The adsorption of sulfur by microporous materials

The sorption of sulfur by the zeolites NaX (= 13X) and CaA (= 5A) and an activated charcoal prepared from sugar was investigated at temperatures between 150 and 350°C and relative sulfur pressures between 10−4 and 10−1. The adsorbate-adsorbate interaction indicated by the S-shaped isotherm for the zeolite NaX points to physical or chemical interaction of sulfur molecules in neighboring supercages. In CaA adsorbate-adsorbate interaction between sulfur species in different supercages is negligible. Below 200°C the rate of sulfur uptake by the zeolite CaA is determined by the diffusion rate of a sulfur species through the zeolitic framework. In activated charcoal a strong adsorbate-adsorbent interaction is present and part of the sulfur is chemisorbed at 350°C. The differences in the density of the adsorbed sulfur determined with three different methods indicate that even at full saturation of the micropore volume with sulfur, there is still some residual adsorption volume.