Preparation and characterization of high efficiency modified activated carbon for the capture of mercury from flue gas in coal-fired power plants

On a global scale, coal-fired power plants supply approximately 25 percent of current energy needs. Mercury, a highly toxic metal, is commonly found as a ubiquitous trace element in coal. Flue gases produced from the combustion of coal contain both mercury and mercury ions. Currently, halogenated activated carbon (e.g. DARCO Hg-LH@) is considered to be the most effective commercially available mercury sorbent. We report the preparation and characteristics of an activated-carbon-based, polyethyleneimine-modified material, which was subsequently cross-linked using elemental sulfur and diethyldithiocarbamate as an accelerator. The synthesized material exhibits a three-fold increase in the removal of elemental mercury compared to DARCO Hg-LH. In contrast to activated carbon, which adsorbs mercury, the material developed in our laboratory reacts with mercury to form metacinnabar (HgS), which can be safely processed or disposed of. Moreover, the prepared material can adsorb up to 99 percent of ionic Mercury (II) species in solution, compared to 78 percent absorption of Mercury (II) by DARCO Hg-LH. These comparative bench-scale results were obtained under identical experimental conditions. In addition, we report data obtained from a simulated bench-scale pilot plant study, supporting the superior performance of the polymer modified material.

► Polyethylene imines and Darco-Hg-LH@ were cross linked with sulfur to prepare MAC.
► MAC chemisorbs elemental mercury to produce harmless, water-insoluble metacinnabar.
► Darco-Hg-LH@ removed Hg0 by converting it to toxic water-soluble Hg+2. MAC can be used in conventional ACI process.
► Elemental mercury captured by MAC is 3X more than adsorbed Hg0 on Darco-Hg-LH@.
► Both sulfur and nitrogen atoms of MAC chelate Hg+2, Darco-Hg-LH@, adsorbs Hg+2.