Quantitative Structures and Thermal Properties of Birch Lignins after Ionic Liquid Pretreatment

Abstract

The use of ionic liquid (IL) in biomass pretreatment has received considerable attention recently because of its effectiveness in decreasing biomass recalcitrance to subsequent enzymatic hydrolysis. To understand the structural changes of lignin after pretreatment and enzymatic hydrolysis process, ionic liquid lignin (ILL) and subsequent residual lignin (RL) were sequentially isolated from ball-milled birch wood. The quantitative structural features of ILL and RL were compared with the corresponding cellulolytic enzyme lignin (CEL) by nondestructive techniques (e.g., FTIR, GPC, quantitative (13)C, 2D and (31)P NMR). The IL pretreatment caused structural modifications of lignin (cleavage of β-O-4 ether linkages and formation of condensed structures). In addition, lignin fragments with lower S/G ratios were initially extracted, whereas the subsequently extracted lignin is rich in syringyl unit. Moreover, the maximum decomposition temperature (T(M)) was increased in the order ILL < RL < CEL, which was related to the corresponding β-O-4 ether linkage content and molecular weight (M(w)). On the basis of the results observed, a possible separation mechanism of IL lignin was proposed.

Understanding the Mechanism of Self-Bonding of Bamboo Binderless Boards: Investigating the Structural Changes of Lignin Macromolecule during the Molding Pressing Process

“…The aliphatic OH content of gradually decreased (from 3.71 to 0.59 mmol/g) with the elevated molding press temperature, implying that the hydroxyl groups in the side-chain of lignin were partly oxidized and eliminated during molding. A similar phenomenon was reported in other pretreatment processes (Wen et al 2012. The S and G-type phenolic hydroxyl groups in these MWLs were greatly increased compared with raw MWL.…”

“…The weight average molecular weight (Mw) and number average molecular weight (Mn) of the non-acetylated MWLs were determined with gel permeation chromatography (GPC) as previously described (Wen et al 2012). For the quantitative 13 C NMR spectra (C13IG), lignin (140 mg) was dissolved in 0.5 mL of DMSO-d6, and 20 μL of relaxation agent (0.01 M chromium (III) acetylacetonate) was added (Holtman et al 2006).…”

Structural Characterization of Lignin and Its Degradation Products with Spectroscopic Methods

“…IL provides an alternative path for lignin removal to classic organosolv pretreatment for enhancing subsequent enzymatic hydrolysis and isolation. Some ILs, such as 1-ethyl-3-methylimidazolium acetate, can extract lignin from poplar and birch with most structural features retained [36]. Some acidic ILs, such as 1-H-3-methylimidazolium chloride, will hydrolyze ether linkages [37] and further degrade lignin.…”

Investigation of the Chemocatalytic and Biocatalytic Valorization of a Range of Different Lignin Preparations: The Importance of β-O-4 Content

“…Alternative extraction methods such as ionic liquid pretreatments seek to combine cellulose isolation with high quality lignin production. 19,20 In spite of a range of lignin valorisation methods noted above, there are only a few observations in the literature concerning the advantages or disadvantages of different lignin isolation methods for downstream lignin valorisation. Kraft lignin has been found to give lower yields of lignin valorisation products in some biocatalytic processes, 11,14 and Bouxin et al have found variable yields of chemocatalytic reduction products using four different lignin preparations.…”