Permeation of pure carbon dioxide and methane and binary mixtures through cellulose acetate membranes

Steady-state permeation rates for pure CO₂ and CH₄ and their binary mixtures through homogeneous dense cellulose triacetate membranes have been measured at three temperatures between 20 and 40°C and pressures up to 2.8 MPa. The pressure dependence of the mean permeability coefficient for CO₂ can be described by the total immobilization model in conjunction with a modified free-volume model. No appreciable pressure dependence of the permeability coefficient for CH₄ is observed, while the permeability coefficients for CH₄ in binary mixture of CO₂ and CH₄ depend on applied gas pressure. The pressure dependences of the mean permeability coefficients for the components in the binary mixture are discussed in terms of the above mobility model. Membrane plasticization induced by CO₂ affects permeation by both gases.     

Facilitated Transport of Penicillin G by Bulk Liquid Membrane with TBP as Carrier

The facilitated transport of penicillin G from aqueous solutions to the stripping phase through bulk liquid membrane (BLM) containing TBP in 3% iso-octanol and n-butyl acetate was studied. Na₂CO₃ solution was used as the stripping phase. Experiments were performed as a function of stirring rate, TBP concentration and type of diluent in the liquid membrane phase, pH, and initial penicillin G concentration in the feed phase, Na₂CO₃ concentration in the stripping phase, etc. The results showed that the BLM process could carry out the simultaneous separation and concentration of penicillin G from dilute aqueous solutions, and arise “up-hill” effect due to the characteristic of non-equilibrium mass transfer. The diffusion of penicillin G complex in the liquid membrane phase played an important role in BLM process. The mass transfer mechanism of BLM for this system was also discussed.     

Effects of temperature and anion species on CO2 permeability and CO2/N2 separation coefficient through ionic liquid membranes

The permeability of carbon dioxide (CO₂) through imidazolium-based ionic liquid membranes was measured by a sweep gas method. Six species of ionic liquids were studied in this work as follows: [emim][BF₄], [bmim][BF₄], [bmim][PF₆], [bmim][Tf₂N], [bmim][OTf], and [bmim][dca]. The ionic liquids were supported with a polyvinylidene fluoride porous membrane. The measurements were performed at T = (303.15 to 343.15) K. The partial pressure difference between feed and permeate sides was 0.121 MPa. The permeability of the CO₂ increases with temperature for the all ionic liquid species. Base on solution diffusion theory, it can be explained that the diffusion coefficient of CO₂ in an ionic liquid affects the temperature dependence more strongly than the solubility coefficient. The greatest permeability was obtained with the [bmim][Tf₂N] membrane. The membrane of [bmim][PF₆] presents the lowest permeability.The separation coefficient between CO₂ and N₂ through the ionic liquid membranes was also investigated at the volume fraction of CO₂ at feed side 0.10. The separation coefficient decreases with the increase of temperature for the all ionic liquid species. The membrane of [emim][BF₄] and [bmim][BF₄] gives the highest separation coefficient at constant temperature. The lowest separation coefficient was obtained from [bmim][Tf₂N] membrane which presents the highest permeability of CO₂.     

Selective permeation of CO2 through poly 2-(N,N-dimethyl)aminoethyl methacrylate membrane prepared by plasma-graft polymerization technique

A membrane having an amine moiety was prepared by plasma-grafting 2-(N,N-dimethyl)aminoethyl methacrylate (DAMA) onto a microporous polyethylene substrate. Permselectivity of the membrane for CO₂ over N₂ was achieved in both dry and water swollen conditions. When the CO₂ partial pressure in the feed gas was 0.047 atm, the selectivity of CO₂ over N₂ reached 130 for the highly swollen water containing membrane. This value was found to agree with that obtained with a mobile carrier membrane (supported liquid membrane) using DAMA as the carrier. The effects of several experimental conditions such as degree of grafting, feed partial pressure and temperature on the membrane performance were studied. It was suggested that the membrane acted as a fixed carrier membrane for CO₂ facilitated transport in under the dry condition and acted as a fixed reaction site membrane in the water swollen condition. The carrier transport mechanism is discussed for dry and aqueous membranes.     

