Combination of green solvents for efficient sugarcane bagasse fractionation

Abstract

This work addresses an unprecedented combination of solvents (choline chloride and oxalic acid deep eutectic solvent, carbon dioxide, and ethanol) that were used to fractionate sugarcane bagasse into three main fractions: 1) glucan rich fibers, 2) dissolved hemicellulose sugars and co-products, and 3) precipitated lignin. To maximize the lignin removal, a two-level three-variable design of experiments assessed the effects of solids loading, DES to biomass mass ratio, and the amount of CO2. Following, kinetic were carried out in temperatures varying from 130 to 190 °C, using anhydrous and hydrated ethanol to improve hemicellulose hydrolysis and delignification. At the best condition, delignification extent as high as 90% were obtained after reaction times of 30 min. These results were accompanied by glucan contents of approximately 85 wt% and by over 80% of fibers' glucan maintenance. Also, over 60% of the hemicellulose sugars were dissolved in a liquid fraction. Finally, the third fraction was composed of the precipitated lignin with negligible carbohydrate contents. Lignin samples presented low apparent average molecular masses, and FT-IR spectra demonstrated the presence of bands typical of lignin samples from herbaceous crops. In general, this work attested to the technical feasibility of using green solvents for the efficient fractionation of sugarcane bagasse into streams that could be exploited to produce fuels, chemicals, and biomaterials.