(471a) Structural Characterization of Lignins Isolated From Birch Wood During Ionic Liquids-Based Biorefinery Process

The use of ionic liquids (ILs) in biomass pretreatment has received considerable attention recently because of their effectiveness at decreasing biomass recalcitrance to subsequent enzymatic hydrolysis. To understand the structural changes of lignin during pretreatment and enzymatic hydrolysis process, in the present study, an ionic liquid lignin (ILL) and enzymatic mild acidolysis lignin (EMAL) was sequentially isolated with high yield (43.4% based on Klason lignin) and purity from ball-milled birch wood. The structural characteristics of the lignins were elucidated using Fourier transform infrared spectroscopy (FT-IR), quantitative ¹³C-NMR, two-dimensional heteronuclear single-quantum coherence (2D-HSQC) NMR spectroscopy, and gel permeation chromatography (GPC). Quantitative ¹³C and 2D-HSQC NMR analysis indicated that ILL and EMAL exhibited similar structural features. The main substructures in birch wood were aryl ether (β-O-4′), resinol (β-β′), and phenylcoumaran (β-5′), and their abundances per 100 Ar units varied from 58.2 to 63.1, from 11.1 to 10.3, and from 1.4 to 1.5, respectively. The S/G ratios were estimated to be 2.2 and 3.2 for ILL and EMAL, respectively. In addition, the molecular weight (M_w) of ILL (7780 g/mol) was lower than that of EMAL (8900 g/mol). The lignin fractions show uniform lignin fragments with lower polydispersity index (PDI). Furthermore, to investigate the relationship between quantitative structures and thermal properties, thermo-gravimetric analysis (TGA) and differential scanning calorimetry was also applied on the lignins.

 Key words: ionic liquid; quantitative structural characteristics; β-O-4′; lignin; thermal properties

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Institute of Biomass Chemistry and Technology, Beijing Forest University, Beijing,

100083, China; Tel.: +86-10-62336972; Fax: +86-10-62336972;

E-mail address: rcsun3@bjfu.edu.cn (R.C., Sun)