Abstract
Bioconversion of hemicellulose sugars is essential for increasing fuel ethanol yields from lignocellulosic biomass. We report for the first time with rape straw, bioethanol production from hemicellulose sugars. Rape straw was pretreated at mild conditions with sulfuric acid to solubilize the hemicellulose fraction. This pretreatment allows obtaining a prehydrolysate, consisting basically in a solution of monomeric hemicellulosic sugars, with low inhibitor concentrations. The remaining water insoluble solid constitutes a cellulose-enriched, free of extractives material. The influence of temperature (120ºC and 130ºC), acid concentration (2-4% w/v) and pretreatment time (30-180 min) on hemicellulose-derived sugars solubilisation was evaluated. The highest hemicellulosic sugars recovery, 72.3%, was achieved at 130ºC with 2% sulfuric acid and 60 min. At these conditions, a concentrated sugars solution, 52.4 g/L, was obtained after three acid consecutive contacts, with 67% xylose and acetic acid concentration above 4.5 g/L. After a detoxification step by activated charcoal or ion-exchange resin, prehydrolysate was fermented by ethanologenic Escherichia coli. An alcoholic solution of 25 g/L and 86% of theoretical ethanol yield was attained after 144 h when the prehydrolysate was detoxified by ion-exchange resin. The results obtained in the present work show sulfuric acid pretreatment under mild conditions and E. coli as an interesting process to exploit hemicellulosic sugars in rape straw.
Highlights
Rape straw obtained from oilseed rape crop (Brassica napus L.) primarily cultivated for seed oil can be considered as an attractive agricultural residue for bioethanol production
We report for the first time with rape straw, bioethanol production from hemicellulose sugars
After a detoxification step by activated charcoal or ion-exchange resin, prehydrolysate was fermented by ethanologenic Escherichia coli
Summary
Rape straw obtained from oilseed rape crop (Brassica napus L.) primarily cultivated for seed oil can be considered as an attractive agricultural residue for bioethanol production Nowadays, this residual biomass that remains in the fields after seed harvest, is poorly exploited (Wood et al, 2014) and it could be used as a feedstock for ethanol production by means of a biochemical process (Castro et al, 2011). Physical and biological methods have been reported in the science literature to detoxify slurries and hydrolysates from different feedstocks. These methods can be applied separately or in combination (Jönsson et al, 2013)
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