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 valuable chemicals from any kind of lignin.