Increasing Feed Pressure Research Articles

WGS-mixture separation and WGS reaction test in a bench-scale multi-tubular membrane reactor

Abstract For pre-combustion CO2 capture in the natural gas combined-cycle power plant, Pd me mbrane reactors are a promising option. A bench-scale multi-tube membrane reactor has been built in ECN and successfully demonstrated the operation for WGS- mixture separation and WGS reaction test with 3 Pd membranes of approx. 5.6 μm thick and 44 cm long in parallel configuration. Both tests were investigated with the following mixture: 4.0% CO, 19.2% CO2, 15.4% H2O, 1.2% CH4 and 60.1% H2 representing the (623 K equilibrium shifted) reformate gas from an oxygen-fed autothermal reformer followed by a shift-reactor, under practical working conditions: T = 673 K , p feed = 20 - 35 bar(a) , p perm = 15 bar(a) . In the separation test, the inhibition effect o f this WGS-mixture resulted in an overall hydrogen permeation drop of approx. 20% compared to H2/N2 mixtures with the same H2 concentration, which enhanced with increasing feed pressure. In the WGS reaction test, the maximum CO conversion and H2 recovery were both achieved as 92% at a feed/permeate pressure of 35/15 bar(a), which is favourable for CO2 capture.

Modeling of unsteady-state permeation of gas mixture through a self-synthesized PDMS membranes

This work presents a comprehensive two-dimensional mathematical model for unsteady state permeation of pure gas and ternary gas mixture through a synthesized single layer PDMS membrane. A numerical model was established for predicting permeation behavior of pure and mixed gases, at different operating conditions of upstream temperatures, pressures and feed compositions. The time lag method was also employed to calculate the diffusion coefficient of each component in a concentration dependant system. The results achieved show that permeability of heavier gas (C3H8) decreases with increasing feed pressure and temperature, whereas those of lighter gases (H2 and CH4) in contrary would increase. Increasing C3H8 concentration in the feed improves permeation of all components, while increasing H2 concentration, significantly increases permeability of H2, in comparison with those of other components. Furthermore, both the comparison between mixed and single gases permeation performances and the effect of cross-link density on PDMS membranes performances were highlighted in this study. The simulation results proved this fact that diffusivity is the dominant parameter on permeability of the lighter gases (H2 and CH4), while solubility has the prevailing affect on permeability of the heavier gases such as C3H8. The simulated results were finally validated with independent pure gas and ternary gas mixture experiments. The results confirmed that there is a reasonable conformity between the predicted values for permeability, solubility, diffusivity and mole fraction in the permeate side of aforementioned components and experimental available data.

Effect of process parameters on nanoemulsion droplet size and distribution in SPG membrane emulsification

A Shirasu-porous-glass (SPG) membrane with a mean pore size of 2.5μm was used to produce an oil/water (O/W) nanoemulsion of flurbiprofen consisting of methylene chloride as the dispersed phase, polyvinyl alcohol (PVA) as the stabilizer and a mixture of Tween 20 and Tween 80 in demineralized water as the continuous phase. Emulsion droplets with a mean droplet size of 25 times smaller than the mean pore size and a narrow droplet size distribution were produced using 5% emulsifier at a feed pressure of 15kPa. Under these conditions the z-average diameter and size distribution of the emulsion droplets formed were influenced by the type of surfactant, agitator speed (150–1200rpm), feed pressure (15–80kPa), stabilizer concentration (0–4, w/v) and the temperature of the continuous phase. Increasing the agitator speed and stabilizer concentration increased the z-average diameter and decreased the size uniformity. There was a linear relationship between the increased feed pressure and the decreased z-average diameter of the emulsion droplets. However, the uniformity of the size distribution decreased with increasing feed pressure. The continuous phase temperature played an important role in particle size and distribution. The nanoemulsion composed of oil, water, PVA and the surfactant mixture at the weight ratio of 10/100/1/5 was prepared using a SPG membrane at an agitator speed of 300rpm, a feed pressure of 15kPa and a continuous phase temperature of 25°C. Our results indicated that these conditions led to relatively uniform emulsion droplets with a narrow size distribution and high zeta potential. This emulsion was stable for at least 13h. Furthermore, the droplets in the emulsion containing the drug were not smaller but were more uniform with a narrower distribution compared to those without the drug.

