Facilitated Transport Membranes Research Articles

Membranes and membrane processes for CO2 separation: MEMFO's long-term effort in reducing carbon emissions

Urgent actions are needed to reduce CO2 emissions and mitigate the increasingly severe impacts of climate change. Since the 1990s, the membrane research group (MEMFO) at the Norwegian University of Science and Technology has been committed to developing effective membranes and membrane processes for CO2 separation. MEMFO's research can be categorized into five main themes: facilitated transport membranes, hybrid membranes, carbon membranes, membrane contactors, and related modeling and process simulation. These themes are tied to industrial applications in CO2 capture from flue gas, biogas upgrading, natural gas sweetening, and hydrogen purification. Promising membranes, identified based on their laboratory-scale performances, have been selected for onsite testing in industrial processes to validate their performances as well as stability and durability. Verified membranes are upscaled for pilot tests. This account paper summarizes MEMFO's research and development outcomes over the past decade and discusses our research strategies and perspectives for future work.

Sulfonated Chitosan Gel Membrane with Confined Amine Carriers for Stable and Efficient Carbon Dioxide Capture.

Capturing carbon dioxide (CO2) from flue gases is a crucial step towards reducing CO2 emissions. Among the various carbon capture methods, facilitated transport membranes (FTMs) have emerged as a promising technology for CO2 capture owing to their high efficiency and low energy consumption in separating CO2. However, FTMs still face the challenge of losing mobile carriers due to weak interaction between the carriers and membrane matrix. Herein, we report a sulfonated chitosan (SCS) gel membrane with confined amine carriers for effective CO2 capture. In this structure, diethylenetriamine (DETA) as a CO2-mobile carrier is confined within the SCS gel membrane via electrostatic forces, which can react reversibly with CO2 and thus greatly facilitate its transport. The SCS ion gel membrane allows for the fast diffusion of amine carriers within it while blocking the diffusion of nonreactive gases, like N2. Thus, the prepared membrane exhibits exceptional CO2 separation capabilities when tested under simulated flue gas conditions with CO2 permeance of 1155 GPU and an ultra-high CO2/N2 selectivity of above 550. Moreover, the membrane retains a stable separation performance during the 170 h continuous test. The excellent CO2 separation performance demonstrates the high potential of gel membranes for CO2 capture from flue gas.

Consideration of the Applicability of an Ionic Liquid–based Facilitated Transport Membrane to a DAC Process

Consideration of the Applicability of an Ionic Liquid–based Facilitated Transport Membrane to a DAC Process

Membrane-Based Technologies for Post-Combustion CO2 Capture from Flue Gases: Recent Progress in Commonly Employed Membrane Materials.

Carbon dioxide (CO2), which results from fossil fuel combustion and industrial processes, accounts for a substantial part of the total anthropogenic greenhouse gases (GHGs). As a result, several carbon capture, utilization and storage (CCUS) technologies have been developed during the last decade. Chemical absorption, adsorption, cryogenic separation and membrane separation are the most widely used post-combustion CO2 capture technologies. This study reviews post-combustion CO2 capture technologies and the latest progress in membrane processes for CO2 separation. More specifically, the objective of the present work is to present the state of the art of membrane-based technologies for CO2 capture from flue gases and focuses mainly on recent advancements in commonly employed membrane materials. These materials are utilized for the fabrication and application of novel composite membranes or mixed-matrix membranes (MMMs), which present improved intrinsic and surface characteristics and, thus, can achieve high selectivity and permeability. Recent progress is described regarding the utilization of metal-organic frameworks (MOFs), carbon molecular sieves (CMSs), nanocomposite membranes, ionic liquid (IL)-based membranes and facilitated transport membranes (FTMs), which comprise MMMs. The most significant challenges and future prospects of implementing membrane technologies for CO2 capture are also presented.

