Characterization of the bio-oil obtained by fast pyrolysis of sewage sludge in a conical spouted bed reactor

• High bio-oil yields are attained in a conical spouted bed reactor.
• The LHV of the bio-oil is higher than that of lignocellulosic materials oil.
• The bio-oil is a valuable source of chemical compounds.
• The content of C and H in the bio-oil increases compared to the original sludge.
• Simulated distillation curve shows that 70% of the bio-oil fits the gasoil range.

Sewage sludge fast pyrolysis bio-oil, produced in a conical spouted bed reactor (CSBR) in the 450–600 °C range, has been characterized. On the one hand, the effect of temperature on bio-oil composition has been analyzed by means of online chromatography and, furthermore, the ultimate analysis and the higher heating value of each liquid have been determined. On the other hand, the bio-oil collected at 500 °C, at which the liquid yield is maximized (77 wt.% on dry ash free), has been characterized in detail by determining its density, viscosity, water content and pH. The major organic compounds in the bio-oil were oxygenated and nitrogenated ones (phenols, ketones, alcohols, amides and nitriles among others). It is noteworthy that the bio-oil obtained in this work contains a lower amount of O than those derived from lignocellulosic materials; therefore, the concentrations of C and H in this bio-oil, as well as the lower heating value (LHV), are higher. In addition, the simulated distillation reveals that > 70% of the sewage sludge pyrolysis oil corresponds to the gasoil range. The fuel properties of sewage sludge bio-oil evidence that it has the potential to substitute conventional fuels; however, some properties need to be improved, i.e., the heating value should be increased and the nitrogen content reduced by subjecting this bio-oil to further treatments.

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