Gas Permeation Performance Research Articles

Single and Binary CO2/CH4 Separation of a Zeolitic Imidazolate Framework‐8 Membrane

AbstractThe performance of a zeolitic imidazolate framework‐8 (ZIF‐8) membrane in single and binary CO2/CH4 gas separation was investigated by means of a gas transport model that included generalized Maxwell‐Stefan and binary friction models. The model concerns gas diffusion through the membrane layer, gas flow through membrane intercrystalline pores, and resistance of the support layer. The effective membrane area considering the actual area for the gas permeated through the membrane was also introduced in this model. The selective ZIF‐8 membrane was successfully synthesized using a microwave‐assisted solvothermal method on an α‐alumina support pre‐attached with ZIF‐8 seeds by solvent evaporation. The simulated data agreed well with the experimental data. The model revealed that the membrane intercrystalline pores and its effective area significantly affected the CO2/CH4 gas permeation and separation performance.

Patching NaA zeolite membrane by adding methylcellulose into the synthesis gel

Uniform NaA zeolite membranes, with good permeation and separation performance were successfully synthesized with the assistance of methylcellulose (MC) via microwave heating (MH). The results of X-ray diffraction spectroscopy (XRD) and Scanning electron microscopy (SEM) showed that this strategy could not only reduce the crystal size, but also promote the patching of the defects in the substrate membrane with a slight increase of the membrane thickness. The gas permeation performance demonstrated that the NaA zeolite membranes with MC modification exhibited excellent H2 permeation, and their permselectivities of H2 over other small molecule gases were obviously larger than those corresponding Knudsen diffusion coefficients. The effects of temperature, pressure and binary mixtures of gases on gas permeation behavior were systemically studied. At 298K and 0.1MPa, the H2 permeation value of M6 membrane achieved as high as 4.23×10−6molm−2s−1Pa−1, meanwhile its permselectivity for H2 over CO2, N2 CO, CH4 and C3H8 was 6.31, 5.87, 7.98, 8.46 and 15.67, respectively.

Low-temperature sintering of porous silicon carbide ceramic support with SDBS as sintering aid

The sintering temperature of porous silicon carbide ceramic support (PSCS) is typically higher than 1500°C. In this paper, sodium dodecyl benzene sulfonate (SDBS) was used as a sintering additive to fabricate PSCS with high gas permeance and high bending strength at a sintering temperature less than 1200°C. The PSCS was prepared by the dry pressing method followed by in-situ reaction. The effects of SDBS loading on the porosity, bending strength, gas permeation performance, and microstructure of the PSCS were investigated. The results showed that without SDBS, the required sintering temperature was as high as 1550°C and resulted in a bending strength of 6.5MPa but the sintering temperature decreased to 1150°C with 8% SDBS and the bending strength increased to 16MPa. The main reason was that SDBS decomposed into Na2O which reacted with SiO2 and ZrO2 to form strong bonding connections. The prepared PSCS with SDBS also showed good gas permeance of 900m3/(m2hkPa), higher than the 750m3/(m2·h·kPa) without SDBS. This work describes the effective use of SDBS as a ceramic additive to reduce sintering temperature, while achieving high gas permeation and bending strength. The use of the low cost and commercially available SDBS produces an excellent ceramic filter with much lower energy consumption, and could also be implemented in other ceramic systems.

Feasibility of using waste polystyrene as a membrane material for gas separation

An alternate reuse route for recycling plastic solid waste (PSW) was successfully developed in this study. Polystyrene (PS) waste was directly re-used as a material for gas-separation membranes using a solution-casting method. The waste materials comprise three types: (1) oriented polystyrene (OPS), (2) expandable polystyrene (EPS), and (3) high-impact polystyrene (HIPS); these were investigated through proximate analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The waste materials have the same composite and thermal properties as the raw materials except for waste EPS, which contains a partially broken molecular chain. Thus, besides the waste EPS, the waste PS-derived membranes were homogenous and symmetrical. The gas permeation performances of the membranes were measured using the time-lag method at different operating pressures. The results showed that the performances of the waste PS- and raw PS-derived membranes are similar. Meanwhile, a HIPS membrane containing butadiene rubber exhibited high CO2 plasticization resistance at high pressure with a CO2 permeability of 67Barrer and CO2/N2 selectivity of 10–11 at an operating pressure of 5atm. Therefore, the novel reuse route of PS waste is feasible as an economically and environmentally friendly method for disposing PSW.

