Purification of C2H4 from an C2H4/C2H6 mixture, one of the most important while challenging industrial separation processes, is mainly through energy‐intensive cryogenic distillation. Now a family of ...gallate‐based metal–organic framework (MOF) materials is presented, M‐gallate (M=Ni, Mg, Co), featuring 3D interconnected zigzag channels, the aperture sizes of which (3.47–3.69 Å) are ideally suitable for molecular sieving of ethylene (3.28×4.18×4.84 Å3) and ethane (3.81×4.08×4.82 Å3) through molecular cross‐section size differentiation. Co‐gallate shows an unprecedented IAST selectivity of 52 for C2H4 over C2H6 with a C2H4 uptake of 3.37 mmol g−1 at 298 K and 1 bar, outperforming the state‐of‐the‐art MOF material NOTT‐300. Direct breakthrough experiments with equimolar C2H4/C2H6 mixtures confirmed that M‐gallate is highly selective for ethylene. The adsorption structure and mechanism of ethylene in the M‐gallate was further studied through neutron diffraction experiments.
Purification of C2H4 from an C2H4/C2H6 mixture using a family of gallate‐based metal–organic framework (MOF) materials is presented. M‐gallate (M=Ni, Mg, Co), features 3D interconnected zigzag channels, the aperture sizes of which are ideal for molecular sieving of ethylene and ethane through molecular cross‐section size differentiation.
Covalent organic frameworks (COFs) are a promising class of porous crystalline materials made up of covalently connected and periodically protracted network topologies through organic linkers. The ...tailorability of organic linker and intrinsic structures endow COFs with a tunable porosity and structure, low density, facilely‐tailored functionality, and large surface area, attracting increasing amount of interests in variety of research areas of membrane separations. COF‐based membranes have spawned a slew of new research projects, ranging from fabrication methodologies to separation applications. Herein, we tried to emphasis the major developments in the synthetic approaches of COFs based membranes for a variety of separation applications such as, separation of gaseous mixtures, water treatment as well as separation of isomeric and chiral organic compounds. The proposed methods for fabricating COF‐based continuous membranes and columns for real world applications are also thoroughly explored. Finally, a viewpoint on the future directions and remaining challenges for COF research in the area of separation is provided.
Covalent Organic Frameworks are an emerging class of porous crystalline materials, having large surface area, high porosity, low density and systematically ordered pore structures. Furthermore, the facile functionalization of COFs makes them suitable candidates for a variety of membrane science based separation applications.
Two‐dimensional covalent organic frameworks (2D COFs) are considered as potential candidates for gas separation membranes, benefiting from permanent porosity, light‐weight skeletons, excellent ...stability and facilely‐tailored functionalities. However, their pore sizes are generally larger than the kinetic diameters of common gas molecules. One great challenge is the fabrication of single‐phase COF membranes to realize precise gas separations. Herein, three kinds of high‐quality β‐ketoenamine‐type COF nanosheets with different pore sizes were developed and aggregated to ultrathin nanosheet membranes with distinctive staggered stacking patterns. The narrowed pore sizes derived from the micro‐structures and selective adsorption capacities synergistically endowed the COF membranes with intriguing CO2‐philic separation performances, among which TpPa‐2 with medium pore size exhibited an optimal CO2/H2 separation factor of 22 and a CO2 permeance of 328 gas permeation units at 298 K. This membrane performance reached the target with commercial feasibility for syngas separations.
Three kinds of lamellar COFs were exfoliated into discrete nanosheets with large aspect‐ratios. The nanosheets were assembled into ultrathin two‐dimensional membranes with staggered stacking patterns, respectively. Taking advantage of narrowed pore size and CO2‐philic adsorption, these single‐phase COF nanosheet membranes were characterized by superior CO2/H2 separation performances.
Ultrafast molecular separation (UMS) membranes are highly selective towards active organic molecules such as antibiotics, amino acids and proteins that are 0.5-5 nm wide while lacking a phase ...transition and requiring a low energy input to achieve high speed separation. These advantages are the keys for deploying UMS membranes in a plethora of industries, including petrochemical, food, pharmaceutical, and water treatment industries, especially for dilute system separations. Most recently, advanced nanotechnology and cutting-edge nanomaterials have been combined with membrane separation technologies to generate tremendous potential for accelerating the development of UMS membranes. It is therefore critical to update the broader scientific community on the important advances in this exciting, interdisciplinary field. This review emphasizes the unique separation capabilities of UMS membranes, theories underpinning UMS membranes, traditional polymeric materials and nanomaterials emerging on the horizon for advanced UMS membrane fabrication and technical applications to address the existing knowledge gap. This work includes detailed discussions regarding existing challenges, as well as perspectives on this promising field.
