CO2 separation facilitated by task-specific ionic liquids using a supported liquid membrane

Innovative strategies for enhancing gas separation: Ionic liquid-coated PES membranes for improved CO2/N2 selectivity and permeance

As a cost-effective advancement in membrane technology, this study investigates the impact of PEG additive and CBT on the structural, stability, and gas permeance properties of PES-coated membranes, utilizing 1-dodecyl-3-methylimidazolium chloride ionic liquid ([DDMI][Cl] IL) as a carrier liquid. BET and FT-IR analyses highlight the significant enhancement in performance through the immobilization of pores with [DDMIM][Cl] IL. The investigation focuses on PES-M5-coated membranes, revealing excellent stability in finger-like pore structures prepared through direct immersion and nitrogen pressure immobilization. PES-M5-coated membranes with [DDMIM][Cl] IL via direct immersion experience lower weight loss than those coated using nitrogen pressure, with critical pressures at 1.4 and 1.25 bar, respectively. The study identifies PES-coated membranes, particularly PES-M25 (20.88 GPU) with macro-void pores and PES-M5 (29 GPU) with finger-like pores, exhibiting the highest CO2 permeance and CO2/N2 selectivity. As a cost-effective advancement in membrane technology, ionic liquids are employed in support membranes to enhance gas separation. Employing pure PES membranes with varying pore structures, created through the NIPS method, the study immobilizes [DDMI][Cl] IL in membrane pores through nitrogen pressure and direct immersion. Results underscore the successful application of porous support materials coated with ionic liquids for continuous CO2 and sulfur compound separation, showcasing competitive permeability and selectivity compared to traditional polymer membranes.

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 150 h operation, as opposed to the full failure of CO2 separation performance within 36 h 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.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Phase coexistence in [C22/C1MIm]+[NO3]- ionic-liquid mixtures and first-order phase transitions from homogeneous liquid to smectic B by varying the cation ratio

We perform molecular dynamics simulations to investigate the transition processes of [C22/C1MIm]+[NO3]- binary mixtures by varying the cation ratio of C22 to C1 at a fixed temperature of 400 K. The cation ratio is tuned by ranging C22 percentage from 0% to 100% with a fixed number of 4096 total simulated ion pairs. Our simulated-annealing results indicate that, at 400 K, pure C1 is a homogeneous liquid whilst pure C22 is an ionic liquid crystal (ILC) of smectic-B (SmB) type. With increasing C22 percentage, the system goes through a first-order phase transition from homogeneous liquid to nano-fragment liquid in the range from 15% to 17.5%, during which some of the individual cationic alkyl side chains locally aggregate to form small bundles "floating" in the polar "solvent" composed of anions and cationic head groups. Although the side chains in each bundle are parallelly aligned, the bundles distribute randomly without a global orientation. As the C22 percentage further increases, another first-order phase transition occurs to bring the system into the SmB ILC phase. Particularly, when the C22 percentage is in the range from 45% to 50%, the SmB phase coexists with the liquid phase containing both individual and bundled alkyl side chains.

Synthesis and performance evaluation of copper and magnesium-based metal organic framework supported ionic liquid membrane for CO2/N2 separation

