Selective adsorption of tert-butylmercaptan and tetrahydrothiophene on modified activated carbons for fuel processing in fuel cell applications

The effects of surface oxidation and KOH impregnation on activated carbon for the selective adsorption of tert-butylmercaptan (TBM) and tetrahydrothiophene (THT) present in natural fuel gas were studied. Physicochemical properties of the adsorbents were characterized by N₂ adsorption, X-ray diffraction (XRD), temperature programmed desorption (TPD), scanning electron microscopy (SEM), and surface pH measurements. Oxidation treatments by HNO₃ or H₂O₂ gave rise to considerable increases in both TBM and THT adsorption capacity, about a threefold enhancement from those on pristine activated carbon. Notably, it was found that the oxidative modifications led to an enhancement in THT adsorption selectivity, whereas KOH impregnation led to a marked increase in TBM adsorption selectivity. The properties of the adsorption sites and the adsorption strength of TBM and THT on the sites were characterized. These results agree well with the experimental sulfur adsorption capacities of the samples and can be explained by an adsorption model proposed in this work.