Effect of Various Microwave Absorbents on the Microwave-Assisted Lignin Depolymerization Process

Microwave absorbents play a vital role in governing the monomeric products from lignin during the microwave-assisted depolymerization (MAD) process. The influence of various microwave absorbents on the conversion efficiency and lignin monomeric products in a dynamic vapor flow reaction system was investigated. Results showed that the selected microwave absorbents could linearly and rapidly heat lignin from 200 to 500 °C within 8 min under a microwave power of 1000 W. The yields of liquid products, guaiacols, and phenols were increased linearly with the heating rate (°C/min). The high microwave absorptivity of absorbents promoted the formation of liquid products and phenolic compounds. To offer further support, the use of MoS2 with a very high microwave absorptivity (185.0 °C/min) showed very high yields of liquid products (34.1 wt %) and phenolics (32.1 wt %). This work provided an effective methodology to enhance the lignin conversion efficiency to monomeric products using microwave absorbents.