Highly selective conversion of alkali lignin into aromatic monomers by pulse dielectric barrier discharge plasma at mild reaction conditions

The highly selective conversion of lignin to aromatic monomers is a challenge due to the stubborn structure of lignin and the lack of high-performance catalysts. Herein, we proposed a route for the oxidative degradation of lignin by pulsed DBD plasma at ambient temperature and pressure, while using water as the solvent without catalysts. The discharge at the gas-liquid interface promotes the generation of oxygen-active species, such as OH center dot, O-2(-), O-3, etc., which induces the rupture of the lignin recalcitrant chemical bonds and promotes the generation of aromatic monomers, while the energy consumption of the reaction process is evaluated. Effects of gas type, flow rate, pulse duty cycle and frequency, input power and time on lignin degradation efficiency and energy yield were evaluated. Under optimal conditions, the degradation efficiency of alkali lignin was up to 72.50%, while the energy yield was up to 4.61 g/kW.h. Gas chromatography-mass spectrometry analysis showed that the relative content of aromatic monomers in the product could reach 92.27%, and a possible path for the formation of aromatic monomers was proposed. This study provides a fast, green and economical strategy for the conversion of lignin into aromatic monomers.