Influence of Different Sulfur Forms on Gas-Phase Mercury Removal by SO₂-Impregnated Porous Carbons

Abstract

Due to widespread global mercury pollution via anthropogenic activities such as coal combustion and its severe toxicity even at low concentrations, it is necessary to remove mercury from power plant flue gas to protect both humans and the ecosystem. Currently, significant efforts are being made to maximize Hg 0 adsorption rates while minimizing the impact on the cost of electricity. The purpose of this study is to explore the influence of different sulfur forms on vapor Hg 0 removal by SO 2 -impregnated porous carbons. After SO 2 impregnation, reductive heat treatment in N 2 and H 2 O 2 oxidation process was used to diverge the sulfur form composition in porous carbons. The ultimate and X-ray photoelectron spectroscopy analysis were used to verify the sulfur species. The pore structures of sorbents were determined by nitrogen adsorption/desorption measurements. Then, their mercury removal performance was investigated in a fixed-bed reactor and the influence of different sulfur forms on equilibrium mercury adsorption capacity and mercury desorption was studied. Finally, the kinetics of mercury adsorption on SO 2 -impregnated sorbents was explored to identify whether the adsorption process is controlled by chemical adsorption. The results showed that apparent increases in the quantities of reduced sulfur species were observed after heat treatment, which is assumed to be beneficial for mercury adsorption. H 2 O 2 oxidation after SO 2 impregnation has caused a loss of reduced and nonoxidized sulfur forms in porous carbons, as well as an increase in insoluble oxidized sulfur species. One interesting finding is that even though the micropore volumes of porous carbons decreased after heat treatment, the Hg 0 adsorption capacities of reduced samples and the thermal stability of adsorbed mercury were both positively raised. After H 2 O 2 treatment, the oxidized SO 2 impregnated samples showed an obvious decrease in Hg 0 adsorption capacity. Compared with nonoxidized and oxidized sulfur forms, the reduced sulfur forms have shown a rather significant correlation with the mercury adsorption performance of SO 2 -impregnated samples. Kinetic analysis illustrates that mercury adsorption on SO 2 -impregnated porous carbons was mainly controlled by chemical adsorption.

The Effects of Physical-Chemical Evolution of High-Sulfur Petroleum Coke on Hg0 Removal from Coal-Fired Flue Gas and Exploration of Its Micro-Scale Mechanism

“…In addition, the partial additive of FeS was oxidized as Fe 2 (SO 4 ) 3 . As shown in Table 2 , combined with the mercury removal performance, both activated HSPCs modified by S and FeS had a good agreement with the previous conclusion of affinity with mercury that compared with sulfide and sulfate, elemental sulfur, sulfoxide, and sulfone have more positive effects on mercury removal [ 32 ]. In addition, Reddy et al [ 58 ] pointed out that CuS-doped carbon had a higher Hg 0 removal performance of 23 mg/g compared to that of FeS-doped carbon, which was attributed to better dispersion of active phase (CuS), lower diffusional resistance for mercury, and also activity of active phase.…”

“…Considering the mercury adsorption reactivity rank that PC–NS > PC–S > PC–SC, the TPD result suggested that various sulfur species played different thermal stability when that affected Hg 0 adsorption capacity. In addition, She et al [ 32 ] found that compared with nonoxidized and oxidized sulfur forms, the reduced sulfur forms showed a rather significant correlation with the mercury adsorption performance of SO 2 -impregnated samples. Furthermore, Reddy et al [ 57 ] reported that sulfonated carbons are a potential candidate for Hg 0 removal due to their –SO 3 H groups.…”

“…Nonetheless, the actual ideal pore structure of petroleum coke has been a rare quantitative study for element mercury removal, including the parameters of particle size, specific surface area, and pore diameter as well as its shape. Due to the lack of sulfur which is in the favor of mercury, extra additives, such as SO 2 [ 32 ] and NH 4 Br [ 33 ], for activation are needed to improve Hg 0 removal performance. In comparison, HSPC has an outlook of few additives for activation due to sulfur-containing itself.…”

Evaluation of Modified Activated Carbons for Mercury Reemission Control During Neutralization of a Simulated Wastewater from the Direct Contact Cooler of a Pressurized Oxy-Combustion Process

“…The observed reduction in mercury reemission was likely due to the capture of oxidized or elemental mercury by sulfur. The enhanced affinity of sulfur-impregnated sorbents for the removal of both elemental and ionic mercury from the gas or liquid phase is well known. − …”

Impact of Nonoxidized Sulfur Species on Elemental Mercury Removal by SO2 Activated Petroleum Cokes

“…Although some research has been carried out on preparing activated petroleum coke for mercury adsorption through SO 2 impregnation, more work is needed to fully understand the influence of different inserted sulfur forms on Hg 0 adsorption characteristics. A previous study of our group has reported that the nonoxidized sulfur is much more effective for Hg 0 uptake than oxidized sulfur . Then, the objective of this study is to identify the impact of reduced sulfur, sulfide sulfur, and elemental sulfur formed during SO 2 activation on Hg 0 adsorption.…”