Gas Permeation Properties Research Articles

Investigation of the gas permeation properties of a polyether sulfone asymmetric membrane via the phase inversion method

AbstractA defect‐free polyether sulfone (PES) asymmetric membrane was prepared by a one‐step phase inversion process and applied gas separation process in this article. The morphology of the PES asymmetric membrane formed via phase inversion that was correlated with the solvent composition, evaporation environment, coagulation bath, and so forth. The results reveal two kinds of coagulation phenomena that lead to different membrane structures and separation results. An instantaneous coagulation PES membrane formed a finger‐like structure within the membrane, and a delayed coagulation PES membrane resulted in a sponge‐like structure membrane. The selectivity of O2/N2 for membrane gas separation indicated that the asymmetric membranes prepared via a one‐step process in this study were defect‐free. Using the phase inversion method to fabricate asymmetric membranes improved the low permeability characteristic of glassy polymers. The maximum permeability of CO2 for the PES asymmetric membrane in the text can approach 30 Barrer. The results of gas separation for the sponge‐like PES membrane showed that the selectivity of O2/N2 and CO2/N2 was 7.1 and 35.6, respectively. This research showed that a PES asymmetric membrane was fabricated via a one‐step process without further defect repair and was applied effectively for CO2 membrane gas separation.

Characterization of anisotropic gas permeability and thermomechanical properties of highly textured porous alumina

AbstractPorous alumina with a highly textured microstructure was fabricated by pulse electric current sintering (PECS) using alumina platelets. Highly oriented porous alumina with a porosity of 3%–50% was obtained by a pressure‐controlled method of PECS. The properties of the highly textured porous alumina were measured in two directions. The nitrogen gas permeance and thermal conductivity at room temperature were higher in the direction along the platelet length due to the higher continuity of pores and the connectivity of alumina platelets, respectively. The anisotropy of the thermal conductivity at room temperature was investigated and explained by the effect of grain size of platelets as well as morphology and orientation of pores. The bending strength was higher with the loading direction along the platelet thickness. The thermal shock strength was clearly different in the two directions. The difference in the thermal shock strength was investigated by the measurement of properties and thermal stress analysis.

Coupled hydromechanical model for evaluating the volume change and fluid permeation behavior of expansive clay smear in a fault upon interaction with CO2

The interaction between clay minerals and CO2 at in-situ conditions of geological carbon sequestration leads to adsorption-induced strain, which increases the mineral's interlayer space. The effect of change in interlayer spacing of minerals on the evolution of macro-permeability, gas storage capacity, gas pore pressure, and stress state of compacted clays is unknown. The present study described a coupled numerical model to investigate the effect of adsorption-induced swelling of smectite-based clay on its gas permeation and mechanical properties upon interaction with CO2. To simulate the interaction of the fill material present in caprock faults with the injected CO2, compacted clay under confined, free and uniaxial confinement conditions are analyzed. It is evident under confined conditions, permeability of the clay filled in fault reduced, and mean compressive stress increased due to gas adsorption-induced strain. On the contrary, the permeability of the clay increased for both free and uniaxial conditions. The magnitude of the swelling stress within the media under uniaxial conditions depends on the degree of expansion caused by the adsorption-induced effect and applied overburden pressure. Overall, the study contributes to a comprehensive approach to evaluate the efficacy of geological formations having faults for long-term storage of CO2 in them.

Pore Structure and Gas Diffusion Features of Ionic Liquid-Derived Carbon Membranes

In the present study, the concept of Ionic Liquid (IL)-mediated formation of carbon was applied to derive composite membranes bearing a nanoporous carbon phase within their separation layer. Thermolytic carbonization of the supported ionic liquid membranes, prepared by infiltration of the IL 1-methyl-3-butylimidazolium tricyanomethanide into the porous network of Vycor® porous glass tubes, was applied to derive the precursor Carbon/Vycor® composites. All precursors underwent a second cycle of IL infiltration/pyrolysis with the target to finetune the pore structural characteristics of the carbonaceous matter nesting inside the separation layer. The pore structural assets and evolution of the gas permeation properties and separation efficiency of the as-derived composite membranes were investigated with reference to the duration of the second infiltration step. The transport mechanisms of the permeating gases were elucidated and correlated to the structural characteristics of the supported carbon phase and the analysis of LN2 adsorption isotherms. Regarding the gas separation efficiency of the fabricated Carbon/Vycor® composite membranes, He/CO2 ideal selectivity values as high as 4.31 at 1 bar and 25 °C and 4.64 at 0.3 bar and 90 °C were achieved. In addition, the CO2/N2 ideal selectivity becomes slightly improved for longer second-impregnation times.

