Mixed Gas Permeation Research Articles

Mixed-gas sorption in polymers via a new barometric test system: sorption and diffusion of CO2-CH4 mixtures in polydimethylsiloxane (PDMS)

Mixed-gas sorption of CO2-CH4 mixtures in rubbery polydimethylsiloxane (PDMS) at 35 °C demonstrated that the presence of CH4 changed the behavior of CO2 sorption and vice versa. This mutual interaction indicated that gases in mixtures do not sorb independently in rubbery membranes. Moreover, we observed that at increasing pressures the interaction between PDMS and CO2-CH4 mixtures enhanced the solubility selectivity of PDMS. Mixed-gas solubility coefficients of CH4 in PDMS were lower than 0.5 cm3(STP) cm−3 atm−1. To accurately measure these values, a new sorption system was designed, constructed, and optimized for low solubility coefficients; an operator-friendly approach to mixed-gas sorption experiments is also discussed in this work. CO2-CH4 mixed-gas diffusivity trends were evaluated from Maxwell-Stefan model fitting of mixed-gas permeation and sorption data. The analysis of both mixed-gas diffusion and sorption data demonstrated that CO2/CH4 mixed-gas permselectivity of PDMS was mainly influenced by CO2 sorption. In mixtures, CH4 diffusion coefficients increased with higher volumetric CO2 concentration, whereas the CO2 diffusion coefficient was essentially concentration independent in both pure- and mixed-gas environments.

Experimental Mixed-Gas Permeability, Sorption and Diffusion of CO₂-CH₄ Mixtures in 6FDA-mPDA Polyimide Membrane: Unveiling the Effect of Competitive Sorption on Permeability Selectivity.

The nonideal behavior of polymeric membranes during separation of gas mixtures can be quantified via the solution-diffusion theory from experimental mixed-gas solubility and permeability coefficients. In this study, CO2-CH4 mixtures were sorbed at 35 °C in 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA)-m-phenylenediamine (mPDA)—a polyimide of remarkable performance. The existence of a linear trend for all data of mixed-gas CO2 versus CH4 solubility coefficients—regardless of mixture concentration—was observed for 6FDA-mPDA and other polymeric films; the slope of this trend was identified as the ratio of gas solubilities at infinite dilution. The CO2/CH4 mixed-gas solubility selectivity of 6FDA-mPDA and previously reported polymers was higher than the equimolar pure-gas value and increased with pressure from the infinite dilution value. The analysis of CO2-CH4 mixed-gas concentration-averaged effective diffusion coefficients of equimolar feeds showed that CO2 diffusivity was not affected by CH4. Our data indicate that the decrease of CO2/CH4 mixed-gas diffusion, and permeability selectivity from the pure-gas values, resulted from an increase in the methane diffusion coefficient in mixtures. This effect was the result of an alteration of the size sieving properties of 6FDA-mPDA as a consequence of CO2 presence in the 6FDA-mPDA film matrix.

Highly Permeable Matrimid®/PIM-EA(H₂)-TB Blend Membrane for Gas Separation.

The effect on the gas transport properties of Matrimid®5218 of blending with the polymer of intrinsic microporosity PIM-EA(H2)-TB was studied by pure and mixed gas permeation measurements. Membranes of the two neat polymers and their 50/50 wt % blend were prepared by solution casting from a dilute solution in dichloromethane. The pure gas permeability and diffusion coefficients of H2, He, O2, N2, CO2 and CH4 were determined by the time lag method in a traditional fixed volume gas permeation setup. Mixed gas permeability measurements with a 35/65 vol % CO2/CH4 mixture and a 15/85 vol % CO2/N2 mixture were performed on a novel variable volume setup with on-line mass spectrometric analysis of the permeate composition, with the unique feature that it is also able to determine the mixed gas diffusion coefficients. It was found that the permeability of Matrimid increased approximately 20-fold with the addition of 50 wt % PIM-EA(H2)-TB. Mixed gas permeation measurements showed a slightly stronger pressure dependence for selectivity of separation of the CO2/CH4 mixture as compared to the CO2/N2 mixture, particularly for both the blended membrane and the pure PIM. The mixed gas selectivity was slightly higher than for pure gases, and although N2 and CH4 diffusion coefficients strongly increase in the presence of CO2, their solubility is dramatically reduced as a result of competitive sorption. A full analysis is provided of the difference between the pure and mixed gas transport parameters of PIM-EA(H2)-TB, Matrimid®5218 and their 50:50 wt % blend, including unique mixed gas diffusion coefficients.

