Abstract
Lignocellulosic biomasses, exhibit resistance to enzymatic hydrolysis due to the presence of lignin and hemicellulose. Ionic liquids proved their applicability in lignin degradation, however, ionic liquid removal has to be performed to proceed to hydrolysis. Therefore, this study reports an in situ hydrolysis of empty fruit bunches (EFB) that combined an ionic liquid (IL) pretreatment and enzymatic hydrolysis. For enzyme production, palm kernel cake (PKC) was used as the primary media for microbial cellulase (PKC-Cel) from Trichoderma reesei (RUTC30). The obtained enzyme exhibited a promising stability in several ionic liquids. Among few, in choline acetate [Cho]OAc, PKC-Cel retained 63.16 % of the initial activity after 6 h and lost only 10 % of its activity in 10 % IL/buffer mixture. Upon the confirmation of the PKC-Cel stability, EFB was subjected to IL-pretreatment followed by hydrolysis in a single step without further removal of the IL. The findings revealed that choline acetate [Cho]OAc and choline butyrate [Cho]Bu were among the best ILs used in the study since 0.332 ± 0.05 g glucose/g and 0.565 ± 0.08 g total reducing sugar/g EFB were obtained after 24 h of enzymatic hydrolysis. Compared to the untreated EFB, the amount of reducing sugar obtained after enzymatic hydrolysis increased by three-fold in the case of [Cho]OAc and [Cho]Bu, two-fold with [EMIM]OAc and phosphate-based ILs whereas the lowest concentration was obtained in [TBPH]OAc. Pretreatment of EFB with [Cho]OAc and [Cho]Bu showed significant differences in the morphology of EFB samples when observed with SEM. Analysis of the lignin, hemicellulose and hemicellulose showed that the total lignin content from the raw EFB was reduced from 37.8 ± 0.6 to 25.81 ± 0.35 % (w/w) upon employment of [Cho]OAc in the compatible system. The PKC-Cel from T. reesei (RUTC30) exhibited promising characteristics that need to be investigated further towards a single-step process for bioethanol production.
Highlights
Lignocellulosic biomass has been attractive as a renewable and sustainable resource for biofuel production
The findings revealed that choline acetate [Cho]OAc and choline butyrate [Cho]Bu were among the best ionic liquid (IL) used in the study since 0.332 ± 0.05 g glucose/g and 0.565 ± 0.08 g total reducing sugar/g empty fruit bunches (EFB) were obtained after 24 h of enzymatic hydrolysis
All substrates showed the competency on cellulase enzyme production with different levels of the activity, and palm kernel cake (PKC) was chosen for the further enzyme production
Summary
Lignocellulosic biomass has been attractive as a renewable and sustainable resource for biofuel production. Combined with an enzymatic hydrolysis, a process where enzyme 128 Page 2 of 15. Ionic liquids have been introduced recently as an alternative method to perform the pretreatment of lignocellulosic biomass. These are organic salts in liquid form at below 100 °C and have been receiving considerable attention as substitutes for volatile organic solvents. They are non-flammable, non-volatile, and recyclable with remarkable properties of outstanding solvating potential, thermal stability, and tunable properties by suitable choices of cations and anions (Ghandi 2014). A study by He et al (2015) on the utilization of IL 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) combined with HCl and water revealed a noticeable increase in reducing sugars after the successive stage of enzymatic saccharification. The yield of the reducing sugars observed after the pretreatment with IL was 95.1 % after a 48-h saccharification process, which is considered a great improvement compared to the untreated (25.6 %) and alkali-treated (82.2 %) corn stover
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