Crosslinked polyvinylalcohol–polysiloxane/fumed silica mixed matrix membranes containing amines for CO 2/H 2 separation

CO 2-selective membranes containing both amine carriers and fumed silica (FS) in crosslinked poly(vinyl alcohol)–poly(siloxane) (PVA–POS) (FS loading < 22 wt%) and crosslinked PVA (FS loading > 22 wt%) were synthesized for CO 2/H 2 separation. The effects of temperature, feed pressure, gas relative humidities (or water contents) on the feed and sweep sides, crosslinking degree of PVA, and FS loading on transport properties including CO 2 permeability, CO 2/H 2 selectivity, and H 2 permeability, were investigated using a mixed gas containing 20% CO 2 and 80% H 2. The optimal temperature identified was 107 °C. The CO 2 permeability and CO 2/H 2 selectivity typically increased with the relative humidities on the feed and sweep sides. Increasing the crosslinking degree of PVA slightly decreased the CO 2 permeability. The CO 2 permeability and CO 2/H 2 selectivity decreased with increasing feed pressure due to the carrier saturation phenomenon. The CO 2/H 2 selectivity increased by 33.8% from 65 to 87 as FS loading increased from 12 wt% to 22.3 wt% while CO 2 permeability remained nearly constant at about 1130 Barrers. Further increase of FS loading decreased both CO 2/H 2 selectivity and CO 2 permeability. At 107 °C and 220 psia, the membrane with 22.3 wt% FS loading showed the best performance with a CO 2 permeability of 1296 Barrers (1 Barrer = 3.35 × 10 −16 mol m/(m 2 s Pa)) and a CO 2/H 2 selectivity of 87.

Mechanistic understanding of CO2-induced plasticization of a polyimide membrane: A combination of experiment and simulation study

Experimental measurements and fully atomistic simulations are carried out to examine the CO2-induced plasticization of a polyimide membrane synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 4,4′-oxydianiline (ODA). With increasing feed pressure, the permeability of CO2 in the 6FDA-ODA membrane initially decreases, crosses a minimum, and then increases. The plasticization pressure is estimated to be at approximately 8 atm. The radial distribution functions between CO2 and polyimide atoms reveal that the imide groups are the preferential sorption sites, followed by the ether and CF3 groups. The experimental and simulated sorption isotherms of CO2 are in fairly good agreement. At low loadings, CO2 molecules are largely trapped with small mobility. With increasing loading, the polyimide membrane exhibits a depressed glass transition temperature, a dilated volume and an increased fractional free volume. In addition, larger and more interconnected voids appear and the mean radius of voids increases from 2.5 to 3.3 Å with increasing CO2 loading. Consequently, the mobility of both CO2 molecules and polymer chains is enhanced. Based on molecular displacement, the percentages of three types of motions (jumping, trapped, and continuous) are estimated for CO2 in the membrane. The continuous motion contributes predominantly to CO2 diffusion. At a high loading, the ether groups in the polyimide chains exhibit a significant effect on plasticization. It is therefore suggested that the plasticization could be suppressed by substituting the ether groups. The microscopic information of this study is particularly useful for the quantitative understanding of plasticization.

Preparation and characterization of a composite PDMS membrane on CA support

AbstractPolydimethylsiloxane (PDMS) is the most commonly used membrane material for the separation of condensable vapors from lighter gases. In this study, a composite PDMS membrane was prepared and its gas permeation properties were investigated at various upstream pressures. A microporous cellulose acetate (CA) support was initially prepared and characterized. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C3H8, CO2, CH4, and H2 in the prepared composite membrane were measured. Using sorption and permeation data of gases, diffusion coefficients were calculated based on solution‐diffusion mechanism. Similar to other rubbery membranes, the prepared PDMS membrane advantageously exhibited less resistance to permeation of heavier gases, such as C3H8, compared to the lighter ones, such as CO2, CH4, and H2. This result was attributed to the very high solubility of larger gas molecules in the hydrocarbon‐based PDMS membrane in spite of their lower diffusion coefficients relative to smaller molecules. Increasing feed pressure increased permeability, solubility, and diffusion coefficients of the heavier gases while decreased those of the lighter ones. At constant temperature (25°C), empirical linear relations were proposed for permeability, solubility, and diffusion coefficients as a function of transmembrane pressure. C3H8/gas solubility, diffusivity, and overall selectivities were found to increase with increasing feed pressure. Ideal selectivity values of 9, 30, and 82 for C3H8 over CO2, CH4, and H2, respectively, at an upstream pressure of 8 atm, confirmed the outstanding separation performance of the prepared membrane. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Preparation and C3H8/Gas Separation Properties of a Synthesized Single Layer PDMS Membrane

