Efficient Cleavage of Lignin–Carbohydrate Complexes and Ultrafast Extraction of Lignin Oligomers from Wood Biomass by Microwave‐Assisted Treatment with Deep Eutectic Solvent

Abstract

Lignocellulosic biomass is an abundant and renewable resource for the production of biobased value‐added fuels, chemicals, and materials, but its effective exploitation by an energy‐efficient and environmentally friendly strategy remains a challenge. Herein, a facile approach for efficiently cleaving lignin–carbohydrate complexes and ultrafast fractionation of components from wood by microwave‐assisted treatment with deep eutectic solvent is reported. The solvent was composed of sustainable choline chloride and oxalic acid dihydrate, and showed a hydrogen‐bond acidity of 1.31. Efficient fractionation of lignocellulose with the solvent was realized by heating at 80 °C under 800 W microwave irradiation for 3 min. The extracted lignin showed a low molecular weight of 913, a low polydispersity of 1.25, and consisted of lignin oligomers with high purity (ca. 96 %), and thus shows potential in downstream production of aromatic chemicals. The other dissolved matter mainly comprised glucose, xylose, and hydroxymethylfurfural. The undissolved material was cellulose with crystal I structure and a crystallinity of approximately 75 %, which can be used for fabricating nanocellulose. Therefore, this work promotes an ultrafast lignin‐first biorefinery approach while simultaneously keeping the undissolved cellulose available for further utilization. This work is expected to contribute to improving the economics of overall biorefining of lignocellulosic biomass.

Unraveling the Structural Transformation of Wood Lignin During Deep Eutectic Solvent Treatment

“…Pioneering works have indicated that DES pretreatment can significantly promote the efficacy of residue cellulose enzymatic hydrolysis. The plant species, which on the pretreatment with different DESs, have been extended to gramineae [corncob (Procentese et al, 2015;Zhang et al, 2016), wheat straw (Jeong et al, 2015), sorghum (Das et al, 2018), and switchgrass (Chen et al, 2018;Kim et al, 2018)], hardwood [eucalyptus (Shen et al, 2019), willow (Lyu et al, 2018;Song et al, 2019), and poplar (Alvarez-Vasco et al, 2016;Liu et al, 2017)], softwood [pine (Lynam et al, 2017), spruce (Wahlström et al, 2016), and fir (Alvarez-Vasco et al, 2016)], and endocarp (Li et al, 2018).…”

High Purity and Low Molecular Weight Lignin Nano-Particles Extracted from Acid-Assisted MIBK Pretreatment

“…However, it is still unsatisfactory in the recovery of the hemicellulose and lignin. Although current studies on pretreatment systems for removing lignin or breaking the biomass recalcitrance has focused on the ionic liquids (ILs) [23][24][25][26][27] and deep eutectic solvents (DESs) pretreatments [28][29][30][31][32], the challenge of the cellulose valorization without compromises of lignin and hemicellulose fractions is still unresolved.…”

Fast and Efficient Method to Evaluate the Potential of Eutectic Solvents to Dissolve Lignocellulosic Components

“…A comparative graph between each ES and the temperature and time to achieve complete alkaline lignin dissolution are presented in the SM ( Figure S8). In general, the dissolution of lignin in a solvent involves disrupting π-π stacking interactions between lignin aromatic groups and establishing strong intermolecular hydrogen bonds with hydrogen bond acceptor and donor groups (e.g., hydroxyl groups) in lignin structure [62,63]. In this context and by taking a close look at the obtained data, it can be observed that the chemical structure of HBDs plays an important role in alkaline lignin dissolution.…”