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

•The use of γ-Al2O3 enhanced the properties of the pyrolysis liquid products.•The differences of polarity and density between the phases improve their separation.•Organic phase has a marked non-polar character and contains more hydrocarbons.•The heating value of the organic phase is quite stable after 30 days of storage.•The nitrogen content of the organic phases is not affected by using γ-Al2O3.

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 (γ-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 γ-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.