Separating Miscible Liquid–Liquid Mixtures Using Supported Ionic Liquid Membranes

Abstract

Supported liquid membranes (SLMs) are promising in separating miscible liquid–liquid mixtures, which has been a key challenge in wastewater treatment and other applications. However, SLMs suffer from poor durability due to the loss of the liquid phase. In current work, ionic liquids (ILs) with high stability have been impregnated into polyvinylidene fluoride membranes to separate miscible benzene–heptane mixtures. The two imidazolium-based ILs, that is, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]­[PF6]) and 1-butyl-3-methylimidazolium tris­(pentafluoroethyl) trifluorophosphate ([BMIM]­[FAP]), were tested in supported ionic liquid membranes (SILMs) for the benzene–heptane separation. Both ILs show successful separation within 48 h as indicated by nuclear magnetic resonance results. Compared to the SILM with [BMIM]­[FAP], the SILM with [BMIM]­[PF6] has lower throughput and higher selectivity. The higher selectivity can be attributed to the higher hydrophilicity of [BMIM]­[PF6], which results in strong repulsion against heptane. The lower throughput can be attributed to the higher hydrophilicity as well since it lowers the solubility of benzene in [BMIM]­[PF6]. The stability of IL in SILMs has also been investigated via multiple separation cycles. The scanning electron microscopy, weight change of SILMs, and separation results indicate that the separation efficiency of the [BMIM]­[PF6] SILM does not degrade for up to 144 h. The SILM has been further optimized with curvature design (i.e., curved SILM) to increase the interfacial area and thus increase the separation throughput, where the curved SILM separation device was 3D-printed. The findings here have important implications on design and application of SILMs in separating miscible liquid–liquid mixtures.

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

“…This makes it clear that the separation of the homogeneous mixture merely relying on intermolecular interactions between the prewet hydrophobic IL and the target hydrophilic IL is of limited utility. Also, the residence time possible in flow is likely insufficient for equilibrium ILM separations, as literature reports of such approaches describe incubation times up to 50 h in batch . Recovery rates using the AAA batch and flow processes slightly varied due in great part to the material loss in the flow device, as discussed above.…”

“…17 ILMs are polymeric membranes (e.g., polyvinyl fluoride) prewet by a hydrophobic IL that preferably permit the permeation of similar organic compounds while others are selectively excluded. 44 In this case, the IL membrane is selective for the IL in the water-IL mixture. Although the reported recovery rates of the water-miscible ILs were observed to reach 70%, non-negligible amounts of polarsoluble impurities still remained and accumulated in the recycled IL products leading to degraded quality of Pt nanoparticles upon subsequent recycling and reuse.…”

“…One example can be found in our previous work where three IL solvents with complete water miscibility were recycled using supported IL membranes (ILMs), with water being a better washing agent than VOCs (i.e., hexanes) in this role . ILMs are polymeric membranes (e.g., polyvinyl fluoride) prewet by a hydrophobic IL that preferably permit the permeation of similar organic compounds while others are selectively excluded . In this case, the IL membrane is selective for the IL in the water-IL mixture.…”

Development of a Purification Method for 89Sr Produced in a Fast Reactor Using a Supported Liquid Membrane

“…The choice of extractant, diluent, solid support, and compositions of the solutions in the feed and strip chambers dictates the selectivity and enrichment of the element or analyte of interest achievable in the process. 8,9 Among the various potential 18C6 group crown ethers, DtBuCH18C6 exhibits a higher extraction efficiency of Sr owing to its reduced association probability, which is attributed to the presence of bulky tertiary butyl groups as well as to its higher hydrophobicity. 10 DtBuCH18C6 has also been used in many applications using various separation techniques.…”

“…This technique, further, combines the advantages of both solvent extraction as well as solid membrane separation and offers certain advantages over the above-mentioned separation processes, which constitute some of the desirable features for remote operation in a hot cell facility, i.e., (i) ease of adaptation to the automation for convenient reprocessing in a hot cell facility, (ii) generation of less radioactive liquid waste, and (iii) needing relatively less manual interventions during radiochemical reprocessing. The choice of extractant, diluent, solid support, and compositions of the solutions in the feed and strip chambers dictates the selectivity and enrichment of the element or analyte of interest achievable in the process. , Among the various potential 18C6 group crown ethers, DtBuCH18C6 exhibits a higher extraction efficiency of Sr owing to its reduced association probability, which is attributed to the presence of bulky tertiary butyl groups as well as to its higher hydrophobicity . DtBuCH18C6 has also been used in many applications using various separation techniques. , Thus, DtBuCH18C6 was used in our study as the associated extractant of choice with SLM for the purification of strontium from the yttrium matrix as well as from the other associated impurities.…”