CO2 Permeation Properties Research Articles

Highly selective CO2 permeable double-network ionogel membrane containing 1-ethyl-3-methylimidazolium dicyanamide

A double-network (DN) ionogel membrane containing 1-ethyl-3-methylimidazolium dicyanamide ([C2mim][DCA]) was developed and evaluated for its mechanical robustness and its CO2 permeation properties. Polyvinyl alcohol (PVA) was used as the initial network for the DN ionogel membrane. It forms a partially-crystalline physical crosslinking within [C2mim][DCA] and acts as a sacrificial bond to toughen the ionogel. A loosely crosslinked poly(N,N-dimethylacrylamide) (PDMAAm) network was formed by free-radical polymerization to interpenetrate with the physically crosslinked PVA network. The more the gel was elongated, the more the physical crosslinking in the PVA network were broken and the more energy was dissipated. As a result, the ion gel toughened. Owing to its excellent toughness, the developed DN ionogel membrane retained 93 wt% of [C2mim][DCA] and exhibited the CO2 permeability and the CO2 perm-selectivity over N2 of 2920 barrer and 61, respectively, the highest level of CO2 separation performance among the latest CO2 separation membranes. The DN ionogel membrane kept the CO2 separation performance required for CO2 capture from flue gases from coal-fired power plants even at 80 °C and 80 % relative humidity.

Development of an ion gel-based CO2 separation membrane composed of Pebax 1657 and a CO2-philic ionic liquid.

A tough ion gel membrane containing a CO2-philic ionic liquid, 1-ethyl-3-methylimidazolium tricyanomethanide ([Emim][C(CN)3]), was developed, and its CO2 permeation properties were evaluated under humid conditions at elevated temperatures. Pebax 1657, which is a diblock copolymer composed of a polyamide block and a polyethylene oxide block, was used as the gel network of the ion gel membrane to prepare a tough ion gel with good ionic liquid-holding properties. The polyamide block formed a semicrystalline structure in [Emim][C(CN)3] to toughen the ion gel membrane via an energy dissipation mechanism. The polyethylene oxide block exhibited good compatibility with [Emim][C(CN)3] and contributed to the retention of the ionic liquid in the ion gel. The developed ion gel membrane showed a good CO2 separation performance of 1677 barrer CO2 permeability and 37 CO2/N2 permselectivity under humid conditions of 75% relative humidity at an elevated temperature of 50 °C, which corresponds to an exhaust gas from a coal-fired power plant.

Optimization and performance studies of PES/SAPO-34 membranes for CO2/N2 gas separation

SAPO-34 nanocrystals were prepared and used as inorganic filler in polyethersulfone (PES) membranes. The influence of preparation conditions on permeation properties of CO2 and N2 gases and CO2/N2 selectivity were studied to achieve the highest separation performance possible for this mixed-matrix membrane. Gas permeation properties of PES/SAPO-34 MMMs with different contents of SAPO-34, PES and initial film thickness were investigated according to a full factorial design of experiments (DOE). The permeation tests and DOE results revealed that the optimized conditions to maximize the selectivity for PES/SAPO-34 are: composition of 18.5 wt% of SAPO-34, 15 wt% of PES, and a casted film thickness of 400 μm resulting in a CO2/N2 selectivity of 30.85. The findings showed that a multivariable model was validated and able to predict the selectivity with determination coefficient R2 of 0.969 and the results are in accordance with values presented in literature for PES/SAPO-34 membranes. An economic analysis shows that the commercial grade price for the optimized membrane is EUR 9.43/m2 which represents around 2.2 times cheaper than polymeric commercial membranes.

High CO2 permeation using a new Ce0.85Gd0.15O2-δ-LaNiO3 composite ceramic–carbonate dual-phase membrane

This work shows the synthesis, characterization and evaluation of dense-ceramic membranes made of Ce0.85Gd0.15O2-δ-LaNiO3 (CG-LN) composites, where the fluorite-perovskite ratio (CG:LN) was varied as follows: 75:25, 80:20 and 85:15 wt.%. Supports were initially characterized by XRD, SEM and electrical conductivity (using vacuum and oxygen atmospheres), to determine the composition, microstructural and ionic-electronic conductivity properties. Later, supports were infiltrated with an eutectic carbonates mixture, producing the corresponding dense dual-phase membranes, in which CO2 permeation tests were conducted. Here, CO2 permeation experiments were performed from 900 to 700°C, in the presence and absence of oxygen (flowed in the sweep membrane side). Results showed that these composites possess high CO2 permeation properties, where the O2 addition significantly improves the ionic conduction on the sweep membrane side. Specifically, the GC80-LN20 composition presented the best results due to the following physicochemical characteristics: high electronic and ionic conductivity, appropriate porosity, interconnected porous channels, as well as thermal and chemical stabilities between the composite support and carbonate phases.

