Ionic Liquid Membranes Research Articles

A facilitated transport membrane composed of amine-containing ionic liquid confined in a GO/CNT network for highly efficient carbon capture

Carbon capture is a key approach to manage carbon dioxide (CO2) emissions and promote net removal of CO2 from the atmosphere. Post combustion flue gas emissions from power plants contribute a significant fraction of CO2 released into the atmosphere. Membrane-based separation strategies offer environmentally sustainable and economically viable solutions for efficient CO2 capture from power plants. Facilitated transport membranes, although showing strong capability for CO2 capture at low concentrations and under humid conditions, suffer from the loss of facilitators, such as amines, leading to decline in performance over long-term operation. Ionic liquids (ILs) are chemically and thermally stable and have low vapor pressure, which is ideal to prevent aforementioned losses. However, making a thin network for effective IL confinement is still a challenge. In this work, we developed a stable high performing IL based CO2 selective membrane that can operate at temperatures as high as 80 °C under humid conditions. An amino acid-based IL (containing facilitated carriers), 1-ethyl-3-methylimidazolium glycinate, [EMIM][GLY], was used as the separating agent. In order to selectively load and confine the IL in a thin selective layer, we designed and fabricated a network composed of stacked graphene oxide (GO) nanosheets intercalated by carbon nanotubes (CNT). While CNT acts as a nanowedge that helps in increasing the nanochannels to facilitate low-resistance gas transport, GO nanosheets act as anchoring sites due to presence of various functional groups resulting in electrostatic interaction between GO and cation of IL. Due to the aforementioned reason, distribution of GO in the network plays a critical role in forming a thin, uniform selective IL layer. The GO distribution was optimized by adjusting the pH of the coating solution; after optimizing IL coating, this results in a thin, defect free selective layer, providing a membrane with high CO2 permeance of ∼1600 GPU and CO2/N2 selectivity of 400, superior to most of the reported IL membranes. This network composed of GO/CNT network not only facilitates fabrication of a stable, ultrathin, high permeance and high selectivity supported IL membrane but also provides a platform for preparation of other IL-based membranes for desired separations.

Accelerated CO2 preferential permeation using graphene oxide confined ionic liquid membranes for CO2/H2 separation

Due to the enhanced mass transfer process of nanochannels and the high affinity of ionic liquids (ILs) for carbon dioxide (CO2), the membranes combined with 2D nanosheets and ILs have attracted significant attention in carbon capture, utilization, and storage (CCUS). However, regulating the structure of IL to enhance the separation performance of CO2 remains a big challenge. Herein, we selected different imidazolium-based ILs and proposed a simple strategy to prepare nano-confined IL membranes by intercalating ILs into graphene oxide (GO). These membranes are subsequently used to remove CO2 from industrial syngases, where they display an abnormal CO2 preferential permeation process relative to the smaller H2 molecule. Meanwhile, CO2 permeation decreases gradually with the increase of alkyl chain length, whereas CO2/H2 selectivity shows a tendency to first increase and then decrease. Interestingly, all GO-confined IL membranes surpass the Robeson upper bound, achieving peak CO2 permeance of 13.85 GPU and CO2/H2 selectivity of 13.58, respectively. Further characterization of the interlayer spacing and density functional theory (DFT) calculations reveal that the high CO2/H2 separation performance mainly arises from the fact that nano-confined ILs can block the transit of H2 through the dense packing structure, simultaneously enhancing CO2 solubility and permeability through the membrane. These quantitative insights into the nanoconfined IL membrane not only deepen the scientific understanding of the abnormal transfer process within the nanochannel but also propose novel methodologies for preparing high-performance CO2 capture membranes.

