Conversion of oil palm empty fruit bunch into bioethanol through pretreatment with CO2 as impregnating agent in alkali explosion

Pretreatment is an important step in lignocellulosic bioethanol production which aims to reduce lignin content and break down lignocellulosic structure thereby increasing the accessibility of enzymes in hydrolysis. Therefore, this research explored the pretreatment process on oil palm empty fruit bunch (EFB) with CO2 impregnation followed by alkali explosion. EFB was impregnated with CO2 at 5 °C for 12 h. After impregnation, EFB was mixed with 2.5 M of NaOH solution (1:5 of S/L ratio) in an alkali explosion reactor. Alkali explosion was conducted at 150 °C, 4 kg/cm2 of pressure with the variation of reaction time for 15, 30, and 45 min. The parameters analyzed in this study include EFB recovery, EFB composition and characteristics, glucose yields, and ethanol yields. EFB composition was analyzed as cellulose, hemicellulose, and lignin while the characteristics of the EFB were examined in functional groups. The results indicated that combined pretreatment using CO2 impregnation followed by 15 min of alkali explosion obtained higher delignification of EFB, glucose, and ethanol yield than only alkali explosion for 30 min. The highest glucose and ethanol yields were 99.33 and 83.80 w/w% of glucose mass in EFB, respectively. These results prove that CO2 can be used as an impregnation agent in lignocellulosic pretreatment and could be combined with alkali explosion.