Separation Of Gas Mixtures Research Articles

Anisotropic porosity and interface synergy enhanced gas permselectivity in heterolayer metal-organic framework membrane.

The pursuit of sustainable, carbon-free separation technology hinges on the efficient separation of gas mixtures with high separation factors and flow rates, i.e. high permselectivity. However, achieving this objective is arduous due to the meticulous engineering at the angstrom scale and intricate chemical manipulation required to design the pores within membranes. To address this challenge, a proof-of-concept for an anisotropic porous membrane has been devised. Employing a meticulous step-by-step methodology, two distinct porous metal-organic frameworks (MOFs) are integrated to form a monolithic anisotropic membrane. By harnessing pore anisotropy (3.4 to 6 Å) aligned with the gas permeation direction and a unique interface characterized by cross-linked pores derived from the two distinct MOFs, this membrane transcends the performance limitations inherent in the individual MOF membranes (~45% enhanced selectivity). This approach not only sheds light on the heterolayer membrane design strategy but also elucidates the intricate CO2/N2 permselectivity relationship inherent in the interface structure.

Revving Up a Designed Copper Catecholate Porous Organic Polymer for Its Potent Ethylene Adsorption than Ethane.

The potential to produce high-purity C2H4 has made ethylene-selective adsorbents for ethane (C2H6)/ethylene (C2H4) gas mixture separation appealing as viable substitutes for traditional cryogenic distillation. In this aspect, porous organic polymers (POPs) are anticipated to become the next-generation potential adsorbent due to their easily customizable functions and functional sites suitable for gas separation. This article reports the selective C2H4 adsorption over C2H6 using microporous copper(I)-coordinated POP (Cu@Di-POP) via fine-tuning of the π complexation and pore size. The specially designed adsorbent has the ideal pore size and coordinated Cu(I) ions to form π-complexation with C2H4 molecules, which enabled it to adsorb C2H4 (at 1 bar, 24.9, 18.9, and 13.4 cm3 g-1 at 273, 298, and 323 K, respectively) while significantly reducing C2H6 adsorption (at 1 bar, 16.9, 12.7, and 8.8 cm3 g-1 at 273, 298, and 323 K, respectively). At 1 bar, Cu@Di-POP exhibited IAST selectivities of 6.09, 5.60, and 4.13 for C2H4/C2H6 at 273, 298, and 323 K, respectively, suggesting its C2H4 selective behavior, which was further confirmed from the experimental breakthrough measurement. Furthermore, the computational studies carried out with density functional theory highlighted an enhanced charge distribution leading to dπ-pπ conjugation between C2H4 π-electrons and Cu d-electrons, thereby showing a relatively higher interaction energy of -37.23 kcal/mol with C2H4 as compared to -16.06 kcal/mol with C2H6 gas molecules.

Modelling across Multiple Scales to Design Biopolymer Membranes for Sustainable Gas Separations: 2-Multiscale Approach

The majority of materials used for membrane-based separation of gas mixtures are non-renewable and non-biodegradable, and the assessment of alternative bio-based polymers requires expensive and time-consuming experimental campaigns. This effort can be reduced by adopting suitable modelling approaches. In this series of works, we propose various modelling approaches to assess the CO2/CH4 separation performance of eight different copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV) using a limited amount of experimental data for model calibration. In part 1, we adopted a fully atomistic approach based on Molecular Dynamics (MD), while, in this work, we propose a multiscale methodology where a molecular description of the polymers is bridged to a macroscopic prediction of its gas sorption behaviour. PHBV structures were simulated using MD to obtain pressure–volume–temperature data, which were used to parametrise the Sanchez–Lacombe Equation of State. This, in turn, allows for the evaluation of the CO2 and CH4 solubility in the copolymers at various pressures and compositions with little computational effort, enabling the estimate of the sorption-based selectivity. The gas separation performance obtained with this multiscale technique was compared to results obtained with a fully atomistic model and experimental data. The solubility–selectivity for the CO2/CH4 mixture is in reasonable agreement between the two models and the experimental data. The multiscale method presented is a time-efficient alternative to fully atomistic methods and detailed experimental campaigns and can accelerate the introduction of renewable materials in different applications.

