Purification of Ionic Liquid Solvents in a Self-Optimizing, Continuous Microfluidic Process via Extraction of Metal Ions and Phase Separation

Abstract

Industrial applications of ionic liquids (ILs)solvents that can serve as green alternatives to volatile organic compoundsare often hampered by their high cost. Solvent recycling provides a feasible pathway to recover IL solvents to reduce lifecycle costs. Herein, we demonstrate a continuous microfluidic process to purify metal-ion-loaded IL solvents, wherein Fe(III) ions are extracted from a prototypical IL, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-NTf2), to deionized (DI) water with subsequent membrane separation of the IL and aqueous phases. Inline analytical tools, design of experiment statistical optimization, and a self-optimizing, modified Nelder-Mead simplex algorithm facilitate locating the best parametric operating conditions to optimize both ion extraction and physical phase separation. This process was then adapted to a more challenging purification application: recovery of the IL trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethyl-pentyl)phosphinate (Cyphos 104) from the rare-earth metal Nd(III). This application demonstrated that optimized conditions obtained from a single stage could be applied across a multistage process. Together, these results demonstrate that statistical and inline optimization tools can be used to identify working parameters for different flow systems with a variety of governing fluid properties, for example, viscosity and interfacial tension.

A Multistep, Multicomponent Extraction and Separation Microfluidic Route to Recycle Water-Miscible Ionic Liquid Solvents

“…Fe(III) ions are a good indicator of the water-IL biphasic extraction because they are spectrophotometrically detectable at 310 nm and complete mass transfer from the IL phase to the aqueous phase can occur. 50 Fe(III) ion-loaded BMIM-OTf, as-received BMIM-NTf 2 , and DI water were injected into the recycler for the step of extraction of Fe(III) ions, and acidified water at pH = 0 was used to recover the washed BMIM-OTf from the IL phase in two stages for the second step. Interestingly, during membrane separation, the aqueous phase became the permeate phase, passing through the normally hydrophobic PTFE membrane.…”

“…To study the efficiency of extracting impurities from the OTf – IL with the recycler, Fe­(NO 3 ) 3 was added to the as-received BMIM-OTf solvent. Fe­(III) ions are a good indicator of the water-IL biphasic extraction because they are spectrophotometrically detectable at 310 nm and complete mass transfer from the IL phase to the aqueous phase can occur . Fe­(III) ion-loaded BMIM-OTf, as-received BMIM-NTf 2 , and DI water were injected into the recycler for the step of extraction of Fe­(III) ions, and acidified water at pH = 0 was used to recover the washed BMIM-OTf from the IL phase in two stages for the second step.…”

“…In the batch procedure, the same reagents at the same volumetric ratios were mixed and then phase separated via centrifugation. We also benchmarked this system performance against an ILM separator, as described above and deployed in our previous work. , This separator utilized an identical 0.1-μm-pore PTFE membrane incubated with BMIM-NTf 2 overnight prior to use. The retentate phase was collected as the washed IL product, in line with the operation of the two-step flow process.…”

“…In-Flow Purification of Fe(III)-Loaded BMIM-OTf in ILM Separation. A membrane separator was designed as previously reported 50 and fabricated using the above-described 3D-printing technique. The separator was prewet thoroughly with BMIM-NTf 2 .…”

A techno-economic approach to guide the selection of flow recyclable ionic liquids for nanoparticle synthesis

“…[33][34][35] For this reason, we used 0.1 M HNO 3 to wash the used ILs in the continuous ow recycler, integrating extraction (via mixing) and separation, adapted from a previous study. 36 All six ILs were serially washed 3× in ow with identical ow rates to complete a purication cycle, corresponding to a typical 3× wash in a by-hand batch workup.…”