Improvement of hydrothermal gasification of alkaline lignin by oxidative treatment with molecular oxygen

Alkaline oxidation is one of the methods for effective delignification of biomass and structural degradation of lignin. The depolymerized lignin has great potential to be valorized by hydrothermal gasification while little attempts have been made. The present authors subjected an alkaline lignin to oxygen oxidation in Na 2 CO 3 solution and investigated gasification performance of the lignin with a continuous flow reactor. The oxidative treatment decreased the molecular weight of lignin and produced large portions of acid-soluble fractions with a lower molecular weight. The depolymerized lignin was near-completely converted to H 2 , CH 4 and CO 2 at 340 °C with a Ru/C catalyst. The Ru/C catalyst maintained its activity for at least 480 min, with a negligible amount of coke deposition (1.0 %-C/h on average) and liquid effluent containing 55 − 150 ppm of organic carbon. The gasification efficiency of the depolymerized lignin achieved by Ru/C was superior to that of the raw lignin.