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. Video Link The video component of this article can be found at https://www.jove.com/video/58575/ 17. This also has precedence in organosolv extraction of lignin, which is a popular method to fractionate lignin. Many variations of this process exist, with the methods employing different temperatures, acid content, extraction times and solvents. Here, the extraction severity has a direct impact on the obtained lignin structure and thus its suitability for further valorization 19,20,21. For example, organosolv lignin produced by the ethanol based Alcell process, operated for 5 years at demonstration scale, had relatively low amount of β-O-4 linkages left as it was operated at relatively high

Microwave‐Assisted Decarbonylation of Biomass‐Derived Aldehydes using Pd‐Doped Hydrotalcites

“…However, the short‐term acute toxicity of 1,4‐dioxane (symptoms include vertigo, drowsiness, anorexia, and ear/nose/lung irritation), and long‐term effects resulting from chronic exposure (such as hepatotoxicity, neurotoxicity, and carcinogenicity in animal models) suggest dioxane is not suitable for the sustainable, large‐scale processing of biomass. The development of greener methods for lignocellulose pretreatment, such as the lignin‐first ethanolsolv process, pave the way for decarbonylation using a bioderived and less hazardous solvent, such as ethanol. Therefore, a solvent screening was conducted using catalyst A to select the optimal solvent; the reactions were performed with closed vials and microwave heating to mitigate boiling point limitations and enable comparison at the same temperature (150 °C).…”

Lignin‐First Fractionation of Softwood Lignocellulose Using a Mild Dimethyl Carbonate and Ethylene Glycol Organosolv Process

“…[6] It is likely that the resulting ethers are less reactive under these conditions. [7] Treatment of lignin with EG under acidic conditions was previously reported by Jasiukaityte-Grojzdek et al, [27] who showedE Gi ncorporation into the lignin structure in a and g positions of the b'-O-4 linkage, even leading to cross-linking of lignin moieties. Additionally, Ono et al [28] studied the incorporation of EG moieties into lignin during softwood acid solvolysis to produce modified lignin, potentially applicable as an amphiphilic polymer and/or functional gels.…”

“…[2,3] Several elegant strategies have been reported for the depolymerization of organosolv lignins; [2,4,5] however, the obtained monomer yields were not only dependento nt he method used but also on the originall ignocellulosef ractionation conditions. [4,[6][7][8] To overcome this, recent attention has shiftedt ol ignin-first strategies, which accomplish the depolymerization of lignin in its native form during the lignocellulose fractionation process. [9] These novel strategies focus on the use of ah eterogeneousm etal catalystand hydrogen gas.…”

“…Also, NMR studies showedp artial condensation in the final lignins as aresult of the isolationprocedure. [6][7][8] Therefore, we set out to investigate the applicationo fo ur previously developedm ethod for the direct treatment of softwood lignocellulose, skipping the tediousl ignin isolation step ( Figure 2). Such as trategy would not differ much from ac lassical lignocellulose fractionation process except the reaction conditions, catalyst, and added stabilization agent (EG) should be specifically tailoredt od eliver the desired monophenolic G-C2-acetal insteado fo rganosolv lignin.…”

Ozone mediated depolymerization and solvolysis of technical lignins under ambient conditions in ethanol

“…This surprising result is likely related to the structural features of this lignin. For instance, the milder organosolv extraction procedure used for this lignin (compared to the Alcell process) results in a structure more similar to native lignin, 71,72 i.e. less condensed and with a higher amount of C-O bonds and methoxy groups (vide supra, Table 1).…”