Association of hard segments in gas separation through polyurethane membranes with aromatic bulky chain extenders

A series of poly(urethane-urea) (PUU) membranes based on contributing hard segments in gas separation were prepared using two novel bulky chain extenders, polytetramethylene-glycol, isophorone and hexamethylene-diisocyanate. The chain extenders were synthesized by cyanuric chloride, aniline/naphthylamine and hydrazine. According to FTIR, AFM and DSC, bulkier PUU membranes showed more phase separation and lower glass transition temperature consistent with higher fractional free volume, which were correlated with single (CO2, CH4, O2 and N2) and mixed (CO2:N2 and CO2:CH4) gas permeation results. The main findings indicate these polyurethanes serve efficiently designed molecular structures favoring bulky hard segments contribution in gas separation. The bulky PUU membranes afford simultaneous increased permeability and selectivity, while maintaining high tensile properties. Enhanced O2/N2 diffusivity selectivity by bulkier PUU and CO2 sorption/desorption study by Ellipsometry confirmed hard segments’ association, too. The bulkiest membrane provided 126% and 54% improvement for single CO2 permeability and CO2/N2 selectivity compared to linear one.

Mixed matrix membranes based on MIL-101 metal–organic frameworks in polymer of intrinsic microporosity PIM-1

This work presents a study on mixed matrix membranes (MMMs) of the polymer of intrinsic microporosity PIM-1, embedding the crystalline Cr-terephthalate metal-organic framework (MOF), known as MIL-101. Different kinds of MIL-101 were used: MIL-101 with an average particle size of ca. 0.2 µm, NanoMIL-101 (ca. 50 nm), ED-MIL-101 (MIL-101 functionalized with ethylene diamine) and NH2-MIL-101 (MIL-101 synthesized using 2-aminoterephthalic acid instead of terephthalic acid). Permeability, diffusion and solubility coefficients and their corresponding ideal selectivities were determined for the gases He, H2, O2, N2, CH4 and CO2 on the “as-cast” samples and after alcohol treatment. The performance of the MMMs was evaluated in relation to the Maxwell model. The addition of NH2-MIL-101 and ED-MIL-101 does not increase the membrane performance for the CO2/N2 and CO2/CH4 separation because of an initial decrease in selectivity at low MOF content, whereas the O2 and N2 permeability both increase for NH2-MIL-101. In contrast, MIL-101 and NanoMIL-101 cause a strong shift to higher permeability in the Robeson diagrams for all gas pairs, especially for CO2, without significant change in selectivity. Unprecedented CO2 permeabilities up to 35,600 Barrer were achieved, which are among the highest values reached with PIM-1 based mixed matrix membranes. For various gas pairs, the permeability and selectivity were far above the Robeson upper bound after alcohol treatment. Short to medium time aging shows that alcohol treated samples with MIL-101 maintain a systematically higher permeability in time. Mixed gas permeation experiments on an aged as-cast sample with 47 vol% MIL-101 reveal that the MMM sample maintains an excellent combination of permeability and selectivity, far above the Robeson upper bound (CO2 = 3500–3800 Barrer, CO2/N2 = 25–27; CO2/CH4 = 21–24). This suggests good perspectives for these materials in thin film composite membranes for real applications.

Hybrid effect of Ag ions and polarized Ag nanoparticles in poly(ethylene oxide)/AgBF4/ionic liquid composites for long‐term stable membranes

Long‐term stability, high propylene/propane selectivity, and high mixed‐gas permeance have been required for the practical application of facilitated olefin transport membranes. In this study, we investigated poly(ethylene oxide) (PEO)/AgBF4/1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIM+BF4−) composite membranes to show high propylene/propane selectivity and permeance with long‐term stability. The PEO/AgBF4/BMIM+BF4− composite membrane showed long‐term stability for more than 100 h with propylene/propane selectivity of 15, and mixed gas permeance of 12 GPU. These results were attributable to the sustainable carrier activity of Ag nanoparticles (NPs) stabilized by ionic liquid BMIM+BF4− when unstable Ag ions were converted into NPs during membrane operation for propylene/propane mixtures. Furthermore, an ionic liquid could plasticize the PEO chains to increase the chain flexibility, resulting in the high permeance despite of the formation of Ag NPs. The chemical and physical properties of the PEO/AgBF4/BMIM+BF4− composite membrane were analyzed by SEM, TEM, FT‐IR, and TGA. POLYM. COMPOS., 40:2745–2750, 2019. © 2018 Society of Plastics Engineers

Poly(1-trimethylsilyl-1-propyne)-Based Hybrid Membranes: Effects of Various Nanofillers and Feed Gas Humidity on CO₂ Permeation.

