KCl Supported by γ-Al2O3 for Selective Adsorption of Gaseous Oxidized Mercury: Flue Gas Influence and Application

Abstract

The KCl supported by γ-Al₂O₃ for selective adsorption of gaseous HgCl₂ has demonstrated high selectivity and adsorption capacity, which is crucial for mercury speciation partitioning from flue gas. However, its influence and stability in complex flue gas remains uncertain. Therefore, this paper explores the impact of common flue gas components (HCl, SO₂, H₂O, CO₂, NO, O₂) on the adsorption process and elucidates the underlying mechanisms from experiment and DFT view. The experimental results demonstrate that the HgCl₂ breakthrough rate increases significantly from 2.119% to 17.921% as the concentration of HCl rises from 0 to 200 ppm. Comparatively, the HgCl₂ breakthrough rate affected by SO₂ and H₂O is less than 8%, weakly reducing the adsorption efficiency of HgCl₂, and that by CO₂, NO, and O₂ is less than 5%, showing negligible effects on the HgCl₂ adsorption efficiency. The DFT indicates that HCl competes with HgCl₂ at the Top-Cl site in KCl, thereby reducing the adsorption efficiency of HgCl₂, with the adsorption energy decreasing from −87.11 to −43.39 kJ/mol. In contrast, SO₂ and H₂O exhibit relatively weak interactions with Top-Cl site of KCl, which exerts little influence on HgCl₂ adsorption. The 100-h running in low-concentration simulated flue gas test in laboratory and on-site test in coal-fired flue gas demonstrate that the KCl/γ-Al₂O₃ achieves a very low HgCl₂ breakthrough rate of less than 10%, highlighting its superior interference immunity for the complex flue gas components and strong suitability and stability for industrial applications. This study provides solid evidence to support the industrial application of KCl/γ-Al₂O₃ for highly selective adsorption of gaseous HgCl₂ in coal-fired power plant.