Lignocellulosic biomass is a source of renewable carbon and is composed of cellulose, hemicellulose and lignin. For a successful bio-refinery, it is imperative to maximize the value obtained from all the lignocellulosic biomass fractions. Various processes have been developed to produce valuable liquid fuels and commodity chemicals from the polysaccharide fractions. Lignin is the largest source of renewable aromatics and, as such, strategies to valorize lignin are required for a bio-refinery to economically compete with fossil-fuel refinery. We developed a lignin-to-bioproduct processing chain for the production of 2-pyrone-4,6-dicarboxylic acid (PDC) through microbial funneling of the phenolic monomers obtained from catalytic depolymerization of lignin. We used chemical and biological upgrading in tandem to produce PDC. We first isolated lignin from the biomass using an acidic γ-valerolactone (GVL) and water solvent system. Process conditions were tuned to minimize lignin degradation during the biomass fractionation. However, the technoeconomic analysis of the processing chain showed the cost of lignin isolation to have the largest impact on the cost of PDC. Therefore, we modified the processing chain to eliminate the costly lignin isolation step by combining biomass fractionation and catalytic depolymerization of the lignin into a single step; while simultaneously preserving the value of the polysaccharide fraction. We demonstrate that the lignin fraction of poplar biomass can be successfully depolymerized by hydrogenolysis over a Pd/C catalyst into a mixture of monomeric and oligomeric phenolic compounds. We show that, using this strategy, we were able to increase the monomer/oligomer product yield. We further show that, using an engineered strain of Novosphingobium aromaticivorans DSM12444, this complex mixture of aromatic compounds can be upgraded to PDC. Combining these improvements on the previous process we demonstrate that the economics of PDC production from lignocellulosic biomass can be improved.

Lignin valorization by integrating chemical depolymerization and microbial funneling: New strategies to produce 2-Pyrone-4,6-dicarboxylic acid

ACS Fall 2021

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