Date Published: June 8, 2016
Publisher: Springer Berlin Heidelberg
Author(s): Amal Ahmed Elgharbawy, Md. Zahangir Alam, Nassereldeen Ahmad Kabbashi, Muhammad Moniruzzaman, Parveen Jamal.
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.
Lignocellulosic biomass has been attractive as a renewable and sustainable resource for biofuel production. Combined with an enzymatic hydrolysis, a process where enzyme converts the biomass to fermentable sugars, it offers the high yields to products vital to economic success (Yang et al. 2011). Despite its potential, lignocellulosic biomass has been quietly well-known for its high recalcitrant to chemical and biological degradation. Cellulose as the main component of lignocellulosic materials is sheltered by lignin and hemicelluloses that wrap the molecule (Laureano-Perez et al. 2005), making it difficult for enzymatic hydrolysis process to take place.
The PKC-Cel exhibited promising characteristics as it showed a high activity at pH 5.0 and 45 °C that need to be investigated further towards a one-step process for bioethanol production. From all ionic liquids tested in this study, [Cho]OAc and [Cho]Bu were found to be the ionic liquids which provide more stability in PKC-Cel-ILs system. Based on the findings, this system is promising and should be further developed and optimized for an efficient process to be achieved. It is recommended to establish a cost effective technique for the IL recovery from the sugar solution. Moreover, it will be more efficient to be able to reuse both the enzyme and the IL after hydrolysis in order for use to claim the cost effectiveness process. Further analysis needs to be performed to evaluate the cost compared to the conventional solvents. Compatibility of PKC-Cel with ionic liquids is also another issue to be addressed in the application of PKC-Cel-ILs in bioethanol production.