Microwave Assisted Acid Pretreatment of Oil Palm Empty Fruit Bunches (EFB) to Enhance Its Fermentable Sugar Production

Abstract

The influence of sulfuric acid concentration in aqueous glycerol during microwave pretreatment on the chemical content and morphological characteristics changes of pretreated EFB were investigated. After pretreatment, the pulp was further subjected to enzymatic hydrolysis. The micro-morphology and crystallinity of original and pretreated EFB were observed by scanning electron microscopy (SEM) and X-ray diffraction. Lignin content of pretreated EFB was determined, while hydrolysate after enzymatic hydrolysis was also analyzed the reducing sugar content. These results indicated that microwave assisted acid pretreatment of EFB caused weight loss. Evaluation on effect of varying acid concentration and residence times results 1 % acid concentration for 12.5 min as the best pretreatment condition. Under the best pretreatment condition, lignin removal was about 59.16 % with the reducing sugar yield per original EFB was 25.09 or 55.85 % per pretreated EFB. The acid–glycerol catalyst successfully improved reducing sugar yield compared to both untreated and biological pretreated samples. SEM images revealed that the pretreated of EFB surface changed noticeably and the increase of crystallinity degree of pretreated EFB indicated a great effect on amorphous region to crystalline region. The addition glycerol in reaction mixture both acid and alkaline has synergistic effect to increase reducing sugar yield. Much volume of glycerol in mixture has great effect to improve enzymatic hydrolysis performance than that of acid ones. The highest reducing sugar yield is produced as much as 98 % when EFB irradiated using glycerol–acid ratio of 1:2 for 12.5 min at 1 % acid concentration. The addition glycerol of 2 fold can increase 3.9 fold reducing sugar yield in the best pretreatment condition. Microwave assisted acid pretreatment in aqueous glycerol was an effective way to increase reducing sugar yield of EFB by lignin removal and fiber disruption.