Selective uptake of gaseous sulfur trioxide and mercury in ZnO-CuS composite at elevated temperatures from SO2-rich flue gas

Abstract

Gaseous SO3 and mercury in the SO2-rich gas have aroused the complexity of multi-pollutants formation and are difficult for disposal. We here proposed a dry-flue gas purification method to capture these two pollutants above the SO3 boiling points (>180 °C), cutting off the downstream transformation. The selective uptake of SO3 and Hg0 at a high temperature from SO2-rich conditions is a challenge. The alkaline sorbent and chalcogen-based active sites were assembled to realize the induce-adsorption for SO3 and Hg0, respectively. The results indicated that the ZnO-CuS composite showed the feasibility for SO3 and Hg0 capture at elevated reaction temperatures. The composite with a molar ratio of 4:3 exhibited the highest performances for both Hg0 and SO3 uptake. ZnO has an excellent SO3 selectivity in SO3/SO2 atmosphere with a high SO3 adsorption energy of −466.5 kJ/mol. CuS was the leading active site for Hg0 adsorption using the surface Sn2− ions in Hg0/SO3/SO2 simulated flue gas. Moreover, the surface sulfation process inevitably happened, but the presence of Hg0 inhibited the reaction of SO3 with S2−, part of Hg0 adsorbed to generate HgS and HgSO4. The induced adsorption surface drove gaseous mercury to enter the inner of the material, widening the temperature window for efficient capture for gaseous mercury and enhancing adsorption stability. Moreover, a pilot-scale experiment using CuS and ZnO materials indicated that higher SO3 and total gaseous mercury removal efficiencies were obtained with the help of dust removal devices.