Fundamental Insights on the Physical and Chemical Properties of Organosolv Lignin from Norway Spruce Bark

Abstract

The interest in the bark and the attempt to add value to its utilization have increased over the last decade. By applying an integrated bark biorefinery approach, it is possible to investigate the recovery of compounds that can be used to develop green and sustainable alternatives to fossil-based materials. In this work, the focus is on extracting Norway spruce ( Picea abies ) bark lignin via organosolv extraction. Following the removal of the extractives and the subcritical water extraction to remove the polysaccharides, a novel cyclic organosolv extraction procedure was applied, which enabled the recovery of lignin with high quality and preserved structure. Main indicators for low degradation and preservation of the lignin structure were a high β-O-4′ content and low amounts of condensed structures. Furthermore, high purity and low polydispersity of the lignin were observed. Thus, the obtained lignin exhibits high potential for use in the direct development of polymer precursors and other bio-based materials. During the extraction sequence, around 70% of the bark was extracted. Besides the lignin, the extractives as well as pectic polysaccharides and hemicelluloses were recovered with only minor degradation, which could potentially be used for the production of biofuel or other high-value products such as emulsifiers or adhesives.

Organosolv biorefinery: resource-based process optimisation, pilot technology scale-up and economics

“…The extractives are the less developed family of chemicals studied after organosolv treatment because they are generally separated by a pre-treatment. 22 However, two recent publications studied the recovery of extractives from spent coffee grounds and exhausted olive pomace, using the organosolv process by the application of a solvent mixture composed of methanol/hexane or ethanol/ water in the presence of sulfuric acid, which found use as the catalyst. Afterwards, the extractives were converted to fatty acids (fatty acids methyl esters and omega-3 fatty acids).…”

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

“…The formation of the α-OAlk/ β-O-4 structure in organosolv lignin extracted using alcohols under acidic conditions has been well understood, i.e., the etherification of the Cα position occurs through a nucleophilic addition reaction of an alcohol to the benzylic cation that is formed under the acidic conditions (Scheme 4A). 52 However, as shown in Scheme 4B, the formation of the alkyl-O-alkyl ether structure associated with QMs during alkali-catalyzed alcohol extraction of lignin is not yet investigated in detail. Especially the main factors determining its formation outcome are, however, not very clear.…”

“…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. 47,49,82 The extent of this α-alkoxylation was reported to depend both on the aromatic composition of the lignin and the chain length of the alcohol.…”

Pyrolysis and Extraction of Bark in a Biorefineries Context: A Critical Review

“…Therefore, it is important to analyze these works. The bark-based biorefinery studies were performed using barks such as Norway spruce, Scots pine, radiata pine, birch, and aspen, based on a previous screening and evaluation of potentially valuable chemical components including extractives, non-cellulosic polysaccharides (mostly pectin and starch), lignin, cellulose, and suberin [27,[29][30][31][32][33][34] (Figures 4-10). Interestingly, although almost all of these studies considered extraction as the first step, they did not consider a further refinement of extracts.…”