Recent progress on functional polymeric membranes for CO2 separation from flue gases: A review

Since A. Fick had observed different transport of gas molecules through nitro-cellulose, membrane-based gas separation has been extensively studied for membrane materials as well as scale-up and application to industrial gas separation field. Numerous scientists have studied the transport mechanism, measurement of gas permeation, membrane materials, and high flux membrane by asymmetric fabrication.Acknowledged to the contribution for quantative measurement of gas permeabilities by H. A. Daynes and R. M. Barrer, a number of materials have been tested and applied for gas separation membranes: polydimethylsiloxane (PDMS), cellulose acetate (CA), polysulfone (PSf), polyethersulfone (PES), and polyimide (PI), etc. PDMS, a kind of highly permeable polymer, has been used in VOCs recovery due to its superior sorption capacitance. CA and fluorinated polyimides have been employed to natural gas calorie-up process and petrochemical industries while PES and PSf have been mainly used for nitrogen enrichment from air.In a dense polymer film, gas permeation through the membrane depends upon both sorption and diffusion known as ‘solution-diffusion’ mechanism proposed by Sir Thomas Graham at 1866. Sorption, a thermodynamic factor, is occurred when a gas molecule in bulk motion adsorb physically on a membrane surface with respect to the concentration difference, and diffusion, a kinetic factor, is related to the extent how fast a gas molecule go through the membrane. Therefore, two factors are simultaneously crucial for efficient permeation and separation.While the conventional polymer membranes exhibited somewhat low permeation and selective performances, along with the recent developments in materials science, recently reported membrane materials showed excellent permeability and selectivity for various gas pairs as well as enhanced thermal, chemical and mechanical stabilities. The recent polymer membranes can be classified largely into two classes; highly diffusive membranes due to their high free volume elements and sorption-enhanced membranes based on high sorption capacity on carbon dioxide and hydrocarbons.Glassy polymers possessing rigid structure and strong intermolecular forces have been generally known to show reduced gas permeabilities although low diffusion through the membrane enabled to separate gas molecules efficiently resulting in high diffusion selectivity. However, superglassy polymers containing distorted structure and the resulting increased free volume elements (FVE) were developed since T. Matsuda et al. reported extraordinarily permeable glassy polymer, poly[1-(trimethylsilyl)-1-propyne](PTMSP). Since PTMSP was developed in 1983, acetylene-based polymers such as poly(4-methyl-2-pentene)(PMP), poly(1-phenyl-1-propyne)(PPP) have been followed by the introduction of various substitution groups. Extraordinarily high permeabilities, for example, 9,700 Barrer of oxygen permeability for PTMSP, were obtained from these acetylene-based polymers, while the separation performances were not successful because of their relatively large FVE size for separation. Fluorinated polymers, famous as the commercial names like AF 1600, AF 2400, Hyflon AD and Cytop, are candidate polymers for gas separation as well. Recent development of polymers with intrinsic microporosities (PIMs) showed competitive performances resulted from the intrinsic FVE due to the bulky and distorted structures. Thermally rearranged (TR) polymer membranes also presented optimized performances for gas separation. Chain rearrangement at the solid state improved the FVE in the polymer matrix followed by superior permselectivities as well as high permeabilities.Sorption-enhanced polymer membranes are beneficial to obtain superior permeability as well as advanced selectivity especially for carbon dioxide, hydrocarbons and VOCs because condensable gas molecules are easier to be adsorbed on the polymer surface. Recent researches are focused on the usage of ethylene oxide group, which has unique interaction with quadrupole monetum of carbon dioxide. From poly(dimethyl siloxane)(PDMS), the original sorption-based polymer, poly(ethylene oxide)(PEO), crosslinked PEO, PEO-based block copolymers such as poly(ethylene oxide-b-amide)(Pebax), poly(ethylene oxide-b-ethylene terephthalate)(PEO-b-PET) will be discussed from the viewpoint of permeabilities, solubilities and also their temperature dependences.In this book chapter, the chemical structure, physical properties, gas permeabilities and selectivities will be surveyed on the focus of up-to-date high performance and higly permeable membranes for gas separation.