An initial investigation of a nano-composite silica ceramic membrane for hydrogen gas separation and purification

The effects of trans-membrane pressure difference on hydrogen recovery are investigated on a preliminary basis. The membrane has been developed for high temperature hydrogen separation from CH4, N2, and Ar gas molecules. Gas permeation and separation performance of the developed membrane was evaluated. The silica fabricated membrane exhibited high H2 gas flux and much lower fluxes for CH4, N2, and Ar and showed a rise in permeance with the inverse of the square root of temperature for H2. Plots obtained with respect to the effects of gauge pressure on H2, N2, CH4 and Ar component gas fluxes through the modified support (silica membrane) at a pressure of 1 bar showed that H2 recorded an almost four-fold high flux value of 0.76 mol/m2.s compared to that of 0.33 mol/m2.s (CH4), 0.25 mol/m2.s (N2) and 0.22 mol/m2.s (Ar). These results were nearly stable for the temperature range investigated (298 K, 373 K and 473 K). In addition, hydrogen maintained a relatively high permeance value of 1.62 × 10−5 mol m−2 s−1 Pa−1 at a low pressure of 0.1 bar under room temperature (298 K) compared to that of N2, CH4 and Ar which were much lower throughout the temperature range studied and in agreement with literature. H2 separation factor (experimental Knudsen) over CH4, N2 and Ar were quite close to the theoretical Knudsen and can therefore be experimentally applied through further optimization in the separation of H2 as a key constituent energy for the future.

Development of hydrogen-selective triphenylmethoxysilane-derived silica membranes with tailored pore size by chemical vapor deposition

Amorphous silica membranes were developed, based on an in silico molecular design, to exhibit excellent hydrogen-selective performance for separating hydrogen from mixtures containing larger organic molecules, such as methylcyclohexane and toluene. Triphenylmethoxysilane (TPMS) was synthesized and used as a novel precursor to prepare membranes by the counter-diffusion chemical vapor deposition method. Under the optimized bubbler temperature and counter-diffusion chemical vapor deposition reaction time, the fresh membranes showed high reproducibility and high hydrogen permeance in the order of 10−6molm−2s−1Pa−1 and high H2/SF6 ideal selectivity of over 12,000 at 573K. Moreover, the TPMS-derived membrane exhibited good stability after hydrogen regeneration, even after placement in a dehumidifier cabinet at room temperature for 90 days. Single gas permeation performance and normalized Knudsen-based permeance evaluation showed that the TPMS-derived membrane (three phenyl groups on the precursor) had a pore size of 0.486nm, and exhibited looser structures with larger pore size than those of a diphenyldimethoxysilane (DPDMS)-derived membrane (two phenyl groups on the precursor). These results suggest that the pore size of silica membranes can be tailored with various structured silica precursors containing phenyl groups.

Microporous Ceramic Tubule Based and Dendrimer-Facilitated Immobilized Ionic Liquid Membrane for CO2 Separation

A solvent evaporation method has been used to prepare a supported ionic liquid (IL) membrane in a microporous ceramic tubule-based module; its separation performance for CO2–N2 and CO2–He mixtures has been reported here over a pressure range of 50−250 psig (344.7−1724 kPag) and temperatures up to 100 °C. Solutions of IL-ethanol having different IL contents were used to prepare 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]) membranes having different thicknesses. Membranes prepared from 25 wt % IL in ethanol solution showed the best gas permeation and separation performance. Ionic liquid membranes prepared from 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim][Tf2N]) under the same conditions displayed a slightly higher gas permeance, but its separation capability was somewhat lower. Tests at higher temperatures using the [bmim][DCA] membrane generated obviously higher gas permeances, but the ideal separation factors of CO2 over N2 and He dropped sharply. These tests were carried out with a dry feed gas. Adding polyamidoamine (PAMAM) dendrimer generation 0 to IL did not show any improvement when the feed gas was dry. After the feed gas was humidified, both the permeance and the separation factor of CO2 over N2 and He were improved greatly. This is due to lower viscosity caused by dissolved water in the IL membrane and additional reactions between CO2 and tertiary amine units of dendrimer in the presence of water. A set of gas mixture-based test results confirmed the facilitating effects of dendrimer to enhance CO2 permeation with humidified feed gas.

Ethylene vinyl acetate/poly(ethylene glycol) blend membranes for CO2/N2 separation

AbstractIn this paper, novel membranes were prepared from blending the ethylene vinyl acetate (EVA), containing 28 wt.% of vinyl acetate, and poly(ethylene glycol) (PEG) (0–20 wt.%) with molecular weights of 200, 1000, and 1500, and considered for CO2/N2 separation over the feed pressure of range 2–8 bar. Physical properties and the morphology of the membranes were evaluated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and scanning electron microscope (SEM) analyses in order to justify the gas permeation and separation performance of the membranes. The results showed that CO2 permeability increases by increasing the PEG content of the blend membranes. However, increasing PEG loading enhanced CO2/N2 selectivity just for the blends containing up to 10 wt.% of PEG and it decreased at higher PEG loadings. The PEG with a molecular weight of 200 showed a more efficient gas separation performance due to its effective role in providing amorphous regions in the blends. Furthermore, higher CO2 permeabilities were obtained at higher feed pressures. The selectivity increased by increasing the feed pressure for neat EVA, EVA/5 wt.% PEG and EVA/10 wt.% PEG membranes, but it had no significant effect on the selectivity of the samples with 15 and 20 wt.% of PEG.© 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

