Desulfurization of Digester Gas on Industrial-Sludge-Derived Adsorbents

Abstract

Waste sludges from heavy industry (shipyard) consisting of metals and waste oil were pyrolyzed either alone or as the 50:50 weight percent mixtures at 500, 650, and 950 °C. Resulting adsorbents were used as H2S removal media from a simulated mixture of dry digester gas. The breakthrough capacity was measured at dynamic conditions. The initial and exhausted materials after the breakthrough tests were characterized using sorption of nitrogen, thermal analysis, and surface pH measurements. The results obtained demonstrate the complex dependence of the capacity on the surface chemistry, porosity (volume and sizes of pores), and water content. In all cases, elemental sulfur is the predominant product of surface reactions. Generally speaking, an exposure of adsorbents to water enhances the H2S removal capacity, especially for materials obtained at low temperature. This is the result of their chemical instability and surface reactivity. This reactivity is linked to the presence of calcium, magnesium, and iron, which are known as catalysts for hydrogen sulfide oxidation. When water is not present, CO2 quickly deactivates alkaline-earth-metal-based centers, and thus, smaller H2S removal capacity is revealed.