A Comparison of Ionic Liquids and Organic Solvents on the Separation of Cellulose-Rich Material from River Red Gum

Abstract

With the aim of separating cellulose-rich material from river red gum, it was pre-treated with three ionic liquids (ILs), i.e. 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) and 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]) as well as with two organic solvents, i.e. methanol and ethanol. All ILs and organic solvents were able to remove more than 20% lignin. The [Emim][OAc] was found to be the most effective IL in removing lignin (i.e. 26.2 wt% lignin was removed) amongst all pre-treatment studies. Noticeable structural differences were observed in the cellulose-rich materials obtained from IL and organic solvent pre-treatments and several analytical instruments such as XRD, FTIR, TGA and SEM were employed for their detailed understandings. ILs, in contrast to organic solvents, produced porous and low crystalline cellulose-rich material. This was believed to be due to the transformation of crystalline cellulose I to amorphous cellulose II during IL pre-treatment. The exciting findings of producing high porosity and low crystallinity cellulose-rich material along with the removal of lignin using IL treatment have the potential to transform the future bio-processing and bio-refining industry. More than 80% IL recovery was achieved in this investigation. A minor structural alteration was observed in the recovered [Bmim][Cl] while no structural change was observed in the recovered [Emim][OAc] and [Bmim][OAc], and this was confirmed by FTIR spectroscopic analyses. This establishes the recyclability and reusability of ILs in the cost effective pre-treatment of biomass.