Mathematical modeling of penicillin G extraction in an emulsion liquid membrane system containing only a surfactant in the membrane phase

An extraction experiment of penicillin G was performed in an emulsion liquid membrane system in which only ECA 4360J exists in the organic membrane phase without a predominant carrier, Amberlite LA-2, used in our previous works and it functions as a carrier as well as a surfactant. A permeation model for the present system has been developed as a primary study to examine the transport mechanism of penicillin G in the previous batch and continuous systems with two carriers of Amberlite LA-2 and ECA 4360J. The model takes into account the mass transfer in the external aqueous film, the extraction reaction between penicillin G and ECA 4360J at the external interface, the diffusion of penicillin G in the emulsion phase, the stripping reaction at the internal interface and the pH change of internal aqueous solution containing Na₂CO₃ with penicillin G transported into the internal phase. The experimental data were well fitted with the present model. Also, an expression for the reaction of penicillin G with ECA 4360J was obtained through a series of equilibrium measurements in liquid–liquid extraction system.     

Evaluation of a membrane-sparged helical tubular photobioreactor for carbon dioxide biofixation by Chlorella vulgaris

A membrane-sparged helical tubular photobioreactor (MSTR) with a cultivation volume of 800 ml was designed in this study. It consisted of a cylindrical-shaped light receiver and a mass transfer system. A helical tube was used to ensure good light regime, and hollow fiber membranes were uniformly fitted inside the reactor, which functioned as a gas sparger and produced small bubbles. Mass transfer coefficients, mixing intensities and capabilities of CO₂ biofixation through the photosynthesis of Chlorella vulgaris in MSTR under different gas, liquid flow rates and light intensities were compared with two other photobioreactors (BCTR and MCTR). BCTR took a perforated pipe as sparger, while MCTR employed a membrane contactor as the whole mass transfer system. To establish if the limitation of CO₂ removal was improved in MSTR, pH, dissolved oxygen, cell damage, and characteristic times for mixing, mass transfer and CO₂ consumption were analyzed during batch culture.     

Mixed-matrix membranes comprising graphene-oxide nanosheets for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation: A comparison between glassy and rubbery polymer matrices

The effect of graphene oxide (GO) nanosheets on the CO₂/CH₄ separation performance of a rubbery (poly(dimethylsiloxane), PDMS) as well as a glassy (polyetherimide, PEI) polymer is studied. Interfacial interactions between the nanosheets and both polymers are revealed by FTIR and SEM. The results of gas permeation through the membranes demonstrate that GO nanosheets enhance CO₂/CH₄ diffusivityselectivity of PEI and CO₂/CH₄ solubility-selectivities of the PEI and PDMS polymers, while diminish CO₂/CH₄ diffusivity-selectivity of PDMS. Furthermore, the possibility of overcoming the common tradeoff between CO₂ permeability and CO₂/CH₄ selectivity of rubbery and glassy polymers by incorporating very low amounts of graphene oxide nanosheets is addressed. In other words, at 0.25 wt % GO loading, the PEI membrane shows simultaneous enhancement of CO₂ permeability (16%) and CO₂/CH₄ selectivity (59%). Also, for the PDMS membrane simultaneous enhancement of CO₂ permeability (29%) and CO₂/CH₄ selectivity (112%) is occurred at 0.5 wt % GO loading. Finally, the capability of the well known Nielsen model to predict the gas permeability behavior of the nanocomposites is investigated.     

