Influence of extractives on the composition of bio-oil from biomass pyrolysis – A review

Abstract

Fast pyrolysis of biomass is a promising method for producing bio-oil, meeting the growing demand for renewable fuels with low environmental impact. However, the complexity of the reactions involved and the limited knowledge about the influence of extractives (proteins, starch, waxes, fats, resins, tannic acid, pigments, sugars, pectin, saponins, essential oils, etc.) on the pyrolysis of the main biomass components (cellulose, hemicellulose and lignin) make it difficult to formulate effective mathematical models to optimize the reaction system and scale the process commercially. This article provides a comprehensive overview of the state of the art regarding the influence of extractives on the pyrolysis of cellulose, hemicellulose, and lignin, as well as on the composition of bio-oil. The text critically discusses the characteristics of biomass and the fast pyrolysis of each of its macromolecules and extractives, establishing a reference base for studying the effects of extractives in this process. Additionally, it offers an updated perspective on how extractives affect the devolatilization of macromolecules, considering factors such as reaction activation, liquid yield, and types of char produced. The influence of extractives on the pyrolysis of each macromolecule and the distribution of chemical species present in bio-oil is also addressed, contributing to a better understanding of the process.