PDMS-Zwitterionic Hybrid for Facile, Antifouling Microfluidic Device Fabrication.

Poly(dimethylsiloxane) (PDMS) has been used in a wide range of biomedical devices and medical research due to its biostability, cytocompatibility, gas permeability, and optical properties. Yet, some properties of PDMS create critical limitations, particularly fouling through protein and cell adhesion. In this study, a diallyl-terminated sulfobetaine (SB-diallyl) molecule was synthesized and then directly mixed with a commercial PDMS base (Sylgard 184) and curing agent to produce a zwitterionic group-bearing PDMS (PDMS-SB) hybrid that does not require a complex or an additional surface modification process for the desired end product. In vitro examination of antifouling behavior following exposure to fresh ovine blood showed a significant reduction in platelet deposition for the PDMS-SB hybrid surface compared to that of a PDMS control (p < 0.05, n = 5). The manufacturability via soft lithography using the synthesized polymers was found to be comparable to that for unmodified PDMS. Bonding via O2 plasma treatment was confirmed, and the strength was measured and again found to be comparable to the control. PDMS-SB microfluidic devices were successfully fabricated and showed improved blood compatibility that could reduce channel occlusion due to clot formation relative to PDMS control devices. Further, gas (CO2) transfer through a PDMS-SB hybrid membrane was also tested with a proof-of-concept microchannel device and shown to be comparable to that through the PDMS control.

Characterization technique of gases permeation properties in polymers: H2, He, N2 and Ar gas

We demonstrate a simple experimental technology for characterizing the gas permeation properties of H2, He, N2 and Ar absorbed in polymers. This is based on the volumetric measurement of released gas and an upgraded diffusion analysis program after high-pressure exposure. Three channel measurements of sorption content of gases emitted from polymers after decompression are simultaneously conducted, and then, the gas uptake/diffusivity as a function of exposed pressure are determined in nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM) rubbers, low-density polyethylene (LDPE) and high-density polyethylene (HDPE), which are used for gas sealing materials under high pressure. The pressure-dependent gas transport behaviors of the four gases are presented and compared. Gas sorption follows Henry’s law up to 9 MPa, while pressure-dependent diffusion behavior is not observed below 6 MPa. The magnitude of the diffusivity of the four gases decreases in the order DHe > DH2 > DAr > DN2 in all polymers, closely related to the kinetic diameter of the gas molecules. The dependence of gas species on solubility is in contrast to that on diffusivity. The linear correlation between logarithmic solubility and critical temperature of the gas molecule was newly observed.

Determination of Gas Permeation Properties in Polymer Using Capacitive Electrode Sensors.

The objective of this work was to develop an effective technique for characterizing the permeation properties of various gases, including H2, He, N2, and Ar, that are absorbed in polymers. Simultaneous three-channel real-time techniques for measuring the sorption content and diffusivity of gases emitted from polymers are developed after exposure to high pressure and the subsequent decompression of the corresponding gas. These techniques are based on the volumetric measurement of released gas combined with the capacitance measurement of the water content by both semi-cylindrical and coaxial-cylindrical electrodes. This minimizes the uncertainty due to the varying temperature and pressure of laboratory environments. The gas uptake and diffusivity are determined as a function of the exposed pressure and gas spices in nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM) polymers. The pressure-dependent gas transport behaviors of four different gases are presented and compared with those obtained by different techniques. A linear correlation between the logarithmic diffusivity and kinetic diameter of molecules in the gas is found between the two polymers.

