Characterization of Ionic Liquid Lignins Isolated from Spruce Wood with 1-Butyl-3-methylimidazolium Acetate and Methyl Sulfate and Their Binary Mixtures with DMSO

Abstract

Ionic liquids (ILs) based on 1-butyl-3-methylimidazolium (bmim) cation have proved to be promising solvents for the fractionation of plant biomass with the production of cellulose and lignin. This study deals with the characterization of lignins isolated from coniferous (spruce) wood using [bmim]OAc and [bmim]MeSO4 ionic liquids and their binary mixtures with DMSO (80:20). Molecular weight distributions, functional composition, and structural features of IL lignins were studied by size-exclusion chromatography, NMR spectroscopy (1D and 2D) and atmospheric pressure photoionization high-resolution mass spectrometry. It was shown that the interaction of ILs with lignin leads to significant chemical changes in the biopolymer; a decrease in the degree of polymerization and in the content of free phenolic hydroxyl groups due to alkylation, the disappearance (in the case of [bmim]OAc) of carbonyl groups and a significant destruction of β-O-4 bonds. The chemical reactions between lignin and 1-butyl-3-methylidazolium cation with covalent binding of ionic liquids or products of their decomposition is evidenced by the presence of a large number of nitrogen-containing oligomers in IL lignins.

Application of 2D NMR Spectroscopy in Combination with Chemometric Tools for Classification of Natural Lignins

“…Qualitative analysis of 2D HSQC NMR spectra of the studied lignins and pseudo-NMR spectra representing loading plots of the main components was carried out by comparison with data from the literature sources [5,9,22,[28][29][30][31][32]. The correctness of the identification was confirmed by the presence of all characteristic cross-peaks of the indicated fragments and the compliance of their chemical shifts with the literature data.…”

“…Despite the fact that there are a large number of publications devoted to the structure of lignins of various origins [1][2][3][4][5], many aspects in this field still remain unclear due to its exceptional complexity. Naturally, the structure of lignin is primarily determined by the botanical origin of the biopolymer [5], but it also depends on the procedure used for isolating lignin preparations from the plant material [1,[6][7][8][9]. At the same time, a number of recent studies showed that lignin structure can be additionally complicated due to the incorporation of non-typical moieties, such as catechin-type phenylpropane units (C) [4] and flavonoids (for example, tricin) [5,10].…”

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

“…The lignin fraction recovered aer IL pretreatment possesses a lower content of interunit ether bonds and is partly condensed. 239,240 Additionally, condensation reactions between the lignin and the IL may occur, at an extent that increases with the operating temperature. 239,240 Overall, the IL lignin fractions possess similar features to organosolv lignin streams and are regarded as a promising substrate for further upgrading toward aromatic chemicals.…”

Are Bio-Based Solvents Helpful in Controlling Environmental Pollution? Insights from The BRICS Countries

“…Abushammala and Mao [27] emphasised the effect of IL structure on the dissolving of wood and the different challenges encountered during the dissolution process. ILs such as 1-butyl-3-methylimidazolium methyl sulfate and 1butyl-3-methylimidazolium acetate are used to fractionate biomass from plants to produce lignin and cellulose [28]. Lignin from wood can be extracted effectively using protic ionic liquid 1-methylimidazolium chloride [29].…”