THE EFFECT OF INITIAL ACID CONCENTRATION ON THE LIGNIN ISOLATED BY THE ACIDOLYSIS OF ASPEN WOOD

Publisher Website
Google Scholar
Abstract
A further study has been made of the isolation, by acidolysis, of lignin from aspen wood meal (Populustremuloides Michx.) using a dioxane–water (9:1) solvent medium containing hydrogen chloride and a low extraction temperature of 87 ± 2° for a short extraction time of 0.5 hour. Lignins so isolated included those: (a) under different initial acid concentrations of 0.0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, and 1.7 equivalents of HCl/liter of solvent medium; (b) from successive extractions under increasing initial acid concentrations of 0.2, 0.4, 0.8, and 1.6 equivalents/liter; and (c) from successive extractions under constant initial acid concentrations of 0.2 equivalent/liter.All the lignin fractions so isolated were studied with respect to their yield, methoxyl content, infrared absorption spectra, and the yields of vanillin and syringaldehyde obtained from them by oxidation using alkaline nitrobenzene.Evidence is presented in support of the non-homogeneity of the whole protolignin. This may be the result of the presence of possibly two basic types. One fraction, comprising around 70–85%, is most readily extracted, has a consistently high methoxyl content (ca. 21%), and is capable of being oxidized to give high yields of syringaldehyde and vanillin in a ratio close to 2.5:1. The second fraction is characterized by a greater difficulty of extraction, lower methoxyl content, and significantly lower yields of the aldehydes in a ratio closer to 1:1.