Effects of CO and CO2 on the Removal of Elemental Mercury over Carbonaceous Surfaces

Coal gasification is a popular method for the optimization of coal utilization and the reduction of environmental pollutant emissions. However, the reductive atmosphere of its products is disadvantageous for removing elemental mercury (Hg 0 ). Activated cokes (AC) was employed in this work for mercury capture in a reducing atmosphere. The high-temperature heating decreases the mercury-removal capability of carbon sorbents because the carbonaceous surface is becoming oxygen-depleted and micropore-decreased after the heating treatment. The mechanism of mercury adsorption in pure nitrogen follows the Mars-Maessen mechanism over the carbon sorbents. To identify the effects of carbon monoxide (CO) and carbon dioxide (CO 2 ) on Hg 0 removal, the Hg 0 -adsorption and thermal desorption experiments were carried in a fixed-bed reaction system. CO inhibits both the chemisorption and physisorption of Hg 0 . CO 2 competes for the active sites, lactone groups and hydroxyl groups, and occupies the micropores, which is beneficial to adsorb Hg 0 physically. When CO and CO 2 coexisted, the removal efficiencies show steadier than those in monocomponent gas (only CO or CO 2 ). CO 2 can resist the negative effect of CO on Hg 0 removal, to some extent, because CO 2 can inhibit the oxidation and disproportionation of CO. This experimental study provides practical guidance for the development of mercury-removal technology with carbon materials in the coal gasification plant.