Adsorption of elemental mercury vapors from synthetic exhaust combustion gas onto HGR carbon

Abstract

An activated carbon commercially available named HGR, produced by Calgon-Carbon Group, was used to adsorbe metallic mercury. The work is part of a wider research activity by the same group focused on the removal of metallic and divalent mercury from combustion flue gas. With respect to previously published papers, this one is aimed at studying in depth thermodynamic equilibria of metallic mercury adsorption onto a commercial activated carbon. The innovativeness lies in the wider operative conditions explored (temperature and mercury concentrations) and in the evaluation of kinetic and thermodynamic data for a commercially available adsorbing material. In detail, experimental runs were carried out on a laboratory-scale plant, in which Hg°vapors were supplied in a nitrogen gas stream at different temperature and mercury concentration. The gas phase was flowed through a fixed bed of adsorbent material. Adsorbate loading curves for different Hg°concentrations together with adsorption isotherms were achieved as a function of temperature (120, 150, 200°C) and Hg°concentrations (1.0−7.0 mg/m 3 ). Experimental runs demonstrated satisfying results of the adsorption process, while Langmuir parameters were evaluated with gas-solid equilibrium data. Especially, they confirmed that adsorption capacity is a favored process in case of lower temperature and they showed that the adsorption heat was -20 kJ/mol. Furthermore, a numerical integration of differential equations that model the adsorption process was proposed. Scanning electron microscopy (SEM) investigation was an useful tool to investigate about fresh and saturated carbon areas. The comparison between them allowed identification of surface sites where mercury is adsorbed; these spots correspond to carbon areas where sulfur concentration is greater.Implications: Mercury compounds can cause severe harm to human health and to the ecosystem. There are a lot of sources that emit mercury species to the atmosphere; the main ones are exhaust gases from coal combustion and municipal solid waste incineration. Furthermore, certain CO 2 capture processes, particularly oxyfuel combustion in a pulverized fuel coal-fired power station, produce a raw CO 2 product containing several contaminants, mainly water vapor, oxygen, and nitrogen but also mercury, that have to be almost completely removed; otherwise these would represent a strong drawback to the success of the process.PAPER HISTORY

Adsorptive Behavior of an Activated Carbon for Bisphenol A Removal in Single and Binary (Bisphenol A—Heavy Metal) Solutions

“…Due to these characteristics, activated carbons have been used for many different applications: as adsorbents, catalysts or catalyst supports. They have been tested as a cleaning material for removing pollutants from gaseous or liquid phases and the purification or recovery of chemicals [22,23]. Adsorption on activated carbon is one of the first water treatments to have been used [24,25] and it is recognized by the United States Environmental Protection Agency (US EPA) as one of the best methods for removing organic and inorganic compounds from water for human consumption.…”

Simultaneous removal of NO and Hg0 using Fe and Co co-doped Mn-Ce/TiO2 catalysts

“…Various kinds of chlorides such as ZnCl2 [5][6][7][8], FeCl3 [7] and NH4Cl [8] were used as predecessors to modify carbonaceous adsorbents to improve the efficiency of mercury removal. The chemisorption between carbonaceous materials and Hg 0 was enhanced after the modification of adsorbent such as sulfur treatment [9] and the addition of CeO2 [7,10] However, using sorbent to remove Hg 0 has some drawbacks [11]: 1) a large amount of sorbent is required for the adsorption of Hg 0 indicating the high cost of sorbent use; 2) the disposal challenges of the exhaust sorbents mixed with fly ash.…”

A Detailed Investigation of Adsorption Isotherms, Enthalpies, and Kinetics of Mercury Adsorption on Nonimpregnated Activated Carbon

“…Well-established large-scale processes (absorptive gas scrubbing, flue gas adsorption) are rather suited for the separation of mercury from large, continuous volume flows with uniform loading. For the separation of mercury from fluctuating waste gas streams, fixed-bed adsorption is a proper method, which has been investigated in many scientific studies. − For economic and technical reasons, particularly suitable adsorbents for Hg 0 adsorption are nonimpregnated − ,− ,, and impregnated activated carbons, ,,,− the development and investigation of which make up the largest part of the literature. − ,,,− , Most references focus on specific technical applications and compare breakthrough curves on different adsorbents in a small temperature and concentration range. Therefore, despite the large number of publications, there is no deep scientific understanding of adsorption mechanisms.…”