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Incorporating molecular amines as mobile carriers in facilitated transport membranes (FTMs) has been demonstrated to significantly enhance the CO2 permeance and CO2/N2 selectivity of the membrane f...

Polymeric membranes have been widely considered as one of the next-generation technologies for CO2 capture from fossil fuel-derived flue gases. This separation modality requires novel polymeric materials that possess efficient CO2/N2 separation properties, as well as chemical and mechanical stability for a multiyear membrane lifetime. In this paper, recent developments in polymeric membranes tailored for post-combustion carbon capture are reviewed. The selected polymeric materials encompass ether oxygen-rich polymers, polynorbornenes, ionic liquid membranes, and facilitated transport membranes. In each of the selected materials, noteworthy research efforts for material design and membrane formation are highlighted. The performances of the selected materials are compared in the CO2/N2 selectivity-CO2 permeance plot. As the only class of materials reviewed herein that have demonstrated the fabrication of thin-film composite membranes in scale, facilitated transport membranes have shown both high selectivity and permeance at relevant conditions for post-combustion carbon capture. However, comprehensive field tests are needed to resolve the technical gap between the material development and the commercial application.

A two-stage membrane process featuring a partial retentate recycling is designed for using amine-containing facilitated transport membranes to decarbonize flue gases from pulverized coal power plan...

Defects in metal–organic frameworks (MOFs) can play an important role in the development of MOFs as promising reverse osmosis (RO) membranes for water desalination. By employing molecular dynamics ...

A field trial with 1.4 m2 spiral-wound (SW) membrane modules fabricated from an amine-containing facilitated transport membrane was conducted with actual flue gas at the National Carbon Capture Center in Wilsonville, AL, U.S.A. Prior to the field test, the membrane modules were systematically evaluated with simulated flue gas to identify the optimal operating conditions, including feed flow rate, feed pressure and operating temperature. With the actual flue gas, the membrane modules showed ca. 1450 GPU CO2 permeance and 185 CO2/N2 selectivity at 67 °C with feed and permeate pressures of 4 and 0.3 atm, respectively. A 500-h stability was demonstrated in spite of the interference of system upsets and flue gas outages. During the field trial, carbon capture rates of better than 40% were achieved by a single SW module with coal-derived flue gas. Except for a few flue gas upsets, the CO2 purities in the captured stream were 94.5% or better on dry basis. The data obtained from this project validates the membrane material and provide basis for the design and fabrication of full-scale SW module with a membrane area larger than 50 m2. It should be noted that no significant amounts of Cr, As and Se were deposited onto the membrane during this 500-h test.

The facilitated transport of CO2 through an amine-containing polymeric membrane on a nanoporous PES substrate was studied at large feed-to-permeate pressure differentials that are relevant to post-combustion carbon capture. With the selective layer reinforced mechanically by incorporation of carbon nanotubes, the carrier saturation of amino groups by excessive CO2 was observed at high feed or permeate vacuum pressure. Nearly complete carrier saturation was observed at 7 atm feed pressure or a permeate vacuum near ambient pressure. At relatively low vacuum pressures, the vacuum degree and operating temperature affected the CO2 transport simultaneously. A vacuum pressure significantly lower than the water saturation pressure at certain temperature resulted in the dehydration of the selective layer, thereby a reduced CO2 permeance. This dehydration was mitigated at a moderate vacuum pressure. At the moderate vacuum pressure, the nanoporous PES substrate controlled the water permeation, leading to a sufficiently hydrated selective layer with high CO2 permeance and CO2/N2 selectivity. Overall, the membrane performed well with 0.3–0.6 atm vacuum pressures at 67 °C and a feed pressure of 4 atm, achieving the best membrane performance with a CO2 permeance of 1451 GPU and a CO2/N2 selectivity of 165.

Fabrication of amine-containing membranes for removal of H2S and CO2 from reformate gas for hydrogen purification for fuel cells was scaled up by using a continuous roll-to-roll membrane fabrication machine. The membrane contained aminoisobutyric acid-potassium salt as the mobile carrier and polyvinylamine as the fixed-site carrier for facilitated transport of acid gases in crosslinked polyvinylalcohol as the membrane matrix. Three key variables controlling the membrane selective layer thickness, i.e., the coating solution, substrate web coating speed, and coating knife gap setting, were identified and studied. Membranes in 14 in. in width and > 150 feet in length were fabricated with a uniform selective layer thickness of around 15 µm. The scale-up membranes demonstrated similar performances as the lab-scale membranes with a CO2 permeance of more than 200 GPU, CO2/H2 selectivity of greater than 200, and H2S/H2 selectivity of higher than 600. The scale-up membranes were used for the fabrication of prototype spiral-wound membrane modules for a field test with autothermal reformate gas as the feed gas. The modeling and optimization of the hydrogen purification process were performed to identify the optimum test conditions for the spiral-wound membrane modules. The modeling results showed that the membrane removed H2S to less than 10 ppm and CO2 to

Amine-containing mixed-matrix membranes incorporated with amino-functionalized multi-walled carbon nanotubes (AF-MWNTs) were synthesized for CO2/H2 separation based on the facilitated transport mechanism. AF-MWNTs were chosen primarily as the mechanical reinforcing filler to enhance the membrane stability. At 107 &deg, C and 0.2-MPa feed pressure, the membrane incorporated with 10 wt.% AF-MWNTs showed a CO2 permeability of 3196 Barrers and a CO2/H2 selectivity of 205. At the higher feed pressure of 1.5 MPa, owing to the carrier saturation phenomenon, the same membrane exhibited reduced transport performance with a CO2 permeability of 776 Barrers and a CO2/H2 selectivity of 31. These separation performances at both the low and high feed pressures were well above the theoretical upper bound. Furthermore, the incorporation of 10 wt.% AF-MWNTs led to a significant improvement on membrane stability. The transport performance and selective layer thickness of this membrane maintained for 100 h, which suggested that the incorporation of AF-MWNTs improved the resistance to membrane compaction upon a high feed pressure. Therefore, this work is considered as one of the crucial steps to enable the application of facilitated transport membranes to high-pressure gas processing such as syngas purification.

