Gas Permeability Of Membranes Research Articles

Electrical field enhanced CO2 permeation through a carbon molecular sieve membrane: A combined density functional based tight binding and computational fluid dynamics study

An important challenge in membrane technology for gas separation is to simultaneously improve their permeability and selectivity. Often, the increase in one performance leads to the decline of the other. This study presents a solution to that problem by utilizing electrical field coupling to improve CO2 permeation through a nitrile-containing poly (arylene-ether-ketone) (PEK-C(CN)) carbon molecular sieve membrane. Density functional based tight binding simulations of CO2, CH4, and N2 adsorption on PEK-C(CN) monolayer were conducted without and with electric field. The findings revealed that the electric field strength and orientation affected the molecules bond lengths, atomic charges, and bond angles. Investigation of their adsorption energy dominantly favored CO2 adsorption. Analysis of the partial density of states confirmed that adsorption interactions with the membrane were due to CO2 responses to the applied electric field. It additionally proved the electrical stability of PEK-C(CN) membrane. Computational fluid dynamics simulations of gas permeation through PEK-C(CN) membrane were performed without and with electric field. Results indicated an average pore distribution around 0.5 nm. The velocity flow distribution aided locate the interconnected pores, bringing to the fore the dominant transportation paths of gas molecules. It was uncovered that although the application of an electric field significantly improved the membrane gas permeability, it was not necessarily beneficial to its selectivity. −5 V was determined to be the optimum potential for an improvement of CO2 permeability from 57.32 Barrer (no field) to 15924.91 Barrer, while also enhancing the selectivity. This work demonstrates the benefits of the electric field and its promising application in gas separation processes.

Two morphology distinct fillers with chemical similarity incorporated into Tröger’ base polymers towards enhanced gas separation

Mixed matrix membranes (MMMs) with one class of fillers always require high loadings to maximize gas permeability. The incompatibility between polymers and high content fillers causes non-selective interfacial voids in the MMMs and poor mechanical properties of MMMs. This work adopts two morphology distinct fillers with chemical similarity to achieve improved gas separation performance of Tröger’ base membranes without sacrificing their mechanical properties. The three-dimensional ZIF-8 nanoparticles are beneficial for membrane gas permeability. The addition of low content ZIF-8 nanosheets can greatly improve H2/CH4 and CO2/CH4 selectivities of the membranes. ZIF-8 particles and ZIF-8 nanosheets with similar chemical properties can mix more homogeneously and disperse well in the polymer matrix with expected hydrogen bonding interaction compared to mixed ZIF-8 and CuBDC nanosheets. Eventually, the resulting dual filler MMMs doped with 4 wt% ZIF-8 nanosheets and 10 wt% ZIF-8 nanoparticles have H2/CH4 ideal selectivity of 60 with H2 permeability of 426 Barrer, which is an increase of 18% and 102% over pure membranes, respectively. Moreover, the membrane has a significantly enhanced CO2/CH4 mixed gas selectivity of 68 at sub-ambient temperature, accompanied by temperature-dependent CO2-induced plasticization behavior. Mixing morphology distinct fillers with chemical similarity is proved to be an effective method to prepare a robust MMM at low filler amounts, and the synergistic effect on gas permeability and selectivity endows these dual filler MMMs with great H2/CH4 and CO2/CH4 separation performance.

PDMS‐silica composite gas separation membranes by direct ink writing

AbstractPolydimethylsiloxane (PDMS)‐based membranes containing amine‐functionalized and unfunctionalized silica particles were fabricated via direct ink writing for CO2/N2 gas separation. The printability of the inks was evaluated by rheological measurements, while spectroscopy, microscopy, thermal measurements, and mechanical testing were employed to characterize the printed membranes. The surface morphology of the membranes revealed the absence of voids, demonstrating their suitability for gas separation. The printed membranes also exhibited desirable thermal and mechanical properties (i.e., thermal degradation temperature of 518 °C and tensile strength as high as 1.178 MPa with 529% elongation). The PDMS‐based membranes generally displayed high permeability for CO2 but slightly low selectivity for the CO2/N2 gas pair. The best‐combined permeability‐selectivity performance of 8794 barrer and selectivity of 11.64 was demonstrated by the printed PDMS membrane containing no SiO2 fillers. The inclusion of unfunctionalized SiO2 particles generally increased the membrane's gas permeability but compromised the selectivity. In contrast, membranes with amine‐functionalized silica showed improved selectivity compared to membranes containing unfunctionalized silica. Overall, the performance and characteristics offered by the PDMS/silica composite membranes demonstrated the potential of 3D printing as an economical and sustainable fabrication approach to developing materials for carbon capture applications.

