Comparative study of the topochemistry on delignification of Japanese beech (Fagus crenata) in subcritical phenol and subcritical water

Abstract

Abstract The delignification of Japanese beech (Fagus crenata) has been evaluated under conditions of subcritical phenol (230°C/1.2 MPa) and subcritical water (230°C/2.9 MPa). In the former, more than 90% of the original lignin was decomposed and removed, while in subcritical water, around half of the original lignin was left as insoluble residue. Ultraviolet (UV) microscopic images of the insoluble residues showed that the lignin in the secondary walls is decomposed and removed under both conditions. These images also revealed that the lignin in the compound middle lamella (CML) is resistant to subcritical water, but not to subcritical phenol. Results of alkaline nitrobenzene oxidation of the residual lignin confirmed these observations. Lignin in Japanese beech wood was phenolated by subcritical phenol, which was efficiently removed due to its high solubility in the reactant. It is obvious that CML is rich in condensed-type linkages facilitating rapid solvolysis by phenol. The topochemistry of the plant has a pronounced impact on its delignification behavior.