Influence of novel surface modifying macromolecules and coagulation media on the gas permeation properties of different polymeric gas separation membranes

Integrally skinned asymmetric membranes for the separation of O₂ and N₂ were fabricated by the phase inversion technique from polysulfone, polyetherimide, and polyimide. Two types of surface modifying macromolecules (SMMs) including hydrophilic SMM (LSMM) and charged SMM (cSMM) were synthesized and blended with the casting solution to modify the membrane surface. The cast film was then immersed in the first coagulant alcohol (methanol, ethanol, or isopropanol) for a predetermined period, before being immersed in the second coagulant (water). The SMMs used in these experiments were laboratory synthesized by the two‐step process of polyurethane prepolymer synthesis and end capping, before being characterized by differential scanning calorimetry. Their molecular structure was determined from the molecular weight obtained by gel permeation chromatography. The membranes were characterized by contact angle measurement and O₂ and N₂ gas permeation performance. Attempts were made to interpret the gas permeation data by delayed demixing affected by solubility parameters of polymer, solvent, and nonsolvent. Furthermore, the permeation performance of cSMM membranes was interpreted by the solvation of the charged sulfonate groups present in cSMM. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of cellulose buffer layer on synthesis and gas permeation properties of NaA zeolite membrane

NaA zeolite membrane coating was successfully synthesized on a porous alumina substrate by hydrothermal treatment. The effects of synthesis parameters like, seeding type (ex situ, in situ), time, temperature, sol concentration, coating stages, application of intermediate layer, etc. on membrane characteristics were investigated. A continuous membrane was formed on a seeded substrate. Surface seeding (ex situ crystallization) not only accelerates the zeolite crystallization process on the support surface, but can also enhance the formation of homogeneous NaA zeolite layer. The NaA zeolite membrane with a synthesis time of 4 h shows the best microstructure and the quality of membrane was improved by employing the multi-stage coating. But the main problem associated with membrane synthesis was crack formation, and it can be reduced by applying intermediate layer, between support surface and seed layer. A thin cellulose layer was applied to the support surface before applying seed crystals. The performance of the membranes was evaluated by gas permeation measurement. The permeance of O₂, N₂ decreased as kinetic diameter of gases increased. The permselectivity of O₂/N₂ was 1.9–2.34. This value showed the molecular sieving effect of NaA zeolite membrane.     

The growth of SAPO 34 membrane layer on support surface for gas permeation application

The formation stage of SAPO 34 zeolite membrane on a tubular mullite support has been investigated. XRD, FESEM, IR and EDAX analysis techniques were used to explain the changes in crystallization stages as well as formation of membrane on tubular clay-alumina support with time. From the studies, the evidence tends to support that crystallization of SAPO 34 started from initial gel, proceed through cluster formation and accumulation followed by segregation and crystallization process. The study also showed the gradual incorporation of Si into AlPO₄ phase and form cubical CHA phase after 120 h of synthesis time.Single gas permeation of CO₂ and H₂ showed that upto 300 KPa of feed pressure permeability of CO₂ is more than that of H₂. But at higher pressure the results show the reverse trend, flux is more for H₂. This may be due to more adsorption of CO₂ on SAPO 34 surface and less desorption from the surface than hydrogen with increasing pressure. The selectivity of H₂/CO₂ increases from 0.85 to 2.67.     

Some mechanistic insights into the action of facilitating agents on gas permeation through glassy polymeric membranes

Incorporation of facilitating agents is one of the promising strategies being researched in recent years to cross the Robeson bounds for gas separations using polymeric membranes. The ways in which such inclusions modify the performance of membranes are not always clear. Here, we study the performance of two glassy membranes, Polyfurfuryl alcohol and Polysulfone, in O₂/N₂ and CO₂/N₂ separations, with Cobalt phthalocyanine in insoluble and solubilized forms as the facilitating agent. The results show that in general, three effects are important: (1) a barrier effect, (2) a facilitation effect, and (3) morphological effects on the polymer matrix due to an incompatibility between the particles and the polymer. These results provide some insight into the action of facilitating agents in soluble and insoluble form, when used as membrane additives. © 2017 American Institute of Chemical Engineers AIChE J, 63: 186–199, 2018     

