Selective adsorption of ethyl mercaptan on NaX zeolite

Adsorption on microporous solid is an alternative technique to remove mercaptans from natural gases. The present study gives equilibrium adsorption data on NaX faujasite for some pure gases representative of natural gas impurities (ethyl mercaptan, toluene and n-heptane) and their binary mixtures. The first part of the paper is devoted to the adsorption of pure gases. Experimental results show that the zeolite has a high adsorption affinity for ethyl mercaptan, toluene and n-heptane. In the second part, we examine adsorption isotherms for binary mixtures of ethyl mercaptan and toluene or n-heptane over a large domain of composition. Coadsorption enthalpies are also determined. These experimental data allow to obtain entropies of adsorbed phases and adsorption selectivities. The analysis of coadsorption data indicates that the zeolite preferentially adsorbs ethyl mercaptan over a large domain of micropore filling and that the adsorption selectivity is related to entropic effects inside zeolite micropores. A displacement of n-heptane by ethyl mercaptan is even observed. In contrast, toluene is preferentially adsorbed by the zeolite at high micropore filling.