In line upgrading of biomass fast pyrolysis products using low-cost catalysts

Abstract

Biomass pyrolysis and the in-line catalytic cracking of the pyrolysis volatile stream has been approached in this study. The pyrolysis step was carried out in a conical spouted bed reactor at 500 °C, whereas the inert sand or the cracking catalysts (γ-Al2O3, spent FCC and olivine) were placed in a fixed bed reactor at 600 °C. Product analysis was carried out on-line by means of chromatographic methods, and the distribution and composition of the main products obtained have been related to the features characterizing each catalyst (physical properties, chemical composition and acidity).

Decarbonylation reactions were favoured over decarboxylation ones when acid catalysts (spent FCC and γ-Al2O3) were used, whereas olivine promoted ketonization and aldol condensation reactions. The Fe species in the olivine structure enhanced reforming and WGS reactions. Bio-oil cracking was more severe as catalyst acidity was increased, leading to an increase in the hydrocarbon fraction. The Al2O3 derived bio-oil was substantially deoxygenated, with a considerable reduction in the phenolic fraction, which accounted mainly for alkyl-phenols. The three materials tested led to a significant decrease in acid and phenolic compounds in the volatile stream, making it suitable for further catalytic valorization for the production of H2, fuels and chemicals.

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