CO2 capture from coal- or natural gas-derived flue gas has been widely considered as the next opportunity for the large-scale deployment of gas separation membranes. Despite the tremendous progress made in the synthesis of polymeric membranes with high CO2/N2 separation performance, only a few membrane technologies were advanced to the bench-scale study or above from a highly idealized laboratory setting. Therefore, the recent progress in polymeric membranes is reviewed in the perspectives of capture system energetics, process synthesis, membrane scale-up, modular fabrication, and field tests. These engineering considerations can provide a holistic approach to better guide membrane research and accelerate the commercialization of gas separation membranes for post-combustion carbon capture.

A novel facilitated transport membrane was synthesized in a composite membrane configuration with a 170-nm selective layer coated on a polyethersulfone nanoporous substrate. In the selective layer, poly(N-vinylformamide-co-vinylamine) with amino groups covalently bound to the polymer backbone was used as the fixed-site carrier and an aminoacid salt, synthesized by deprotonating sarcosine with 2-(1-piperazinyl)ethylamine, was blended as the mobile carrier. The membrane demonstrated a CO2 permeance of 975 GPU (1 GPU = 10-6 cm3 (STP) cm-2 s-1 cmHg-1) and a CO2/N2 selectivity > 140 at 57 °C with 1 atm feed and permeate pressures. The membrane performance was also characterized with a vacuum pulled on the permeate side to simulate actual separation process conditions. However, the rubbery selective layer of the synthesized membrane sank into the nanoporous substrate, resulting in a drastically reduced CO2 permeance. To address this issue, multi-walled carbon nanotubes (MWNTs) wrapped by a copolymer poly(1-vinylpyrrolidone-co-vinyl acetate) were dispersed in the selective layer as reinforcement nanofillers. The gas permeation measurements showed that the incorporation of MWNTs strengthened the polymer matrix and the selective layer penetration was refrained by a 3 wt% MWNT loading. The presence of MWNTs also mitigated the polymer compaction if the feed gas was compressed.

Membrane and membrane process have been considered as one of the most promising technologies for mitigating CO2 emissions from the use of fossil fuels. In this paper, recent advances in polymeric membranes for CO2 capture are reviewed in terms of material design and membrane formation. The selected polymeric materials are grouped based on their gas transport mechanisms, i.e., solution‐diffusion and facilitated transport. The discussion of solution‐diffusion membranes encompasses the recent efforts to shift the upper bound barrier, including the enhanced CO2 solubility in several rubbery polymers and novel methods to construct shape-persisting macromolecules with unprecedented sieving ability. The carrier-bearing facilitated transport membranes are categorized based on the specific CO2-carrier chemistry. Finally, opportunities and challenges in practical applications are also discussed, including post-combustion carbon capture (CO2/N2), hydrogen purification (CO2/H2), and natural gas sweetening (CO2/CH4).

Composite membrane with superior performance can be employed for CO2 separation from flue gas. The separation performance of a composite membrane can be improved by fine-tuning the selective layer and porous substrate. The optimal substrate should have suitable interfacial property and surface morphology, as well as minimal gas permeation resistance. The present study discusses the approach to improve the hydrophilicity and morphology of nanoporous polyethersulfone (PES) substrates by incorporating a small amount of hydrophilic additives, such as sulfonated polysulfone (SPSf), hydroxylated polyethersulfone (PES-OH), and polyvinylpyrrolidone (PVP). The surface and bulk morphologies of the PES substrate were modified to reduce the gas permeation resistance by incorporation of the hydrophilic additives. Moreover, a thinner selective layer containing hydrophilic polymers can be coated on top of the improved PES substrates due to the enhanced hydrophilicity. Both the morphological and hydrophilic modifications can improve the separation performance of the composite membrane. The developed PES substrates described in this paper are suitable for the preparation of composite membrane in gas separation. A resistance-in-series model was employed to evaluate the effect of modified substrates on separation performance improvement. It was found that, with a defined selective layer, the separation performance of a composite membrane was affected by the lateral diffusion on the selective layer-substrate interface and the Knudsen diffusion in the nanoporous substrate. For the selective-layer material in this study, the data fitting showed that 25–30% of the total resistance was caused by the lateral diffusion, while 5% of the total resistance was due to the Knudsen diffusion in the substrate.

A Zn benzotriazolate metal–organic framework (MOF), [Zn(ZnO2CCH3)4(bibta)3] (1, bibta2– = 5,5′-bibenzotriazolate), has been subjected to a mild CH3CO2–/HCO3– ligand exchange procedure followed by thermal activation to generate nucleophilic Zn–OH groups that resemble the active site of α-carbonic anhydrase. The postsynthetically modified MOF, [Zn(ZnOH)4(bibta)3] (2*), exhibits excellent performance for trace CO2 capture and can be regenerated at mild temperatures. IR spectroscopic data and density functional theory (DFT) calculations reveal that intercluster hydrogen bonding interactions augment a Zn–OH/Zn–O2COH fixation mechanism.

