(129d) Catalytic Conversion of Xylan to Value-Added Carboxylic Acids

The success of biofuel production relies on the effective utilization of the C5 and C6 sugars presented in hemicellulose and cellulose, respectively.  Both hemicellulose and cellulose are carbohydrates with different structures and sugar monomer units.  They share some similarities but significant differences exist.  There are only few studies on hemicellulose partly because C5 sugars, the monomers of hemicellulose, cannot be utilized by fermentation to produce bio-ethanol.  Hemicellulose and its derivatives have long been considered as the low-value by-products which are not well utilized in biorefinery industry.  The aqueous phase partial oxidation (APPO) method has been demonstrated to produce levulinic acid in high yields from cellulose in our group.  Since cellulose and hemicellulose are both composed of sugar monomer units through glycosidic bonds, the APPO technology herein was applied to convert hemicellulose to carboxylic acids.  However, unlike cellulose with a rigid crystalline structure and strong hydrogen bonding, hemicellulose is amorphous and can be easier to break down.  The APPO of hemicellulose was therefore operated at a lower temperature.  And the reaction mechanism of the APPO of hemicellulose was different from the cellulose reaction mechanism.  The APPO of xylan in hot temperature water is a multi-step process: firstly, xylan is hydrolyzed to xylose, and xylose is converted to furfural by dehydration, and then is further oxidized to form carboxylic acids over the heterogeneous catalyst.  We found that the product distribution is highly depended on the catalysts.