In this paper, a new polydimethylsiloxane (PDMS) membrane was synthesized and its ability for separation of heavier gases from lighter ones was examined. Sorption, diffusion, and permeation of H2, N2, O2, CH4, CO2, and C3H8 in the synthesized membrane were investigated as a function of pressure at 35°C. PDMS was confirmed to be more permeable to more condensable gases such as C3H8. This result was attributed to very high solubility of larger gas molecules in hydrocarbon−based PDMS in spite of their low diffusion coefficients relative to small molecules. The synthesized membrane showed much better gas permeation performance than others reported in the literature. Increasing upstream pressure increased solubility, permeability and diffusion coefficients of C3H8, while these values decreased slightly or stayed constant for other gases. Local effective diffusion coefficient of C3H8 and CO2 increased with increasing penetrant concentration which indicated plasticization effect of these gases over the range of penetrant concentration studied. C3H8/gas solubility, diffusivity and overall selectivities also increased with increasing feed pressure. Ideal selectivity values of 4, 13, 18, 20, and 36 for C3H8 over CO2, CH4, H2, O2, and N2, respectively, at upstream pressure of 7 atm, confirmed the outstanding separation performance of the synthesized mebrane.

Treatment of landfill leachates by nanofiltration

Landfill leachate contains high concentrations of organic matter, color, heavy metals and toxic substances. This study presents the feasibility of a commercial nanofiltration membrane (NF-300) in the removal of pollutants from a landfill leachate generated from the Treatment Stabilization and Disposal Facility in Gujarat state of India. Two different leachate samples (Leachates A and B) were collected from the downstream side of closed landfill cells A and B. The average quality of the leachate was 67 719 mg/L COD, 217 mg/L ammonical nitrogen, 22 418 mg/L BOD, 3847 mg/L chlorides and 909 mg/L sulphate. The operating variables studied were applied pressure (4–20 atm), feed flowrate (5–15 L/min) and pH (2, 4, 5.5 and 6.7). It was observed that the solute rejection ( R O) increased with increase in feed pressure and decreased with increase in feed concentration at constant feed flowrate. In the present study, the rejection of cations followed the sequence: R O (Cr 3+) > R O (Ni 2+) > R O (Zn 2+) > R O (Cu 2+) > R O (Cd 2+) for leachates A and B. The order of solute rejection sequence is inversely proportional to the diffusion coefficients. The rejection of sulphate ions by the NF-300 membrane was 83 and 85%, while the rejection of chlorides was 62 and 65% for leachates A and B, respectively. The NF-300 membrane was characterized by using the combined-film theory-Spiegler–Kedem (CFSK) model based on irreversible thermodynamics and the ion transport model based on the extended Nernst–Planck equation. The membrane transport parameters were estimated using the Levenberg–Marquadt method. The estimated parameters were used to predict the membrane performance and the predicted values are in good agreement with the experimental results.

Characterization of polyethersulfone/polyimide blend membranes prepared by a dry/wet phase inversion: Precipitation kinetics, morphology and gas separation

Flat sheet gas separation membranes of polyethersulfone (PES), polyimide (Matrimid, MI) and their blends were fabricated by a spin casting method followed by a dry/wet induced phase inversion process. The mixing compatibility and thermal stability of the blend membrane were studied by Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA) respectively. The forming behavior was investigated by the ternary phase diagram and an optical microscope with PES, MI and PES/MI blend (5:5). In this ternary system, the average of diffusion coefficient, D e , of PES, MI and EM5050 were respectively 8.35 × 10 −5, 10.22 × 10 −5 and 3.09 × 10 −5 cm 2/s. The morphology of membranes was studied by a scanning electron microscope (SEM). All prepared membranes had an ultrathin dense skin layer (<1 μm) on the top of the membrane. The blend membrane with MI composition from 40 to 80 wt.% showed sponge-like sub-layer whereas pristine membrane as well as the rest of the composition showed the finger-like sub-layer (macrovoids). Gas permeance of N 2, increased with increase in feed pressure irrespective of blend composition. The permselectivity of PES/MI (30/70 wt.%) decreased from 5.4 to 4.9 with increase in the feed pressure.

