Selective permeation of carbon dioxide through synthetic polymer membranes having pyridine moiety as a fixed carrier

Sorption and permeation of CO₂ were investigated by using synthetic polymer membranes having pyridine moiety or pyridine–Cu(II) complex group as a fixed carrier. The solubility data for CO₂ were interpreted by the dual sorption model, Henry's law plus Langmuir-type adsorption. The permeation results of CO₂ through the present membranes containing pyridine moiety were analyzed in terms of the partial immobilization model, while the solubilities and permeablities of O₂ and N₂ obeyed Henry's law. Permselectivity of the present membrane for CO₂ was achieved. These results were explained by the acid-base interaction between CO₂ molecules and fixed carrier in the present membrane.     

Selective permeation through hydrophobic–hydrophilic membranes

Hydrophobic–hydrophilic composite membranes, containing polystyrene as the dispersed phase and polyacrylamide as the continuous phase, have been prepared by the concentrated emulsion polymerization method. They are highly absorptive for methyl chloride, benzene, and toluene, but poorly absorptive for cyclohexane. The absorption from toluene–cyclohexane mixtures was found to increse with increasing temperature and toluene concentration and to decrease with increasing fraction of polyacrylamide in the composite. The absorption is controlled by diffusion. The permeation rate through the membrane, which was determined by the pervaporation method, exhibits similar trends with respect to temperature, concentration, and fraction of polyacrylamide as absorption does. Higher permeation was obtained by increasing the temperature and by increasing the toluene concentration or by decreasing the fraction of polyacrylamide. The selectivity which was in the range of 4–8 varies inversely with the permeation rate through the membrane which was in the range of 2 × 10³?1.0 × 10⁴ g/m² h.     

Gas permeation through a glassy polymer membrane: chemical potential gradient or dual mobility mode?

The flux equation for gas transport through a glassy polymer membrane is expressed in terms of a chemical potential gradient. It is an implicit function of the operating pressure. By studying the specific properties of this function, it can be simplified to an explicit form, which is mathematically identical to the expression proposed by the dual mobility model. Using this new model, all the data obtained by the dual mobility model can be described adequately. However, the physical significance of the parameters of the present model is completely different from the parameters of a dual mobility model. The present model assumes that only the molecules sorbed by the Henry mode contributed to the flux, and those sorbed by the Langmuir mode remained completely immobilized. This model provides an indirect method for the determination of partial molar volumes of gases in polymer membranes. It has been shown that the steady-state flux depends on the sorption rate at the interface, and not on the Henry constant. It has been found that the contribution of pressure in the diffusional transport of gases is of the same order and may be even higher than that of the concentration, which contradicts the popular perception that ‘the diffusion process is related basically to the concentration gradient’.     

Active transport of alkali metal ion through a membrane composed of gluconolactone-containing polymer

Summary The membrane composed of gluconolactone-containing polymer was prepared by the following three steps, (1) the copolymerization between acrylonitrile and a styrene derivative carrying a protected glucose substituent, (2) casting a membrane from the DMF solution of the copolymer, and (3) a sequence of reactions for the membrane. It exhibited active transport of Na⁺ ion against the concentration gradient.     

Spectrophotometric determination of water vapor permeation through polymer films

A novel method for measuring the permeation of water vapor through polymer films is described. A cellulose detector film incorporating cobalt chloride in a blue anhydrous from is sealed between two pieces of test film in a specially designed cell. The cell is placed in a controlled temperature and humidity cabinet, and the disappearance of the blue color of the cobalt chloride is recorded spectrophotometrically as water vapor diffuses through the test film into the detector film. This simple method of determining water-vapor-transmission rates is more rapid than standard gravimetric procedures because of the highly sensitive detection technique.     

The permeation of hydrocarbons through a polyethylene membrane

Permeation data of a number of linear, branched and cyclic hydrocarbons have been determined up to a pressure of 70% of the saturation vapour pressure and a temperature range of 30–50°C. The concentration of solvent in the membrane at the liquid site has been determined by desorption. An average diffusion coefficient has been computed assuming the liquid concentration in the membrane at the permeate side to be zero. The activation energy of the permeation has been correlated with molecular structure.     

水蒸气在中空纤维复合膜中渗透的微分阻力模型

建立了水蒸气在中空纤维复合膜中渗透的微分阻力模型,用实验验证了模型的可靠性。采用该模型估算出中空纤维膜的结构参数,研究了水蒸气在各层膜中的阻力,并以H2O/C2H2系统为例,考察了膜的结构参数对H2O/C2H2选择性的影响。     

Dual permeation of acid dyes through nylon 6 membrane

Permeation of acid dyes in nylon 6 membrane was measured and analyzed by the dual sorption and diffusion mechanism, comprising partition and Langmuir-type modes. The results were compared with our previous work on diffusion in the same system by the film roll method. Diffusion coefficients of both dye species were found to be similar in magnitude.     

