Effect of acetic acid (AcOH) addition on chemical conversion of Japanese beech (Fagus crenata), as a hardwood, and Japanese cedar (Cryptomeria japonica), as a softwood, was investigated in the course of treatment in a semi-flow reactor with hot-compressed water (H-CW). One-step treatment of Japanese beech was preliminarily performed to examine the effect of AcOH concentrations on the decomposition behavior at 150–290°C/10 MPa/30 min. Based on the obtained results, two-step semi-flow H-CW treatment with 1 wt% AcOH at 210°C/10 MPa/15 min (1st stage) and 260°C/10 MPa/15 min (2nd stage) was thus selected as the most appropriate treatment and a comparative study of the two woods was accordingly conducted. The differences in decomposition behavior observed between the two woods clearly proved that the addition of AcOH played an important role in enhancing the hydrolysis and decomposition of cell wall components in Japanese cedar due to the lesser amount of acetyl residue in softwood hemicelluloses and its lignin structure.
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