Copolyimide Membranes Research Articles

Sulfonated copolyimide membranes derived from a novel diamine monomer with pendant benzimidazole groups for fuel cells

Sulfonated polyimides are among the most interesting proton exchange membrane materials with high proton conductivity and good mechanical characteristics. As a major challenge the hydrolytic instability of the polymer backbone is addressed by introducing basic moieties in the polymer main chain. A series of sulfonated copolyimides (SPI) are prepared via random copolymerizatio of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) with a new diamine monomer with pendant benzimidazole groups, 2,2′-bis(4-(1H-benzo[d]imidazol-2-yl)phenoxy)benzidine (BIPOB), and a sulfonated diamine monomer 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS) at different diamine molar ratios (BAPBDS/BIPOB, 4/1, 6/1, 9/1 and 12/1). With ion exchange capacities in the range of 1.60–2.24meqg−1, transparent and ductile membranes are obtained by solution casting. The incorporation of benzimidazole pendant groups significantly improves the hydrolytic stability as well as the radical oxidative stability of the membranes. In addition, the SPI membranes exhibit high proton conductivities of 0.1Scm−1 in the fully hydrated state at 60°C and high elastic modulus and tensile strength. Preliminary fuel cell tests demonstrate the technical feasibility and stability of the materials.

Synthesis of ultra-high-strength electroactive polyimide membranes containing oligoaniline in the main chain by thermal imidization reaction

A series of electroactive polymers of poly(amic acid) (PAA) containing aniline trimers were synthesized from electroactive diamine (amino-capped aniline trimer, ACAT), 4,4′-oxydianiline (ODA), and 4,4′-(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride) (BSAA). The prepared PAA polymers were heated to cyclize to polyimide (PI) membranes by a conventional thermal imidization reaction. The structure and electroactivity of the PIs were characterized by Fourier transform infrared (FT-IR) spectroscopy, UV–visible spectroscopy, and cyclic voltammetry (CV). The effects of different molar ratios of ACAT and ODA on the physical properties of electroactive PI (EPI) membranes were investigated by dynamic mechanical analysis (DMA), tensile test, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The as-prepared EPI membranes showed significantly enhanced mechanical strength and thermal stability than those of non-electroactive PI (NEPI) and electroactive copolyimide (ECPI) membranes. For example, upon loading of ACAT, the tensile strength, thermal decomposition (Td) temperature, and glass transition (Tg) temperature of the EPI membranes increased by >200%, ∼45°C, and ∼35°C, respectively.

Pervaporation dehydration of acetone using P84 co-polyimide flat sheet membranes modified by vapor phase crosslinking

In this work, a unique vapor crosslinking method is applied for the first time to fabricate polyimide-based pervaporation membranes for the dehydration of acetone. By controlling the temperature and duration of the crosslinking reaction using ethylenediamine (EDA) vapor and using the right dope formulation to cast P84 co-polyimide membranes with balanced macrovoid and sponge-like morphology, we have optimized the crosslinking parameters to obtain a membrane with a separation factor of 53 (i.e., a water permeate concentration of 90%) and a high flux of 1.8kgm−2h−1 for pervaporation dehydration of acetone at 50°C from a feed of 85/15 acetone/water. With the aid of characterizations for surface chemistry and physics of the modified membranes, such as FTIR-ATR, XPS, and XRD, the crosslinking between EDA and P84 is confirmed at the selective layer of the membrane, as well as structure–performance relationship. This new modification method for pervaporation membranes is attractive for creating a new class of membranes for the separation of organic solvents and biofuel.

Permeability, Solubility, Diffusivity, and PALS Data of Cross-linkable 6FDA-based Copolyimides

The intrinsic gas transport properties of thermally treated cross-linkable 6FDA-based copolyimide membranes have been studied. Grafting various sizes of cyclodextrin (CD) to the copolyimide matrix and then thermally decomposing CD at elevated temperatures are an effective method to micromanipulate microvoids and free volume as well as gas sorption and permeation. The pressure-dependent solubility and permeability coefficients were found to follow the dual-mode sorption model and partial immobilization model, respectively. Solubility and permeability coefficients of CH4, CO2, C3H6, and C3H8 were conducted at 35 °C for different upstream pressures. The Langmuir saturation constant, CH′, increases with an increase in annealing temperature. On the other hand, Henry’s solubility coefficient kD and Langmuir affinity constant b do not change noticeably. The CH4 permeability decreases with pressure, while some membranes exhibit serious plasticization with an increase in CO2, C3H6 and C3H8 pressures. The diffusivi...

