The impacts of deacetylation prior to dilute acid pretreatment on the bioethanol process
Xiaowen ChenJoseph ShekiroMary Ann FrandenWei WangMin ZhangErik M. KuhnDavid K. JohnsonMelvin P. Tucker
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Abstract:
Dilute acid pretreatment is a promising pretreatment technology for the biochemical production of ethanol from lignocellulosic biomass. During dilute acid pretreatment, xylan depolymerizes to form soluble xylose monomers and oligomers. Because the xylan found in nature is highly acetylated, the formation of xylose monomers requires two steps: 1) cleavage of the xylosidic bonds, and 2) cleavage of covalently bonded acetyl ester groups.In this study, we show that the latter may be the rate limiting step for xylose monomer formation. Furthermore, acetyl groups are also found to be a cause of biomass recalcitrance and hydrolyzate toxicity. While the removal of acetyl groups from native corn stover by alkaline de-esterification prior to pretreatment improves overall process yields, the exact impact is highly dependent on the corn stover variety in use. Xylose monomer yields in pretreatment generally increases by greater than 10%. Compared to pretreated corn stover controls, the deacetylated corn stover feedstock is approximately 20% more digestible after pretreatment. Finally, by lowering hydrolyzate toxicity, xylose utilization and ethanol yields are further improved during fermentation by roughly 10% and 7%, respectively. In this study, several varieties of corn stover lots were investigated to test the robustness of the deacetylation-pretreatment-saccharification-fermentation process.Deacetylation shows significant improvement on glucose and xylose yields during pretreatment and enzymatic hydrolysis, but it also reduces hydrolyzate toxicity during fermentation, thereby improving ethanol yields and titer. The magnitude of effect is dependent on the selected corn stover variety, with several varieties achieving improvements of greater than 10% xylose yield in pretreatment, 20% glucose yield in low solids enzymatic hydrolysis and 7% overall ethanol yield.Keywords:
Corn stover
Hemicellulose
Lignocellulosic Biomass
Stover
Enzymatic Hydrolysis
Corn stover
Stover
Lignocellulosic Biomass
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Hemicellulose
Corn stover
Stover
Degradation
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White rot fungi with different degradation patterns may have different effects on the thermal characteristics and pyrolysis products of biomass. Therefore, the influences of two fungal pretreatments with different degradation effects on thermal characteristics and pyrolysis products of corn stover were investigated. Auricularia polytricha AP degraded lignin, cellulose and hemicellulose with lignocellulolytic enzymes. Stereum hirsutum ZT had no ability to degrade hemicellulose and lignin, despite its higher xylanase activity. Thermogravimetry and kinetic parameter analysis demonstrated that the initial pyrolysis temperature and activation energies of corn stover treated by fungi were lower than that of untreated corn stover. Pyrolysis-gas chromatography–mass spectroscopy analysis suggested that differences within pyrolysis vapors could be observed between biopretreated and untreated corn stover, and that the degradation pattern of fungi made a difference to the pyrolysis products.
Corn stover
Hemicellulose
Thermogravimetry
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Stover
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Hemicellulose
Corn stover
Enzymatic Hydrolysis
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