Mesoporous silica modified alumina improves pressure stability of supported ionic liquid membranes

Supported liquid membranes (including those containing ionic liquids) offer the opportunity for high selectivity for a target gas imparted by the properties of the functional liquid or liquid mixture, along with high flux resulting from gas permeation through a liquid rather than a solid. One disadvantage of supported liquid membranes is limitations on the transmembrane pressure (TMP) they can sustain. Liquids held in the pores of the support by capillary forces are prone to “blow-out” at relatively modest TMP values. Here, we modify anodic aluminum oxide (AAO) membranes with uniformly sized ∼6–8 nm diameter cylindrical silica mesopores to improve the blow-out TMP. This modification increases the feasible TMP for various ionic liquids from ∼4 bar to more than ∼20 bar. Additionally, the liquid in the membrane at depths where the AAO membrane has not been modified (i.e., greater than a few microns) is expelled from the large pores, reducing the effective thickness of the liquid in the membrane and increasing permeance. This approach is analogous to asymmetric polymeric membranes, which are the standard of the commercial membrane industry. These findings open up the opportunity for investigation and use of supported liquid membranes at much higher TMPs than has been previously possible.

Cationic Imidazolium-Urethane-Based Poly(Ionic Liquids) Membranes for Enhanced CO2/CH4 Separation: Synthesis, Characterization, and Performance Evaluation.

The escalating emissions of CO2 into the atmosphere require the urgent development of technologies aimed at mitigating environmental impacts. Among these, aqueous amine solutions and polymeric membranes, such as cellulose acetate and polyimide are commercial technologies requiring improvement or substitution to enhance the economic and energetic efficiency of CO2 separation processes. Ionic liquids and poly(ionic liquids) (PILs) are candidates to replace conventional CO2 separation technologies. PILs are a class of materials capable of combining the favorable gas affinity exhibited by ionic liquids (ILs) with the processability inherent in polymeric materials. In this context, the synthesis of the IL GLYMIM[Cl] was performed, followed by ion exchange processes to achieve GLYMIM variants with diverse counter anions (NTf2-, PF6-, and BF4). Subsequently, PIL membranes were fabricated from these tailored ILs and subjected to characterization, employing techniques such as SEC, FTIR, DSC, TGA, DMA, FEG-SEM, and CO2 sorption analysis using the pressure decay method. Furthermore, permeability and ideal selectivity assessments of CO2/CH4 mixture were performed to derive the diffusion and solubility coefficients for both CO2 and CH4. PIL membranes exhibited adequate thermal and mechanical properties. The PIL-BF4 demonstrated CO2 sorption capacities of 33.5 mg CO2/g at 1 bar and 104.8 mg CO2/g at 10 bar. Furthermore, the PIL-BF4 membrane exhibited permeability and ideal (CO2/CH4) selectivity values of 41 barrer and 44, respectively, surpassing those of a commercial cellulose acetate membrane as reported in the existing literature. This study underscores the potential of PIL-based membranes as promising candidates for enhanced CO2 capture technologies.

Ionic liquid fluoropolymer membranes for the separation of R-410A: Understanding the effect of ionic liquid on membrane characteristics and separation performance

Environmental legislation such as the American Innovation and Manufacturing Act will phase out today's generation of high-global warming hydrofluorocarbon refrigerants over the next two decades. Energy-efficient technologies are needed to separate these often azeotropic and complex mixtures. Membrane technology and extractive distillation with ionic liquids as entrainers have been individually developed for the separation of azeotropic refrigerant mixtures. This study provides details for the separation of R-410A through combining the benefits of glassy, amorphous polymers with ionic liquids to form ionic liquid polymer membranes. Two different classes of ionic liquid polymer membranes are considered: polyvinyl acetate composite membranes with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, and 1-hexyl-3-methylimidazolium chloride, and Hyflon AD 60 with 1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide. The membranes are characterized with FTIR, helium pycnometry, differential scanning calorimetry, and a high-pressure view-cell to characterize the effect of ionic liquid on polymer properties. The Hyflon AD 60 composite membranes were evaluated for the separation of R-410A through pure-gas permeability, selectivity, solubility, and diffusivity measurements, which show exceptional selectivity for separation of R-410A. Results provide insights on the effect of ionic liquid on the separation of R-410A and indicate that improved separation performance of glassy polymers can be achieved with the addition of ionic liquid.

