Optimizing dilute acid pretreatment for enhanced recovery and co-fermentation of hexose and pentose sugars for ethanol and butanol production

[Display omitted] •Economic sustainability of biofuels relies on efficient C5 and C6 sugar use.•Optimized DA pretreatment: C6-rich solid, C5-rich liquid, and minimal inhibitors.•Fermentative routes evaluated: ABE fermentation for 2G butanol, SIcF for 2G.•ethanol.•Cellulosic and hemicellulosic hydrolysates were suitably fermentable.•Pretreatment severity to predict sugars and by-products in other conditions. A systematic study of dilute acid pretreatment of sugarcane bagasse was performed to optimize the recovery of hexose-rich solid and pentose-rich liquid while minimizing fermentation inhibitors. Pretreatment experiments evaluated the effects of pretreatment time (10–90 min) and acid concentration (0.5–3.0 % w/w). The optimized pretreatment (1.4 % w/w sulfuric acid, 56.4 min at 121 °C) led to a solid fraction with 60.4 % cellulose and a liquid stream rich in pentose, in which 92.7 % of sugars was recovered as xylose (17.8 g/L). Besides that, low concentrations of by-products (3 g/L – the sum of acetic and formic acid, furfural, and HMF) were identified in the liquid fraction. Both fractions were integrated into enzymatic processes for further co-fermentation of C5- and C6- sugars. Two fermentative routes were evaluated: simultaneous isomerization of xylose and co-fermentation of glucose and xylulose (SIcF) for 2G ethanol production and acetone-butanol-ethanol (ABE) fermentation of glucose and xylose for biobutanol, utilizing Saccharomyces cerevisiae and Clostridium acetobutylicum, respectively. SIcF yielded 0.48 gethanol/gsugars (24 g/L ethanol) with complete glucose consumption and 58.2 % xylose conversion. ABE fermentation produced 0.36 gABE/gsugars (15.7 g/L ABE and 9.5 g/L butanol), with 96 % glucose consumption and 29.6 % xylose conversion. The proof-of-concept demonstrated that the hydrolysates were satisfactorily fermentable by microorganisms, thus validating the pretreatment optimization for fermentation applications.