A comprehensive review on how ionic liquids enhance the pyrolysis of cellulose, lignin, and lignocellulose toward a circular economy

Abstract

The sustainable use of plant biomass (PB) to produce new valuable compounds helps alleviate the world's excessive reliance on fossil fuels. Among the different processes available, pyrolysis has drawn significant attention for its efficiency in converting PB (including lignin, hemicellulose, and cellulose) into solid, liquid, and gas products by thermal degradation. Moreover, the participation of ionic liquids (ILs) in the pyrolysis process can further facilitate this process, improve the quality of pyrolysis products, and enhance the operational parameters. This review article presents an in‐depth examination of how ILs enhance the pyrolysis of lignin, cellulose, and lignocellulose toward sustainability and circular economy (CE). The structural chemistry of the components of PB, namely cellulose, lignin, and hemicellulose, is first discussed. Furthermore, the role of ILs in the pyrolysis of cellulose, lignin, and lignocellulose is thoroughly investigated. These roles include pre‐treating agent before pyrolysis, catalyst after or during pyrolysis, template during pyrolysis, and extractant after pyrolysis. In the following, the sustainability of PB pyrolysis with the participation of ILs is examined from three aspects: environmental, social, and economical. Finally, the PB pyrolysis was investigated from the CE aspect. There is no doubt that the participation of ILs in the pyrolysis process positively affects the operating conditions and product quality, so the whole process is only one step away from complete sustainability.