In recent decades, anthropogenic industrial-based activities (i.e., energy production and its conveyance) has led to the emission of deleterious greenhouse gases such as CO 2 , H 2 S, and NO 2 as an important environmental concern. Membrane-based gas separation processes have been currently of paramount attention in critical industrial applications such as purification, biogas recovery, water treatment, gas processing and H 2 recovery. Polymeric nanocomposite membranes (PNM) have illustrated indisputable potential of utilization to mitigate the release of gaseous pollutants to the ecosystem and reduce their hazardous environmental effects. Incorporation of novel nanoparticles including activated carbon, nanofibers and carbon nanotubes have revolutionized the efficiency of polymeric membranes for gas separation. This review paper aims to present disparate applications of polymeric nanocomposite membranes for mitigating the emission of toxic/acidic gases to environment. Moreover, performance, applications and challenges towards the use of nanocomposite membranes are reviewed comprehensively and future perspectives towards their development in industrial applications are recommended. Finally, prevalent nanocomposite membranes for the separation of various gaseous mixtures are presented.

Carbon dioxide (CO2) emissions have been the root cause for anthropogenic climate change. Decarbonisation strategies, particularly carbon capture and storage (CCS) are crucial for mitigating the risk of global warming. Among all current CO2 separation technologies, membrane separation has the biggest potential for CCS as it is inexpensive, highly efficient, and simple to operate. Polymeric membranes are the preferred choice for the gas separation industry due to simpler methods of fabrication and lower costs compared to inorganic or mixed matrix membranes (MMMs). However, plasticisation and upper-bound trade-off between selectivity and permeability has limited the gas separation performance of polymeric membranes. Recently, researchers have found that the blending of glassy and rubbery polymers can effectively minimise trade-off between selectivity and permeability. Glassy poly(ethersulfone) (PES) and rubbery poly(ethylene) glycol (PEG) are polymers that are known to have a high affinity towards CO2. In this paper, PEG and PES are reviewed as potential polymer blend that can yield a final membrane with high CO2 permeance and CO2/nitrogen (N2) selectivity. Gas separation properties can be enhanced by using different solvents in the phase-inversion process. N-Methyl-2-Pyrrolidone (NMP) and Dimethylformamide (DMF) are common industrial solvents used for membrane fabrication. Both NMP and DMF are reviewed as prospective solvent blend that can improve the morphology and separation properties of PES/PEG blend membranes due to their effects on the membrane structure which increases permeation as well as selectivity. Thus, a PES/PEG blend polymeric membrane fabricated using NMP and DMF solvents is believed to be a major prospect for CO2/N2 gas separation.

Polymeric membranes have emerged as a competitive technology in gas separation processes due to their notable energy efficiency, environmentally friendly attributes and minimal system footprint. To enhance the performance of conventional polymeric membranes, significant research efforts have been dedicated to modifying their surface properties in the last decade. Among the various techniques explored, membrane surface modification using coating methods, such as dip-coating, spray-coating, grafting and interfacial polymerization stands out as one of the most popular and straightforward approaches. Scientists have utilized a diverse array of coating solutions comprising either polymeric materials or hybrid materials in these methods, yielding promising outcomes. This article aims to present a comprehensive review of the advancements made in surface coating approaches employed for modifying hollow fiber membrane surfaces over the past decade. The review encompasses an evaluation of how different coating approaches and solutions affect the surface's physicochemical properties and the gas separation performance of the membranes. Furthermore, the article delves into discussing technical challenges associated with these surface coating approaches, providing an insightful analysis. Lastly, the review concludes by outlining perspectives and recommending future research directions for this area of study, highlighting the potential avenues for innovation and advancement in surface-coated hollow fiber membranes for gas separation applications.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Blended matrix polymer membranes have attracted attention today due to their high efficiency in gas separation. In this study, PS / SAPO 34 polymer membranes were synthesized and evaluated by phase separation method. ynthesized PS/SAPO-34 mixed matrix membranes (MMMs) were characterized via FESEM, TGA and DSC analyses. Various parameters such as air gap distance, dope extrusion rate, and jet strech were examined. After that, the process of separation of CO2 and CH4 gases was investigated. The results showed that the addition of SAPO nanoparticles improved membrane performance. The highest selectivity was obtained at temperature 28 and pressure 0.5 bar. Permeation results manifested that the PS/SAPO-34 fabricated at optimum conditions has incredible worth from the prospective of industrial separations of CO2 from flue and natural gas.