Construction of PEO@g-C3N4 supported ionic liquid membrane with interactive network structure for enhanced carbon capture efficiency

Polyethylene oxide (PEO) shows a high CO2-philic due to its dipolar-quadrupolar interaction with CO2 molecules. As a result, it is an excellent candidate for gas separation applications, yet it faces problems such as crystallization and low permeance. Herein, we show a versatile strategy to enhance gas permeation fluxes, which is mainly achieved by hindering the crystallization of PEO and the stacking of nanosheets. Specifically, graphite-like phase carbon nitride (g-C3N4) nanosheets are introduced and interaction networks (PGCN) are constructed by taking full advantage of the dipole-level quadrupole moment interactions between the ether-oxygen groups contained in PEO and CO2. In order to compensate the membrane surface defects for enhancing gas selectivity, we used the suspension coating method to create a PEO@g-C3N4 supported ionic liquid membrane (PGCN/ILX SILM) by coating IL on the surface of membrane. The results show that, when the IL concentration is 30 wt%, the PGCN/IL30 % membrane separates CO2/N2 with a CO2 permeance of 1396 GPU and an optimal selectivity of 58. While overcoming the “Trade-off” effect, it has demonstrated good thermal stability and long-term stable operation for 72 h. The development of this work will generate solutions for overcoming PEO crystallization and achieving efficient CO2 capture.

High-flux ultrasonic processing for lithium separation using ionic liquid impregnated composite membranes

Battery industry, one of the most crucial components of the modern world, relies heavily on lithium production, and brines from the spent battery materials is one of the most important sources to exploit lithium. A new ultrasonic assisted membrane processing is proposed for lithium separation simulated brine. The effects of membrane composition, feed concentration, and ultrasonic conditions on the lithium extraction efficiency have been explored. The composite membrane including polysulfone (PSF) as the support and 1-alkyl-3-methylimidazolium hexafluorophosphate and tributyl phosphate as ionic liquid membrane. A porous PVC membrane has been used for prevention of the ILM loss. The optimal ultrasonic frequency is approximately 250 kHz, which matches the bulk modulus of the membrane and enhances the separation efficiency. Higher frequencies and optimized amplitude and pulse cycle settings further improve the lithium flux and selectivity. Moreover, higher flux and selectivity are achieved when separating lithium from alkali metal chlorides at higher feed concentrations, ranging from 250 ppm to 1000 ppm. The mechanism of enhanced lithium extraction by ultrasonics is attributed to the combination of microbubble formation, cavitation, and heat generation, which disrupt the concentration gradient and facilitate lithium transport across the membrane.

Tailoring CO2/CH4 Separation Efficiency with [THTDP][Cl]/Pebax-1657 Supported Ionic Liquid Membranes: Design, Characterization, and Theoretical Insights

Tailoring CO2/CH4 Separation Efficiency with [THTDP][Cl]/Pebax-1657 Supported Ionic Liquid Membranes: Design, Characterization, and Theoretical Insights

Enhancing CO2 transport with plasma-functionalized ionic liquid membranes

The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate treated with radiofrequency plasma is proposed for functionalization and immobilization on polyethersulfone supports to form supported ionic liquid membranes for CO2 separation. The effects of treatment time and transmembrane pressure difference on CO2 permeance were evaluated. The best gas permeation performance was obtained with a treatment time of 10 min and the transmembrane pressure difference was 0.25 MPa. Characterization of the materials by Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and nuclear magnetic resonance spectroscopy demonstrates that the IL is grafted with carboxyl groups and deprotonated through plasma treatment. A preliminary mechanism for the plasma treatment and facilitated transport of CO2 has been proposed on this basis.