Effects of pressure and temperature on CO2 facilitation of amino acid salt-containing membranes for post-combustion carbon capture

Polymeric facilitated transport membranes (FTMs) that contain amino acid salts (AASs) provide a cost-effective option for reducing the CO2 emissions associated with burning fossil fuels. In the current work, we examined the effects of CO2 partial pressure and temperature on the CO2 absorption properties of three AAS mobile carriers, piperazine glycinate (PZ-Gly), 2-(1-piperazinyl)ethylamine glycinate (PZEA-Gly), and 2-(1-piperazinyl)ethylamine sarcosinate (PZEA-Sar), and their facilitation of CO2 transport by employing 13C NMR spectroscopy. The CO2 loading and the distribution of reaction products, i.e., carbamate and bicarbonate products, were analyzed and quantified for each AAS sample. The 13C NMR analysis revealed that PZEA-Sar had a greater CO2 loading and favored the more efficient bicarbonate pathway in comparison to PZ-Gly and PZEA-Gly. In addition, we noted marked differences in the formation of carbamate and bicarbonate products when the CO2 partial pressure and temperature were adjusted. The concentration gradient of the reaction products formed indicated that the diffusion of carbamate products was the most influential factor in CO2 transport under reduced CO2 partial pressure. However, as the partial pressure of CO2 increased, bicarbonate products began to play a more significant role. At elevated temperatures, a lower absorption of CO2 was observed, resulting in the reduced generation of both reaction products. This suggests that the enhanced CO2 permeance of FTMs is mainly attributed to the accelerated diffusion of the reaction products. The findings of this study contribute to a comprehensive understanding of the transport mechanism by which AAS carriers enhance CO2 facilitation, allowing for the refinement of more efficient FTM designs.

Engineering metal-covalent organic framework-based hybrid oxygenation membranes for facilitated blood-gas exchange

Oxygenation membranes operate as indirectly contacting barriers between blood and gas in extracorporeal membrane oxygenation (ECMO), improving oxygenation and removing carbon dioxide from blood. However, the low gas exchange efficiency of the current poly (4-methyl-1-pentene) (PMP) artificial lung membrane results in a high prime volume. Facilitated transport membrane is a fascinating strategy to construct high-performance membranes for blood-gas exchange. This study put forward hybrid strategy by using metal-covalent organic frameworks (MCOFs) to construct facilitated transport membrane of PMP flat membranes and hollow fiber membranes (HFMs) via thermally induced phase separation (TIPS) to achieve facilitated blood-gas exchange. Cu-TAPB-COF nanosheets (CuCON) with framework structure and abundant active metal sites were synthetized and introduced into PMP to construct hybrid oxygenation membranes, reducing the resistance of gas exchange channels and ensuring the high affinity toward CO2 and O2. Cu+ and benzene rings existed in aromatic skeleton as well as the tunable structure, that could ensure the stability of MCOF and the uniform distribution of facilitated transport sites. The prepared PMP-CuCON-1 HFMs exhibited O2 and CO2 exchange rate of ∼467.5 ml min−1 m−2 and ∼309.1 ml min−1 m−2 in blood gas exchange process, which was 143.1% and 261.3% higher than the commercial PMP HFM, respectively. Asymmetric structure ensured resistance to plasma leakage for more than two weeks, and Cu+ kept stable in CuCON and hybrid membranes. The hybrid membrane exhibited superior blood-gas exchange performance and good hemocompatibility, possessing great potential for application.

C2-Hydrocarbon Mixture Separation on Polyethylene Membranes with Grafted Sulfonated Polystyrene in H+, Li+ and Na+ Forms

The olefin separation from their mixture with paraffins by facilitated transport membranes is a very important process for the further macromolecular compounds production. Membranes loaded with silver ions, which are responsible for the facilitated olefin transport, are instable with time due to their reduction, while those containing protons catalyze the polymerization of olefins. In this work, membranes based on polyethylene with grafted sulfonated polystyrene in various ionic forms (H+, Li+, Na+) were used for the first time for the separation of the ethylene/ethane mixture. The influence of sulfonation time, relative humidity, and various ionic forms on ethylene separation was studied. The SEM study shows a non-uniform sulfur distribution over the membrane thickness for membranes sulfonated for different reaction times. With increasing sulfonation time and relative humidity the ethylene permeability and the factor of its separation with ethane increase. Separation factors for membranes in the Li+-form are shown to be as high as for membranes in the H+-form. A possible mechanism for the facilitated ethylene transport is discussed.