H2 is an important industrial gas, and high purity H2 is required for applications. Recent advances in both H2-selective and CO2-selective membranes for H2 purification are reviewed with an emphasis on the development of CO2-selective facilitated transport membranes for H2 purification. With CO2-selective facilitated transport membranes, examples of high-pressure and low-pressure H2 purification applications are discussed. In high-pressure H2 purification in the Integrated Gasification Combined Cycle (IGCC) operation, experimental and modeling results demonstrated the potential of amine-containing facilitated transport membranes to achieve an economically attractive cost of electricity. CO2-selective membranes for low-pressure H2 purification for fuel cells have been developed for both PEMFC and SOFC. The membranes have been scaled-up, and they have shown promising gas transport performances for the respective applications.

A vacuum-assisted deposition setup was developed in pilot scale to scale up and continuously deposit zeolite-Y (ZY) nanoparticles on 14-in wide nanoporous polyethersulfone (PES) substrate. The deposited substrate was used for composite membrane fabrication for carbon capture from flue gas. The effects of operating parameters, including ZY dispersion concentration, pressure differential, and web speed, on the ZY layer thickness and uniformity were studied. A ZY dispersion concentration of 0.08 wt%, a pressure differential of 3.7 in Hg, and a web speed of 3 ft/min were identified as the optimal operating conditions for depositing a thin and uniform ZY layer with a thickness of approximately 160 nm. A mathematical model with two adjustable parameters was derived from Darcy's law to correlate the operating parameters to the ZY layer thickness. After coating a polymeric amine-containing selective layer on the deposited substrate, the formed composite membrane showed a CO2 permeance of 800 GPU with a CO2/N2 selectivity over 150 at the typical flue gas temperature of 57 °C, which was superior to the performance of the membrane coated on the bare PES substrate. This improvement was due to the reduced selective layer penetration and effective diffusional length from the deposited substrate.

An oxidatively stable borate-containing membrane for H2 purification in fuel cell application was developed. The membrane comprised a quaternaryammonium hydroxide as the mobile carrier for the facilitated transport of CO2, a quaternaryammonium fluoride-containing polymer as the fixed-site catalyst for the reaction between CO2 and water molecules, a borate-based additive as another catalyst for the same reaction, and a crosslinked polyvinylalcohol-polysiloxane as the membrane matrix. The effect of borate-based additive on the membrane performance was investigated. The optimized membrane containing tetrafluoroboric acid achieved a CO2 permeance of 100 GPU and CO2/H2 selectivity >100. The oxidative stability of the membrane was demonstrated for at least 144 h at 120 °C with humid air as the sweep gas. As the membrane thickness was reduced from 15 µm to 10 µm, a significant drop in CO2/H2 selectivity was observed due to the increase of the H2 permeance while the CO2 permeance was not significantly improved. The water permeation through the membrane was reduced by adding the number of the substrate layers underneath the membrane. The water permeance was reduced almost proportionally as the number of the substrate was increased up to 3 pieces. The membrane was scaled up by using a continuous roll-to-roll machine to fabricate 14-inch. wide flat-sheet membranes with >1400 feet in total length. The scale-up membrane performed similarly compared to the lab-scale membranes. The membrane developed in this work has the potential for membrane processes that use air as the sweep gas including the H2 purification for fuel cell applications.

A spiral-wound membrane module comprising face compression “O” rings for effective seal of gases was developed, including a spiral-wound membrane element, Plexiglas fiber-reinforced plastic tube, and membrane housing. The spiral-wound membrane modules demonstrated essentially no leakage. The concentration polarization phenomenon was observed at a dry feed gas flow rate of less than 1000 sccm before humidification. Hence, the performances of the spiral-wound membrane modules were evaluated using both dry feed and sweep gas flow rates each at 1000 sccm before humidification at the typical flue gas temperature of 57 °C. The feed and sweep gas pressures were at 1.5 and 1 psig, respectively. By using either a simulated flue gas or an actual flue gas, the spiral-wound membrane modules showed similar performance results with a CO2 permeance of greater than 800 GPU and a CO2/N2 selectivity of more than 140, which were essentially identical to the results obtained from the flat-sheet membrane used for the module fabrication and tested in laboratory with the simulated flue gas. The pressure drops of the modules were satisfactory, i.e., less than 1.5 psi/m. During the field test using the actual flue gas at the National Carbon Capture Center in Wilsonville, Alabama, the performances of the modules revealed some unexpected issues including the feed spacer indentations on the membrane selective layer and the leakage at glue lines. These issues were resolved by improving the spiral-wound membrane module fabrication using a smoother feed spacer and a longer glue curing time. The field test results of the modules have shown their good potential for the post-combustion CO2 capture from coal-fired power plants.

Membrane technology is a cost-effective and energy-efficient separation process for CO2 removal from flue gas. Recently, there have been remarkable advances in the development of polyvinylamine (PVAm)/piperazine glycinate (PG)-containing facilitated transport membranes for CO2 removal. The advanced PVAm/PG-containing membranes have demonstrated desirably high CO2/N2 selectivity of greater than 140 and good CO2 permeance of > 700 GPU (1 GPU = 10−6 cm3 (STP)/(s cm2 cmHg)) at the typical flue gas temperature of 57 °C. This work investigated the scale-up fabrication of the PVAm/PG-containing membranes and demonstrated it successfully. Effective and efficient continuous fabrication of the membranes in a roll-to-roll manner was developed using the thin-film coating (TFC) assembly of the pilot-scale machine at Ohio State. The design of the TFC assembly was improved and several operating parameters were optimized for the fabrication with desirable membrane thickness and gas transport performance. A total of > 2000 feet long and 14-in. wide membranes with a selective layer thickness of

