Reactive organosolv lignin extraction from wheat straw: Influence of Lewis acid catalysts on structural and chemical properties of lignins

Lewis acids have been studied as catalysts in the organosolv treatment of wheat straw. Fractionation of the lignocellulosic biomass and fragmentation of lignin have been performed in aqueous ethanol in the presence of FeCl2, CuCl2, FeCl3, Ga(OTf)(3), ZrOCl2 or Sc(OTf)(3). The lignins were characterised in terms of molecular weight, beta-O-4 linkage content and chemical functions through size exclusion chromatography; thioacidolysis; P-31 and C-13 NMR spectroscopies. The degree of delignification and the yield of Klason lignin increased with the hardness of the Lewis acid. About half of the delignification products were Water-soluble monomers and oligomers. The nature of the Lewis acid influenced also the characteristics of the precipitated lignins. The molecular mash, the amount of OH groups and of aliphatic C-O bonds decreased as cation hardness increased. (C) 2014 Elsevier B.V. All rights reserved.