Pyrolysis oil upgrading for co-processing in standard refinery units

Abstract

This thesis considers the route that comprises the upgrading of pyrolysis oil (produced from lingo-cellulosic biomass) and its further co-processing in standard refineries to produce transportation fuels. In the present concept, pyrolysis oil is produced where biomass is available and then transported to a central upgrading unit. This unit is located next or inside a standard petroleum refinery, enabling the use of existing facilities. The obtained product can be further distributed using existing distribution networks. The present thesis describes and discusses pyrolysis oil upgrading by high pressure thermal treatment (HPTT) and hydrodeoxygenation (HDO), and its subsequent co-processing in lab-scale refinery units. The oil produced by HPTT had higher energy density than the feed due to its lower oxygen and water content. Conversion and transfer of water soluble organics to the oil phase was observed, increasing the energy recovery in the final product. However, severe and fast polymerisation was also observed. This polymerisation created a product with high coking tendency that could not be co-processed in lab-scale refinery units. HDO of pyrolysis oil (and fractions obtained by adding water to it) also created an oil with lower oxygen and water content. However, during HDO, polymerisation was avoided. HDO oils (with high remaining oxygen content) produced at different conditions and from various pyrolysis oil fractions, could be co-processed with Long Residue in a lab-scale catalytic cracking unit. The resulting yields to gasoline and light cycle oil (diesel precursor) were near the same as obtained using the pure fossil reference feed. The presence of such fossil co-feed enabled hydrogen transfer reactions from the fossil feed to the HDO oils components and appeared to be crucial to obtain a good product distribution. Co-processing HDO oils with straight run gas oil in a lab-scale hydrodesulphurisation unit was performed without operational problems, but competition between oxygen and sulphur removal reactions was detected. Dedicated HDO experiments showed that mass transfer resistances can limit the extent of the hydrotreating reactions (favouring in this way the extent of undesired polymerisation reactions, thus deteriorating product quality) and need careful consideration when designing demo units and industrial HDO reactors.