Acid post-hydrolysis of xylooligosaccharides from hydrothermal pretreatment for pentose ethanol production

• The acid post-hydrolysis of a hydrothermal hemicellulosic hydrolysate was studied.
• The performances of three acids: oxalic, maleic and sulfuric acid was compared.
• The C5-rich post-hydrolysates were fermented with a wild-type yeast.
• Sulfuric acid showed the best kinetic of post-hydrolysis of xylooligosaccharides.
• Acid post hydrolysis increases overall ethanol yield from sugarcane bagasse.

Hydrothermal pretreatment solubilizes about 65% of the hemicelluloses in sugarcane bagasse. However, nearly 80% of the xylose recovered from the hemicellulosic hydrolysate is present as xylooligosaccharides (XO’s), which cannot be directly fermented into pentose (C5) ethanol. In this work a kinetic study of the post hydrolysis process considering the use of three acids – sulfuric, oxalic and maleic – was performed. Xylose and furfural post-hydrolysis profiles showed the reaction time in which xylose peaked with minimum furfural production. Among the three studied acids, sulfuric acid showed the fastest kinetics of post-hydrolysis with XO’s being fully hydrolyzed in less than 1 h reaction time. C5 fermentation experiments showed that the detoxified post-hydrolysates fermented with ethanol yields ranging from 0.10 to 0.31 g ethanol g−1 reducing sugars. Most samples were fermented from 48 to 72 h of experiment with productivities ranging from 0.02 to 0.43 g ·L−1 ·h−1.

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