(35b) Mapping Reaction Pathways of Biomass Fast Pyrolysis Using Isotopically Labeled Plant Cell Culture

Biomass fast pyrolysis (BFP) provides a potential solution to escape the current fossil-based economy by converting biomass into “bio-oil,” a liquid that can be upgraded to hydrocarbon fuels. To optimize bio-oil production and design effective stabilization, a better understanding of BFP reaction mechanisms is sorely needed. Prior studies have attempted to map the flux of reactants to products using single small-molecule isotope studies. Though such investigations can be informative, the complexity of lignocellulosic biomass will invariably lead to side reactions that result in difficult-to-explain product slates. Instead of using isotopically labeled small molecules, plant cells are grown with isotopically labeled cell walls, with the purpose of mapping the reactions that occur amongst fast pyrolysis products. As growing whole plants in a labelled CO₂ environment is difficult, time consuming, and expensive, isotopically labeled Arabidopsis thaliana cells, grown heterotrophically are used instead. In our method, a suspension cell culture of A. thaliana cells (referred to as T87 cells) was grown in the dark and preferentially labelled by feeding ¹³C-containing biosynthetic precursors (glucose for carbohydrate and phenylalanine for lignin). Labeled glucose predominantly forms cellulose and hemicellulose when unlabeled phenylalanine is also in the mixture. Likewise, labeled phenylalanine mostly forms lignin when unlabeled glucose is present. After a week of liquid culture, the partially labeled T87 cells were harvested, dried, and injected into a microscale pyrolysis unit interfaced to a gas chromatography/mass spectrometer (py-GC/MS). The results of this analysis are used to map the reaction pathways of pyrolysis for several reactants into products. Ultimately, an improved understanding of how biomass is transformed into energy products is gained.