Acetic acid-assisted hydrothermal fractionation of empty fruit bunches for recovery of hemicellulosic sugar

Recently, acetic acid has been proposed as an alternative to hot water for pretreatment because of its higher hydrolysis efficiency than that of hydrothermal pretreatment. Effective use of acetic acid as a catalyst in the pretreatment process of lignocellulosic biomass could prove preferable to stronger acids because of its lower corrosiveness, reduced neutralization requirements, and lower cost due to its generation as a byproduct of the bacterial fermentation processes used for converting biomass to other products. In the present work, acetic acid-assisted hydrothermal (AAH) fractionation was studied for the recovery of the hemicellulosic sugar, mostly xylan, from empty fruit bunches (EFB). For maximizing the AAH fractionation condition, a central composite design (CCD) was used to test the effects of the following process variables: reaction temperature of 146.3–213.7 °C, reaction time of 6.6–23.4 min, and acetic acid concentration of 1.6–8.4%. The maximum xylose recovery yield (50.7%) from the EFB was obtained using AAH fractionation at optimum conditions (6.9 wt.% acetic acid at 170 °C and for 18 min), whereas, only 16.2% of xylose yield was obtained from the LHW fractionation at the same reaction conditions (170°C and 18 min). This study confirmed that AAH fractionation could achieve clean fractionation which could consequently result in more complete utilization of each component. However, the mechanism of AAH for a hemicellulose hydrolysis is still unclear, and more study should be conducted in the future.