Gas permeability and permselectivity of plasma‐treated polypropylene membranes

The effects of NH₃‐plasma and N₂‐plasma treatment on rubbery polypropylene (PP) membrane upon permeation behavior for CO₂, O₂, and N₂ were investigated from their permeability measurements. The NH₃‐plasma and N₂‐plasma treatment on PP membranes could increase both the permeability coefficient for CO₂ and the ideal separation factor for CO₂ relative to N₂. For O₂ transport, both the permeability coefficient for O₂ and the ideal separation factor for O₂ relative to N₂ also increased. NH₃‐plasma and N₂‐plasma treatment on PP membranes possibly brings about an augmentation of permeability for CO₂ and permselectivity of CO₂ relative to N₂ simultaneously, but unfortunately the plasma‐treated PP membrane does not reach the level of CO₂ separation membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Gas permeability and permselectivity of plasma‐treated polyethylene membranes

The effects of NH₃‐plasma and N₂‐plasma treatments on rubbery polyethylene (PE) membranes on the permeation behavior for carbon dioxide (CO₂), O₂, and N₂ were investigated with permeability measurements. The NH₃‐plasma and N₂‐plasma treatments on PE membranes increased both the permeation coefficient for CO₂ and the ideal separation factor for CO₂ with respect to N₂. For O₂ transport, both the permeation coefficient for O₂ and the ideal separation factor for O₂ with respect to N₂ were increased. NH₃‐plasma and N₂‐plasma treatments on polymer membranes possibly bring about an augmentation of permeability and permselectivity simultaneously. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 383–387, 2006     

Gas permeation performance of cellulose hollow fiber membranes made from the cellulose/N‐methylmorpholine‐N‐oxide/H2O system

Cellulose hollow fiber membranes (CHFM) were prepared using a spinning solution containing N‐methylmorpholine‐N‐oxide as solvent and water as a nonsolvent additive. Water was also used as both the internal and external coagulant. It was demonstrated that the phase separation mechanism of this system was delayed demixing. The CHFM was revealed to be homogeneously dense structure after desiccation. The gas permeation properties of CO₂, N₂, CH₄, and H₂ through CHFM were investigated as a function of membrane water content and operation pressure. The water content of CHFM had crucial influence on gas permeation performance, and the permeation rates of all gases increased sharply with the increase of membrane water content. The permeation rate of CO₂ increased with the increase of operation pressure, which has no significant effect on N₂, H₂, and CH₄. At the end of this article a detailed comparison of gas permeation performance and mechanism between the CHFM and cellulose acetate flat membrane was given. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1873–1880, 2004     

Mixed matrix membranes of Pebax1657 loaded with iron benzene‐1,3,5‐tricarboxylate for gas separation

Mixed matrix membranes offer major advantages in gas separation processes due to desirable properties found in both organic and inorganic membranes. In this study, a novel mixed matrix membrane was prepared for such application by incorporating iron benzene‐1,3,5‐tricarboxylate (Fe‐BTC) into the poly(amide‐6‐b‐ethylene oxide) (Pebax1657) polymer. Membranes with various loadings of 5, 10, and 20 wt% Fe‐BTC in the polymer matrix were fabricated to investigate the effect of filler loading on the membrane performance. Membranes, prepared by solution‐casting were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared, X‐ray diffraction, and tensile test. Pure gas separation of CO₂, CH₄, and N₂ and ideal gas selectivity of CO₂/CH₄ and CO₂/N₂ were performed and permeation tests were carried out under 4, 8, and 12 bar pressures. Results show that adding Fe‐BTC into the Pebax1657 matrix improved both permeability and selectivity of the filled membranes. For instance, 10 wt% loading of Fe‐BTC into the Pebax1657 matrix led to CO₂ permeability increase of 49% as well as CO₂/CH₄ and CO₂/N₂ selectivities enhancements of about 36% and 16%, respectively. POLYM. COMPOS., 38:1363–1370, 2017. © 2015 Society of Plastics Engineers     

