Upgrading of biomass sourced pyrolysis oil review: focus on co-pyrolysis and vapour upgrading during pyrolysis

Fast pyrolysis bio-oil (FPBO) from lignocellulosic feedstocks has been successfully used as a fuel for boilers in heating applications. However, the oil quality limits application as a transport fuel due in part to the high oxygen and resulting acid content of the pyrolysis oil which complicates storage, handling and use in traditional petroleum based systems. Reduction of the acid or oxygen content can be accomplished via a number of refinery approaches from catalytic upgrading of the liquid post production to co-pyrolysis. While past reviews have focused on catalytic upgrading of the post-production oil, this work compares studies in post-production catalytic processes, in situ and ex situ pyrolysis vapour upgrading and co-pyrolysis. The review includes studies of "natural" additives/catalysts, sourced from waste biomass, as the co-pyrolysis material or catalyst. Additive/catalysts sourced from waste biomass are potentially a more sustainable approach than commercial catalysts. In general, upgrading the liquid post pyrolysis can improve quality; however, the overall oil yield decreases and cost increases due to the additional upgrading step. Co-pyrolysis and/or in and ex situ vapour upgrading during pyrolysis potentially enhance FPBO quality while recovering high-value chemicals.