Selective CO2 permeation properties of a membrane composed of a three-component polymer blend and cesium carbonate

ABSTRACT A high-performance CO2 separation membrane was fabricated using a composite polymer composed of a crosslinked acrylic acid polymer sodium salt, sodium polyacrylate, polyvinyl alcohol, and cesium carbonate. Evaluation tests were conducted by varying the relative humidity (RH), temperature, total pressure (Ptotal), and CO2 partial pressure (PCO2) to determine optimal parameters for enhanced performance in selective CO2 permeation over He. The membrane shows a high separation performance and durability at 50% RH and 85°C, where the CO2/He selectivity exceeds 550 under conditions of Ptotal:0.1 MPa and PCO2:0.08 MPa. Furthermore, the operational stability of the membrane was evaluated at 85°C, 50% RH, Ptotal:0.7 MPa, and PCO2:0.56 MPa. The as-fabricated membrane was stable for 300 h of continuous operation in the separation performance evaluation test. The findings of this study suggest that the developed membranes can be applied for CO2 separation from gas mixtures such as CO2/H2 with high efficiency and stability.

Eutectic ceramics of the CeO2 – ZrO2 – MgO system produced by laser-assisted directional solidification

Oxide eutectics have great potentiality as structural or functional materials, owing to the outstanding properties derived from the eutectic microstructure. Among them, the eutectic of the ZrO2 – MgO system is particularly noteworthy because of the unusual combination of thermomechanical, optical and electrical properties. In a recent application, Zr1-δMgδO2-δ – MgO eutectic oxides have been used to produce porous supports for molten-carbonate based CO2 separation membranes. Here we explore composite ceramic oxides of the CexZr1-xO2 – MgO (x ​≤ ​0.5) system with eutectic microstructure, with the motivation that incorporating cerium may enhance the CO2 permeation properties. Eutectic composites with different cerium content are produced by a laser-assisted directional solidification technique at variable solidification rate, v. In all cases the composite bicrystal consists of two phases, MgO and a fluorite-like (CexZr1-x)1-yMgyO2-y phase. A purely fibrilar microstructure is found for x ​≥ ​0.3 ​at v ​= ​25 ​mm/h, with MgO fibres embedded within the fluorite-like matrix. The MgO mol% in the eutectic composites decreases from ∼53% for x ​= ​0 to ∼48% for x ​= ​0.5. X-ray and Raman results evidence long-range ordering in a quasi-tetragonal monoclinic symmetry for x ​= ​0.5. Impedance spectroscopy results are consistent with a change from ionic to mainly electronic conductivity when the atmosphere is changed from air or Ar to 5%H2–Ar.

High-pressure CO2 permeation properties and stability of ceramic-carbonate dual-phase membranes

CO 2 permeation properties and stability of ceramic-carbonate dual-phase membranes at high pressures/temperatures are critical to their CO 2 separation and membrane reactor applications, but such data are not available in the literature. This work aims to study the effect of high transmembrane pressure on CO 2 permeation flux and the stability of molten carbonate in the dual-phase samarium-doped ceria (SDC) and molten-carbonate (MC) membranes. Dead-end porous SDC tubular supports were made by a cold isostatic press (CIP)/sintering method with a low porosity (below 7%), and gas-tight SDC-MC membranes were prepared by direct infiltration of molten lithium and sodium carbonate mixture into SDC pores, with a MC volume fraction less than 7%. CO 2 permeation/separation tests were performed on the SDC-MC membranes using feed gas of equal molar CO 2 /N 2 mixture at feed pressures up to 15 atm and sweep gas of helium at 1 atm. CO 2 permeation flux for the SDC-MC membranes depends logarithmically on feed/permeate CO 2 pressure ratio in 660–810 o C. The temperature dependence of CO 2 permeation shows activation energy of 30 kJ/mol. Due to the small MC volume fraction and hence low effective carbonate conductivity, CO 2 permeation of the SDC-MC membranes is dominated by the carbonate ionic conduction in the MC phase. The SDC-MC membranes remain in the same structure, morphology, and gas-tightness after CO 2 separation tests at high feed pressures and temperatures, showing high stability of SDC-MC membranes for high-temperature, high-pressure separation and chemical reaction applications. • Strong ceramic-carbonate dual-phase membranes can be made by the cold isostatic press method. • High-pressure CO 2 permeation flux depends logarithmically on feed/permeate CO 2 partial pressure ratio controlled by carbonate ionic conduction. • Samarium-doped ceria-molten carbonates membranes are stable at high pressures/high temperatures.

