CAREER: Toward a mechanistic and quantitative understanding of oxidative conversion of biorefinery lignin to open chain hydrocarbon fuel - a new approach to dispel lignin myth

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PI Name: Xiao ZhangProposal ID: 1454575 The bioeconomy of the future will be realized by industrial biorefineries which produce sustainable biofuels, bioproducts, and biopower from renewable plant biomass resources such as grass, agricultural residues, and forest residues. In most current cellulosic biofuel operations, the cellulosic fractions of plant biomass are converted to sugars and then fermented into biofuels. The residual lignin is burned for biopower. Liginin is typically the second most abundant material in plant biomass next to cellulose. Conversion of the lignin into liquid fuel, as opposed to burning it, can significantly increase biofuel production from biomass, and reduce the carbon footprint of biorefinery operations. However, lignin is a complex material which is very difficult to convert to products of value. This research award seeks to develop an innovative chemical reaction pathway to selectively convert lignin to open chain hydrocarbons similar to those that make up jet fuel. If successful, the results from the research will lead to new processes to produce sustainable fuel, and improve the economics and environmental sustainability of biorefinery operations. The conversion of the lignin to liquid fuel can significantly increase biofuel production from biomass. However, current lignin conversion technologies are mostly based on hydrogenation/ hydrodeoxygenation reaction pathways that require high temperatures, pressures, and substantial hydrogen (H2) consumption. The technical goal of this CAREER award is to develop a fundamental understanding of the reaction mechanisms and kinetics of a new, atom-efficient chemical pathway to selectively convert lignin residue from cellulosic biofuel production to open-chain hydrocarbon fuels through sequential oxidative aromatic ring opening, olefin metathesis, and diene oligomerization reactions. Towards this end, the research plan has three objectives. The first objective is to prepare and characterize representative biorefinery lignin samples that reflect the breadth of variations in lignin properties, structure, and the functionality resulting from various biochemical conversion processes. The second objective is to determine the key reaction kinetic parameters of oxidative depolymerization of biorefinery lignin, and establish a quantitative relationship between lignin structural properties and dicarboxylic acid product selectivity under different reaction conditions. The third objective is to elucidate reaction mechanisms and gain an understanding of reaction kinetics in olefin metathesis of lignin-derived dicarboxylic acids and oligomerization of branched conjugated dienes to jet fuel precursors. The results from this research will provide the foundation for a systems-level understanding of biorefinery lignin conversion chemistry, leading to new processes for large-scale lignin utilization. The education and outreach programs associated with this award seek to train future scientists and engineers in biomass conversion technologies to help provide a trained workforce for the biorefineries of the future. Educational programs will be developed in conjunction with industrial partners to proactively recruit high school and undergraduate and graduate students, especially those from underrepresented groups, and provide students with practical and research-based experiences in biomass conversion technologies that support current and future biorefinery operations. Specific activities include the Future Scientists and Engineers for Biorefinery program, the Biorefinery-Oriented Summer Practicum, and the Industrial Leadership Seminar Series.