CO2 Permeability Research Articles

Naphthalene Tetrazole-Based Nickel Metal-Organic Framework as a Filler of Polycarbonate Membranes to Improve CO2 and H2 Separation.

A tetrazole-naphthalene linker was used to prepare a nickel MOF (metal-organic framework) (NiNDTz) with interesting properties: a specific surface area SBET of 320 m2g-1 (SLangmuir 436 m2g-1), high thermal stability (Tdonset = 300 °C), and CO2 uptake of 1.85 mmolg-1, attributed to the tetrazole groups to be used as fillers in gas separation membranes. The role of these groups was crucial in the mechanical properties of mixed membranes prepared using polycarbonate as a polymer matrix, providing a very homogeneous filler distribution and also in the gas separation properties since a simultaneous increase in permeability and selectivity was achieved, especially in the hybrid membrane containing 20% filler (PC@NiNDTz-20%). This membrane exhibited an excellent balance between permeability (P) and selectivity (α) with an increase in the permeability of CO2 and H2, 177 and 185%, respectively, and improvements in the selectivity of these gases against greenhouse gases such as methane and ethylene (between 15 and 28% improvement). These results make this membrane competitive to deal with separations in which these gases are involved, and are of special interest for the H2/CH4 separation since it clearly improves the performance of pure PC and no better PC-based membranes have been reported in the literature for this separation.

Rigid-flexible coupled organosilica membranes toward high-efficiency molecules separation

Membrane-based technology has garnered significant interest in the separation and purification of molecules due to its inherent advantages, such as high efficiency, low energy consumption, and ease of operation. In this study, rigid-flexible coupled organosilica membranes were fabricated through co-polymerization using 1,2-bis(triethoxysilyl)acetylene (BTESA) containing rigid acetylene bridges and 1,2-bis(triethoxysilyl)propane (BTESP) containing flexible propane bridges. The incorporation of flexible propane bridges into BTESA networks allowed for precise adjustment of the network structures, resulting in composite BTESA-P membranes with improved molecular sieving properties. BTESA-P membrane demonstrated significant promise for applications in both CO2 capture and pervaporation (PV) dehydration due to its high potential. BTESA-P30 membrane, fabricated using the rigid-flexible coupled strategy, demonstrated a CO2 permeance of 3807 GPU and a CO2/N2 selectivity of approximately 40. These results surpassed those of numerous previously reported membranes, indicating significant potential for CO2 capture applications. BTESA-P30 membrane exhibited significant competitiveness in the decarbonization process of natural gas. More significantly, analogous occurrences are evident in gas permeation and PV separation process, where the permeation mechanism of gas and PV separation is primarily governed by molecular sieving. The utilization of diverse organosilica precursors in the rigid-flexible coupled strategy proposed in this study offers increased potential for membrane structure design and energy-efficient separation of molecules.

Process Operability Analysis of Membrane-Based Direct Air Capture for Low-Purity CO2 Production.

Addressing climate change constitutes one of the major scientific challenges of this century, and it is widely acknowledged that anthropogenic CO2 emissions largely contribute to this issue. To achieve the "net-zero" target and keep the rise in global average temperature below 1.5 °C, negative emission technologies must be developed and deployed at a large scale. This study investigates the feasibility of using membranes as direct air capture (DAC) technology to extract CO2 from atmospheric air to produce low-purity CO2. In this work, a two-stage hollow fiber membrane module process is designed and modeled using the AVEVA Process Simulation platform to produce a low-purity (≈5%) CO2 permeate stream. Such low-purity CO2 streams could have several possible applications such as algae growth, catalytic oxidation, and enhanced oil recovery. An operability analysis is performed by mapping a feasible range of input parameters, which include membrane surface area and membrane performance metrics, to an output set, which consists of CO2 purity, recovery, and net energy consumption. The base case for this simulation study is generated considering a facilitated transport membrane with high CO2/N2 separation performance (CO2 permeance = 2100 GPU and CO2/N2 selectivity = 1100), when tested under DAC conditions. With a constant membrane area, both membranes' intrinsic performances are found to have a considerable impact on the purity, recovery, and energy consumption. The area of the first module plays a dominant role in determining the recovery, purity, and energy demands, and in fact, increasing the area of the second membrane has a negative impact on the overall energy consumption, without improving the overall purities. The CO2 capture capacity of DAC units is important for implementation and scale-up. In this context, the performed analysis showed that the m-DAC process could be appropriate as a small-capacity system (0.1-1 Mt/year of air), with reasonable recoveries and overall purity. Finally, a preliminary CO2 emissions analysis is carried out for the membrane-based DAC process, which leads to the conclusion that the overall energy grid must be powered by renewable sources for the technology to qualify within the negative emissions category.