Preparation and High Performance of Cellulose Acetate Films by Grafting with Imidazole Ionic Liquid.

Cellulose acetate (CA) grafted with imidazole ionic liquids (CA-ILs) was synthesized by reacting CA with imidazole ionic liquids ([HO2CMmim]Cl, [HO2CEtmim]Cl, and [HO2CMmim]Br) by using tetrahydrofuran (THF) as the solvent and pyridine as the catalyst. The CA and CA-IL films were fabricated by using the casting solution method. The CA-IL films exhibited good film forming ability and mechanical properties. The successful grafting of CA with imidazole ionic liquids was confirmed by Fourier transform infrared (FTIR), 1H NMR, scanning electron microscopy (SEM), and elemental analysis, and the grafting degrees were 2.24, 2.45, and 3.30%, respectively. The CO2 permeation properties of the CA-IL films were 65.5, 105.6, and 88.3 Barrer, increased up to 2.0, 3.2, and 2.7 times, respectively, as compared to pure CA (32.6 Barrer). The CO2/CH4 selectivities of the CA-IL films were 15.6, 12.6, and 19.2, increased up to 1.7, 1.4, and 2.1 times, respectively, as compared to pure CA (9.26). Therefore, it can be concluded that the imidazole ionic liquids are immensely useful for improving the gas separation performance of CA films.

Influence of synthesis parameters on preparation of AlPO-18 membranes by single DIPEA for CO2/CH4 separation

CO2-selective AlPO-18 membranes were prepared hydrothermally on macroporous supports with a low-cost template N, N-diisopropylethylamine (DIPEA). The effects of synthesis parameters (such as gel dilution, synthesis temperature, synthesis time and aging time) on the structure, morphology and single gas permeation properties of CO2 and CH4 through AlPO-18 membranes were investigated in detail. The synthesis conditions had little effect on the membrane morphology but strongly affected the CO2/CH4 gas permeation properties of as-synthesized AlPO-18 membranes. The best membrane was obtained at a synthesis temperature of 433 K for 15 h after aging the precursor gel (1Al2O3: 1P2O5: 4DIPEA: 120H2O: 4IPA) for 24 h. The CO2 single gas permeance of this membrane was 1.1 × 10−6 mol/(m2 s Pa), with an ideal CO2/CH4 selectivity of 56 at 303 K and a 0.1 MPa pressure drop. The mixed gas CO2 permeance of same membrane with an equimolar CO2/CH4 mixture was 1.1 × 10−6 mol/(m2 s Pa) with a CO2/CH4 selectivity of 75 at 303 K and a 0.2 MPa pressure drop.

Enhancement of CO2 permeation properties of polymeric membrane by incorporating metal organic framework

This research work focuses on the fabrication of mixed matrix membranes (MMMs) for the enhancement of CO2 removal from CH4. Zeolitic imidazolate framework (ZIF-8) with a framework of 0.34 nm pore size which favours CO2 adsorption is used as filler in this work. Different loadings of ZIF-8 filler were incorporated into polysulfone (PSf) polymer matrix. From the EDX mapping, the morphology of the ZIF-8/PSf MMMs has shown compatibility between the polymer and filler phases. The MMMs demonstrated an increment of 8°C in glass transition temperature, Tg compared to the pure PSf. Based on the permeation results, MMM loaded with 1 wt% of ZIF-8 showed the highest performance with CO2 and CH4 permeability of 33.12 Barrer and 0.85 Barrer respectively, and CO2/CH4 ideal selectivity of 38.8. The development of this new type of MMM has great potential to be utilized in CO2/CH4 separation process.

