In Situ Synthesis of Protic Ionic Liquids for Biomass Pretreatment
Ionic liquids (ILs) have emerged as versatile solvents that are facilitating advances in many industries such as energy storage, separations, and bioprocessing. Despite their great promise, the cost of many ILs remains excessively high, thus limiting their scalability and commercialization. Therefore, the aim of this paper was to develop a simple and integrated process for synthesizing protic ionic liquids (PILs) in situ, while utilizing them directly as pretreatment solvents for biomass deconstruction/biorefining. The in situ method eliminates the major steps associated with increased cost and carbon footprint, thereby yielding an economically advantaged and environmentally efficient process. The PIL hydroxyethylammonium acetate ([Eth][OAc]) was utilized in the pretreatment and enzymatic hydrolysis of sorghum biomass with the in situ method, which demonstrated equivalent sugar yields relative to the presynthesized [Eth][OAc]. Techno-economic analysis demonstrated the economic advantage of the in situ synthesis over other PIL synthesis methods, due to its reduction of production costs up to $2.9/kg, while the life-cycle assessment showed the environmental efficiency of the process, yielding >30% reduction of GHG per kilogram of PIL. Therefore, this method demonstrates an improvement in the sustainability impact for the utilization of PILs for biomass pretreatment and other IL-utilizing processes.