Combination of low pressure steam heating and dilute acid pretreatment of palm biomass for fermentable sugar production

Abstract

Bioethanol derived from empty fruit bunch (EFB) biomass can be potentially used to supplement increasing demand of fossil fuels. Carbohydrate fraction of EFB is an excellent property to be exploited as fermentable sugars that can be converted into bioethanol. In order to produce fermentable sugars from EFB, pretreatment process is required to break complex structure. This process is a challenging process due to incalcitrant structure of lignocellulosic material. With this regards, extensive researches have been done to improve efficiency of pretreatment method for maximum fermentable sugars production. In this study, the attempt to employ a combination of low pressure steam heating (LPSH) and dilute acid pre-treatment for fermentable sugar production was investigated. A dilute acid pretreatment was chosen after the preliminary study was done in comparison with other two different pretreatments, which were lime and ammonia method. In this study, a two-stage-acid hydrolysis was used after the pretreatment step. The hydrolysate was then fermented by Baker’s yeast to convert the released glucose into bioethanol. The saccharification of sugar yields was evaluated using glucose kit Boehringer Mannheim/R-Biopharm and Megazyme xylose kit whereas morphological changes were determined using scanning electron microscopy and crystallinity was determined using X-ray diffraction . The low pressure pretreatment method was carried out in a pressure cooker. The first attempt of utilization of LPSH method at a pressure of 5 psi followed by dilute acid pre-treatment using 4% (v/v) sulphuric acid has shown an increment from 43.1 to 62.1 % (w/w) fermentable sugars compared to dilute acid alone. Further study was done using LPSH at different residence time from 5 to 45 minutes with combination, at different concentration of 1 to 4% (v/v). From this study, the maximum fermentable sugars obtained was 78.6% (w/w) by increasing the LPSH condition to 10 psi, for 30 minutes with combination of 3% (v/v) of dilute sulfuric acid pretreatment with an increment of 45% of glucose as compared to single pretreatment. The combination strategy of pre-treatment was proven to be an effective approach to enhance sugar increment. From the sugars obtained, 8.87mg/mL of ethanol was produced from the fermentation process which proves that the sugar obtained is fermentable.