Catalytic post-treatment of the vapors from sewage sludge pyrolysis by means of γ-Al2O3: Effect on the liquid product properties

The present work describes an experimental study on sewage sludge pyrolysis in a bubbling Fluidized Bed Reactor (FluBR) and the effect of a catalytic post-treatment of the hot pyrolysis vapors on the pyrolysis liquid product properties, using gamma-alumina (gamma-Al2O3) as a catalyst in a secondary Fixed Bed Reactor (FixBR) placed downstream from the FluBR reactor. The catalytic treatment improved the pyrolysis liquid phase separation, obtaining a liquid with a single organic phase instead of the two usually obtained in sewage sludge pyrolysis without applying gamma-Al2O3. The catalytic post-treatment yielded enhanced organic phases with improved properties (higher heating value, stability, viscosity and chemical composition) and only a minor decrease in the liquid yield. The improvement in the liquid properties was caused by a reduction in the proportion of oxygen-containing compounds. In addition, its composition and physicochemical properties could make it a potential raw material for its co-processing in conventional refineries along with crude oil or oil-derived fractions, if the problem of the high nitrogen content in the liquid is alleviated. (C) 2014 Elsevier B.V. All rights reserved.