The CO₂ emission is enhancing drastically because of the continuous emission from industries and transport sector. Although the CO₂ emission had decreased in the first half of 2020 by 8.8% due to COVID-19 restrictions however, it is again on the rise and it might exceed the estimated level in 2030. The current methods used for CO₂ separation have serious operational and environmental constraints. To overcome these problems we have devised a supported ionic liquid membrane (SILM) incorporated with the blend of bimetallic metal-organic framework (MOF) of copper and magnesium ions (Cu_xMg_x) and Trihexyltetradecylphosphonium chloride [P₆₆₆₁₄] [Cl] ionic liquid (IL). Cu_xMg_x MOF were synthesized and characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and energy dispersive X-ray analysis (EDX). Cu_xMg_x MOF with [P₆₆₆₁₄] [Cl] IL were immobilized on a flat sheet of polytetrafluoroethylene (PTFE) membrane. Single gas permeation tests of membranes loaded with 0.2/0.8 wt/wt% MOF/IL solution showed the highest CO₂ permeability of 2937 Barrer and CO₂/N₂ selectivity of 33.26. The performance of SILM was also investigated with different water loadings of (30 wt % and 50 wt %) in addition to MOF/IL solution and at different feed pressure varying from 0.5 to 2 bars. Membranes showed enhancement in CO₂ permeability to 3738 and 4628 Barrer whereas CO₂/N₂ selectivity decreased to 23.53 and 21.8 with membranes loaded with 30 and 50 wt % water, respectively, at a feed pressure of 2 bar. The gas permeation results show that the incorporation of Cu_xMg_x MOF with IL in polymeric membrane enhances the CO₂/N₂ separation under humid conditions but slightly decreases CO₂/N₂ selectivity with an increase in feed pressure. The SILM synthesized in this research is highly viable for industrial flue gases because of the incorporation of phosphonium-based ILs that have high thermal stability.

Ionic Liquid Mixtures for Direct Air Capture: High CO2 Permeation Driven by Superior CO2 Absorption with Lower Absolute Enthalpy

This paper reports a series of liquid materials suitable for use as high-performance separation membranes in direct air capture. Upon mixing two ionic liquids (ILs), namely N-(2-aminoethyl)ethanolamine-based IL ([AEEA][X]) and 1-ethyl-3-methylimidazolium acetate ([emim][AcO]), the resulting mixtures with a specific range of their composition showed higher CO₂ absorption rates, larger CO₂ solubilities, and lower absolute enthalpies of CO₂ absorption compared to those of single ILs. NMR spectroscopy of the IL mixture after exposure to ¹³CO₂ allowed elucidation of the chemisorbed species, wherein [AEEA][X] reacts with CO₂ to form CO₂-[AEEA]⁺ complexes stabilized by hydrogen bonding with acetate anions. Supported IL membranes composed of [AEEA][X]/[emim][AcO] mixtures were then fabricated, and the membrane with a suitable mixing ratio showed a CO₂ permeability of 25,983 Barrer and a CO₂/N₂ selectivity of 10,059 at 313.2 K and an applied CO₂ partial pressure of 40 Pa without water vapor. These values are higher than those reported for known facilitated transport membranes.

One pot synthesis of UiO-66@IL composite for fabrication of CO2 selective mixed matrix membranes

In this study, a facile and extensible one pot approach was utilized to synthesize ionic liquid inside a porous metal organic framework (UiO-66). Different characterization techniques were used to confirm the successful synthesis of UiO-66@IL composite. The MMMs were characterized and tested for CO₂ separation from CH₄ or N₂ at ambient and elevated temperatures. SEM images exhibited well dispersion of the filler particles with no notable defect even at high loadings. Single and mixed gas permeation results indicated significant performance (CO₂ permeability: 143 Barrer and CO₂/CH₄, CO₂/N₂ selectivity: 28.32, 61.11 respectively) by enhancing the permeability of CO₂ by 74% and selectivity to 31% and 26% for CO₂/CH₄ and CO₂/N₂ compared with neat Pebax®1657 membrane.

Effectiveness of ionic liquid-supported membranes for carbon dioxide capture: a review

The world's population explosion creates a need for natural resources for energy, which will become a significant contributor to global climate change. As we all know, carbon dioxide (CO₂) is one of the most critical elements of the global greenhouse gas effect. CO₂ capture and storage innovations have piqued researchers' attention in recent decades. Compared to other methods, membrane separation has some positive performance in CO₂ capture. CO₂ capture with membrane separation using enhanced ionic liquids (ILs) is described in this review. ILs have made an appearance in CO₂ capture work as the potential additive, and companies and academics have been interested in CO₂ separation for the past two decades. This article comprehensively analyzes the current modern approach in ILs and IL-based membranes for gas separation processes. Based on the latest literature and performance data, this work provides a complete compressive examination of types of ILs and IL-supported membrane performances. ILs for CO₂ capture were also explored, and IL-based membranes for different ILs were also studied. This study emphasizes the supremacy of novel ILs for CO₂ capture in membrane separation.