실크 정련 세리신 단백질의 분리특성과 응용(1)

In this study we have evaluated the separation characteristics and concentration of sericin using tubular type ultrafiltration membrane in silk degumming solution that extracted from electrolytic reduction water process. Ultrafiltration membranes have used in sericin separation performance and the separation characteristics of membrane satisfied typical Hagen-Poiseuille equation. It had the increase of flux according to the increase of feed pressure and temperature in occasion of pure water flux. And also the flux and solute rejection had about <TEX>$25{\sim}60{\ell}/m^2{\cdot}h$</TEX> and more than 95% in sericin feed solution with concentration 1.00~1.89% at feed pressure force of <TEX>$3{\sim}8kgf/cm^2$</TEX> respectively. In addition, the separation performance of tubular type ultrafiltration membrane for silk degumming solution was very steady-state with long experiment time.

Observation of cake layer formation and removal on microporous hollow-fibre membranes

The cake layer in submerged membrane bioreactor (sMBR) processes is leading to an additional flow resistance and it is through this that the long-term filtration performance of the system is af fected. Therefore, air is injected into the suspension to induce flow and to generate shear in order to partly remove the cake layer. Furthermore, the bubble-induced movement of hollow-fibres has been identified to significantly improve the shear production with air bubbling . Hence, this paper will report about experiments conducted on different scales and in different operating modes including novel magnetic resonance imaging (MRI) techniques to visualise the cake layer and quantify the local permeate production. Within the first part of this study, experiments have been performed with a number of model substances to characterise the impact of operating parameters on the filtration performance of stationary hollow-fibre membranes of the PURON® system. The setup consists of a tubular test cell equipped with a single hollow-fibre and is operated with a constant TMP in cross-flow mode without air bubbling. Suspensions containing silica particles of different particle size distributions dispersed in solutions of xanthan gum, with different dynamic viscosities, were filtrated for approximately 30 min while the permeate flux was measured. It was shown that the dynamic viscosity and the shear thinning characteristics of the suspensions are similar compared to established viscosity models of activated sludge . Moreover, the filtration tests have shown that the long-term permeate flux is increasing with an increasing cross-flow velocity, a decreasing solids concentration, a decreasing average particle size and an increasing dynamic viscosity, whereas the long-term permeate flux is independent from the feed pressure. These trends are consistent with published theories which demonstrate that the thickness of the reversible cake layer increases with a decreasing cross-flow velocity and an increasing feed pressure. While an increase in cross-flow velocity is leading to an enhanced entrainment of deposited matter, and thereby to a higher permeate flux, a higher feed pressure is leading to a temporary increase in permeate flux only. However, this benefit is compensated by an increased filtration resistance due to a thicker cake layer, so that the long-term permeate flux is independent from the feed pressure. The contribution to the conference will further include experiments with two different setups operated in submerged mode covering a variation of operating parameters, fluid characteristics, and membrane bundle design. The objectives of these studies are (i) to validate the above-mentioned theory by measuring the cake layer thickness via MRI respectively to (ii) estimate the impact of packing density on the filtration performance of a hollow-fibre bundle. While the first approach is limited to single and not-moving fibres, the latter is complementary to previous studies since both fibre movement and fibre-fibre interactions are taken into account. Hence, in conclusion, the findings out of cross-flow and submerged single fibre tests will be compared to trials with more complex configurations.

Efficient Capture of CO2from Simulated Flue Gas by Formation of TBAB or TBAF Semiclathrate Hydrates

Capturing CO2 by forming hydrate is an attractive technology for reducing the greenhouse effect. The most primary challenges are high energy consumption, low hydrate formation rate, and separation efficiency. This work presents efficient capture of CO2 from simulated flue gas (CO2 (16.60 mol %)/N2 binary mixtures) by formation of semiclathrate hydrates at 4.5 and 7.1 °C and feed pressures ranging from 2.19 to 7.31 MPa. The effect of 0.293 mol % tetra-n-butyl ammonium bromide (TBAB) and tetra-n-butyl ammonium fluoride (TBAF) on the hydrate formation rate, reactor space velocity, and CO2 separation efficiency was studied in a 1 L stirred reactor. The results showed the hydrate formation rate constant increased with increasing feed pressure and reached the maximum at 2.82 × 10−7 mol2/(s·J) with TBAB and 8.26 × 10−7 mol2/(s·J) with TBAF. The space velocity of the hydrate reactor increased with increasing feed pressure and reached a maximum of 13.46 h−1 with TBAB and 25.96 h−1 with TBAF. CO2 recovery was about...