Matrimid‐based carbon tubular membranes: The effect of the polymer composition

In this article, we present a development study of new membrane materials and enhancements of productive membranes to improve the current performance of polymeric membranes. Carbon membranes are a promising material for this matter as they offer an improvement in the gas‐separation performance and exhibit a good combination of permeability and selectivity. Carbon membranes produced from the carbonization of polymeric materials have been reported to be effective for gas separation because of their ability to separate gases with almost similar molecular sizes. In this study, a carbon support membrane was prepared with Matrimid 5218 as a polymeric precursor. The polymer solution was coated on the surface of a tubular support with the dip‐coating method. The polymer tubular membrane was then carbonized under a nitrogen atmosphere with different polymer compositions of 5–18 wt %. The carbonization process was performed at 850°C at a heating rate of 2°C/min. Matrimid‐based carbon tubular membranes were fabricated and characterized in terms of their structural morphology, thermal stability, and gas‐permeation properties with scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and a pure‐gas‐permeation system, respectively. Pure‐gas‐permeation tests were performed with the pure gases carbon dioxide (CO₂) and N₂ at room temperature at a pressure of 8 bar. On the basis of the results, the highest CO₂/N₂ selectivity of 75.73 was obtained for the carbon membrane prepared with a 15 wt % polymer composition. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42394.     

Enhanced CO2 separation performance for tertiary amine‐silica membranes via thermally induced local liberation of CH3Cl

A facile method for the fabrication of amine‐silica membranes with enhanced CO₂ separation performance was proposed via the thermally induced liberation of small molecules from quaternary ammonium salt. Quaternary ammonium‐silica (QA‐SiO_1.5) xerogel powders/films were fabricated via sol‐gel processing and their thermal stability was systematically studied using thermogravimetric mass spectrometer, Fourier transform infrared, energy dispersive spectroscopy, and positron annihilation lifetime spectroscopy analysis. CO₂ sorption performances of QA‐SiO_1.5 derived xerogel powders were quantitatively compared after assigning their relevant parameters to a dual‐mode sorption model. The gas permeation performances of membranes derived from QA‐SiO_1.5 were evaluated in terms of kinetic diameter and temperature dependence of gas permeance, and activation energy (E_p) required for gas permeation. The results indicate that liberation of the CH₃Cl molecules from these membranes significantly improved both CO₂ permeation and CO₂/N₂ separation capabilities. Therefore, the present study provides insight that should be useful in the development of high‐performance CO₂ separation membranes via the effect of the thermally induced liberation of small molecules. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1528–1539, 2018     

A highly selective polybenzimidazole‐4,4′‐(hexafluoroisopropylidene)bis(benzoic acid) membrane for high‐temperature hydrogen separation

A polymeric gas separation membrane utilizing polybenzimidazole based on 4,4′‐(hexafluoroisopropylidene)bis(benzoic acid) was prepared. The synthesized membrane has an effective permeating area of 8.3 cm² and a thickness of 30 ± 2 µm. Gas permeation properties of the membrane were determined using H₂, CO₂, CO, and N₂ at temperatures ranging from 24°C to 200°C. The PBI‐HFA membranes not only exhibited excellent H₂ permeability, but it also displayed superior gas separation performance particularly for H₂/N₂ and H₂/CO₂. The permeation parameters for both permeability and selectivity [ and α(H₂/N₂); and α(H₂/CO₂)] obtained for the new material were found to be dependent on trans‐membrane pressure difference as well as temperature, and were found to surpass those reported by Robeson in 2008. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42371.     

