Effects of Sulfur, Nitric Acid, and Thermal Treatments on the Properties and Mercury Adsorption of Activated Carbons from Bituminous Coals

Abstract

The influences of sulfur, HNO 3 , and thermal treatments on the properties and Hg adsorption of activated carbon (AC) derived from bituminous coals were evaluated. These ACs were impregnated with either polysulfide or elemental sulfur at 120, 200, and 600°C. Additional ACs were treated with HNO 3 at 95°C to incorporate oxygen functionalities, and then subjected to temperature-programmed desorption to 950°C to remove surface oxygen groups and create nascent active sites on the AC surface. Polysulfide and elemental sulfur impregnation at < 200°C did not improve Hg 0 adsorption. However, improvement in HgCl 2 adsorption by up to 97% was observed. Elemental sulfur impregnation at 600°C enhanced Hg 0 and HgCl 2 adsorption by up to 42% and 404%, respectively, for ACs derived from a low-organic-sulfur coal. Improvements in Hg 0 adsorption for ACs from high-organic-sulfur coals were not observed after sulfur impregnation. HNO 3 and thermal treatments reduced Hg-active groups such as sulfur. Oxygen surface groups and the nascent carbon sites appeared to be more reactive towards other flue gas components than Hg, because HNO 3 and thermal treatments led to a reduction in Hg 0 and HgCl 2 adsorption. These results suggest that AC's physical and chemical properties after sulfur treatment influence Hg 0 adsorption, while HgCl 2 adsorption is mainly affected by AC's chemical characteristics.

Influences of Copper(II) Chloride Impregnation on Activated Carbon for Low-Concentration Elemental Mercury Adsorption from Simulated Coal Combustion Flue Gas

“…A similar tendency was also observed in CuCl 2 -impregnated HCACs. These experimental results support our previous observation that the impregnated agents could be doped into the porous adsorbents by means of surface coverage or pore filling, or by both mechanisms at the same time (Hsi et al, 2002(Hsi et al, , 2011(Hsi et al, , 2012(Hsi et al, , 2013.…”

“…Detailed descriptions pertaining to experimental apparatus and procedures for Hg 0 adsorption tests have been described elsewhere (Hsi et al, 2011(Hsi et al, , 2012(Hsi et al, , 2013Chiu et al, 2014;Hsi et al, 2014); nevertheless, we present them here again for clarity. The adsorption tests were carried out under two conditions: (1) Hg 0 /N 2 condition and (2) simulated coalcombustion flue gas condition containing 6 vol% O 2 , 14 vol% CO 2 , 10 vol% H 2 O, 50 ppm v HCl, 200 ppm v SO 2 , 200 ppm v NO, and balance N 2 .…”

“…These observations again support that the total surface area and total CuCl 2 amount of adsorbents could markedly influence Hg 0 adsorption but not the only determining factors on both Hg 0 adsorption equilibrium and kinetics, which was implied by the slope of the breakthrough curves and adsorption duration. Specific forms of Cu and oxygenated groups playing as catalytic and adsorption sites and pores with specific size ranges allowing rapid transport of the Hg molecules into the interior of the activated carbon and as energy sinker govern the adsorption process (Hsi et al, 2002(Hsi et al, , 2011(Hsi et al, , 2013.…”

“…The adsorptive environment, namely, flue gas condition, also plays a key role influencing the Hg 0 adsorption effectiveness of activated carbon. For the past decade, sulfur impregnation has been widely reported to considerably enhance the equilibrium Hg 0 adsorption capacity of activated carbon (Hsi et al, 2001(Hsi et al, , 2002Vitolo et al, 2002;Feng et al, 2006;Ho et al, 2008;Hsi et al, 2011Hsi et al, , 2012Hsi et al, , 2013Hsi et al, , 2014. Besides sulfur, activated carbon impregnated with metal salts has demonstrated the competitive adsorption performance to those treated with sulfur.…”

Simultaneous Control of Elemental Mercury/Sulfur Dioxide/Nitrogen Monoxide from Coal-Fired Flue Gases with Metal Oxide-Impregnated Activated Carbon

“…Activated carbon has been considered excellent adsorbent for Hg control (Granite et al, 2006;Hsi and Chen, 2012;Hsi et al, 2013). Some studies have reported the individual and simultaneous removal of Hg, SO 2 , and NO under flue gas conditions by carbon-based materials (e.g., activated carbon, activated coke, and activated carbon fibers) (Stencel and Rubel, 1995;Tsuji and Shiraishi, 1997;Mochida et al, 1999).…”