Predictive transport modelling in polymeric gas separation membranes: From additive contributions to machine learning

Testing of nanostructured gas separation membranes in the flue gas of a post-combustion power plant

Membrane-based gas separation offers significant potential for carbon capture and clean energy applications; however, inconsistent experimental conditions often hinder direct comparison of membrane performance. In this work, machine learning (ML) is applied to predict gas permeability in polymeric membranes using a dataset comprising 3618 entries from 603 polymers across six gases (CO2, N2, H2, He, O2, and CH4). Ensemble regression algorithms (Random Forest, Gradient Boosting, XGBoost, and Extra Trees) were developed and rigorously assessed. Model accuracy was evaluated using mean absolute error (MAE) and root mean square error (RMSE), both expressed in Barrer for physical relevance. Among the models, Random Forest exhibited the most reliable performance, achieving an MAE of 346.92 Barrer and an RMSE of 888.69 Barrer, highlighting its strong predictive capacity across diverse membrane-gas systems. Feature importance analysis, combined with SHAP interpretation, indicated that membrane structure, operating parameters, and gas-specific properties play key roles in determining permeability. Benchmarking predictions against the Robeson upper bound further identified high-performing membranes for CO2/N2 and CO2/CH2 separations. Overall, the study demonstrates the effectiveness of ML-driven screening in accelerating membrane discovery and supporting the design of next-generation gas separation materials.

Membrane-based gas separation has attracted a great deal of attention recently due to the requirement for high purity gasses in industrial applications like fuel cells, and because of environment concerns, such as global warming. The current methods of cryogenic distillation and pressure swing adsorption are energy intensive and costly. Therefore, polymer membranes have emerged as a less energy intensive and cost effective candidate to separate gas mixtures. However, the use of polymeric membranes has a drawback known as the permeability-selectivity tradeoff. Many approaches have been used to overcome this limitation including the use of polymer blends. Polymer blending technology synergistically combines the favorable properties of different polymers like high gas permeability and high selectivity, which are difficult to attain with a single polymer. During polymer mixing, polymers tend to uncontrollably phase separate due to unfavorable thermodynamics, which limits the number of completely miscible polymer combinations for gas separations. Therefore, compatibilizers are used to control the phase separation and to obtain stable membrane morphologies, while improving the mechanical properties. In this review, we focus on immiscible polymer blends and the use of compatibilizers for gas separation applications.

To prevent greenhouse emissions into the atmosphere, separations like CO2/CH4 and CO2/N2 from natural gas, biogas, and flue gasses are crucial. Polymer membranes gained a key role in gas separations over the past decades, but these polymers are often not organized at a molecular level, which results in a trade-off between permeability and selectivity. In this work, the effect of molecular order and orientation in liquid crystals (LCs) polymer membranes for gas permeation is demonstrated. Using the self-assembly of polymerizable LCs to prepare membranes ensures control over the supramolecular organization and alignment of the building blocks at a molecular level. Robust freestanding LC membranes were fabricated that have various, distinct morphologies (isotropic, nematic cybotactic, and smectic C) and alignment (planar and homeotropic), while using the same chemical composition. Single gas permeation data show that the permeability decreases with increasing molecular order while the ideal gas selectivity of He and CO2 over N2 increases tremendously (36-fold for He/N2 and 21-fold for CO2/N2) when going from randomly ordered to the highly ordered smectic C morphology. The calculated diffusion coefficients showed a 10-fold decrease when going from randomly ordered membranes to ordered smectic C membranes. It is proposed that with increasing molecular order, the free volume elements in the membrane become smaller, which hinders gasses with larger kinetic diameters (Ar, N2) more than gasses with smaller kinetic diameters (He, CO2), inducing selectivity. Comparison of gas sorption and permeation performances of planar and homeotropic aligned smectic C membranes shows the effect of molecular orientation by a 3-fold decrease of the diffusion coefficient of homeotropic aligned smectic C membranes resulting in a diminished gas permeation and increased ideal gas selectivities. These results strongly highlight the importance of molecular order and orientation in LC polymer membranes for gas separation.