Polydimethylsiloxane/postmodified MIL‐53 composite layer coated on asymmetric hollow fiber membrane for improving gas separation performance

Composite layer containing postmodified MIL‐53 (P‐MIL‐53) was exploited to be coated on as‐fabricated asymmetric hollow fiber membrane for improving gas separation performance. The morphology and pore size distribution of P‐MIL‐53 particles were characterized by SEM and N₂ adsorption isotherm. The EDX mapping and FTIR spectra were performed to confirm the presence of P‐MIL‐53 deposited on the outer surface of hollow fiber membranes. The results of pure gas permeation measurement indicated that incorporation of P‐MIL‐53 particles in coating layer could improve permeation properties of hollow fiber membranes. By varying coating times and P‐MIL‐53 content, the membrane coated with PDMS/15%P‐MIL‐53 composite by three times achieved best performance. Compared to pure PDMS coated membrane, CO₂ permeance was enhanced from 29.96 GPU to 40.24 GPU and ideal selectivity of CO₂/N₂ and CO₂/CH₄ also increased from 23.28 and 26.95 to 28.08 and 32.03, respectively. The gas transport through composite membrane was governed by solution‐diffusion mechanism and CO₂ preferential adsorption of P‐MIL‐53 contributed to considerable increase of CO₂ solubility resulting in accelerated permeation rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44999.     

Preparation,characterization, and applicability of novel calix[4]arene‐based cellulose acetate membranes in gas permeation

Cellulose acetate (CA) is well known glassy polymer used in the fabrication of gas‐separation membranes. In this study, 5,11,17,23‐tetrakis(N‐morpholinomethyl)‐25,26,27,28‐tetrahydroxycalix[4]arene (CL) was blended with CA to study the gas‐permeation behavior for CO₂, N₂, and CH₄ gases. We prepared the pure CA and CA/CL blended membranes by following a diffusion‐induced phase‐separation method. Three different concentrations of CL (3, 10, and 30 wt %) were selected for membrane preparation. The CA/CL blended membranes were then characterized via Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X‐ray diffraction analysis. The homogeneous blending of CL and CA was confirmed in the CA/CL blended membranes by both SEM and AFM analysis. In addition to this, the surface roughness of the CA/CL blended membranes also increased with increasing CL concentration. FTIR analysis described the structural modification in the CA polymer after it was blended with CL too. Furthermore, CL improved the tensile strength of the CA membrane appreciably from 0.160 to 1.28 MPa, but this trend was not linear with the increase in the CL concentration. CO₂, CH₄, and N₂ gases were used for gas‐permeation experiments at 4 bars. With the permeation experiments, we concluded that permeability of N₂ was higher in comparison to those of CO₂ and CH₄ through the CA/CL blended membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39985.     

CO2‐facilitated transport through poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate)/polysulfone composite membranes

Poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate) (VSA–SA)/polysulfone (PS) composite membranes were prepared for the separation of CO₂. VSA–SA contained secondary amines and carboxylate ions that could act as carriers for CO₂. At 20°C and 1.06 atm of feed pressure, a VSA–SA/PS composite membrane displayed a pure CO₂ permeation rate of 6.12 × 10^?6 cm³(STP)/cm² s cmHg and a CO₂/CH₄ ideal selectivity of 524.5. In experiments with a mixed gas of 50 vol % CO₂ and 50 vol % CH₄, at 20°C and 1.04 atm of feed pressure, the CO₂ permeation rate was 9.2 × 10^?6 cm³ (STP)/cm² s cmHg, and the selectivity of CO₂/CH₄ was 46.8. Crosslinkages with metal ions were effective for increasing the selectivity. Both the selectivity of CO₂ over CH₄ and the CO₂ permeation rate had a maximum against the carrier concentration. The high CO₂ permeation rate originated from the facilitated transport mechanism, which was confirmed by Fourier transform infrared with attenuated total reflectance techniques. The performance of the membranes prepared in this work had good stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 275–282, 2006     

Modelling of multicomponent gas separation with asymmetric hollow fibre membranes—methane enrichment from biogas