In this paper, facilitated transport membranes comprising polyvinylamine (PVAm) as fixed carrier and different amino acid salts (AAS) as mobile carriers were synthesized for post-combustion capture. The AAS carriers were prepared by deprotonating alanine (Ala), lysine (Lys), and proline (Pro) with 2-(1-piperazinyl)ethylamine (PZEA). CO2 separation performances of the membranes with these AAS carriers were compared, and the AAS effectiveness to facilitate transport of CO2 was in the order of PZEA-Pro > PZEA-Lys > PZEA-Ala. The membrane comprising 35 wt% PVAm and 65 wt% PZEA-Pro at 57 °C rendered a promising CO2 permeance of 936 GPU and a CO2/N2 mixed gas selectivity of 193. When the PVAm was reduced to 15 wt%, i.e., its 20 wt% was replaced by the mobile carrier of PZEA-Sar (sarcosinate), the permeance further improved to 947 GPU with a remarkable CO2/N2 selectivity of 210. Moreover, thermal gravimetric analysis showed a good thermal stability of the membrane, and membrane stability testing also gave stable transport performance. Furthermore, spectroscopic ellipsometry analysis exhibited a uniform membrane selective layer and an excellent agreement on the membrane thickness of ca. 170 nm measured independently by SEM. In addition, the membranes presented in this paper surpassed both the Robeson upper bound and the modified upper bound, indicating a great potential for CO2 capture.

A single-stage membrane process has been designed for using facilitated transport membranes (FTMs) to decarbonize the coal-derived syngas from an integrated gasification combined cycle (IGCC) power plant. The necessary process model and costing method have also been developed to assess the technical feasibility and process economics. In order to account for the carrier saturation phenomenon associated with FTMs, a homogeneous reactive diffusion model is integrated into the process model. The techno-economic study reveals that the mitigated carrier saturation upon bulk CO2 removal can lead to appreciable increases in the CO2 permeance and CO2/H2 selectivity, which can be utilized to achieve 95% CO2 purity and 95% H2 recovery with a CO2/H2 selectivity of 50 at the complete carrier saturation. FTMs with different facilitated transport characteristics can also be arranged in a hybrid membrane configuration to render a H2 recovery of 99% and a cost of electricity of $118.5/MWh, which is 12.5% lower than that of the benchmark Selexol process.

Facilitated transport membranes have been intensively studied for CO2 separation and capture, in which amine carriers are the key for membrane separation performance. It has been reported that sterically hindered amines possess superior CO2 loading capacity over unhindered amines. In this work, we successfully introduced the effect of the steric hindrance to the nitrogen site of amine into polyvinylamine membranes. Sterically hindered poly(N-vinylamine)s, namely poly(N-methyl-N-vinylamine), poly(N-isopropyl-N-vinylamine), and poly(N-tertiary-butyl-N-vinylamine), were synthesized from modifying unhindered poly(N-vinylamine). The effect of steric hindrance on membrane performance was investigated under the typical flue gas CO2 capture conditions, i.e., 57 °C and ~ 1 atm, showing that poly(N-methyl-N-vinylamine) was the one with the optimal steric hindrance degree for the best membrane performance. Compared with unmodified polyvinylamine, poly(N-methyl-N-vinylamine) demonstrated 24% improvement on CO2 permeability and 14% increase in CO2/N2 selectivity at 57 °C. The membrane performance enhancement by amine steric hindrance was found to be greatly influenced by temperature. At 102 °C, poly(N-methyl-N-vinylamine) demonstrated a CO2 permeability of 6804 Barrers, a CO2/N2 selectivity of 350, and a CO2/H2 selectivity of 162, which were approximately 4 times those of unmodified polyvinylamine. This work has extended the study on sterically hindered polyamines for CO2 facilitated transport and developed a next-generation fixed-site carrier membrane.

Post-combustion carbon capture using membranes is a key approach to control CO2 emissions from power plants using fossil fuels. The minor contaminants, such as SO2 and O2, may influence the long-term membrane performance. With the presence of SO2 in the feed gas, SO2 could preferably react with amine carriers and hinder the permeation of CO2 in the amine-containing facilitated transport membranes. Possible amine degradation and competitive reactions would reduce membrane performance with real flue gas. With SO2 concentrations of 0.7–5 ppm, two amine-containing facilitated transport membranes were tested at 57 and 102 °C, respectively. Unstable membrane performance was observed at 102 °C for the membrane containing Lupamin® as fixed-site carrier and potassium glycinate (K-Gly) as mobile carrier in the presence of SO2. On the contrary, two membranes containing polyvinylamine (PVAm) as fixed-site carrier and amino acid salts as mobile carriers showed stable separation performance in the presence of 1–3 ppm SO2 at 57 °C. Therefore, the operating temperature plays a significant role in the membrane stabilities in the presence of SO2. In addition, the infrared (IR) spectra of the membrane components exposed to SO2 with respect to exposure time were collected. It was found that the amines reacted with SO2 to form sulfite products irreversibly at 102 °C. The spectral results were consistent with the observed membrane separation performance. The stable membrane performances of the facilitated transport membranes at 57 °C with SO2 at ppm levels indicate the applicability of the developed amine-containing membranes for use in CO2 capture from real flue gas.

CO 2 -selective facilitated transport membranes are well-known for providing remarkably high CO 2 /H 2 selectivity along with high permeance at high temperatures (100 – 120 °C). This work demonstrates the development of a new class of facilitated transport membranes containing quaternaryammonium hydroxide small molecules and quaternaryammonium hydroxide- and fluoride-containing polymers as mobile carriers and fixed-site carriers, respectively, for CO 2 separation and H 2 purification. The active nature of tetramethylquaternaryammonium hydroxide as a mobile carrier was successfully demonstrated with high CO 2 permeance. However, the membrane performance was improved significantly by the incorporation of quaternaryammonium hydroxide- and/or fluoride-containing polymers in the membrane. The resulting hydroxide- and fluoride-containing membranes exhibited CO 2 permeance >50 GPU and CO 2 /H 2 selectivity >100 at 120 °C using humid air as the sweep gas. The membrane composition was optimized, and the transport stability of the membrane was investigated. The membrane showed oxidative stability during the 145-h transport measurement at 120 °C using air as the sweep gas. Furthermore, the effects of sweep steam content and membrane thickness were investigated. As the sweep steam content was increased (especially for steam content >50%), both CO 2 permeance and CO 2 /H 2 selectivity increased. As the membrane thickness was reduced from 15 µm to 2 µm, a sharp drop in the CO 2 /H 2 selectivity was observed whereas the CO 2 permeance did not seem to increase as prominently as the H 2 permeance. In addition, the membrane was successfully scaled up using a roll-to-roll continuous membrane fabrication machine, and the scale-up membrane showed similar performance as the lab-scale membrane.