Polyurethane-based gas separation membranes: A review and perspectives

To reduce the emission of carbon dioxide from a conventional coal-fired power plant, carbon dioxide can be separated from the flue gases by using polymer membranes. In this chapter a theoretical investigation into the technological and economic outlook of this option is described.At present the best types of membranes available for separating carbon dioxide from nitrogen are non-porous polymer membranes based on polyimide, polydimethylphenyleneoxide, polydimethylsiloxane and cellulose acetate. The carbon dioxide can be recovered by applying a single membrane stage configuration. The disadvantage of such a configuration is that it leads to a carbon dioxide gas that is highly diluted with nitrogen. This is an unwanted situation because the carbon dioxide is a liquid in the conditions (8000 kPa and 10°C) under which it will be transported, whereas nitrogen remains gaseous under these conditions. Moreover, the transport facilities and storage capacity for carbon dioxide will not be utilized optimally.Three methods for purifying the carbon dioxide are considered. In the first method the carbon dioxide product gas is purified by feeding it to a second membrane unit. This configuration is called the two-stage cascade. The second method makes use of the different phases of nitrogen and carbon dioxide at high pressures. In this method the carbon dioxide product gas is compressed to 8000 kPa and cooled down to 25°C. Subsequently the nitrogen, contaminated with some carbon dioxide vapour, is separated from the condensed carbon dioxide. This nitrogen off-gas is released to the atmosphere. The third method is similar to the second one, except that the nitrogen off-gas is recycled back to the membrane unit.With a computer program based on a cross-flow permeation model for polymer membranes, the recovery design is optimized to obtain the lowest recovery costs per tonne carbon dioxide avoided.For the membranes examined, a lowest cost figure of 51 US$ per tonne carbon dioxide avoided is calculated. This figure is found for a polyimide-based membrane in a single membrane stage configuration combined with separation of the carbon dioxide by compression and venting the nitrogen off-gas. In this set-up 75% of the carbon dioxide is recovered and the carbon dioxide is nearly pure. For a 90% recovery either the two-stage cascade or the single membrane stage with recycling of the nitrogen off-gas are attractive routes, leading to recovery costs of about 65 US$ per tonne carbon dioxide avoided. Recovery with polymer membranes is calculated to be 50 to 100% more expensive than recovery using cold distillation or a chemical absorption technique. Although some cost reductions are feasible, membrane separation is not expected to become a competing option for carbon dioxide recovery from flue gases of conventional coal-fired power plants in the near future.KeywordsInvestment CostPolymer MembraneRecovery CostMembrane UnitIsentropic EfficiencyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The development in the area of surface modification of polymeric synthetic membranes since 2000 is reviewed. Many patents, articles, and reviews have been written on the development in the area of surface modification of polymeric synthetic membranes subjected to RO, UF, NF, gas separation (GS), and biomedical applications, mainly since 2000, but recently more attention has been given to the modification of their surfaces to obtain desirable results. In particular, most emphasis has been given to plasma treatment, grafting of polymers on the surface, and modifying the surfaces by adding SMMs (surface‐modifying molecules). New additives are synthesized to make the polymeric membrane surfaces either to be more hydrophilic or hydrophobic, aimed at improvement in selectivity and permeability of the membranes for GS, NF, and RO. Improvement in antifouling by surface modification is also a popular topic in the membrane industries. In the last 8 years, tremendous research efforts have been made on the development of antifouling membranes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Recent progress in PIM-1 based membranes for sustainable CO2 separations: Polymer structure manipulation and mixed matrix membrane design