(476a) Green Carboxylic Acids by Direct Conversion of Cellulosic Biomass

Lignocellulosic biomass has long been recognized as a potential sustainable feedstock for biofuels.  But lack of cost-effective bio-refining processes hinders the replacement of petroleum-based fuels with biofuels.  We are exploring a non-traditional pathway to convert lignocellulosic biomass into advanced biofuels.  The key step of our strategy is the catalytic aqueous phase partial oxidation (APPO), a novel biomass deconstruction process which transforms cellulosic biomass to C3-C5 carboxylic acids, using environmental friendly water and air as the reaction solvent and media over inexpensive heterogeneous catalysts.  The APPO products can be further cost-effectively upgraded into drop-in fuel components consisting of primarily paraffinic hydrocarbons by using the existing petroleum refining infrastructure.  Compared to other conventional processes, the APPO has the advantages of feedstock flexibility, mild operation conditions, no external hydrogen usage, environmental friendliness, and ease of the product upgrading.  

For demonstration, the aqueous phase partial oxidation of cellulosic biomass has been examined in hot compressed water with various catalysts.  The conversion and the selectivity of the reaction towards different carboxylic acids were found to highly depend on the catalyst properties and the reaction temperatures.  Glucose, fructose, cellubiose, and cellulose were used as the model feed compounds to probe the reaction mechanism. The difference of the products over the same catalyst indicates that cellulose deconstruction reaction proceeds via initial hydrolysis of cellulose to water soluble oligomers, followed by oxidation of the intermediates to produce carboxylic acids. Under optimized reaction conditions, ~ 50 mol% yield of levulinic acid (carbon molar basis) was obtained by converting cellulose over the selected catalyst in the presence of lean air. The underlying physical and chemical mechanisms that control the partial oxidation of biomass in aqueous media to selectively produce platform building block chemicals, including levulinic acid, for the synthesis of advanced biofuels are discussed.