Direct evaluation of void effect on gas permeation in mixed matrix membrane by non-equilibrium molecular dynamics

The effect of the void between filler (MFI-type zeolite) and matrix (a polymer of intrinsic microporosity) in the mixed matrix membrane (MMM) on CO2/CH4 gas permeability was investigated at the atomistic scale by non-equilibrium molecular dynamics (NEMD). In our NEMD, the permeation through the void at the interface between the filler and the matrix, the matrix, and the filler were simulated simultaneously. The permeating path was analyzed to clarify the void effect at the interface between the matrix and the filler on permeance and selectivity. NEMD results clearly showed that permeation through the filler and matrix was the fastest that could be expected using the MMM design concept. Furthermore, permeation through the void also showed high CO2 selectivity, although the permeation rate was lower than that through the filler inside and the matrix. The CO2 permeation through the filler and matrix was dominant at about 43% of the total permeance, whereas the permeation through the void was about 40% of the total permeance. This means that the void at the interface significantly influenced the permeability and selectivity. This suggests that controlling the void structure/affinity between the filler and the matrix could drastically improve MMM permeation properties.

Attapulgite Nanorod-Incorporated Polyimide Membrane for Enhanced Gas Separation Performance.

Polyimide (PI) membrane is an ideal gas separation material due to its advantages of high designability, good mechanical properties and easy processing; however, it has equilibrium limitations in gas selectivity and permeability. Introducing nanoparticles into polymers is an effective method to improve the gas separation performance. In this work, nano-attapulgite (ATP) functionalized with KH-550 silane coupling agent was used to prepare polyimide/ATP composite membranes by in-situ polymerization. A series of characterization and performance tests were carried out on the membranes. The obtained results suggested a significant increase in gas permeability upon increasing the ATP content. When the content of ATP was 50%, the gas permeability of H2, He, N2, O2, CH4, and CO2 reached 11.82, 12.44, 0.13, 0.84, 0.10, and 4.64 barrer, which were 126.87%, 119.40%, 160.00%, 140.00%, 150.00% and 152.17% higher than that of pure polyimide, respectively. No significant change in gas selectivity was observed. The gas permeabilities of membranes at different pressures were also investigated. The inefficient polymer chain stacking and the additional void volume at the interface between the polymer and TiO2 clusters leaded to the increase of the free volume, thus improving the permeability of the polyimide membrane. As a promising separation material, the PI/ATP composite membrane can be widely used in gas separation industry.

Design of a Gas Permeation and Pervaporation Membrane Model for an Open Source Process Simulation Tool.

Gas permeation and pervaporation are technologies that emerged several decades ago. Even though they have discovered increasing popularity for industrial separation processes, they are not represented equally within process simulation tools except for commercial systems. The availability of such a numerical solution shall be extended due to the design of a membrane model with Visual Basic based on the solution-diffusion model. Although this works approach is presented for a specific process simulator application, the algorithm can generally be transferred to any other programming language and process simulation solver, which allows custom implementations or modeling. Furthermore, the modular design of the model enables its further development by operators through the integration of physical effects. A comparison with experimental data of gas permeation and pervaporation applications as well as other published simulation data delivers either good accordance with the results or negligible deviations of less than 1% from other data.

Improving Anti-Humidity Property of a SnO2-Based Chemiresistive Hydrogen Sensor by a Breathable and Hydrophobic Fluoropolymer Coating.

Metal-oxide-based chemiresistive hydrogen sensors exhibit high sensitivity, long-term stability, and low cost and have been extensively applied in safety monitoring of H2. However, the sensing performances are dramatically affected by the water vapor, resulting in reduced response value and increased response/recovery time. To improve the anti-humidity property of sensors, coating the breathable and hydrophobic membrane on the surface of the sensing film is an effective strategy. In this work, the poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF-2400) was dip-coated on the surface of SnO2 in a commercial hydrogen sensor (TGS2615) as a breathable and hydrophobic membrane. For safety, He instead of H2 was used to test the gas permeability of membranes. The Teflon membrane shows a high He permeability of up to 40,700 Barrer and an excellent He/H2O selectivity of 99. Moreover, Teflon shows high processability to form a defect-free coating on the rough surface of the sensing film and high chemical stability under the operando condition of the sensor. Thus, the Teflon-modified sensor possesses excellent selectivity with a value of 5, and the resistance is stable at 10,554 ± 3% Ω for 20 days in 80% RH. The modified sensor shows an improved anti-humidity property with a 75% response to 200 ppm H2 at 80% RH and has a low coefficient of variation value of 7.23% that shows advances than other reported sensors modified by coatings. The commercially available Teflon and the simple coating technology make the strategy easily scale up and show promising applications.

