Hydrothermal pretreatment enhanced enzymatic hydrolysis and glucose production from oil palm biomass

Abstract

The present works investigate hydrothermal pretreatment of oil palm empty fruit bunch and oil palm frond fiber in a batch tube reactor system with temperature and time range from 170 to 250°C and 10 to 20min, respectively. The behavior of soluble sugars, acids, furans, and phenols dramatically changed over treatment severities as determined by HPLC. The cellulose-rich treated solids were analyzed by SEM, WAXD, and BET surface area. Enzymatic hydrolysis was performed from both pretreated slurries and washed solid, and data obtained suggested that tannic acid derived from lignin degradation was a potential cellulase inhibitor. Both partial removal of hemicellulose and migration of lignin during hydrothermal pretreatment caused structural changes on the cellulose-hemicellulose-lignin matrix, resulting in the opening and expansion of specific surface area and pore volume. The current results provided important factors that maximize conversion of cellulose to glucose from oil palm biomass by hydrothermal process.

Influence of High-Pressure Steam Pretreatment on the Structure of Rice Husk and Enzymatic Saccharification in a Two-Step System

“…The pH was observed to be the lowest (pH 3.42) when the RH was pretreated at 220 °C for 10 min. These results were in accordance with the work of Zakaria et al (2015a), who reported a similar decrease in the pH from 4.10 to 3.39 when the temperature increased from 170 to 210 °C during the hydrothermal pretreatment of oil palm frond fibre (OPFF). The decrease in pH was attributed to the accumulation of acetic acid, which resulted from the cleavage of acetyl groups located in the hemicellulose matrix, and resulted in hemicellulose degradation (Möller et al 2011;Xiao et al 2013;Ho et al 2014).…”

“…As for the increase in the lignin content, a similar result was observed in previous studies that used acidic conditions (Donohoe et al 2008;Sabiha-Hanim et al 2011;Pu et al 2013;Zakaria et al 2014). Lignin (high molecular weight) is usually dissolved during pretreatment, but is later redeposited (low molecular weight) on biomass during the condensation process (Zakaria et al 2015a). Meanwhile, according to Li et al (2007), lignin is removed to a limited extent during steam pretreatment at high pressure, but is redistributed on the outer fibre surface as a result of melting and the depolymerisation/repolymerisation reactions (Chua and Wayman 1979).…”

“…However, when the pretreatment temperature increased from 200 to 220 °C, specifically for 7 and 10 min, the cellulose content decreased from 66.36% to 56.45% and 54.42%, respectively. This phenomenon was previously observed by Zakaria et al (2015a) and Baharuddin et al (2013) in the hydrothermal and HPSP of oil palm biomass. Zakaria et al (2015a) observed a reduction in the cellulose content from 58.5% to 53.2% when the temperature was increased from 200 to 210 °C.…”

“…This phenomenon was previously observed by Zakaria et al (2015a) and Baharuddin et al (2013) in the hydrothermal and HPSP of oil palm biomass. Zakaria et al (2015a) observed a reduction in the cellulose content from 58.5% to 53.2% when the temperature was increased from 200 to 210 °C. Similarly, Baharuddin et al (2013) observed a decrease in the cellulose from 70.6% to 65.9% when the temperature was increased from 210 to 230 °C.…”

“…Based on the results of this analysis, the pretreated RH had a sugar yield that was 16 times higher than that of the untreated RH. The thermal treatment caused a breakdown of resins and gums into soluble and insoluble oil, dissolution of hemicellulose, removal of phenolic compounds, and migration of lignin, all of which loosened the intact structure of the cellulose-hemicellulose-lignin matrix, and enhanced enzymatic hydrolysis (Hsu et al 2010;Pu et al 2013;Zakaria et al 2015a). This could have also been due to the hemicellulose barrier to the cellulose structure and irreversible binding to the cellulase enzymes, which generates unproductive hydrolysis.…”