Ladder polymers of intrinsic microporosity from superacid-catalyzed Friedel-Crafts polymerization for membrane gas separation

Polymers of intrinsic microporosity have attracted comprehensive attention in membrane-mediated gas separation because of their rigid and contorted structure that facilitates well-defined microporosity for fast and selective gas transport. We report a new macromolecular design synthesizes semi-ladder and fully-ladder polymers of intrinsic microporosity containing 9H -xanthene units by superacid-catalyzed Friedel-Crafts polymerization named SACPs. The prepared SACP membranes display high microporosity with amorphous chain packing structure, high FFV, and high BET surfaces areas. In particular, SACP-3 exhibited the most elevated BET surfaces area of 568 m 2 /g, fractional free volume (FFV) of 0.243, and bimodal micropore size distribution with two maxima at ∼5 and ∼8 Å, respectively. Due to its fully ladder architecture, SACP-3 exhibits highly permeable gas transport with CO 2 permeability of 6497 Barrer and CO 2 /CH 4 selectivity of 7.8, respectively. The microporosity and gas permeation properties of SACP membranes are also demonstrated to be highly tailorable by employing different monomers. The facile polymerization procedure, excellent solubility and processability, highly diverse tunability, and outstanding gas separation performance render SACP membranes attractive for many membrane-mediated gas separation processes. • A new spirobisindane-based fully-ladder polymer of intrinsic microporosity is synthesized with high BET surface area and FFV. • Superacid-catalyzed ladder polymer of intrinsic microporosity displays a bimodal micropore size distribution. • Rigid ladder polymer shows superior plasticization resistance than less microporous semi-ladder polymer.

Effect of Immobilization of Phenolic Antioxidant on Thermo-Oxidative Stability and Aging of Poly(1-trimethylsilyl-1-propyne) in View of Membrane Application.

The effect of phenolic antioxidant Irganox 1076 on the structure and gas permeation behavior of poly(1-trimethylsilyl-1-propyne) (PTMSP) was investigated. Isotropic films as well as thin film composite membranes (TFCM) from pure PTMSP and with added antioxidant (0.02 wt%) were prepared. PTMSP with antioxidant has a significantly higher thermal degradation stability in comparison to pure polymer. The thermal annealing of isotropic films of PTMSP with antioxidant was carried out at 140 °C. It revealed the stability of gas permeation properties for a minimum of up to 500 h of total heating time after a modest permeation values decrease in the first 48 h. X-ray diffraction data indicate a decrease in interchain distances during the heat treatment of isotropic films and indicate an increase in the packing density of macromolecules during thermally activated relaxation. Isotropic films and TFCMs from pure PTMSP and with antioxidant stabilizer were tested under conditions of constant O2 and N2 flow. The physical aging of thick and composite PTMSP membranes point out the necessity of thermal annealing for obtaining PTMSP-based membranes with predictable properties.

Olefin-Metathesis-Derived Norbornene-Ethylene-Vinyl Acetate/Vinyl Alcohol Multiblock Copolymers: Impact of the Copolymer Structure on the Gas Permeation Properties.

Commercial metathesis polynorbornene is used for the fabrication of high-damping coatings and bulk materials that dissipate vibration and impact energies. Functionalization of this non-polar polymer can improve its adhesive, gas barrier, and other properties, thereby potentially expanding its application area. With this aim, the post-modification of polynorbornene was carried out by inserting ethylene–vinyl acetate–vinyl alcohol blocks into its backbone via the cross-metathesis of polynorbornene with poly(5-acetoxy-1-octenylene) and subsequent deacetylation and hydrogenation of the obtained multiblock copolymers. For the first time, epoxy groups were introduced into the main chains of these copolymers, followed by the oxirane ring opening reaction. The influence of post-modification on the thermal, gas separation, and mechanical properties of the new copolymers was studied. It was shown that the gas permeability of the copolymer significantly depends on its composition, as well as on the amounts of hydroxyl and epoxy groups. The developed methods efficiently improve the barrier properties, reducing the oxygen permeability by 15–33 times in comparison with polynorbornene. The obtained results are promising for various applications and can be extended to a broader family of polydienes and other polymers containing backbone double bonds.