High temperature separation of carbon dioxide/hydrogen mixtures using facilitated supported ionic liquid membranes

Efficiently separating CO₂ from H₂ is one of the key steps in the environmentally responsible uses of fossil fuel for energy production. A wide variety of resources, including petroleum coke, coal, and even biomass, can be gasified to produce syngas (a mixture of CO and H₂). This gas stream can be further reacted with water to produce CO₂ and more H₂. Once separated, the CO₂ can be stored in a variety of geological formations or sequestered by other means. The H₂ can be combusted to operate a turbine, producing electricity, or used to power hydrogen fuel cells. In both cases, only water is produced as waste. An amine-functionalized ionic liquid encapsulated in a supported ionic liquid membrane (SILM) can separate CO₂ from H₂ with a higher permeability and selectivity than any known membrane system. This separation is accomplished at elevated temperatures using facilitated transport supported ionic liquid membranes.     

Carrier‐Mediated Transport of Hg(II) through Bulk and Supported Liquid Membranes

The transport of Hg (II) ions from an aqueous solution into an aqueous receiving solution through bulk and supported liquid membranes containing a calix[4]arene derivative 1 as a carrier was examined. The kinetic parameters of bulk liquid membrane studies were analyzed assuming two consecutive, irreversible first‐order reactions. The influence of temperature, stirring rate, carrier concentration and solvent on the kinetic parameters (k₁, k₂, R_m ^max, t_max, J_d ^max, J_a ^max) has also been investigated. The membrane entrance rate, k₁, and the membrane exit rate, k₂, increased with increasing temperature and stirring rate. The activation energy values are calculated as 4.87 and 48.63 kj mol^?1 for extraction and reextraction, respectively. The values of calculated activation energy indicate that the process is diffusionally controlled by species. Also, the transport behavior of Hg²⁺ from aqueous solution through a flat‐sheet supported liquid membrane has been investigated by the use of calix[4]arene derivative 1 as carrier and Celgard 2500 as the solid support. A Danesi mass transfer model was used to calculate the permeability coefficients for each parameter studied. The highest values of permeability were obtained with 2‐nitrophenyloctyl‐ether (NPOE) solvent and the influence was found to be in the order of NPOE>chloroform>xylene.     

Enhanced fluidity liquid chromatography for hydrophilic interaction separation of nucleosides

The application of enhanced fluidity liquid (EFL) mobile phases to improving isocratic chromatographic separation of nucleosides in hydrophilic interaction liquid chromatography (HILIC) mode is described. The EFL mobile phase was created by adding carbon dioxide to a methanol/buffer solution. Previous work has shown that EFL mobile phases typically increase the efficiency and the speed of the separation. Herein, an increase in resolution with the addition of carbon dioxide is also observed. This increase in resolution was achieved through increased selectivity and retention with minimal change in separation efficiency. The addition of CO₂ to the mobile phase effectively decreases its polarity, thereby promoting retention in HILIC. Conventional organic solvents of similar nonpolar nature cannot be used to achieve similar results because they are not miscible with methanol and water. The separation of nucleosides with methanol/aqueous buffer/CO₂ mobile phases was also compared to that using acetonitrile/buffer mobile phases. A marked decrease in the necessary separation time was noted for methanol/aqueous buffer/CO₂ mobile phases compared to acetonitrile/buffer mobile phases. There was also an unusual reversal in the elution order of uridine and adenosine when CO₂ was included in the mobile phase.     

Competitive permeation of gas and water vapour in high free volume polymeric membranes

