Kinetics of Oxidative Degradation of Lignin-Based Phenolic Compounds in Batch Reactor

Vanillin, vanillic acid, acetovanillone, syringaldehyde, syringic acid, and acetosyringone are products obtained from lignin oxidation in an alkaline medium. The evaluation of their individual degradation under oxidation conditions mimicking lignin oxidation is an important tool to better understand this reaction and maximize the yield of target value-added products. In this context, the main objective of the present work was to study the kinetics of degradation of the selected lignin-based phenolic compounds. The effect of temperature, initial concentration, and oxygen partial pressure was evaluated, and a simple mathematical model was developed to describe the data from the degradation of the phenolics during oxidation reactions. The results indicate that, for all the evaluated compounds, the reaction order is first order with respect to both the initial phenolic compound concentration and oxygen concentration. A high degradation rate was found for the reactions performed at 413 K, and an activation energy in the range of 53–86 kJ/mol was found for all the studied phenolic compounds. Moreover, syringic acid is the phenolic compound more prone to degradation, while vanillin is the less one.