Deposition of sulfur from H2S on porous adsorbents and effect on their mercury adsorption capacity

The deposition of elemental sulfur on porous adsorbents (commercial pre-sul furised activated carbons and alumina, an HY zeolite and a selenised adsorb ent) has been observed when the adsorbents are exposed to a gaseous stream containing hydrogen sulfide and oxygen. The sulfur deposition from H2S is m ore marked for the activated carbons and the alumina, it is substantially d ecreased when zeolite is used, and is practically insignificant for the sel enium-based adsorbent. For the pre-sulfurised activated carbons, further su lfur deposition is initially beneficial in terms of increasing their mercur y chemisorbing capacity but, subsequently, the structural properties are af fected and this results in a drastic reduction in adsorption capacity. Furt her sulfur deposition on the pre-sulfurised alumina seems immediately to co mpromise its capacity to chemisorb mercury. The selenium-based adsorbent sh ows problems with detachment of the fine mercuric selenide powder from the matrix. Sulfur deposition on the initially unsulfurised zeolite improves it s mercury adsorption capability. The initially sulfur-free zeolite could be a promising adsorbent for the treatment of this specific type of gas strea m, In fact, after a moderate level of sulfur deposition from oxidation of h ydrogen sulfide, it can simultaneously chemisorb the mercury vapours by rea ction with the sulfur itself while, unlike the activated carbons and alumin a, maintaining its required structural properties for a relatively long per iod. (C) 1999 CNR. Published by Elsevier Science Ltd. All rights reserved.