POSS-hybrid membranes for the removal of sulfur aromatics by pervaporation

Membrane-based separations are a promising attempt for desulfurization of fuels in petrochemical industry. The focus on research is to investigate membranes, which are more efficient and show better separation characteristics. Hybrid membranes made of an organic polymer and inorganic compounds combine both in one material and new properties can be realized. Here new hybrid membranes of polyimides and POSS (polyhedral oligomeric silsesquioxane) compounds for desulfurization by the membrane-based separation process pervaporation were investigated. The POSS compounds can act as cross-linking agent between polymer chains through reactive organic side groups, resulting in improved membrane properties.In pervaporation experiments the behavior of glycidyl-POSS hybrid membranes with different amount of POSS as additives have been analyzed for a binary mixture consisting of benzothiophene and n-dodecane in comparison to a native copolyimide membrane. Thereby the concentration of benzothiophene has been varied. The hybrid membranes showed lower fluxes due to cross-linking, correlating with PALS and WAXD results. At higher temperatures also higher selectivity is found. Furthermore in stress strain measurements the glycidyl-POSS hybrid membranes showed improved properties in comparison to a native membrane.

Synthesis and characterization of a phosphonated graft copolyimide for direct methanol fuel cells application

The synthesis method and characterization of novel phosphonate graft copolyimides series via 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) were proposed. A branched polyimide structure was achieved by coupling the hydrophilic phosphonated polymide and hydrophobic polyimide with 3, 3′-diaminobenzidine.A phosphonated branched copolyimide exhibited high thermal stability, with a starting decomposition temperature in nitrogen of ~450 °C. The proton conductivity and the methanol permeability of phosphonate graft copolyimide membrane were studied. At room temperature and hydrated condition, the phosphonated membrane with highest IEC ~ 1.43 meq/g showed slightly lower proton conductivity than Nafion®117, however its methanol permeability is 5 times lower than Nafion®117. The decrease in methanol permeability with desirable proton conductivity could increase the feasibility of polymer electrolyte membranes for DMFC application.

Thermal degradation of crosslinked copolyimide membranes to obtain productive gas separation membranes

By removing anhydride groups from crosslinked copolyimide membranes at 430 °C, partially pyrolysed membranes were obtained and gas separation properties were evaluated and related to the content of labile groups. The spaces occupied by the linking anhydride groups prevailed as micropores, which greatly improved the gas transport properties.The release of the labile groups was confirmed by TGA and FT-IR spectroscopy which permitted us to establish that polymer main chains did not suffer any substantial change during the pyrolytic treatment. During the heating step new cross-linking points are created, no Tg below 450 °C could be observed and the process prevents the collapse of micropores.The pyrolysed membrane obtained from the precursor with the lowest content of anhydride groups showed the highest permeability values: 101, 25, 17 and 446 barrers to O2, N2, CH4 and CO2 respectively, and a selectivity to CO2/CH4 of 26, good enough to place this membrane close to Robeson's new upper bound (2008), while the crosslinked precursor membrane fell below Robeson's old upper bound (1991).

Investigation of cross-linked and additive containing polymer materials for membranes with improved performance in pervaporation and gas separation.

Pervaporation and gas separation performances of polymer membranes can be improved by crosslinking or addition of metal-organic frameworks (MOFs). Crosslinked copolyimide membranes show higher plasticization resistance and no significant loss in selectivity compared to non-crosslinked membranes when exposed to mixtures of CO2/CH4 or toluene/cyclohexane. Covalently crosslinked membranes reveal better separation performances than ionically crosslinked systems. Covalent interlacing with 3-hydroxypropyldimethylmaleimide as photocrosslinker can be investigated in situ in solution as well as in films, using transient UV/Vis and FTIR spectroscopy. The photocrosslinking yield can be determined from the FTIR-spectra. It is restricted by the stiffness of the copolyimide backbone, which inhibits the photoreaction due to spatial separation of the crosslinker side chains. Mixed-matrix membranes (MMMs) with MOFs as additives (fillers) have increased permeabilities and often also selectivities compared to the pure polymer. Incorporation of MOFs into polysulfone and Matrimid® polymers for MMMs gives defect-free membranes with performances similar to the best polymer membranes for gas mixtures, such as O2/N2 H2/CH4, CO2/CH4, H2/CO2, CH4/N2 and CO2/N2 (preferentially permeating gas is named first). The MOF porosity, its particle size and content in the MMM are factors to influence the permeability and the separation performance of the membranes.

