15-08: Aqueous Phase Catalytic Hydrodeoxygenation and Hydroprocessing of Lignin Derived Reactive Intermediates

This project is aimed at fundamental research on aqueous phase catalysis of depolymerized lignin. Previous results from our lab indicate that inter-unit lignin C-O-C bonds undergo selective hydrolysis during hydrothermal flow-through pretreatment, generating a reactive suite of depolymerized lignin fragments which retain their native structural functionalities (e.g. p-coumaran),  in addition to functionalized aryl oxygenates which are prone to side reactions. We have demonstrated these intermediates are amenable to hydrodeoxygenation, as well as hydrogenation – thereby aiding their relatively facile conversion to hydrocarbons (primarily aliphatics); correspondingly, a mechanistic framework has been established therefrom. Our proposed reaction sequences accounts for solubility, molecular weight, and functional group interactions (i.e. surface/substrate interaction for hydrodeoxygenation mediated C-O scission and reduction of aryl rings). Synthetic strategies have been developed for producing model lignin-derived reactive intermediates for catalyst testing to elucidate their behaviors during HDO, and the routes they follow to hydrocarbons. Knowledge pertaining to the kinetics and reaction chemistry of these intermediates was gleaned from analysis on the hydrocarbon and oxygenated suites generated from their reactions over a variety of heterogeneous catalysts. This, in turn, has appreciably informed our catalyst screening and formulation efforts, and we have been able to attain high levels of deoxygenation and carbon efficiency, while maintaining hydrothermal catalyst stability. Holistically, our research leads us to believe that lignin could be a suitable, renewable feedstock for producing a spectrum of hydrocarbon species in the C₈-C₁₆ range that are commonly found in gasoline, diesel and especially jet fuel blendstocks.