Optimization of Microwave-Assisted Oxalic Acid Pretreatment of Oil Palm Empty Fruit Bunch for Production of Fermentable Sugars

Abstract

Pretreatment is an important step in the conversion of biomass to bioethanol. In this study microwave-assisted oxalic acid (MOA) pretreatment was chosen to pretreat oil palm empty fruit bunch (OPEFB) to enhance enzymatic saccharification of the biomass. The objective of this study was to determine an optimum pretreatment condition for reducing sugar production, which could be further fermented by yeast to produce ethanol. Preliminary study was conducted to determine the range of duration of heating and temperature that will be used in the optimization by using response surface methodology (RSM). Central composite design (CCD) was used with three independent variables (duration of heating, temperature and acid concentration). Reducing sugar yield per initial biomass was used as a response variable. Preliminary study, that was conducted at 160, 170, 180, 190, and 200 °C for 5, 7.5, 10, 12.5, and 15 min, shows that pretreatment at temperature of 170–190 °C for 5–10 min produced higher reducing sugars than other conditions. Optimization using RSM shows that the optimum condition of MOA pretreatment of OPEFB was at 190 °C for 3 min with 1.1% oxalic acid, which resulted in as much as 34.60% reducing sugars after enzymatic saccharification. The pretreated OPEFB was then characterized and compared with untreated OPEFB. MOA pretreatment successfully removed 50.57% of lignin and 76.56% of hemicellulose from the OPEFB that were confirmed by a decrease or disappearance of the absorption bands of functional groups at 1339–1650 cm−1 and 1735 cm−1, respectively.