Electric field-driven assembly of (110) oriented metal–organic framework ZIF-8 monolayer with high hydrogen selectivity

Metal-organic framework (MOF) membranes have showed great potential in gas separation. To date, it is still a great challenge to precisely control the optimal orientation of MOF membranes with an enhanced gas separation performance. Herein, we prepared a compact and (110) oriented ZIF-8 membrane with a thickness of about 265 nm on graphite substrate within 1 h at room temperature via electric-field-driven strategy. Since the membrane is an intergrown one-crystal layer, grain boundary retardation of the flux is eliminated. Furthermore, due to the reduction of the transport pathways through the oriented structure, the (110) oriented ZIF-8 membrane exhibits a high gas separation performance. At 100 °C and 1 bar for the separation of equimolar binary gas mixtures H2/CO2, H2/CH4 and H2/C3H8, separation factors of 49.5, 90.9 and 121.8 can be obtained, with H2 permeance of about 1.7 × 10-7 mol·m−2·s−1·Pa−1. The developed strategy exhibits excellent reproducibility and scalability, and a large area ZIF-8 membrane can be consistently prepared on the graphite substrate, thus facilitating the preparation and application of the ZIF-8 membrane on a large scale. Further, the electric-field-driven strategy is also helpful for the preparation oriented ZIF-67 and ZIF-L membranes, confirming its versatility for the preparation of oriented MOF membranes.

Nanoporous carbon materials: modern production methods and applications

The review presents data on the nomenclature and production methods of the most intensively investigated classes of nanoporous carbon materials, which are increasingly used in science, medicine, and various fields of economy. The traditional activated carbons, which are produced by conventional biomass and fossil hydrocarbon processing methods, are compared with nanoporous carbon materials obtained using modern synthetic methods. Recommendations are given on the use of template synthesis to obtain carbon materials with a controlled nanoporosity. Self-template synthesis, in which environmentally benign and readily available organic salts can be used as precursors, is considered as a promising avenue of research. This approach markedly reduces the cost of template synthesis of nanoporous carbons and allows for the preparation of carbon materials with specific particle morphology from organometallic precursors. Methods for the preparation of functional materials with ordered architectures of micro- and mesopores are considered, including modern functionalization and doping approaches. A part of the review is devoted to advanced applications of nanoporous carbon materials such as water treatment, energy and hydrogen storage, separation of gas mixtures, development of catalysts and sensors, and solution of other significant problems. The conclusion summarizes the experience of application of various methods for the preparation of nanoporous carbon materials, identifies the most problematic issues of the development and practical use of these materials, and presents the authors' view on further development of this area of materials science.<br> The bliography includes 353 references.

Structure and Dynamics of Carbon Dioxide inside ”Hot” Ice with Cylindrical Channels

Inclusion compound based on crystalline water is increasingly recognized as a promising solution for carbon dioxide (CO2) capture, either for carbon sequestration from greenhouse gas emissions or for gas mixture separation. Molecular dynamics simulations revealed that water crystallizes into a novel porous structure in a carbon nanobrush environment even at room temperature, thus termed ”hot” ice whose structure code is dtc. This study employs a hybrid Grand Canonical/isothermal-isobaric Monte Carlo (GCMC) simulations to investigate CO2 confinement inside the cylindrical channels of ice dtc structure. The results show that CO2 occupancy, here expressed as CO2-to-water mole ratio, is approximately 2:5 at maximum. The simulations also demonstrate the mechanical stability of ice dtc structure under positive pressures when its voids are filled with CO2. Furthermore, molecular dynamics simulations are performed to provide molecular insights into the structures and dynamics of CO2 inside the porous channels framework. The results show that CO2 molecules form a bilayer structure inside the cylindrical channels, where certain molecule orientation angles are favored. Dynamics analysis shows that CO2 molecules are relatively immobile in all directions at maximum occupancy.

