ACS Sustainable Chemistry & Engineering March 2020

Abstract

A continuous process to depolymerize maple wood lignin dissolved in γ-valerolactone (GVL) to monomeric phenols is demonstrated in a stirred reactor using a mesoporous Zr-KIT-5 catalyst. The yield of identified aromatic monomers is stable for 18 h of continuous operation and reaches 7 wt % when the lignin feed is subjected to thermo-solvolytic pretreatment. Without the thermal pretreatment, the monomer yield is only 2.3 wt %. The thermal pretreatment causes partial lignin depolymerization (0.8 wt % monomer yield) improving catalyst pore accessibility of the lignin fragments. The 7 wt % monomer yield observed in the two-step lignin depolymerization route surpasses monomer yields observed in batch processes using identical feeds: ∼2.6 wt % during hydrogenolysis in methanol over Pd/C catalyst and ∼1.6 wt % with a microporous H-ZSM-5 catalyst. While the major monomers observed in the various techniques are guaiacol, syringol, and phenolic derivatives, their relative distribution varies depending on the technique. The demonstration of continuous acid-catalyzed lignin depolymerization solution with stable activity and high monomer yields, eliminating the need for additional reagents and issues related to handling solid lignin feed, represents a significant advance in lignin depolymerization science and technology.

Citation

Kakasaheb Y. Nandiwale, Andrew M. Danby, Anand Ramanathan, Raghunath V. Chaudhari, Ali Hussain Motagamwala, James A. Dumesic, and Bala Subramaniam. Enhanced Acid-Catalyzed Lignin Depolymerization in a Continuous Reactor with Stable Activity. ACS Sustainable Chemistry & Engineering 2020 8 (10), 4096-4106