Characterization of the precipitated lignin from Japanese beech as treated by semi-flow hot-compressed water

Japanese beech (Fagus crenata) was decomposed by a semi-flow process in hot-compressed water (HCW) at 150 similar to 230 degrees C/10 MPa for 25 min. Mainly hemi-celluloses and partly the lignin moiety of the wood was affected and liquefied in water. A part of the liquefied products can be precipitated after 12 h standing at ambient conditions. The precipitates are composed of around 90% of lignin, which was quantified and characterized by various chemical and spectroscopic methods in comparison of milled wood lignin (MWL), which is considered to be a representative compound for the native lignin in wood. The yield of the precipitated lignin (L-precip) is higher than that of MWL and its syringyl content is also higher as demonstrated by alkaline nitrobenzene oxidation (NBO) giving rise to higher syringaldehyde/vanillin (SA/VA) ratios. Its OH phen group content was also high. The interpretation is that L-precip is mainly from the secondary wall, and accordingly, the presented semi-flow HCW treatment offers the possibility for an efficient lignin isolation.