and 8.0 MPa were 0.6 and 1.0, which were lower than those of traditional liquefaction processes. As the S/Fe atomic ratio increased from 0 to 0.6 (at the initial H 2 pressure of 4.0 MPa), the oil yield and coal conversion increased by 4.0% and 3.8%, and this could be attributed to the synergistic effects between the relatively sulfur-rich structure of pyrrhotite (Fe 0.8917 S) and the relatively high partial pressure of H 2 S. In addition, over 85% of sulfur was retained in the solid products, and the effect of S/Fe atomic ratio on the sulfur distribution was tiny. However, increasing H 2 pressure was conducive to the transfer of sulfur to the gaseous products.
High oxygen content in lignite increases hydrogen consumption during hydroliquefaction, and simultaneously the produced water decreases hydrogen partial pressure, which negatively affects lignite liquefaction behaviors. Therefore, the liquefaction performances and oxygen-removal behaviors of Xilinhaote (XL) lignite during liquefaction at different temperatures in the presence of Na 2 CO 3 (NC) and FeOOH (FO) were investigated. Results showed that the oxygen contents of liquefaction residues (LRs) obtained at 330−380 °C were 9.37−13.84% without catalyst and decreased to 7.90−13.02% and 6.38−11.73% with the addition of FO and NC, respectively. The addition of NC could promote the polarized breakdown of aromatic C aryl − C alkyl ether bonds via ionic pathways in the presence of water, which facilitated the depolymerization of lignite macromolecular structures, resulting in significant increase in coal conversions at 330−380 °C. To enhance liquefaction performance, an optimized two-stage catalytic liquefaction process for lignite with high oxygen content was proposed, which integrated the deoxygenation treatment of lignite over Na 2 CO 3 and the hydrogenation of Na 2 CO 3 -treated lignite over iron catalyst. In the twostage catalytic liquefaction processes, coal conversions and oil yields significantly increased to 90.66−92.73% and 52.73− 57.56%, respectively, compared to 84.61% and 43.52% in single-stage liquefaction of XL over FO at 450 °C. Furthermore, in the two-stage catalytic liquefaction process, the treatment of XL over NC in stage I presented higher coal conversion (92.73%) and oil yield (57.56%) than those over FO in stage I (90.66% and 52.73%). Surprisingly, H 2 consumption of the former (2.17%) was lower than that of the latter (2.91%).
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