Influence of Oxygen on Hg⁰ Adsorption on Non-Impregnated Activated Carbons

Abstract

Both physisorptive and chemisorptive mechanisms play a role in the adsorption of mercury. The present publication investigates the influence of oxygen on the adsorption of Hg 0 by breakthrough curve measurements and temperature-programmed desorption (TPD) experiments. The presence of O 2 in the gas phase promotes chemisorption. Because of slow adsorption mechanisms, no equilibrium capacities of mercury chemisorption can be determined. For further investigations, coupled adsorption and desorption experiments with concentration swing adsorption and TPD experiments are performed. The results of TPD experiments are simulated and quantitatively evaluated by means of an extended transport model. From the number of desorption peaks, we obtain the number of different adsorption and desorption mechanisms. A detailed simulation of the peaks yields the reaction order, the frequency factor, and the activation energy of the desorption steps. The kinetic reaction parameters allow a mechanistic interpretation of the adsorption and desorption processes. Here, we suppose the formation of a complex between the carbon surface, mercury, and oxygen.

Impact of H2O on the Adsorption of Hg0 on Activated Carbon

“…Since more mercury is chemisorptively bound to the activated carbons at low temperatures, this effect seems to dominate over the deceleration of the reaction kinetics by lowering the rate constant. In contrast, Ambrosy et al 37 found faster kinetics with increasing temperature in the case of chemisorption of Hg 0 with oxygen. This can be understood by assuming that the required activation energy for the chemisorption of mercury with water is lower than for the chemisorption of mercury with oxygen.…”

“…In the energy balance of the fluid phase G, the energy exchange between the fluid and solid phases, the transport terms of convection and dispersion, the storage terms of the gas phase, and the heat transport through the adsorber wall are considered. 30,37…”

“…The energy balance of the solid phase S includes the heat released during adsorption, the heat stored in the packing, and the heat transfer between the gas phase and the solid phase. In the energy balance of the fluid phase G, the energy exchange between the fluid and solid phases, the transport terms of convection and dispersion, the storage terms of the gas phase, and the heat transport through the adsorber wall are considered. , The quantities α p and α w ,i represent the heat transfer coefficients from the fluid to the solid phase and from the gas phase to the adsorber inner wall. The parameters c p,s , c p,A , and c p,G describe the specific heat capacities of the adsorbent, the adsorptive, and the gas phase.…”

Simulative Investigation of the Application of Nonimpregnated Activated Carbon in a Multilayer Adsorber for the Separation of Hg0 from Discontinuous Waste Gas Streams

“…Literature shows that both physisorptive and chemisorptive interactions play a role in the adsorption of mercury on activated carbons. In previous publications, we have already reported in detail on the current state of literature on simulative and experimental investigations of the adsorption of Hg 0 . − …”

“…For a complete separation of elemental mercury, Hg 0 -impregnated activated carbons with high capacity are used, which bind mercury by chemisorption. − However, the kinetics of chemisorptive deposition are very slow. − As a result, a rapid breakthrough of mercury is observed, especially when cleaning discontinuous waste gas streams with pronounced concentration peaks. For such applications the concept of a multilayer adsorber might be suitable.…”