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 adsorbents tested for removal of hydrogen sulfide from moist air. The adsorbents were obtained by pyrolysis of zinc chloride-impregnated granular fertilizer at 400, 600, 800, and 950 degreesC in a nitrogen atmosphere. Subsamples of the materials obtained were washed with hydrochloric acid to remove the excess zinc chloride and other soluble chlorides. This treatment results in a significant increase in the sample porosity. The highest H2S removal capacity was obtained for the sample carbonized at 600 degreesC. This results from release of zinc chloride vapor during heat treatment, which acts to form micropores in the carbonaceous deposit. When inorganic oxides and salts are present in sufficient quantities, hydrogen sulfide undergoes surface reactions and is left on the surface in the form of nonvolatile sulfides and sulfates. The pores are gradually filled as the surface reaction proceeds. If catalytic metal oxides are removed, hydrogen sulfide is oxidized predominantly to sulfuric acid through the catalytic effect of the adsorption sites in the small micropores of the carbonaceous deposit. The removal of H2S occurs until all pore entrances are blocked with the oxidation product.