A PLC-Embedded Implementation of a Modified Takagi–Sugeno–Kang-Based MPC to Control a Pressure Swing Adsorption Process

The paper presents a case study that applies a model predictive control (MPC) approach in a Micro850 programmable logic controller (PLC) to a laboratory pressure swing adsorption (PSA) process used for separating gas mixtures of CO2 and CH4. PLC is an industrial hardware characterized by its robustness to hazardous environments and limited computational capacities, which poses computational challenges for MPC implementation. This paper’s main contribution is the application of the modified Takagi–Sugeno–Kang-based MPC (MTSK-MPC) algorithm to this PSA unit, which provides features to investigate and implement feasible MPC designs in PLCs. The investigation consists of a sensitivity analysis of how some design parameters influence the PLC memory and the MPC implementation and a comparative evaluation of the computational processing from different MPC algorithms and simulations. The comparison comprises software-in-the-loop simulations with three algorithms in the PC: an implicit MPC, an explicit MPC, and the MTSK-MPC. Additionally, it includes a hardware-in-the-loop simulation with the implemented MTSK-MPC in Micro850. The results show that the MPC algorithms achieve close performance, tracking setpoint changes and rejecting output disturbances, with the MTSK-MPC presenting the lower processing time among the MPCs in the PC. The study concludes that the implementation of MTSK-MPC in the Micro850 is feasible.

Spatiotemporal evolution of molar fraction in acoustic-resonance tube filled with He-Ar mixture.

This study proposes a time-evolution method to simulate acoustic gas-mixture separation. The proposed method can calculate the separation process without any arbitrary parameters except for space and time resolutions. The molar-fraction distribution within the system during the separation can be calculated, and the results show that a large molar-fraction gradient occurs in the separation tube, while a distribution also occurs in the resonance tube. Although the simulation results for the case with a high-pressure amplitude diverge from that of the experiment during the process of the separation, the simulation results for the case with a low-pressure amplitude agree well with those of the experiment.

Combining machine learning and molecular simulation to explore MOF materials that contribute to CF4/N2 separation

High-throughput molecular simulations and machine learning algorithms have been widely used to identify promising metal–organic frameworks for gas separation. However, most studies are limited to screening high-performance materials from existing databases, which fails to fully utilize the predictive function of machine learning. This paper combines genetic algorithms and high-throughput screening to deeply mine anion-pillared MOF (APMOF) performance feature relationships and predict high-performance materials that are not in the database. Considering the actual industrial conditions (CF4/N2 = 10/90), we chose the ratio of CF4:N2 = 1:9 to simulate the adsorption separation of gas mixtures of MOF materials at a temperature of 298 K and a pressure of 1 bar. First, the CF4/N2 separation properties of MOFs in the APMOF library were obtained based on molecular simulations. Then, the filtered data were coded according to the method of “building block classification − structural interval categorization”. Then, the machine learning algorithm was used for model training to obtain a high-precision model. Finally, the tangent adaptive genetic algorithm was used to recombine the genes of the materials, and the new MOF materials were successfully reverse-engineered. The study found that the pore-limit diameter of APMOFs is most conducive to the separation of CF4/N2 by MOFs when the pore-limit diameter of APMOFs is within two times the molecular dynamics diameter of CF4. 134 MOF materials were predicted to have CF4/N2 selectivities exceeding 46.30. The use of organic ligands such as 4,4′-bipyridyl or 1,4-bis(4-pyridyl)benzene (bpb) increases the likelihood of these materials being high-performance for CF4/N2 separation. The combination of computational screening methods and machine learning can expedite the design and development of new high-performance MOFs. This approach can also provide guidance for the synthetic direction and pattern of materials, which can assist experimentalists in their synthesis.

Using Porous Liquids to Perform Liquid-Liquid Separations.

Porous liquids (PLs) are a new type of fluid sorbent investigated mainly for the separation of gas mixtures. Here, we explore their application to the separation of miscible liquids, using MEG/water (MEG=monoethylene glycol) and EtOH/water as proof-of-principle. Recovery of used MEG is industrially important but its extraction into conventional solvents from water is difficult. PLs ZIF-8@PDMS (PL1, PDMS=polydimethylsilicone) or ZIF-8@sesame oil (PL2) each consisting of 25 wt % of the hydrophobic microporous material ZIF-8 dispersed in PDMS or sesame oil respectively, were formulated and found to be exceedingly physically stable to sedimentation. A 5 nm PEEK membrane was used to provide a permeable barrier between the PL and the alcohol/water phase. MEG was selectively extracted through the membrane from approximately 50 : 50 wt % MEG/water mixtures into the PL phase and this procedure could be applied repeatedly. It was effective for MEG/water mixtures as dilute as 3 : 97 wt %. The PL could also be regenerated (80 °C at 0.01 bar) and re-used, suggesting its potential for continuous, cyclic extraction. Furthermore, PL3 (silicalite-1@PDMS) was effective in selective alcohol extraction from beverages. It shows potential for lowering the alcohol concentration in gin or wine due to its excellent chemical stability and nontoxicity. Overall, we show that the enhanced adsorption properties of PLs due the presence of empty pores,which provides unusually high gas solubilities, also makes them, in principle, applicable to liquid-liquid separations.

