Biphasic extraction of mechanocatalytically-depolymerized lignin from water-soluble wood and its catalytic downstream processing. Issue 12 (22nd February 2017)

• Record Type: Journal Article
• Authors: Calvaruso, Gaetano; Clough, Matthew T.; Rinaldi, Roberto
• Is Part Of: Green chemistry. Volume 19:Issue 12(2017)
• Page Start: 2803
• Page End: 2811
• Publication Date: 2017-02-22
• Subjects: Environmental chemistry -- Industrial applications -- Periodicals; Environmental management -- Periodicals; 660
• DOI: 10.1039/c6gc03191a
• Languages: English
• ISSNs: 1463-9262

Abstract

Abstract : During saccharification of water-soluble wood, a dual 2-MeTHF/water solvent system enables extraction of low molecular weight lignin fragments. Abstract : Mechanocatalysis is an efficient method for deep depolymerization of lignocellulosic materials. It renders full conversion of lignocellulose into water-soluble products, a mixture of oligosaccharides and lignin oligomers. In an aqueous monophasic system, it is known that further saccharification of these products affords high yields of fermentable sugars in addition to a lignin precipitate. Although much attention has been devoted to upgrading of the carbohydrate fraction, the reactivity of mechanocatalytically-isolated lignin has hitherto been overlooked. In this report, we demonstrate the saccharification of water-soluble lignocellulose in a biphasic mixture of water and 2-methyltetrahydrofuran, to prevent lignin fragments from recondensation, not only with other lignin fragments but also with oligosaccharides and their degradation products. The lignin stream extracted in the biphasic system exhibits a molecular weight much lower than that of the lignin precipitate obtained from monophasic aqueous saccharification, and that of lignin isolated by an Organosolv process with no added acid catalyst. Surprisingly, β-O-4 and phenylcoumaran (β-5 + α-O-4) linkages are quantitatively hydrolyzed during saccharification in the biphasic system. However, the extracted lignin still incorporates resinol bonding motifs (β-β + γ-O-α). Because of the lower molecular weight, low carbohydrate content, and high solubility in organic solvents, the catalytic downstream processing of the extracted lignin leads to higher yields of liquid products ( e.g. 2-methoxyphenols and 2, 6-dimethoxyphenols) by RANEY® Ni-catalyzed hydrogenolysis (200 °C, 7 MPa H2 ), compared to reactions performed on the lignin precipitate or Organosolv lignin.