CO2 Permeation Properties Research Articles

Fabrication and CO2 permeation properties of amine-silica membranes using a variety of amine types

We developed a series of molecule-scale hybrid amine-silica membranes synthesized from organoalkoxysilane precursors of 3-(triethoxysilyl)propan-1-amine (PA-Si) and 3-(triethoxysilyl)-N-methylpropan-1-amine (SA-Si), and made these functional using either unhindered amines or a 3-(triethoxysilyl)-N,N-dimethylpropan-1-amine (TA-Si) that is sterically hindered. CO2 adsorption-desorption measurements of amine-silica powdered xerogels were conducted to observe the effect of amine type on CO2 adsorption and desorption/diffusion properties. The results revealed that TA-Si xerogel powders demonstrated faster kinetics for both adsorption and desorption processes compared with those of the PA-Si and SA-Si samples due to the steric hindrance effect of the amine, which reduced the CO2 binding energy and thereby boosted both the forward and reverse reaction rates of CO2-amine. In single-gas permeation performances, all the membranes exhibited excellent molecular sieving at higher temperatures and all the gases considered, except CO2, tended to permeate the membranes via activated diffusion. The effect of amine type on CO2 separation performance was compared using CO2 permeance, CO2/N2 selectivity, activation energy for permeation (Ep) of CO2 [Ep(CO2)], and differences in Ep between CO2 and N2 [Ep(CO2)-Ep(N2)]. The TA-Si membrane demonstrated superior CO2 separation performance, and achieved the highest values for both CO2 permeance and selectivity. A relatively smaller difference in CO2 separation performance was observed between PA-Si and SA-Si membranes despite some differences in basicity. This suggests that, rather than the basicity, it was the steric hindrance effect that played the greatest role in CO2 transport performance across amine-silica membranes.

High CO2 separation performance of amino acid ionic liquid-based double network ion gel membranes in low CO2 concentration gas mixtures under humid conditions

This work focused on separating low concentrations of CO2 (500–1000ppm) from humid mixtures of CO2/N2 using an amino acid ionic liquid (AAIL)-based ion gel membrane. The effects of relative humidity (RH), CO2 partial pressure, and temperature on the CO2 separation performance were investigated. At 303K, RH 70%, and a CO2 partial pressure of 0.1kPa, the ion gel membrane showed high CO2 permeability (around 52,000 barrer) and CO2/N2 selectivity (8100), both of which were considerably higher than those observed using a conventional facilitated transport membrane (FTM). Changes in RH were found to slightly affect the CO2 permeation properties of the ion gel membrane, while the CO2 separation performance of the conventional FTM was strongly dependent on RH, decreasing sharply at RH <50%. Enhanced CO2 permeability of the ion gel membrane was observed with decreasing CO2 partial pressure, indicating a facilitated transport mechanism. Moreover, increasing the temperature at a constant RH was found to enhance CO2 permeability, while CO2/N2 selectivity remained constant. The outstanding and stable performance of the AAIL-based ion gel membrane demonstrated its potential for CO2 separation from gas mixtures containing low concentrations of CO2 across a wide RH range around room temperature.

The effect of temperature on the permeation properties of Sulphonated Poly (Ether Ether) Ketone in wet flue gas streams

Membrane technology can be used to recover high purity water from power station flue gas streams. In this work, the effect of temperature on water vapour and CO2 permeation properties of Sulphonated Poly (Ether Ether) Ketone (SPEEK) with two different ion exchange capacities were investigated (IEC 1.6meq/g and 1.9meq/g). It was found that both permeabilities increased with increasing water activity due to increased water solubility as water concentration increased. SPEEK with IEC 1.9meq/g exhibited higher water permeability and selectivity than IEC 1.6meq/g. At humidities greater than 50%, both water vapour and CO2 permeabilities also increased as temperature increased up to 50°C due to the increase in diffusion of the penetrating molecules. However as temperature increased further, a significant drop in the permeability of both water and carbon dioxide occurred. This decrease was attributed to the formation of water clusters that filled the free volume in the polymer and hindered the diffusion of isolated molecules. This decrease in diffusion coupled with a reduction in solubility with increasing temperature resulted in the performance decline.