Selective permeation and separation of steam from water–methanol–hydrogen gas mixtures through mordenite membrane

Separation properties of a mordenite membrane for water–methanol–hydrogen mixtures were studied in the temperature range from 423 to 523 K under pressurized conditions. The mordenite membrane was prepared on the outer surface of a porous alumina tubular support by a secondary-growth method. It was found that water was selectively permeated through the membrane. The separation factor of water/hydrogen and water/methanol were 49–156 and 73–101, respectively. Even when only hydrogen was fed at 0.5 MPa, its permeance was as low as 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ up to 493 K, possibly suggesting that water pre-adsorbed in the micropores of mordenite hindered the permeation of hydrogen. The hydrogen permeance dramatically increased to 6.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 503 K and reached to 1.4 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 523 K because of the formation of cracks in the membrane. However, the membrane was thermally stabilized in the presence of steam and/or methanol.     

Gas permeation through glassy polymer membranes with relatively low glass-transition temperature

When the glass-transition temperature of the polymer is not so much higher than the experimental temperature, the pressure dependence of the mean permeability coefficient of the poly-mer membrane to a gas is apt to deviate from the prediction by the conventional dual-mode mobility model, and to obey a similar model with concentration-dependent diffusivities because of the plasticization action of sorbed gas in the polymer membrane. In this work, sorption and permeation for oxygen and carbon dioxide in a membrane of polystyrene whose glass-transition temperature is 95°C, were measured to discuss the mechanism of gas diffusion in glassy polymer membranes with relatively low glass-transition temperature at 30, 40 and 50°C respectively.     

Amorphous hydrogenated carbon films as barrier for gas permeation through polymer films

The influence of amorphous hydrogenated carbon (a-C:H) coatings on the gas permeation through polymer films was investigated. a-C:H films were deposited from a 13.56-MHz RF glow discharge in methane or acetylene atmosphere. Thin poly(ethylene terephthalate) and polyimide foils were used as substrates. The permeation of the gases H₂, N₂, O₂ and CO₂ was measured and the reduction of the permeability coefficient was correlated to composition and density of the a-C:H films. The stoichiometry of the layers was analyzed using ion-beam techniques on films deposited onto silicon samples. The a-C:H/PET surfaces were analyzed using optical microscopy and atomic force microscopy (AFM). Multilayer structures comprising different types of a-C:H films were also investigated. A reduction of the permeability coefficient by 80% for hard, dense and 94% for soft, polymer-like layers was found. Surprisingly, the barrier efficacy of the coating decreases with increasing a-C:H film density. This unexpected result is attributed to the appearance of a network of deep cracks spread out over the whole coating.     

Ultrafast water-selective permeation through graphene oxide membrane with water transport promoters

Graphene oxide (GO), as a representative two-dimensional material, has shown great prospect in developing high-performance separation membranes via forming ordered and tunable nanochannels. However, for aqueous molecular separations, the implementation of an excellent separation performance remains a critical challenge due to the membrane swelling phenomenon and the trade-off effect between permeation flux and separation factor. Herein, a facile and tunable approach is presented for introducing water transport promoters into GO interlayer channels to construct water transport highways. The combination of covalently cross-linked channel structure, facilitated water-selective sorption, and expedited water-preferential diffusion overcome the trade-off effect, achieving a superior performance from an ultrathin GO membrane with a flux of 5.94 kg/m²∙h and a water/butanol separation factor of 3,965, which exceeds the performance of state-of-the-art membranes for water/butanol separation. The strategy proposed here is straightforward, holding great potential to produce high-efficiency GO and other two-dimensional (2D)-material membranes for precise aqueous molecular separations.     

Analysis of polymer membrane formation through spinodal decomposition

A phenomenological model used in a previous work for spinodal decomposition of polymer-solvent systems is further analyzed. From the dimensionless form of the nonlinear Cahn-Hilliard equation, the dimensionless induction time is found to be a constant number for suddenly quenched systems. Computer simulation is carried out for prediction of early stage behavior with thermal history corresponding to a linear temperature drop followed by a constant temperature vs. time. In the areas of polymer membrane formation and phase separation studies, the universality of the constant dimensionless Induction time for suddenly quenched systems allows the determination of the minimum time needed for phase separation via spinodal decomposition. Also, simulation results for the double linear temperature history allows the convenient prediction of early stage spinodal decomposition behavior at every point of a membrane cross section undergoing thermal inversion phase separation.     

