EAGER: Permeability of Biomass and Impact of Transport on Reaction Rates Under Supercritical Carbon Dioxide Treatment

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Biomass has vast potential to replace petroleum as a feedstock for fuels and chemicals, but low cost and environmentally-friendly processes for biomass conversion need to be developed. Biomass conversion processes involve complex chemistry and transport phenomena. Carbon dioxide at supercritical states has shown promise as a solvent for pretreatment and direct extraction of biomass to high-value chemicals. One limitation of this approach is low conversion efficiency. There are also inconsistent results across different studies which have been attributed to, among other factors, differences in the density and morphology of the biomass. This project will investigate mass transfer limitations within the biomass before and after supercritical carbon dioxide treatment to understand the impact of these limitations on conversion rates and extents. This project will advance the viability of supercritical carbon dioxide treatment as an effective biomass conversion strategy to produce high value chemicals. This work will also facilitate the development of new tools for studying chemical kinetics and transport phenomena associated with biomass conversion.The evolution of biomass composition and morphology during supercritical carbon dioxide treatment is poorly understood, despite their demonstrated importance to conversion extent and efficiency. The objective of this project is to investigate the evolution of biomass morphology during supercritical carbon dioxide treatment in order to assess the role of mass transfer in the conversion of hemicellulose, cellulose and lignin. This objective will be achieved through experimental characterization of evolving biomass morphology with treatment duration through the use of established techniques and the development of novel techniques. Specifically, new insights into the evolution of biomass morphology for a range of biomass structures, densities and particle sizes will be gained. The use of supercritical carbon dioxide with environmentally benign co-solvents, such as water, has been shown to be effective at hydrolysis of biomass polymers via the formation of carbonic acid. Thus, research will focus on this co-solvent system and results will be incorporated into a model that accounts for hydrolysis chemistry and evolving biomass morphology to describe the conversion process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.