Mercury Adsorption Characteristics as Dependent upon the Physical Properties of Activated Carbon

Abstract

Activated carbon is a widely used sorbent for the removal of mercury from coal combustion flue gas. Many studies have been conducted to understand the physical properties of activated carbon and the flue gas conditions that are important for increasing its mercury adsorption capability. The Brunauer–Emmett–Teller (BET) surface area and pore volume of activated carbon and the injection of acidic gases have been reported to influence the performance of activated carbon in mercury adsorption. However, the mercury adsorption mechanism of activated carbon is not understood in terms of the physical properties of activated carbon and the composition of the flue gas. Therefore, two representative raw materials of activated carbon, wood and coal, were used in this study. Activated carbon samples with varying physical properties were prepared by applying different carbonization and activation conditions. The prepared activated carbons were tested for mercury adsorption in three different simulated gas compositions: (1) a baseline gas condition and (2) two simulated flue gas conditions. The mercury adsorption efficiency was shown to linearly increase with the BET surface area of activated carbon in the baseline gas condition. The coal activated carbon showed a higher mercury adsorption efficiency than the pinewood activated carbon. In the simulated flue gas conditions, the mercury adsorption efficiency rapidly increased and then very slightly increased with each physical property of activated carbon.

Adsorption of mercury by activated carbon prepared from dried sewage sludge in simulated flue gas

“…Activated carbon was prepared from dried sewage sludge using a rotary kiln reactor with a length of 25 cm and a diameter of 12.5 cm. A detailed description of the rotary kiln reactor can be found in our previous publication (Min, Ahmad, and Lee 2017). The temperature of the rotary kiln reactor increased to a temperature of 400°C at a rate of 10°C/min and was maintained for 1 hr in an N 2 environment for carbonization.…”

“…Sulfur trioxide has also been found to significantly inhibit the removal of mercury by activated carbons Presto, Granite, and Karash 2007). In our previous study, activated carbons were tested for their mercury adsorption efficiency under three simulated flue gas conditions (Min, Ahmad, and Lee 2017). With injection of SO 2 and NO into the baseline gas, mercury adsorption efficiency of activated carbon significantly increased.…”

“…Coal is the raw material used in many commercial activated carbons. Activated carbon made from lignocellulosic biomass, such as pinewood, has a large pore volume, owing to its highly volatile components (Marsh and Rodriguez-Reinoso 2006;Min, Ahmad, and Lee 2017). Several studies have shown that the Brunauer-Emmett-Teller (BET) surface area and mesopore and micropore volumes of activated carbon influence its mercury adsorption efficiency (Hsi et al 1998;Serre and Silcox 2000;Skodras et al 2007;Yan et al 2004).…”

“…Several studies have shown that the Brunauer-Emmett-Teller (BET) surface area and mesopore and micropore volumes of activated carbon influence its mercury adsorption efficiency (Hsi et al 1998;Serre and Silcox 2000;Skodras et al 2007;Yan et al 2004). Our previous study showed that the mercury adsorption efficiency increased as the BET surface area and micropore volume of activated carbon increased, whereas the mesopore volume of activated carbon had low correlation to mercury adsorption in the baseline gas condition, including carbon dioxide (CO 2 ), O 2 , water vapor (H 2 O), and Hg° (Min, Ahmad, and Lee 2017). The mesopore volume also increased the mercury adsorption efficiency of activated carbon in the simulated flue gas with SO 2 and NO in addition to the baseline gas condition.…”

“…The objective of this study was to test activated carbon prepared from dried sewage sludge for its mercury adsorption capacity. Our previous study results showed that the effects of physical properties of pinewood and coal activated carbons are critical in determining their mercury adsorption capacity in simulated flue gas without HCl but decrease in the presence of HCl (Min, Ahmad, and Lee 2017). This study was designed to investigate the effect of the physical property such as BET surface area of activated carbon prepared from sewage sludge, which has much lower BET surface than pinewood and coal activated carbons, on its mercury adsorption efficiency using simulated flue gas without and with HCl.…”