Poly(1-trimethylsilyl-1-propyne) (PTMSP) is a high free volume polymer with exceptionally high gas permeation rate but the serious aging problem and low selectivity have limited its application as CO2 separation membrane material. Incorporating inorganic nanoparticles in polymeric membranes has been a common approach to improve the separation performance of membranes, which has also been used in PTMSP based membrane but mostly with respect to tackling the aging issues. Aiming at increasing the CO2 selectivity, in this work, hybrid membranes containing four types of selected nanofillers (from 0 to 3D) were fabricated using PTMSP as the polymer matrix. The effects of the various types of nanofillers on the CO2 separation performance of the resultant membranes were systematically investigated in humid conditions. The thermal, chemical and morphologic properties of the hybrid membranes were characterized using TGA, FTIR and SEM. The gas permeation properties of the hybrid membranes were evaluated using mixed gas permeation test with the presence of water vapour to simulate the flue gas conditions. Experiments show that the addition of different fillers results in significantly different separation performances; The addition of ZIF-L porous 2D filler improves the CO2/N2 selectivity at the expenses of CO2 permeability, while the addition of TiO2, ZIF-7 and ZIF-8 increases the CO2 permeability but the CO2/N2 selectivity decreases.

A Novel Time Lag Method for the Analysis of Mixed Gas Diffusion in Polymeric Membranes by On-Line Mass Spectrometry: Pressure Dependence of Transport Parameters.

This paper presents a novel method for transient and steady state mixed gas permeation measurements, using a quadrupole residual gas analyser for the on-line determination of the permeate composition. The on-line analysis provides sufficiently quick response times to follow even fast transient phenomena, enabling the unique determination of the diffusion coefficient of the individual gases in a gas mixture. Following earlier work, the method is further optimised for higher gas pressures, using a thin film composite and a thick dense styrene-butadiene-styrene (SBS) block copolymer membrane. Finally, the method is used to calculate the CO2/CH4 mixed gas diffusion coefficients of the spirobisfluorene-based polymer of intrinsic microporosity, PIM-SBF-1. It is shown that the modest pressure dependence of the PIM-SBF-1 permeability can be ascribed to a much stronger pressure dependence of the diffusion coefficient, which partially compensates the decreasing solubility of CO2 with increasing pressure, typical for the strong sorption behaviour in PIMs. The characteristics of the instrument are discussed and suggestions are given for even more versatile measurements under stepwise increasing pressure conditions. This is the first report on mixed gas diffusion coefficients at different pressures in a polymer of intrinsic microporosity.

Pebax/ionic liquid modified graphene oxide mixed matrix membranes for enhanced CO2 capture

The development of mixed matrix membranes (MMMs) is mostly challenged by the filler dispersion and the fabrication of defect-free membranes with an ultra-thin selective layer. Graphene oxide based MMMs are promising materials for gas separation application. The low filler content and preference of extended GO lamella to align perpendicular to a membrane surface, and hence the gas flow direction permits the development of thin film composite membrane (TFC). Here, facilitated transport MMMs were fabricated by incorporating ionic liquid functionalized graphene oxide (GO-IL) into poly(ether-block-amide) (Pebax 1657). The 1-(3-aminopropyl)-3-methylimidazolium bromide ionic liquid was reacted to graphene oxide sheets, enhancing the CO2 solubility and CO2/gas selectivity of the MMMs. Moreover, hydrogen bonding interactions between the ionic liquid and amide moieties in Pebax provide a homogeneous dispersion of GO-IL. The pure (H2, CO2, O2, N2, CH4) and mixed (CO2/H2, CO2/N2) gas permeability of the membranes were performed at 25 °C and 4 bar. The gas permeability measurements indicate an improvement of over 90% in CO2/N2 selectivity and 50% in CO2 permeability for the GO-IL MMMs compared to the pure Pebax membrane. The resulting TFC membranes showed high CO2 permeance up to 900 GPU (10−6 cm3 (STP) cm−2 s−1 cm Hg−1) and the CO2/N2 and CO2/H2 selectivities of about 45 and 5.8, respectively. Our finding underlines the importance of GO-IL nanosheet to design high selective thin film membranes, providing a direction to fulfil the concept of mixed matrix membranes for practical applications.