Dynamic Monte Carlo study on the permeation of polymer chains through small holes

The permeation of polymer chains through a small hole is simulated using dynamic Monte Carlo method. The dependence of the permeation velocity v on concentration C of polymer chain, chain length n and hole size s is investigated. The velocity v increases non-linearly with C, differing from linear dependence of hard sphere system, indicating that inter-chain interaction plays an important role in the permeation process. At the same concentration, the velocity decreases with the chain length n via a relation v=a+bn^−?, where the exponent ? increases linearly with C. Such a behavior is different from a single chain system. The possible physical reason is addressed. The velocity is proportional to hole size when the chain size is smaller than the hole size, but it decreases obviously if the chain size is much larger than the hole size.     

Molecular dynamics simulation of small gas molecule permeation through CAU-1 membrane

CAU-1 is one of aluminum-based amine-functionalized Metal–Organic Frameworks(MOFs). Gas permeation and separation behaviors through CAU-1 membrane were simulated by the dual-control plane nonequilibrium molecular dynamics(DCP-NEMD) method. The thickness of membrane was 3.55 nm.Gases CO_2, N_2, CH_4, H_2, He, Kr and Xe were chosen for the calculation in both single component and binary mixtures. The permeation process was calculated in grand canonical(l VT) ensemble with periodic boundary conditions(PBC) in x-and y-directions at different temperatures. The calculated permeance of H_2, CH_4, N_2, CO_2 and Kr decreased with increasing temperature in both single and binary system, while that of Xe with kinetic molecule of 0.41 nm increased with increasing temperature. It shows Xe permeation is governed by activated diffusion. The simulated separation factors of CO_2/N_2 and CO_2/CH_4 of 4.2 and 1.3 respectively were lower than the experimental ones when only considering van der Waals interaction. Further consideration of electrostatic potential leads to improved calculation CO_2/N_2 and CO_2/CH_4 separation factor of 23.0 and 12.9 respectively that were consistent with the experimental ones of 26.2 and 14.8. It suggests the necessity of considering the Coulomb interactions between CO_2 and NH_2-on the pore wall of CAU-1 for permeation of CO_2. For H_2/N_2 and H_2/CH_4 the ideal selectivities also keep consistent with our experimental results. Interestingly, the simulated separation factor for noble Kr/Xe reaches infinite, predicting that CAU-1 membrane possesses potential separation properties for radioactive Kr/Xe.     

Selective permeation of o-, m-, and p-isomers of benzene derivatives through polymer membranes based on cyclodextrin complexation in the bulk aqueous solution

Transport behavior of several aromatic compounds through a poly(vinyl chloride)membrane and poly(vinyl alcohol)-poly(ethylenimine) composite membranes was studied in the presence of cyclodextrin in the aqueous solution. o-Isomers of nitrophenol, nitroaniline, and iodophenol were effectively separated from their mixture of regio isomers based on the preferential complexation between cyclodextrin and the m- and p-isomers over the o-isomers. Pumping of p-nitroaniline across the membrane was also observed by addition of cyclodextrin. The results were explained as a consequence of the selective complex formation between cyclodexarin and substrate and the low membrane permeability of the complexes.     

Fabrication and analysis of polymer microstructures through ion microprobe techniques

In this work, we explored the capabilities of energetic focused beams of light ions for the fabrication and analysis of microstructures produced on commercial polyethylene terephthalate (PET) foils. To that end, single lines and multi‐structure patterns were drawn directly on the foils using Proton Beam Writing (PBW) techniques followed by chemical etching. The characterization of the microstructures was carried out with on‐axis Scanning Transmission Ion Microscopy (STIM) employing H⁺¹, He⁺², and Li⁺³ ions in the MeV range. Scanning Electron Microscopy (SEM) was employed as well. The results show that a polymer like PET can be patterned trough a proper combination of irradiation parameters and etching times. However, aspect ratios obtained in this way are quite poor. Moreover, STIM images obtained from different regions of the ion energy spectra reveal patterns and cavities seen neither by conventional STIM, where the whole energy spectrum is used, nor by SEM. Moreover, striking differences are observed when different ions are used for STIM analysis. The results suggest that heavier ions provide additional information of the structures under analysis when compared with usual STIM employing protons. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43253.     

Time-dependent permeation of carbon dioxide through a polyimide membrane above the plasticization pressure

The time-dependent permeation behavior of a glassy polyimide is studied above and below the plasticization pressure with carbon dioxide as the permeating gas. The work particularly focuses on the quantification of the slow increase in permeability at feed pressures above the plasticization pressure. Significant differences in permeation behavior were found for membranes with and without permeation history. Introducing the quantity “conditioning time” allows one to compare the results obtained for membranes with different permeation history. The concept of conditioning time furthermore allows one to quantify the aging of a membrane plasticized during previous permeation. © 1995 John Wiley & Sons, Inc.