Hydrogenolysis Offers an Improved Method to Break Down Lignin

The Science

Explore lignin hydrogenolysis in a continuous-flow reactor as a method to improve depolymerization.

• Evaluated the kinetics and reaction mechanisms of lignin hydrogenolysis in a continuous-flow reactor.
• Optimized reaction parameters to increase monomer yield and suppress formation of unwanted byproducts.
• Assessed hydrogenolysis of lignin isolated from poplar.

The Impact

• Lignin hydrogenolysis in the continuous-flow reactor produced lignin-derived monomer yields around 29%, close to the calculated theoretical maximum for lignin from pretreated biomass.
• Unreacted lignin retained its native structure, allowing material to be recycled through the reactor to minimize carbon loss into unusable compounds.
• Combining a continuous-flow reactor with biomass treatment processes could enhance the yield and value of product streams from a biorefinery.

Summary

Researchers performed reaction kinetics and mechanistic studies on lignin model compounds to understand lignin hydrogenolysis pathways, demonstrating that lignin end-units and internal units react significantly differently. Understanding the reaction mechanism and its sensitivity to variables helped researchers establish a continuous lignin upgrading process from various fractionated lignins. Near-theoretical yields of lignin platform monomers with >80% overall product selectivity were obtained in a continuous hydrogenolysis process using a Pd/C catalyst.

References

Li, Y., B. Demir, L. M. Vázquez Ramos, M. Chen, J. A. Dumesic, J. Ralph. 2019. “Kinetic and Mechanistic Insights into Hydrogenolysis of Lignin to Monomers in a Continuous Flow Reactor,” Green Chemistry 21(13), 3561–72. DOI:10.1039/c9gc00986h.