Separation behavior of amorphous amino-modified silica nanoparticle/polyimide mixed matrix membranes for gas separation

In this work, amorphous amino-modified silica nanoparticles (AAMSN) were successfully synthesized via the sol-gel method and combined with the polyimide (PI) 4,4′-oxydiphthalic anhydride-2,2′-bis(trifluoromethyl) benzidine (ODPA-TFMB) to prepare mixed matrix membranes (MMMs) for gas separation. The physicochemical properties of the AAMSNs were characterized by thermogravimetric analysis, X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy, and the CO2 capture and O2 enrichment behaviors of MMMs with different AAMSN contents were compared with those of a control PI membrane. The sorption isotherm and permeation data revealed that addition of AAMSNs not only increases the diffusion coefficient of the resulting membranes but also increases their adsorption coefficient due to the amorphous characteristics of the nanoparticles and good adhesion between these particles and the PI. The CO2 permeation properties and CO2/N2 selectivity of the MMM with 20 wt% AAMSN were 210.1 barrer and 30.8, respectively, while those of the control membrane were 66.7 barrer and 27.8, respectively. Mixed gas permeation results also showed that the gas permeability of the MMMs improves and their gas selectivity is maintained compared with those of the control PI membrane. The unique structure of the AAMSN/PI membrane makes it an attractive candidate for CO2 capture and O2 enrichment applications.

CO2 separation over light gases for nano-composite membrane comprising modified polyurethane with SiO2 nanoparticles

Owing to the potential of polymeric and nanocomposite membranes for industrial application in CO2 capturing and gas separation processes, permeation properties of CO2, N2 and O2 through the polymer matrix have been an object of extensive research. We measured the permeation rates of gases (pure and mixed gas) within a novel nanocomposite membrane composed of poly tetramethyleneglycol (PTMG), hexamethylene diisocyanate (HDI), and diamine chain extender, 4,4-methylenebis(2-chloroaniline) (MOCA) at various silica loadings and operating conditions. The novel polyurethane was prepared by a two-step bulk polymerization technique based on the molar ratios of the used constituents 1 : 3 : 2 for PTMG: HDI: MOCA, respectively The FTIR spectra indicated that the extent of phase separation decreased by increase in the SiO2 content From the DSC and XRD analyses, the existence of small crystalline areas within the soft and hard segments of matrix was proved High thermal stability of new nanocomposites was authenticated by a 90 °C increase in the decomposition temperature upon including the SiO2 particles into the polymer matrix By providing a longer diffusion path, a reduction in the permeation of penetrants occurred after the incorporation of SiO2 content By raising the temperature from 25 to 45 °C, the gas permeation value of CO2, O2 and N2 rose steeply: 35, 54 and 81% in neat PU and 49, 64 and 137% in PU containing 15 wt%, respectively Conversely, the obtained results for increasing the feed gas pressure from 6 to 10 bar revealed that the penetration of non-condensable gases, O2 and N2, decreased while the permeation rate of CO2 polar gas surged dramatically Nevertheless, a simultaneous increment in the selectivity amounts of both gas pairs was revealed. For the gaseous mixtures, the trend of changes in permeability and selectivity values were almost identical with those of pure gas: decrease in permeation, and vice versa increase in gas pair selectivity Eventually the separation results of the prepared membranes indicated a strong tendency to move towards Robeson's line by incorporation of SiO2 nanoparticles into the matrix of membranes.

CO2 permeation through asymmetric thin tubular ceramic-carbonate dual-phase membranes

Ceramic-carbonate dual-phase dense membrane is a promising high temperature CO2 separation membrane with remarkable CO2 permeance and theoretically infinite CO2 selectivity. This paper reports synthesis and CO2 permeation properties of asymmetric tubular dual-phase membranes with a thin samarium doped ceria (Ce0.8Sm0.2O1.9, SDC)-carbonate separation layer and a thick porous SDC-Bi1.5Y0.3Sm0.2O3-δ (BYS) support. The asymmetric tubular thin (0.12 mm) dual-phase membrane has much higher CO2 permeance and lower activation energy for permeation than the thick (1.0–1.5 mm) membranes. At 900 °C with 50%CO2/N2 feed at 1 atm, the CO2 permeation flux and permeance for the thin membrane reach 1.53 × 10−2 mol m−2 s−1 (or 2.05 mL(STP) cm−2 min−1) and 3.16 × 10−7 mol m−2 s−1 Pa−1, respectively, with activation energy for permeation of 62.5 kJ/mol. These dual-phase membranes exhibit slightly higher CO2 permeance with essentially same activation energy for permeation, and stable operation, for CO2 permeation with simulated syngas (with the composition of 49.5%CO, 36%CO2, 4.5%N2, 10%H2) feed. The CO2 permeation fluxes of the tubular asymmetric membranes can be well described by the power-function flux equation. The analysis of CO2 permeation data with the model shows that the CO2 separation performance of the tubular asymmetric membranes can be further improved by optimizing the microstructure of ceramic porous supports. This work demonstrates that asymmetric SDC-carbonate dual-phase membrane has high potential for practical application in high temperature CO2 separation.