Polybenzimidazole-based polymeric ionic liquids (PILs): Effects of ‘substitution asymmetry’ on CO2 permeation properties

Polymeric Ionic Liquids (PILs) are being considered as promising membrane materials for CO2 separation. Present work aims at investigating effects substitution asymmetry on imidazole moiety of two structurally different polybenzimidazoles (PBI-BuI and PBI-HFA) on physical, gas sorption and transport properties of the resulting film forming PILs possessing symmetric substitution, while keeping one of the N-substituent as methyl group. PILs were obtained with high degree of substitution. The halide anion of these PILs was exchanged with BF4¯, Tf2N¯ and HFB¯ anions. Effects of substituents, cationic backbone and type of anions on gas permeation properties of PILs using pure gases (He, H2, N2 and CO2) were examined at 20atm upstream pressure and correlated with their physical properties. Combination of typical ionic liquid character (effective towards enhancing CO2 sorption) and looser chain packing (ease in gas diffusion) offered improved CO2 permeation characteristics. As an outcome, some of the PILs exhibited higher CO2 permeation than that of hydrogen, typically known as ‘reverse selectivity’. These asymmetrically substituted PILs enhanced not only the gas permeability, but also selectivity than their symmetrically substituted counterparts.

Preparation and Properties of Polysulfone-poly(ethylene glycol) graft copolymer membrane.

In this study, Graft copolymers composed of PSf backbones and PEG side chains were synthesized to prepare gas separation membranes with enhancing permeability and selectivity on carbon dioxide separation. PSf-g-PEG copolymers were synthesized by two steps, chloromethylation and graft reactions. Grafted PEG segment of PSf was controlled by molecular weight of PEG. Thermal properties of prepared mebrane were studied by TGA and DSC. T(g) of the copolymers was decreased with increasing of molecular weight of PEG. Hydrophilicity of PSf-g-PEG copolymer membrane was measured using contact angle method, and PEG grafted polymers showed lower contact angles due to higher hydrophilicity. Gas permeation properties of CO2 and N2 gases through the membranes were measured using time-lag method. The permeability of CO2 was enhanced with PEG moiety contents and increasing of number of PEG segment. The selectivity of CO2/N2 was increased with introducing of PEG due to higher solubility with CO2 gas.

CO2-facilitated transport performance of poly(ionic liquids) in supported liquid membranes

Six types of PILs were designed and synthesized by radical polymerization reaction and ion exchange reaction and the 1H NMR analysis and TG-MS analysis proved the successful procedure and their CO2 permeation properties were evaluated. 1-butyl 3-methylimidazole double trifluoromethane sulfonate ([bmim][Tf2N])-based facilitated transport membrane, with 10 wt% poly([ViEtIm] Tf2N), showed an excellent CO2 permeability of 920 Barrer, similar to that of the others investigated. PILs were distributed in the SILM using the “like dissolves like” theory to investigate the gas permeation separation performance before and after doping of the PILs in SILM. Owing to the reversible interaction between the CO2 molecules and electropositive PIL chains, this supported ionic liquid membrane selectively transfer CO2 more rapidly. The polymer chains play the role of mobile CO2 carrier in the SLM, and introduce facilitated transport mechanism. This concept may provide a means for fabricating a highly permeable and selective membrane to break through Robeson’s upper bound.

Polyaniline in situ modified halloysite nanotubes incorporated asymmetric mixed matrix membrane for gas separation

The embodiment of polyaniline in situ modified halloysite nanotubes (PANi–HNTs) on the gas permeation properties of CO2, CH4, O2, and N2 gases in polysulfone (PSf) membrane has been investigated. Halloysite nanotubes (HNTs) were modified by in situ polymerization of aniline. Asymmetric mixed matrix membranes (MMMs) were synthesized by varying the PANi–HNTs concentrations of 0.5–2.5wt.% of polymer in the PSf solutions. The MMMs were characterized by SEM, ATR-IR, DSC and XRD. Membrane characterization reveals the structural change of the filler and interaction of PANi with PSf polymer matrix. The permeance of pure gases and the ideal selectivities were determined using an indigenously built high-pressure gas separation manifold. Increasing the PANi–HNTs incorporation in polymer enhanced the permeance of CO2 from 17.4 to 68.4GPU, CH4 from 0.8 to 4.8GPU, O2 from 3.9 to 18.8GPU and N2 from 0.7 to 3.1GPU, respectively. The use of PANi–HNTs loaded PSf membranes provides a means for separation of CO2/CH4, CO2/N2 and O2/N2.