Amine functionalized supported ionic liquid membranes (SILMs) for CO2/N2 separation

Supported ionic liquid membranes (SILMs), containing aprotic N-heterocyclic anion ionic liquids (AHA ILs) in an inorganic inert support, exhibit CO2/N2 permselectivity values as high as 640 at 35.0 °C and 0.03 bar CO2, which represents conditions similar to post-combustion carbon capture (PCCC) from a natural gas power plant. A Fickian model fit to the experimental data estimates CO2 permeability at direct air capture (DAC) conditions of 10,400 barrer and a CO2/N2 permselectivity of 4000 for the best performing IL, triethyl(octyl)phosphonium 4-bromopyrazolide ([P2228][4-BrPyra]). The most important criterion for high selectivity is a large equilibrium constant for binding between the IL and CO2, which results in high CO2 solubility. ILs with smaller molar volumes and with no fluoroalkyl chains enhance N2 rejection. Low viscosity and high IL molar density also enhance CO2/N2 permselectivity and CO2 permeance.

Expression of Concern: Biocompatible cellulose acetate supported ammonium based ionic liquid membranes; way forward to remediate water pollution

Expression of Concern: Biocompatible cellulose acetate supported ammonium based ionic liquid membranes; way forward to remediate water pollution

Stability and kinetic insights for ibuprofen removal from aquaculture wastewater using green supported ionic liquid membranes

Pharmaceutical residues in aquaculture effluent have become a growing environmental concern due to their potential ecological impacts. Supported ionic liquid membranes (SILM) offer a promising solution for extracting micropollutants from contaminated sources. SILM was developed using Aliquat 336 in sunflower oil (SFO) as a carrier solution, specifically targeting ibuprofen (IBP) in aquaculture wastewater. Different solid supports are fabricated through the nonsolvent-induced phase separation (NIPS) process and characterized by SEM, EDX, contact angle, FTIR and porosimeter. PVDF support is selected as solid support for immobilization of the carrier solution owing to its properties of having an asymmetrical shape, thickness of 48.8 µm, porosity of 72% and contact angle of 89.0° (feed side) and 85.3° (stripping side). The percentage of carrier loss obtained was only 1.10%. The optimal conditions for IBP removal were obtained at 0.50 M Aliquat 336, with a feed phase pH of 5.5 and stripping phase pH of 8. Further tests on real aquaculture wastewater affirmed the system’s efficacy in removing IBP and maintaining the stability at least the fifth cycle of membrane reusability. This study underscores the viability of proposed SILM system in mitigating IBP from aquaculture sector.

Supported Ionic Liquid Membrane with Highly-permeable Polyamide Armor by In Situ Interfacial Polymerization for Durable CO2 Separation.

Supported ionic liquid membranes (SILMs), owing to their capacities in harnessing physicochemical properties of ionic liquid for exceptional CO2 solubility, have emerged as a promising platform for CO2 extraction. Despite great achievements, existing SILMs suffer from poor structural and performance stability under high-pressure or long-term operations, significantly limiting their applications. Herein, a one-step and in situ interfacial polymerization strategy is proposed to elaborate a thin, mechanically-robust, and highly-permeable polyamide armor on the SILMs to effectively protect ionic liquid within porous supports, allowing for intensifying the overall stability of SILMs without compromising CO2 separation performance. The armored SILMs have a profound increase of breakthrough pressure by 105% compared to conventional counterparts without armor, and display high and stable operating pressure exceeding that of most SILMs previously reported. It is further demonstrated that the armored SILMs exhibit ultrahigh ideal CO2/N2 selectivity of about 200 and excellent CO2 permeation of 78 barrers upon over 150h operation, as opposed to the full failure of CO2 separation performance within 36h using conventional SILMs. The design concept of armor provides a flexible and additional dimension in developing high-performance and durable SILMs, pushing the practical application of ionic liquids in separation processes.