Graphene Oxide/Melamine/Ionic liquid membranes for selective CO2 separation

Highly permeable and selective membranes with long-term stability are needed to reduce operating and capital costs of industrial gas-separation units. In this study, we fabricate new membranes made of melamine (M)- and imidazolium-based ionic liquid (IL)-modified graphene oxide (GO) deposited on a porous support and buried with a polydimethylsiloxane (PDMS) layer. The CO2/N2 and CO2/CH4 ideal selectivities of the composite membranes are respectively 65 % and 70 % higher than those of the membranes containing only the IL. This significant improvement in ideal selectivity is attributed to synergic effects of nanochannels created by GO, fixed facilitated transport provided by the IL and numerous amine groups in the melamine structure, and the increased polarity of the membrane caused by the presence of the IL. The composite membrane has a pure CO2 permeance of 47 GPU with a high CO2/N2 ideal selectivity of 109 and a satisfactory CO2/CH4 ideal selectivity of 39. The composite membrane maintains stable performance over a 60-hour operation, highlighting its long-term reliability. The outstanding performance, coupled with the ease of fabrication, underscores the potential of these composite membranes for practical and efficient CO2 removal from both natural and flue gas streams in real-world applications.

Modeling analysis of water-gas-shift reaction on catalyst-packed ceramic-carbonate dual-phase membrane reactor for hydrogen production

Water-gas shift (WGS) reaction for hydrogen production and CO2 removal/capture in a catalyst-packed CO2-permselective membrane reactor is studied experimentally and simulated with a computational model. The reactor utilizes a tubular dense ceramic-carbonate dual-phase membrane with a commercial high-temperature WGS catalyst. Equations governing CO2 permeation through the membrane and WGS reaction kinetics on the catalyst were obtained through independent CO2 permeation experiments and a fixed-bed reaction kinetic study. The simulation results using the validated model are presented to examine the effects of feed gas composition, steam/CO ratio, gas hourly space velocity, temperature, reactor pressure, sweep to feed molar flow rate ratio, and the membrane area to catalyst volume ratio on the performance of the membrane reactor for WGS with CO2 removal. Under optimized conditions, the catalyst-packed membrane reactor for WGS demonstrates significantly enhanced CO conversion and product H2 purity by effectively removing/capturing CO2 from the WGS reaction side.

Effect of moisture content on properties, microstructure and carbon sequestration of CO2-cured cement mortar mixed with chelator

Chelator has the effect of improving the mineralization curing degree of cement-based materials. However, the moisture content in the pores of concrete will affect the permeability and dissolution of CO2 as well as the complexation and migration of Ca2+ by chelator, thus influencing the performance of CO2-cured concrete containing chelator. To obtain optimal moisture content for CO2-cured cement mortar mixed with chelator (CMC), the effects of the residual water cement ratio (RW) on the properties, microstructure, and carbon sequestration of CO2-cured CMC was investigated in this paper. The findings showed that the reduction of RW was beneficial for improving the mechanical properties and impermeability of mineralization curing CMC, but excessive reduction of RW weakened the action effect of chelator on accelerating the development of compressive strength. The optimal RW for mineralization curing ordinary cement mortar was 0.15 to achieve the fastest development of its mechanical properties, while the optimal RW for CMC was 0.2. It was also found that chelator was beneficial for shortening the curing period of CO2-cured mortar by more than half. Chelator significantly improved the aperture structure of CO2-cured mortar with a RW of 0.2 and promoted the transformation of larger to smaller pores through increasing the porosity of pore size between 0.01 and 0.02 μm by 7.1% and decreasing the portion of pores above 1 μm in the mortar by 24.2% after mineralization curing for 48 h. The reduction of RW was conducive to the permeation and diffusion of CO2, significantly enhancing the capacity of carbon sequestration of CMC. The RW was decreased from 0.5 to 0.2, and the carbon sequestration rate of CMC was increased by 551.6% after 48 h of mineralization curing. Meanwhile, compared to CO2-cured ordinary cement mortar, the carbon sequestration rate of CMC could be increased by 9.7% and 12.1% after 4 h and 48 h of curing, respectively.

