In comparison to the adsorption of hydrocarbons, the adsorption of mercury on activated carbons reveals many unexpected results. Both physisorptive and chemisorptive mechanisms play a role even in the adsorption on nonimpregnated activated carbons. In this work, the adsorption of Hg0 from a N2 carrier gas stream is studied on three commercial adsorbents. Single and cumulative breakthrough curves are measured in a fixed bed at temperatures of 25–100 °C and mercury concentrations of 50–1000 μg m–3. Isosteric heats of adsorption are calculated from the measured adsorption isotherms. Here, adsorption enthalpies in the range of 50% of the vaporization enthalpy are determined. In addition, desorption experiments are conducted to distinguish the contributions of physisorption and chemisorption. A dynamic simulation of experimental breakthrough curves yields diffusion coefficients, which are discussed with respect to the concentration and temperature dependence of diffusion mechanisms in mercury physisorption.

In mercury adsorption on activated carbons both physisorptive and chemisorptive mechanisms play a role. The systematic investigation of Hg0 chemisorption is difficult because equilibrium capacities cannot be determined due to slow adsorption mechanisms. Therefore, the present publication suggests a three‐step approach: 1) Breakthrough curves are used to assess the dynamics of Hg0 adsorption. 2) The contributions of physisorption and chemisorption can be distinguished by coupled adsorption and desorption experiments. 3) Temperature programmed desorption (TPD) experiments are performed to get information about specific chemisorptive binding sites on the surface. This approach was tested on four characteristic examples of impregnated and non‐impregnated activated carbons.

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.

In technical processes, fixed-bed adsorbers with impregnated activated carbon are used for chemisorptive mercury separation. In the case of discontinuous waste gas streams with strongly varying mercury concentrations (e.g., in crematories or metal-recycling plants), mercury may quickly break through the impregnated activated carbon layer due to the slow kinetics of chemisorptive adsorption. Under these conditions a promising purification concept is a multilayer adsorber. In the first layer, strongly fluctuating mercury concentrations should first be smoothed by physical adsorption and desorption on nonimpregnated activated carbon before the mercury is completely separated in the second layer of impregnated activated carbon by chemisorption. In this paper, experimentally validated dynamic simulations are used to show that, under suitable operating conditions and design parameters, effective smoothing of fluctuating mercury concentrations is possible in the first layer of a multilayer adsorber with nonimpregnated activated carbons.

Auf der ACHEMA 2018 stellten sich 24 Firmen mit Bezug zum Themenfeld Adsorption vor. Das weit gefächerte Ausstellerfeld reichte von Adsorbentienherstellern über Messgeräteentwickler bis hin zu Anlagenbauern. Aufgrund der zeitlichen Nähe zur Fachmesse IFAT/Entsorga waren in diesem Jahr etwas weniger Aussteller vertreten als in den vorausgehenden Jahren. Der Bericht umreißt die wichtigsten Trends und Neuerungen aus der Adsorptionstechnik, die auf den Ständen präsentiert und in Gesprächen von den Ausstellern thematisiert wurden.