Hydrogen-donating behavior and hydrogen-shuttling mechanism of liquefaction solvents under Fe- and Ni-based catalysts

• Published in: Fuel (Guildford) 2024-07, Vol.368, p.131586, Article 131586
• Main Authors: Liu, Haiyun, Zhang, Rui, Zheng, Xin, Xie, Jing, Tang, Bowen, Li, Zhi, Guo, Erguang, Hu, Haoquan, Jin, Lijun
• Format: Article
• Language: English
• Subjects: Catalyst; Coal direct liquefaction; H-donating; Hydrogen transfer; Liquefaction solvent
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2024.131586

[Display omitted] •Effect of Fe- or Ni-based catalyst on the pathway of hydrogen transfer is examined.•Fe-based catalyst minimize H-shuttle effect of solvent, while Ni catalyst enhances it.•DHA exhibits lower capacity of hydrogen donor than THN as liquefied solvent.•THN more effectively transfers gaseous H2 to radicals from coal pyrolysis than DHA. The H-donating solvent plays a crucial role in both oil yield and products distribution during direct coal liquefaction. Meanwhile, liquefaction catalyst significantly influences the H-donating behavior of the solvent and the pathways of hydrogen transfer. In view of insufficient understanding on the impact of catalysts on H-donating behavior of solvent and hydrogen transfer pathways in direct liquefaction, in this study, non-H-donating solvents including naphthalene, 1-methylnaphthalene and pyrene (Py) and H-donating solvents including tetralin (THN) and 9,10-dihydroanthracene (DHA) were chosen as the solvents. The Shenhua nano-sized Fe-based and the prepared Ni/Al2O3 catalysts were used to investigate their effect on H-donating behavior of the solvent and H-shuttling mechanism. Results show that liquefaction solvent obviously affects coal conversion and products distribution no matter Fe-based or Ni-based catalyst was used. When non-H-donating solvent is used as liquefaction solvent, coal conversion is lower than that with THN or DHA as solvent. The addition of Py to THN as solvent improves the utilization of effective hydrogen in non-catalytic liquefaction, which is ascribed to hydrogen transfer effect of Py; however, hydrogen transfer mainly occurs through direct combination of gaseous H2 with radicals generated from coal pyrolysis in presence of Fe-based catalyst, with minimal shuttle action of solvent hydrogen. On the contrary, the Ni-based catalyst aids in enhancing the hydrogen shuttle effect of the solvent, and the hydrogen transfer path primarily involves H2 to solvent and then to coal, which is ascribed to good hydrogenation ability of Ni-based catalyst. Under the action of Fe-based catalyst, DHA as liquefaction solvent exhibits lower H-donating capability compared to THN, and approximately 65% of total hydrogen consumption is effectively utilized for coal liquefaction, along with about 35% of total hydrogen consumption for the hydrogenation, ring opening, and side-chain scission reactions of DHA. However, about 96% of total hydrogen consumption is effectively utilized for coal liquefaction when THN u