Polymeric homogeneous composite membranes for separations in organic solvents

AbstractA new generation of organic solvent nanofiltration (NF) composite membranes was prepared combining a support layer with a selective layer made both from the same polymeric material (P84 copolyimide). These membranes, homogeneous in composition, but composite in structure, were defined as polymeric homogeneous composite (PHC) membranes. The composite membranes have the advantage over the asymmetric ones that each layer can be optimized independently. Moreover, the use of the same material for the preparation of both, the selective and the support layer, ensures a high affinity between the two layers and increases the long‐term stability of the composite membranes, reducing the possibility of delamination phenomena. In the design of the PHC membranes, a great attention was devoted to the support layer development. The effects of the composition of the casting solutions on the structure of porous P84 copolyimide membranes were investigated allowing to identify the conditions for the preparation of highly permeable, chemically, and mechanically stable P84 sponge like porous membranes. PHC membranes were prepared by coating and controlled solvent evaporation of a P84 solution on the optimized support crosslinked by reaction with a diamine (1,5‐diamino‐2‐methylpentane). Pure solvent permeation test and rejection experiments were carried out on the P84 supports and the corresponding PHC membranes in aggressive organic solvents like N‐methyl‐2‐pyrrolidone and N,N‐dimethyformamide, in which the original polymer was soluble. The PHC membrane resulted completely stable over long times (>96 h). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Influence of the Water Content on the Diffusion Coefficients of Li+ and Water across Naphthalenic Based Copolyimide Cation-Exchange Membranes

The transport of lithium ions in cation-exchange membranes based on sulfonated copolyimide membranes is reported. Diffusion coefficients of lithium are estimated as a function of the water content in membranes by using pulsed field gradient (PFG) NMR and electrical conductivity techniques. It is found that the lithium transport slightly decreases with the diminution of water for membranes with water content lying in the range 14 < λ < 26.5, where λ is the number of molecules of water per fixed sulfonate group. For λ < 14, the value of the diffusion coefficient of lithium experiences a sharp decay with the reduction of water in the membranes. The dependence of the diffusion of lithium on the humidity of the membranes calculated from conductivity data using Nernst-Planck type equations follows a trend similar to that observed by NMR. The possible explanation of the fact that the Haven ratio is higher than the unit is discussed. The diffusion of water estimated by (1)H PFG-NMR in membranes neutralized with lithium decreases as λ decreases, but the drop is sharper in the region where the decrease of the diffusion of protons of water also undergoes considerable reduction. The diffusion of lithium ions computed by full molecular dynamics is similar to that estimated by NMR. However, for membranes with medium and low concentration of water, steady state conditions are not reached in the computations and the diffusion coefficients obtained by MD simulation techniques are overestimated. The curves depicting the variation of the diffusion coefficient of water estimated by NMR and full dynamics follow parallel trends, though the values of the diffusion coefficient in the latter case are somewhat higher. The WAXS diffractograms of fully hydrated membranes exhibit the ionomer peak at q = 2.8 nm(-1), the peak being shifted to higher q as the water content of the membranes decreases. The diffractograms present additional peaks at higher q, common to wet and dry membranes, but the peaks are better resolved in the wet membranes. The ionomer peak is not detected in the diffractograms of dry membranes.