Gas separation properties of poly(amide-6-b-ethylene oxide)/amino modified multi-walled carbon nanotubes mixed matrix membranes

Amino modified multi-walled carbon nanotubes (MWNTs-NH2) were incorporated into poly(amide-6-b-ethylene oxide) (Pebax 1657) to prepare mixed matrix membranes (MMMs). The permeation properties of CO2, N2, CH4 and H2 were studied and the physical properties of Pebax/MWNTs-NH2 MMMs were characterized by X-ray diffractometer (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The incorporation of MWNTs-NH2 increased the amorphous region of Pebax phase in Pebax/MWNTs-NH2 MMMs, which was beneficial for the improvement of gas permeabilities. The apparent activation energy for permeation (Ep) for CO2 decreased with the increase of pressure, while those for N2, CH4 and H2 almost did not change. The Ep for CO2, N2, CH4 and H2 slightly decreased with the incorporation of MWNTs-NH2. Compared with pristine Pebax membrane, CO2 permeability increased almost 3 times for Pebax/MWNTs-NH2 MMMs with 33wt% MWNTs-NH2. With the increase of MWNTs-NH2 content, the normalized permeabilities of N2, CH4 and CO2 showed almost the same increment and the selectivities of CO2/N2, CO2/H2 and CO2/CH4 remained constant, which were consistent with the Maxwell model prediction. Thus, the incorporation of MWNTs-NH2 significantly improved the gas permeation properties of Pebax/MWNTs-NH2 MMMs.

High flux CO2 transporting nanochannel fabricated by the self-assembly of a linear-brush block copolymer

Linear-brush poly(styrene)-b-poly[oligo(ethylene glycol) methyl ether methacrylate] (PS-b-POEGMA) block copolymer incorporating a UV-crosslinkable coumarin group in a PS block, self-assembled into a cylindrical structure with POEGMA cylinders perpendicular to the film surface, which exhibit excellent CO2 separation properties. The block copolymer was successfully synthesized by a combination of atom transfer radical polymerization (ATRP) and click chemistry. The molecular characterization of the diblock copolymer was performed with 1H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The cylindrical phase structure was confirmed by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The POEGMA amorphous phase was confirmed by differential scanning calorimeter (DSC). Gas permeation properties of CO2, N2 and He were determined around room temperature. Compared to the linear BCP, the total gas selectivity and especially CO2 permeation flux increased dramatically. The functional block units and self-assembled microphase structures synergetically played key roles in the high performance of the membrane.

CO2 separation applying ionic liquid mixtures: the effect of mixing different anions on gas permeation through supported ionic liquid membranes

In order to increase flexibility in tailoring the permeability and selectivity of supported ionic liquid membranes (SILMs) for flue gas separation and natural gas purification, this work explores the use of ionic liquid mixtures. For that purpose, gas permeation properties of CO2, CH4 and N2 in several binary ionic liquid mixtures based on a common cation ([C2mim]+) and different anions such as bis(trifluoromethylsulfonyl)imide ([NTf2]−), acetate ([Ac]−), lactate ([Lac]−), dicyanamide ([DCA]−) and thiocyanate ([SCN]−) were measured at 293 K using a time-lag apparatus. In addition to gas permeation results, the thermophysical properties of those mixtures, namely viscosity and density, were also determined so that trends between the two types of properties could be evaluated. The results show that mixing [Ac]− or [Lac]− with [NTf2]− promotes the decrease of gas permeability and diffusivity of the SILMs based on those binary mixtures, essentially due to their high viscosities. The pure ionic liquids containing anions with nitrile groups, [DCA]− or [SCN]−, and also their mixtures with [C2mim][NTf2] exhibit permselectivities ranging from 19.1 to 23.0 for CO2/CH4, and from 36.6 to 67.8 for CO2/N2, as a consequence of a reduction in the CH4 and N2 permeabilities, respectively. Furthermore, it is shown that mixing anions with different chemical features allows variations in ionic liquid viscosity and molar volume that impact the gas permeation properties of SILMs, offering a clear pathway for the optimization of their CO2 separation performances.

