Hybrid Chemical and Biological Valorization of Residual Biorefinery Lignin

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PI name: Zhiyou WenProposal number: 1605034Plant biomass such as wood, grass straw, and agricultural residues represent an abundant, cheap, and renewable feedstock for the production of liquid transportation fuels and chemicals. Biomass consists mainly of the carbohydrate polymers cellulose and hemicellulose, and the complex phenolic polymer lignin. The cellulosic biorefinery is in emerging platform for large-scale biofuels production that converts the cellulosic and hemicellulosic fractions to sugars, which are then fermented to produce bioethanol. A byproduct of this process is the residual lignin in the plant biomass. After cellulose, lignin is the second-most abundant biopolymer on Earth and accounts for 15-40% of plant biomass. Although lignin is an energy-rich material, it is difficult to convert into biofuels and is often simply burned for heat, a relatively low-value application of this resource. A cost-effective method for utilizing lignin is needed to improve economic viability and environmental sustainability of the biorefinery. This project seeks to convert the lignin into a biofuel feedstock by an innovative two-step process. The first process converts the lignin byproduct into a dense oil by heating it up in the absence of air, a process called pyrolysis, and the second process uses bacteria to break down the complex pyrolysis oils to aromatic compounds which can be made into fuels and chemicals. The educational activities associated with this project include hands-on outreach activities for middle and high-school students on the topics related to biomass utilization using Lego toys which resemble biomass biopolymers.The overall goal of the research is to develop and gain fundamental understanding of a hybrid pyrolysis-bioconversion process to make biofuel precursors from biorefinery residual lignin. The proposed process enables the bioconversion of lignin-derived phenolic monomers to fuels and chemicals in a two-step process. The first step focuses on the thermocatalytic depolymerization of lignin into heterogeneous phenolic monomers. In the second step, the various monomers generated by lignin pyrolysis are then microbially converted into the catechol and protocatechute, which enter central metabolism and are then converted into acetyl-CoA and pyruvate, two key metabolic precursors for the production of various advanced biofuels and chemicals. The project has three research objectives. The first objective is to characterize of the lignin monomers derived from the fast pyrolysis process. The second objective is to study the capability of selected bacterial strains to utilize these lignin monomers, and then explore how tailoring the conditions of the pyrolysis process makes beneficial changes in the pyrolysis oil that improves the bioconversion efficiency of the lignin monomers. This will be accomplished in part by emulsifying the lignin monomers in an aqueous phase and strain engineering of bacteria for improved performance. The third objective is to develop a bench-scale fermentation process for accomplishing objective 2 in a scalable platform, and then use this information for preliminary techno-economic and life-cycle analyses.