Mixed gas and pure gas transport properties of copolyimide membranes

AbstractCopolyimides were synthesized from dianhydride of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with various diamine contents of 4,4′‐oxydianiline (ODA) and 2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (TeMPD) by chemical imidization in a two‐step procedure. Polyimides (PIs) were characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, as well as specific volume and free volume. The gas transport properties for pure gas and blends of CO2 and CH4 for the homopolymers and 6FDA‐ODA/TeMPD copolymers were investigated at 35°C and 150 psi pressure. In pure gas permeation, permeability of CO2 and CH4 increased with increasing TeMPD content in the diamine moiety, whereas the ideal selectivity decreased with increasing TeMPD content. In the mixed gas permeation, permeabilities and separation factor were measured as a function of CO2 feed molar fraction for five PI membranes. The behavior of pure gas and mixed gas permeabilities and separation factor of CO2/CH4 mixtures as the chemical nature of the diamine and the CO2 molar fraction in the feed gas were varied and are discussed in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013

Proton conductive properties of composite membranes containing uniaxially aligned ultrafine electrospun polyimide nanofiber

The nanofiber electrospun from the five-membered ring sulfonated polyimide containing the fluorinated group showed an ultrafine and uniform non-beaded structure and the optimized electrospinning conditions produced the sulfonated polyimide nanofibers with several appropriate diameters ranging from 80 to 160 nm. Novel sulfonated copolyimide membranes containing uniaxially aligned ultrafine sulfonated copolyimide nanofibers were prepared for proton exchange membrane fuel cell applications. The proton conductivity of the composite membrane in the parallel direction to the nanofibers alignment increased with the decreasing nanofiber diameter and the increasing amount of nanofibers in the composite membrane and reached 0.3 S cm−1 at 90 °C and 98% RH. In addition, the parallel proton conductivity indicated significantly higher values when compared to that determined for the composite membrane in the perpendicular direction or for the membrane without nanofibers prepared by a conventional solution-casting method. The composite membranes also showed higher chemical stabilities than those of the membrane without nanofibers. Consequently, nanofibers proved to be promising proton exchange materials and the composite membranes containing nanofibers may have potential application for use in fuel cells.

Sulfonated block-graft copolyimide for high proton conductive and low gas permeable polymer electrolyte membrane

This paper addresses issues surrounding the design of the proton exchange membrane for fuel cells, and more specifically, the role of the polymer architecture on the proton conductivity and gas permeability. In this study, we describe the syntheses and characterizations of sulfonated block, graft, random-graft, and block-graft copolymers. The proton conductivity and oxygen permeability of the novel sulfonated block-graft copolyimide, S-bg-PI, showed 0.44 S cm−1 at 80 °C and 98%RH and 3.2 × 10−12 cm3(STP) cm/(cm2 sec cmHg) at 35 °C and 76 cmHg, respectively, while those of Nafion indicated 0.15 S cm−1 and 1.1 × 10−10 cm3(STP) cm/(cm2 sec cmHg) under the same conditions, respectively. The apparent selectivity ratio calculated from the proton and oxygen transports of S-bg-PI was 103 times larger than that determined in Nafion, indicating that the novel sulfonated block-graft copolyimide membrane has excellent properties for fuel cell applications.

Synthesis and characterization of sulfonated copolyimides via thermal imidization for polymer electrolyte membrane application

A series of soluble copoly(amic acid) precursors were synthesized with varying compositions by the conventional polycondensation of 3,3′,4,4′-biphenyltetracarboxylic anhydride (BPDA) and 3,3′-sulfonyldianiline (SDA) using 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS), a sulfonated diamine, as a third component in NMP. The synthesized precursor polymers are soluble in polar aprotic solvents. The chemical structures and inherent viscosities of the copoly(amic acid)s were determined by 1H NMR spectroscopy and viscometry, respectively. The free standing sulfonated copolyimide membranes were fabricated from solutions of the copoly(amic acid)s by a thermal imidization process and subsequent soaking in sulfuric acid solution. The chemical structure and thermal properties of the sulfonated copolyimides in the films were investigated in detail using FT-IR, DSC, and TGA. The sulfonated copolyimides show mainly three-step thermal degradation, with the degradation behavior being independent of the composition. In addition, the properties of the membranes were investigated, including their water uptake (WU), ion exchange capacity (IEC) and proton conductivity. The WU and IEC values of the sulfonated copolyimides were 8.12–38.0% and 0.18–2.05meq/g, respectively, depending on the composition of the sulfonated diamine, and the proton conductivity of the copolyimides was dependent on the content of the sulfonated diamine. The proton conductivity values of the membranes were lower than that of Nafion 117, although their IEC values were higher.

