8 - Recent developments in the catalytic hydrotreatment of pyrolysis liquids

Fast pyrolysis is a promising technology to convert lignocellulosic biomass to a liquid energy carrier. The product, known as fast pyrolysis liquid (PL), has a higher energy density than solid biomass and is more easily transported and stored. The applications of PLs are limited due to a high water and oxygen content and limited storage stability. As such, upgrading technologies have been developed to broaden the application range of PLs. Catalytic hydrotreatment is such an attractive upgrading technology for PLs and leads to improved product properties like, among others, a higher thermal stability and energy density and, reduced oxygen and water content, etc. Catalytic hydrotreatment is typically carried out at elevated temperatures (250-400°C) and hydrogen pressures (100-200. bar) in the presence of heterogeneous catalysts. This chapter starts with a short overview of fast pyrolysis technology followed by the properties and molecular composition of PLs. The core of the chapter is dedicated to a description of the state of the art regarding the catalytic hydrotreatment of the PLS to improve the product properties and to make the products suitable as a transportation fuel or as a co-feed in existing oil refineries. Various length scales are considered, ranging from molecular aspects to process studies in a dedicated continuous set-up. Catalyst screening studies are provided and will be discussed in detail, both in the presence and absence of external solvents. Proposed molecular transformations are summarised, and their implications on both process and product properties will be discussed