Methyl mercaptan adsorption/oxidation on activated carbons

Activated carbons of different origins were used as adsorbents for methyl mercaptan (MM). The samples were further oxidized and urea-treated to study the effect of oxidation and introduction of nitrogen on their MM adsorption capacities. The surface of the carbons was characterized by Boehm titration, potentiometric titration, thermal analysis (TA) and X-ray Fluorescence Analysis (XRF).;The content of carbon, hydrogen, and nitrogen was determined by elemental analysis. The porous structure of the carbons was studied using nitrogen adsorption isotherms at -196°C. The adsorption capacities of the carbons towards MM were found from the dynamic tests. The results showed that MM capacities of the carbons studied were higher in wet conditions than in dry conditions, indicating the lack of chemisorbed oxygen in a latter case. It was found that the ability of carbon to adsorb MM depends strongly on its surface chemistry, particularly on the surface pH, the presence of basic oxygen-containing groups and ash content. Both nitrogen and iron were noticed to catalytically enhance the adsorption of MM through an electron transfer mechanism.;From a structural point of view, the adsorption process was enhanced by the presence of small micropores, where the reaction products are stored. These reaction products were analyzed by TA and Gas Chromatography---Mass Spectrometry (GC/MS).;The results revealed that the main product of MM adsorption/oxidation is dimethyl disulfide (DMDS), which is adsorbed in pores smaller than 50 A. In some cases oxidation proceeded further leading to the formation of methyl methanethiosulfonate (MMTS).;The competition for adsorption sites between water (moist conditions) and DMDS was noticed. The latter molecule, due to its strong adsorption, won the competition in the carbon pore system. On the other hand, water facilitated dissociation of MM, considering that the surface pH of the carbon is above the required threshold of about 7.6, and thus ensured the efficient removal process.;From the inverse gas chromatography (IGC) experiments the heats of adsorption were calculated at different temperatures. It was found that in dry and anaerobic conditions the heat of MM adsorption depends on surface chemistry and particularly on the presence of basic oxygen-containing groups.