Study on the advantageous effect of nano-clay and polyurethane on structure and CO2 separation performance of polyethersulfone based ternary mixed matrix membranes

In recent years, many efforts have been made to develop new membrane materials for natural gas sweetening (CO2/CH4) and post-combustion CO2 capture from flue gas (CO2/N2), especially in coal-fired and natural gas-fired power plants. This study focused on the effect of polyurethane and nano-clay on structure and CO2 separating properties of polyethersulfone (PES) based three-component mixed matrix membranes (MMMs). The different weight fractions polyurethane (PU) (5−30 wt.%) together with clay nano-sheets (Cloisite® 15A) (0.5−10 wt.%) were blended to fabricate a novel PES-based ternary MMMs. The principal purpose was to investigate the effect of loading PU polymer and layered clay particles with 2D channels on the gas separation performance of the PES membranes. Pure gas permeability for N2, CH4, and CO2, and ideal gas separation for CO2/N2 and CO2/CH4 mixtures were examined through neat PES and modified PES membranes. By incorporating 20 wt.% of PU into PES, the permeability of CO2 and selectivities of CO2/N2 and CO2/CH4 were improved by 4, 1.4, and 1.7 times higher than the neat PES membrane, while by loading 20 wt.% of PU and 2 wt.% of nano-clay, the CO2 permeability, and CO2/N2, and CO2/CH4 selectivities were improved by 7.8, 1.8, and 2.2 times higher than the neat membrane, respectively. In general, PU and clay nano-sheets together as a filler into the PES matrix exhibited a meaningful improvement in the gas permeation and separation properties of PES and can be admitted as a worthy membrane for CO2 separation from the flue gas and natural gas.

Preparation of polybenzimidazole‐based mixed matrix membranes containingmodified‐COK‐12 mesoporous silica and evaluation of the mixed‐gas separation performance

AbstractThis work reports the preparation and characterization of mixed matrix membranes (MMMs) based on mesoporous ordered COK‐12 silica modified with 3‐aminopropyltrimethoxysilane as filler, and a series of polybenzimidazoles with different main‐chain structure as polymer matrix. Polybenzimidazoles (PBIs) were prepared from 3,3′‐diaminobenzidine and several dicarboxylic acids with different chemical structure. The physicochemical studies, as well as thermal, structural, and morphological properties of MMMs were determined by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction (XRD), and scanning electron microscopy. In addition, gas permeability properties of MMMs were tested by using a gas mixture of CO2/CH4at different upstream pressures. Results indicated that thermal stability of PBI above 400°C is kept even after the addition of the modified COK‐12 silica. Thed‐spacing of the PBI membranes determined by XRD was slightly increased with the addition of the modified COK‐12 silica particles. The permeability tests carried out at operating pressures of 50 and 150 psi showed that the addition of amino‐modified COK‐12 silica particles improved significantly the CO2permeability of MMMs with respect to the pristine PBI. At the same time, the selectivity values were also enhanced, which in some cases were found to be more than double compared to the respective pristine membrane. The contribution of the modified COK‐12 silica on the gas transport properties was more promising in MMMs comprising PBIs with less rigid backbone chemical structure.

Castor-oil based polyurethane/NiCo-OLDH nanocomposites with improved flame retardant properties

Polymer nanocomposites are known for improved thermal properties, mechanical properties, gas permeability and flame retardant properties compare to neat polymer matrix or conventional composites. Polymer matrix nanocomposites are widely used in defense use, equipment, automobiles and aircraft components, housings, packaging, coating applications. The present work aims to prepare polymer matrix nanocomposites to improve the flame retardant properties of a matrix where reinforcement is flame retardant in nature. The castor-oil based polyurethane has been synthesized by reacting castor-oil and isophorone diisocyanate which is flammable. It is very important to mention that inorganic nanofillers i.e. layered double hydroxides have been used as a reinforcement in castor-oil based polyurethane to increase the flame retardant, thermal and mechanical properties of nanocomposites. In this study, nickel–cobalt organomodified layered double hydroxide (NiCo-OLDH) has been prepared by the co-precipitation method. The prepared NiCo-OLDH has been characterized by various techniques. The average particle size of the OLDH nanoparticles is 68 nm as analyzed by particle size analyzer. The morphology of the OLDHs are in fibril form as shown in transition electron microscopy (TEM). The different weight percentages of NiCo-OLDH (1.5–5%) have been incorporated into synthesized castor oil based polyurethane (COBPU) to prepare COBPU/NiCo-OLDH nanocomposites using solvent blending method and characterized by FTIR, XRD, SEM, TGA techniques. FTIR has been used to confirm the functional group and metal oxide present in the nanocomposites. COBPU/NiCo-OLDH nanocomposites have shown a 10 % improvement in thermal stability and an increased in tensile strength of 26% as compared to neat COBPU. Flame retardancy as measured by LOI of the nanocomposites are in the range of 23–28%.