Zeolite-like MOF nanocrystals incorporated 6FDA-polyimide mixed-matrix membranes for CO2/CH4 separation

MOF mixed-matrix membranes (MMMs) are regarded as promising candidates for energy-efficient natural gas purification. This work reports the fabrication of high-performance 6FDA-polyimide MMMs, based on the incorporation of zeolite-like MOF (ZMOF) as fillers, and their associated permeation studies for CO2/CH4 separation. To eliminate micron-sized crystals, a facile repeating sedimentation approach was used to harvest nanocrystals from the as-synthesized bulk ZMOF crystalline powder material. This enables the deployment of ZMOF nanocrystals with relatively uniform dimension and morphology in the polymer matrix. Typical 6FDA-polyimides encompassing distinct diamine moieties (6FDA-DAM, 6FDA-DETDA-DABA or PDMC) were explored as polymer matrices to disclose the transport property matching the hosted ZMOF filler. Mixed-gas permeation measurements revealed that the incorporation of the ZMOF filler affords a concurrent enhancement of the CO2 permeability and the CO2/CH4 selectivity for the three tested 6FDA-polyimides. Particularly, the highly permeable 6FDA-DAM showed a considerably enhanced performance for CO2/CH4 that transcends the 2008 Robeson upper-bound. Detailed analysis of the sorption data and diffusion coefficients suggest that the enhanced transport property in the ZMOF-based MMM is plausibly attributed to the combination of the higher CO2 sorption capacity and selectivity, and favorable gas diffusivity via the CO2-philic framework of ZMOF in moderately confined pores.

The performance of affordable and stable cellulose-based poly-ionic membranes in CO2/N2 and CO2/CH4 gas separation

The majority of commercial membrane units for large-scale natural gas sweetening are based on cellulose acetate (CA). However, the low selectivity and risk for and plasticisation affect adversely the performance of CA-based systems. Herein, we present a new class of CA-derived poly(ionic liquid) (PIL) as a thin film composite (TFC) membrane for CO2 separations. CA is modified with pyrrolidinium cations through alkylation of butyl chloride, substituting the hydroxyl group in the polymer backbone, and further anion exchange to bis(trifluoromethylsulfonyl)imide, P[CA][Tf2N]. The synthesised PIL material properties are extensively studied. The CO2 separation performance of the newly synthesised materials is evaluated by gravimetric gas sorption experiments, single gas time-lag experiments on thick membranes, and mixed-gas separation experiments on TFC membranes. The results are compared to the parent material (CA) as well as a reference PIL (poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl)imide (P[DADMA][Tf2N])). The ideal CO2/N2 sorption selectivity of P[CA][Tf2N] is constant up to 10 bar. The single gas transport measurements in P[CA][Tf2N] reveal improved ideal CO2 selectivity for the CO2/N2 gas pair and increased CO2 permeability for the CO2/CH4 gas pair compared to the reference PIL. Mixed-gas permeation tests demonstrated that P[CA][Tf2N]-based membranes with a 5 µm thick selective layer has a two-fold higher CO2 flux compared to conventional CA. These results present CA modification into PILs as a successful approach promoting the higher permeate flows and improved process stability in a wide range of concentrations and pressures of CO2/N2 and CO2/CH4 gas mixtures.

Pentiptycene-Based Polyurethane with Enhanced Mechanical Properties and CO2-Plasticization Resistance for Thin Film Gas Separation Membranes.