Highly permeable glassy polymeric membranes based on poly (1‐trimethylsilyl‐1‐propyne) (PTMSP) and a polymer of intrinsic porosity (PIM‐1) were investigated for water sorption, water permeability and the separation of CO₂ from N₂ under humid mixed gas conditions. The water sorption isotherms for both materials followed behavior indicative of multilayer adsorption within the microvoids, with PIM‐1 registering a significant water uptake at very high water activities. Analysis of the sorption isotherms using a modified dual sorption model which accounts for such multilayer effects gave Langmuir affinity constants more consistent with lighter gases than the use of the standard dual mode approach. The water permeability through PTMSP and PIM‐1 was comparable over the water activities studied, and could be successfully model ed through a dual mode sorption model with a concentration dependent diffusivity. The water permeability through both membranes as a function of temperature was also measured, and found to be at a minimum at 80 ° C for PTMSP and 70 °C for PIM‐1. This temperature dependence is a function of reducing water solubility in both membranes with increasing temperature countered by increasing water diffusivity. The CO₂ ‐ N₂ mixed gas permeabilities through PTMSP and PIM‐1 were also measured and model ed through dual mode sorption theory. Introducing water vapour further reduced both the CO₂ and N₂ permeabilities. The plasticization potential of water in PTMSP was determined and indicated water swelled the membrane increasing CO₂ and N₂ diffusivity, while for PIM‐1 a negative potential implied that water filling of the microvoids hampered CO₂ and N₂ diffusion through the membrane. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 719–728     

Preparation and characterisation of polyaniline based membranes for gas separation

Transport rates (permeability) and ideal separation factors for several gas pairs through dense polyaniline membranes are reported. The ideal separation factors for all gas pairs tested were found to be independent of the polyaniline membrane thickness whereas the permeability of the single gases showed significant variations. Both dedoped and redoped films (film thickness between 9 and 67 μm) were studied. The highest selectivities α_(A/B) found were 7.6 for the gas pair H₂/CO₂ in the case of the dedoped membrane and 10 for the gas pair H₂/CO₂, 6 for O₂/N₂ and 200 for H₂/N₂ in the case of the redoped membrane. Statistical analysis of a large number of membranes allowed the critical comparison with results obtained by other groups.Comparison with other membrane materials shows that an approximately sixfold enhancement of the respective separation factors is possible for gas pairs containing hydrogen. Similar separation factors are observed for the gas pairs CO₂/O₂, CO₂/N₂ and N₂/O₂.Membranes for which Knudsen diffusion was observed exhibited regularly distributed micropores (400 nm diameter).     

Modeling solubility of acid gases in alkanolamines using the nonelectrolyte Wilson-nonrandom factor model

The nonelectrolyte Wilson-nonrandom factor local composition model (N-Wilson-NRF) by Haghtalab and Mazloumi is applied for modeling the vapor–liquid equilibrium of the acid gases (CO₂ and H₂S)–alkanolamine–water systems. The model is used to calculate the nonideality of species in liquid phase through the activity coefficient equations. In this work, we use the N-Wilson-NRF model for short-range forces in the aqueous electrolyte system of alkanolamines by using the concept of ion-pair. For the long-range interaction the Pitzer–Debye–Hückel theory is applied. The model is used to correlation of the solubility data of CO₂ and H₂S in aqueous monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) and 2-amino-2methyl-1-propanol (AMP) systems over wide range of temperature (0–140 °C), partial pressure (0.001–1000 kPa) and acid gases loading (0.001–1.0 mol gas/mol amine). To show the predictability of the model, the interaction parameters without any additional adjustable parameters are used to predict the solubility of CO₂ in aqueous AMP solution at different conditions. The results of the model show a very good agreement with the experimental data.     

Comparison of three models for permeation of CO2/CH4 mixtures in poly(phenylene oxide)

