Valorization of alkaline lignin and optimization of vanillin production by heterogeneous Fenton-type catalysts

Abstract

Fenton processes are a promising approach toward high-value chemical production from waste lignin. In this study, heterogeneous Fenton oxidation was employed to convert alkaline lignin into vanillin. The effects of Fe⁰, Fe²⁺, Fe³⁺, and H₂O₂ concentrations, temperature (25–50 °C), and reaction time (15–60 min) on vanillin production from lignin was investigated using response surface methodology under a three-level factorial design. The study reveals that the concentrations of Fe⁰, Fe²⁺, Fe³⁺, and H₂O₂ had an important effect on vanillin yield, whereas reaction temperature and time had positive effects on the process of vanillin production. Based on the numerical optimization and desirability function, the optimum conditions were 38.05 mg/L Fe⁰, 49.45 mg/L Fe²⁺, 71.35 mg/L Fe³⁺, and 1884.4 ppm H₂O₂ at 41.404 °C for 60 min at pH 3. Under these conditions, the vanillin yield obtained was 0.690%, which was increased by 2.59-fold from lignin. The experimental results agreed with the predicted values. We show that heterogeneous Fenton oxidation has the potential to convert lignin into high-value aromatic compounds when carried out under optimum conditions.