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Adsorption of Gaseous Mercury for Engineering Optimization: From Macrodynamics to Adsorption Kinetics and Thermodynamics

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journal contribution
posted on 25.03.2021, 21:13 by Qinyuan Hong, Haomiao Xu, Jiaxing Li, Lu Tong, Zhenxuan Tang, Yuanxiang Xu, Wenjun Huang, Zan Qu, Naiqiang Yan
Adsorption is one of the most promising methods for gaseous mercury (Hg0) uptake from industrial flue gas, and the designing and synthesis of a sorbent are of significance for utilization. However, for a pilot-scale experiment, the macrodynamics, adsorption kinetics, and thermodynamics should be optimized before real applications. This study designed a scale-up fixed-bed reaction unit that worked with CuS-coated Al2O3 sorbent to investigate the influence of the gaseous diffusion, particle size, and wall effect on Hg0 removal performances. The results showed that the lower gas flow rate enhanced the mercury removal efficiencies. The combination of CuS/Al2O3 (1–2 mm) and a reaction tube (20 mm) mitigated the influence of size and wall effects, which maintained nearly complete mercury removal over 10 h under at 80 °C and had the average adsorption rate of 0.6 μg g–1 min–1. Moreover, CuS/Al2O3 possessed a higher SO2 resistance under a 1%–6% concentration range, guaranteeing a real application under SO2-rich industrial gas. The Hg0 adsorption was controlled by external diffusion processes based on the kinetic analysis. The negative ΔG (−30.71 to approximately −38.93 kJ mol–1), positive ΔS (123.39–138.80 J (mol K)−1), and positive ΔH (5.65–12.86 kJ mol–1) inferred the spontaneous, irreversible, and endothermic progress of Hg0 adsorption. The above key parameters have guiding significance for sorbent preparation and bed design in subsequent expanded applications.

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