H2S/CO2 separation using sterically hindered amine membranes

With the growing interest in carbon capture from syngas and natural gas, H2S/CO2 separation is gradually becoming important in the gas processing and carbon capture industries. This work describes the development of amine-based facilitated transport membranes (FTMs) suitable for syngas desulfurization. Six amino acid salt carriers with varying steric hindrance were synthesized and used to fabricate FTMs. Their H2S/CO2 separation performances were evaluated at 107 °C and 7 bar feed pressure, using a dry feed composition of 1.5% H2S and 98.5% CO2. H2S/CO2 selectivity improved significantly as amine steric hindrance was increased. While mildly hindered amines showed low H2S/CO2 selectivities of around 5, sterically hindered and tertiary amines showed substantially improved separation performance, with selectivities in the range of 10–20. A highly hindered carrier containing the di-tert-butyl amine moiety showed the highest selectivity of 19.6, along with an H2S permeance of 560 GPU. The di-tert-butyl amine-based FTM was used to study the effect of temperature and feed H2S content on H2S/CO2 separation performance. The performances of the newly devised FTMs exceed the H2S/CO2 upper bound, and the learnings shed light on the design of amine carriers for acid gas separations.

Boosting CO2/N2 Separation from Cellulose Nanocrystal-Reinforced and Amine-Rich Facilitated Transport Membranes Comprising Deprotonated Amino Acid Salt and Ultrahigh-Molecular-Weight Polyvinylamine

Boosting CO₂/N₂ Separation from Cellulose Nanocrystal-Reinforced and Amine-Rich Facilitated Transport Membranes Comprising Deprotonated Amino Acid Salt and Ultrahigh-Molecular-Weight Polyvinylamine

Rational design, synthesis, and characterization of facilitated transport membranes exhibiting enhanced permeability, selectivity and stability

Despite outperforming conventional polymer membranes in the short time frame, facilitated transport membranes (FTMs) are prone to photo/chemical aging, which causes a rapid decay of their performance. Moreover, when embedded in polymer materials to fabricate mixed matrix membranes, structural defects may form at the metal-polymer interface, causing a selectivity loss. To overcome these issues, a series of poly(amic acid)s (PAAs) have been synthesized using 4,4’-oxydiphathalic anhydride (ODPA) and Jeffamine monomers of varying molecular weight, and used to fabricate silver nanoparticles via the chelating reaction with silver ions, in attempts to simultaneously i) achieve defect-free mixed matrix membranes (MMMs), ii) target CO2 selective transport, and iii) enhance long-term stability. The occurrence of the chelating reaction between silver and the PAA was confirmed, and as a result, individual and un-aggregated PAA-coated silver nanoparticles were obtained and incorporated into a commercial polymer, Pebax 1657, to fabricate defect-free mixed matrix membranes. The effect of the PAA length and ether functional group concentration on the structure and performance of the resulting mixed matrix membranes was systematically investigated. Remarkably, inclusion of only 2 wt% nanoparticles in Pebax enhances the CO2 permeability by 50% and CO2 selectivity by 100% relative to neat polymer. A detailed analysis of the sorption and diffusion coefficients was performed to elucidate the molecular origin of the observed membrane performance. Finally, preliminary data show that the newly synthesized materials exhibit high chemical stability upon exposure to pure H2.

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.

Metal-covalent organic framework nanosheets engineered facilitated transport membranes for toluene/n-heptane separation

Facilitated transport membranes is a promising strategy to fabricate efficient separation membranes for aromatic/aliphatic mixtures. However, building up selective channels with uniformly distributed facilitated transport sites is still challenging. In this study, Cu-TAPB-COF (CuCOF) nanosheets, a kind of metal-covalent organic frameworks (MCOFs), were synthetized and introduced into poly (ether-block amide) (Pebax®2533) matrix to construct facilitated transport membranes for toluene/n-heptane mixtures. As the aromatic skeleton linked by covalent interaction, CuCOF could provide continuous low mass transfer resistance channel. And Cu(I) exist in skeleton could serve as uniformly distributed facilitated transport sites and maintain a long-term stability. The resulting membrane exhibited a higher adsorption selectivity and lower swelling degree compared with pure Pebax membrane. The membrane exhibited high pervaporation separation performance for 50 wt% toluene/n-heptane mixture. When the filling contents of CuCOF was 2.0 wt%, the membrane achieved a permeation flux of 937 g m−2 h−1 and the separation factor of 4.7.