Synthesis, characterization, and gas separation properties of novel fluorinated co-polyimides with bulky side groups

A series of random 6FDA-MFPAP/BAMF co-polyimides with different MFPAP:BAMF molar ratios (2:1, 1:1, 1:2, and 1:3) were synthesized from a novel diamine, 4-(3-methoxy-4-(difluoromethoxy)-phenyl)-2,6-bis(4-aminophenyl)pyridine (MFPAP); a commercial fluorene diamine (BAMF); and a dianhydride, 4,4'-(hexafluoroiso-propyl)diphthalic anhydride (6FDA). The prepared co-polyimides exhibited outstanding thermal performances ( T g > 345 °C, T d > 509 °C), good optical properties (λ cut-off > 342 nm, λ 80% > 410 nm), and hydrophobic properties (contact angle >91.8°). They also showed excellent solubility in both high and low boiling point organic solvents. The pure gas (He, CO 2 , O 2, and N 2 ) permeability of the co-polyimide membranes was measured using the constant volume-variable pressure method. The gas permeabilities of the membranes were superior to those of the commercial Kapton, Matrimid and P84, where the He permeability coefficient of 6FDA-MFPAP/BAMF (2:1) was 55.39 barrer. This can be reasonably explained and supported by the fractional free volume and molecular chain spacing of the polyimides. In addition, the gas transport performances of the copolymers have significantly improved over their corresponding homopolymers (6FDA-MFPAP and 6FDA-BAMF). And the 6FDA-MFPAP/BAMF co-polyimides with 2:1 and 1:1 M ratios of MFPAP/BAMF had the best gas separation performance for the gas pairs He/CO 2 and O 2 /N 2 , respectively, which was close to the Robeson upper limit in 1991. A series of containing bulky side group novel fluorinated co-polyimides with outstanding thermal performances, excellent solubilities, good optical properties, and hydrophobic properties were synthesized based on a novel diamine MFPAP, fluorene diamine BAMF and dianhydride 6FDA, they exhibit good gas separation properties and show the potential of application in gas separation field. • A series of novel fluorinated co-polyimides with bulky were designed and synthesized. • Polymers exhibited excellent soluble, thermal, optical and hydrophobic properties. • Diamine MFPAP effectively modulate the FFV and gas transport performance of PIs. • Gas transport performance of MFPAP/BAMF (1:1) and (2:1) PIs are closest to the 1991 upper bond.

Expanded polytetrafluoroethylene functionalized with free radical scavengers and hydrophilic groups for superior chemical stability of proton exchange membranes

Introduced free radical scavengers and decreased gas crossover have a significant impact on a proton exchange membrane's (PEM's) chemical stability and performance. A novel PEM containing expanded polytetrafluoroethylene (ePTFE) functionalized with free radical scavengers and hydrophilic groups was designed and fabricated to enhance the PEM's electrochemical performance and chemical stability. ePTFE with unsaturated bonds was prepared by a chemical modification reaction using benzoin and potassium tert-butoxide; hydrogen bromide acted as a halogenating agent, and 3-mercapto-1,2,4-triazole worked as a free radical scavenger grafted onto the ePTFE molecular chains. The ePTFE was functionalized by hydrophilic groups, and radical scavenger groups led to perfluorosulfonic acid (PFSA) ionomers that had better compatibility with the modified ePTFE. The prepared membrane's gas permeability, proton conductivity, and electrochemical performance were thereby significantly improved. In addition, the generated free radicals were quickly eliminated by the free radical scavenger groups, thus enhancing the PEM's chemical stability. The microstructure, morphology, and performance of the PEM at various degradation levels were systematically evaluated. This work reveals that expanded polytetrafluoroethylene functionalized with free radical scavengers and hydrophilic groups not only reduced the hydrogen peroxide and active free radicals generated but also effectively eliminated the free radicals, thereby mitigating chemical degradation of the PEM. This paper provides a promising way to improve the proton conductivity and chemical stability of PEMs, offering excellent application potential for boosting fuel cell lifetime and performance.

