Removal of mercaptans on activated carbons

Although morcaptans present in air or gaseous fuel can cause similar environmental and catalyst poisoning effects as hydrogen sulfide, their adsorption on activated carbons has been addressed less frequently in the scientific literature [48, 78, 132-139]. Very often their adsorption is studied 

The main difference between hydrogen sulfide and methyl mercaptan (MM) is the presence of hydrocarbon moiety in the case of the latter compoimd. It causes that MM molecule is much stronger adsorbed by physical forces on the surface of activated carbons than hydrogen sulfide. The likely surface oxidation product is dimethyldisulfide not elemental sulfur or sulfur dioxide. 

Sample pH pHE Water preadsorbed [mg g l Brth. Time [min] CH3SH capacity [mgg ] CH3SH desorbed [mgg ] 

Analysis of the surface oxidation products using either TA or GC/MS indicated that the predominant product of surface oxidation is DMDS. In the case of the coconut shell based carbon with veiy small pores present, S208, the traces of methyl methane thiosulfonate (CzHsOaSa) were detected. It can be the product of the reaction of DMD with oxygen  

Support for the presence of these oxidation products was only less than 3 pH unit decrease in the pH, which excluded the fonnation of sulfonic acid [136]. The overall effect of oxidation on the capacity was mixed and it was believed that the observed changes were the results of the combined influence of the surface chemistry and porosily. More acidic was the surface, less strong was the sorption of MM, which was reflected in the amount of desorbed MM by air purging after the adsorption process. 

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