Synthesis and gas permeation properties of a single layer PDMS membrane

In this work, a new polydimethylsiloxane (PDMS) membrane was synthesized and its sorption, diffusion, and permeation properties were investigated using H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ as a function of pressure at 35°C. PDMS, as a rubbery membrane, was confirmed to be more permeable to more condensable gases such as C₃H₈. The synthesized PDMS membrane showed much better gas permeation performance than others reported in the literature. Based on the sorption data of this study and other researchers' works, some valuable parameters such as Flory‐Huggins (FH) interaction parameters, χ, etc., were calculated and discussed. The concentration‐averaged FH interaction parameters of H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ in the synthesized PDMS membrane were estimated to be 2.196, 0.678, 0.165, 0.139, 0.418, and 0.247, respectively. Chemical similarity of O₂, CH₄, and C₃H₈ with backbone structure of PDMS led to lower χ values or more favorable interactions with polymer matrix, particularly for CH₄. Regular solution theory was applied to verify correctness of evaluated interaction parameters. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration, which indicated the plasticization effect of these gases over the range of penetrant concentration studied. According to high C₃H₈/gas ideal selectivity values, the synthesized PDMS membrane is recommended as an efficient membrane for the separation of organic vapors from noncondensable gases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

支撑层对硅橡胶复合膜渗透汽化分离性能的影响

引言 为了扩大渗透汽化技术的应用领域,科研工作者需要进一步增强渗透汽化膜的分离性能.从工业化的观点而言,用于实际应用的渗透汽化膜大多是复合膜,它由选择层(或分离层)和支撑层组成.一般认为,选择层决定着复合膜的选择性和通量,支撑层起支撑和机械稳定作用.Nijhuis[1]在从甲苯-水体系中分离甲苯的过程中对均质膜和以聚砜为支撑层的复合膜的分离性能进行了比较;Sturken[2]分别用聚醚酰亚胺和聚偏氟乙烯为支撑层的硅橡胶膜从二氯乙烷-水体系中提取二氯乙烷,他们得到了相同的结论:支撑层的影响可以忽略.然而Scholz[3],Heinzelmann[4],Rautenbach[5],Borges[6],Vankelecom[7],Farooq[8],Lipnizki[9]等均在各自研究中发现,由于基膜和分离层的物理化学性质以及制膜方法等众多因素的存在使得支撑层在一定程度上影响复合膜的分离性能;Feng[10]对均质硅橡胶膜和有微孔支撑层的硅橡胶复合膜的分离性能进行了比较,发现均质硅橡胶膜优先透过异丙醇,而有微孔亲水性支撑层的硅橡胶复合膜则优先透过水,这表明在一定的情况下,支撑层甚至起主导作用并能够决定复合膜的分离性能.因此,通过系统研究以不同多孔材料为支撑层的复合膜对有机物-水溶液的分离性能的影响,能够找到最优的复合膜支撑层,从而能够提高复合膜的分离性能.然而,至今关于支撑层对渗透汽化膜分离性能影响的系统研究仍相当少.     

Effect of metal‐support interface on hydrogen permeation through palladium membranes

Thin palladium membranes of different thicknesses were prepared on sol‐gel derived mesoporous γ‐alumina/α‐alumina and yttria‐stabilized zirconia/α‐alumina supports by a method combining sputter deposition and electroless plating. The effect of metal‐support interface on hydrogen transport permeation properties was investigated by comparing hydrogen permeation data for these membranes measured under different conditions. Hydrogen permeation fluxes for the Pd/γ‐Al₂O₃/α‐Al₂O₃ membranes are significantly smaller than those for the Pd/YSZ/α‐Al₂O₃ membranes under similar conditions. As the palladium membrane thickness increases, the difference in permeation fluxes between these two groups of membranes decreases and the pressure exponent for permeation flux approaches 0.5 from 1. Analysis of the permeation data with a permeation model shows that both groups of membranes have similar hydrogen permeability for bulk diffusion, but the Pd/γ‐Al₂O₃/α‐Al₂O₃ membranes exhibit a much lower surface reaction rate constant with higher activation energy, due possibly to the formation of Pd‐Al alloy, than the Pd/YSZ/α‐Al₂O₃ membranes. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Influence of binding interface between active and support layers in composite PDMS membranes on permeation performance