Performance of Nanocomposite Membranes Containing 0D to 2D Nanofillers for CO₂ Separation: A Review.

Membrane technology has the potential to be an eco-friendly and energy-saving solution for the separation of CO2 from different gaseous streams due to the lower cost and the superior manufacturing features. However, the performances of membranes made of conventional polymers are limited by the trade-off between the permeability and selectivity. Improving the membrane performance through the addition of nanofillers within the polymer matrix offers a promising strategy to achieve superior separation performance. This review aims at providing a complete overview of the recent advances in nanocomposite membranes for enhanced CO2 separation. Nanofillers of various dimensions and properties are categorized and effects of nature and morphology of the 0D to 2D nanofillers in the corresponding nanocomposite membranes of different polymeric matrixes are discussed with regard to the CO2 permeation properties. Moreover, a comprehensive summary of the performance data of various nanocomposite membranes is presented. Finally, the advantages and challenges of various nanocomposite membranes are discussed and the future research and development opportunities are proposed.

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

Abstract SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO2, CH4, and N2 gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO2, CH4, and N2, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO2/CH4 and CO2/N2, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R2 > 99%).

Study of Separation Behavior of Activated and Non-Activated MOF-5 as Filler on MOF-based Mixed-Matrix Membranes in H2/CO2 Separation

In this study, cubic and tetragonal structures of MOF-5 (C-MOF-5 and T-MOF-5) were successfully synthesized, characterized and incorporated into cellulose acetate (CA) polymer matrix in the range of 6, 9 and 12 wt % to fabricate mixed matrix membranes (MMMs). The effects of smaller pore size of T-MOF-5 and more ZnO molecules in T-MOF-5, on the H2 and CO2 permeation properties of C-MOF-5/CA and T-MOF-5/CA MMMs were investigated. The all novel MMMs were prepared using the solution casting method and characterized by FTIR, TGA and SEM. SEM images as well as results of FTIR and TGA analyses confirmed good adhesion between both MOF-5s and CA matrix. Addition of both C-MOF-5 and T-MOF-5 into the CA improved the gas transport properties of the CA, especially in H2 separation. The H2/CO2 selectivity continued the increasing trend at 9 wt % and did not significantly reduce even at 12 wt % due to good adhesion between both MOF-5s and CA. The highest H2/CO2 selectivity was obtained at 12 and 9 wt % loading of C-MOF-5 and T-MOF-5, respectively. By changing the filler from C-MOF-5 to T-MOF-5, the increasing and reducing of adsorption site of H2 and CO2 (respectively), and also reducing in pore size, caused the appearance of H2 permeability to not change much but the CO2 permeability to reduce. Accordingly, the H2/CO2 selectivity in all T-MOF-5/CA MMMs is higher than that in all C-MOF-5/CA MMMs. According to obtained results, the activated MOFs (i.e., C-MOF-5 in this study) are not always the best choices for separation process.

Effect of poly(ethylene glycol) molecular weight on CO2/N2 separation performance of poly(amide-12-b-ethylene oxide)/poly(ethylene glycol) blend membranes

Membranes from block copolymer poly (amide-12-b-ethylene oxide) (Pebax1074) and its blends with different molecular weight poly (ethylene glycol) (PEG) (200, 400, 600, 1500, 4600 and 8000) were prepared. The thermal properties and structures of Pebax1074/PEG blend membranes were characterized by DSC and SEM, and the gas permeation properties of CO2 and N2 were also investigated at different temperatures. For Pebax1074/PEG blend membranes with low molecular weight PEG (MW≤ 600), higher gas permeabilities than Pebax1074 were achieved. The permeability increased with the increase of PEG molecular weight. The addition of low molecular weight PEG resulted in decrease in activation energy of permeation. For Pebax1074/PEG blend membranes with high molecular weight PEG (MW≥ 1500), due to the melt of PEO phase crystals, the gas permeation properties of blend membranes were temperature-dependent, which could be divided into crystalline region, transition region and amorphous region according to two different transition temperatures. PEG molecular weight and operation temperature determined different gas permeation properties of Pebax1074/PEG blend membranes in three regions. The activation energies of permeation in crystalline region were larger than those in amorphous region.

