Optimization of dilute acid-catalyzed hydrolysis of oil palm empty fruit bunch for high yield production of xylose

Cost-effective hydrolysis of lignocellulose at low acid concentrations to get high yield of sugars is commercially attractive but challenging. Oil palm empty fruit bunch (EFB) was hydrolyzed to get fermentable sugars using sulfuric acid and/or phosphoric acid whose concentrations were maintained at <1% (w/v) to favor their direct use in the subsequent fermentation processes as essential nutrient elements (S and P). Two types of kinetic models were used to describe the hydrolysis process and the Biphasic model was found to better predict the experimental results than the Saeman model and thereby used to guide the optimization of the hydrolysis process. It predicts that 80–90% xylose yield is achieved when EFB hydrolysis is conducted at 140–160 °C, liquid to solid ratios of 10–20 ml/g, 0.25–0.5% (w/v) of sulfuric acid and 0.1–0.2% (w/v) of phosphoric acid. The maximal xylose yield of 91.3% was experimentally obtained for EFB hydrolysis catalyzed by 0.5% (w/v) of H2SO4 and 0.2% (w/v) of H3PO4 at 160 °C, a liquid to solid ratio of 20 ml/g for 10 min, which is in well agreement with the model prediction and is comparable with the reported maximal xylose yields of 80–90% at higher acid concentrations (>1%, w/v). The combined use of H2SO4 and H3PO4 has a synergistic effect in improving xylose yield compared to using H2SO4 alone. An EFB particle diameter of 2 mm is optimal for getting the highest xylose yield.

► Hydrolysis of lignocellulose by H2SO4 and H3PO4 at <1% (w/v) for direct use in fermentation.
► Combined use of H3PO4 and H2SO4 has a synergistic effect in improving xylose yield.
► Maximal xylose yield was comparable with those reported at higher acid concentrations.