Development of dilute sulfuric acid pretreatment method for the enhancement of xylose fermentability

•A significant dilute sulfuric acid pretreatment process has been developed for sorghum biomass hydrolysis.•5-HMF (0.6−0.68 g/L), Formic acid (1.45-1.59 g/L), Acetic acid (3.3-3.82 g/L) and Phenolic compounds (1.04-1.18 g/L).•Growth of Pichia stipits was not deterred due the presence of low concentration of fermentative inhibitors.•Enhanced ethanol yield of 86-91% was achieved during the fermentation of prehydrolyzates at 30 °C, pH 6 and 120 rpm.

Dilute acid pretreatment of sorghum stalks was performed for the characteristic xylulosic ethanol production using Pichia stipitis. In this regard, various pretreatment parameters were studied for the maximum xylose production with minimized xylose decomposition. As a result, 89% of xylan conversion was attained along with 22 mg of xylose decomposition at 121 °C with 0.2 M sulfuric acid for 120 min. In addition to this, prehydrolyzate liquors were detoxified with calcium hydroxide [Ca(OH)2] at different pH levels (i.e., 8.5-11.5) to investigate the fermentative inhibitors removal and their impact on xylulosic ethanol production. Consequently, the highest theoretical ethanol yield (91%) was achieved during the fermentation of prehydrolyzate detoxified at pH 11.5. Moreover, 0.46 gp/gs ethanol yield and 0.48 g/L/h ethanol productivity was achieved within 24 h incubation time of Pichia stipits NCIM 3498.

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