Experimental study on the mechanism of mercury removal with Fe2O3 in the presence of halogens: Role of HCl and HBr

• The Hg0 removal efficiency differed largely on Fe2O3 with HCl at different temperatures.
• The Hg0 removal mechanism was divided into three stages based on the reaction temperature.
• We conducted an experimental comparison of HCl and HBr in capturing Hg0.

Experiments were conducted in a bench-scale fixed bed reactor with α-Fe2O3 and γ-Fe2O3 samples to investigate the mechanism of Hg0 oxidation in the presence of HCl at 80–680 °C respectively. HCl is one of the main impurities in coal-derived fuel gas and its contribution to Hg0 removal is complex and necessary to research. The experimental results showed that the Hg0 removal mechanism with HCl could probably be divided into three stages based on the reaction temperature. At low temperature, the Eley–Rideal mechanism with HCl pre-adsorption was the most probable Hg0 oxidation pathway. As the temperature increased more than 280 °C, Hg0 removal efficiency differs significantly on α-Fe2O3 and γ-Fe2O3, and the most suitable mechanism was Langmuir–Hinshelwood. With the increasing temperature to 680 °C, the homogeneous reaction between HCl and Hg0 as well as Langmuir–Hinshelwood are responsible for the transformation of Hg0. We also discovered that the reaction time played a significant impact on the Hg0 removal at low temperature, and caused the secondary mercury removal efficiency owing to the probable product of FeCl3. Additionally, HBr was adopted to compare with HCl, which obviously enhanced the Hg0 oxidation on α-Fe2O3.

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