Gas Transport Properties Of Membranes Research Articles

Blended membranes with ionic liquids tailoring by hydroxyl group for efficient NH3 separation

Ionic liquids (ILs)-based membranes are prospective for efficient NH3 separation due to their designability and high gas affinity. This work developed Pebax blended membranes with aprotic IL [EtOHmim][NTf2] and protic IL [EtOHim][NTf2] tailoring by hydroxyl group to improve NH3 separation performance and deeply investigate ILs structure-membrane property-separation performance relationship. The incorporation of ILs remarkably improves NH3 separation performance and leads to different gas transport properties of membranes confirmed by experiments and simulation calculations. The Pebax/EtOHmim-100 blended membrane exhibits exceptional NH3 permeability of 3729.3 barrer, which is 2.65 times higher than that of neat Pebax membrane. The increased FFV and moderate hydrogen bonding interaction simultaneously raise NH3 diffusivity and solubility, resulting in an evident increase of NH3 permeability. Although stronger hydrogen bonding interaction between [EtOHim][NTf2] and NH3 significantly improves NH3 solubility, it also blocks the NH3 fast diffusivity in the membrane, so the NH3 permeability of Pebax/EtOHmim blended membranes is lower than that of Pebax/EtOHmim blended membranes. Moreover, the solubility selectivity depended on interactions between ILs and gas molecules plays a dominant role in the enhancement of NH3 selectivity, thus the highest NH3/N2 selectivity of 1822.3 and NH3/H2 selectivity of 200.7 is obtained by Pebax/EtOHim-100 membrane owing to the stronger hydrogen bonding interaction between [EtOHim][NTf2] and NH3. This work not only demonstrate that the introduction of ILs is beneficial for improving NH3 separation performance of membranes but also emphasize the importance of moderate interaction between ILs and NH3 molecules for containing-NH3 separation.

Polymers of intrinsic microporosity containing aryl-phthalimide moieties: synthesis, modeling, and membrane gas transport properties

High-performance polymers for membrane gas separation require the careful design of the structure-porous relationship.

The Effect of the Type and Concentration of the Crosslinking Diene on the Gas Transport Properties of Membranes Based on Polyoctylmethylsiloxane

The effect of the type and amount of crosslinking reagent on the gas transport properties of polyoctylmethylsiloxane (POMS) membranes is studied for the first time. 1,7-Octadiene (OD), divinyltetramethyldisiloxane (DMDS), and two samples of polydimethylsiloxane (PDMS 500, PDMS 25000 with the molecular weights of 500, 25 000 g/mol, respectively) are used as crosslinking reagents. The permeability, diffusion, and solubility coefficients are measured for n-butane, methane, carbon dioxide, and nitrogen, and the corresponding ideal selectivities of permeability, diffusion, and solubility are calculated. It is shown that the optimal membrane properties of POMS with the use of DMDS as the crosslinking reagent are achieved at a concentration of DMDS of 3%: the maximum values of the permeability coefficient of n-butane (9400 Barrer) and ideal selectivity of permeability of n-butane/methane (26.1). A decrease in both the selectivity of solubility and selectivity of diffusion is observed for the n-butane/methane gas pair in the DMDS, PDMS 500, and PDMS 25000 series of crosslinking reagents with an increase in the fraction of a siloxane crosslinking reagent.

Effect of Polyvinyl Alcohol Modified Silica Particles on the Physical and Gas Separation Properties of the Polyurethane Mixed Matrix Membranes

Silicon based particles were prepared using tetraethoxysilane (TEOS) as a silica monomer, and low concentration of polyethylene oxide-polypropylene oxide block copolymer (pluronic) with polyvinyl alcohol (PVA) as templating agents. The synthesized particles showed higher polarity compare with conventional silica particles. PU/silica mixed matrix membranes (MMMs) were prepared by solution casting technique. The membranes were characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). FT-IR result confirmed the existence of PVA in the final structure of the synthesized silica network. The SEM micrographs indicated an appropriate distribution of silica particles in the polymer matrix. Gas transport properties of membranes were studied for pure CO2, CH4, O2 and N2 gases at 10 bar and 25 ∘C. The results showed that the permeabilities of CH4 and CO2 enhanced whereas that of other gases decreased with increasing the modified silica contents. In the membrane with 10 wt.% silica content, an enhancement of CO2/CH4 (α ≈ 7.7) and CO2/N2 (α ≈ 91.4) selectivities was observed.