High-efficiency CO(2) separation using hybrid LDH-polymer membranes

Membrane-based gas separation exhibits many advantages over other conventional techniques; however, the construction of membranes with simultaneous high selectivity and permeability remains a major challenge. Herein, (LDH/FAS)_n-PDMS hybrid membranes, containing two-dimensional sub-nanometre channels were fabricated via self-assembly of unilamellar layered double hydroxide (LDH) nanosheets and formamidine sulfinic acid (FAS), followed by spray-coating with a poly(dimethylsiloxane) (PDMS) layer. A CO₂ transmission rate for (LDH/FAS)₂₅-PDMS of 7748 GPU together with CO₂ selectivity factors (SF) for SF(CO₂/H₂), SF(CO₂/N₂) and SF(CO₂/CH₄) mixtures as high as 43, 86 and 62 respectively are observed. The CO₂ permselectivity outperforms most reported systems and is higher than the Robeson or Freeman upper bound limits. These (LDH/FAS)_n-PDMS membranes are both thermally and mechanically robust maintaining their highly selective CO₂ separation performance during long-term operational testing. We believe this highly-efficient CO₂ separation performance is based on the synergy of enhanced solubility, diffusivity and chemical affinity for CO₂ in the sub-nanometre channels.

Facilitated Transport Membranes With Ionic Liquids for CO2 Separations

In recent years, significant development milestones have been reached in the areas of facilitated transport membranes and ionic liquids for CO2 separations, making the combination of these materials an incredibly promising technology platform for gas treatment processes, such as post-combustion and direct CO2 capture from air in buildings, submarines, and spacecraft. The developments in facilitated transport membranes involve consistently surpassing the Robeson upper bound for dense polymer membranes, demonstrating a high CO2 flux across the membrane while maintaining very high selectivity. This mini review focuses on the recent developments of facilitated transport membranes, in particular discussing the challenges and opportunities associated with the incorporation of ionic liquids as fixed and mobile carriers for separations of CO2 at low partial pressures (<1 atm).

CO2 Separation with Polymer/Aniline Composite Membranes

Polymer composite membranes containing aniline were prepared for CO₂/N₂ separation. Aniline was selected for high separation performance as an additive containing both the benzene ring to interfere with gas transport and an amino group that could induce the accelerated transport of CO₂ molecules. As a result, when aniline having both a benzene ring and an amino group was incorporated into polymer membranes, the selectivity was largely enhanced by the role of both gas barriers and CO₂ carriers. Selective layers coated on the polysulfone were identified by scanning electron microscopy (SEM) images and the interaction with aniline in the polymer matrix was confirmed by FT-IR spectroscopy. The binding energy of oxygen in the polymer matrix was investigated by XPS, and the thermal stability of the composite membrane was confirmed by TGA.

Recent Advances in Applications of Supported Ionic Liquids

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The supported ionic liquids have shown immense potential for numerous applications in catalysis and separation science. In the present review, the remarkable contribution of supported ionic liquids has been highlighted. The main emphasis has been laid on describing the facile separation of gas from binary gas mixtures owing to the capability of selective transport of permeable gases across supported membranes and removal of environmentally hazard sulfur compounds from fuels. The catalytic action of supported ionic liquids has been discussed in other applications such as biodiesel (biofuel) synthesis by transesterification/esterification processes, waste CO2 fixation into advantageous cyclic carbonates, and various chemical transformations in organic green synthesis. This review enclosed a maximum of the published data of the last ten years and also recently accomplished work concerning applications in various research areas like separation sciences, chemical transformations in organic green synthesis, biofuel synthesis, waste CO2 fixation, and purification of fuels by desulfurization.

