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

Abstract

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 10–20ml/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 20ml/g for 10min, 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 2mm is optimal for getting the highest xylose yield.