In this work, the influence of water on the adsorption of mercury is systematically investigated on basic and washed activated carbons. Breakthrough curves were measured and temperature-programmed desorption (TPD) experiments were performed with mercury and water. Both physisorptive and chemisorptive interactions are relevant in the adsorption of mercury. The experiments show that the presence of water in the pores promotes chemisorption of mercury on washed activated carbons while there is little influence on chemisorption on basic materials. Washing exposes or forms oxygen functional groups that are chemisorptive sites for mercury. Obviously, effective chemisorption of mercury requires both the presence of water and of oxygen functional groups. As mercury chemisorption is preceded by a physisorptive step, higher physisorptive mercury loading at lower temperature (30 °C) enhances chemisorption though the reaction rate constant is smaller than at higher temperature (100 °C). Sequential adsorption and partial desorption of water at lower temperature changes the surface chemistry without inhibiting mercury physisorption. Here, the highest chemisorption rates were found. The number of desorption peaks in the TPD experiments corresponds to the number of adsorption and desorption mechanisms with different oxygen functional groups in the presence of water. The results of the TPD experiments were simulated using a transport model extended by an approach for chemisorption. The simulation results provide reaction parameters (activation energy, frequency factor, and reaction order) of each mechanism. As in many heterogeneously catalyzed reactions, the activation energy and the frequency factor are independent of mercury loading and increase with increasing temperature.

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.

The adsorption of elemental mercury (Hg 0 ) on activated carbons modified with 0.2, 0.6, and 1 M HCl is systematically examined. Breakthrough curves are measured, and coupled adsorption and desorption experiments with temperature-programmed desorption (TPD) are performed. The experiments show that impregnation with HCl produces surface-bound chlorine, which significantly increases the capacity of activated carbons for mercury. Physisorptive interactions between elemental mercury and the activated carbon surface dominate on the basic materials. In contrast, on HCl-modified activated carbons, chemisorptive interactions of Hg 0 with surface-bound chlorine lead to a complex involving carbon, chlorine, and mercury. Using TPD, two mechanisms could be identified that yield reaction products with different energetic values. By continuously recording Hg 0 and Hg total concentrations, the formation of Hg 0 and Hg x Cl 2 during desorption of the complexes from the surface could be studied. It is shown that Hg x Cl 2 found in TPD is not present as a solid salt in the pores but is formed by thermal degradation of the mercury chlorine complex on the carbon surface. The mass fraction of Hg measured in TPD which is bound in Hg x Cl 2 depends on the Hg loading of the activated carbons, with a maximum mass fraction of 27%. We propose that an important step in the chemisorptive reaction with increasing mercury loading is the conversion of a HgCl 2 complex into a Hg 2 Cl 2 complex.

Nach einer la ¨ngeren pandemiebedingten Pause fand 2022 in Frankfurt wieder die ACHEMA statt, auf der sich auch zahlreiche Firmen aus dem Bereich Adsorption pra ¨sentierten. Das weit gefa ¨cherte Ausstellerfeld reichte von Adsorbentienherstellern u ¨ber Messgera ¨teentwickler bis hin zu Anlagenbauern. Der Bericht umfasst Trends und Neuerungen aus der Adsorptionstechnik, die auf den Sta ¨nden pra ¨sentiert und in Gespra ¨chen mit den Ausstellern thematisiert wurden.

No abstract