(357f) Selective Separation and Recovery of Ionic Liquids (ILs) As Pretreatment Solvents for an Effective Recycling Approach

The use of ionic liquids (ILs) and deep eutectic solvents (DESs) as biomass pretreatment solvents is one of the most effective methods for achieving high yields of biomass-derived fermentable sugars (for bioenergy production). However, the cost of the pretreatment chemical and its recovery rate are the most significant challenges that must be addressed before commercial deployment. These involve developing strategies to discover ILs/DESs from cheap and affordable reagents, as well as, developing effective techniques to recover and recycle them, therefore, reducing the make-up chemical needed for future cycles. Consequently, the present study focuses on developing an integrated process for separating and recovering pretreatment solvents after use that will eliminate solid-liquid separations and enable process intensification. To enable this process, we utilize a subclass of ILs (called protic ionic liquids PILs) that can be readily recovered with little energy input. The objectives of this study involves (1) examine the interaction between IL and lignin (and polysaccharides) to understand the factors that enable lignin extraction, (2) determine the different process configurations to integrate recycling with pretreatment and downstream processes, and (3) track each component during the pretreatment process to study the impact of IL treatment/recycling regimes on the biomass composition, structure, and the quality of the recovered products. Preliminary results show that the ILs can be recovered at a rate of 85-98% depending on the solids loading of the biomass while releasing sugars at a rate of ≥70% of the theoretical yield. Additionally, different analogues the ILs were screened to improve processing conditions. By varying the chemical structure of the cations, we can increase recyclability without affecting the pretreatment effectiveness or sugar release. Finally, the most favorable process configuration that maximizes both IL recovery, along with, pretreatment effectiveness (sugar yield and lignin solubility) is highlighted.