The high fractional free volume (FFV) endowed polymers of intrinsic microporosity (PIMs) with high gas permeability but low selectivity. Herein, an intermediate temperature range was deliberately ...utilized to tune PIM‐1 membrane microstructure in nitrogen atmosphere to enhance gas separation performance. During intermediate thermal manipulation, the synergistic effects of thermal‐induced cross‐linking and decomposition on PIM‐1 membranes have optimized the micropores for significantly increasing membrane molecular‐sieving ability with the boosted selectivity of 350 (H2/N2), 1,472 (H2/CH4), 3,774 (H2/C3H8), and 197 (CO2/CH4) respectively, with the H2 permeability of 234 Barrer, correspondingly, surpassing the “Robeson's Upper Bound”. The facile strategy simultaneously utilizing the thermal‐induced cross‐linking and decomposition, might provide a new platform to develop the high‐performance membranes for highly‐efficient hydrogen purification and CO2 separations.
In recent years, viscoelastic particle manipulation within microfluidic systems has received much attention due to the ease with which micron-sized objects may be maneuvered and isolated on the basis ...of size. While several factors, including both fluid and particle properties, regulate the precise locations and trajectories of micron-sized species flowing along a microchannel, the role of channel cross-section shape is critical, since it directly influences the fluid velocity profile and thus the direction and magnitude of hydrodynamic forces. It is therefore surprising that this parameter has not been comprehensively investigated for cell-based separations, especially since most viscoelastic microfluidic systems are only able to efficiently sperate cells over limited size ranges. To address this shortcoming, we present a viscoelastic microfluidic system integrating a triangular cross-section microchannel, for efficient and tunable size-based separations of micron-sized species. We find that particle focusing patterns can be controlled by simple variation of volumetric flow rates, which allows for the efficient separation of particles and cells of variable size. To showcase the efficacy of the approach, we present a size-based separation of various blood components, including white blood cells, platelets, and rare cells. By quantifying the number of particles collected at the outlets, we achieve recovery efficiencies of over 98%.
•Viscoelastic particle manipulation is used to separate micron-sized particles.•A triangular cross-section microfluidic channel design is used for particle separation.•Passive separation of different blood components at low blood dilutions.•Size-selective separation of blood components via tunable viscoelastic focusing.
CHA zeolite (chabazite) crystals and membranes were prepared from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect ...of cesium and fluoride salts on the crystallization of chabazite crystals and membranes were investigated. Highly crystalline chabazite and uniform chabazite membranes were only obtained from the gel containing the cesium and fluoride salts. Single CO2, N2 and CH4 permeances and mixed gas separations in CO2/N2 and CO2/CH4 binary mixtures through chabazite membranes were measured. Temperature and pressure affected the permeances and separation selectivities in two mixtures. The best membrane showed CO2/N2 and CO2/CH4 separation selectivities as high as 16 and 46 together with CO2 permeances of ~ 1.0 × 10-7 mol/(m2 s Pa) at a high temperature of 473 K in equimolar dry CO2/N2 and CO2/CH4 binary mixtures, respectively. The CO2/N2 and CO2/CH4 selectivities lost only 11% and 15%, and CO2 permeances lost only 18% and 20% in equimolar wet CO2/N2 and CO2/CH4 mixtures (8% in mole of water vapor) at 473 K compared to these values in dry mixtures, respectively. The OSDA-free chabazite membranes were hydrothermally stable in the presence of vapor water for 4 d at 378 K.
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•Tubular CHA zeolite (chabazite) membranes were prepared from the OSDA-free gel.•The Cs and F ions played important roles on chabazite crystal and membrane growth.•OSDA-free chabazite membranes had highly CO2-selective in CO2/CH4 and CO2/N2 mixtures.•This membrane showed good stabilities in long-term operations and under humid conditions.
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•Improved SSZ-13 membrane was prepared using asymmetric support.•Separations in CO2/CH4 and N2/CH4 mixtures were studied.•The effect of water vapor was investigated.•Single gas ...permeances were modeled.
High-quality SSZ-13 membranes were synthesized on 200 nm asymmetric α-alumina supports via a single hydrothermal secondary growth. Single CO2, N2 and CH4 permeances and mixed gas separations in CO2/CH4 and N2/CH4 binary mixtures through SSZ-13 membranes were measured. Synthesis conditions such as membrane substrate, gel composition and membrane calcination were modified. The best SSZ-13 membrane displayed N2 and CO2 permeance as high as 8.9 × 10−8 mol/(m2 s Pa) and 5.6 × 10−7 mol/(m2 s Pa) and N2/CH4 and CO2/CH4 selectivities of 10 and 56.5 for equimolar N2/CH4 and CO2/CH4 gas mixtures at 298 K and 0.2 MPa feed pressure, respectively. Nitrogen permeance of current SSZ-13 membrane in the mixture was 3.7 times higher than that of our previous SSZ-13 membrane. The membrane synthesis was reproducible. Temperature and pressure dependences of separation performance in the two binary mixtures were also discussed. Single CO2, N2 and CH4 permeances dependent of pressure were predicted by the Maxwell–Stefan diffusion model and the predicted values were fitted well with the measured ones. The stability of SSZ-13 membrane in the wet mixture was investigated. The current SSZ-13 membrane has excellent potentials for CO2 and N2 removals from natural gas.
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