Jianping Yang

Regenerable Cobalt Oxide Loaded Magnetosphere Catalyst from Fly Ash for Mercury Removal in Coal Combustion Flue Gas

To remove Hg(0) in coal combustion flue gas and eliminate secondary mercury pollution of the spent catalyst, a new regenerable magnetic catalyst based on cobalt oxide loaded magnetospheres from fly ash (Co-MF) was developed. The catalyst, with an optimal loading of 5.8% cobalt species, attained approximately 95% Hg(0) removal efficiency at 150 °C under simulated flue gas atmosphere. O2 could enhance the Hg(0) removal activity of magnetospheres catalyst via the Mars-Maessen mechanism. SO2 displayed an inhibitive effect on Hg(0) removal capacity. NO with lower concentration could promote the Hg(0) removal efficiency. However, when increasing the NO concentration to 300 ppm, a slightly inhibitive effect of NO was observed. In the presence of 10 ppm of HCl, greater than 95.5% Hg(0) removal efficiency was attained, which was attributed to the formation of active chlorine species on the surface. H2O presented a seriously inhibitive effect on Hg(0) removal efficiency. Repeated oxidation-regeneration cycles demonstrated that the spent Co-MF catalyst could be regenerated effectively via thermally treated at 400 °C for 2 h.

Mercury Adsorption and Oxidation over Cobalt Oxide Loaded Magnetospheres Catalyst from Fly Ash in Oxyfuel Combustion Flue Gas.

Cobalt oxide loaded magnetospheres catalyst from fly ash (Co-MF catalyst) showed good mercury removal capacity and recyclability under air combustion flue gas in our previous study. In this work, the Hg(0) removal behaviors as well as the involved reactions mechanism were investigated in oxyfuel combustion conditions. Further, the recyclability of Co-MF catalyst in oxyfuel combustion atmosphere was also evaluated. The results showed that the Hg(0) removal efficiency in oxyfuel combustion conditions was relative high compared to that in air combustion conditions. The presence of enriched CO2 (70%) in oxyfuel combustion atmosphere assisted the mercury oxidation due to the oxidation of function group of C-O formed from CO2. Under both atmospheres, the mercury removal efficiency decreased with the addition of SO2, NO, and H2O. However, the enriched CO2 in oxyfuel combustion atmosphere could somewhat weaken the inhibition of SO2, NO, and H2O. The multiple capture-regeneration cycles demonstrated that the Co-MF catalyst also present good regeneration performance in oxyfuel combustion atmosphere.

Multiform Sulfur Adsorption Centers and Copper-Terminated Active Sites of Nano-CuS for Efficient Elemental Mercury Capture from Coal Combustion Flue Gas

Nanostructured copper sulfide synthesized with the assistance of surfactant with nanoscale particle size and high Brunauer-Emmett-Teller surface area was for the first time applied for the capture of elemental mercury (Hg0) from coal combustion flue gas. The optimal operation temperature of nano-CuS for Hg0 adsorption is 75 °C, which indicates that injection of the sorbent between the wet flue gas desulfurization and the wet electrostatic precipitator systems is feasible. This assures that the sorbent is free of the adverse influence of nitrogen oxides. Oxygen (O2) and sulfur dioxide exerted a slight influence on Hg0 adsorption over the nano-CuS. Water vapor was shown to moderately suppress Hg0 capture efficiency via competitive adsorption. The simulated adsorption capacities of nano-CuS for Hg0 under pure nitrogen (N2), N2 + 4% O2, and simulated flue gas reached 122.40, 112.06, and 89.43 mgHg0/g nano-CuS, respectively. Compared to those of traditional commercial activated carbons and metal sulfides, the simulated adsorption capacities of Hg0 over the nano-CuS are at least an order of magnitude higher. Moreover, with only 5 mg loaded in a fixed-bed reactor, the Hg0 adsorption rate reached 11.93-13.56 μg/g min over nano-CuS. This extremely speedy rate makes nano-CuS promising for a future sorbent injection technique. The anisotropic growth of nano-CuS was confirmed by X-ray diffraction analysis and provided a fundamental aspect for nano-CuS surface reconstruction and polysulfide formation. Further X-ray photoelectron spectroscopy and Hg0 temperature-programmed desorption tests showed that the active polysulfide, S-S dimers, and copper-terminated sites contributed primarily to the extremely high Hg0 adsorption capacity and rate. With these advantages, nano-CuS appears to be a highly promising alternative to traditional sorbents for Hg0 capture from coal combustion flue gas.

Stability of mercury on a novel mineral sulfide sorbent used for efficient mercury removal from coal combustion flue gas

AbstractNano-structured zinc sulfide (Nano-ZnS) has been demonstrated to be a promising alternative to activated carbon (AC) for controlling mercury emission from coal combustion flue gas. The ultimate fate of the mercury-laden Nano-ZnS after mercury capture is mostly disposed in landfill with fly ashes. Thus, the stability of mercury adsorbed on the Nano-ZnS is of considerable significance in the secured disposal of fly ash after mercury removal and in the commercial application of the Nano-ZnS sorbent for removal of mercury from coal combustion flue gas. In this work, a modified toxicity characteristic leaching procedure (TCLP) was conducted to evaluate the leachability of mercury on the Nano-ZnS. The effects of leachate pH value, leaching time, liquid-to-solid ratio, and acid rain types on mercury leaching from the mercury-laden Nano-ZnS were systematically investigated. The TCLP results show that the concentration of mercury in leachate was far below the safe limit (200xa0μg/L) as imposed by the US Environmental Protection Agency (EPA) for classifying a material as a hazardous waste. All the key parameters that generally affected metal leaching rate exhibited slight effect on mercury leaching from the mercury-laden Nano-ZnS. Leaching tests at various highly severe conditions resulted in less than 0.01% mercury leaching from the mercury-laden Nano-ZnS. Sequential selective extraction tests demonstrated that mercury sulfide (HgS) was the dominant adsorption product on the Nano-ZnS, which guaranteed the excellent stability of mercury adsorbed on the Nano-ZnS.n Graphic abstractᅟ

Dual Roles of Nano-Sulfide in Efficient Removal of Elemental Mercury from Coal Combustion Flue Gas within a Wide Temperature Range

Nanostructured zinc sulfide (Nano-ZnS) has been demonstrated to be an efficient adsorbent for removal of elemental mercury (Hg0). However, the Hg0 removal performance deteriorates once the flue gas temperature deviates from the optimal temperature of 180 °C. In this study, ultraviolet (UV) light, which is generally generated through corona discharge in electrostatic precipitators (ESPs), was adopted to enhance Hg0 removal by Nano-ZnS. With the UV irradiation, Nano-ZnS exhibited excellent performance in Hg0 removal within a much wide temperature range from room temperature to 240 °C. A Hg0 removal efficiency of 99% was achieved at 60 °C even under extremely adverse conditions, that is, gas flow with an extremely high gas hourly space velocity but without hydrogen chloride. At low temperatures, Hg0 was mainly oxidized by superoxide radicals (•O2-) and hydroxyl radicals (•OH) generated by UV photostimulation to form mercuric oxide (HgO). At high temperatures, most Hg0 was immobilized as mercuric sulfide (HgS), as both the enhanced chemisorption and the accelerated transformation of HgO to HgS facilitated the formation of HgS. Compared with commercial activated carbon, injection of Nano-ZnS can utilize the UV in ESPs to warrant a higher Hg0 removal efficiency within a much wider temperature range.