Butane isomer separation with composite zeolite MFI mebranes

Zeolite MFI crystal layers were grown on different α-alumina supports. Permeation and separation characteristics of selected zeolite MFI composite membranes were measured for the system of butane isomers. Flux, permeation and separation factors were measured as a function of feed pressure, temperature and feeding amount of butane isomers. The experiments, based on Wicke–Kallenbach method, were carried out using steady-state membrane apparatus MEMFIS. The observed fluxes and permeances of n-butane were higher in comparison with isobutane for all membranes. The separation factors exhibited the maxima in the dependence on temperature and decreased with increasing feed pressure. It follows from the comparison of single component and binary mixture experimental data that n-butane permeance was strongly reduced by the presence of isobutane as a co-permeating component in the binary mixture. However, isobutane was practically not influenced by the presence of n-butane. Long-term continuous membrane separation resulted in gradual decrease of butane isomers flux and corresponding separation factor. The flux decrease was more pronounced for isobutane. Reactivation of the membranes showed a slight increase of butane isomers flux but continuous decrease of separation factor.

Gas permeation through a synthesized composite PDMS/PES membrane

In this paper, a defect-free polydimethylsiloxane (PDMS)-based composite membrane was synthesized and characterized. The membrane consisted of a thin PDMS film (4 μm) and polyethersulfone (PES) as a support material. At first, a macroporous PES support was prepared by phase inversion method and its thickness, porosity, pore size distribution and surface porosity were determined. PES characterization results confirmed suitability of the support for the composite membrane preparation. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C 3H 8, CO 2, CH 4 and H 2 through the synthesized composite membrane were measured at various upstream pressures and based on solution–diffusion mechanism, their diffusion coefficients were calculated. Flory–Huggins (FH) interaction parameters, χ, of the gases with the polymer matrix were calculated based on Flory–Rehner (FR) expression for the crosslinked PDMS membrane and discussed. The concentration-averaged FH interaction parameters of H 2, CH 4, CO 2 and C 3H 8 in the synthesized PDMS membrane were estimated to be 2.526, 0.102, 0.435 and 0.248, respectively. Higher χ values exhibited less favorable interactions between the gas and the membrane and vice versa. Chemical similarity of CH 4 with backbone structure of PDMS, led to the lowest concentration-averaged χ values for CH 4. Increasing feed pressure increased permeability, solubility and diffusion coefficients of bigger gases while decreased those of smaller ones. Hence, C 3H 8/gas ideal selectivity also increased with increasing feed pressure. Only, local effective diffusion coefficient of C 3H 8 increased with increasing penetrant concentration which indicated plasticization effect of C 3H 8 over the range of penetrant concentration studied.

Effect of feed pressure on the performance of the photovoltaic powered reverse osmosis seawater desalination system

This paper describes the potential of the development of a seawater desalination system that combines the technologies of reverse osmosis (RO) and photovoltaic (PV) to deliver 100 m 3/day of sweet water. Silicon cells are chosen for the PV array and the polyamide thin-film composite seawater Filmtec membranes are selected for the RO system. The software ROSA is adopted to study the influences of the feed pressure on the performance of the system. It is found that as the feed pressure increases, the specific energy of the plant decreases but the percentage of recovery increases.

Separation of binary heavy metals from aqueous solutions by nanofiltration and characterization of the membrane using Spiegler–Kedem model

Heavy metals are important sources of environmental pollution and are non-degradable, and therefore, continue to exist in water. Membrane technology is one option for the separation of heavy metals from wastewater without generating any pollution load. This paper presents the binary heavy metals (cadmium and nickel) separation capability of a commercial nanofiltration membrane from aqueous solutions. The influence of applied pressure, feed solute concentration, feed flowrate, feed pH and nature of anion on the retention of cadmium and nickel ions is studied. It is observed that the rejection increases with increase in feed pressure and decreases with increase in feed concentration at constant feed flowrate. The maximum observed solute rejection of nickel and cadmium ions are 98.94% and 82.69%, respectively, for an initial feed concentration of 5 ppm. The NF membrane is characterized by using the Spiegler–Kedem model based on irreversible thermodynamics coupled with film theory. Boundary layer thicknesses, as well as the membrane transport parameters are estimated by using the Levenberg–Marquardt method. The estimated parameters are used to predict the membrane performance and found that the predicted values are in good agreement with the experimental results.

