Microwave-Assisted Lignin Wet Peroxide Oxidation to C4 Dicarboxylic Acids

Innovative methodologies, such as microwave-assisted reaction, can help to valorize lignin with higher productivity and better energy efficiency. In this work, microwave heating was tested in the wet peroxide oxidation of three lignins (Indulin AT, Lignol, and Eucalyptus globulus lignins) as a novel methodology to obtain C-4 dicarboxylic acids. The effect of temperature, time, and catalyst type (TS-1 or Fe-TS1) was evaluated in the production of these acids. The TS-1 catalyst improved succinic acid yield, achieving up to 9.4 wt % for Lignol lignin. Moreover, the microwave heating specifically enhanced Lignol conversion to malic acid (34 wt %), even without catalyst, showing to be an attractive path for the future valorization of organosolv lignins. Overall, compared to conventional heating, microwave heating originated a rapid lignin conversion. Nevertheless, for prolonged times, conventional heating led to better results for some target products, e.g., malic and succinic acids.

Automated summary

This study investigates the utilization of microwave-assisted reaction for the wet peroxide oxidation of lignins. The results show that the TS-1 catalyst improves the yield of succinic acid from lignins. Additionally, microwave heating enhances the conversion of Lignol lignin to malic acid, making it an attractive method for future valorization.