Application of an Ionic Liquid as a Bulk Liquid Membrane for Nicotinic Acid Separation: Determination and Optimization Study

Nicotinic acid (NA) is a crucial molecule that is commonly employed in the pharmaceutical, biochemical, and food sectors. It is essential to separate nicotinic acid from both industrial effluents and production broth. In this study, the separation of NA from aqueous media by bulk ionic liquid membrane (BILM) has been investigated. 1-Butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], has been utilized as a membrane solvent and tributyl phosphate (TBP), has been utilized as a carrier in ionic liquid membrane. The effects of nicotinic acid concentration (0.02–0.1 mol/L) in aqueous solution, the carrier concentration (0–2 mol/L) in ionic liquid membrane, and the stripping phase type (water/NaOH) and NaOH concentration (0.1–0.2 mol/L) have been examined. Furthermore, Box-Behnken design (BBD) has been applied to determine the relationship between these parameters. The effects of these parameters on the separation were determined by calculating the feed and stripping phase efficiencies. Maximum extraction and stripping efficiencies have been obtained at optimum BILM conditions of nicotinic acid concentration in aqueous solution of 0.02 mol/L, carrier concentration ionic liquid membrane of 2 mol/L, and NaOH concentration of 0.2 mol/L. These efficiency values have also been determined as 90.05% (experimental value) and 95.21% (BBD value) for extraction and 93.92% (experimental value) and 82.36% (BBD value) for stripping, respectively.

Ultrasound assisted efficient separation of lithium from brine with a composite polyether sulfone-ionic liquid membrane.

Green, selective and efficient extraction of lithium as one of the most important components for energy storages with ultrasound-assisted membrane separation of lithium from brine, which contains alkali metal chlorides, is conducted using a composite membrane. The composite membrane is formed by sealing a supported ionic liquid membrane (consisting of 1-alkyl-3-methylimidazolium hexafluorophosphate ([RMIM][PF6]) + TBP) with a polyethersulfone (PES) membrane and a PVC thin film membrane. The aim of the study is to optimize the separation process for the selective extraction of lithium from alkali metals. Various parameters, including membrane composition, feed concentration, and ultrasonic conditions, are adjusted to identify the best operating conditions. The results reveal that a membrane containing xIL = 0.5 of [MOIM][PF6] exhibits higher selectivity compared to other membranes studied. The flux of lithium initially increases with shorter sonication times, but it decreases as the duration of ultrasonic irradiation is prolonged. The optimal frequency for the ultrasonic treatment, which matches the bulk modulus of the membrane, is approximately 250 kHz. Higher frequencies result in higher flux and selectivity in lithium separation; besides, optimizing the amplitude and pulse cycle of the ultrasound at 75% leads to increased flux. Moreover, higher flux and selectivity (percentage of lithium with respect to the all of the ion flux) are achieved when separating lithium from alkali metal chlorides at higher feed concentrations, ranging from 250 ppm to 1000 ppm. The selectivity is influenced by the hydrophobicity, which depends on the behavior of the ionic liquid membrane. The process is promising for the future of the lithium mining from brine.

Separation of Lactic Acid and Acetic Acid through Supported Ionic Liquid Membranes Containing Cyphos IL 101

Separation of Lactic Acid and Acetic Acid through Supported Ionic Liquid Membranes Containing Cyphos IL 101

Pervaporation properties of silylated ionic liquid-derived organosilica membrane

We previously reported gas/vapor permselectivities, microstructures, and permeation mechanisms of silylated ionic liquid (IL)-derived organosilica membranes (IL organosilica membranes), which are a class of chemically stabilized IL membranes. In this study, an IL organosilica membrane was used for organic liquid separation using pervaporation (PV) for the first time. Unary PV tests were conducted using alcohols, ketones, aromatic hydrocarbons, and alkanes. We investigated the relationship between the permeances of the organic compounds and differences in the Hansen solubility parameters between the membrane and organic compounds to evaluate the selective permeability of the organic compounds through the membrane. Second, binary PV tests were conducted to separate (1) alcohols/alkanes and (2) aromatics/alkanes. In the toluene/n-hexane (toluene 48 mol%) separation tests, a toluene/n-hexane permeance ratio of 11 was obtained with a toluene permeance of 2.6 × 10−6 mol m−2s−1Pa−1. Further, the membrane exhibited high selectivity for 1-hexanol in a binary 1-hexanol/n-hexane mixture. The IL organosilica membrane exhibited excellent potential for affinity-based organic liquid separation.