Using Porous Liquids to Perform Liquid‐Liquid Separations

Porous liquids are new types of fluid sorbent investigated mainly for the separation of gas mixtures. Here, we explore their application to the separation of miscible liquids, MEG (monoethylene glycol)/water and EtOH/water) as proof of principle. Recovery of used MEG is industrially important but its extraction from water is difficult. PLs ZIF 8@PDMS (PL1, PDMS = polydimethylsilicone) or ZIF‐8@sesame oil (PL2) each consisting of 25wt% of the hydrophobic microporous material ZIF‐8 dispersed in PDMS/sesame oil, were formulated and found to be exceedingly physically stable. 5 nm PEEK membranes were used to provide permeable barriers between the PL and the alcohol/water phase. MEG was selectively extracted through the membrane from 50wt% MEG/water mixtures into the PL phase. It was effective for MEG/water mixtures as dilute as 3:97wt%. The PL could be regenerated and re‐used, suggesting its potential for continuous cyclic extraction. Furthermore, PL3 (silicalite‐1@PDMS) has demonstrated effectiveness in achieving selective alcohol extraction from beverages. It shows great potential for lowering the alcohol concentration in gin/wine due to its excellent chemical stability and nontoxicity. Overall, the enhanced adsorption properties of PLs due the presence of empty pores, which provides unusually high gas solubilities, also makes them, in principle, applicable to liquid‐liquid separations.

Compact 3D-Printed Unit for Separation of Simple Gas Mixtures Combined with Chemiresistive Sensors.

Inexpensive chemiresistive sensors are often insufficiently selective as they are sensitive to multiple components of the gas mixture at the same time. One solution would be to insert a device in front of the sensor that separates the measured gas mixture and possibly isolates the unwanted components. This study focused on the fabrication and characterization of a compact unit, which was fabricated by 3D printing, for the separation and detection of simple gas mixtures. The capillary, the basic part of the compact unit, was 4.689 m long and had a diameter of 0.7 mm. The compact unit also contained a mixing chamber on the inlet side and a measuring chamber with a MiCS-6814 sensor on the outlet side. Mixtures of ethanol and water at different concentrations were chosen for characterization. The measured calibration curve was found to have a reliability of R2 = 0.9941. The study further addressed the elements of environmental friendliness of the materials used and their sustainability.

CFD simulation for CO2 separation using diamond-structured thermally rearranged (TR) polymer membrane: Effect of CO2 feed concentration, feed pressure and temperature

Abstract CO2 separation in natural gas purification is important in improving the properties of natural gas such as energy content, volume and corrosivity. Membrane separation using TR-450 polymer membrane is a potential approach to remove CO2 from natural gas efficiently. The study of CO2/CH4 binary gas mixture separation was simulated using a thermally-rearranged (TR) HAB- 6FDA membrane at 450 °C with a partial part of Schwarz Diamond structure because it exhibits advanced mechanical properties with low stiffness for relatively high strength. TR-450 membrane exhibits excellent separation performance that has the potential to exceed the Robeson plot 1991. Computational fluid dynamics (CFD) was used to simulate the fluid behavior within the geometry created using CAD software. The effect of feed pressure, temperature and CO2 feed concentration on the separation performance of TR-450 membrane was also studied. The results indicated that an increase in feed pressure leads to a decrease in CO2 recovery, hence the lower separation performance. It was also found that increasing the feed temperature leads to an increase in CO2 recovery. Concerning the concentration of CO2 in the feed, elevated levels impact the performance of membrane separation. The enhanced membrane separation performance demonstrated by the TR-450 membrane under various conditions underscores the necessity for additional investigation to unveil its potential in industrial gas separation applications.