Beneficiation of low-grade diasporic bauxite with hydrocyclone

Low-grade diasporic bauxite was treated with hydrocyclone of small cone-angle. The effects of apex diameter, feed pressure and feed concentration on separation indexes were tested, and then the separation process was discussed by hydrokinetics tentatively. The results show that the increase of apex diameter changes the spacial locality of the envelope of zero vertical velocity, resulting in decrease of the ratio of Al 2O 3/SiO 2 in overflow and increase of the recovery of Al 2O 3 in underflow, while feed pressure and feed concentration have no remarkable effect on the spacial locality of the envelope of zero vertical velocity, however, the separation indexes are improved by the increase of feed pressure, but are worsened by the increase of feed concentration.

Application of nanofiltration for the rejection of nickel ions from aqueous solutions and estimation of membrane transport parameters

The present work deals with the application of a thin-film composite polyamide nanofiltration membrane for the rejection of nickel ions from aqueous wastewater. The operating variables studied are feed concentration (5–250 ppm), applied pressure (4–20 atm), feed flowrate (5–15 L/min) and pH (2–8). It is observed that the observed rejection of nickel ions increases with increase in feed pressure and decreases with increase in feed concentration at constant feed flowrate. The maximum observed rejection of the metal is found to be 98% and 92% for an initial feed concentration of 5 and 250 ppm, respectively. The effect of pH on the rejection of nickel ions and permeate flux are studied, and found that the variation in pH is having more effect on the latter than the former. The experimental data are analyzed using membrane transport models; combined-film theory-solution-diffusion (CFSD), combined-film theory-Spiegler–Kedem (CFSK) and combined-film theory-finely porous (CFFP) models; to estimate membrane transport parameters and mass transfer coefficient, k. Also, enrichment factor, concentration polarization modulus and Peclet number are found from various parameters. From CFFP model the effective membrane thickness and active skin layer thickness are found.

Treatment of Acid Mine Drainage (AMD) by Ultra-Low-Pressure Reverse Osmosis and Nanofiltration

Secondary treatment of acid mine drainage (AMD) from a copper mine in China which has very low-concentration heavy metal ions and high conductivity (2,800 μs/cm), was attributed to the high concentration of dissolved monovalent and divalent ions. Commercially available polyamide ultra-low pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes were used to remove heavy metal ions and reclaim AMD. Effects of operation pressure, pH, temperature, water recovery efficiency, and operation time on ULPRO and NF performance were investigated. Experimental results show that the rejection increased with an increase of feed pressure and decreased with an increase of feed temperature, and it is dependent on feed pH. Generally, the rejections of heavy metal and total conductivity were greater than 97 and 96% for the ULPROM tested, respectively, which suggested the suitability of such membrane for AMD for the recovery of heavy metal and reclaiming wastewater. However, NF process was capable of removing about 90% of the heavy metals in the AMD and decreased 48% of the total conductivity.

Materials dependence of mixed gas plasticization behavior in asymmetric membranes

The mass transport of asymmetric membranes for the separation of carbon dioxide/methane mixtures is determined by competitive sorption and plasticization. With increasing feed pressure in mixed gas experiments, the selectivity decreases due to both effects. Distinction whether one or the other mechanism is responsible for the selectivity loss is important since competitive sorption is related to intrinsic material properties and cannot be tailored, whereas plasticization can be suppressed by various chemical means. This paper describes the systematic analysis for five different asymmetric membranes with respect to the balance between competitive sorption and plasticization. Four asymmetric membranes where prepared for this study, one membrane was based on a commercial precursor. Of these membranes, three are based on the polyimide Matrimid: pure Matrimid, and blends of Matrimid with polyethersulfone as well as Matrimid with a polyimide P84. These membranes are compared with two other ones: cellulose acetate and polyphenyleneoxide PPO. The blend of Matrimid with P84 shows the highest mixed gas selectivity and is very resistant against plasticization without any further chemical modification.