In the fabrication of zeolitic imidazolate frameworks (ZIFs) thin films and membranes, the preparation of stable ZIFs dispersions is crucial. Herein, ultra-stable ZIF-8 aqueous dispersions were obtained successfully for the first time. It was found that, after the synthesis of ZIF-8, with the increased washing times, the positive surface potentials of ZIF-8 particles decrease, resulting in increased aggregate size. The ZIF-8 dispersions washed for zero times are very stable in water, and there is no settlement even after centrifuging at 8000 rpm for 6 min. The aggregate size of ZIF-8 dispersions in ethanol aqueous solutions decreases with increased ethanol content, and there is no apparent settlement in absolute ethanol even after 13 days. The ultra-stable ZIF-8 dispersions display great potentials in fabrication of thin films and membranes.

s Pharmaceutics and biotechnology play a vital role for both human beings and the environment. In pharmaceutics and biotechnology, separation processes, using supported liquid membranes (SLMs) in particular, are extensively applied for the removal and recovery of active ingredients from diluted aqueous solutions produced by fermentation and/or enzymatic synthesis. This chapter reviews the significant advances and widespread activities of SLMs in pharmaceutics and biotechnology, especially for the selective removal and recovery of antibiotics such as Cephalexin, Cephalosporin C, Penicillin G, and Amoxicillin. Important parameters that impact the mass transfer performance of SLMs are discussed and highlighted. Future perspectives on the development of SLMs are also highlighted.

Over the past decade, CO2 separation and capture have become the new bandwagon for polymer science and membrane research. This review presents the fundamentals of CO2/gas separation in polymeric membranes and discusses how these principles underpin opportunities and challenges for post-combustion carbon capture (CO2/N2), hydrogen purification (CO2/H2), and natural gas and biogas sweetening (CO2/CH4). Emerging polymeric membrane materials are discussed, including a few polymers containing a high content of polar functional groups (i.e., ether oxygen-rich polymers and polymeric ionic liquids), shape-persisting glassy polymers (i.e., perfluoropolymers, thermally rearranged polymers, iptycene-containing polymers), and reactive polymers featuring facilitated transport. Moreover, the promising candidates for each CO2 separation application are highlighted. Finally, the permeability-selectivity data reviewed were plotted against their 2008 and 2019 upper bounds.

Membranes for post-combustion CO2 capture are required to have a high CO2 permeance due to the limited driving force. For facilitated transport membranes synthesized with polyvinylamine (PVAm), a defect-free selective layer of

Incomplete oxidation on the anode side of a solid oxide fuel cell (SOFC) leaves a considerable amount of unused fuel (e.g., H2 and CO) in the anode exhaust. In order to enhance fuel utilization, CO2-selective membranes can be employed to remove the CO2 in the anode exhaust before returning the recovered fuel to the SOFC. In this study, two membrane processes have been designed for integration with a SOFC system, one with an air sweep (SOFC-MBair) and the other with a vacuum (SOFC-MBvac), on the permeate side. The transport properties of developed membranes were applied to the processes, and techno-economic analysis (TEA) was carried out to estimate the CO2 removal cost of each process. The parameters investigated were the anode exhaust recycle percentage, stack fuel utilization of the SOFC, power output, as well as the area and transport properties of the membranes. Notably, at 100% anode exhaust recycle, the system fuel utilization can be boosted to >99% for both processes. By tuning the stack fuel utilization, a steam-to-carbon ratio above 1.5 is achievable. It was found that the SOFC-MBvac process can achieve a lower CO2 removal cost than the SOFC-MBair process. For the SOFC-MBvac process, by considering the value of the recovered fuel, the CO2 removal cost not only can be fully rebated by the recovered fuel value, but also there is a profit of about $38 per tonne of CO2 captured. Moreover, by taking into account a CO2 sale price of $40/tonne for enhanced oil recovery, a profit of about $66 per tonne of CO2 captured may be achieved. Furthermore, more cost reduction or profit is attainable by developing membranes with higher CO2 permeances. In addition, a zero-carbon electricity generation can be achieved by the SOFC-MBvac process.

Membrane separation is a promising technology for CO2 separation and capture because of the high energy efficiency, small footprint and operational simplicity. A CO2 facilitated transport membrane is an important group of membranes for CO2 separation. In this review, the facilitated transport mechanism is described in conjunction with the chemical reactions of CO2 and amine carriers. A wide range of facilitated transport membranes is discussed, including amine-based fixed-site carrier membranes, amine mobile carrier-containing membranes and other facilitated transport membranes with different types of carriers and/or inorganic fillers to further improve the performance of facilitated transport membranes. This review concludes with remarks on the future perspectives of the facilitated transport membranes for CO2 separation and capture applications.

