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

Adsorption is one of the most promising methods for gaseous mercury (Hg-0) 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 macrody-namics, 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 Hg-0 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 degrees C and had the average adsorption rate of 0.6 mu g 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 Hg-0 adsorption was controlled by external diffusion processes based on the kinetic analysis. The negative Delta G (-30.71 to approximately -38.93 kJ mol(-1)), positive Delta S (123.39-138.80 J (mol K)(-1)), and positive Delta H (5.65-12.86 kJ mol(-1)) inferred the spontaneous, irreversible, and endothermic progress of Hg-0 adsorption. The above key parameters have guiding significance for sorbent preparation and bed design in subsequent expanded applications.

Automated summary

This study designed a scale-up fixed-bed reaction unit with CuS-coated Al2O3 sorbent to investigate the influence of gaseous diffusion, particle size, and wall effect on Hg-0 removal. Lower gas flow rate enhanced mercury removal efficiency, and the combination of CuS/Al2O3 with a certain particle size and reaction tube maintained nearly complete mercury removal. The Hg-0 adsorption process was found to be controlled by external diffusion processes, with the parameters suggesting a spontaneous, irreversible, and endothermic progress.