A mathematical model for the dynamic performance of gas separation with high flux, asymmetric hollow fibre membranes was developed considering the permeate pressure build‐up inside the fibre bore and cross flow pattern with respect to the membrane skin. The solution technique provides reliable examination of pressure and concentration profiles along the permeator length (both residue/permeate streams) with minimal effort. The proposed simulation model and scheme were validated with experimental data of gas separation from literature. The model and solution technique were applied to investigate dynamic performance of several membrane module configurations for methane recovery from biogas (landfill gas or digester gas), considering biogas as a mixture of CO₂, N₂ and CH₄. Recycle ratio plays a crucial role, and optimum recycle ratio vital for the retentate recycle to permeate and permeate recycle to feed operation was found. From the concept of two recycle operations, complexities involved in the design and operation of continuous membrane column were simplified. Membrane permselectivity required for a targeted separation to produce pipeline quality natural gas by methane‐selective or nitrogen‐selective membranes was calculated. © 2012 Canadian Society for Chemical Engineering     

Quest for high performance carbon capture membranes: Fabrication of SAPO-34 and CNTs-doped polyethersulfone-based mixed-matrix membranes

Gas separation process is an effective method for capturing and removing CO₂ from post-combustion flue gases. Due to their various essential properties such as ability to improve process efficiency, polymeric membranes are known to dominate the market. Trade-off between gas permeability and selectivity through membranes limits their separation performance. In this study, solution casting cum phase separation method was utilized to create polyethersulfone-based composite membranes doped with carbon nanotubes (CNTs) and silico aluminophosphate (SAPO-34) as nanofiller materials. Membrane properties were then examined by performing gas permeation test, chemical structural analysis and optical microscopy. While enhancing membranes CO₂ permeance, SAPO-34 and CNTs mixture improved their CO₂/N₂ selectivity. By carefully adjusting membrane casting factors such as filler loadings. Using Taguchi statistical analysis, their carbon capture efficiency was improved. The improved mixed-matrix membrane with loading of 5 wt% CNTs and 10 wt% SAPO-34 in PES showed highly promising separation performance with a CO₂ permeability of 319 Barrer and an ideal CO₂/N₂ selectivity of 12, both of which are within the 2008 Robeson upper bound. A better mixed-matrix membrane with outstanding CO₂/N₂ selectivity and CO₂ permeability was produced as a result of the synergistic effect of adding two types of fillers in optimized loading.     

Optimizing membrane synthesis parameters via Taguchi method: An approach to prepare high performance mixed-matrix membranes for carbon capture applications

Mixed-matrix membranes (MMMs) comprising polysulfone (PSF) and zeolite 4A (Z4A) were prepared for carbon capture applications. Membranes of varying compositions were fabricated by solution casting technique. Viscous solutions of dissolved ingredients were cast on a clean glass plate followed by evaporation and drying of prepared membrane. Fabricated composite membranes were subjected to morphological, structural, and permeation analyzes. The morphological results showed a uniform dispersal of zeolite nanoparticles with agglomerates formation at higher nanofiller loadings. The structural analysis corroborated the noninteractive behaviour of organic polymer and inorganic zeolite phases. Permeation results suggested that the fabricated membranes were more permeable to CO₂ gas, which can be described by higher diffusivity and structural affinity for CO₂. Taguchi statistical analysis was employed to optimize carbon capture performance of developed hybrid membranes by carefully controlling the membrane casting parameters such as loading levels of functional nanofiller, sonication time, and drying time of casting solution. The statistical investigation of permeation results suggested the sensitivity of casting parameters on membrane performance in the following manner: zeolite loading > sonication time > drying time. The optimized membrane casting parameters obtained from signal-to-noise ratio analysis performed on Minitab led to synthesis of a composite membrane with both high CO₂/N₂ selectivity and CO₂ permeability. The chosen technique also assisted in justifying the dependence of permeation results on various membrane casting parameters, associating it with the morphological results. The technique also facilitated the optimization of the membrane characteristics and is recommended for future study based on membrane separation processes.     

