One-pot ionic liquid pretreatment and saccharification of switchgrass

Abstract

Biomass pretreatment using certain ionic liquids (ILs), such as 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]), can be highly effective at reducing the recalcitrance of lignocellulosic biomass to enzymatic degradation. However, current commercial enzyme cocktails, derived from filamentous fungi and developed for dilute acid pretreatment, are inhibited by the most effective ILs used for pretreatment and require excessive amounts of water to remove the ILs from biomass after pretreatment in order to be effective. The associated IL recycling and waste disposal costs of this process pose significant economic and process engineering challenges for the commercial scale-up of IL pretreatment-based technologies. For the first time, we have demonstrated a one-pot, wash-free process that combines IL pretreatment and saccharification into a single vessel. After treating the switchgrass with [C₂mim][OAc] and dilution with water to a final IL concentration of 10–20%, the pretreatment slurry was directly hydrolyzed using a thermostable IL tolerant enzyme cocktail previously developed at the Joint BioEnergy Institute (JBEI). This one-pot process liberated 81.2% glucose and 87.4% xylose (monomers and oligomers) at 72 h at 70 °C with an enzyme loading of 5.75 mg g⁻¹ of biomass at 10% [C₂mim][OAc]. Glucose and xylose were selectively separated by liquid–liquid extraction with over 90% efficiency, thus eliminating extensive water washing as a unit operation. This study opens avenues for developing more efficient and cost effective processes for product recovery and IL recycling.