Polymeric Ionic Liquid Compositions for In-Situ Product Removal Bioreactor Applications

Abstract

Although the biosynthesis of n-butanol and succinic acid can afford renewable fuels, solvents, and chemical intermediates, these bioprocesses suffer from the cytotoxicity of their end products, leading to reduced production rates. In-situ product removal using a two-phase partitioning bioreactor (TPPB) can alleviate this problem by sequestering reaction products in a secondary, non-aqueous phase. Effective sorbents for TPPB applications are biocompatible materials with a high thermodynamic affinity for the product, as quantified by partition coefficient (PC), and a preference for solute over water, as measured by selectivity (α). In this work, the absorptive capacity of imidazolium-based ionic liquids (ILs) are combined with the attractive physical properties of polymeric sorbents by synthesizing a range of polymeric ionic liquid (PIL) compositions. Careful measurements of PIL molecular weight, glass transition temperature (Tg) and crystallinity were followed by systematic studies of the effect of imidazolium cation substituents and counter-anions on PC and α for the n-butanol-water system. P[(VC12-linIm)(Br)] was identified as the most promising PIL n-butanol absorbent by virtue of a PCBuOH = 7.4 ± 0.3, and αb/w = 97 ± 7. An expanded study of the ternary PIL/water/n-butanol phase diagram was integrated with material balance equations for a solute recovery process to gain insight into the impact of polymer phase fraction, PC, α, feed concentration, and Tg on the recovery of n-butanol from dilute fermentation media. The final phase of the project exploited experience gained on the preparation and phase behavior of P[(VC12-linIm)(Br)] to prepare a hydroxide-functionalized PIL. The utility of this base-functionalized material to chemisorb succinic acid from dilute aqueous solution was demonstrated along with its resilience toward repeated regeneration and reuse.