Synthesis, characterization, and CO2 permeation properties of acetylene‐terminated polyimide membranes

AbstractA novel fluorine‐containing telechelic polyimide end‐capped with acetylene group which derived from 4,4‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,4‐diaminodiphenyl ether (DADE), and 4‐(2‐phenylethynyl) phthalic anhydride (PEPA) was synthesized using polycondensation. The physical and CO2 permeation properties of its crosslinked membranes prepared by the cyclotrimerization reaction of the acetylene groups at the polymer chain end using tantalum (V) chloride (TaCl5) as a catalyst under thermal treatment was investigated in terms of CO2‐induced membrane plasticization. The crosslinked membranes showed a gel content in organic solvent, which was good solvent of noncrosslinked membranes, and improved their thermal stability. Based on the measurement of the high‐pressure time dependence on CO2 permeation, the crosslinked 6FDA–DADE–PEPA membranes exhibited more resistance to CO2‐induced plasticization than noncrosslinked 6FDA–DADE and thermal treated 6FDA–DADE–PEPA. Furthermore, the increase in TaCl5 content resulted in more resistance to plasticization. The cyclotrimerization reaction of the acetylene groups at the polymer chain ends using a transition metal catalyst under thermal treatment was found to be more effective than conventional thermal treatments for suppressing membrane plasticization without the membrane densification. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Effects of Si–O–Si Agglomerations on CO2 Transport and Separation Properties of Sol-Derived Nanohybrid Membranes

Nanohybrid membranes comprising organic and inorganic components with high CO2 affinity are ideal substitutes for traditional high footprint gas separation technologies. The CO2 permeability of these membranes resembles those of polydimethylsiloxane (PDMS), the most permeable rubbery material, while possessing CO2/H2 separation factors that supersede PDMS. Such membranes are synthesized using a simple acid-catalyzed sol–gel process. In this work, we investigate the relationship between the CO2 permeation properties of these nanohybrid membranes and membrane and siloxane network morphology by attuning the reaction kinetics of the sol–gel process. The CO2 permeability of these nanohybrid membranes can reach 1810 barrer, an improvement of 7.5 folds; while H2 permeability increase by 5.7 fold, from 30 to 170 barrer. The mechanism behind gas transport enhancements observed in these nanohybrid membranes is elucidated using positron annihilation lifetime spectroscopy and sorption measurements. Relative fractiona...

Gas permeation performance of cellulose hollow fiber membranes made from the cellulose/N‐methylmorpholine‐N‐oxide/H2O system

AbstractCellulose hollow fiber membranes (CHFM) were prepared using a spinning solution containing N‐methylmorpholine‐N‐oxide as solvent and water as a nonsolvent additive. Water was also used as both the internal and external coagulant. It was demonstrated that the phase separation mechanism of this system was delayed demixing. The CHFM was revealed to be homogeneously dense structure after desiccation. The gas permeation properties of CO2, N2, CH4, and H2 through CHFM were investigated as a function of membrane water content and operation pressure. The water content of CHFM had crucial influence on gas permeation performance, and the permeation rates of all gases increased sharply with the increase of membrane water content. The permeation rate of CO2 increased with the increase of operation pressure, which has no significant effect on N2, H2, and CH4. At the end of this article a detailed comparison of gas permeation performance and mechanism between the CHFM and cellulose acetate flat membrane was given. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1873–1880, 2004

The transport properties of CO2 and CH4 for brominated polysulfone membrane

The sorption and permeation properties of CO2 and CH4 for synthesized brominated polysulfone, BPSf (bromobisphenol A polysulfone) were measured, and compared with the values for PSf (bisphenol A polysulfone), MPSf (bisphenol A methylated polysulfone) and TMSPSf (bisphenol A trimethylsilylated polysulfone) to investigate the structure-property relationships. Especially, the effect of polarity of substituents on the transport properties was studied. The effect of operating pressure on the permeation properties of polysulfones was examined. The permeation properties for a mixture of CO2 and CH4 were also measured, and these results were compared with those obtained from the experiments of pure gases. The sorbed concentrations and permeability coefficients are well fitted to the dual mode model. The permeability coefficients of each gas of a binary mixture are less than those of pure gases, and the extent of reduction in permeability coefficient is larger for less permeable polymer. The ideal separation factor for four polysulfones increases in the following order: TMSPSf< PSf< BPSf< MPSf. The ideal separation factor for BPSf is higher than other polysulfones having similar permeability coefficients of CO2 with BPSf. It can be explained that the strong polarity of bromine in BPSf increases cohesive energy density of polymer, and reduces the chain packing-inhibiting ability. The ranking of permeability coefficient correlates well with fractional free volume. The variation of d-spacing is not consistent with the permeability coefficient.