Understanding the Distribution and Structural Feature of Eucalyptus Lignin Isolated by γ-Valerolactone/Water/Acid System

Abstract

In this study, an effective isolation method with γvalerolactone (GVL)/water/acid system was carried out to extract lignin from Eucalyptus camaldulensis Dehnh. The detailed spatial distribution and structural features of lignin were studied thoroughly. The Raman spectra demonstrated that a preferential delignification first occurred in the cell corner middle lamella (CCML) and then in the secondary wall (S) region. The isolated lignin yields increased with the increment of acid concentration and treatment time, and the obtained lignin had a relatively high purity by comparison with double enzymatic lignin (DEL). Moreover, the breakage of β-O-4′ linkages and the degree of condensation increased with the increment of the treatment intensity, resulting in a small amount of β-O-4′ linkages existing in the extracted lignin. There was an obvious decrease of aliphatic hydroxyl groups and an increment of phenolic hydroxyl groups in the lignin preparations with the elevation of acid concentration and the treatment time. These findings could be used for better understanding the structural changes of lignin during the GVL/water/acid isolation process and for improving the utilizations of lignin in the industrial biorefinery process.

Enhanced biochemical process for purifying xylo-oligosaccharides from pre-hydrolysis liquor

“…The signals of these units in S-AC spectrum were much weaker than those in the S-F spectrum, indicating only a small quantity of lignin in puri ed PHL. Noticeably, the lignin in F-PHL appeared to have the typical condensed S units, which was also reported by others in the extraction of lignin from Eucalyptus via γvalerolactone/water/acid system [43].…”

“…However, compared to the peak intensity of lignin in F-PHL, the relative peak intensity of lignin in S-CH, S-LX, S-AC was weak or disappeared, indicating the high e ciency of the present purifying methods in removing lignin from XOS. For instance, the typical characteristic peaks of lignin appeared at 1600 cm − 1 and 1515 cm − 1 (aromatic ring), 1336 cm − 1 (syringyl (S) ring), 1250 cm − 1 (guaiacyl (G) ring breathing with C − O stretching) [43]. In addition, the major absence of absorption at 1730 cm − 1 of PHL samples including S-CH, S-LX, S-AC, was due to the low abundance of acetyl groups, which was consistent with remarkable removal of acetyl groups of xylan in PHL ( Fig.…”

Analysis of Cellulose and Lignocellulose Materials by Raman Spectroscopy: A Review of the Current Status

“…Similarly, a review of Raman microscopy applications to understand plant cell walls and their structure-function relationships has been provided [15]. Some other confocal Raman microscopy work focused on the altered lignin structure of CAD (cinnamyl alcohol dehydrogenase) deficient transgenic poplar [38], study of lignin distribution in Eucalyptus cell walls during GVL/water/acid treatment [39], identification of hemicellulose features in poplar cell wall (in conjunction with multivariate analysis) [40], effects of weathering on wood surfaces [41], and characterization of ionic liquid swelled cell walls [42,43,44].…”

Optimization of Lignin Extraction Variables by Response Surface Methodology from Pine Saw Dust, and Quantification of Major Structural Units in Isolated Lignin Fraction

“…At the optimal combination of 48 h of time, 10% solids loading, and 10 mL HCl dose, a lignin yield as was isolated from wheat straw with 62% (wt%) formic acid at 130 °C for 20 min of time [56]. However, in another study, a value of as high as 44.4 β-O-4 was reported when Eucalyptus camaldulensis Dehnh was treated with 80% GVL/20% H2O mixture catalyzed by 20 m M H2SO4 for 30 min of time [57]. Almost similar values of β-O-4 linkages were quantified as 45.54 units when abaca biomass was subjected to lignin isolation under alkaline conditions of 20 wt% NaOH with 10 wt.% H2O2 at a temperature of 105 °C for a process time of 3 h [58].…”