A review on adsorbent/catalyst application for mercury removal in flue gas: Effect of sulphur oxides (SO2, SO3)

Abstract

Mercury is harmful to the human body and to the ecological environment. Mercury emission from coal-fired power plants is one of the main sources of anthropogenic mercury emissions. Adsorbents and catalysts are popular materials developed to capture mercury from flue gas. Sulphur oxides (SO2, SO3) are the main components of flue gas; their concentration is more than 3 orders of magnitude higher than that of mercury. Sulphur oxides have a significant effect on mercury adsorption and catalytic processes. However, the effect mechanisms of sulphur oxides on mercury removal by adsorbents/catalysts are not uniform. In this review, the effects of SO2 and SO3 on the mercury removal process by adsorbents/catalysts are provided separately, and the suggested influence mechanisms are also summarized. SO2 has a two-sided effect on the performance of mercury removal by adsorbents and catalysts. Oxidation and activated adjacent sites are considered to be the main reasons for the promotion effect of SO2. Competitive adsorption, active consumption and sulphate deposition are the main reasons for inhibition of mercury removal by SO2. O2, H2O, SO2 concentration and temperature have an impact on the effect of SO2 on mercury removal. SO3 can enhance the mercury removal efficiency of metal oxides-containing materials by increasing mercury oxidation rate. This review aims to promote a basic understanding of the effect of sulphur oxides on the mercury removal process and outline the future research direction of sorbents/catalysts for mercury removal, thereby advancing the research, development and application of materials with high sulphur resistance ability and removal efficiency.