Technologies for the production of renewable natural gas from organic wastes and their opportunities in existing Canadian pipelines

Of all the types of renewable energy, Renewable Natural Gas (RNG) market has been more supported and developed in Canada due to the lower project cost and the existing NG pipeline infrastructure. RNG is defined as a methane-rich gas obtained through combining Anaerobic Digestion (AD) of underutilized renewable sources (organic waste streams) and upgrading technologies. Membrane separation technology is considered one of Canada's most popular upgrading technologies due to the country-old knowledge regarding gas permeation membranes widely used in the NG industry. Membrane systems are used to recover methane from biogas to a level that meets current natural gas pipeline specifications set out by gas utility companies or meets natural gas vehicle fuel standards set out by engine manufacturers. Here we review standards for gas injection into existing Canadian pipelines, commercial biogas upgrading systems in Canada, and Current biogas upgrading to RNG projects in Canada. We focus more on membrane technology and discuss the possible driving force, module, and configuration alternatives. Finally, this review comprehensively examines membrane types and advances in composite type membranes.

Residual solvent induced physical morphology and gas permeation in polyamide-imide membrane: Experimental investigation and molecular simulations

The present study focuses on understanding various residual solvent effects on the physical morphology and separation characteristics of polyamide-imide (Torlon) membranes. The dense membranes were indigenously synthesized by phase inversion technique using various solvents including, N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMAc) and N-methyl pyrrolidone (NMP) respectively. The effect of various solvents on the physical morphology and separation characteristics were studied using a combination of both experimental techniques and atomistic simulations. The Hansen solubility and Floury-Huggins parameters were used to understand the polymer–solvent interactions and further extended to correlated to separation characteristics. Scanning electron microscope (SEM) and atomic force microscopy (AFM) methods were used to investigate the resulted physical morphology of the membranes. Thermogravimetric analysis (TGA) and 1H NMR spectra revealed residual solvent, hydrogen-bonding interactions with the Torlon polymer membrane. The experimental gas permeation studies demonstrated that the CO2 permeability in Torlon membranes follows the order T-NMP > T-DMAc > T-DMF. However, the membrane with the T-DMAc solvent exhibited higher ideal selectivity of 34.65 at 12.5 bar for CO2/CH4 separation due to the lower diffusion coefficient of CH4 in the presence of residual DMAc. The predicted solubility and diffusion coefficients of CO2 and CH4 were shown to be in good agreement with the experimental results. Additionally, structural analysis of simulated models provided further insights into residual solvent effects on the microscopic properties and gas permeation. Overall, the Torlon membrane with the residual DMAc solvent showed positive effects on the transport properties and in turn enhance the diffusive selectivity.

Aquaporin expression and cholesterol content in eel swimbladder tissue.

Leakiness of the swimbladder wall of teleost fishes must be prevented to avoid diffusional loss of gases out of the swimbladder. Guanine incrustation as well as high concentrations of cholesterol in swimbladder membranes in midwater and deep‐sea fish has been connected to a reduced gas permeability of the swimbladder wall. On the contrary, the swimbladder is filled by diffusion of gases, mainly oxygen and CO2, from the blood and the gas gland cells into the swimbladder lumen. In swimbladder tissue of the zebrafish and the Japanese eel, aquaporin mRNA has been detected, and the aquaporin protein has been considered important for the diffusion of water, which may accidentally be gulped by physostome fish when taking an air breath. In the present study, the expression of two aquaporin 1 genes (Aqp1aa and Aqp1ab) in the swimbladder tissue of the European eel, a functional physoclist fish, was assessed using immunohistochemistry, and the expression of both genes was detected in endothelial cells of swimbladder capillaries as well as in basolateral membranes of gas gland cells. In addition, Aqp1ab was present in apical membranes of swimbladder gas gland cells. The authors also found high concentrations of cholesterol in these membranes, which were several fold higher than in muscle tissue membranes. In yellow eels the cholesterol concentration exceeded the concentration detected in silver eel swimbladder membranes. The authors suggest that aquaporin 1 in swimbladder gas gland cells and endothelial cells facilitates CO2 diffusion into the blood, enhancing the switch‐on of the Root effect, which is essential for the secretion of oxygen into the swimbladder. It may also facilitate CO2 diffusion into the swimbladder lumen along the partial gradient established by CO2 production in gas gland cells. Cholesterol has been shown to reduce the gas permeability of membranes and thus could contribute to the gas tightness of swimbladder membranes, which is essential to avoid diffusional loss of gas out of the swimbladder.

