Mercury removal mechanism of mechanochemical sulfur modified straw coke: Density functional theory calculation and kinetic fitting

Abstract

Mechanochemical sulfur modified straw coke (S-SC) has broad application prospects for flue gas mercury removal due to its high mercury removal efficiency, low cost, and stable mercury removal products. The density functional theory calculation and kinetic fitting were combined to explore the mercury removal mechanism about the influence of the oxygen-containing functional groups and variable sulfur forms on Hg0 removal by S-SC in the atmosphere with or without SO2 based on the previous experimental study. The results show that oxygen-containing functional groups promote Hg0 adsorption by the naked raw straw coke (NSC), which follows C = O > COOH > C-O. Elemental sulfur (S4) benefits Hg0 adsorption on NSC significantly with Hg0 adsorption energy of −237.5 kJ/mol in the stable form of HgS. C = O will weaken the promoting effect of S4 on Hg0 adsorption but can effectively reduce SO2 and Hg0 adsorption competition. For 21 %-ES-SC, Hg0 adsorption on active sites (mainly chemical adsorption) is the primary control step, and external mass transfer plays an important role. This work deeply elucidates the mercury removal mechanism by S-SC and gives a studying strategy of a combination of micro and macro analysis. It can provide guidance for the development of high-performance flue-gas mercury removal adsorbents.