The development of thin film composite (TFC) membranes offers an opportunity to achieve the permeability/selectivity requirements for optimum CO2 separation performance. However, the durability and performance of thin film gas separation membranes are mostly challenged by weak mechanical properties and high CO2 plasticization. Here, we designed new polyurethane (PU) structures with bulky aromatic chain extenders that afford preferred mechanical properties for ultra-thin-film formation. An improvement of about 1500% in Young's modulus and 600% in hardness was observed for pentiptycene-based PUs compared to the typical PU membranes. Single (CO2, H2, CH4, and N2) and mixed (CO2/N2 and CO2/CH4) gas permeability tests were performed on the PU membranes. The resulting TFC membranes showed a high CO2 permeance up to 1400 GPU (10-6 cm3(STP) cm-2 s-1 cmHg-1) and the CO2/N2 and CO2/H2 selectivities of about 22 and 2.1, respectively. The enhanced mechanical properties of pentiptycene-based PUs result in high-performance thin membranes with the similar selectivity of the bulk polymer. The thin film membranes prepared from pentiptycene-based PUs also showed a twofold enhanced plasticization resistance compared to non-pentiptycene-containing PU membranes.

A novel time lag method for the analysis of mixed gas diffusion in polymeric membranes by on-line mass spectrometry: Method development and validation

A novel method to determine the individual diffusion coefficients of gases in a mixture during their permeation through polymeric membranes is described. The method was developed in two independent laboratories, using rubbery Pebax® and glassy Hyflon® AD60X membrane samples as standards, and validated using the Tröger's base containing Polymer of Intrinsic Microporosity, PIM-EA-TB. Monitoring of the permeate composition in real time by a quadrupole mass spectrometer allowed the analysis of the permeation transient for gas mixtures. Two operation modes, either with a vacuum in the permeate and a direct connection to the mass spectrometer via a heated restriction, or using a sweeping gas and a heated capillary sample inlet, give excellent agreement with the traditional time lag method for single gases. A complete overview of the method development, identification of the critical parameters, instruments calibration, data elaboration and estimation of the experimental accuracy are provided. Validation with PIM-EA-TB, shows that the method can also successfully detect anomalous phenomena, related to pressure and concentration dependency of the transport properties, physical aging or penetrant-induced dilation. Rapid online analysis of the permeate composition makes the method also very suitable for routine mixed gas permeability measurements.

Post-crosslinking of triptycene-based Tröger's base polymers with enhanced natural gas separation performance

A novel triptycene-based diamine, 2,6-diaminotriptycene-14-carboxylic acid, was synthesized and used for preparing carboxylic acid containing triptycene-based Tröger's base copolymers, CoPIM-TB-1 and CoPIM-TB-2, with another diamine monomer, 2,6-diaminotriptycene. The copolymers were subsequently post-crosslinked by glycidol to form C-CoPIM-TB-1 and C-CoPIM-TB-2. Glycidol crosslinking greatly impeded inter-chain mobility of the triptycene-based copolymers and subsequently restricted both physical aging rate and CO2 induced plasticization. Gas permeabilities of 40 days old C-CoPIM-TB-2 film decreased by 7%, 5%, and 9%, to gases H2, CO2, and O2, respectively, which were slower than those of the uncrosslinked PIM-Trip-TB polymer of which permeabilities decreased by 21%, 42%, and 30%, respectively. Mixed gas permeation results showed no CO2 induced plasticization at a CO2 partial pressure up to 20 atm. Moreover, separation performance of C-CoPIM-TB-1 and C-CoPIM-TB-2 went over the Robeson 2008 upper bounds for gas pairs including O2/N2, CO2/CH4, CO2/N2 and H2/N2. All these results indicated a great potential for the post-crosslinked Triptycene-Based Tröger's Base polymers for natural gas sweetening.

Nafion/PEG hybrid membrane for CO2 separation: Effect of PEG on membrane micro-structure and performance

In the present work, PEGDME with different molecular weight (Mn ∼ 250 and 500 g/mol) was added into Nafion-based membranes as CO2-philic additive, aiming at improving their CO2 capture performance. The physical, chemical and morphological characteristics of the hybrid membranes were thoroughly investigated using different techniques, including TGA, XRD, SEM and FTIR. The gas transport properties were studied by means of mixed gas permeation tests at different relative humidity conditions. CO2 permeability is greatly enhanced upon the addition of the PEGDME. The addition of 40 wt% PEGDME 250 into the Nafion matrix shows a CO2 permeability of 57.4 Barrer at the dry state, which is 36 folds higher than the pristine Nafion. The presence of water vapor in the gaseous streams further enhances the CO2 permeability and CO2/N2 selectivity, reaching a value of 446 Barrer and 37, respectively, under fully saturated conditions. However, the further increase of the PEGDME content in the Nafion matrix leads to undesirable micro phase separation (defects were observed from the morphological analysis), causing serious loss of the selectivity. Finally, in order to improve the theoretical understanding of the transport mechanism, a modified Maxwell model was successfully applied to describe the separation performances of the resulted Nafion/PEGDME hybrid membrane. The model results suggest that an interconnected CO2-philic structure is obtained upon the addition of PEGMDE and water to the ionomer matrix, forming preferential pathways for gas permeation able to enhance the membrane performance.