High-molecular-weight polyvinylamine (PVAm)/piperazine glycinate (PG) membranes were successfully synthesized for CO2/N2 separation from flue gas. PVAm with different molecular weights was synthesized through free radical polymerization by adjusting the monomer concentration and initiator amount. The synthesized PVAm showed both a higher molecular weight and a higher solution viscosity than the commercially available PVAm (Lupamin® 9095 from BASF Corporation). The high viscosity of the PVAm solution at a low concentration allowed the preparation of much thinner membranes. It could also help reducing penetration of the polymer solution into the pores of the substrate, further reducing the mass transfer resistance. Consequently, a high CO2 permeance could be obtained from thin membranes with the thickness of 100–200 nm. In the membrane, PVAm acted as the fixed-site carrier for CO2 facilitated transport whereas PG was incorporated into the PVAm polymer matrix and served as the mobile carrier. The PVAm/PG blend solution was coated onto different substrates including polyethersulfone (PES) and polysulfone (PSf) substrates. Sodium dodecyl sulfate (SDS) surfactant was incorporated in the coating solution to improve the adhesion between the membrane layer and the substrate in some cases. The resultant PVAm/PG membranes exhibited a high CO2 permeance of about 1100 GPU and a high CO2/N2 mixed gas selectivity of more than 140 at the typical flue gas temperature of 57 °C along with 17% water vapor.

New amine-containing polymer/zeolite Y composite membranes were successfully synthesized for CO2/N2 separation from flue gas. The polyvinylamine (PVAm) with a high molecular weight ( M W ¯ =719,000) was synthesized and used as the fixed-site carrier for CO2 facilitated transport. The PVAm was incorporated with different aminoacid salts (mobile carriers), including potassium glycinate (KG), lithium glycinate (LiG) and piperazine glycinate (PG). The amine-containing polymer blend solution was coated onto a zeolite Y seed layer on top of a polyethersulfone (PES) substrate. The composite membrane with a selective amine layer thickness of more than 200 nm showed a better CO2/N2 separation performance compared to the membrane without the zeolite Y seed layer, which was due to the fact that the zeolite Y layer had a smaller interparticle pore size than the PES substrate, resulting in minimizing the penetration of amine-containing polymer solution into the pores underneath and thus reducing the mass transfer resistance of CO2 molecules through the membrane. The effects of different kinds of mobile carriers and various compositions and thicknesses of the amine-containing polymer layer were investigated. The resultant amine-containing polymer/zeolite Y composite membrane exhibited a CO2 permeance up to ~1100 GPU and a CO2/N2 mixed gas selectivity of at least 200 at the typical flue gas temperature of 57 °C. This high separation performance showed a great potential for the application of carbon capture from flue gas.

A novel concept of multilayer polymer/zeolite Y composite membrane structure was developed and investigated for CO2 capture from flue gas. Zeolite Y nanoparticles with an average particle size of 40 nm were successfully deposited onto flexible polymer supports with uniform coverage by the vacuum-assisted dip deposition approach. The zeolite Y dispersion concentration was varied for different commercial polymer supports to obtain a crack-free zeolite Y layer. Scanning electron microscopy (SEM) analysis indicated that a uniform zeolite Y layer could be formed either on Biomax polyethersulfone (PES) membrane or on TM10 polyvinylidene fluoride (PVDF) membrane with appropriate vacuum-assisted dip deposition conditions. Atomic force microscopy (AFM) analysis showed that the zeolite Y/Biomax PES substrate was smoother than the zeolite Y/TM10 PVDF substrate. The Pebax®/PEG-200 membrane prepared on the zeolite Y/Biomax PES substrate exhibited higher CO2 permeance than that prepared on the bare Biomax PES support since the penetration of the polymer membrane was minimized by the smaller interparticle pore size on the zeolite Y layer. The membrane of the multilayer composite structure showed a CO2 permeance of 745 GPU and a CO2/N2 selectivity of 25.4 under flue gas operating conditions at 57 °C and ~1 atm. This concept has provided the basis for high performance membranes with the selective polymer cover layer containing amino groups and for grown zeolite Y membranes with continuous polycrystalline structure supported by the flexible polymer substrate.

Solid oxide fuel cells (SOFCs) have been commercialized due to their ability to provide a reliable energy supply at a high efficiency. However, because of the incomplete oxidation on the anode side, there is still a considerable amount of unused fuel (e.g., H2 and CO) present in the anode exhaust. A CO2-selective membrane was proposed to remove CO2 in the anode exhaust and recycle the retained H2 and CO back to the SOFC. The challenge lies in maintaining a high CO2/H2 selectivity (>100) and a good CO2 permeance (>100 GPU) at an operating temperature of 120 °C. Earlier studies have yielded facilitated transport membranes that employed tetramethylammonium hydroxide (TMAOH) as the mobile carrier for CO2. However, a better stability of the membrane at a higher temperature of 130 °C was desired. In this study, fluoride- and hydroxide-containing species, including tetramethylammonium fluoride (TMAF), cesium fluoride (CsF), potassium fluoride (KF), and N,N-dimethylpiperidinium hydroxide (DMPOH), were examined for their potential of replacing TMAOH to facilitate CO2 transport. The thermal stability of the quaternaryammonium-containing compounds was characterized by TGA and NMR, and the catalyzing activities of the fluoride-containing species were compared using NMR. Based on the characterization results, TMAF was chosen as the substitute for TMAOH, and the membrane synthesized with the optimal composition was tested for transport performances at various temperatures. In particular, a CO2 permeance of 108 GPU and a CO2/H2 selectivity of 106 were obtained at 120 °C. The TMAF-containing membrane also demonstrated an improved stability than the TMAOH-containing membrane at 130 °C.