Synergistic improvement in gas separation performance of MMMs by porogenic action and strong molecular forces of ZIF-93

In the present study, ZIF-93 metal–organic frameworks were prepared. N2 adsorption tests revealed that the particle size, specific surface area, and pore size of ZIF-93 were 30 nm–45 nm, 869.40 m2/g, and 0.36 nm, respectively. Pebax-based mixed matrix membranes (MMMs) were prepared using ZIF-93 as the filler. The pore diameters of ZIF-93 lied between the kinetic diameters of CO2 and N2; thus, its pore structure provided a fast transfer channel for CO2 and increased the permeability of the membrane. Further, X-ray diffraction showed that the membrane became denser upon introducing ZIF-93 because of the formation of a bridging structure between the Pebax molecular chains and ZIF-93. A denser stacking by moving the Pebax molecular chains closer to each other effectively bettered the CO2 selectivity of the mixed matrix membrane. The test results showed that when the ZIF-93 loading was 10 wt%, the CO2 permeability was 84.85 barrer and the CO2/N2 selectivity was 65.76 at 0.4 MPa, which are 51.57 % and 65.50 % higher than those of the pure Pebax membrane, respectively. When the feed pressure was increased to 0.8 MPa, the CO2 permeability was 94.5 barrer and the CO2/N2 selectivity is 87.5, which are 51.57 % and 65.50 % higher compared with those of the pure Pebax membrane, in order. The membrane performance significantly exceeded that of the 2008 Robeson curve.

Effect of process conditions on CO2 permeance and selectivity of polyvinyl alcohol/sodium polyacrylate membrane

ABSTRACT In this study, polymer membrane for CO2 separation was produced by blending polyvinyl alcohol and sodium polyacrylate. Tests were conducted on the produced membranes to evaluate their CO2 and He separation performance under various conditions. The optimal amount of cesium carbonate to be added to the prepared membrane in terms of separation performance was determined. It was found that the highest performance was obtained at 85°C. Effects of other process conditions such as total pressure, CO2 partial pressure, and humidity on membrane performance were also investigated. In particular, CO2 permeance of around 3.0E–10 (m3(STP)/m2 s Pa)) and selectivity of nearly 500 were observed for the separation of CO2 and helium at the CO2 partial pressure of Ptotal of 0.1 MPa. Through the above examinations, the present study was not only produced a high-performance separation membrane, but also found test conditions under which this membrane exhibited higher separation performance.

Nanocomposite membranes comprising covalent organic framework and polymer of intrinsic microporosity for efficient CO2 separation

The fabrication of new mixed-matrix membranes (MMMs) with superior gas permeability and selectivity are highly sought for industrial development of membrane separation technology for CO2 capture. This study reports improvement in CO2 permeability and selectivity by employing porous covalent organic framework (COF-TpPa-1). Herein, we report a novel PIM-1 doped with COF-TpPa-1 in various concentrations ranging from 0 to 10 wt% to prepare COF-TpPa-1/PIM-1 MMMs. Good compatibility between COF-TpPa-1 particles and PIM-1 matrix rendered an ideal interfacial morphology. The MMMs composed of 7 wt% COF-TpPa-1 exhibit a CO2 permeability of 6336 Barrer with an enhancement of 104 % compared to pristine sample and CO2/N2 ideal selectivity 20.1 among five tested compositions. The CO2 permeability of COF-TpPa-1 7 wt% doped membrane was 88 % more than pristine PIM-1 after 30 days aging, while CO2/N2 selectivity was well maintained, coupled with excellent anti-plasticization and mixed-gas separation properties. The overall gas separation performance of MMMs exceeds the Robeson Upper bound (2008) for CO2/N2 and O2/N2. The measured experimental permeability exhibited excellent agreement with the Singh thermal conductivity model at low loading (<5 wt%). This work provides a potential approach to fabricate PIM-1-based high performance MMMs with COF fillers for efficient CO2 separation.

