Depolymerization of Native Lignin into Vanillin, Vanillic Acid, and Other Related Compounds via Alkaline Aerobic Oxidation: Reaction Mechanisms and Process Control Using Organic Cations

Abstract

Vanillin is one of the platform chemicals in industry, which is used not only as a traditional fragrance but also as a raw material for medicines and polymer materials. Industrial vanillin production by alkaline aerobic oxidation of lignin is carried out with degradation of lignosulfonate at temperatures around 170°C under pressurized air in the presence of Cu2+ as a catalyst. However, this method has problems such as low vanillin yields and by production of sulfur-containing wastewater, and various studies have been conducted to solve them. Research on the mechanism of the vanillin formation reaction by aerobic oxidation of lignin and the search for a method to control this reaction has also been conducted. In this chapter, we review relevant studies from the above perspective, mainly those conducted by the authors’ research group.