Polymer–ionic liquid composite membranes for propane/propylene separation by facilitated transport

Silver-mediated separations: A comprehensive review on advancements of argentation chromatography, facilitated transport membranes, and solid-phase extraction techniques and their applications

The use of silver(I) ions in chemical separations, also known as argentation separations, is a powerful approach for the selective separation and analysis of many natural and synthetic organic compounds. In this review, a comprehensive discussion of the most common argentation separation techniques, including argentation-liquid chromatography (Ag-LC), argentation-gas chromatography (Ag-GC), argentation-facilitated transport membranes (Ag-FTMs), and argentation-solid phase extraction (Ag-SPE) is provided. For each of these techniques, notable advancements, optimized separations, and innovative applications are discussed. The review begins with an explanation of the fundamental chemistry underlying argentation separations, mainly the reversible π-complexation between silver(I) ions and carbon-carbon double bonds. Within Ag-LC, the use of silver(I) ions in thin-layer chromatography, high-performance liquid chromatography, as well as preparative LC are explored. This discussion focuses on how silver(I) ions are employed in the stationary and mobile phase to separate unsaturated compounds. For Ag-GC and Ag-FTMs, different silver compounds and supporting media are discussed, often with relation to olefin-paraffin separations. Ag-SPE has been widely employed for the selective extraction of unsaturated compounds from complex matrices in sample preparation. This comprehensive review of Ag-LC, Ag-GC, Ag-FTMs, and Ag-SPE techniques emphasizes the immense potential of argentation separations in separations science and serves as a valuable resource for researchers seeking to learn, optimize, and utilize argentation separations.

Comparison of olefin/paraffin separation by ionic liquid and polymeric ionic liquid stationary phases containing silver(I) ion using one-dimensional and multidimensional gas chromatography

Silver(I) ions have been used in various studies as components within polymer membranes or ionic liquids (ILs) to enable separation of olefins from paraffins. Polymeric ionic liquids (PILs) are a class of polymers synthesized from IL monomers and typically possess higher thermal and chemical stability than the ILs from which they are formed. Until now, very little is known about the difference in strength of silver(I) ion-olefin interactions when they take place in an IL compared to a PIL. In this work, the chromatographic separation of olefins by stationary phases composed of silver(I) bis[(trifluoromethyl)sulfonyl]imide ([Ag⁺][NTf₂^-]) incorporated into the 1-hexyl-3-methylimidazolium NTf₂ ([HMIM⁺][NTf₂^-]) IL and poly(1-hexyl-3-vinylimidazolium NTf₂) (poly([HVIM⁺][NTf₂^-])) PIL at varying concentrations was investigated. Olefins were more highly retained by silver(I) ions in PILs than in ILs as the silver(I) salt concentration in the stationary was increased. The potential separation power of silver(I)-containing IL and PIL stationary phases in comprehensive two-dimensional gas chromatography (GC×GC) was compared to the conventional one-dimensional system. The separation selectivity of alkenes and alkynes from paraffins was significantly increased, while dienes and aromatic compounds showed insignificant changes in retention. The chemical structural features of IL and PIL that enhance silver(I) ion stability and olefin separation were investigated by using silver(I) trifluoromethanesulfonate ([Ag⁺][OTf^-]), 1-decyl-3-methylimidazolium NTf₂ ([DMIM⁺][NTf₂^-]) IL, poly(1-decyl-3-vinylimidazolium NTf₂ (poly([DVIM⁺][NTf₂^-])) PIL, [HMIM⁺][OTf^-] IL and poly([HVIM⁺][OTf^-]) PIL. Longer alkyl substituents appended to the IL (and PIL) cation increased the strength of silver(I) olefin interaction, and [OTf^-] anions in the IL (and PIL) tended to preserve silver(I) ion from thermal reduction, while also retaining olefins less than the [NTf₂^-]-containing columns. In general, silver(I) ions in PILs possessing analogous chemical structures to ILs exhibited higher silver(I) ion-olefin interaction strength but were less thermally stable.

