Physical, chemical, thermal and biological pre-treatment technologies in fast pyrolysis to maximize bio-oil quality: A critical review

Pyrolysis converts lignocellulosic biomass into bio-oil, which result in at least four times with more energy density than raw biomass. Bio-oil could be exploited in heating, power generation or extraction of chemicals. However, quality of bio-oil is not adequate enough to be used in equipment for energy applications. Product yield and l composition of bio-oil have a close relationship with feedstock chemical composition, thus some pre-treatments are used to optimize bio-oil properties, such as chemical composition, heating value and ash content, achieving a better bio-oil quality before pyrolysis. This work reviews the key characteristics of lignocellulosic biomass and the role of chemical composition during pyrolysis reaction to expect a bio-oil with low oxygen content, low water content and low acidity. Therefore, physical, thermal, chemical and biological treatments prior to pyrolysis, are presented and discussed as a possible solution that leads to an improvement in bio-oil quality.