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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 Na2CO3(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 Caryl–Calkylether 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 Na2CO3and the hydrogenation of Na2CO3-treated lignite over iron catalyst. In the two-stage 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, H2consumption of the former (2.17%) was lower than that of the latter (2.91%).

In this paper, the influence of Na2CO3 (NC) on the hydroliquefaction performances of Hongliulin (HLL) coal with a Fe-based catalyst, γ-FeOOH (FC), under mild conditions were investigated, and the properties of the resulting preasphaltene (PA) and asphaltene (AS) were examined. Results show that the addition of NC to FC-catalyzed liquefaction significantly promoting coal conversion and oil production and reducing water production under mild conditions, especially at high initial H2 pressure. The H2 consumption of mild liquefaction (0.53～1.93%) are much smaller than that of the traditional liquefaction processes, and the addition of NC to FC can enhance H2 consumption, especially the runs with weak hydrogen donor solvents. The addition order of NC and FC is an important factor which can effect the activity of FC and NC binary catalysts. There exists a prominent synergistic effect between NC and FC in HLL coal hydroliquefaction, and the synergistic effect could be ascribed to the combined promotion actions of NC for the hydrolyzation of abundant oxygen-containing moieties (such as ether bonds and carbonyl groups) in HLL coal and the depolymerization of macromolecular structures of HLL coal.