Biofuels & Bioenergy

Biomass forestry and agricultural residues can be thermally decomposed via fast-pyrolysis to maximize the production of bio-oil. This bio-oil offers advantages in terms of storage, transport and flexibility in applications like fuels for transportation. Nevertheless, this application is still in a relatively early stage of development, and fundamental understanding of the thermal decomposition behavior of biomass during fast-pyrolysis is crucial to control the end-product composition. Bio-oil obtained by conventional non-catalytic fast-pyrolysis is formed by complex mixtures of compounds and contains a high oxygen concentration (35-40 wt.%), acid pH and water contents between 20-50% wt. Catalytic fast-pyrolysis can promote partial deoxygenation reactions that could proceed by different pathways: dehydration, decarbonylation and decarboxylation, leading to the H2O, CO and CO2 formation, respectively. In this work, catalytic and no-catalytic fast-pyrolysis of Eucalyptus woodchips have been carried out at lab-scale. For catalytic tests, nanostructured materials having mild acidic properties and high accessibility (e.g. h-ZSM5 zeolite) have been employed. The catalytic properties of these materials for biomass catalytic pyrolysis have been also modified and adjusted by incorporation of different metal oxides. Likewise, Pd-containing h-ZSM5 zeolite has been tested. The catalysts activity has been analyzed in terms of their capacity to deoxygenate the bio-oil and compared with the non-catalytic tests. For that purpose, several parameters, including mass products yield (gas, char, coke and bio-oil (bio-oil*+H2O), gas composition, bio-oil* elemental analysis and H2O content, have been determined. The catalysts tested led to a higher gas yield than the thermal pyrolysis route, mostly due to the higher production of both CO and CO2. On the other hand, two phases (organic and aqueous) were distinguished in the catalytic bio-oil as a consequence of its higher H2O content (from 26.9 to 33.8-41.1 wt.%). All of these resulted in partially deoxygenated bio-oils*, whose oxygen contents decreased from 37.3 to 27.5-32.3 wt.%; but to the detriment also of the bio-oil* yield, which decreased from 42.5 to 26.1-30.7 wt.%.