Preparation and gas permeation of crown ether-containing co-polyimide with enhanced CO2 selectivity

In present work, crown ether-containing co-polyimide with improved gas permselectivity was developed for CO2/N2 and CO2/CH4 separation. Crown ether segment grants the co-polyimide material good affinity with CO2 as well as strong rigidity of polymer chain. This co-polyimide was prepared by the condensation polymerization and chemical imidization of 4, 4-hexafluoro-isopropylidene diphthalic anhydride, 4, 4′-diaminodiphenylmethane and trans-di(aminobenze)-18-C-6 (trans-DAB18C6). The synthesized materials were characterized by FT-IR, 1H NMR, XRD, TGA, DSC, GPC and electronic tensile machine. The fractional free volume (FFV) and fractional accessible volume (FAV) were calculated with molecular dynamics simulations. The mixed-gas permeation properties of the co-polyimide membranes were investigated to inspect the influence of trans-DAB18C6 content and feed gas pressure. Effects of testing temperature and humidity, casting solvent on membrane with 25mol% trans-DAB18C6 were investigated. The molecular dynamics simulations results showed that （FAV）CO2 decreased, while the ratios of （FAV）CO2/（FAV）N2 and （FAV）CO2/（FAV）CH4 increased progressively with trans-DAB18C6 content. The CO2 permeability increased firstly, and decreased subsequently with trans-DAB18C6 content. At the same time, both CO2/N2 and CO2/CH4 selectivities increased progressively. The co-polyimide membrane with 25mol% trans-DAB18C6 displayed the maximum CO2 permeability of 109.0 barrer and CO2/CH4 selectivity of 92.7, which surpassed the 2008 Robeson upper bound. The long term operation stability study demonstrated that the membrane had good stability.

Mixed matrix membranes based on amine and non-amine MIL-53(Al) in Pebax® MH-1657 for CO 2 separation

Abstract Mixed matrix membranes (MMM) based on poly(ether-b-amide) or Pebax® as the matrix and MIL-53(Al)/NH2-MIL-53(Al) metal–organic frameworks (MOF) as fillers were prepared by solution casting. The objective of the work was to determine the effect of MOF functionalization and concentration on the permeability and selectivity of different gases (CH4, N2, H2 and CO2). Scanning electron microscopy (SEM) confirmed that good particle dispersion up to the optimum content was obtained, while Fourier transform infrared spectroscopy (FTIR) confirmed the successful MOF inclusion in MMM. The MMM thermal and mechanical stability were verified by thermogravimetric (TGA) and dynamic mechanical (DMA) analyses, respectively. Finally, the gas separation performances were investigated via single gas and mixed gas permeation tests at 35 °C and 10 bar. The results show that CO2 single gas permeability, as well as CO2/CH4 and CO2/N2 ideal selectivity, were enhanced by introducing either MIL-53(Al) or NH2-MIL-53 (Al), while the highest CO2 permeability (149 Barrer) was obtained at 10 wt% NH2-MIL-53 with a 174% improvement over the neat Pebax® value. The highest ideal selectivity for CO2/CH4 and CO2/N2 was 23.3 (51% increase) and 59.4 (49% increase) also at 10 wt% MIL-53, respectively. Higher CO2 permeability and selectivity was attributed to high porosity introduced by the presence of MOF, as well as the selective adsorption of CO2 on MOF. For mixed gas results, it was found that 20 wt% NH2-MIL-53 had significant CO2/CH4 separation performance, particularly at low CO2 volume fraction (20 vol%) with a separation factor as high as 69.4. Overall, the results showed that MOF surface modification can be necessary under specific conditions.

