Study on Gas Permeation and CO2 Separation through Ionic Liquid-Based Membranes with Siloxane-Functionalized Cations

Transport and Energetics of Carbon Dioxide in Ionic Liquids at Aqueous Interfaces

A major hurdle in utilizing carbon dioxide (CO2) lies in separating it from industrial flue gas mixtures and finding suitable storage methods that enable its application in various industries. To address this issue, we utilized a combination of molecular dynamics simulations and experiments to investigate the behavior of CO2 in common room-temperature ionic liquids (RTIL) when in contact with aqueous interfaces. Our investigation of RTILs, [EMIM][TFSI] and [OMIM][TFSI], and their interaction with a pure water layer mimics the environment of a previously developed ultrathin enzymatic liquid membrane for CO2 separation. We analyzed diffusion constants and viscosity, which reveals that CO2 molecules exhibit faster mobility within the selected ILs compared to what would be predicted solely based on the viscosity of the liquids using the standard Einstein-Stokes relation. Moreover, we calculated the free energy of translocation for various species across the aqueous-IL interface, including CO2 and HCO3-. Free energy profiles demonstrate that CO2 exhibits a more favorable partitioning behavior in the RTILs compared to that in pure water, while a significant barrier hinders the movement of HCO3- from the aqueous layer. Experimental measurement of the CO2 transport in the RTILs corroborates the model. These findings strongly suggest that hydrophobic RTILs could serve as a promising option for selectively transporting CO2 from aqueous media and concentrating it as a preliminary step toward storage.

Recent Advances in Poly(Ionic Liquid)-Based Membranes for CO2 Separation

Poly(ionic liquid)-based membranes have been the subject of intensive research in the last 15 years due to their potential for the separation of CO₂ from other gases. In this short review, different types of PIL-based membranes for CO₂ separation are described (neat PIL membranes; PIL-IL composite membranes; PIL-polymer blend membranes; PIL-based block copolymer membranes, and PIL-based mixed matrix membranes), and their state-of-the-art separation results for different gas pairs (CO₂/N₂, CO₂/H₂, and CO₂/CH₄) are presented and discussed. This review article is focused on the most relevant research works performed over the last 5 years, that is, since the year 2017 onwards, in the field of poly(ionic liquid)-based membranes for CO₂ separation. The micro- and nano-morphological characterization of the membranes is highlighted as a research topic that requires deeper study and understanding. Nowadays there is an array of advanced structural characterization techniques, such as neutron scattering techniques with contrast variation (using selective deuteration), that can be used to probe the micro- and nanostructure of membranes, in length scales ranging from ~1 nm to ~15 μm. Although some of these techniques have been used to study the morphology of PIL-based membranes for electrochemical applications, their use in the study of PIL-based membranes for CO₂ separation is still unknown.

Overview of Membrane Science and Technology in Portugal

Membrane research in Portugal is aligned with global concerns and expectations for sustainable social development, thus progressively focusing on the use of natural resources and renewable energy. This review begins by addressing the pioneer work on membrane science and technology in Portugal by the research groups of Instituto Superior Técnico—Universidade de Lisboa (IST), NOVA School of Science and Technology—Universidade Nova de Lisboa (FCT NOVA) and Faculdade de Engenharia—Universidade do Porto (FEUP) aiming to provide an historical perspective on the topic. Then, an overview of the trends and challenges in membrane processes and materials, mostly in the last five years, involving Portuguese researchers, is presented as a contribution to a more sustainable water–energy–material–food nexus.

A Review on Ionic Liquid Gas Separation Membranes

Ionic liquids have attracted the attention of the industry and research community as versatile solvents with unique properties, such as ionic conductivity, low volatility, high solubility of gases and vapors, thermal stability, and the possibility to combine anions and cations to yield an almost endless list of different structures. These features open perspectives for numerous applications, such as the reaction medium for chemical synthesis, electrolytes for batteries, solvent for gas sorption processes, and also membranes for gas separation. In the search for better-performing membrane materials and membranes for gas and vapor separation, ionic liquids have been investigated extensively in the last decade and a half. This review gives a complete overview of the main developments in the field of ionic liquid membranes since their first introduction. It covers all different materials, membrane types, their preparation, pure and mixed gas transport properties, and examples of potential gas separation applications. Special systems will also be discussed, including facilitated transport membranes and mixed matrix membranes. The main strengths and weaknesses of the different membrane types will be discussed, subdividing them into supported ionic liquid membranes (SILMs), poly(ionic liquids) or polymerized ionic liquids (PILs), polymer/ionic liquid blends (physically or chemically cross-linked 'ion-gels'), and PIL/IL blends. Since membrane processes are advancing as an energy-efficient alternative to traditional separation processes, having shown promising results for complex new separation challenges like carbon capture as well, they may be the key to developing a more sustainable future society. In this light, this review presents the state-of-the-art of ionic liquid membranes, to analyze their potential in the gas separation processes of the future.

The permeability and selectivity of nanocomposite membrane of PEBAx 1657/PEI/SiO2 for separation of CO2, N2, O2, CH4 gases: A data set

The poly ether-block-amide (PEBAx)/Poly-ether-imide (PEI)/SiO₂ nanocomposite membranes were fabricated using the solution casting method and utilized for separation of N₂, O₂, CH_4, and CO₂ gases. The effect of SiO₂ nanoparticles loading on permeability and selectivity of gases using the nanocomposite membranes was tested. The data showed that the permeability of the gases increased with increasing SiO₂ nanoparticle content. dBy adding SiO₂ nanoparticles (10 wt%), the permeability of N₂, O₂, CH_4, and CO₂ gases elevated from 0.39, 1, 1.83 and 11.1 to 2.01, 1.95, 2.98 and 19.83 Barrer unit, respectively (at a pressure of 2 Bar). In contrast, with increasing SiO₂ content the selectivity of the studied gases decreased. The morphology, crystallinity and the functional groups of the fabricated membranes were evaluated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) techniques. The data presented confirm the influence of the nanoparticles on the membrane structure and thus on the permeability and selectivity of the membranes.

Molecular Simulation of Ionic Polyimides and Composites with Ionic Liquids as Gas-Separation Membranes

Polyimides are at the forefront of advanced membrane materials for CO₂ capture and gas-purification processes. Recently, ionic polyimides (i-PIs) have been reported as a new class of condensation polymers that combine structural components of both ionic liquids (ILs) and polyimides through covalent linkages. In this study, we report CO₂ and CH₄ adsorption and structural analyses of an i-PI and an i-PI + IL composite containing [C₄mim][Tf₂N]. The combination of molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations is used to compute the gas solubility and the adsorption performance with respect to the density, fractional free volume (FFV), and surface area of the materials. Our results highlight the polymer relaxation process and its correlation to the gas solubility. In particular, the surface area can provide meaningful guidance with respect to the gas solubility, and it tends to be a more sensitive indicator of the adsorption behavior versus only considering the system density and FFV. For instance, as the polymer continues to relax, the density, FFV, and pore-size distribution remain constant while the surface area can continue to increase, enabling more adsorption. Structural analyses are also conducted to identify the nature of the gas adsorption once the ionic liquid is added to the polymer. The presence of the IL significantly displaces the CO₂ molecules from the ligand nitrogen sites in the neat i-PI to the imidazolium rings in the i-PI + IL composite. However, the CH₄ molecules move from the imidazolium ring sites in the neat i-PI to the ligand nitrogen atoms in the i-PI + IL composite. These molecular details can provide critical information for the experimental design of highly selective i-PI materials as well as provide additional guidance for the interpretation of the simulated adsorption systems.