Rational Design of Mixed Matrix Membranes Modulated by Trisilver Complex for Efficient Propylene/Propane Separation

The application of membrane-based separation processes for propylene/propane (C₃ H₆ /C₃ H₈ ) is extremely promising and attractive as it is poised to reduce the high operation cost of the established low temperature distillation process, but major challenges remain in achieving high gas selectivity/permeability and long-term membrane stability. Herein, a C₃ H₆ facilitated transport membrane using trisilver pyrazolate (Ag₃ pz₃ ) as a carrier filler is reported, which is uniformly dispersed in a polymer of intrinsic microporosity (PIM-1) matrix at the molecular level (≈15 nm), verified by several analytical techniques, including 3D-reconstructed focused ion beam scanning electron microscropy (FIB-SEM) tomography. The π-acidic Ag₃ pz₃ combines preferentially with π-basic C₃ H₆ , which is confirmed by density functional theory calculations showing that the silver ions in Ag₃ pz₃ form a reversible π complex with C₃ H₆ , endowing the membranes with superior C₃ H₆ affinity. The resulting membranes exhibit superior stability, C₃ H₆ /C₃ H₈ selectivity as high as ≈200 and excellent C₃ H₆ permeability of 306 Barrer, surpassing the upper bound selectivity/permeability performance line of polymeric membranes. This work provides a conceptually new approach of using coordinatively unsaturated 0D complexes as fillers in mixed matrix membranes, which can accomplish olefin/alkane separation with high performance.

Membrane-Based Olefin/Paraffin Separations

Efficient olefin/paraffin separation is a grand challenge because of their similar molecular sizes and physical properties, and is also a priority in the modern chemical industry. Membrane separation technology has been demonstrated as a promising technology owing to its low energy consumption, mild operation conditions, tunability of membrane materials, as well as the integration of physical and chemical mechanisms. In this work, inspired by the physical mechanism of mass transport in channel proteins and the chemical mechanism of mass transport in carrier proteins, recent progress in channel-based and carrier-based membranes toward olefin/paraffin separations is summarized. Further, channel-based membranes are categorized into membranes with network structures and with framework structures according to the morphology of channels. The separation mechanisms, separation performance, and membrane stability in channel-based and carrier-based membranes are elaborated. Future perspectives toward membrane-based olefin/paraffin separation are proposed.

A Bibliometric Survey of Paraffin/Olefin Separation Using Membranes

Bibliometric studies allow to collect, organize and process information that can be used to guide the development of research and innovation and to provide basis for decision-making. Paraffin/olefin separations constitute an important industrial issue because cryogenic separation methods are frequently needed in industrial sites and are very expensive. As a consequence, the use of membrane separation processes has been extensively encouraged and has become an attractive alternative for commercial separation processes, as this may lead to reduction of production costs, equipment size, energy consumption and waste generation. For these reasons, a bibliometric survey of paraffin/olefin membrane separation processes is carried out in the present study in order to evaluate the maturity of the technology for this specific application. Although different studies have proposed the use of distinct alternatives for olefin/paraffin separations, the present work makes clear that consensus has yet to be reached among researchers and technicians regarding the specific membranes and operation conditions that will make these processes scalable for large-scale commercial applications.

Graphene oxide nanoslit-confined AgBF4/ionic liquid for efficiently separating olefin from paraffin

Facilitated transport membrane for separating light olefins, using transition metals like silver and copper as carriers, is a promising way to replace traditional energy-consuming methods. Here, we construct ionic liquid (IL) to fill the nanoslits of laminated graphene oxide (GO) membrane with silver ions as a carrier to separate ethylene/ethane. The nanoslits of GO membrane efficiently prevent the loss of silver ion IL solution. The IL further slows down the reduction of silver ions. The membrane with silver concentration of 0.25 M shows the best performance with a selectivity of 54 for ethylene/ethane and ethylene permeance of 2.9 GPU. This performance is superior to other silver ion IL solution membranes and competitive among the reported facilitated transport membranes.

Morphology and pervaporation performance of ionic liquid and waterborne polyurethane composite membranes