Effect of the binding interfaces of composite polydimethylsiloxane (PDMS) membranes on their pervaporation performance was studied. The membranes were made up of PDMS as active skin layer and polysulfone (PSF) or polyamide (PA) as supporting layer. PDMS‐PSF membrane was numbered 1, and PDMS‐PA membrane numbered 2. The pervaporation experiments were carried out by using the composite membranes and dilute ethanol–water mixture. The experimental measurements for the permeation performance under various operating conditions (e.g., feed concentration and temperature) showed that the specific permeation rate of membrane 2 was over membrane 1 by seven times at least. A resistance‐in‐series model was applied to formularize the transport of the permeants. Influence of the binding interfaces between the active skin layer and support layers in these membranes on pervaporation performance was analyzed. The cross section morphology of the membranes and chemical element distribution along membrane thickness were examined by using SEM and EDS. It was found that, although the PDMS intrusion layer into PSF near the interface was only about 2 μm, it gave significant effect on the permeation performance. It implied that the resistance produced by the intrusion layer into PSF was apparently larger than that of PDMS intruding PA and over intrinsic PDMS resistance. These should be probably attributed to structures and formation of the binding interfaces. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2468–2477, 2007     

A “free volume” model of permeation of gas and liquid mixtures through polymeric membranes

A recent “free volume” model of gas permeation (3) has been extended to the transport of gas mixtures through nonporous polymeric membranes. The present model assumes that the rates of transport of the components of a mixture depend on the free volume of the gas-polymer system, and that the effect of these components on the free volume is additive. The latter assumption limits the model to relatively dilute systems, with total penetrant concentrations of perhaps less than 0·2 volume-fraction. The prediction of permeation fluxes and permeability coefficients requires the knowledge of specified free-volume parameters which can be determined from measurements of diffusion coefficients and viscosities of the pure penetrant-polymer systems. When the systems are sufficiently dilute to obey Henry's law, the permeability coefficients for the components of a gas mixture can be predicted using only permeability measurements with the pure components. The extended free-volume model can be applied also to the permeation of liquid mixtures. The theoretical predictions are compared with the results of several experimental studies, and the potential usefulness and limitations of the model are discussed.     

Influence of quench medium on the structure and gas permeation properties of cellulose acetate membranes

Integrally skinned asymmetric cellulose acetate membranes made by the wet phase inversion for removal of CO₂ from natural gas were investigated. The membrane was cast with the membrane-forming systems of cellulose acetate–acetone and quench media, such as methanol, ethanol and isopropanol, respectively, without heat-treating and multistage exchange process. By means of evaluation on separating characteristics of the membrane for CO₂/CH₄, observation of morphologies by scanning electron photomicrographs and analysis of the phase diagrams on the membrane-forming systems, it has shown that the membrane-forming system of cellulose acetate–acetone–methanol is quite suitable to prepare integrally skinned asymmetric cellulose acetate membranes for gas separation with good selectivity CO₂/CH₄ = 30 and flux coefficient = 2.4 × 10⁻⁵ cm³/cm² − s − cm Hg. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1269–1276, 1998     

The effect of intermediate layer on synthesis and gas permeation properties of NaA zeolite membrane

NaA zeolite membrane coating was successfully synthesized on an alumina porous disc by hydrothermal treatment. The effects of synthesis parameters, such as seeding condition (in situ, ex situ), synthesis time, synthesis stages, application of intermediate layer, etc., on membrane characteristics were investigated. Surface seeding accelerates the zeolite crystallization process on the support surface, and also enhances the formation of homogeneous NaA zeolite layer. But the main problem associated with membrane coating synthesis is crack formation. Formation of crack was reduced by applying intermediate layer, between the support surface and seed layer. A thin Boehmite layer was applied to the support surface before applying seed crystals to enhance the adherence between zeolite seed layer and boehmite layer by hydrogen bonding and also to increase the mechanical strength of the membrane layer. The quality of the membrane layer can be improved by employing the multi-stage coating methods. The permeance of O₂, N₂ decreased as kinetic diameter of gases increased, which shows the molecular sieving effect of the NaA membrane. The permselectivity of O₂/N₂ was 1.9–2.0. This value of permselectivity ratio is higher than Knudsen diffusion ratio 0.94; it was also confirmed the molecular sieving properties of synthesized NaA zeolite membrane.     

