Sewage Sludge/Metal Sludge/Waste Oil Composites as Catalysts for Desulfurization of Digester Gas

Abstract

Composite adsorbents based in mixtures of sewage sludge/metal sludge and waste oil were prepared by pyrolysis at 650 and 950 °C. The materials were characterized using adsorption of nitrogen, Fourier transform infrared (FTIR), X-ray diffraction (XRD), inductively couple plasma (ICP), scanning electron microscopy (SEM), pH measurements, and thermal analysis. As-received materials were used as adsorbents of hydrogen sulfide from digester gas. To evaluate the importance of waste oil addition, the results were compared to those obtained on sewage sludge/metal sludge composites. The results clearly showed the importance of the carbonaceous phase from the oil precursor for enhancing the catalytic properties. Besides providing porosity, necessary for a dispersion of inorganic sludge base catalyst, an addition of a carbon phase alters the surface chemistry via providing a more reducing environment during the pyrolysis and via providing the carbon for more efficient formation of such compounds as carbides. The results indicated that the adsorbents obtained at 950 °C are much more active in the process of hydrogen sulfide oxidation than those obtained at 650 °C. In the case of the high temperature of heat treatment, longer treatment is beneficial for the development of surface catalytic properties. As a result of this, the carbon phase was stabilized via increasing its degree of aromatization and it became more porous owing to the release of activation agents from the decomposition and rearrangement of an inorganic phase. In very small pores, oxygen important for oxidation can be chemisorbed.