Solvent-Enabled Control of Reactivity for Liquid-Phase Biomass Conversion Reactions

Catalytic upgrading of biomass to renewable chemicals and fuels requires the selective removal of oxygen from highly functionalized biomass components. This requirement of achieving high selectivity is illustrative of an important class of catalytic processes in the chemical and pharmaceutical industries, namely processes that take place through consecutive reaction steps, A → B → C, where species B is the desired product. The challenge for such catalytic processes is to identify catalysts and/or reaction conditions that allow for the selective conversion of A to B, but that do not facilitate the conversion of B to C, such that it is possible to produce species B with high yield. We will present results for Brønsted acid-catalyzed conversions of a carbohydrate (fructose), an alcohol (t-butanol), and a furan (hydroxymethylfurfural, HMF) in liquid-phase organic solvents mixed with water, and we show that the rates of these reactions can be understood in terms of solvation effects for the acidic proton and the transition states for the catalytic reactions. Accordingly, we show that these solvent effects can be employed to achieve high yields for production of HMF by dehydration of fructose, by promoting the conversion of fructose to HMF, while not facilitating the subsequent conversion of HMF to levulinic acid. We will then show how solvent effects can be used to achieve high yields of HMF (e.g., 60%) from acid-catalyzed conversion of cellulose, combined with the oxidation of HMF to produce furan-dicarboxylic acid (FDCA). We will then show how this cellulose conversion strategy can be combined with the integrated conversion of ligno-cellulosic biomass to produce furfural (from hemicellulose), FDCA (from cellulose), and a stream of clean lignin.