H2S adsorption/oxidation on adsorbents obtained from pyrolysis of sewage-sludge-derived fertilizer using zinc chloride activation

Sewage-sludge-derived fertilizer, Terrene, was used as a precursor of adsor bents tested for removal of hydrogen sulfide from moist air. The adsorbents were obtained by pyrolysis of zinc chloride-impregnated granular fertilize r at 400, 600, 800, and 950 degreesC in a nitrogen atmosphere. Subsamples o f the materials obtained were washed with hydrochloric acid to remove the e xcess zinc chloride and other soluble chlorides. This treatment results in a significant increase in the sample porosity. The highest H2S removal capa city was obtained for the sample carbonized at 600 degreesC. This results f rom release of zinc chloride vapor during heat treatment, which acts to for m micropores in the carbonaceous deposit. When inorganic oxides and salts a re present in sufficient quantities, hydrogen sulfide undergoes surface rea ctions and is left on the surface in the form of nonvolatile sulfides and s ulfates. The pores are gradually filled as the surface reaction proceeds. I f catalytic metal oxides are removed, hydrogen sulfide is oxidized predomin antly to sulfuric acid through the catalytic effect of the adsorption sites in the small micropores of the carbonaceous deposit. The removal of H2S oc curs until all pore entrances are blocked with the oxidation product.