Effect of a cyclic heating process on the CO 2 /N 2 separation performance and structure of a ceramic nanoporous membrane supporting the ionic liquid 1-methyl-3-octylimidazolium tricyanomethanide

This work presents an investigation of the CO2 and N2 mixed-gas permeation rates through a supported ionic liquid membrane (SILM) developed on a ceramic composite nanofiltration substrate with a separation layer pore size of 10 nm. The ionic liquid 1-methyl-3-octylimidazolium tricyanomethanide was used as supported liquid phase. The hybrid membrane was subjected to a cyclic heating process including isothermal steps of 180 °C, under inert gas flow. In this context, the effect of temperature (over the range of 25–180 °C) and feed composition on the permeation properties and CO2/N2 separation performance was studied prior to and after completion of each heating cycle. For all heating cycles, the highest CO2/N2 selectivity values (up to 50.4) were provided at ambient temperature unlike to CO2 permeance that was favored by elevation of temperature, reaching to 2.48 · 10−9 mol·m−2·s−1·Pa−1 at 180 °C. Thermal analysis by means of DSC and TGA investigations allowed to determine the physical state and thermal stability of the immobilized IL phase, thereby providing a better understanding of the determined gas permeation properties. Confinement into the nanopores of the developed SILM substantially affected the thermal behaviour and assisted decomposition of the ionic liquid phase upon heat treatment. UV/Vis spectroscopy indicated formation of functionalized by-products during prolonged periods of heating at 180 °C that could form stable chemical complexes with CO2 molecules, thus drastically affecting both CO2 solubility and diffusivity, and CO2/N2 separation efficiency.

Effect of Ethylene Oxide Functional Groups in PEBA-CNT Membranes on CO2/CH4 Mixed Gas Separation

Poly (ether-block-amide) /poly (ethylene glycol)/ carbon nanotubes mixed matrix membranes have been successfully fabricated using solvent evaporation method to determine the effect of ethylene oxide groups on the performance of produced membranes. The effects of CNTs (2-8 wt%) and PEG (up to 50 wt%)were investigated in both single and mixed gas test setup in different temperature and pressure. Finally the membranes were structurally characterized using Scanning Electron Microscopy, X-Ray Diffraction, Fourier Transform Infrared Spectroscopy, and Atomic Force Microscopy.Results showed that addition of carbon nanotubes enhanced the gas separation performance of membranes and presences of ether groups in poly ethylene glycol improved the CO2 permeability. Membrane containing 8 wt % carbon nanotubes and 50 wt % poly ethylene glycol showed the best performance with CO2/CH4 selectivity of 45 and CO2permeability of 302 at pressure of 14 bars. Also, mixed gas permeation experiments were carried out and results showed dramatic decrease in CO2 selectivity due to membrane plasticizing. The permeability of CO2 in mixed gas test for membrane containing 50 wt% pol ethylene glycol and 8 wt% was 193 with CO2/CH4 selectivity of 19 in room temperature. Furthermore, membranes produced by 6 and 8 wt% carbon nanotubes and 50 wt% poly ethylene glycol placed above Robeson’s trade-off line. The effect of temperature on performance of fabricated membrane was finally investigated. Results showed an increase in permeability and decrease in selectivity for all membranes.

Facilitated olefin transport through membranes consisting of partially polarized silver nanoparticles and PEMA-g-PPG graft copolymer

We report the preparation of solid-state facilitated olefin transport membranes based on a low-cost, one-pot, room-temperature synthesized graft copolymer, i.e., poly(ethylene-alt-maleic anhydride)-g-O-(2-aminopropyl)-O′-(2-methoxyethyl) polypropylene glycol (PEMA-g-PPG). An electron acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), was employed to activate the surface of the silver nanoparticles (AgNPs), leading to partial polarization. The AgNPs interacted with TCNQ as well as the PEMA-g-PPG graft copolymer to form facilitated olefin transport membranes, as characterized by Fourier transform infrared spectroscopy, UV–vis spectroscopy, and X-ray photoelectron spectroscopy. The PEMA-g-PPG/AgNP membrane activated by TCNQ showed long-term stability (with a mixed gas permeance of 7.8 GPU and propylene/propane selectivity of 17.5) of up to 100h, while that without TCNQ showed poor stability. The membrane based on PEMA-g-PPG showed better performance than those based on conventional matrices of poly(ethylene oxide) (PEO), poly(vinyl pyrrolidone) (PVP), or poly(ether-block-amide) (PEBAX).