Lignin Valorization

When using biomass polysaccharides for generation of bioproducts, lignin is typically considered waste material. This lignin stream, however, represents an energy-dense, carbon-rich, and aromatic feedstock that can be used to create a range of renewable products including aromatic phenolic/chemicals, carbon fibers, advanced polymer composites, etc. Thus, we have projects focused on advancing lignin fractionation and conversion technologies.

The amount of underutilized lignin that is already available could displace a significant fraction of the non-renewable feedstocks that are currently used for the production of aromatic chemicals. However, the biological purpose of lignin (i.e., cell wall strength and rigidity) makes depolymerization difficult, and thus it is very challenging to selectively disassemble lignin into its constituent aromatic monomer. We want to understand the catalytic mechanism, transport phenomena, and reaction pathways that control selective depolymerization of lignin into aromatic chemicals.

We are studying hybrid conversion approaches (one that integrates catalytic depolymerization and microbial upgrading) for the production of value-added compounds from lignin. Most natural biological systems do not have a significant ability to depolymerize lignin. However, there are microbial systems that can utilize phenol and a range of other lignin-derived compounds. These systems can funnel a wide-distribution of lignin-derived compounds into a single biological intermediate and upgrade them via metabolic pathways. We want to probe which compounds in the lignin-derived products that are preferred substrates (and why) as well as adjust catalytic and processing conditions to increase yield and selectivity towards those compounds.

There is an urgent need for biomass processing technologies that 1) fully exploit the potential of biomass as a feedstock, 2) provide access to a diverse set of commodity and value-added products, 3) use less harsh processing conditions, and 4) minimize degradation and waste formation. Accordingly, the economical, sustainable, and scalable fractionation of biomass into separate lignin and carbohydrates with maximized control over the resulting molecular characteristics of each fraction is a major key to the valorization of biomass.

My lab has developed an expertise (to be used in this study) that focuses on the analysis of lignin and lignin depolymerization products in an effort to capture and then resolve the molecular com-plexity of lignin as a catalytic substrate and of lignin depolymerization product mixtures as catalytic intermediates and products. Our goal has been to adopt and develop methods (1) that facilitate quantitative analysis such that mass balances for lignin depolymerization reactions can be formed and (2) that can be used to resolve complex reaction networks. Thus, multiple analysis tools are re-quired to profile lignin and lignin depolymerization products in a manner that can inform catalysis research.