Advanced biofuels production by upgrading of pyrolysis bio-oil

The present work is a review on the production of bio-oils from biomass pyrolysis, with special emphasis on the different catalytic methods developed so far for the upgrading of this liquid fraction in order to significantly improve its properties, so it can be used as advanced biofuel. After a discussion of the main variables and factors affecting biomass pyrolysis, a number of processes are described here for bio-oil upgrading, including catalytic pyrolysis, esterification, aldol condensation, ketonization, and hydrodeoxygenation (HDO). All of them are featured by the use of tailored catalysts that may play different roles, such as completing depolymerization of biomass, promoting deoxygenation reactions, and favoring C-C bonds formation in order to increase the proportion of components present in the final bio-oil within the range of liquid fuels. The review highlights the challenges that must still be faced for biomass pyrolysis/bio-oil upgrading to become a commercial process. Among them, catalyst deactivation is a general issue to be considered as bio-oil has a strong tendency to polymerize, forming carbonaceous deposits on the catalysts, and contains a large share of water with acidic pH that may damage the catalyst components in liquid-phase upgrading treatments. Likewise, process integration of bio-oil upgrading treatments, through more or less complex schemes, is an aspect that should be deeply analyzed in the future as it may be a key element determining the commercial feasibility of the overall process. (C) 2017 John Wiley & Sons, Ltd.