Исследование адсорбционного разделения газовых смесей в условиях нестационарности

The influence of the initial concentration, rate and temperature of adsorption on the adsorption separation of gas mixtures (CO2, CH4, N2, H2S) is investigated. Components: N2 – 5%, H2S – 5%, CO2 – 5% and CH4 – 85%. And as an adsorbent granule of clinoptilolite of irregular shape were used. Isothermal adsorption of CO2 was obtained at different temperatures (293, 313, and 323 K). The obtained isotherms of CO2 adsorption showed that with an increase in temperature, the adsorption of CO2 decreased. The type of isotherms corresponds to Langmuir. The output curves of gas mixture adsorption depending on the gas flow rate and various main components of CO2 were also experimentally studied. The output curves of the adsorption of the CO2 component were studied at various gas flow rates of 20, 50, and 80 mL/min. Equilibrium time increases with a decrease in the gas flow rate. Output curves were also obtained depending on the initial CO2 concentrations of 5%, 10% and 20%. It was determined that with a decrease in the initial concentration of CO2, the equilibrium time also increases. Gas mixture components sorbed downwards: H2S→CO2→CH4→N2. The resulting system of model equations describing the adsorption separation of gas mixtures in a fixed adsorbent layer represents a complete mathematical model of the process under unsteady conditions. The obtained regularities of the process of adsorption of gas mixtures testify to the fact that the process takes place under non-stationary conditions. The proposed models for the optimal design of industrial absorbers can be used for adsorption separation of gas mixtures in the conditions of their unsteady flow.

On the increased interfacial resistance of hydrogen in carbon nanotube arrays and its effect on gas mixture separation

We outline a surface scattering kernel for rarefied gas flows through ideally ordered nanomaterials, such as high aspect ratio carbon nanotubes. The derived model allows for a comparison of the tangential momentum accommodation coefficient, and, hence, the total effective friction, for different species of gases as a function of the particle diameter. This surface kernel is incorporated with a Fokker–Planck model as an approximation to transport of a rarefied gas through ideally ordered carbon nanotubes. The results of this analysis predict that H2 experiences higher friction in such systems in comparison with larger molecules such as CH4. The results are proposed as a potential explanation of the reduced gas transport of hydrogen gas in nanoporous systems.

Nanoporous Metal–Organic Framework Based on Furan-2,5-Dicarboxylic Acid with High Potential in Selective Adsorption and Separation of Gas Mixtures

Nanoporous Metal–Organic Framework Based on Furan-2,5-Dicarboxylic Acid with High Potential in Selective Adsorption and Separation of Gas Mixtures

Efficient adsorption separation of methane from C2–C3 hydrocarbons in a Co(II)-nodes metal–organic framework

Methane (CH4) as a substitute for other mineral fuels plays a crucial role in reducing energy consumption and preventing environmental pollution. The present study employs a solvothermal method to fabricate a porous framework Co-metal–organic framework (Co-MOF) containing two distinct secondary building units (SBUs): an anionic [Co2(μ2-OH)(COO)4(H2O)] and a neutral [CoN2(COO)2]. Notably, within the anionic SBUs, the coordinated water molecules induce the generation of divergent unsaturated Co(II) centers in the unidirectional porous channels, thereby creating open metal sites. The adsorption performance of Co-MOF towards pure component gases was systematically investigated. The results demonstrated that Co-MOF exhibits superior adsorption capacity for C2–C3 hydrocarbons compared to CH4, which offering the potential for efficient adsorption and separation of CH4 from C2–C3 hydrocarbons. The gas selectivity separation ratios of Co-MOF for C2H6/CH4 and C3H8/CH4 were calculated using the ideal adsorbed solution theory method at 273/298 K and 0.1 MPa. The results revealed that Co-MOF achieved remarkable equilibrium separation selectivity for CH4 and C2–C3 hydrocarbon gases among non-modified MOFs, signifying the potential of the synthesized Co-MOF for efficient recovery and purification of CH4 from C2–C3 hydrocarbons. Breakthrough experiments further demonstrate the ability of Co-MOF to purify methane from C2–C3 hydrocarbons in practical gas separation scenarios. Additionally, molecular simulation calculations further substantiate the propensity of anionic SBUs to interact with C2–C3 hydrocarbon compounds. This study provides a novel paradigm for the development of porous MOF materials in the application of gas mixture separation.

