Removal of hydrogen sulfide from biogas on sludge-derived adsorbents

Desulfurization adsorbents were prepared from the mixtures of sewage sludge and metal sludge of various compositions and individual sludges by pyrolyses at 650, 800 and 950 °C. The resulting materials were used as adsorbents of hydrogen sulfide from simulated digester gas mixture. The adsorbents before and after H₂S removal were characterized using adsorption of nitrogen, elemental analysis, pH measurements, and thermal analysis. The behavior of materials as desulfurization media does not depend strongly on the humidification pretreatment. The pyrolysis temperature and composition of the mixture play a role in the development of final properties of adsorbents. When the content of sewage sludge is high the strong synergetic effect is noticed after high temperature of pyrolysis. Such factors as development of mesoporosity and new catalytic phases formed as a result of solid-state reactions contribute to this behavior. The removal of hydrogen sulfide on the materials obtained is complex due to the competition between H₂S and CO₂ for adsorption centers and deactivation of those centers by CO₂/H₂CO₃.