Ethanol organosolv pretreatment of sugarcane bagasse assisted by organic acids and supercritical carbon dioxide

Abstract

The scCO₂-assisted organosolv pretreatment of sugarcane bagasse was carried out using aqueous ethanol and organic acid catalysts. Variables involved were temperature (150-190 °C), time (0-60 min), type of catalyst (acetic, citric, and oxalic acids), amount of CO₂ (25-50 g), ethanol titer in water (0-80 vol%), and catalyst concentration (0.5 to 1.5 % w·v^-1). The best delignification (86 wt%) and glucan retention (89 wt%) were achieved at 170 °C for 15 min using 60 vol% ethanol in water, 1 wt% oxalic acid, and 25 g CO₂. Organic acid esterification was a limitation for pretreatment operations using ethanol titers above 60 vol%. Enzymatic hydrolysis of pretreated materials at 1 % (w·v^-1) glucans released 74.3 ± 0.2 % glucose in 96 h using Cellic CTec3 (Novozymes) at 9.89 FPU·g_glucans^-1. The concentrated pretreatment liquor allowed lignin recovery by water precipitation in high yields, while the aqueous supernatant contained low levels of fermentation inhibitors.

Keywords: Fractionation; Organosolv ethanol; Oxalic acid; Sugarcane bagasse; Supercritical carbon dioxide.