Two models for the permeability of pure gases have been extended to include binary gas mixtures. The first is an extension of a pure gas permeability model, proposed by Petropoulos, which is based on gradients of chemical potential. This model predicts the permeability of components in a gas mixture solely on the basis of competition for sorption sites within the polymer matrix. The second mixed gas model follows an earlier analysis by Barrer for pure gases which includes the effects of saturation of Langmuir sites on the diffusion as well as the sorption processes responsible for permeation. This generalized “competitive sorption/diffusion” model includes the effect of each gas component on the sorption and diffusion of the other component in the mixture. The flux equations from these two models have been solved numerically to predict the permeability of gas mixtures on the basis of pure gas sorption and transport parameters. Both the mixed gas Petropoulos and competitive sorption/diffusion model predictions are compared with predictions from the earlier simple competitive sorption model based on gradients of concentration. An analysis of all three models is presented for the case of CO₂/CH₄ permeability in poly(phenylene oxide) (PPO). As expected, the competitive sorption/diffusion model predicts lower permeability than either of the models which consider only competitive sorption effects. The permeability depression of both CO₂ and CH₄ predicted by the competitive sorption/diffusion model is roughly twice that predicted by the competitive sorption model, whereas the mixed gas Petropoulos model predictions for both gases lie between the other two model predictions. For the PPO/CO₂/CH₄ system, the methane permeability data lie above the predictions of all three models, whereas CO₂ data lie below the predictions of all models. Consequently, the competitive sorption/diffusion model gives the most accurate prediction for CO₂, while the simple competitive sorption model is best for methane. The effects of mixed gas sorption, fugacity, and CO₂-induced dilation were considered and do not explain the inaccuracies of any of the models. The relatively small errors in mixed gas permeability predictions using either of the three models are likely to be related to “transport plasticization” of PPO owing to high levels of CO₂ sorption and its effect on polymer segmental motions and gas diffusivity.     

Switchable gas permeability of a polypropylene-liquid crystalline composite film

The development of functionalized polyolefins for use as stimuli-responsive commodity polymers has recently received much attention. In this work, a microporous polypropylene (PP) scaffold is used to align and fortify a smectic liquid crystalline network (LCN) which can switch its gas permeability upon pH changes. The LCN is a photopolymerized liquid crystalline mixture of a dimerized benzoic acid derivative monoacrylate and a diacrylate crosslinker. In the hydrogen-bonded state, the composite membrane shows a high-molecular order and a low permeability for He, N₂, and CO₂ gases. By pH switching from the hydrogen-bonded state to the salt form, the molecular order is reduced, and the gas permeability is increased by one order of magnitude. This increase is mainly attributed to a loss in order of the system, increasing the free volume, resulting in an increased diffusibility. By exposing the composite film to basic or acidic environments, reversible switching between low and high gas permeability states is observed, respectively. The physical constraints imposed by the PP scaffold strengthens the membrane while the reversible switching inside the liquid crystalline polymer is maintained. This switching of gas permeation properties is not possible with the fragile freestanding LCN films alone.     

A dynamic approach to diffusion and permeation measurements

A dynamic method for investigating the mechanism of permeation and diffusion through polymers has been explored. The permeation cell consists of two compartments separated by the membrane. The permeant (gas, vapor, or liquid) is introduced into one compartment; a carrier gas (helium) flows at constant rate through the other and sweeps the permeant which diffuses through the membrane to the thermal conductivity detector. Both compartments are at atmospheric pressure; thus no or little membrane support is required, and leakage problems are minimal. Moreover, the same membrane can be used over a wide temperature range and for diverse permeants. The detector signal is at any instant proportional to the permeation rate. A simple mathematical formalism for deriving the diffusion coefficient from the transient permeation rates has been developed. The measured diffusion and permeability coefficients of CO₂, O₂, and N₂ through low-density polyethylene closely agree with literature values. Permeation of hexane and benzene through polyethylene follows a complex diffusion law, and the rate depends on the thermal history of the system. The dynamic method is particularly suited to the study of transitions in polymers. Changes in permeation rates, usually occurring at transition points, can easily be discovered by slow temperature scanning of the system.     

