Abstract
Sweet sorghum is a unique bioenergy crop that produces stalks with fermentable free sugars. The purpose of this study was to evaluate how the production of hemicellulosic saccharides and bioethanol from sweet sorghum stalks (SSS) can be influenced by a dilute sulfuric acid (H2SO4) pretreatment under different isothermal conditions. The bioethanol production from untreated SSS and pretreated solid phases was achieved through the Simultaneous Saccharification and Fermentation (SSF) process. A good SSS fractionation and an extensive hemicellulose hydrolysis into soluble saccharides were obtained, the most abundant hemicellulose-derived compounds present in the pretreated liquid phase being monosaccharides, with up to 17.22 g/L of glucose and 16.64 g/L of xylose in the pretreatments performed with 3% and 1% H2SO4 for 30 min at 134 °C, respectively. The SSF process of untreated SSS allowed a maximum bioethanol concentration of 9.78 g/L, corresponding to a maximum glucan conversion into ethanol of 49.8%. Bioethanol production from untreated SSS led to a higher bioethanol concentration and conversion than in the case of using acid pretreated solid phases obtained under the most severe conditions (with 3% H2SO4 for 30, 60 and 120 min at 134 °C), suggesting that, in the case of this biomass naturally rich in soluble sugars, the acidic pretreatment could negatively influence the fermentative process.
Highlights
The increasing demand for fossil fuels and the environmental concerns regarding global warming, greenhouse gas emissions and energy security have accelerated the uptake of biofuels from alternative feedstocks in the transport sectors
Biofuels such as bioethanol bring a number of important benefits: (i) they are obtained from renewable biomass resources: (ii) they are environmentally friendly; (iii) they can use a large part of the existing industrial infrastructure; and (iv) the carbon dioxide resulting from their combustion does not contribute to the intensification of the “greenhouse effect” [1,2]
This work aimed to investigate the effect of pretreatment with dilute sulfuric acid under various isothermal conditions on the production of hemicellulosic saccharides from Romanian sweet sorghum, as well as on the bioethanol production from untreated sorghum stalks (SSS) and pretreated solid phases through Simultaneous Saccharification and Fermentation (SSF)
Summary
The increasing demand for fossil fuels and the environmental concerns regarding global warming, greenhouse gas emissions and energy security have accelerated the uptake of biofuels from alternative feedstocks in the transport sectors. Biofuels such as bioethanol bring a number of important benefits:. Considering that, sweet sorghum is one of the most promising sources for bioethanol production that could limit food and feed crops-based biofuels from cereal and other starch-rich crops [5]. Sweet sorghum is a unique bioenergy crop that produces lignocellulosic stalks with high amounts of energy biomass and fermentable sugars [7,9]
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