Blending an aromatic-selective ionic liquid (IL, namely 1-ethyl-3-methylimidazolium hexafluorophosphate, [emim][PF₆]) with waterborne polyurethane (WPU) enabled us to obtain [emim][PF₆]-modified waterborne polyurethane composite membranes. We characterized the structure and properties of the [emim][PF₆]/WPU composite membranes by ATR-FTIR, DSC, UV, SEM, EDX, swelling tests, and pervaporation testing. Characterization of the change in the morphology of the membranes in response to the IL loading indicated that a preferential interaction between the IL and soft segments of WPU was induced by hydrogen bonding. This interaction inhibited a potential interaction with benzene (Bz), which initially lowered the permeability. However, at high IL loading, the IL incorporation became ineffective owing to macrophase separation, which caused an increase in the permeability, as indicated by the SEM results. Swelling testing of the [emim][PF₆]/WPU composite membranes showed that the membranes exhibited preferential adsorption of Bz, and the swelling degree of the composite membranes in Bz solvent increased from 58% to 98% and remained almost constant in cyclohexane solvent as the IL content was increased. The [emim][PF₆]/WPU composite membranes enhanced the separation selectivity of Bz/Cy for an IL loading < 10 wt%. The best separation factor was 8.4, and the total flux was 0.19 kg (m² h)⁻¹ (50 wt% Bz/Cy mixtures at 50 °C) at w([emim][PF₆]) : w(WPU) = 10 : 100. In addition, the composite membrane exhibited excellent stability over long-term operation. These results demonstrated that the [emim][PF₆]/WPU composite membranes could be effective for separation of Bz/Cy mixtures by the pervaporation method.

Possible model of interactions in [emim][PF₆]/WPU composite membranes.

Interfacial Design of Ternary Mixed Matrix Membranes Containing Pebax 1657/Silver-Nanopowder/[BMIM][BF4] for Improved CO2 Separation Performance

In this research, Pebax1657 as an organic phase and silver nanoparticles as an inorganic phase were used for preparation of binary mixed matrix membranes (MMMs). Silver nanoparticles as a filler could enter the polymer chains and enhance the gas permeability by increasing the fractional free volume of membranes. Afterward, ternary MMMs were fabricated by addition of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]) ionic liquid, in order to have better polymer/filler adhesion and eliminate interfacial defects and nonselective voids. In addition, positively polarized silver nanoparticles in the presence of the IL could interact with PEO segment of the polymer and increase the CO₂ affinity of membranes, which results in increasing the CO₂/light gases permselectivity of MMMs. Gas permeation properties of MMMs were studied at a temperature of 35 °C and operating pressures from 2 to 10 bar. Moreover, fabricated membranes were characterized by fourier transform infrared-attenuated total reflectance (FTIR-ATR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimeter (DSC). The analysis revealed that there is a proper adhesion between positively charged surface of nanoparticles and the polymer, and both filler and IL decrease the crystallinity of the membranes, which could enhance the polar gas transport properties. Gas permeation results showed significant enhancement in CO₂ permeability (325 Barrer) for binary membrane (Pebax 1657/1%Ag) at 35 °C and 10 bar. Moreover, ternary MMM (Pebax 1657/0.5%Ag/50%IL) encountered significant increase in both permeability and selectivity in comparison with neat membrane. Indeed, the CO₂ permeability increased from 110 Barrer to 180 (about 64%). Moreover, the related CO₂/CH₄ and CO₂/N₂ selectivities were increased from 20.8 to 61.0 (more than 193%) and from 78.6 to 187.5 (about 139%), respectively.

Facilitated Transport of Propylene Through Composite Polymer-Ionic Liquid Membranes. Mass Transfer Analysis

Separation of light gaseous olefins from paraffin’s of the refinery process off-gasses has been traditionally performed by cryogenic distillation, which is a highly capital and energy intensive operation. This handicap creates an incentive for the investigation of alternative olefin/paraffin separation technologies. In this regard, membrane technology supposes a potential solution for process intensification. Previous works of our research group reported the use of facilitated transport composite membranes integrating the use of PVDF-HFP polymer, BMImBF4 ionic liquid and AgBF4 silver salt. In this type of membranes, the silver cations react selectively and reversibly with the olefin, allowing the separation via mobile and fixed carrier mechanisms. Ionic liquids were selected as membrane additives because in addition to their negligible vapor pressure that avoids solvent losses by evaporation, they provide stability to the metallic cation dissolved inside, and modify the structure improving the facilitated transport. This technology offers a commercial attractive separation alternative thanks to their modular form of operation, high values of selectivity and permeability and low operational costs. In the present work, propane/propylene permeation experiments involving the use ionic liquids and different membrane compositions were performed. Moreover, basing on the transport and equilibrium parameters previously obtained, a mathematical model description of the system will be proposed fitting the remaining parameters and allowing the design and optimization of the propane/propylene separation process at industrial levels.

Turning into poly(ionic liquid)s as a tool for polyimide modification: synthesis, characterization and CO2 separation properties

A synthetic method for the transformation of polyimides into poly(ionic liquid)s with improved properties is suggested.