Fan Cao

Catalytic oxidation of Hg0 by MnOx–CeO2/γ-Al2O3 catalyst at low temperatures

MnOx-CeO2/γ-Al2O3 (MnCe) selective catalytic reduction (SCR) catalysts prepared by sol-gel method were employed for low-temperature Hg(0) oxidation on a fixed-bed experimental setup. BET, XRD and XPS were used to characterize the catalysts. MnCe catalysts exhibited high Hg(0) oxidation activity at low temperatures (100-250 °C) under the simulated flue gas (O2, CO2, NO, SO2, HCl, H2O and balanced with N2). Only a small decrease in mercury oxidation was observed in the presence of 1200 ppm SO2, which proved that the addition of Ce helped resist SO2 poisoning. An enhancing effect of NO was observed due to the formation of multi-activity NOx species. The presence of HCl alone had excellent Hg(0) oxidation ability, while 10 ppm HCl plus 5% O2 further increased Hg(0) oxidation efficiency to 100%. Hg(0) oxidation on the MnCe catalyst surface followed the Langmiur-Hinshelwood mechanism, where reactions took place between the adsorbed active species and adsorbed Hg(0) to form Hg(2+). NH3 competed with Hg(0) for active sites on the catalyst surface, hence inhibiting Hg(0) oxidation. This study shows the feasibility of a single-step process integrating low-temperature SCR and Hg(0) oxidation from the coal combustion flue gas.

Adsorption of Hg0 from Coal Combustion Flue Gases by Novel Iodine-Modified Bentonite/Chitosan Sorbents

Adsorption experiments of vapor-phase elemental mercury (Hg 0 ) were carried out by using modified bentonite/chitosan in a laboratory-scale fixed-bed reactor. VM3000 online mercury analyzer was applied to detect the inlet and outlet mercury concentrations. The characterizations of the sorbents were analyzed using the method of nitrogen (N 2 ) adsorption-desorption, Thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). It is observed that porosity and specific surface area decreases after modifying. The TGA analysis demonstrates these sorbents will operate stably at flue-gas temperatures below 140°C, which can meet the temperature requirement of mercury removal after the electrostatic precipitator. The XRD analysis indicates that the iodine and chitosan is found in the inlayer of bentonite, and the chemical reactions of iodine and sulfuric acid with the amide of chitosan occurr. Fixed-bed adsorber tests show that iodine-modified bentonite-chitosan sorbents exhibit better mercury capture than that of iodine-modified chitosan. For the iodine-modified chitosan-supported bentonite sorbents, mercury removal capacity could be significantly promoted when an appropriate content of H 2 SO 4 was added. The mercury capacities of modified chitosan sorbents increase with increasing temperature. The increase in mercury removal efficiency with an increase in temperature is a typical of a chemisorption mechanism.

Removal of Elemental Mercury by Novel Chemically Modified Noncarbon Sorbents

Adsorption experiments of vapor-phase elemental mercury (Hg0) were carried out by using two types of chemically modified CTS/SiO2 sorbents in a laboratory-scale fixed-bed reactor. The characterizations of the sorbents were analyzed using the methods of nitrogen (N2) adsorption/desorption, field-scanning electron microscope (FSEM), Fourier transform infra-red spectroscopy (FTIR) and X-ray diffraction (XRD). The results revealed that the surface areas of the sorbents CTS/SiO2 increased significantly after supporting. More active sites, such as S and Cl, can be easily obtained after silanization. And it was found that Cl and S were well distributed on surface as well as Si, especially in the smaller particles of the modified sorbents. Fixed-bed adsorber tests showed that mercury removal efficiency increased with the temperature, and it improved with the presence of O2. The mercury efficiency of silanized CTS-SH/SiO2 can reached more than 80% at a temperature of 120 ¿, which is about 3~4 times higher than that of the same sorbent at 80¿.