CO2/CH4 Separation in Amino Acid Ionic Liquids, Polymerized Ionic Liquids, and Mixed Matrix Membranes.

The ability to efficiently separate CO2 from other light gases using membrane technology has received a great deal of attention due to its importance in applications such as improving the efficiency of natural gas and reducing greenhouse gas emissions. A wide range of materials has been employed for the fabrication of membranes. This paper highlights the work carried out to develop novel advanced membranes with improved separation performance. We integrated a polymerizable and amino acid ionic liquid (AAIL) with zeolite to fabricate mixed matrix membranes (MMMs). The MMMs were prepared with (vinylbenzyl)trimethylammonium chloride [VBTMA][Cl] and (vinylbenzyl)trimethylammonium glycine [VBTMA][Gly] as the polymeric support with 5 wt% zeolite particles, and varying concentrations of 1-butyl-3-methylimidazolium glycine, [BMIM][Gly] (5-20 wt%) blended together. The membranes were fabricated through photopolymerization. The extent of polymerization was confirmed using FTIR. FESEM confirmed the membranes formed are dense in structure. The thermal properties of the membranes were measured using TGA and DSC. CO2 and CH4 permeation was studied at room temperature and with a feed side pressure of 2 bar. [VBTMA][Gly]-based membranes recorded higher CO2 permeability and CO2/CH4 selectivity compared to [VBTMA][Cl]-based membranes due to the facilitated transport of CO2. The best performing membrane Gly-Gly-20 recorded permeance of 4.17 GPU and ideal selectivity of 5.49.

Orientation of two-dimensional materials mf-BN in Pebax mixed matrix membranes by magnetic fields for enhancing CO2/N2 separation performance

Two-dimensional materials possess a high aspect ratio and excellent spatial utilization, making them potential filler for the fabrication of mixed matrix membranes (MMMs). However, the disordered arrangement of two-dimensional materials can negatively impact membrane performance. In this study, hexagonal boron nitride (h-BN) two-dimensional material loaded with polyethyleneimine (PEI) and magnetic material Fe3O4 was prepared. The filler (mf-BN) was incorporated into Pebax-1657, and the orientation of mf-BN in the MMM was controlled using a magnetic field. Horizontally and vertically oriented mf-BN/Pebax MMMs were successfully prepared and subjected to gas separation tests. The results demonstrate that oriented MMMs exhibit superior performance compared to non-oriented ones. When the mf-BN loading is 20 wt%, the CO2/N2 selectivity for horizontally and vertically oriented MMMs respectively reaches 83.9 and 76.8. The CO2 permeability increases to 114.7 and 139.8 Barrer, respectively. The magnetic field orientation of filler presents a promising approach for further enhancing the performance of MMMs.

Co-fa nanoplates incorporated 6FDA-DAM mixed-matrix membranes for enhanced CO2/CH4 separation

Plate-like or sheet-like porous materials with nanometer thickness have been considered as the preferred fillers to improve mixed-matrix membranes (MMMs)-based separation. Herein, hexagonal Co-fa (HG-Co-fa) nanoplates were simply synthesized without the addition of any modifier and used as fillers to construct 6FDA-DAM-based MMMs for efficient CO2/CH4 separation. HG-Co-fa nanoplates exhibit high dispersion and interface compatibility in 6FDA-DAM matrix. The results demonstrated that the CO2/CH4 separation performance of 6FDA-DAM was obviously improved after the incorporation of HG-Co-fa nanoplates. The resultant MMMs with nanoplate loading of 10 wt% showed CO2/CH4 selectivity of 27 and CO2 permeability of 1419 Barrer at 25 ℃ and 0.2 MPa, surpassing 2008 Robeson upper bound. Meanwhile, the high lattice integrity and structural stability of HG-Co-fa nanoplates contribute to the excellent thermal and mechanical stability of MMMs, contributing to their anti-plasticization property up to 14 bar and long-term stability up to 240 h, indicating their potential for natural gas separation.

