Extraction of Lignin with High β-O-4 Content by Mild Ethanol Extraction and Its Effect on the Depolymerization Yield

Abstract

Lignin valorization strategies are a key factor for achieving more economically competitive biorefineries based on lignocellulosic biomass. Most of the emerging elegant procedures to obtain specific aromatic products rely on the lignin substrate having a high content of the readily cleavable β-O-4 linkage as present in the native lignin structure. This provides a miss-match with typical technical lignins that are highly degraded and therefore are low in β-O-4 linkages. Therefore, the extraction yields, and the quality of the obtained lignin are of utmost importance to access new lignin valorization pathways. In this manuscript, a simple protocol is presented to obtain lignins with high β-O-4 content by relatively mild ethanol extraction that can be applied to different lignocellulose sources. Furthermore, analysis procedures to determine the quality of the lignins are presented together with a depolymerization protocol that yields specific phenolic 2-arylmethyl-1,3-dioxolanes, which can be used to evaluate the obtained lignins. The presented results demonstrate the link between lignin quality and potential for the lignins to be depolymerized into specific monomeric aromatic chemicals. Overall, the extraction and depolymerization demonstrates a trade-off between the lignin extraction yield and the retention of the native aryl-ether structure and thus the potential of the lignin to be used as the substrate for the production of chemicals for higher-value applications.

Mild organosolv pretreatment of sugarcane bagasse with acetone/phenoxyethanol/water for enhanced sugar production

“…The quantitative 2D HSQC NMR and 31 P NMR experiments were carried out according to a previous publication. 26,27…”

A guide to lignin valorization in biorefineries: traditional, recent, and forthcoming approaches to convert raw lignocellulose into valuable materials and chemicals

“…16). 17,199,[210][211][212][213][214] The latter were shown to possess a considerably lower tendency to undergo condensation reactions and b-O-4 ′ bond cleavage as compared to benzylic carbenium ions or parent b-aryl ether motifs with ahydroxyl groups. 118,199,211,215 Noteworthy, lignin etherication is a reversible reaction and native-like lignin structures may be obtained by subjecting etheried lignin to mildly acidic conditions.…”

“…118,199,211,215 Noteworthy, lignin etherication is a reversible reaction and native-like lignin structures may be obtained by subjecting etheried lignin to mildly acidic conditions. Lignin stabilization by aliphatic alcohols was reported to be an effective strategy for protecting lignin against repolymerization during pretreatment, 17,213,214,216 ultimately opening the way to the successful downstream conversion of lignin to chemicals. 118,211,213,[215][216][217][218] A great advantage offered by organosolv pretreatment compared to other fractionation methods is the possibility of producing three separate product streams: a celluloseenriched pulp, an aqueous fraction enriched with hemicellulose derivatives (e.g.…”

Formation of lignin alkyl-O-alkyl ether structures via 1,6-addition of aliphatic alcohols to β-O-4-aryl ether quinone methides

“…[77][78][79] The organosolv process can be considered as a more efficient option to preserve the native structure of lignin during extraction, albeit with some minor structural changes. 46,80,81 Specifically, the α-OH group in the most abundant β-O-4 linkage was substituted by the alcohol solvent, resulting in the formation of the α-OAlk/β-O-4 structure in the alcohol organosolv lignin. 46,52 This α-alkoxylation has been demonstrated to open new reaction pathways by a nucleophilic addition reaction of alcohol to the active benzylic cations formed under acidic conditions, and thereby preventing undesired condensation reactions.…”