Polyurethane‐mesoporous silica gas separation membranes

The concept of mixed matrix membrane comprising dispersed inorganic fillers into a polymer media has revealed appealing to tune the gas separation performance. In this work, the membranes were prepared by incorporation of mesoporous silica into polyurethane (PU). Mesoporous silica particles with different pore size and structures, MCM‐41, cubic MCM‐48 and SBA‐16, were synthesized by templating method and functionalized with 3‐aminopropyltriethoxysilane (APTES). High porosity and aminated surface of the mesoporous silica enhance the adhesion of the particles to the PU matrix. The SEM and FTIR results showed strong interactions between the particles and the PU chains. Moreover, the thermal stability of the hybrid PUs improved compared to the pure polymer. Gas transport properties of the membranes were measured for pure CO2, CH4, O2, and N2 gases at 10 bar and 25°C. The results showed that the gas permeabilities enhanced with increasing in the loading of modified mesoporous silica particles. High porosity and amine‐functionalized particles render opportunities to enhance the gas diffusivity and solubility through the membranes. The enhanced gas transport properties of the mixed matrix membranes reveal the advantages of mesoporous silica to improve the gas permeability (CO2 permeability up to ~70) without scarifying the gas selectivity (α(CO2/N2)~ 30 for 5 wt% SBA‐16 content).

Enhanced gas transport properties of mixed matrix membranes consisting of Matrimid and RHO type ZIF-12 particles

Zeolitic imidazolate frameworks (ZIF) have been showed as potential active inorganic fillers in high-performance gas separation membranes. Among them, zeolitic imidazolate framework-12 crystals were synthesized as a porous filler material by alcohol-based solution method using benzimidazole–toluene interactions and they were incorporated into a commercial glassy polyimide Matrimid 5218 with various ZIF-12 loadings (0, 10, 20, 30, 40wt.%), as the continuous phase. As-synthesized ZIF-12 was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), multipoint Brunauer–Emmett–Teller (BET) surface analysis, Fourier Transform Infrared Spectroscopy (FT-IR) and Thermogravimetric Analysis (TGA). SEM images of ZIF-12 particles assert regular external surfaces with a rhombic dodecahedron structure. Matrimid mixed matrix membranes (MMMs) loaded with different amounts of ZIF-12 were prepared by solution casting method and characterized by XRD, FT-IR, TGA and SEM analyses. Our findings showed that there was a good dispersion and wetting of ZIF-12 particles in the continuous phase. Gas transport properties of the membranes were investigated by single gas permeation experiments of H2, CO2 and CH4 at 4bar feed pressure and 35°C. The permeability values increased as the ZIF-12 loading increased up to 20wt.%. However, at higher loadings, 30 and 40wt.%, the permeability decreased for all gases and the CO2/CH4 and H2/CH4 selectivities increased depending on the influence of the ZIF-12 filler. The maximum ideal separation factor for CO2/CH4 and H2/CH4 were found about 66.70 and 212.00, significantly higher than the pure polymer ideal separation factor.

Gas permeability of homogeneous and composite membranes based on poly(trimethylsilylpropyne)/poly(vinyltrimethylsilane) blends

Gas transport properties of membranes based on a blend of two silicon-hydrocarbon polymers, poly(trimethylsilylpropyne) (PTMSP) and poly(vinyltrimethylsilane) (PVTMS), have been investigated. The N2 and CO2 permeability of the membranes decreases by two orders of magnitude, and CO2/N2 selectivity increases about threefold with increasing PVTMS content in the blend from 0 to 100%. The effect of the volume contraction of the membranes has been found. The results of the experiments and calculations showed that the membrane properties throughout all the range of concentrations are in good agreement with the single-phase blend permeability model. The results of the research open the possibility of preparing PTMSP/PVTMS membranes with stable gas separation properties combining a high permeability of PTMSP and a rather high selectivity of PVTMS.

