High-solid ethylenediamine pretreatment to fractionate new lignin streams from lignocellulosic biomass

Abstract

In an attempt to augment the profitability and sustainability of lignocellulosic biorefineries, lignin valorization has been deemed as an indispensable requirement. However, unsatisfactory solubility and recalcitrant condensed structures heavily limits the processability of lignin towards high value applications. Here, we exploited a high-solid ethylenediamine (EDA) pretreatment of corn stover and discovered a new aminolignin with an extraordinary aqueous solubility (greater than 86 wt% at pH = 2–8) and minimal condensed structures (Mw = 1200–1400 Da). We brought light to the unique amination reactions that took place in EDA pretreatments, such as α-amination, ammonolysis, and Schiff base reactions. These EDA induced amination introduced hydrophilic amine and amide groups into lignin substructures, which could be the main reason for the rapid room temperature solubilization of lignin, due to the great increase of lignin-water hydrogen bonds and polarity of lignin according to computational simulation. Furthermore, extremely high solid loadings (58 wt%) limited the mobility and accessibility of reactive lignin intermediates owing to pretreatment system keeping in the solid state, physically obstructing the lignin condensation. Chemically, α-amination of β-O-4 structures decreased the generation of condensed lignin as well. This solid-state EDA pretreatment is of great significance for improving the aqueous solubility of lignin and minimizing its condensation, and thus it holds promise for the development of lignin-first biomass fractionation.