Selective Production of Organic Acids and Depolymerization of Lignin by Hydrothermal Oxidation with Diluted Hydrogen Peroxide

Abstract

There has been a great interest in converting lignin into chemicals, but lignin is not used as feedstock for chemical production at present. Considering the rigid structure of lignin, we have developed a new method to recover chemicals from lignin under severe conditions. This method is the hydrothermal oxidative degradation using 0.1% hydrogen peroxide solution in the flow reactor at 150−200 °C. When alkali lignin was oxidized for 2 min at 200 °C, the total yield of organic acids was as large as 0.45 g/g-lignin. The organic acids consisted of formic, acetic, and succinic acids, and the high-molecular-weight lignin also remained after the oxidation. On the other hand, when organosolv lignin was oxidized at 160 °C, lignin molecules were depolymerized into the oligomer of MW = ca. 300 and the total yield of organic acids was 0.20 g/g-lignin. The product distribution depended on the difference in the structures between the two lignin samples. It was clarified that the proposed method is valid to produce valu...