Fractionation of Lignocellulosic Residues Coupling Steam Explosion and Organosolv Treatments Using Green Solvent γ-Valerolactone

Abstract

A two-step fractionation of lignocellulosic residues of Phragmites australis in its main components (cellulose-pulp, soluble hemicellulose sugars, and lignin) is described, based on the biomass-derived solvent γ-valerolactone (GVL). The solvent used is an excellent substitute for traditional organic solvents as it is not toxic, it is renewable, and it can be recycled after the extraction process. Prior the GVL-organosolv extraction process, a steam explosion pretreatment was performed in order to break up the tight lignocellulosic structure and partially depolymerise hemicellulose into soluble sugars, making lignin easier to be solubilised. Three common extraction techniques were compared: soxhlet, closed vessel microwave-assisted, and open vessel on a hotplate stirrer. The two-step approach resulted in a cellulose-rich solid, water-soluble hemicellulose sugars and lignin-rich GVL liquor which was further purified for lignin isolation. The two best resulting pulps presented a high cellulose content (75.47% and 78.68%) starting from 38.13% and a content of lignin down to 11.96% and 13.09% starting from 23.02%. Almost all hemicellulose was removed with a final content of 0.72% and 2.20% starting from 20.5%.