Boosting membranes for CO2 capture toward industrial decarbonization

Membrane technology for carbon capture is becoming increasingly attractive to combat the excessive greenhouse gas emitted into the atmosphere, which involves the benefits of cost-effectiveness, environmental-friendly, easy scalability, high energy efficiency, simplicity in design, etc. However, most state-of-the-art membrane materials suffer from either low CO2 permeability, low selectivity towards CO2 separation, poor resistance to plasticization, or inadequate long-term stability, rendering it still challenging to be upscaled to an industrial level. Therefore, the development of advanced membrane materials as well as a reasonable design of the membrane separation process is crucial and urgent for its real-life application in the future. This account reviews the details of some recent research progress in our group on carbon capture from different scenarios including post-combustion carbon capture, biogas upgrading and natural gas sweetening and hydrogen purification. Notably, considerable efforts have been invested in the development of some novel membrane materials in our group, such as facilitated transport membranes, carbon molecular sieving membranes, mixed matrix membranes, composite membranes, and poly(ionic liquids)-based membranes. Meanwhile, some studies focusing on the techno-economic feasibility analysis of membrane technology have also demonstrated its promising application on practical carbon capture.

Modeling of hollow fiber facilitated transport membrane modules for post combustion carbon capture process: Evaluation of non-ideal effect and module characteristic

Membrane separation technology has been regarded as a promising alternative for carbon capture process due to its low consumption and low footprint. Facilitated transported membranes exhibit attractive CO2/N2 separation performance due to the existence of CO2-philic reactive carriers. However, the highly pressure and temperature dependent CO2 permeance of it, as well as non-ideal effect, make the simulation of carbon capture process based on simplifying model challenging. Herein, we established a rigorous model for hollow fiber facilitated transport membrane considering both non-ideal effect and variable permeance. This rigorous model was applied for post-combustion carbon capture, and compared with simple model which only considering variable permeance. It was found that rigorous model has a 44%-55% lower carbon capture capacity due to the declined driving force and permeance. Pressure loss accounts for the deviation at low stage cut (10%), while Joule-Thomson effect and concentration polarization effect become greater at high stage cut (20%). Thanks to the mild condition of post combustion flue gas, the impact of real gas behavior can be neglected. Moreover, the attractive configuration of hollow fiber facilitated transport membrane was found to be with relative short fiber length, moderate packing fraction and large fiber inner diameter.

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 (≈15nm), verified by several analytical techniques, including 3D-reconstructedfocused 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.

Industrial-scale spiral-wound facilitated transport membrane modules for post-combustion CO2 capture: Development, investigation and optimization

Membrane separation technology is one of the most promising strategies for post-combustion CO2 capture. The high-performance membrane module is one of the most critical components in the CO2 capture membrane system. The spiral-wound module is a promising type for industrial application; however, most of the research remains in the laboratory. In this work, industrial-scale spiral-wound membrane modules containing facilitated transport membranes have been developed and investigated. Under given practical operating conditions, an apparent gas separation performance was defined as an indicator to study the effects of various feed conditions on membrane performance within the module. As a crucial process parameter, the operating pressure was considered a variable to investigate the module performance at a fixed feed-to-permeate pressure ratio, and techno-economic indicators were also studied. Furthermore, a multi-core module containing up to 14 membrane elements was designed based on the experimental results of the arrangement mode cases. This work could bridge the research gap between membrane development and membrane system engineering. It could also provide essential data for the industrial application of post-combustion CO2 capture.

Modeling of pre-combustion carbon capture with CO2-selective polymer membranes

CO2-selective polymer membranes were recently applied to pilot-scale and bench-scale pre-combustion capture and the obtained CO2 capture ratios were reported to be less than 90%, which limits their application in industrial processes such as IGCC plants. This work is aimed to explore the possibility of achieving a CO2 capture ratio >95% and CO2 purity >95% in a gas-separation unit equipped with currently-available CO2-selective polymer membranes. A mathematical model for single-stage membrane gas separation was developed, and the effect of membrane characteristics (permeance and selectivity), as well as the operating parameters such as feed and permeate pressure, and feed flow rate on the performance of CO2 capture was investigated. The simulation results reveal the optimal conditions that are necessary for a high-performance CO2 capture process using the real industrial syngas and highlight the potential of facilitated transport membranes for CO2 removal in both the oxygen-blown and air-blown IGCC processes.

