Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) using Na-Y and AgNa-Y zeolites for fuel cell applications

Adsorptive removal of tetrahydrothiophene (THT) and tert-butyimercaptan (TBM) that are widely used sulfur odorants in pipeline natural gas was studied using AgNa-Y zeolites at ambient temperature and atmospheric pressure. The AgNa-Y were obtained via Ag+-exchange with Na+ of Na-Y at various exchange levels, and the contributions of formed adsorption sites (Ag+, Na+, Ag-0, H+, and Ag2O) in the THT and TBM adsorption uptake and selectivity were characterized. THT adsorption strength on these sites followed an order of Ag+ > Na+ similar to Ag-0 > H+ > Ag2O. The adsorption strength of THT on Na+ sites was sufficiently high, thus an increase in the Ag+-exchange level did not lead to a notable increase in the breakthrough THT uptake. Differently, adsorption of TBM on Na+ sites was weak, whereas that on Ag+ sites was strong. This resulted in a marked increase in the breakthrough TBM uptake with an increase in the Ag+-exchange level, showing an order of magnitude higher uptake on AgNa-Y compared with that on Na-Y. Noticeably, the adsorption strength of THT on these adsorption sites was higher than that of TBM. This resulted in an almost 100% adsorption selectivity for THT over TBM, when these two sulfur species coexisted in the feed stream. (c) 2007 Elsevier B.V. All rights reserved.