On the possibility of water regeneration of unimpregnated activated carbons used as hydrogen sulfide adsorbents

A bituminous coal and a coconut shell activated carbon were oxidized using nitric acid under conditions chosen to preserve their pore structures. The surface chemistry of the carbons was characterized using Boehm titration an d thermal analysis. The carbons were then used as hydrogen sulfide adsorben ts. The exhausted carbons were washed in order to remove the products of ox idation. The changes in the porous structure, surface pH, total sulfur cont ent, and speciation of sulfur compounds were evaluated using sorption of ni trogen, thermal analysis, acid-base titrations, and ion chromatography. It was found that the presence of a trace amount of carbonates in coal-based c arbon dramatically affects the mechanism of hydrogen sulfide immobilization . As a result of this, unreactive, insoluble, and bulky sulfur polymer whic h hinders the wash out of the deposits is formed. On the other hand, modera tely oxidized samples; despite their lower H2S removal capacity, favor the formation of soluble sulfur oxides which are washed out as sulfuric acid. T he H2S breakthrough capacity tests on regenerated samples revealed more tha n 30% recovery in their capability to effectively remove hydrogen sulfide.