Fine-tuning zeolite pore structures with carbon coating for enhanced gas separation in polyimide-based mixed matrix membrane

Impregnated zeolite-carbon (IZC), also known as pore-modified zeolite, was used as a potential filler in a P84 co-polyimide-based hollow fiber mixed matrix membrane (HF MMM) to enhance gas separation. The presence of carbon structure on the zeolite framework pore was to avoid the trapped moisture that could lead to permeability reduction. This work seeks to investigate the impact of IZC addition (0.5, 1.0, and 1.5 wt%) to the P84 membrane and examine its permeability and separation performance. Adding IZC filler to the P84 membrane generates the enhancement of gas selectivity and permeability. The optimal enhancement was observed at 1 wt% of IZC loading, in which selectivity of CO2/CH4, CO2/N2, O2/N2, H2/N2, and H2/CH4 was enhanced by 50.506, 51.042, 5.693, 16.712, and 16.338%, respectively. On the other hand, H2, CO2, and O2 permeability at the loading were improved from 11.182 to 26.761, from 4.683 to 14.501, and from 1.637 to 3.546 Barrer, respectively. The improvement of gas selectivity was contributed by the presence of carbon in the zeolite framework, providing a molecular sieving effect while tuning carbon properties with pore regularity by templating in the zeolite framework enhances the gas permeability.

CO2-Philic Nanocomposite Polymer Matrix Incorporated with MXene Nanosheets for Ultraefficient CO2 Capture.

The incorporation of two-dimensional (2D) functional nanosheets in polymeric membranes is a promising material strategy to overcome their inherent performance trade-off behavior. Herein, we report a novel nanocomposite membrane design by incorporating MXene, a 2D sheet-like nanoarchitecture known for its advantageous lamellar morphology and surface functionalities, into a cross-linked polyether block amide (Pebax)/poly(ethylene glycol) methyl ether acrylate (PEGMEA) blend matrix, which delivered exceptional CO2/N2 and CO2/H2 separation performances that are critical to industrial CO2 capture applications. The finely dispersed Ti3C2Tx nanosheets in the blend polymer matrix led to an expansion of the free volume within the resultant mixed matrix membrane (MMM), giving rise to a substantially enhanced CO2 permeability of up to 1264.6 barrer, which is 102% higher than that of the pristine polymer. Moreover, these MXene-incorporated MMMs exhibited preferential sorption for CO2 over light gases, which contributed to an exceptional CO2/N2 and CO2/H2 selectivity (64.3 and 19.2, respectively) even at a small loading of only 1 wt %, allowing the overall performance to not only surpass the latest upper bounds but also exceed many previously reported high-performance nanosheet-based nanocomposite membranes. Long-term performance tests have also demonstrated the good stability of these membranes. This composite membrane design strategy reveals the remarkable potential of combining a blend copolymer matrix with ultrathin MXene nanosheets to achieve superior gas separation performance for environmentally important gas separations.

