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.