Biomass pretreatment generates inhibitory products, which reduce the overall yield of xylose for ethanol production. Understanding of hemicellulose depolymerization into xylose is essential to identify the pretreatment conditions that maximize xylose formation, but minimize the generation of these inhibitory products, such as formic acid and furfural. Thus, the goal of this project is to understand how dilute acid pretreatment parameters affect hemicellulose depolymerization, maximize xylose concentrations, and minimize by-products formation.
To progress towards this goal, rates and mechanisms of hemicellulose release must be determined. Birchwood xylan was used as the starting material to produce xylose oligomers. The hydrolyzed birchwood xylan was then fractionated using centrifugal partition chromatography (CPC) with the solvent system composed of butanol: methanol: water at a 5:1:4 volumetric ratio. The oligomers in the fractionated CPC were identified and quantified using high performance liquid chromatography (HPLC) and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), with the calibration curves setup based on the analysis of the commercial grade xylose oligomers reference standards. The identity of fractionated xylose oligomers was also confirmed using mass spectrometry (MS) analysis. The fractionated xylose oligomers were subsequently used in the kinetic study.
The developed kinetic model demonstrated that the formation or degradation of the compounds could be predicted using first order kinetics. At all hydrolysis conditions, DP 1 degraded mostly into formic acid, rather than into furfural. The degradation rates of DP 1 and formic acid were determined to be most influenced by temperature and pH, as reflected by the Arrhenius Equation parameters calculated for the respective compounds. Pretreatment condition was more favorable for maximizing the yield of xylose monomer at the temperatures between 120 and 160 deg C, at a pH between 0.43 and 7, because of lower degradation rate of DP 1, and higher degradation rates of xylose oligomers, resulting in a net accumulation of DP 1