Mixed matrix membranes (MMMs) with amine-functionalized ZIF-L for enhanced CO2 separation performance

Amine-functionalized Metal-Organic Frameworks (MOFs) stand out as highly promising materials in membrane separation technology. Nevertheless, the incorporation of amine-functionalized additives may lead to uncontrollable alterations in MOF morphology. Two intact blade-like MOFs (PEI (Polyethylenimine)-ZIF-L and PAMAM (Polyamidoamine)-ZIF-L) were successfully synthesized by controlling the conditions and then introduced into Pebax 2533 to fabricate Mixed Matrix Membranes (MMMs). Hydrogen bonding and other interactions with Pebax can be formed by PEI-ZIF-L and PAMAM-ZIF-L to enhance interfacial compatibility. Simultaneously, a reversible reaction with CO2 molecules can be undergone by the amine groups, resulting in facilitated transport in MMMs. The CO2 separation performance of the MMMs is enhanced by this process, with the facilitation being more pronounced under humid conditions. Under humid conditions, the CO2 permeabilities of Pebax-PEI-ZIF-L (2 wt%) and Pebax-PAMAM-ZIF-L (2 wt%) MMMs were 639.4 Barrer and 702.7 Barrer, respectively, while the CO2/N2 selectivities were 26.68 and 24.35, respectively. Both permeability and selectivity exhibited a significant increase of 200% and 130%, respectively, compared to pure Pebax. Furthermore, the MMMs demonstrated excellent long-term stability during 72 h of continuous operation in a humid environment, showcasing significant potential for industrial applications, particularly in humid flue gas carbon capture.

High gas permeance in CO2-selective thin film composite membranes from bis(phenyl)fluorene-containing blends with PIM-1

A novel approach to improve the initial performance as well as to prevent physical aging of superglassy high free volume polymer PIM-1 is reported. Bis(phenyl)fluorene-based polymer of intrinsic microporosity (Cardo-PIM-1) was used at different loadings in PIM-1 to fabricate thin film composite (TFC) membranes and freestanding membranes. The gas performances of both TFCs and thick freestanding membranes exhibited similar trends; higher CO2 permeance and higher CO2/CH4 selectivity at relatively low loadings (≤5 wt %). TFCs containing 5 wt % Cardo-PIM-1 achieved a CO2 permeance of (12600 ± 866 GPU), which corresponds to about a threefold increase as compared to the pristine TFC-PIM-1 membranes (2850 ± 254 GPU) and higher CO2/CH4 selectivity (14.6 ± 1.3) as compared to pure PIM-1 (10 ± 3). With regards to physical aging, PIM-1 TFC membranes experienced a 96 % reduction in CO2 permeance after 1 year. However, for the TFCs containing 5 wt % cardo the reduction was considerably lower (59%) and all took place at an initial stage of up to 37 days, remaining at a good and stable CO2 permeance of c.a. 5000 GPU for the remaining testing period of up to one year.

SSZ-13 membranes on novel silica carbide monoliths for efficient CO2 separation

The usage of normal alumina supports brings the uncertain and undesirable aluminum transformation to the high-silica zeolite membranes to reduce Si/Al ratio in framework. In this current study, a novel aluminum-free silica carbide (SiC) monolithic support is used for the synthesis of SSZ-13 membranes with enhanced Si/Al ratio for the first time. Moreover, this high-porosity and monolithic SiC support enables membrane to increase gas permeance and surface-to-volume ratio. High-quality SSZ-13 membranes were prepared after rational modification of synthesis parameters such as synthesis temperature and time and support material. The effects of test temperature, pressure drop, feed flow rate and humidity on separation performance of the monolithic membranes were studied. The formation mechanism of SSZ-13 membrane was also investigated. The Si/Al ratio and CO2 permeance of SSZ-13 membranes on SiC monolith were 100% and 60% higher than that of membrane on alumina monolith, respectively. This monolithic membrane had comparable separation performance but about 2.3 times higher surface-to-volume ratios to the reported tubular zeolite membranes. This solution could be suitable to prepare other high-silica and all-silica zeolite membranes.

