SusChEM: Mapping Reaction Pathways of Biomass Pyrolysis and Catalytic Pyrolysis using Isotopically Labeled Plant Cell Culture

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Plant 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. One way to make fuel out of biomass is through a process called fast pyrolysis, where the solid plant material is rapidly heated in the absence of air to decompose it to a mixture of gas, solid char, and a liquid called bio-oil, which can be upgraded to liquid transportation fuel. Plant biomass is a mixture of three biologically- produced polymers - cellulose, hemicellulose, and lignin - arranged into a complex three-dimensional network. The origin of pyrolysis products from this complex mixture is not well understood, since all these materials interact with one another during biomass pyrolysis. This lack of understanding has hampered efforts to maximize bio-oil production from a given plant species. This project seeks to map the origin of biomass pyrolysis products to specific biomass components within real biomass materials. A key innovation is the use of plant cell technology to label the cellulose and lignin components so that their fate can be tracked during fast pyrolysis. The educational activities associated with this project include a summer residential program for high school students using topics developed from the research. Students will see how plants capture and store carbon and energy, use chemical probes to help discover biological processes, and discuss the opportunities and challenges of obtaining fuels and chemicals form renewable resources.The overall goal of the research is to identify and map reaction pathways for fast pyrolysis of lignocellulosic biomass to specific cellulosic and lignin molecular constituents. The research plan has two objectives to trace the origins of the fast pyrolysis products. The first objective is to develop a methodology to enable mapping of the reaction pathways through carbon-13 labeling. Towards this end, cells of the model plant Arabidopsis thaliana will be heterotrophically cultured on a mixture of unlabeled and 13-C labeled glucose and phenylalanine, precursors for cellulose and lignin biosynthesis respectively, to separately tag the carbohydrate and lignin fractions in the Arabidopsis cell wall. Arabidopsis stem cuttings will then be pyrolyzed, with and without catalyst, using 13C-labeled Arabidopsis cells as probes at different temperatures. The results will be compared to the products of simple mixtures of unlabeled cells with labeled small-molecule building blocks. By tracking the fate of the labeled sites, it will be possible to construct a reaction network that describes both their incorporation in the plant matter, and the chemical events that form the pyrolysis products. The second objective is to use the methodology developed under objective 1 on woody plants within genera Populus and Paniceae that are relevant to bioenergy production. The research outcomes will lead to improved, mechanism-based reaction and kinetic models for predicting product yields from reaction pathways for fast pyrolysis from real lignocellulosic biomass substrates, not just model compounds. This information can then be used to identify reactor design and operation strategies to stabilize and optimize the yield of bio-oil and its downstream conversion into liquid transportation fuel.