Deep Eutectic Solvents (DESs) for the Isolation of Willow Lignin (Salix matsudana cv. Zhuliu)

Abstract

Deep eutectic solvents (DESs) are a potentially high-value lignin extraction methodology. DESs prepared from choline chloride (ChCl) and three hydrogen-bond donors (HBD)—lactic acid (Lac), glycerol, and urea—were evaluated for isolation of willow (Salix matsudana cv. Zhuliu) lignin. DESs types, mole ratio of ChCl to HBD, extraction temperature, and time on the fractionated DES-lignin yield demonstrated that the optimal DES-lignin yield (91.8 wt % based on the initial lignin in willow) with high purity of 94.5% can be reached at a ChCl-to-Lac molar ratio of 1:10, extraction temperature of 120 °C, and time of 12 h. Fourier transform infrared spectroscopy (FT-IR) , 13C-NMR, and 31P-NMR showed that willow lignin extracted by ChCl-Lac was mainly composed of syringyl and guaiacyl units. Serendipitously, a majority of the glucan in willow was preserved after ChCl-Lac treatment.

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

“…After the pretreatment, however, the MIBK-lignin was decreased to 767 and 1227 in M n and M w, respectively, indicating the linkages between lignin units, generally, the aryl ether linkages were broken. According to the previous results [21,[26][27][28] showed in Table 2, the molecular weights of the extracted lignin from other systems and deep eutectic solvents (DESs), etc., still remained in several thousand grams per mole, which may ascribe to the condensation of the small lignin fractions by forming excess carbon-carbon bonds. This indicated, in some way, that less condensation occurred during the pretreatment of MIBK-lignin, which is considered as the result of the weak acidic conditions and the protection of the MIBK phase.…”

“…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.…”

Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy

“…A large variety of depolymerization or condensation reactions typically occur within the lignin structure under such conditions. Quantitative 31 P NMR analyses of lignins isolated from various biomass pretreatment technologies have been highlighted in recent studies 101,[108][109][110][111][112][113][114][115][116][117] . As lignin has become a key genetic engineering target for the enhancement of wood quality and biofuel production 118,119 , quantitative 31 P NMR analyses also have been carried out on transgenic lignin 97,120 .…”

EXTRACTION OF LIGNIN FROM SUGARCANE BAGASSE BY DEEP EUTECTIC SOLVENTS (DESs)

“…However, this process is more expensive than the previous procedures. Recently, application of deep eutectic solvents (DESs) has emerged as a new technique to extract lignin by using green solvents with dominant properties such as their low cost, low toxicity, and biodegradability [5,6]. DESs are formed by hydrogen bonding of two chemicals acting as hydrogen-bond donors (HBD) or hydrogen-bond acceptors (HBA) [7].…”

“…Some previous works used effectively the acid-based DESs to dissolve lignin from biomass, applied to lignin extraction procedure. DESs have been used for the isolation of lignin from willow [5], wheat straw [9], and birch wood [10]. The recent results have revealed that DESs based on choline chloride and organic acid were effective in extracting lignin from biomass [11] and the lignin obtained from the DESs based method has specific structural properties [12].…”