Effect of autohydrolysis of Eucalyptus globulus wood on lignin structure. Part 1: Comparison of different lignin fractions formed during water prehydrolysis

Abstract

The effect of autohydrolysis of Eucalyptus globulus wood was studied with regard to conditions applied in a prehydrolysis-kraft process on the physico-chemical properties of lignin obtained in both the wood residue and hydrolysate. As a reference, milled wood lignin (MWL) was isolated from native wood and compared to three lignin fractions formed during prehydrolysis: 1) lignin from the wood residue isolated as MWL, 2) lignin precipitated from the prehydrolysate during cooling and separated by centrifugation, and 3) lignin degradation products soluble in the prehydrolysate extracted with ethylacetate. All lignin fractions were subjected to Fourier transform infrared (FTIR) spectroscopy, methoxy group determination, elemental analysis, size exclusion chromatography and quantitative nuclear magnetic resonance (NMR) spectroscopy. The results indicate that extensive lignin degradation occurs during prehydrolysis through homolytic cleavage of the aryl-ether bonds resulting in a substantial molecular weight loss of the residual lignin in the treated wood and in the lignin fractions isolated from the prehydrolysate. The aryl-ether cleavage is coupled with a strong increase in phenolic hydroxyl groups and a decrease in aliphatic hydroxyl groups. Indication for condensation reactions were found by NMR spectroscopy.

Impact of Hot-Water Extraction on Acetone-Water Oxygen Delignification of Paulownia Spp. and Lignin Recovery

“…This beneficial effect of HWE may be attributed to the resulting changes in the physicochemical structure of wood, including an increase in porosity, a higher content of phenolic hydroxyl groups, a lower molecular weight of residual lignin, and, most likely, a weaker association between lignin and carbohydrates in extracted wood [1,8,9,[42][43][44][45]. Between the two Paulownia species, both exhibit same remarkable DS in AWO after HWE; the DD of E Parr PT is greater than that of E Parr PE, indicating a more disrupted physicochemical structure of hot-water extracted PT wood (in accordance with its greater solubility and DD in Table 2).…”

Optimal conditions for hemicelluloses extraction from Eucalyptus globulus wood: hydrothermal treatment in a semi-continuous reactor

“…It is also remarkable that the kinetics for cellulose fractionation are always lower than the kinetics for hemicellulose degradation, which agrees with the fact that cellulose is stronger than hemicellulose against hydrothermal degradation. [56].…”

Alternative Technologies for Biofuels Production in Kraft Pulp Mills—Potential and Prospects

“…Their content is determined by the auto-hydrolysis duration. This change in the lignin reactivity during hydrolysis can make the processing of PHL very difficult, affecting also the efficiency of subsequent cooking operations [61]. Since the content of degradation products are determined by the auto-hydrolysis duration, the time becomes an important aspect for the feasibility study.…”