Catalytic Conversion of Cellulose to Carboxylic Acids through Aqueous Phase Partial Oxidation
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Finding a drop in alternative to petroleum based fuels, which can compete both on performance and price, represents one of the greatest chemical engineering challenges of the twenty first century. Cellulosic biomass, is inexpensive, available regionally, and considered to be the feedstock of choice for producing alternative liquid fuels and green chemicals. However, cellulosic biomass conversion is not without inherent challenges: a refractory crystalline structure, coupled with high water content and oxygen content, make the catalytic conversion extremely difficult. A novel, environmental friendly process, is proposed to utilize high temperature water, and a partially oxidative atmosphere, to hydrolyse cellulose to oligosaccharides, which will react on the surface of the catalyst through oxidation reactions to carboxylic acids with high selectivity. Noble metal loaded metal oxides and metal oxides were tested for their catalytic activity in the process. Gold nanoparticle loading was found to promote a yield of 12% by carbon weight of lactic acid as a result of Lewis acidity and oxidation reactions. By utilizing zirconia, the "APPO" process was able to convert cellulose to levulinic acid at a yield of 42% by carbon weight. This represents approximately 50% of the max theoretical conversion and is the highest reported conversion of cellulose to carboxylic acids by utilizing a heterogeneous catalyst. Furthermore, a novel reaction pathway was purposed for the APPO process with zirconia that bypasses HMF and relies on gluconic acid as a key intermediate.