In-depth process parameter investigation into a protic ionic liquid pretreatment for 2G ethanol production

Abstract

Protic ionic liquids (PILs) are promising pretreatment agents that can efficiently deconstruct lignocellulosic biomass for 2G ethanol production. PIL synthesis is less costly than that of aprotic imidazolium-based ILs thereby reducing the final ethanol price. However, a more comprehensive investigation is still necessary in order to better understand how PILs affect biomass during pretreatment. An investigation of process parameters was carried out for pretreatment of sugarcane bagasse using the PIL monoethanolammonium acetate, [MEA]OAc], focussing on main pretreatment parameters — time, temperature, solids loading, and water content. Optimal conditions were found to be 2 h, 150 °C, 15 wt% solids loading and 20 wt% water content. Lignin solubilization of almost 60 wt% was achieved with no carbohydrate losses, leading to 78.6% and 49% of cellulose and hemicellulose yields during saccharification. The addition of hemicellulases increased the hemicelluloses yield in saccharification to up to 66% with a high enzyme loading, 5.8 wt%. Ethanol, isopropanol, isoamyl alcohol and water were tested as anti-solvents; none of which led to higher sugar yields or modified recovered lignin structures, as confirmed by spectroscopic methods. Lignin analysis revealed the presence of S, G and H moieties, low degree of condensation, and a potential to produce aromatic compounds that could add value to the biorefinery.