Models for Facilitated Transport Membranes: A Review

Facilitated transport membranes are particularly promising in different separations, as they are potentially able to overcome the trade-off behavior usually encountered in solution-diffusion membranes. The reaction activated transport is a process in which several mechanisms take place simultaneously, and requires a rigorous theoretical analysis, which unfortunately is often neglected in current studies more focused on material development. In this work, we selected and reviewed the main mathematical models introduced to describe mobile and fixed facilitated transport systems in steady state conditions, in order to provide the reader with an overview of the existing mathematical tools. An analytical solution to the mass transport problem cannot be achieved, even when considering simple reaction schemes such as that between oxygen (solute) and hemoglobin (carrier) (A+C⇄AC), that was thoroughly studied by the first works dealing with this type of biological facilitated transport. Therefore, modeling studies provided approximate analytical solutions and comparison against experimental observations and exact numerical calculations. The derivation, the main assumptions, and approximations of such modeling approaches is briefly presented to assess their applicability, precision, and flexibility in describing and understanding mobile and fixed site carriers facilitated transport membranes. The goal is to establish which mathematical tools are more suitable to support and guide the development and design of new facilitated transport systems and materials. Among the models presented, in particular, those from Teramoto and from Morales-Cabrera et al. seem the more flexible and general ones for the mobile carrier case, while the formalization made by Noble and coauthors appears the most complete in the case of fixed site carrier membranes.

Acidic Gases Separation from Gas Mixtures on the Supported Ionic Liquid Membranes Providing the Facilitated and Solution-Diffusion Transport Mechanisms

Nowadays, the imidazolium-based ionic liquids containing acetate counter-ions are attracting much attention as both highly selective absorbents of the acidic gases and CO₂ carriers in the supported ionic liquid membranes. In this regard, the investigation of the gas transport properties of such membranes may be appropriate for better understanding of various factors affecting the separation performance and the selection of the optimal operating conditions. In this work, we have tested CH₄, CO₂ and H₂S permeability across the supported ionic liquid membranes impregnated by 1-butyl-3-methylimidazolium acetate (bmim[OAc]) with the following determination of the ideal selectivity in order to compare the facilitated transport membrane performance with the supported ionic liquid membrane (SILM) that provides solution-diffusion mechanism, namely, containing 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF₄]). Both SILMs have showed modest individual gases permeability and ideal selectivity of CO₂/CH₄ and H₂S/CH₄ separation that achieves values up to 15 and 32, respectively. The effect of the feed gas mixture composition on the permeability of acidic gases and permeselectivity of the gas pair was investigated. It turned out that the permeation behavior for the bmim[OAc]-based SILM toward the binary CO₂/CH₄, H₂S/CH₄ and ternary CO₂/H₂S/CH₄ mixtures was featured with high acidic gases selectivity due to the relatively low methane penetration through the liquid phase saturated by acidic gases.

Enhancement of gravimetric forced flow through system to determine sorption, swelling, and mass transfer characteristics of liquid sorbents

An existing apparatus for forced flow through of liquid sorbents has been enhanced with an optically accessible system including a transparent crucible, high pressure viewing cell, and camera. With this optical system, the active surface area between gas and liquid can be determined in situ for the first time under industrial process conditions while maintaining the accuracy of a magnetic suspension balance. Additionally, occurring swelling and the resulting buoyancy changes can now be corrected, further improving the quality of the data. Validation measurements focusing on the sorption isotherms, swelling, and bubble geometry of 1-butyl-3-methylimidazolium tetrafluoroborate with nitrogen at 303 K and up to 17 MPa, as well as with carbon dioxide at 303 K, 323 K, and 373 K at up to 3.5 MPa were completed. Absorption of nitrogen resulted in no observable volume change, whereas absorption of carbon dioxide resulted in temperature independent swelling of up to 9.8%. The gas bubble's structure and behavior during its ascend through the liquid was optically tracked in situ. Combining these two data sets with the absorption kinetics forms the basis to determine the measuring system independent mass transfer coefficients, which are applicable in other laboratory scale and industrial processes.

Functionalized ionic liquid membranes for CO2 separation

It is imperative to develop efficient, reversible and economic technologies for separating CO₂ which mainly comes from flue gas, natural gas and syngas.