Substrate morphology has a significant effect on the CO2 transport performance of a thin-film composite (TFC) membrane. In this study, a new mixed solvent comprising 2-pyrrolidone (2-PD) and 2-methoxyethanol (2-ME) was used to prepare polyethersulfone (PES) substrates with bicontinuous structure by water vapor-induced phase separation, followed by immersion in water as nonsolvent. Compared with the commonly used solvent, N-methyl-2-pyrrolidone (NMP), the 2-PD/2-ME mixed solvent is more hydrophilic and can decrease the thermodynamic stability of the casting solution significantly. As a result, the phase separation was induced via the spinodal decomposition mechanism. The open morphology bestowed the optimized substrate with a very high CO2 permeance of 133,226 ± 3870 GPU (1 GPU = 10–6 cm3(STP) s–1 cm–2 cmHg–1 = 3.3464 × 10-9 kg-mol s–1 m–2 Pa–1), which was 5 times more permeable than the baseline substrate synthesized with NMP. By using this new substrate, the prepared TFC membrane containing amines showed an increased CO2 permeance of 908 ± 8 GPU at 57 °C, which was 48 GPU higher than that with the baseline substrate. Meanwhile, the CO2/N2 selectivity was retained at 162 ± 4 at 57 °C. In addition, the good scalability of the new PES substrate was demonstrated by roll-to-roll fabrication of a 50′ long scale-up PES substrate with a width of 21ʺ.

Facilitated transport membranes for CO2 capture from flue gas were scaled up and subsequently fabricated into spiral-wound modules. In order to increase the membrane area in each module conveniently, a multi-leaf rolling procedure utilizing a carrier layer was used, and the fabrication steps were documented in detail. The prototype module comprised up to 7 membrane leaves (each membrane leaf had dimensions of 14″ by 36″) and had a total membrane area of up to 2.94 m2. By controlling the spacer thicknesses, the packing density in each of the modules was enhanced, while the pressure drops on both feed and permeate sides were maintained below 1.5 psi/m. The fabricated membrane modules showed consistent transport results as the corresponding scale-up membranes. For instance, a CO2 permeance of 1450 GPU and a CO2/N2 selectivity of 185 were achieved with a simulated flue gas at 67 °C. Furthermore, the pressure drop and concentration polarization phenomenon were quantitatively correlated to the feed flow rate. The developed correlations were used to predict the separation performance of a full-size (8″ × 40″) module.

A Zn benzotriazolate metal-organic framework (MOF), [Zn(ZnO

A new Pebax®/zeolite Y composite membrane with three layers on top of the polyethersulfone (PES) substrate was designed and successfully synthesized for CO2 capture from flue gas. The three layers were the zeolite Y inorganic layer, selective Pebax® layer, and polydimethylsiloxane (PDMS) cover layer, respectively, from bottom to top. Zeolite Y with a particle size of about 40 nm was synthesized and deposited onto the PES substrate. On top of the zeolite Y layer, a selective polymer layer was deposited with the blend solution of Pebax® and ethylene oxide (EO)-containing small molecules. A PDMS cover layer was applied on top of the Pebax® layer for defect abatement. The composite membrane showed a better CO2/N2 separation performance compared to the membrane without the zeolite Y layer, which was due to two reasons. First, the hydrophilic zeolite Y layer improved the adhesion between the Pebax® polymer layer and the substrate, which allowed for the preparation of much thinner and defect-free membranes. Second, the zeolite Y layer had a smaller interparticle pore size than the PES substrate and then minimized the penetration of polymer solution into the pores, which reduced the mass transfer resistance of CO2 molecules through the membrane. The effects of different Pebax® blend compositions and various coating conditions on the membrane separation performance were also investigated. This work for the first time reports a thin Pebax® membrane with a high CO2 permeance and a relatively good CO2/N2 selectivity at 57 °C. The resulting Pebax®/zeolite Y composite membrane exhibited a CO2 permeance up to 940 GPU and a CO2/N2 mixed gas selectivity of 30 at 57 °C, indicating promising potential for CO2 capture from flue gas.

In recent years, integrated gasification combined cycle (IGCC) technology has gained significant attention for large-scale power generation with carbon capture. In an IGCC power plant, the syngas is typically directed to the gas turbine (for power generation) after CO2 and H2S removal. This work describes the transport properties of the CO2-selective polymeric facilitated transport membranes for syngas purification at different pressures (2–15 bar) and 107 °C. These membranes contain amines as CO2-carriers that are dispersed in a crosslinked polyvinylalcohol (PVA) matrix. Furthermore, a two-stage membrane process is proposed for CO2 removal from syngas in an IGCC plant. A process modeling and cost-sensitivity analysis of the proposed two-stage membrane process was performed. The effects of feed pressure, temperature, membrane permeance, and selectivity on the overall increase in the cost of electricity (COE) were analyzed. An increase in the COE of 14–18% was estimated for 90% CO2 removal and >99% H2 recovery using the two-stage membrane process in an IGCC power plant.

Advances in nanotechnology in recent years enhance the R&D in nanostructured membranes. This paper reviews the recent developments of the nanostructured polymer-based membranes, formed by incorporating nanomaterials and/or porous membranes with nanoscale pores, for gas separations, reverse osmosis, ultrafiltration, and other potential applications. Significant progress has been made on the development of nanostructured membranes for gas separations, particularly for CO2 separations from H2, N2 and CH4. Continued improvements on the nanostructured reverse osmosis polyamide membranes via interfacial polymerization have been made along with the efforts on developing novel nanostructured membranes for desalination. The modification of both the surface and bulk properties of the ultrafiltration membranes by nanomaterials can improve the membrane performance and open up the possibility of new applications in addition to those for the current ultrafiltration membrane processes.