Magnetic properties of the magnetic hybrid membranes based on various polymer matrices and inorganic fillers

Magnetic hybrid membranes based on ethylcellulose (EC), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and various magnetic praseodymium and neodymium powder microparticles as fillers were obtained. Permeability, diffusion and sorption coefficients of O2, N2 and synthetic air components were estimated for homogeneous and heterogeneous membranes using the Time Lag method based on constant pressure permeation technique. The microstructure studies and the phase analysis of magnetic membranes were also performed using SEM and XRD. The influence of magnetic parameters, like coercivity, remanence and saturation magnetization of created membranes on the gas transport properties was studied. The results showed that their coercivity depended on composition and microstructure of the magnetic powder. On the other hand, remanence and saturation magnetization increased with the increase of the powder addition in the membrane. It was found that the magnetic membrane's gas transport properties were improved with the increase of membrane's remanence, saturation magnetization and magnetic particle filling. The decrease in powder particle size and associated increase of the membrane's coercivity also positively influenced the gas transport and separation properties of investigated membranes. It was observed that the magnetic ethylcellulose and poly(2,6-dimethyl-1,4-phenylene oxide) membranes had higher gas permeability, while their permselectivity and solubility coefficient values were rather maintained or slightly increased. The results also showed that the magnetic powder content enhanced significantly gas diffusivity in EC and PPO membranes. It was also analyzed the dependence of the drift coefficient w on the magnetic parameters of investigated membranes. The correlation between the membrane selectivity, permeability and magnetic properties with their XRD characteristics was stated.

Preparation and Characterization of Polycarbonate-Blend-Raw/Functionalized Multi-Walled Carbon Nano Tubes Mixed Matrix Membrane for CO2 Separation

Membrane composed of PC as base of polymer matrix with different ratio of multiwall carbon nano tubes (MWCNTs) as nanofillers and poly ethylene glycol (PEG) as second polymer was prepared by solution casting method. Both raw-MWCNTs (R-MWCNTs) and functionalized carboxyle-MWCNTs (C-MWCNTs) were used in membrane preparation. The MWCNTs loading ratio and pressure effects on the gas transport properties of membranes were examined in relation to pure He, N2, CH4, and CO2 gases. Results showed that the use of C-MWCNT instead of R-MWCNTs in mixed matrix membranes (MMMs) fabrication with base of PC provides better performance and also it increases (CO2/CH4) and (CO2/N2) selectivities to 27.38 and 25.42 from 25.45 and 19.24, respectively (at 5 wt% of MWCNTs). PEG as the second rubbery polymer was utilized to improve the separation performance and mechanical properties. In blend MMMs, highest (CO2/CH4) selectivity at 2 bar pressure increased to 35.64 for PC/PEG/C-MWCNT blend MMMs which was 27.28 for PC/MWCNTs MMMs at 10 wt%. Increase of feed pressure led to gas permeability and gas pair selectivity improvement in approximately all of membranes. Analysis of mechanical properties showed improvement in tensile modules with the increase of MWCNTs loading ratio and use of PEG in prepared MMMs.

Polyimide/Polyethersulfone Dual-Layer Hollow Fiber Membranes for Hydrogen Enrichment

We have developed functional poly(1,5-naphthalene-2,2′-bis(3,4-phthalic)hexafluoropropane diimide (6FDA-NDA)/polyethersulfone (PES) dual layer hollow fiber membranes and studied the H2/CO2 separation performance with and without 1,3-diaminopropane (PDA) modification. The effects of air gap on the membrane gas transport properties are investigated and it is observed that the optimal air gap for maximizing the ideal permselectivity is strongly dependent on the kinetic diameters of gas pair molecules. A higher air gap diminishes the population of Knudsen pores in the apparently dense outer skin and induces greater elongational stresses on polymer chains. The latter enhances polymer chain alignment and packing which possibly results in the shift and sharpening of the free volume distribution. The diamine modification of 6FDA-NDA/PES dual layer hollow fiber membranes effectively enhances the H2/CO2 permselectivity and suppresses the CO2-induced plasticization. At higher temperatures, the H2 permeance of the PD...

Effects of membrane thickness and heat treatment on the gas transport properties of membranes based on P84 polyimide

AbstractP84 polyimide membranes with thicknesses ranging from 6 to 310 μm were successfully fabricated by spin coating. The glass transition temperature of the P84 powder was found to be 315°C using differential scanning calorimetry, whereas its decomposition temperature was 536°C using thermogravimetric analysis. Scanning electron microscopy was used to examine the morphology of the membranes. The permeability of single gas (He, N2, O2, and CO2) and the ideal selectivity of gas pair (O2/N2, He/CO2, CO2/N2, and He/O2), as a function of membrane thickness, were determined. The results showed that the permeability of a single gas increased with increasing membrane thickness, whereas the selectivity of a given gas pair was nearly independent of the membrane thickness. The average selectivity of O2/N2, He/CO2, CO2/N2, and He/O2 were found to be 8.2, 10.0, 12.9, and 15.8, respectively. The effects of heat treatment on the membrane morphology and gas transport properties were investigated for three annealing temperatures, i.e., 80°C, 200°C, and 315°C. The membrane annealed at 315°C was cracked due to the stress sustained either during heating or cooling, thereby resulting in little or no selectivity. The permeabilities of P84‐118 membrane (118 μm thickness) annealed at 80°C were 16.2, 0.196, 1.20, and 2.01 Barrer for He, N2, O2, and CO2, respectively. The permeabilities of P84‐118 membrane annealed at 200°C decreased by 9.75%, 47.96%, 25.83%, and 30.85% for He, N2, O2, and CO2, respectively, as compared with those at 80°C, whereas the ideal selectivities increased by 42.65%, 30.52%, 32.85%, and 21.63% for O2/N2, He/CO2, CO2/N2, and He/O2, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of physical aging on the gas transport properties of poly(methyl methacrylate) membranes