Effect of glycol and filler types on some polymeric composite properties

Two unsaturated polyesters based on maleic anhydride, phthalic anhydride, and sebasic acid with each of linear 1,6‐hexanediol (PE_L) and cyclic 1,4‐cyclohexanediol (PE_C) were prepared. Their structures were characterized by IR and ¹H NMR spectra. Their composites were prepared by mixing different ratios (60, 70, and 80%) with talc and kaolin with polyester/styrene mixture. The effect of linear and cyclic glycols and the effect of filler type and concentration of these composites were studied in terms of their electrical properties and the hardness before and after aging. The thermal behavior of styrenated polyesters and their composites was studied using thermogravimetric analysis. It has been found that both fillers increase the thermal stability and decrease the weight loss. The permittivity ε′ and the dielectric loss ε″ were measured in the frequency range 100 Hz up to 100 kHz at room temperature 25°C ± 1. The polyester composite samples containing 70% filler lead to good electrical properties in addition to its resistance to thermal aging. The hardness value was increased by increasing the filler content before and after aging. The polyester composites based on cyclic glycol and loaded with 80% kaolin gave the highest hardness values. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of sorption behavior on transport properties of gases in polymeric membranes

The purpose of this work was to study the relationships between the gas sorption and transport properties in polymeric membranes. The intrinsic gas transport properties: permeation, diffusion, and sorption in a series of dense membranes with various carbonyl group densities were investigated. The poly(methyl methacrylate) (PMMA), polycarbonate (PC), and cyclic olefin copolymer (COC) membranes have similar helium permeability, but the helium permeability of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membrane was very high. The variation of permeability for these four membranes consists with their fraction free volume. In this study, a direct relationship was found between the carbonyl group density and Langmuir affinity constant. Furthermore, dependence of the fractional free volume on the membrane Langmuir capacity constant was observed.     

Preparation and gas permeation of immobilized fullerene membranes

Fullerene‐dispersed membranes were homogeneously prepared under the conditions in which a 10 wt % polystyrene solution containing 1 wt % fullerene was dried under a reduced pressure of 50 cmHg at room temperature. The fullerene membranes prepared with 1,2‐dichlorobenzene were found to have the darkest color, and showed no evidence of fullerene crystals in their photomicrographs. UV‐visible and infrared absorption spectra of the fullerene membranes showed fullerene bands, which indicated that the fullerene was homogeneously dispersed in the membranes. The permeability coefficients of pure nitrogen, oxygen, carbon dioxide, ethane, and ethylene were found to increase significantly in the fullerene membranes compared to those in the polystyrene membranes, although the ideal separation factors for oxygen/nitrogen and ethylene/ethane in the fullerene membranes (i.e., 4.3 and 1.7, respectively) were slightly less than the separation factors in the polystyrene membranes. The permeability increase originated from the increase in diffusion coefficients in the fullerene membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 529–537, 2000     

Thin film composite membranes with desirable support layer for MeOH/MTBE pervaporation

A comprehensive study was performed on a new application of thin film composite membranes and selecting a stable sublayer for them as pervaporation membranes in organic solvent separation. For this purpose, four different polymeric sublayers of polyethersulfone (PES), cellulose acetate, polyacrylonitrile, and polyetherimide were prepared, and the interaction of methanol (MeOH) and methyl tert butyl ether (MTBE) with them was investigated. The contact angle results, scanning electron microscopy images, and swelling and mechanical strength measurements obviously displayed the effect of immersion in organic solvents on the sublayers. Finally, a polyamide active layer was subsequently deposited on the PES membrane surface as the stable sublayer via interfacial polymerization based on a multistep statistical optimization strategy involving fractional factorial design and a response surface method. The prepared TFC membranes were tested in the pervaporation of a MeOH/MTBE mixture and exhibited excellent performance compared with the current membranes in this context. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47519.     

Effect of surface properties of polysulfone support on the performance of thin film composite polyamide reverse osmosis membranes

In this work, influence of initial conditions and surface characteristics of porous support layer on structure and performance of a thin film composite (TFC) polyamide reverse osmosis (RO) membrane was investigated. The phase inversion method was used for casting of polysulfone (PSf) supports and interfacial polymerization was used for coating of polyamide layer over the substrates. The effect of PSf concentrations that varied between 16 wt % and 21 wt %, and kind of the solvent (DMF and NMP) used for preparation of initial casting solution were investigated on the properties of the final RO membranes. SEM imaging, surface porosity, mean pore radius, and pure water flux analysis were applied for characterization of the supports. The substrate of the membrane, which synthesized with 18 wt % of PSf showed the most porosity and the synthesized RO membrane had the lowest salt rejection. In case of the solvents, the membranes synthesized with DMF presented better separation performance that can be attributed to their lower thickness and sponge‐like structure. The best composition of support for TFC RO membranes reached 16 wt % PSf in DMF solvent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44444.     

