In situ self-activation strategy for the synthesis of double-layered S/Cl co-doped sorbents for elemental mercury immobilization from oxy-fuel combustion flue gas

Mercury capture from oxy-fuel combustion flue gas remains an enormous challenge for carbon capture and storage because of the lack of cost-effective, sulfur-resistant and water-resistant sorbent. In this work, double-layered S/Cl co-doped sorbents (CDSs) were synthesized through an in situ self-activation method i.e. co-pyrolysis of waste tire and PVC plastic, which were adopted for elemental mercury (Hg0) immobilization from oxy-fuel combustion flue gas. A synergistic effect between waste tire and PVC plastic was observed during co-pyrolysis. For this reason, chlorine was successfully doped into the CDSs in the form of covalent chlorine and ionic chlorine. The CDSs showed high Hg0 removal efficiency (>80 %) over a wide temperature range (20–140 °C) and excellent sulfur and water resistance. Both the initial Hg0 adsorption rate and adsorption capacity of CDSs were far higher compared with raw tire char. The Hg0 removal mechanisms was further proposed, where Hg0 preferentially reacted with covalent chlorine instead of active sulfur species. Density functional theory calculations revealed that the Hg0 adsorption over CDSs was chemisorption with an adsorption energy of −249.85 kJ/mol. The synergistic effect between sulfur and chlorine was beneficial for the formation of HgCl2 whereas it had negligible effect on the formation of HgCl.