Asymmetric effects in catalytic membranes

A catalytic membrane hybrid system based on a cermet membrane with a channel size 〈d〉 of ～0.12 μm has been produced using sol-gel processing. A layer of a superfine methanol conversion catalyst with the composition Cr₂O₃ · Al₂O₃ · ZnO has been formed on the inner surface of the channels, and a thin oxide coating of composition P_0.03Ti_0.97O_{2 ± δ} with a homogeneous porous structure and 〈d〉 ～ 2 nm has been formed on the geometric membrane surface. The methanol conversion rate and the gas permeability of the membrane depend considerably on the methanol vapor and gas (H₂, He, CO₂, Ar, CH₄) flow directions. When methanol vapor diffuses toward the mesoporous layer, the catalytic activity is one order of magnitude higher and the gas permeability coefficients are 3–8 times lower than in the case of the reverse flow of the gaseous molecules. The temperature dependence of the gas permeability taking into account the possible types of mass transfer in porous solids suggests that, when the gases move toward the mesoporous coating consisting of phosphorus-modified titanium oxide, surface flow and activated diffusion dominate, whereas the reverse gas motion is dominated by free molecular flow.     

Hydrocarbon solubility,permeability, and competitive sorption effects in polymer of intrinsic microporosity (PIM‐1) membranes

The sorption and permeation of pentane, hexane, and toluene through highly permeable polymer of intrinsic microporosity (PIM‐1) membranes were investigated. It was established that the hydrocarbons sorbed strongly within the micro‐void regions of the PIM‐1 membrane. The sorption concentration was similar for the paraffins, pentane and hexane, but greater for aromatic toluene at high vapor activities. The magnitude of the hydrocarbon permeability was associated with the critical temperature of the hydrocarbon. The PIM‐1 membrane displayed selectivity for the three hydrocarbons over CO₂. As a consequence, the presence of the three hydrocarbons dramatically reduced the permeability of CO₂ and N₂ under mixed gas–vapor conditions to 68%–95% below the dry gas value. For all three hydrocarbons the N₂ permeability was more strongly impacted than CO₂ permeability, and hence the ideal CO₂/N₂ selectivity of PIM‐1 increased. It was determined that CO₂ and N₂ solubility decreased because of hydrocarbon competitive sorption while CO₂ and N₂ diffusivity also decreased because of anti‐plasticization, which was due to the presence of hydrocarbon clusters within the membrane structure. There was a clear correlation between the magnitude of anti‐plasticization and the critical temperature of the hydrocarbon. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 397–404     

Gas transport through homogeneous and asymmetric polyethersulfone membranes

Both homogeneous and asymmetric polyethersulfone (PES) membranes were prepared by solvent casting. The sorption and permeation behavior of CO₂, O₂, and N₂ using these two kinds of cast PES membranes and commercially available homogeneous PES film was investigated to extract the pressure dependence of gas permeability and the permselectivity for CO₂ relative to N₂, and to confirm the validity of the working assumption that a skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane. The pressure dependence of the mean permeability coefficient to CO₂ in homogeneous membranes obeys the dual-mode mobility model. The ideal separation factor for CO₂ relative to N₂ at an upstream pressure of 0.5 MPa attains ca. 40, while the permeability to CO₂ is about 2.7 Barrer at the same upstream pressure. The same separation factor in asymmetric membranes amounts to 35. The diffusion behavior for the skin layer in an asymmetric membrane with a thin skin layer can be simulated approximately by that in a homogeneous dense membrane. © 1993 John Wiley & Sons, Inc.     

Gas transport in polybutadiene treated with aqueous bromine

Diffusion, solubility, and permebility coefficients were measured for He, Co₂, Ar, and CH₄ in polybutadiene (PB) and in polybutadiene reacted in the solid state to various extents with aqueous bromine. Analysis of the sorption curves and X-ray emission spectra showed that the bromination created a heterogeneous membrane with an outer brominated skin and an unreacted core. At relatively low extent of bromination, the diffusion and permeability coefficients for CO₂, Ar, and CH₄ decreased by two orders of magnitude, while the transport coefficients for He were virtually unchanged. The permeability coefficients for CO₂, Ar, and CH₄ became immeasurably small after about 3% bromination. The ideal separation factor for gas pairs with different molecular size increased with bromination, suggesting applications in gas separation processes. © 1993 John Wiley & Sons, Inc.