Moderate pretreatment of oil palm empty fruit bunches for optimal production of xylitol via enzymatic hydrolysis and fermentation

Moderate pretreatment methods were evaluated on oil palm empty fruit bunches (OPEFB) in order to obtain xylose-rich hydrolysate for xylitol production via enzymatic hydrolysis and fermentation. Assessments on the effects of catalysts (autohydrolysis/water, acetic acid, or ammonia) and the corresponding concentration and pretreatment time at moderate pressure/temperature were conducted while the process performance was evaluated by enzymatic hydrolysis. Most hemicellulose was still retained in the pretreated solid at the evaluated pretreatment conditions, hydrolysis of both the pretreated solid and spent liquor are necessary to obtain most of xylose from OPEFB. Pretreatment using 5% ammonia gave the highest xylose yield; however, great amount of acid would be needed for pH adjustment for the following enzymatic hydrolysis process and thereby autohydrolysis was preferred. The optimum yield was obtained from autohydrolysis at 1.5 barg/127.9 °C for 60 min, which gave xylose yield of 0.085 g xylose/g OPEFB (or 39.1% of hemicellulose). The obtained hydrolysate could be directly used as substrate for fermentation.