(Invited) Recycling of NAFION(™) Ion Exchange Membranes: Opportunities and Challenges

We will show how end-of-life membranes, whether from alternative energy applications such as fuel cells or water electrolysis or even large Chlor-alkali applications can be effectively recovered and introduced back into other commercial applications. The recovered polymer will be characterized and it’s properties will be compared to virgin polymer. The raw recovered polymer is delivered in a solid powdered form, and as such this material can be considered as a new novel material with unique processing properties. We will show how the recovered ionomer can be formed into a readily soluble form or as a robust insoluble powder. We will demonstrate the viability for the recovered polymer in cross-cutting applications, such as flow batteries, acid catalysis, and gas permeation membranes. These applications are hampered by the high cost of NAFION(™) however are typically much less technically challenging as compared to the more common applications of chlor-alkali membranes or fuel cell membranes. We will also discuss the important aspects of economic models and associated scale of processes that will generate the proper financial incentives for all entities that participate in a new circular economy.

Guest-host and functionalized side-chain azopolyimide membranes for controlled gas separation

This paper presents two series of azopolyimide membranes containing 4-[4-(6-hydroxyhexyloxy)phenylazo]benzene. The azobenzene groups are located as either covalently-bonded side groups or molecularly dispersed in polymer (host) matrix. The prepared azopolyimides exhibit a high stability of cis isomers, where the return reaction from cis to trans is not completed 7 days after switching off the excitation light. The incorporation of azo moieties as both side-chain groups and a dispersion in a polymer matrix decreases membrane gas permeability while increasing or maintaining selectivity for O2/N2, He/N2, and CO2/N2 gas pairs. The advantage of the azopolymers is the large difference in their permeability for CO2 and O2 after light irradiation (permeability changes up to 29%). These large light-induced changes in the permeability of trans- and cis-azomembranes along with a slow reversible cis-trans reaction may be of interest for use in applications where long-term stability of photoinduced properties is necessary i.e. for control dosing of gases.

Gas Permeation Model of Mixed-Matrix Membranes with Embedded Impermeable Cuboid Nanoparticles.

In the packaging industry, the barrier property of packaging materials is of paramount importance. The enhancement of barrier properties of materials can be achieved by adding impermeable nanoparticles into thin polymeric films, known as mixed-matrix membranes (MMMs). Three-dimensional numerical simulations were performed to study the barrier property of these MMMs and to estimate the effective membrane gas permeability. Results show that horizontally-aligned thin cuboid nanoparticles offer far superior barrier properties than spherical nanoparticles for an identical solid volume fraction. Maxwell’s model predicts very well the relative permeability of spherical and cubic nanoparticles over a wide range of the solid volume fraction. However, Maxwell’s model shows an increasingly poor prediction of the relative permeability of MMM as the aspect ratio of cuboid nanoparticles tends to zero or infinity. An artificial neural network (ANN) model was developed successfully to predict the relative permeability of MMMs as a function of the relative thickness and the relative projected area of the embedded nanoparticles. However, since an ANN model does not provide an explicit form of the relation of the relative permeability with the physical characteristics of the MMM, a new model based on multivariable regression analysis is introduced to represent the relative permeability in a MMM with impermeable cuboid nanoparticles. The new model possesses a simple explicit form and can predict, very well, the relative permeability over an extensive range of the solid volume fraction and aspect ratio, compared with many existing models.

Can the time-lag method be used for the characterization of liquid permeation membranes?

Although the time-lag method is one of the most common tools for the characterization of gas permeation membranes, it is entirely unknown in the vast area of liquid permeation membranes. The time-lag method requires a dynamic permeation test initiated by a step-change in the driving force for the species permeation, which is relatively easy for gas permeation, but not for liquid permeation. In this paper, we present preliminary trials to overcome this obstacle for liquid permeation membranes by performing a sudden change in the osmotic pressure by changing the draw solution concentration. To accomplish this, we have modified a standard forward osmosis testing system to monitor the changes in the mass of feed and draw solutions, and the conductivity of feed solution in real-time. To demonstrate the system's operation, we tested commercial, low-pressure reverse osmosis thin film composite membranes in the active-layer-facing-draw-solution orientation. We present and discuss the resulting time-dependent changes in the water flux and the reverse salt flux, and the processing of the experimental data. The shapes of time-dependent water and salt masses are similar to the pressure decay curves and pressure rise curves, respectively, in a time-lag gas permeation experiment.

