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Lignocellulosic biomass (LCB) utilization demands pretreatment to disrupt the compact structure and reduce the recalcitrance originating from LCB constituents interaction. Alkaline pretreatment (AP) selectively solubilizes lignin, enhances the accessible surface area, and eventually alters the pretreated residue structure. During pretreatment, heterogeneous susceptibility/recalcitrance of LCB constituents towards pretreatments and various phenomena such as phase transition, de/repolymerization, and lignin solubility are primarily responsible for structure alteration. Lignin structure comprises various kinds of bonds/linkages (β-O-4′, β-β′, and β-5′), and each one might be differently susceptible to a specific pretreatment. Differently susceptible lignin bonds/linkages and the relationship between AP and lignin bond degradation are not fully understood. Sequential alkaline pretreatment (SAP) was applied at constant pretreatment severity to investigate the lignin degradation, structure of residual lignin in the pretreated residue, and the heterogeneous susceptibility/recalcitrance of lignin bonds to categorize the labile/recalcitrant lignin moieties/bonds during SAP. Cellulolytic enzyme lignin (CEL) was isolated from un/pretreated residues and characterized by FTIR, GPC, and 2D NMR (HSQC). Semi-quantification of 2D NMR spectra anticipated the heterogeneous degradation of lignin ether bonds/C-C linkages as β-5′ degraded completely than β-O-4′ and β-β′. It might be due to the accessibility of cellulose/hemicellulose-lignin matrix as each pretreatment step degraded LCB and exposed embedded structure. [Display omitted] • Sequentially alkaline pretreatment (SAP) employed to understand lignin degradation. • Lignin degradation, lignin moieties and bonds susceptibility during SAP studied. • Comparatively, β–O–4′ degraded more with each pretreatment step than β–β′ and β–5′. • β–β′ degraded gradually, and β–5′ became recalcitrant after first pretreatment step. [ABSTRACT FROM AUTHOR]

As the vital renewable feedstock originated from carbon-neutral resources, due to prominent aromaticity lignin owns the potential to produce high value-added products. Multi-functional lignin valorization demands efficient lignin extraction at milder conditions to keep its structure intact to substitute petroleum-based reactants. Lignin extraction severity (LES) is considered as the primary factor affecting the structure of extracted lignin and ultimately determines its applications. Except for the LES, the selection of suitable reagents for lignin extraction concerned with specific applications is crucially important. To explore the influence of different reagents, this study focused on lignin extraction employing the commonly used strong acids at the same LES. Four lignin preparations were extracted using 80% aqueous dioxane with the addition of H 2 O (L1), HCl, H 2 SO 4 and HNO 3 (pH = 1.30 ± 0.01 L2, L3 and L4, respectively). Analytical high-sensitive NMR (31P and 2D-HSQC) together with other characterizations (FTIR and GPC) were successfully employed and quantified while unveiling the structural heterogeneity among extracted lignin preparations. At the same LES, different reagents yielded lignin with varying structural characteristics and were potentially suitable for different applications. • Selection of suitable reagents was important for tailor-made lignin extraction towards its application. • Synergistic effect of H+ ions and anions caused lignin structure alteration. • The same severity factor with different reagents yielded lignin with different structural characterizations for different applications. • Quantification revealed the structural heterogeneity among extracted lignin preparation. [ABSTRACT FROM AUTHOR]

An efficient ChCl-MeOH-AlCl 3 ·6H 2 O-Ru-C catalytic system was developed, and ChCl-MeOH-AlCl 3 ·6H 2 O-DES could effectively help to improve the performance of Ru-C, which achieved a high yield of aromatic small aromatic phenol ketones, VMK, SA, DMH and DHE (92.4%). And ChCl-MeOH-AlCl 3 ·6H 2 O-DES could achieve high selective lignin dissolution (93.1%) from Evodia lepta residue. [Display omitted] • ChCl-MeOH-AlCl 3 ·6H 2 O DES was developed for in-situ lignin hydrogenolysis. • Ru-C in the DES significantly improved the product yield and profile. • The system led to 93.1% delignification and 95.3% cellulose retention. • The system led to a high total aromatic phenol ketone yield of 92.4%. • Ru-C performance was improved by the DES system. A deep eutectic solvent (DES) system of ChCl-MeOH-AlCl 3 ·6H 2 O was developed for simultaneous dissolution of lignin from Evodia lepta residue and in-situ hydrogenolysis of lignin to aromatic phenol ketones using a Ru-C catalyst. The use of this DES led to a delignification of reached 93.1 % and cellulose and hemicellulose retentions of 95.3 % and 47.8 % respectively at the molar ratio of 1:12:0.2. While the total aromatic phenol ketones yield reached 92.4 % under 130 °C for 3 h with 17.2 % yields of vanillyl methyl ketone, 9.1 % syringylacetone, 25.4 % dihydroeugenol, and 40.7 % 4-propyl-2,6-dimethoxyphenol. The improved Ru-C properties in the DES system like thermal stability, the specific surface area and reduction potential contributed on the exceptional high product yields. The aromatic phenol ketones were 312.5 % higher than the reported yields of hydrogenolysis of aromatic monomers by ethanol/1,4-dioxane/formic acid under 300 °C–2 h conditions. [ABSTRACT FROM AUTHOR]