Preparation of water‐swollen hydrogel membranes for gas separation

Water‐swollen hydrogel (WSH) membranes for gas separation were prepared by the dip‐coating of asymmetric porous polyetherimide (PEI) membrane supports with poly(vinyl alcohol) (PVA)–glutaraldehyde (GA), followed by the crosslinking of the active layer by a solution method. Crosslinked PVA/GA film of different blend compositions (PVA/GA = 1/0.04, 0.06, 0.08, 0.10, 0.12 mol %) were characterized by differential scanning calorimetry (DSC) and their water‐swelling ratio. The swelling behavior of PVA/GA films of different blend compositions was dependent on the crosslinking density and chemical functional groups created by the reaction between PVA and GA, such as the acetal group, ether linkage, and unreacted pendent aldehydes in PVA. The permeation performances of the membranes swollen by the water vapor contained in a feed gas were investigated. The behavior of gas permeation through a WSH membrane was parallel to the swelling behavior of the PVA/GA film in water. The permeation rate of carbon dioxide through the WSH membranes was 10⁵ (cm³ cm^?2 s^?1 cmHg) and a CO₂/N₂ separation factor was about 80 at room temperature. The effect of the additive (potassium bicarbonate, KHCO₃) and catalyst (sodium arsenite, NaASO₂) on the permeation of gases through these WSH membranes was also studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1785–1791, 2001     

Preparation of poly(ether‐block‐amide)/poly(amide‐co‐poly(propylene glycol)) random copolymer blend membranes for CO2/N2 separation

A series of poly(amide‐co‐poly(propylene glycol)) (PA‐PPG) random copolymers with different content of PPG were designed by polycondensation reaction. These random copolymers were blended up to 60% with commercially available Pebax 2533. The blend membranes were characterized by Fourier‐transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), scanning electron microscope (SEM). Gas permeation properties of these blend membranes were investigated using five single‐gases (CO₂, H₂, O₂, CH₄, and N₂) at different temperature of 25–55°C and 1.0 atm. The impacts of content of PA‐PPG with different PPG content and operating temperature on CO₂ separation properties of Pebax/PA‐PPG blend membranes were studied. The results showed that CO₂ permeability gradually increased with the increasing operating temperature, whereas CO₂ permeability gradually decreased with the increase in content of PA‐PPG. CO₂/N₂ selectivity gradually increased with the increase in content of PA‐PPG. In particular, Pebax/PA‐PPG (50)–60% displayed excellent CO₂ and O₂ separation properties (P_CO2 = 79.7 Barrer and P_O2 = 13.6 Barrer, CO₂/N₂ = 34.7 and O₂/N₂ = 5.9) at 25°C and 1.0 atm. POLYM. ENG. SCI., 59:E14–E23, 2019. © 2018 Society of Plastics Engineers     

Metal‐organic framework membrane process for high purity CO2 production

Gas separation by metal‐organic framework (MOF) membranes is an emerging research field. Their commercial application potential is, however, still rarely explored due in part to unsatisfied separation characteristics and difficulty in finding suitable applications. Herein, we report “sharp molecular sieving” properties of high quality isoreticular MOF‐1 (IRMOF‐1) membrane for CO₂ separation from dry, CO₂ enriched CO₂/CH₄, and CO₂/N₂ mixtures. The IRMOF‐1 membranes exhibit CO₂/CH₄ and CO₂/N₂ separation factors of 328 and 410 with CO₂ permeance of 2.55 × 10^?7 and 2.06 × 10^?7 mol m^?2 s^?1 Pa^?1 at feed pressure of 505 kPa and 298 K, respectively. High grade CO₂ is efficiently produced from the industrial or lower grade CO₂ feed gas by this MOF membrane separation process. The demonstrated “sharp molecular sieving” properties of the MOF membranes and their potential application in production of value‐added high purity CO₂ should bring new research and development interest in this field. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3836–3841, 2016     

