Structural Characteristics and Distribution of Lignin in Eucalyptus Globulus Pulps Obtained by a Combined Autohydrolsis/Alkaline Extraction Process for Enzymatic Saccharification of Cellulose

Abstract

Eucalyptus globulus wood chips were subjected to autohydrolysis pretreatment at 175ºC at three different residence times. Part of the recovered solids were submitted to alkaline extraction with NaOH solution to remove leachable lignin. The chemical composition of the fibrous material was analyzed by HPLC, Py-GCMS and 2D-NMR HSQC, while morphological changes were evaluated by SEM and LSCM. The pretreated materials were hydrolyzed with cellulases at a substrate loading of 10% (w/v) for up to 72 h. Glucose yields (based on dry wood) obtained in the enzymatic hydrolysis ranged between 38% and 65%, depending on reaction time in the autohydrolysis pretreatment. After the alkaline extraction, no significant change was observed in the yields in the enzymatic hydrolysis at 72 h, but at the lower severities, the initial rates of saccharification increased. The main effect of the hydrothermal pretreatment was removal of hemicelluloses, resulting in enriched cellulose pulps. SEM and LSCM images of the hydrothermal pretreated samples showed a disruption of the fiber surface, mainly in those samples obtained at the higher severity. Py-GC/MS and HSQC analysis showed that no major changes in the lignin structure occurred in the samples obtained by autohydrolysis and further alkaline extraction. By autohydrolysis at the higher severity (So=4.02), the lateral chains in lignin were cleaved and the formation of lignin droplets was observed. Hemicelluloses removal and lignin redeposition as droplets in certain regions of the fiber surface was associated with the higher accessibility of cellulose and the yield increase of the enzymatic hydrolysis.

Investigation of the Chemocatalytic and Biocatalytic Valorization of a Range of Different Lignin Preparations: The Importance of β-O-4 Content

“…Eucalyptus organosolv lignin was prepared from Eucalyptus globulus wood chips by acidic ethanol/water extraction as previously described . Eucalyptus autohydrolysis lignin was prepared from Eucalyptus globulus wood chips by autohydrolysis pretreatment at 175 °C followed by alkaline extraction, as described previously . Miscanthus ionosolv lignin was prepared from Miscanthus x giganteus by treatment with the ionic liquid triethylammonium hydrogen sulfate ([TEA]­[HSO 4 ]) containing 20 wt % water at 20% solids loading and 150 °C for 1 h, as described previously …”

“…24 Eucalyptus autohydrolysis lignin was prepared from Eucalyptus globulus wood chips by autohydrolysis pretreatment at 175 °C followed by alkaline extraction, as described previously. 25 Miscanthus ionosolv lignin was prepared from Miscanthus x giganteus by treatment with the ionic liquid triethylammonium hydrogen sulfate ([TEA][HSO 4 ]) containing 20 wt % water at 20% solids loading and 150 °C for 1 h, as described previously. 26 1 H− 13 C NMR spectra were recorded in d 6 -DMSO on a Bruker Avance III spectrometer, using the protocols previously described.…”

“…24 Eucalyptus autohydrolysis lignin was prepared from Eucalyptus globulus wood chips by autohydrolysis pretreatment at 175 o C followed by alkaline extraction, as described previously. 25 Miscanthus ionosolv lignin was prepared from 30,31 , including assignment of NMR signals for tricin flavonoid. 32 Gel permeation chromatography and thioacidolysis were carried out using the previously described method.…”

Morphological and Thermochemical Changes upon Autohydrolysis and Microemulsion Treatments of Coir and Empty Fruit Bunch Residual Biomass to Isolate Lignin-Rich Micro- and Nanofibrillar Cellulose

“…Moreover, the presence of lignin has been shown to enhance barrier properties and tunable surface properties of nanocellulose films and nanopapers. , With the goal of retaining the native lignin in coir and EFB fibers, we report a methodology to isolate from these residual sources, lignin-rich micro- and nanofibrillar cellulose (generally termed here as MNFC). Our multistage procedure involves previously reported protocols for autohydrolysis and microemulsion treatment, both of which are mild and, to a great extent, preserve the original cellulosic content. Our study includes morphological, structural, and thermal analyses which were performed after each processing step to develop a thorough understanding of defibrillation and lignin redistribution.…”

Chemical and Microstructural Changes in Eucalyptus Globulus Fibers Subjected to Four Different Pretreatments and Their Influence on the Enzymatic Hydrolysis

“…Moreover, results of the present study are consistent with previous studies published by our research group. Thus, it this form of lignin is identified as an important factor for the high conversion of cellulose to glucose, the heterogeneous redistribution of lignin, resulting in, a significant decrease in the recalcitrance of pretreated materials 22,34,35 . In the pretreatment, when hemicellulose is removed, the lignin is more exposed to changes that promote its redistribution in the form of micro-droplets, generating random areas on the fibers with lower lignin content.…”