Fractionation of Technical Lignin from Enzymatically Treated Steam-Exploded Poplar Using Ethanol and Formic Acid

Abstract

Lignocellulosic biorefineries produce lignin-rich side streams with high valorization potential concealed behind their recalcitrant structure. Valorization of these residues to chemicals, materials, and fuels increases the profitability of biorefineries. Fractionation is required to reduce the lignins' structural heterogeneity for further processing. We fractionated the technical biorefinery lignin received after steam explosion and saccharification processes. More homogeneous lignin fractions were produced with high β-O-4′ and aromatic content without residual carbohydrates. Non-toxic biodegradable organic solvents like ethanol and formic acid were used for fractionation and can be adapted to the existing biorefinery processes. Macromolecular properties of the isolated fractions were carefully characterized by structural, chemical, and thermal methods. The ethanol organosolv treatment produced highly soluble lignin with a reasonable yield, providing a uniform material for lignin applications. The organosolv fractionation with formic acid and combined ethanol-formic acid produced modified lignins that, based on thermal analysis, are promising as thermoresponsive materials.

Physicochemical Properties, Thermal Stability, and Pyrolysis Behavior of Antioxidative Lignin from Water Chestnut Shell Obtained with Ternary Deep Eutectic Solvents

“…The FTIR spectrum for the lignin isolated with ChCl/EG/p-TsOH is shown in Figure 2b. The FTIR absorption peaks in the lignin were assigned as reported in the literature [2,13,31,34]. The absorption peak at 3423 cm −1 was assigned to the stretching vibration in the aromatic and aliphatic hydroxyl groups.…”

“…The FTIR spectrum for the lignin isolated with ChCl/EG/p-TsOH is shown in Figure 2b. The FTIR absorption peaks in the lignin were assigned as reported in the literature [2,13,31,34].…”

“…The molecular weight of lignin directly affects its physicochemical properties. Lignin with low molecular weight and high hydroxyl content is suitable for the preparation of bioactive materials [ 13 ], while lignin with high molecular weight is an ideal raw material for the preparation of carbon fibers and other materials due to its high carbon content and high viscosity [ 14 ]. Lignin obtained using different methods varies greatly, mainly in terms of chemical structure and molecular weight.…”