Conversion of D-xylose and hemicellulose in water/ethanol mixtures

During hydrothermal dehydration of d-xylose, side reactions reduce the furfural yield and are mainly responsible for humin formation. Short-chain alcohols, like ethanol, are able to suppress such furfural-consuming side reactions. Therefore, acid-catalyzed xylose conversion in different water/ethanol mixtures was examined to evaluate the alcohol influence. In terms of the xylose conversion, no deceleration could be observed, although an increase of the activation energy with rising ethanol proportion was determined. Furfural yield in water was 36–52% and could be increased by adding ethanol up to 90%. Simultaneously, the mass of formed humins could be decreased by an average of 60%. However, the activation energy for furfural degradation does not show a clear trend. If organosolv hemicellulose is used instead of xylose, an increase in furfural yield cannot be observed. An ethanol content of 50 wt % even leads to a reduction of the yield. Nevertheless, by the addition of ethanol, a decline in the amount of...