Delignification Mechanism during High-Boiling Solvent Pulping Part 3. Structural Changes in Lignin Analyzed by 13C-NMR Spectroscopy

Abstract

Summary Milled wood lignin as well as wood meal from todo fir (Abies sachalinensis MAST) was treated with 70% aqueous 1,4-butanediol solution at 220°C without acid catalyst in order to elucidate the delignification mechanism during high-boiling solvent (HBS) pulping. HBS lignin was recovered from black liquor by precipitation, and was subjected to gel permeation chromatography and quantitative 13C-NMR study. The average molecular weight of MWL decreased. The content of phenolic hydroxyl groups in MWL increased from 0.28 to 0.68/OMe. The decrease in the content of β-O-4 substructures was evident, which may be attributed to the homolytic cleavage of phenolic β-aryl ethers. The changes in the content of β-5 and β-β substructures were rather small. The benzyl ether formation of β-O-4 structures with 1,4-butanediol was also confirmed by 13C-NMR. However, the signals corresponding to Hibbert's ketones were not observed, which suggests that acidolysis was not an important degradation pathway during HBS pulping.

Lignin Structural Changes During Liquefaction in Acidified Ethylene Glycol

“…Thus, the larger LGS fragments, which had an increased molar mass, are simultaneously converted into LBP constituents, leaving only low-molecular mass lignin-derived subunits in LGS-240. This is confirmed with the newly appeared signals (30,31,27,28) corresponding to the carbonyl groups and signals (18,19,20) characteristic of the non-etherified syringic acid and syringic acid ester. From the obtained results the assumption could be made that lignin degradation products are further modified mainly by esterification and etherification with EG.…”

“…Principal differences between the LGS spectra at the beginning and at the end of the treatment were observed in the aromatic carbon region. The signals in the aromatic carbon region (102.0 to 193.0 ppm) in LGS-5 and LGS-240 spectra shown in Figure 7 were designated according to the literature [28][29][30] and summarized in Table 7.…”

“…The comparison of the LGS-5 and LGS-240 spectra revealed a significant decrease of signals (22,23,24) corresponding to the non-etherified syringyl and guaiacyl substructures Downloaded by [Edita Jasiukaityte-Grojzdek] at 10:59 11 July 2012 and the appearance of peaks (30,31,27,28) characteristic to the carbonyl (C = O) groups in aliphatic, aromatic esters and acids. In addition, the overall reduction of signal intensity in aromatic carbon region may be attributed to the formation of larger lignin-EG structures with reduced solubility in water followed by their elimination from LGS with time as was determined by SEC.…”

Dissolution and acetylation of ball-milled birch (Betula platyphylla) and bamboo (Phyllostachys nigra) in the ionic liquid [Bmim]Cl for HSQC NMR analysis

“…Then, the extractive free birch and bamboo meals were ball-milled for 8 h and then extracted with dioxanewater (96:4, v/v). The isolated MWLs were purifi ed as described by Kishimoto et al (2003Kishimoto et al ( , 2004 . The yields of birch and bamboo MWLs were 5.8 % and 1.4 % , respectively, based on the extractive free dry plant material.…”

Enhancement of Lignin Biopolymer Isolation from Hybrid Poplar by Organosolv Pretreatments

“…In addition, ethanol-based organosolv pretreatment has been studied for different types of LCM including hardwoods (e.g., willow [20], poplar [21]), softwoods (e.g., lodgepole pine [22,23]), and herbaceous crops (e.g., miscanthus [5,17]). Other alcohols such as methanol and 1, 4-butanediol have also been explored in previous literature [24][25][26]. So far, most studies have just investigated the effect of single alcohol on the lignocellulosic pretreatment.…”