Highly selective multi-block poly(ether-urea-imide)s for CO2/N2 separation: Structure-morphology-properties relationships

Polyethylene oxide (PEO)-containing multi-block copolymers are good candidates for CO2 membrane separations because of their strong affinity for CO2 but PEO crystallization and weak mechanical properties are two limitations to be overcome at high PEO content. In this work, PEO block incorporation within new linear multi-block copolymers avoided PEO crystallization. The copolymers consisted in Jeffamine soft blocks (SB) and particularly stiff urea-imide hard blocks for improved physical cross-linking and excellent film-forming ability. Varying the SB content from 41 to 70 wt% led to different copolymer physical properties, morphology and CO2 permeation properties. The copolymer with the lowest SB content was a rigid glassy material with very weak phase separation. Its soft and hard blocks formed large interpenetrated domains, resulting in low CO2 permeability (2 Barrer) but extreme selectivity (αCO2/N2 = 207) for CO2/N2 separation at 2 bar and 35 °C. CO2 permeability greatly improved with the SB content due to strong phase separation. The copolymer with the highest SB content was a thermoplastic elastomer with soft blocks forming well-separated highly permeable percolating nano-domains. Its CO2 permeability (57 Barrer) and high selectivity (αCO2/N2 = 50) are among the best properties reported for PEO-containing multi-block copolymers for CO2 capture.

Synthesis and CO2 permeation properties of novel sulfonium-substituted poly(diphenylacetylene)s

Substitution of thiourea to poly(diphenylacetylene) having 2-bromoethoxy groups (2a) gave an sulfonium-containing poly(diphenylacetylene) [3a (Br − )]. The counteranions of 3a (Br − ) could be exchanged using CF3COOK and (CF3SO2)2NLi, and the polymers 3a (TFAc − ) and 3a (Tf 2 N − ) were obtained. Polymer 3a (Br − ) was hydrolyzed with NaOHaq to afford the polymer 4a possessing mercapto groups. The CO2 permeability coefficients (\(P_{{{\text{CO}}_{ 2} }}\)) and the separation factor (\(P_{{{\text{CO}}_{ 2} }} /P_{{{\text{N}}_{ 2} }}\)) of 3a (Br − ) were 15 barrers and 16, respectively. The selectivity was low compared to the analogous polymer, poly(diphenylacetylene) having imidazolium salts (\(P_{{{\text{CO}}_{ 2} }} /P_{{{\text{N}}_{ 2} }} = 4 4\)), because 3a (Br − ) interacted strongly with CO2, and the diffusion of CO2 was suppressed. The \(P_{{{\text{CO}}_{ 2} }}\) and \(P_{{{\text{CO}}_{ 2} }} /P_{{{\text{N}}_{ 2} }}\) of 3a (TFAc − ) were 43 barrers and 24, respectively, and those of 3a (Tf 2 N − ) were 52 barrers and 26, respectively. Both permeability and selectivity increased as the counteranion became bulkier. The mercapto group containing poly(diphenylacetylene) (4a) showed a relatively high CO2 permeability (\(P_{{{\text{CO}}_{ 2} }} = 1 30\) barrers).

Effects of low and high molecular mass PEG incorporation into different types of poly(ether-b-amide) copolymers on the permeation properties of CO2 and CH4

Blend membranes were prepared by incorporating two types of polyethylene glycol (PEG) (molecular masses of 400 and 1000 g mol−1) into three grades of poly(ether-block-amide) (PEBAX), namely PEBAX 1074, PEBAX 1657, and PEBAX 2533. The PEGs, which were used as blending agents, were employed at mass fractions ranging from 10 to 40 wt.% based on the mass of PEBAX. The gas separation performance of each neat or blend membrane, comprising its CO2 and CH4 permeabilities and its ideal CO2/CH4 selectivity, was studied at room temperature (25 °C) and at pressures of 2–8 bar. X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analyses were used to determine the crystallinities of and the chemical bonds in the prepared membranes, respectively. Scanning electron microscopy (SEM) was also utilized to observe the morphologies of the membranes. The results obtained from experimental investigations showed that the incorporation of low molecular mass PEG significantly increased the permeability but only slightly affected the ideal CO2/CH4 selectivity, while the incorporation of high molecular mass PEG decreased the permeability considerably but sharply increased the ideal CO2/CH4 selectivity. This behavior intensified as the polyether content of the PEBAX was decreased.