The influence of solvent properties and biomass feedstock characteristics on deep eutectic solvent mediated lignin and hemicellulose fractionation

Deep eutectic solvents (DESs) have received attention due to their ability to fractionate lignin and hemicelluloses from lignocellulosic biomass, though the lack of standard methods to predict the performance of DESs is a concern. The Kamlet-Taft solvatochromic parameters quantify hydrogen bonding and polarity properties of DESs and have been used to draw broad structure-reactivity relationships. This analysis has not been applied to similarly structured DESs despite known differences in treatment performance. Additionally, examination of structure-reactivity trends between different feedstocks has not been considered. Herein, DESs composed of choline chloride and monocarboxylic acids were employed in fractionation experiments with both hardwood and softwood biomass sources aiming to correlate fractionation performance with Kamlet-Taft parameters. Solubilized lignin was recovered and analyzed via 2D-HSQC Nuclear Magnetic Resonance (NMR) and Gel Permeation Chromatography (GPC). Delignification correlated with decreased basicity, showing predictability for both feedstock types. Arabinan and mannan removal was correlated with increasing net acidity and decreasing basicity as increased acidity enhanced hydrolysis of glycosidic linkages in galactoglucomannans and arabinoxylans. This work evaluates the Kamlet-Taft parameters as a tool to screen DESs for fractionation performance across different feedstocks and an investigation of the factors which contribute to differences in lignin removal between feedstocks.