Autoclave-assisted weak acid pretreatment of oil palm empty fruits bunches for fermentable sugar production

Pretreatment of oil palm empty fruit bunches (OPEFB) catalyzed by weak acids (oxalic, formic, and citric acid) in an autoclave under moderate condition is one of the appropriate pretreatment alternatives to recover reducing sugar both from cellulose and hemicellulose. This sugar can be fermented to be various bioprocess products. In this study, the effect of weak acid concentration (1-5% for oxalic acid; 5-20% for formic and citric acid), pretreatment temperature (115-125 degrees C), time (60-90 min), and solid loading (5-10%) was investigated. To improve total reducing sugar yield, residual solid after pretreatment was subsequently hydrolyzed by Cellic CTec2. With the increasing weak acid concentration, pretreatment temperature, and time, more reducing sugar was obtained in spent liquor of pretreatment. On the contrary, the increase of solid loading declined the reducing sugar yield. After residual solid was enzymatically hydrolyzed, the amount of reducing sugar significantly elevated for nearly all weak acids, except 5% oxalic acid pretreatment. However, the pretreatment by 5% oxalic acid gave the maximum yield of total reducing sugar at 125 degrees C for 60 min and using 5% solid loading. The reducing sugar obtained in spent liquor and hydrolysate at this optimum condition was 0.245 g/g OPEFB and 0.352 g/g OPEFB, respectively.