Gas permeation properties of nickel nanoparticle-embedded PPO/PVP polymers based carbon membrane

Mixed-matrix membranes (MMM) of thermally stable poly (2,6-dimethyl-1,4-phenyleneoxide) (PPO) polymer and thermally labile Polyvinylpyrrolidone (PVP) polymer, PPO/PVP, and its nickel nanoparticle (NP)-incorporated, PPO/PVP/Ni, were prepared to study their gas separation properties. Field emission scanning electron microscopy (FESEM) images were used to study their surface morphology, surface porosity, average pore size, and X-ray diffraction (XRD) patterns for crystallite size of Ni NPs and their phase purity. In particular, surface study of MMMs revealed that due to the inclusion of nickel NPs, the pore structure of the PPO/PVP/Ni membrane has been decreased. The gas permeation of H2, O2 and N2 was measured by single gas permeation method. The PPO/PVP/Ni exhibits much higher permeation results as compared to that of PPO/PVP. Additionally, the former provides higher selectivity for the H2/N2 gas pair as compared to O2 /N2 gas pair. Furthermore, the permeation results show that the incorporating of nickel NPs (1 wt%) to the PPO/PVP/Ni membrane caused the permeances to increase by nearly 45 times when compared to the PPO/PVP membrane.

Preparation of Hollow Fiber Membranes Based On Poly(4-methyl-1-pentene) for Gas Separation

New hollow fiber gas separation membranes with a non-porous selective layer based on poly(4-methyl-1-pentene) (PMP) granules have been obtained using the solution-free melt spinning process. The influence of the preparation conditions on the geometry of the obtained samples was studied. It was found that a spin head temperature of 280 °C and a specific mass throughput of 103 g mm−2 h−1 are optimal to obtain defect-free, thin-walled hollow fibers in a stable melt spinning process, using the given spinneret geometry and a winding speed of 25 m/min. The gas permeability and separation properties of new fibers were studied using CO2/N2 and CO2/CH4 mixtures, and it was found that the level of gas selectivity characteristic of homogeneous polymer films can be achieved. The features of the gas mixture components permeability below and above the PMP glass transition temperature have been experimentally studied in the range of CO2 concentrations from 10 to 90% vol. The temperature dependences of the permeability of the CO2/CH4/N2 mixture through the obtained HF based on PMP have been investigated, and the values of the apparent activation energies of the permeability have been calculated, which make it possible to predict the properties of membrane modules based on the obtained membranes in a wide temperature range.

Switchable gas permeability of a polypropylene‐liquid crystalline composite film

AbstractThe development of functionalized polyolefins for use as stimuli‐responsive commodity polymers has recently received much attention. In this work, a microporous polypropylene (PP) scaffold is used to align and fortify a smectic liquid crystalline network (LCN) which can switch its gas permeability upon pH changes. The LCN is a photopolymerized liquid crystalline mixture of a dimerized benzoic acid derivative monoacrylate and a diacrylate crosslinker. In the hydrogen‐bonded state, the composite membrane shows a high‐molecular order and a low permeability for He, N2, and CO2 gases. By pH switching from the hydrogen‐bonded state to the salt form, the molecular order is reduced, and the gas permeability is increased by one order of magnitude. This increase is mainly attributed to a loss in order of the system, increasing the free volume, resulting in an increased diffusibility. By exposing the composite film to basic or acidic environments, reversible switching between low and high gas permeability states is observed, respectively. The physical constraints imposed by the PP scaffold strengthens the membrane while the reversible switching inside the liquid crystalline polymer is maintained. This switching of gas permeation properties is not possible with the fragile freestanding LCN films alone.