A core-shell IL@MOF composite with ultra-high selectivity in multiple CO2 purification systems

Porous adsorbents are widely used for the adsorptive separation of carbon dioxide (CO2) from gas mixtures, offering a promising solution to address both the energy crisis and environmental issues. However, developing highly efficient CO2 selective adsorbents has been challenging due to the similar physicochemical properties of CO2 and other gases. To overcome this challenge, we herein have developed a core–shell composite utilizing ionic liquids (ILs) and metal–organic frameworks (MOFs) based on the dissolution-diffusion mechanism. The unique solubility differences of ILs for various gas molecules, particularly their strong solubility for CO2, allow only CO2 to be adsorbed while excluding other gases. As a result, the composite exhibits a remarkable separation selectivity for CO2/C2H2, CO2/CH4 and CO2/N2. Breakthrough experiments have verified the outstanding performance of this core–shell composite in separating gas mixtures containing CO2 impurities. Remarkably, this composite can be synthesized by a simple method, which is more practical for large-scale production.

Shaping of MIL-53-Al and MIL-101 MOF for CO2/CH4, CO2/N2 and CH4/N2 separation

Metal-organic frameworks (MOF) are promising materials for gas storage and separation. The formulation and shaping of MOFs in mechanically stable bead forms is an essential requirement for their practical application as an adsorbent for gas and liquid mixture separations. In this work, MIL-53-Al and MIL-101 MOF beads are synthesized using sodium alginate as a binder, and calcium chloride as a gelling agent. The synthesized MIL-53-Al and MIL-101 MOF beads are characterized by powder X-ray diffraction (PXRD), BET surface area, porosity analysis from N2 uptake data at 77 K, FTIR, TGA, and scanning electron microscopy (SEM). The isothermal equilibrium adsorption uptake of CH4 and N2 gases is measured up to 10 bar pressure while the CO2 equilibrium uptake is measured up to 1 bar at 298 and 313 K respectively. The isotherm data of all adsorbates are fitted in Dual Site Langmuir (DSL) isotherm equations. The adsorption selectivity for CH4/N2, CO2/CH4, and CO2/N2 binary systems are predicted using the Ideal Adsorbed Solution Theory (IAST) method. The dynamic column breakthrough experiments are carried out on MIL-53-Al beads for CH4/N2 (30:70 and 50:50 v/v), CO2/CH4 (45:55 v/v) and CO2/N2 (15: 85 v/v) feed mixtures. The IAST selectivity and breakthrough time obtained under the same superficial velocity, pressure, and temperature conditions follow the order CO2/N2 > CO2 /CH4 > CH4/N2. The MIL-53-Al beads show higher CH4/N2, CO2/CH4, and CO2/N2 selectivity for the targeted mixtures than MIL-101 beads.

Hydrate-based technique for natural gas processing: Experimental study of pressure-dropping and continuous modes

Gas hydrate crystallization is perspective and energy-efficient technology for gas mixtures processing, including natural gas. There were compared pressure-dropping and continuous gas hydrate crystallization methods for separation of gas mixture closed to natural gas. The studied mixture has been chosen similar to the natural gas composition: CH4 (75.68 mol.%) - С2H6 (7.41 mol.%) - C3H8 (4.53 mol.%) - н-C4H10 (2.47 mol.%) - CO2 (5.40 mol.%) - H2S (1.39 mol.%) - N2 (3.01 mol.%) - Xe (0.11 mol.%). Experiments were provided in the 4 L high pressure reactor, using water solution of SDS (0.20 wt.%). The experiment conditions were 280.15 K and pressure of 4.25 MPa. The components separation factors and recovery for two modes have been researched and compared for choosing more effective options. After comparing these characteristics, it was concluded that continuous process is more productive than pressure-dropping mode. At the stage cut (θ) of 0.9, the gas components total recovery (R) for the continuous mode have exceeded the total recovery for the pressure-dropping mode by 8.15 %, and at θ = 0.8, exceeded by 6.11 %. The recovery and separation factors have the highest values for H2S, C3H8, Xe in the continuous mode: 97.62 %, 94.90 %, 84.98 % and 8.7, 10.53, 6.36, respectively. Thus, the choosing of the more effective stage cut depends on the aim of the process: the highest purity or the largest recovery.