Significantly enhanced gas separation properties of membranes by debromination and thermal rearrangement simultaneously

One important challenge in advanced gas separation membranes is breaking the trade-off effect between gas permeability and selectivity. Here, we developed a method by combining the debromination and thermal rearrangement (TR) techniques together to significantly enhance the gas separation properties of the resulting membrane for the first time. First, we designed a co-polyimide (DBOH) containing both hydroxyl and bromine (50/50) groups in the ortho position of the imide group. After thermal treatment at 450 °C, the TR and debromination happened simultaneously as proved by TG-MS, FT-IR and XPS results, the resulting DBPO showed a larger d-spacing (7.03–9.71 Å), a 18-fold enhanced BET surface area, and 2-fold improved in ultra-microporosity (<7 Å) than its DBOH precursor. Hence, DBPO demonstrated not only an over 100 times improved CO2 permeability (7933 vs 76 Barrer) but also keep a high CO2/CH4 selectivity of 31, and the overall performance surpassed the latest 2019 trade-off curve. Besides, wonderful anti-plasticization and mixed-gas separation properties were also observed for DBPO, which showed a CO2 permeability of 3324 Barrer and CO2/CH4 selectivity of 14.7 even under the upstream CO2/CH4 mixed-gas pressure of 435 psi (1 psi = 6894.8 Pa), outperforming the latest 2018 CO2/CH4 mixed-gas upper limit. It showed 100 times improved CO2 permeability while maintain selectivity of DBPO is attributed to the significantly enhanced ultra-microporosity that increases the diffusion and solubility coefficient, whereas maintain their diffusion and solubility selectivity. Conclusively, the debromination coupled with TR provides a novel direction for designing advanced TR membranes.

Molecular dynamics simulation of CO2 permeation and separation in Zr-MOF membranes

Global warming due to greenhouse gas emissions has continuously threatened the climate and environment. Zirconium-based metal-organic frameworks (Zr-MOFs) with Zr6 inner cores represent a subfamily of nanoporous materials with good physicochemical stabilities, showing significant prospects for practical applications in gas separation. A molecular simulation study is reported here to investigate the membrane separation of CO2/N2 and CO2/CH4 mixtures in five Zr-MOFs (Zr-fum, UiO-66, DUT-52, Zr-cca, UiO-67) with similar ligand in their structures and different pore-limiting diameter (PLD) ranging from 0.36 nm to 0.59 nm. The gas permeation and separation performance are evaluated with the concentration gradient-driven molecular dynamics (CGD-MD) method. The results show that the separation of both gas mixtures is dominated by the preferential sorption of CO2 over N2 and CH4, respectively. Meanwhile, the PLD of MOFs is also a significant factor governing permeation. MOFs with a larger PLD have a higher permeability and a lower selectivity for CO2/N2 and CO2/CH4 separation. Free-energy profiles were calculated to describe the insights into CO2 separation, that the larger PLD can cause a lower energy barrier when gases transport through the pore of MOFs. The results were compared with the grand canonical Monte Carlo and equilibrium molecular dynamics (GCMC + EMD) approach, a traditional method to predict gas adsorption and diffusion in MOFs. As the GCMC+EMD approach neglected the interaction between components and potential mass transfer resistance at the surface of the membranes, the results obtained from the CGD-MD method in this work are more reliable. This study provides microscopic insights into CO2 separation in Zr-MOF membranes and suggests their potential use for gas separation.

Amine‐Rich Molecular Nodule‐Assembled Membrane Having 5 Angstrom Channels for CO2/N2 Separation

AbstractPorous organic cages (POCs) with abundant porosity and interconnected cavities have garnered significant research attention as a distinct class of porous materials due to their potential applications in gas sorption and separation. However, the ordered arrangement of POCs to eliminate inter‐cage defects remains challenging in the assembly of molecular‐selective membranes, which greatly hinders the effectiveness of pore sieving. Here, amine‐rich molecular nodules (AMNs) are created by reduction of the porous organic cage CC2, in which the spatial structure incurs a vertex collapse into the interior of the original tetrahedral structure, which eliminates the large window of CC2. By an interfacial reaction with terephthaloyl chloride, the AMNs assemble into a cross‐linked topological network having angstrom‐scale channels for selective CO2/N2 separation. The AMN‐assembled membrane displays a high CO2 permeance of 752 GPU, a CO2/N2 selectivity of 67 at 1 bar, as well as high‐pressure resistance, operational stability, and scalable manufacture potential, which provides a cost‐effective and practical solution for developing membranes for capturing CO2 from industrial flue gas.