Investigations of novel nitrile-based ionic liquids as pre-treatment solvent for extraction of lignin from bamboo biomass

In this work, nitrile-based ionic liquids (ILs) i.e., 1-propyronitrile-3-butylimidazolium chloride [C2CNBim]Cl, 1-propyronitrile-3-allylimidazolium chloride [C2CNAim]Cl, 1-propyronitrile-3-(2-hydroxyethyl)imidazolium chloride [C2CN HEim]Cl and 1-propyronitrile-3-benzyllimidazolium chloride [C2CN Bzim]Cl were used as pre-treatment solvent for the extraction of lignin from bamboo biomass. The pre-treatment process was investigated with respect to several factors such as the types of ionic liquid cation used, the effect of pretreatment temperature and time, sample loading and particle size, the effect of recycling the ionic liquid on lignin extraction and the effect of multi-extraction to enhance the recovery of lignin which were collectively found to have an impact on the lignin extraction as a whole. The crystallinity of the cellulose-rich material obtained from the extraction was analyzed using XRD while the extracted lignin was characterized using FTIR, NMR, TGA and elemental analysis. From the XRD analysis, the crystallinity of the cellulose-rich material obtained after treatment with the synthesized nitrile-based ILs was found to remain the same. Among the nitrile-based ILs used, [C2CN Bzim]Cl demonstrate the best performance for the extraction process in a predetermined condition (T = 120 °C, t = 24 h) where 53% of the lignin from the bamboo was successfully extracted. This was confirmed from the FTIR and NMR analysis showing the characteristic peaks indicating the presence of lignin in the spectra of the respective samples tested.