A Review of the Chemical and Physical Mechanisms of the Storage Stability of Fast Pyrolysis Bio-Oils
Understanding the fundamental chemical and physical aging mechanisms is necessary to learn how to produce a bio-oil that is more stable during shipping and storage. This review provides a basis for this
understanding and identifies possible future research paths to produce bio-oils with better storage stability. Included are 108 references. The literature contains insights into the chemical and physical mechanisms that affect the relative storage stability of bio-oil. Many chemical reactions that are normally thought to require catalysis, proceed quite nicely without them (or with catalysts indigenous to the bio-oil) during the long reaction times available in storage. The literature was searched for information about the equilibrium constants and reaction rates of selected aging mechanisms, to determine whether they apply to storage times. The chemical reactions reported to occur in pyrolytic liquids made from biomass are presented. As the bio-oil composition changes during aging, the mutual solubility of the components changes to make phase separation more likely. With these insights into the aging mechanisms, the use of additives to improve storage stability is examined. Comparisons are then made to the storage stability of petroleum fuels. The review is summarized, conclusions are drawn, and recommendations are made for future research to improve the storage stability of bio-oils.