13C NMR study of amino acid salts in facilitated transport membranes for post-combustion carbon capture

Some of amino acid salts (AASs) have been demonstrated to be effective mobile carriers in facilitated transport membranes (FTMs) to achieve superior CO2 permeance and CO2/N2 selectivity for CO2 capture from flue gas. Understandings of how the structures of different AASs affect the chemistry of the amine–CO2 reaction are essential for the future development of more efficient AAS mobile carriers. In this study, the reaction chemistry of selected AASs with CO2 was investigated by 13C nuclear magnetic resonance (NMR) spectroscopy. The CO2 loading and the distribution of major reaction products, including carbamate and bicarbonate products of each studied AAS were quantitatively analyzed. The positive correlation between the CO2 loading of AAS (mol CO2/g AAS) and the CO2 permeance of FTMs suggested that AAS with a higher CO2 loading may improve the performance of FTMs. Our results also showed that increasing the steric hindrance of AAS could be a practical way to promote the bicarbonate reaction pathway and thus potentially increase the CO2 loading (mol CO2/mol AAS). Moreover, 2-(1-piperazinyl)ethylamine (PZEA) was found to be a more effective multi-amine than piperazine (PZ) for synthesizing AASs due to the presence of more effective nitrogen sites per molecule. The superior CO2 permeance of the PZEA-Sar membrane is also attributed to its more uniform membrane formation. The knowledge gained from this study will inform the rational design of more effective AAS carriers for CO2 capture.

A review on facilitated transport membranes based on π-complexation for carbon dioxide separation

The emission of CO2 from human activities is the principal reason for global warming. Membrane separation technology has been extensively regarded as a tremendous potential option for mitigating CO2 emissions when utilizing fossil fuels as a major source of energy. As an important group of CO2 separation membranes, the fixed CO2 carrier-facilitated transport membrane guided by π-complexation reactions is a rising research field and has attracted much attention in the last ten years due to its desirable CO2 separation performance in the dry state and high resistance to oxidation. In this review, facilitated transport theories derived from π-complexation reactions are discussed for an in-depth understanding, rational design and tunable fabrication of facilitated transport membranes. According to the different fixation methods of metal ions (CO2 active carrier), polymer electrolyte membranes and mixed matrix membranes are discussed in detail as two strategies for fabricating CO2-facilitated transport membranes. Future perspectives toward π-complexation reaction-facilitated transport membranes are proposed.

Two-stage membrane-based process utilizing highly CO2-selective membranes for cost and energy efficient carbon capture from coal flue gas: A process simulation study

Membrane technology for CO2 capture has become an attractive strategy due to its cost and energy efficiency and low materials costs. In the past decade, membrane-based process designs for post-combustion power plant CO2 capture have been developed, utilizing existing highly CO2-permeable membranes with relatively low CO2/N2 selectivity (<50), and have obtained reasonably economic carbon capture. However, few membrane-based process designs were proposed for moderate to highly CO2-selective membranes (CO2/N2 selectivity of 50–300, and >300, respectively), which have vastly emerged in recent years, such as various facilitated transport membranes (FTMs). Herein, we proposed a two-stage membrane-base process design targeting economic carbon capture from coal-fired flue gas. This process design features the utilization of highly CO2-selective membranes for one-stage CO2 enrichment to 95% dry-base purity in the first stage and recycle of the remaining CO2 by a highly CO2-permeable membrane in the second stage, in order to achieve economic CO2 capture with 90% capture rate and >95% CO2 product purity. Through an integration-iteration membrane model and the Aspen Plus process simulation, a sensitivity study of operating pressures (feed and permeate pressures) and membrane properties (CO2 permeance and CO2/N2 selectivity) was conducted. Critical CO2/N2 selectivity of 300–400 was found for the highly CO2-selctive membranes to meet the demand for cost and energy efficient results. The lowest possible membrane area of 4.8 × 105 m2 and fractional energy of 19.3% were obtained, which is comparable to or even more attractive than reported membrane-based process designs. This work provides a new membrane process design option for highly CO2-selective membranes and gives insights on the influence of membrane performance and operation condition.