Kinetic Modeling of Switchgrass-Derived Xylose Oligomers Degradation during Pretreatment in Dilute Acid or in Water

Abstract

Switchgrass hemicellulose can be converted into sugars, such as xylose, for biobased product manufacturing. However, during pretreatment, the hemicellulose can also be converted into xylose oligomers, furfural and formic acid, which are detrimental to subsequent enzymatic hydrolysis and fermentation. Pretreatment conditions that maximize xylose production from hemicellulose, while also minimizing xylose oligomers, furfural, and formic acid generation, would improve the economics of biobased product manufacturing by increasing yields and reducing enzyme and microorganism costs. The current study utilized switchgrass purified-xylose oligomers as model compounds to follow xylose oligomers, and furfural generation during pretreatment, using 0 to 1 wt % acid sulfuric acid at temperatures of 160 and 180 °C. The resulting kinetic data were used in simple first order rate expressions. On the basis of the empirically derived Arrhenius models but not verified by experimental data, maximum xylose yields can be obtained at low temperatures and high acid concentrations. Pretreatment conditions with high temperatures yielded high reaction rates and shortened reaction times, but at the expense of increased concentrations of degradation compounds.