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Hydrolysis of Lignocellulosic Biomass in Hot-Compressed Water with Supercritical Carbon Dioxide.

ABSTRACT: This study investigated the decomposition behavior of bamboo under hydrothermal and hydrolysis conditions with H₂O/CO₂ in a semicontinuous-flow reactor at 9.8 MPa. At 255 °C, with and without CO₂, xylan in bamboo completely decomposed into xylo-oligosaccharide (XOD). The yield of glucan degradation products with CO₂ was significantly higher compared with that under the hydrothermal reaction (25.7 vs 14.9 wt %, respectively). The reaction rate of glucan decomposition with CO₂ was slightly higher than the rate of hydrothermal reaction (k _H₂O/CO₂ /k _H₂O = 1.3). Increasing the fluid velocity of the hydrothermal reaction (3-10 mL/min) significantly accelerated the solubilization rate, but the ultimate yield of the soluble fraction was unchanged. The ultimate yield of the soluble fraction was slightly affected by physical effects. Hydrolysis with CO₂ under severe conditions exhibited effective degradation of glucan. The catalytic activity of the H₂O/CO₂ system under hydrolysis can be explained by the system's chemical effect.

SUBMITTER: Sasaki M

PROVIDER: S-EPMC8190814 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background:Liquid hot water (LHW) pretreatment has been considered as one of the most industrially viable and environment-friendly methods for facilitating the transformation of lignocelluloses into biofuels through biological conversion. However, lignin fragments in pretreatment hydrolysates are preferential to condense with each other and then deposit back onto cellulose surface under severe conditions. Particularly, lignin tends to relocate or redistribute under high-temperature LHW pretreatment conditions. The lignin residues on the cellulose surface would result in significant nonproductive binding of cellulolytic enzymes, and therefore negatively affect the enzymatic conversion (EC) of glucan in pretreated substrates. Although additives such as bovine serum albumin (BSA) and Tween series have been used to reduce nonproductive binding of enzymes through blocking the lignin, the high cost or non-biocompatibility of these additives limits their potential in industrial applications. Results:Here, we firstly report that a soluble soy protein (SP) extracted from inexpensive defatted soy powder (DSP) showed excellent performance in promoting the EC of glucan in LHW-pretreated lignocellulosic substrates. The addition of the SP (80 mg/g glucan) could readily reduce the cellulase (Celluclast 1.5 L®) loading by 8 times from 96.7 to 12.1 mg protein/g glucan and achieve a glucan EC of 80% at a hydrolysis time of 72 h. With the same cellulase (Celluclast 1.5 L®) loading (24.2 mg protein/g glucan), the ECs of glucan in LHW-pretreated bamboo, eucalyptus, and Masson pine substrates increased from 57%, 54% and 45% (without SP) to 87%, 94% and 86% (with 80 mg SP/g glucan), respectively. Similar effects were also observed when Cellic CTec2, a newer-generation cellulase preparation, was used. Mechanistic studies indicated that the adsorption of soluble SP onto the surface of lignin residues could reduce the nonproductive binding of cellulolytic enzymes to lignin. The cost of the SP required for effective promotion would be equivalent to the cost of 2.9 mg cellulase (Celluclast 1.5 L®) protein (or 1.2 FPU/g glucan), if a proposed semi-simultaneous saccharification and fermentation (semi-SSF) model was used. Conclusions:Near-complete saccharification of glucan in LHW-pretreated lignocellulosic substrates could be achieved with the addition of the inexpensive and biocompatible SP additive extracted from DSP. This simple but remarkably effective technique could readily contribute to improving the economics of the cellulosic biorefinery industry.

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Hydrolysis of Lignocellulosic Biomass in Hot-Compressed Water with Supercritical Carbon Dioxide.

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