The gas transport properties of poly(methyl methacrylate) (PMMA) membranes were examined as a function of physical aging time. A clear decrease of the gas permeability coefficient was observed. Interpretation of the permeation properties using results from differential scanning calorimeter and dynamic mechanical analyzer indicated that the smaller segmental motion of the polymer chains would be more restrict with aging time, discriminating against molecules with decreasing free volume. Free volume variations of PMMA membranes as a function of aging time was investigated by means of positron annihilation lifetime spectroscopy. It is indicated that there is obviously change in the fractional free volume in an aged membrane. The trend of fractional free volume changes consistent with the I 3 variation. These results correlated well with gas transport properties of membranes. Physical aging reduced the measured solubility coefficients and calculated diffusivity coefficients, which was shown to be consistent with decreasing of the free volume. Both diffusivity and solubility selectivity decrease with increasing aging time, however, the effect of physical aging on selectivity coefficients of polymeric membrane was controlled by the change of diffusivity selectivity.

The effects of 1,3-cyclohexanebis(methylamine) modification on gas transport and plasticization resistance of polyimide membranes

We have identified that 1,3-cyclohexanebis(methylamine) (CHBA) can be effectively used as a new cross-linking agent for the chemical modification of polyimide membranes. We have also observed that the combined effects of diamino cross-linking and thermal annealing would significantly change the chemical compositions, micro-structure, gas sorption, gas transport properties and plasticization resistance of polyimide membranes. The membrane's physicochemical changes after diamino cross-linking and thermal annealing were characterized by FTIR-ATR, XPS, gel content, UV, SEM-EDX and TGA and the possible reaction mechanisms during chemical modification and annealing have been proposed. Interestingly, it is found that the chemical reactions between diamino and polyimides are reversible during thermal annealing and the membrane micro-structures are modified and charge transfer complexes (CTCs) are formed during the post-treatments. The gas sorption and gas transport properties of membranes before and after modifications are reported and discussed. The gas sorption concentration continuously decreases with an increase in the degree of cross-linking and the subsequent thermal annealing. Experimental results illustrate that thermal annealing not only improves CO 2/CH 4 selectivity of the cross-linked membranes but also greatly enhances the plasticization resistance by the formation of CTCs. The critical plasticization pressure is significantly improved from about 300 psia of the original samples to more than 720 psia of the cross-linked and 200 °C thermal treated samples. Based on the experimental results, a novel approach to enhance plasticization resistance of polyimide membranes by means of diamino cross-linking and followed by thermal annealing is elucidated.

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997

Surface fluorination of poly (phenylene oxide) composite membranes: Part II. Characterization of the fluorinated layer

Composite membranes, comprising a selective layer of poly (2,6-dimethyl-1,4-phenylene oxide) on a microporous ceramic support, were surface fluorinated under mild conditions. The treatment parameters, fluorine feed concentration and treatment time, were each varied independently while the other parameter was kept constant. The fluorinated region was characterized using dynamic contact angle analysis and X-ray photoelectron spectroscopy (XPS). The fluorine to carbon ratio increased as a function of treatment time, but showed little variation when the feed concentration was varied. A relatively high oxygen to carbon ratio was observed which showed little change over the range of fluorination conditions. Angle-dependent XPS showed the concentration of fluorine species to be higher at greater depths below the surface. Fluorination times of 5 to 7 min minimized the water contact angle and maximized the total and polar surface free energies. Water contact angles decreased after fluorination but showed no definite trend as a function of feed concentration. The composition of the fluorinated region is discussed in relation to the gas transport properties of membranes fluorinated under similar conditions (Part I of this study).