Preparation of two-dimensional nanoconfined ionic liquid membrane and its molecular mechanism of CO2 separation

The realization of efficient and stable carbon dioxide (CO2) separation technology holds profound significance for the development of green chemistry. In comparison with other CO2 separation technologies, membrane separation technology has the advantages of low energy consumption and simple operation. When used in conjunction with gas separation membranes, ionic liquids are always placed into the nanochannel constructed by two-dimensional nanosheets, forming the nanoconfined ionic liquid membrane (NC-ILM), which has exhibited excellent CO2 separation performance with high permeation and selectivity. In this review, we have summarized the structure and properties of nanoconfined ILs, the separation mechanism, and investigated methods of NC-ILMs, further discussing the challenges and strategies for the future application of NC-ILMs. Those results on the NC-ILMs not only can deepen the understanding of the molecular mechanism of separating CO2 but also promote the preparation technology of the related membrane with precise nanochannels.

Mechanistic fouling study of Hybrid imidazolium-based ionic liquid membrane during emulsified oil removal from oily wastewater; oil type effect

To overcome the strict discharge effluent regulations of oily wastewater, the treatment with membranes has a good perspective. In this work, [C12mim][Cl] ionic liquid was induced into the polyether sulfone membrane to improve membrane hydrophilicity and anti-fouling resistance. To reveal the membrane fouling type, the permeate flux of the membrane was modeled according to Hermia's equations and combined equations driven from four main fouling mechanisms equation. In addition, to develop a proper interpretation and fully new insights mechanisms, the elemental and topographical analyses, and chemical surface characterizations using FESEM, EDS MAPPING, AFM, FESEM, Zeta analyses, and contact angle and interfacial tension measurements were performed on the four different oily wastewaters and the membrane. So, the impact of interfacial tension, wettability, mean particle size, particle size distribution (polydispersity index), zeta potential, acidic and basic nature of oil, and the properties of polar fractions of oil including the asphaltene and resin concentrations and their weight percent of polar heteroatoms were thoroughly examined. The results revealed a reduction in permeate flux as the API gravity was reduced due to the particle size of the oily wastewater emulsion increased. Consequently, the wettability of the membrane altered towards a more oil-wet state leading to a reduction in the roughness of the membrane surface. The attachment and cover of the surface mainly by the acidic component of the oil with a higher affinity to attach the oxygen element of the membrane were proposed as the dominant mechanism of cake layer fouling.

Microbial Fuel Cell Using a Novel Ionic Liquid-Type Membrane–Cathode Assembly for Animal Slurry Treatment and Fertilizer Production

The implementation of a microbial fuel cell for wastewater treatment and bioenergy production requires a cost reduction, especially when it comes to the ion exchange membrane part and the catalysts needed for this purpose. Ionic liquids in their immobilized phase in proton exchange membranes and non-noble catalysts, as alternatives to conventional systems, have been intensively investigated in recent years. In the present study, a new microbial fuel cell technology, based on an ionic liquid membrane assembly for CoCu mixed oxide catalysts, is proposed to treat animal slurry. The new low-cost membrane–cathode system is prepared in one single step, thus simplifying the manufacturing process of a membrane–cathode system. The novel MFCs based on the new low-cost membrane–cathode system achieved up to 51% of the power reached when platinum was used as a catalyst. Furthermore, the removal of organic matter in suspension after 12 days was higher than that achieved with a conventional system based on the use of platinum catalysts. Moreover, struvite, a precipitate consisting of ammonium, magnesium, and phosphate, which could be used as a fertilizer, was recovered using this membrane–cathode system.