Selective permeation of sour gases through polymeric membranes modified by sulfolanes. I. Study of selective permeation of CO2 through modified polymeric membranes determined on different systems

Several sulfolanes such as 3-methylsulfolane, sulfolane, and 3-sulfolene were tested as modifiers in poly(trimethylsilyl methyl methacrylate) (PTMSMMA) and poly(trimethylsilyl propyne) (PMSP) to improve the selectivity of CO₂. The gas permeabilities for the PTMSMMA-blend membranes containing high 3-methylsulfolane content were determined on a nonvacuum system in which the membranes started to be measured at their steady states at 30°C; those for all the other membranes were determined in a vacuum system in which those membranes were measured after they reached their unsteady states at 30°C. The PTMSMMA-blend membrane containing 40% 3-methylsulfolane was found to give the best separation of CO₂ under the conditions in this study compared to all the PTMSMMA-blend membranes and the others prepared in our work; its ideal separation factors for CO₂ over N₂ were above 40 and its permeability coefficients of CO₂ increased to above 250 Barrer. The modifications of PMSP membranes by impregnating with sulfolane and blending with sulfolene were found to be effective in improving the selectivity for CO₂ over N₂ for the PMSP membrane. The ideal separation factors for CO₂ over N₂ for the modified PMSP membranes impregnated with 30% sulfolane and blended with 25% 3-sulfolene were improved to above 10 and 13, respectively. © 1996 John Wiley & Sons, Inc.     

Effects of carbonisation on pore evolution and gas permeation properties of carbon membranes from Kapton polyimide

Carbon membranes were prepared by carbonisation of Kapton^® polyimide at different temperatures under vacuum and nitrogen flow. Pore structure development of the membranes during carbonisation was studied. Carbonisation temperature was critical in the modification of membrane structure. At the same temperature, the carbon membranes fabricated under nitrogen atmosphere had higher gas permeances than those fabricated under vacuum. During heat treatment, the value of d-spacing for the carbon membranes decreased with increasing temperature, however, vacuum and nitrogen atmosphere had different influences on the changes in the d-spacing. CO₂ adsorption showed that the carbon membranes prepared at 1273 K under vacuum had the highest micropore volume whilst the membranes prepared at 1073 K under vacuum had the highest characteristic adsorption energy. N₂ adsorption showed that the samples obtained at 873 K under vacuum had the highest nitrogen uptake. Mesopores were deemed to be connected through micropores and narrow channels between meso- and/or micropores were supposedly present. The micropores predominantly controlled the transport properties of the carbon membranes. The membrane samples obtained at 1173 K under vacuum yielded ideal separation factors of 558.27, 60.87, 19.69 and 138.53 for He/N₂, CO₂/N₂, O₂/N₂ and CO₂/CH₄, respectively, with permeances of 7.26, 0.79, 0.26, 0.13 and 0.006 mol/(m² s Pa) for He, CO₂, O₂, N₂ and CH₄, respectively.     

Incorporation effects of fluorinated side groups into polyimide membranes on their physical and gas permeation properties

The effects of incorporation of fluorinated alkyl side groups into polyimide membranes were investigated in terms of their physical and gas permeation properties. Four polyimides with fluorinated side groups and four polyimides without the side groups were prepared by polycondensation of 2‐(perfluorohexyl)ethyl‐3, 5‐diamino benzoate (PFDAB) and m‐PDA with four aromatic dianhydrides (6FDA, ODPA, BTDA, and PMDA), respectively. It was found that the incorporation of fluorinated side groups into the polyimide membranes decreased their surface free energies (T_gs), solubility parameters, and fractional free volume (FFV)s and therefore, enhanced the permeabilities for CO₂, O₂, N₂, and CH₄ gases but reduced the selectivities for CO₂/ CH₄, O₂ /N₂, CO₂/N₂ gas pairs depending upon the structure of dianhydride monomers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2756–2767, 2000