Concentration of unconventional methane resources using microporous membranes: Process assessment and scale-up

Unconventional methane resources are usually diluted in air, which prevents their use as feedstock in chemical or thermal processes. Some of them (e.g. coal mine ventilation air or diluted landfill biogas) are emitted directly to the atmosphere without harnessing, increasing the contribution of methane to global warming. Gas permeation membranes offer an alternative for the concentration of these methane resources, increasing considerably their harnessing possibilities. Microporous materials, such as carbon molecular sieve, zeolite or metal organic frameworks, have emerged as alternative to polymeric materials for the preparation of these membranes.The present work is based on simulations of the separation of methane and nitrogen mixtures, using SAPO-34 and carbon molecular sieve membranes. Mass transfer has been modelled in two scales: the membrane material (modelled using the Maxwell-Stefan multicomponent surface diffusion model) and the membrane module (based on the plug flow model). A sensitivity analysis of the influence of the main operating variables on the membrane performance has revealed that the most important ones are transmembrane pressure difference, methane feed concentration and membrane loading. It has been found that SAPO-34 membranes are more suited to concentrate methane in lean mixtures, while the carbon membrane perform better with rich mixtures.The membrane process has been scaled-up for a feed gas flow rate of 1000 m3/h n.t.p. with target methane recovery of 70% for two cases: lean (1%) and rich (50%) methane feed mixtures.

Recovering latent and sensible energy from building exhaust with membrane-based energy recovery ventilation

Energy can be recovered from building exhaust via water vapor transport and heat transfer across gas permeation membranes, thereby reducing latent and sensible loads during both heating and cooling seasons. The process known as membrane-based energy recovery ventilation (ERV) has been commercialized by several HVAC manufacturers, but so far has mostly been offered in flat sheet membrane configurations. In this study, we investigate the use of polydimethyl siloxane membranes packaged into hollow fiber modules, which offer the advantage of high packing density, but which have so far not been commercially adopted due to concerns about parasitic pressure loss. We evaluate here the work required to overcome friction of circulating air through membrane fibers, and we assess the net energy savings that account for these losses relative to the energy saved by water vapor and heat transfer. The concept of normalized net energy savings is introduced to provide a useful metric for comparing performance independent of flow volume and membrane size, and we observe up to 2.75 W/m2 of net latent energy savings. Case studies are used to illustrate the potential of this technology, and energy savings of 1.15 and 1.03 kWh/yr/lpm are demonstrated for Detroit, MI, and Houston, TX, respectively.

Leveraging Nanocrystal HKUST-1 in Mixed-Matrix Membranes for Ethylene/Ethane Separation.

The energy-intensive ethylene/ethane separation process is a key challenge to the petrochemical industry. HKUST-1, a metal–organic framework (MOF) which possesses high accessible surface area and porosity, is utilized in mixed-matrix membrane fabrication to investigate its potential for improving the performance for C2H4/C2H6 separation. Prior to membrane fabrication and gas permeation analysis, nanocrystal HKUST-1 was first synthesized. This step is critical in order to ensure that defect-free mixed-matrix membranes can be formed. Then, polyimide-based polymers, ODPA-TMPDA and 6FDA-TMPDA, were chosen as the matrices. Our findings revealed that 20 wt% loading of HKUST-1 was capable of improving C2H4 permeability (155% for ODPA-TMPDA and 69% for 6FDA-TMPDA) without excessively sacrificing the C2H4/C2H6 selectivity. The C2H4 and C2H6 diffusivity, as well as solubility, were also improved substantially as compared to the pure polymeric membranes. Overall, our results edge near the upper bound, confirming the effectiveness of leveraging nanocrystal HKUST-1 filler for performance enhancements in mixed-matrix membranes for C2H4/C2H6 separation.

Minimizing Solvent Toxicity in Preparation of Polymeric Membranes for Gas Separation.

Toxic solvents such as dimethylformamide (DMF) are widely used for the preparation of polymeric membranes due to the strong dissolving power. Environmentally friendly solvents are available, but the developed membranes suffered from low performance due to the poor solubility of the polymer in the solvent. In this work, polyetherimide membranes were prepared using DMF with the addition of the biodegradable solvent γ-butyrolactone (GBL). Results show that mixing 75 wt % of DMF with 25 wt % GBL enhanced the membrane gas permeability toward hydrogen, methane, helium, carbon dioxide, and nitrogen. The overall permeability was increased by 9.6% compared to the permeability of the membrane made by 100 wt % DMF. Hydrogen-to-methane selectivity was also raised from 26.3 to 29.3.