7 - Stabilisation of pyrolysis oils

Abstract

The chemical and physical instability of crude pyrolysis oils produced by lignocellulose liquefaction constitutes a practical bottleneck for bio-oil storage and transportability and for upgrading to advanced biofuels. Technological innovations are required for enabling efficiency and widespread implementation. The term stability and/or instability should herein be understood as the thermally induced chemical and physical changes that proceed with time and by this deteriorate the oil properties away from the ranges of application specifications. This chapter addresses the cutting edge regarding fundamental knowledge on causes of instability, with emphasis on the key properties of pyrolysis oils and the chemical and physical time changes. A comparison is made with conventional fuel stability, which is a natural reference point in this chapter’s perspective. Further, an update on technology, that is, different concepts and methods for improving bio-oil stability, is presented, including in situ and ex situ chemical (esterification, hydrotreating, and (hydro)cracking), physical (solvent addition, fuel blending, emulsification, etc.), and thermal means. Recommendations on directions for future development are suggested in the concluding remarks. The need for novel materials (catalysts and adsorbents) and concepts, coprocessing, integration and hybridization, and enabling availability of hydrogen, are among the aspects addressed.