Nanoprobe imaging molecular scale pores in polymeric membranes

A long-standing goal of materials microscopy is the imaging of nanoporous polymeric membranes at nanometer resolution. In particular, no technique has been developed to “see” nanopores with dimensions in the 0.5–2 nm range. These pores are crucial in the functional performance of nanofiltration (NF) membranes used for molecular separation processes. The major problem in imaging at this scale is insufficient electron contrast of polymers, which has made distinguishing their structural phases at the nanoscale not practically feasible. Here we describe an in situ physicochemical characterization technique to measure size of the transport active pores. Nanopores in an asymmetric organic solvent nanofiltration (OSN) membrane are filled with high contrast osmium dioxide (OsO2) nanoparticles, whose spatial arrangement is mapped under transmission electron microscopy (TEM). Due to the uniquely small size range of these probes, they target nanopores in the membrane skin layer. Thus, pore size distribution and even polymer chain structure can be evaluated. The pore size is found to correlate well with membrane separation performance, and the molecular separation mechanism of the nanofiltration P84 co-polyimide membrane is shown to be due to size exclusion of the larger nanoparticles.

Characterization of maleimide dimers in photo-cross-linked copolyimide films

Copolyimide membranes are established materials for the separation of gaseous and liquid mixtures. Cross-linking of the polymer strands improves the physical and chemical stability. The photo-cross-linking of a 6FDA-ODA/6FDA-DABA 4 : 1 copolyimide membrane containing maleimide side groups as linker was investigated by FTIR spectroscopy. IR absorption spectra of the copolyimide backbone, 3-hydroxypropyldimethyl maleimide and the copolyimide functionalized with 3-hydroxypropyldimethyl maleimide were measured before and after different irradiation times and compared to each other. For band assignment a normal mode analysis was performed. The backbone of the polymer and the maleimide linker can be well distinguished due to their different spectral band positions. Only the films containing a maleimide moiety perform a photoreaction, the polymer backbone does not interfere. Based on the difference spectra and the results of the DFT calculations it was shown that the trans- and the cis-cycloadduct as well as the previously suggested 2-2'-adduct without a cyclobutane ring are formed upon UV irradiation. Evidence for an oxetane-like photoproduct was not found. Different time constants for the increase of the product bands were observed. The cycloadduct accumulates with a shorter time constant (τ = 2 to 5 min) than the 2-2'-adduct (τ = 75 min). The yield of the photo-cross-linking reaction was determined by spectral deconvolution and kinetic fitting of several marker bands. For the copolyimide synthesized in this work, a maximum value of 6% was reached. The stiffness of the copolyimide backbone inhibits further photo-cross-linking.

Polymeric membranes for light olefin/paraffin separation

Olefins are produced in the petrochemical industry by steam cracking of parrafins, followed by repeated compression and distillation to separate the complex vapour mixtures. The second step is considered to be a highly energy-intensive process and have been extensively studied for possible replacements. The use of membranes has been the focal point of research as a new means of olefin/paraffin separation due to its lower operating and capital costs. In this article, a comprehensive review is presented for the application of polymeric membranes in light olefin/paraffin separation. It covers all types of membrane materials starting from the conventional polymers to more advanced ones such as polyimide and copolyimide membranes. Permeation and separation characteristics of all polymeric membranes are summarized and discussed in great details.

Natural gas purification and olefin/paraffin separation using cross-linkable 6FDA-Durene/DABA co-polyimides grafted with α, β, and γ-cyclodextrin

