Ionic liquid pretreatment of sweet sorghum bagasse to improve fermentable sugars and platform chemicals obtained from subcritical water hydrolysis

Sweet sorghum bagasse (SSB) is a promising feedstock for cellulosic ethanol production because of its composition and productivity. The use of SSB pretreated with 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) before subcritical water hydrolysis (SWH) aiming the production of fermentable sugars and platform chemicals was investigated. Modifications in the composition of SSB at different conditions (100°C and 120°C; 2, 4, and 6 h) were evaluated by the thermogravimetric analysis. Sequentially, pretreated SSB was submitted to subcritical water hydrolysis, whose conditions were 220°C and 260°C, and solvent/feed ratios of 80 and 100 g water/g sample (R-80 and R-100) were considered. Maximum enrichment in hemicellulose content and minimum cellulose content was reached in 2 h for pretreatment at 100°C. SSB pretreated with [Bmim]Cl presented enrichment in hemicellulose content from 37.95 to 90.07%, and a 76.9% reduction in lignin content. Therefore, pretreated SSB from this condition was submitted to SWH, resulting in 19.18 g of fermentable sugars per 100 g of sample at 220°C and R-100. The yield of fermentable sugars using SSB pretreated with [Bmim]Cl increased 2.05 times compared with unpretreated under the same condition of SWH (220°C/R-100/10 min). The higher platform chemicals production from pretreated SSB was 15.25 g per 100 g of sample at 220°C and R-80, lower when compared with untreated SSB at 220°C and R-100. Optimizing the solvent/feed ratio is crucial for balancing fermentable sugar and platform chemical production via SWH. [Bmim]Cl pretreatment and ratio optimization enhance product yields significantly.