Simultaneous Adsorption of Gaseous Hg⁰ and Hg(II) by Regenerable Monolithic FeMoS_x/TiO₂: Mechanism and its Application in the Centralized Control of Hg Pollution in Coal-Fired Flue Gas

Abstract

FeMoS x /TiO2 was investigated as a regenerable sorbent to simultaneously adsorb Hg0 and Hg­(II) from coal-fired flue gas for the centralized control of Hg pollution discharged from coal-fired power plants. The performance of FeMoS x /TiO2 for Hg­(II) and/or Hg0 adsorption was evaluated on a fixed-bed reactor at 80 oC, and the mutual interference between Hg0 adsorption and Hg­(II) adsorption was analyzed using individual adsorption, simultaneous adsorption, and two-stage adsorption. FeMoS x /TiO2 displayed an excellent capacity for individual Hg0 adsorption (41.8 mg g–1) and a moderate capacity for individual Hg­(II) adsorption (0.48 mg g–1). Two types of adsorption sites were present on FeMoS x /TiO2 for gaseous Hg adsorption (S0 and FeS2/MoS3 sites). X-ray photoelectron spectroscope and kinetic analyses demonstrated that Hg0 and Hg­(II) could adsorb onto S0 sites, whereas only Hg0 was adsorbed onto FeS2/MoS3 sites. As Hg0 competed with Hg­(II) for the S0 sites, the amount of Hg­(II) adsorbed slightly decreased by 16% in the presence of Hg0. However, Hg0 adsorption onto the FeS2/MoS3 sites predominated over the Hg0 adsorption onto FeMoS x /TiO2 and it was not inhibited in the presence of Hg­(II). Therefore, the amount of Hg0 adsorbed on FeMoS x /TiO2 was only decreased by 2% in the presence of Hg­(II).

Hg0 Conversion over Sulfureted HPMo/γ-Fe2O3 with HCl at Low Temperatures: Mechanism, Kinetics, and Application in Hg0 Removal from Coal-Fired Flue Gas

“…The kinetics of HgCl 2 adsorption onto sulfureted HPMo/γ-Fe 2 O 3 is deduced in the SI, and it was demonstrated that HgCl 2 was mainly adsorbed on the S 0 adsorption sites. Therefore, the kinetics for HgCl 2 adsorption was approximately described as prefix− normald [ Hg ( g ) 2 + ] normald t = k 2 θ 3 [ S 2 − ] [ φ 1 ] exp ( − k 2 false[ normalS 2 − false] θ 3 t ) = A 2 0.25em exp ( − B 2 t ) A 2 = k 2 θ 3 [ S 2 − ] [ φ 1 ] B 2 = k 2 [ ...…”

“…This suggests that S 2 2– in FeS 2 /MoS 3 may act as an oxidant for Hg 0 oxidation . Therefore, the chemical adsorption of Hg 0 onto sulfureted HPMo/γ-Fe 2 O 3 was approximately expressed as follows ,, Hg false( normalg false) 0 → Hg false( ad false) 0 Hg false( ad false) 0 + normalS 2 2 − → normalS 2 − + HgS …”

“…As Hg 0 was only partially oxidized to HgCl 2 over the FeS 2 /MoS 3 adsorption sites, the Hg 2+ concentration was much lower than 110 μg m –3 . As θ 3 was related to the gaseous HgCl 2 concentration, θ 3 for Hg 0 conversion with HCl was much less than that for 110 μg m –3 of Hg 2+ adsorption. Meanwhile, [φ 1 ] decreased significantly in the presence of HCl.…”

“…The MHSV was generally 3,000,000 cm 3 g –1 h –1 , with a catalyst mass of 10 mg and a total flow rate of 500 mL min –1 . Gaseous Hg 0 was generated using an Hg 0 permeation tube (Green Calm Instruments, Suzhou, China), and gaseous HgCl 2 was obtained by the oxidation of gaseous Hg 0 over CuO/TiO 2 with HCl. , The concentrations of gaseous Hg 0 and Hg t were monitored online using an atomic absorption spectrophotometer (Lumex R-915+) once per second without and with a SnCl 2 solution, respectively. ,, …”

“…Meanwhile, Cl* radicals cannot react with hydrocarbons to form organic chlorinated compounds in the temperature range of 80–100 °C. Furthermore, the abrasion of catalysts is remarkably retarded as most particulate matter has been removed by upstream ESPs . However, most metal oxide SCR catalysts, such as V 2 O 5 -MoO 3 /TiO 2 , V 2 O 5 -WO 3 /TiO 2 , and phosphotungstic acid-grafted γ-Fe 2 O 3 (HPW/γ-Fe 2 O 3 ), exhibit poor Hg 0 oxidation ability at 80–100 °C, and H 2 O and SO 2 still exhibit strong inhibition of Hg 0 oxidation. ,, To improve Hg 0 oxidation ability and the resistance to H 2 O and SO 2 , V 2 O 5 -MoO 3 /TiO 2 and HPW/γ-Fe 2 O 3 were sulfureted with H 2 S. , Both sulfureted V 2 O 5 -MoO 3 /TiO 2 and sulfureted HPW/γ-Fe 2 O 3 exhibited excellent performance for Hg 0 conversion and moderate resistance to H 2 O and SO 2 .…”