Rapid growth of faujasitic membranes on polyethersulfone support was investigated. The membrane growth occurred in a novel zeolite reactor, where the extent of supersaturation of the synthesis gel 8.5 Na 2 O: 1 Al 2 O 3 : 10.9 SiO 2 : 487H 2 O was controlled by removal of water from the reaction system. The gel remaining after removal of half the water from the reaction was isolated and used as a coating on the polymer support. Along with this reactive gel, coating of a uniform film of nanozeolite seed deposition on the porous polymer support was also investigated. Eight variations of the gel-seed combinations were examined for membrane growth. The optimal membrane synthesis condition was defined as coating of the PES support by a nanozeolite seed layer of 250–300 nm thickness, and then introduction into the reactor after water is removed, and continuing the reflux process with reintroduction of the water for another hour. Further characterization included X-ray diffraction, optical microscopy and detailed scanning electron microscopy. Leak test of a dye through the membrane and the mechanical stability of the membrane via a tape test were performed. The transport properties of these membranes for CO 2 /N 2 separation were evaluated. There were three ways the membrane samples were prepared and handled for transport measurements. Prior to transport measurements, all samples were covered with PDMS. Initial attempts placed the seeded PES support into the growth reactor. These samples all exhibited poor transport properties with CO 2 /N 2 selectivities less than 10. For the second group, the seeded PES supports were placed in a holder that ensured flatness during the zeolite growth process. There was significant improvement in the transport properties, with half of the membranes exhibiting CO 2 /N 2 selectivity greater than 20. With the third group of membranes also grown in the flat geometry, care was taken to keep them flat through all the subsequent steps including washing, drying and putting on the PDMS layer. Transport properties improved further. The twelve membranes in this group exhibited CO 2 /N 2 separation factor in the range of 16–110 with CO 2 permeance in the range of 180–2000 GPU (1 GPU = 3.3 × 10 −10 mol/m 2 ·Pa).

Thin film nanocomposite (TFN) membranes incorporated with NaY zeolite nanoparticles were prepared via interfacial polymerization (IP) of trimesoyl chloride and m-phenylenediamine on nanoporous polysulfone supports. The isolated zeolite-filled polyamide layer was observed by transmission electron microscopy, and the nanoparticles dispersed in the dense nodular polyamide on the polysulfone side. The effects of IP reaction time and zeolite loading on membrane separation performance were investigated. The results showed that a longer IP reaction time was necessary to form a denser zeolite–polyamide layer for higher salt rejection, and the optimum zeolite loading was determined to be 0.15 wt%. Under the optimum conditions, the water flux increased from 0.95 to 1.78 m3/m2/day (23.3 to 43.7 gal/ft2/day (gfd)) with the incorporation of the zeolite nanoparticles, while providing a high salt rejection of 98.8% (2000 ppm NaCl solution, 225 psi (1.55 MPa), 25 °C). The TFN membranes were then post-treated with aqueous solutions containing glycerol, camphorsulfonic acid-triethylamine salt, and sodium lauryl sulfate to further improve the water flux. By optimizing the post-treatment solution composition, an improved brackish water desalination performance was achieved with 2.06 m3/m2/day (50.6 gfd) water flux, which was more than double compared to that of the TFC membrane without the zeolite nanoparticles, along with 98.4% salt rejection.

Amine-containing CO 2 facilitated transport membranes have great potential to be applied for hydrogen purification from synthesis gas. In some applications, the humidity of the retentate stream is required as well as the purity of hydrogen. The membranes are highly hydrophilic, and they exhibit not only high CO 2 permeance but also high water vapor permeance. In this work, the transport of water vapor and CO 2 through the membranes composed of an amine-containing selective layer and a microporous polysulfone substrate was investigated. From the experiments conducted, water vapor permeance appeared to be independent of the selective layer thickness, indicating that the substrate is the controlling factor of the mass transfer resistance to water vapor transport. Moreover, water vapor permeance appeared to reduce linearly with increasing the number of the substrate layers. But, CO 2 permeance and CO 2 /H 2 selectivity did not change significantly as the number of the substrate layers increased. These results indicated that the CO 2 separation performance is governed by the selective layer as expected. In addition, the membranes synthesized from Lupamin ® containing 34% polyvinylamine and 66% salt (sodium formate) demonstrated better CO 2 separation performance than those from pure polyvinylamine, presumably due to better water retention capability of the salt than polyvinylamine.

Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications.

Novel thin-film-composite reverse osmosis membranes were synthesized successfully for seawater desalination by incorporating the hydrophilic additive, o-aminobenzoic acid–triethylamine (o-ABA–TEA) salt, into the aqueous m-phenylenediamine (MPD) solution to react with trimesoyl chloride (TMC) in the organic solution during the interfacial polymerization on a nanoporous polysulfone support. The membrane synthesis conditions, including o-ABA–TEA salt concentration, isopropanol (IPA) concentration, additional amine drying time, and hydrocarbon removal time, were optimized by characterizing membrane performances using synthetic 3.28 wt% NaCl solution under seawater desalination conditions at 800 psi (5.52 MPa) and 25 °C. The synthesized membranes showed a very high flux of 1.81 m3/m2/day (44.4 gallons/ft2/day (gfd)) and a salt rejection of 99.41%. The improvement of membrane hydrophilicity was confirmed by comparing the contact angles of the membranes synthesized with and without the hydrophilic additive. The high-flux membrane was further tested using seawater from Port Hueneme, CA and exhibited a very good and stable desalination performance for 30 days. The fouling-resistant properties of the membranes synthesized with and without the hydrophilic additive were evaluated by using sodium alginate, a common contaminant derived from seaweed, as the model foulant. The membrane synthesized with hydrophilic additive showed significantly smaller water flux decline. The surface morphologies of the membranes were analyzed using atomic force microscopy (AFM). The results showed a smoother membrane surface for the membrane incorporated with the hydrophilic additive.

Water-gas-shift (WGS) membrane reactor is a promising approach to purify hydrogen produced by hydrocarbon or biomass reforming to fuel cell grade (