Using a cross-linkable co-polyimide (6FDA-Durene/DABA (9/1)), we have developed new flexible and high-performance gas separation membranes that can enhance both membrane permeability and plasticization resistance simultaneously by grafting various sizes of cyclodextrin to the polyimide matrix and then decomposing them at elevated temperatures. The gas permeability of thermally treated pristine polyimide (referred as the original PI) and CD grafted co-polyimide (referred as PI-g-CDs for 200 and 300 °C and partially pyrolyzed membranes (PPM)-CDs for 350, 400, and 425 °C) has been determined using O 2, N 2, CO 2, CH 4, C 3H 6, and C 3H 8 at 35 °C. The permeability of all gases increases with an increase in thermal treatment temperature from 200 to 425 °C. However, permeability increases more for those grafted with bigger size CD. Permeability of the original PI thermally treated at 425 °C is about 4–6 times higher than that treated at 200 °C. The permeability increase jumps to 8–10 times for PPM-α-CD and 15–17 times for PPM-γ-CD due to CD decomposition at high temperatures and bigger CD creating bigger micro-pores. Interestingly, the permeability ratios of PPM-α-CD to PPM-γ-CD and PPM-β-CD to PPM-γ-CD at 400 and 425 °C are around 0.6 and 0.8, respectively. These numbers are almost the same as the cavity diameter ratios of α-CD to γ-CD and β-CD to γ-CD. Clearly, the bigger CD creates the bigger micro-pores. Permselectivity decreases first with an increase in thermal treatment temperature up to 350 °C and then increases. Permselectivity of thermally treated CD grafted co-polyimide membranes is also slightly higher than that of the original PI due to higher degrees of cross-linking in CD grafted co-polyimide membranes. In addition, for co-polyimide membranes grafted by CDs, the higher thermal treatment temperature results in membranes with the better plasticization resistance to CO 2 and the better separation performance for 50:50 CO 2/CH 4 mixed gases. The best result for pure gas tests is achieved for PPM-γ-CD-425. This membrane has a CO 2 permeability of 4211 Barrers with a CO 2/CH 4 ideal selectivity of 22.44 and a C 3H 6 permeability of 521 Barrers with a C 3H 6/C 3H 8 ideal selectivity of 18.09. It can also resist against CO 2 plasticization until 30 atm. The CO 2 permeability drops slightly to 3976 Barrers with almost the same CO 2/CH 4 selectivity of 22.84 in mixed gas tests.

Preparation and properties of ionic cross-linked sulfonated copolyimide membranes containing pyrimidine groups

A series of sulfonated copolyimides containing pyrimidine groups (SPIs) were synthesized by random copolymerization of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 2-(4-aminophenyl)-5-aminopyrimidine (PAPRM), and 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS). Proton exchange treatment in 1.0 M sulfuric acid solution resulted in ionic cross-linking of the sulfonated copolymers due to the acid (sulfonic acid)-base (pyrimidine group) interactions and the membrane with more basic PAPRM moiety could absorb sulfuric acid to favor the proton transfer. The effects of the structure of the diamines on the properties of SPI membranes were evaluated by studying the membrane parameters including water uptake, proton conductivity, water stability, and methanol permeability. The basic pyrimidine groups introduced in the main chains could effectively resist membrane swelling due to the strong interchain interactions through basic pyrimidine groups and sulfonic acid groups. Compared with the corresponding uncross-linked copolyimides (NTDA/ODADS/ODA), the acid–base copolyimides displayed excellent water stability. The SPI membranes also exhibited improved mechanical properties and decreased methanol permeability. However, the cross-linked membranes showed lowered proton conductivities than the uncross-linked ones because a small part of the sulfonic acid groups had been consumed during the cross-linking process. Copyright © 2010 John Wiley & Sons, Ltd.

Functionalized copolyimide membranes for the separation of gaseous and liquid mixtures

Functionalized copolyimides continue to attract much attention as membrane materials because they can fulfill the demands for industrial applications. Thus not only good separation characteristics but also high temperature stability and chemical resistance are required. Furthermore, it is very important that membrane materials are resistant to plasticization since it has been shown that this phenomenon leads to a significant increase in permeability with a dramatic loss in selectivity. Plasticization effects occur with most polymer membranes at high CO2 concentrations and pressures, respectively. Plasticization effects are also observed with higher hydrocarbons such as propylene, propane, aromatics or sulfur containing aromatics. Unfortunately, these components are present in mixtures of high commercial relevance and can be separated economically by single membrane units or hybrid processes where conventional separation units are combined with membrane-based processes. In this paper the advantages of carboxy group containing 6FDA (4,4′-hexafluoroisopropylidene diphthalic anhydride) -copolyimides are discussed based on the experimental results for non cross-linked, ionically and covalently cross-linked membrane materials with respect to the separation of olefins/paraffins, e.g. propylene/propane, aromatic/aliphatic separation e.g. benzene/cyclohexane as well as high pressure gas separations, e.g. CO2/CH4 mixtures. In addition, opportunities for implementing the membrane units in conventional separation processes are discussed.