Efficient separation and physico-chemical characterization of lignin from eucalyptus using ionic liquid–organic solvent and alkaline ethanol solvent
2013
Sun, Yong-Chang | Xu, Ji-Kun | Xu, Feng | Sun, Runcang
Ionic liquid (IL) 1-butyl-3-methylimidazolium acesulfamate ([BMIM]Ace)-organic solvents mixtures were utilized in the dissolution and extraction of lignin from eucalyptus. The resulting carbohydrate-enriched materials were subsequently extracted with 70% ethanol containing 1M NaOH. The results showed that the yield of alkaline ethanol lignin (AEL, 8.0–23.3%) was relatively higher than that of IL–organic solvents lignin (IOL, 11.5–15.4%, based on the Klason lignin content). The chemical structures of the lignin fractions obtained were characterized by carbohydrate analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), and 2 D HSQC nuclear magnetic resonance (NMR) spectroscopy. The IOL fractions exhibited a larger molecular weight (Mw, 9050–6590g/mol) and a higher polydispersity compared to the AEL fractions (Mw, 3820–2440g/mol) except for IL–dioxane lignin (Mw, 1005g/mol). Moreover, 2 D NMR spectra of ILL and AEL fractions showed a predominance of β-O-4′ aryl ether linkages (77.4 and 79.0% of total side chains, respectively), followed by β–β′ resinol-type linkages (12.1 and 13.8%), and lower amounts of β-5′ (4.2 and 3.3%) and spirodienone linkages.
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