Effect of fluorine doping on the network pore structure of non-porous organosilica bis(triethoxysilyl)propane (BTESP) membranes for use in molecular separation

Long-chain organosilica bis(triethoxysilyl)propane (BTESP) membranes typically have a flexible non-porous structure. Fluorine was used to tune the network pore structure of BTESP membranes in an effort to improve the gas permeation properties. The network pore size was enlarged and the effect of calcination temperature on the network structure was evaluated based on gel and membrane characterizations. Fluorine-doped BTESP membranes calcined at 350 °C and 650 °C have shown H2 permeance on the orders of 1.2 × 10−6 mol m−2 s−1 Pa−1 and 1.5 × 10−6 mol m−2 s−1 Pa−1 with H2/N2 selectivities of 8 and 6, respectively, which indicates similar pore sizes with lower condensation effect at high temperature of 650 °C, that was suppressed due to the presence of Si–F and C–F bonds. Undoped BTESP membranes, on the other hand, showed H2/N2 selectivity that was significantly lower—from 24 to 11 at 650 °C. FT-IR and N2 adsorption isotherms clearly indicated that fluorine significantly decreased the Si–OH density and increased the surface area and micropore volume. Further water adsorption analysis revealed that fluorine significantly increased the hydrophobicity of the BTESP network structure. Overall, the results of this study endorse the effectiveness of fluorine to control the network pore structure in both wet and dry molecular separation systems.

Highly Permeable Mixed Matrix Hollow Fiber Membrane as a Latent Route for Hydrogen Purification from Hydrocarbons/Carbon Dioxide.

This work reported on the fabrication and investigation of a mixed matrix hollow fiber membrane (MMHFM) by incorporating commercially available alumina particles into a polyetherimide (PEI) polymer matrix. These MMHFMs were prepared by the dry-wet spinning technique. Accordingly, optimizing the spinning parameters, including the air gap distance and flow rate ratio, is key to determining the gas separation performance. However, there are few studies regarding the effect of the filler dimensions. Consequently, three sizes of alumina particles, 20 nm, 30 nm, and 1000 nm, were respectively added into the PEI phase to examine the influence of filler size on gas permeation property. Moreover, the permeation properties of lower hydrocarbons (i.e., ethane and propane) were also measured to evaluate potential for emerging applications. The results indicated the as-synthesized membrane exhibited a remarkable hydrogen permeance of 1065.24 GPU, and relatively high separation factors of 4.53, 5.77, and 5.39 for H2/CO2, H2/C2H6, and H2/C3H8, respectively. This resulted from good compatibility between the larger fillers and the PEI polymer, as well as a reduction in the finger-like voids. Overall, the MMHFM in this work was deemed to be a promising candidate to separate hydrogen from gas streams, based on the comparison of the separation performance against other reported studies.

Atmospheric-pressure PECVD synthesis of polymer-supported molecular sieving silica membranes for gas separation: Effect of pore size of polymeric support

Molecular sieving silica-based membranes were prepared on porous polymeric supports by atmospheric-pressure plasma-enhanced chemical vapor deposition. The effect of polymeric support pore size on the gas permeation properties of polymer-supported silica-based membranes was investigated using nanofiltration (NF) and ultrafiltration membranes as polymeric supports. The silica-based layer was uniformly formed on the surfaces of the polymeric supports, irrespective of their different pore sizes. The selectivity of the resultant polymer-supported membranes was found to increased with decreasing support pore size. The NF-supported membrane exhibited an improved H2/N2 permeance ratio of > 40, which was comparable to those of ceramic-supported membranes, demonstrating the successful synthesis of molecular sieving silica-based membranes onto a porous polymeric support.

Freeze cast support for hydrogen separation membrane

BaCe0.65Zr0.20Y0.15O3-δ - Gd0.2Ce0.8O2-δ (BCZY-GDC) membranes have received increasing attention for their full H2 selectivity, high thermal and chemical stability, and intrinsic lower cost respect the Pd–based technology. The microstructure of the substrate plays a fundamental role to increase the gas diffusivity through the porous support. In this work, BCZY-GDC ceramics for hydrogen separation application were produced for the first time using ice-templating technique to obtain membrane supports with well-organized aligned porosity and lower pore tortuosity. After slurry composition optimization, the effect of cooling rate on the microstructure was accurately investigated. Samples produced with cooling speed of 30 °C/h showed homogeneous microstructures and well-aligned porosity with the best compromise between gas permeability and mechanical properties. Particularly gas permeability values are one order of magnitude higher with respect to the ones registered for tape cast BCZY-GDC substrates with isotropic porosity conventionally used for protonic applications.