Size effects of graphene oxide on mixed matrix membranes for CO2 separation

Graphene oxide (GO)‐polyether block amide (PEBA) mixed matrix membranes were fabricated and the effects of GO lateral size on membranes morphologies, microstructures, physicochemical properties, and gas separation performances were systematically investigated. By varying the GO lateral sizes (100–200 nm, 1–2 μm, and 5–10 μm), the polymer chains mobility, as well as the length of the gas channels could be effectively manipulated. Among the as‐prepared membranes, a GO‐PEBA mixed matrix membrane (GO‐M‐PEBA) containing 0.1 wt % medium‐lateral sized (1–2 μm) GO sheets showed the highest CO₂ permeation performance (CO₂ permeability of 110 Barrer and CO₂/N₂ mixed gas selectivity of 80), which transcends the Robeson upper bound. Also, this GO‐PEBA mixed matrix membrane exhibited high stability during long‐term operation testing. Optimized by GO lateral size, the developed GO‐PEBA mixed matrix membrane shows promising potential for industrial implementation of efficient CO₂ capture. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2843–2852, 2016     

Fabrication of Homogenous Polymer‐Zeolite Nanocomposites as Mixed‐Matrix Membranes for Gas Separation

Interfacial void‐free mixed‐matrix membranes (MMMs) of polyimide (PI)/zeolite were developed using 13X and Linde type A nano‐zeolites and tested for gas separation purposes. Fabrication of a void‐free polymer‐zeolite interface was verified by the decreasing permeability developed by the MMMs for the examined gases, in comparison to the pure PI membrane. The molecular sieving effect introduced by zeolite 13X improved the CO₂/N₂ and CO₂/CH₄ selectivity of the MMMs. Separation tests indicated that the manufactured nanocomposite membrane with 30 % loading of 13X had the highest permselectivity for the gas pairs CO₂/CH₄ and CO₂/N₂ at the three examined feed pressures of 4, 8 and 12 atm.     

Carbon dioxide separation and dry reforming of methane for synthesis of syngas by a dual‐phase membrane reactor

High‐temperature CO₂ selective membranes offer potential for use to separate flue gas and produce a warm, pure CO₂ stream as a chemical feedstock. The coupling of separation of CO₂ by a ceramic–carbonate dual‐phase membrane with dry reforming of CH₄ to produce syngas is reported. CO₂ permeation and the dry reforming reaction performance of the membrane reactor were experimentally studied with a CO₂–N₂ mixture as the feed and CH₄ as the sweep gas passing through either an empty permeation chamber or one that was packed with a solid catalyst. CO₂ permeation flux through the membrane matches the rate of dry reforming of methane using a 10% Ni/γ‐alumina catalyst at temperatures above 750°C. At 850°C under the reaction conditions, the membrane reactor gives a CO₂ permeation flux of 0.17 mL min^?1 cm^?2, hydrogen production rate of 0.3 mL min^?1 cm^?2 with a H₂ to CO formation ratio of about 1, and conversion of CO₂ and CH₄, respectively, of 88.5 and 8.1%. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2207–2218, 2013     

Mechanism of gas transport of NH3‐plasma‐treated poly(phenylene oxide) membrane

The effect of NH₃‐plasma treatment on glassy poly(phenylene oxide) (PPO) membranes on the diffusion process for carbon dioxide (CO₂), oxygen (O₂), and nitrogen (N₂) was investigated from the permeability measurements. The sorption equilibria and permeation behavior for O₂ and CO₂ in untreated PPO membranes were simulated well in terms of the dual‐mode sorption and mobility model. For O₂ transport, NH₃‐plasma treatment on PPO membrane had an influence on the diffusion process of Henry's law species, whereas for CO₂ transport, it promoted the transport of Langmuir mode, presumably through an increased Langmuir capacity constant for CO₂. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1845–1852, 2000