A novel multi-armed and star-like poly(ethylene oxide) membrane for CO2 separation

A series of cross-linked poly(ethylene oxide) (PEO) membranes with a multi-armed and star-like structure was prepared by photo-polymerization. The structure characterization was performed by Fourier transform infrared spectroscopy (FTIR). The thermal property was evaluated by differential scanning calorimetry (DSC). The inter-segmental distance of polymer chain was investigated by wide-angle X-ray diffraction (WAXD). The density was determined by a hydrostatic weighing method. The permeation performances for N2, CH4 and CO2 were reported. The relationship between gas permeation performances and physical properties was also discussed. The star-like PEO membranes exhibit excellent permeation–separation performances for CO2/N2 and CO2/CH4. The permeation–separation performance for CO2/N2 exceeds the Robeson upper-boundary. The star-like PEO membranes display a positive potential application for industrial-scale CO2 separation.

Pore‐size evaluation and gas transport behaviors of microporous membranes: An experimental and theoretical study

A modified gas‐translation (GT) model based on a GT mechanism was successfully applied to the pore‐size evaluation and gas transport behavior analysis of microporous membranes with different pore‐size distributions. Based on the gas permeation results of three microporous membranes derived from different alkoxides, the effects of activation energy and the selection of a standard gas on the pore‐size evaluation were discussed in a comparative study. The presence of nano‐sized defects had an important influence on the gas permeation performance of microporous membranes, depending largely on the original pore size of the membrane in question. Moreover, the gas‐separation effect of the pore‐size distribution in a silica membrane was theoretically studied and revealed a significant increase in gas permeance for relatively large gas species but not for small ones. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2268–2279, 2015

실리카-지르코니아 분리막 성능에 대한 다공성 지지체와 중간층의 영향

실리카-지르코니아 분리막 성능에 대한 다공성 지지체와 중간층의 영향

Separation of CO2/CH4 through Carbon Tubular Membranes: Effect of Carbonization Temperature

Carbon membranes have received much attention as advance materials in the gas separation technology due to their superior gas permeation performance and thermal and chemical stability. In order to increase the mechanical strength of the membrane, supported carbon membrane were produced using ceramic tube as support layer. Carbon tubular membranes were produced by carbonizing polymeric tubular membrane under different process parameter. In this study, carbon tubular membranes originating from Matrimid were prepared and characterized n term of its gas permeation properties. The preparation method involved dip-coating of the ceramic tubes with a Matrimid-based solution. The carbon tubular membranes were obtained by carbonization of the resultant polymeric tubular membrane under Argon gas flow in the horizontal tube furnace. The effects of the carbonization temperature on the gas permeation performance were investigated. Pure gas permeation tests were performed using CO2 and CH4 at room temperature with pressure 8 bars. The permeance and selectivity data indicate that the highest CO2/CH4 selectivity of 87.30 was obtained for carbon tubular membrane prepared at carbonization temperature of 850 ºC.

Selective Permeation of Hydrogen Gas Using Cellulose Nanofibril Film

Biobased membranes that can selectively permeate hydrogen gas have been developed from aqueous dispersions of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCN) prepared from wood cellulose: TOCN-coated plastic films and self-standing TOCN films. Compared with TOCNs with sodium, lithium, potassium, and cesium carboxylate groups, TOCN with free carboxyl groups (TOCN-COOH) had much high and selective H2 gas permeation performance. Because permeabilities of H2, N2, O2, and CO2 gases through the membranes primarily depended on their kinetic diameters, the gas permeation behavior of the various TOCNs can be explained in terms of a diffusion mechanism. Thus, the selective H2 gas permeability for TOCN-COOH was probably due to a larger average size in free volume holes present between nanofibrils in the layer and film than those of other TOCNs with metal carboxylate groups. The obtained results indicate that TOCN-COOH membranes are applicable as biobased H2 gas separation membranes in fuel cell electric power generation systems.

Preparation and characterization of ITQ-29/polysulfone mixed-matrix membranes for gas separation: Effect of zeolite composition and crystal size

This work concerns the preparation and characterization of ITQ-29 zeolite crystals with high Si/Ge ratio (100–∞) and different particle size for obtaining mixed matrix membranes. The Si/Ge molar ratio and seeding content of the synthesis gel appeared to have an effect on the final crystal size, and particles of 2.5μm were obtained for pure silica composition with good crystallinity. These were introduced, at 4, 8 and 12wt% loadings, into a commercial polysulfone matrix to prepare mixed matrix membranes that showed promising results in the separation of H2/CH4 mixtures (highest H2 permeability 21.9 Barrer and a separation factor of 118 for the 4wt% ITQ-29/polysulfone membrane). The thermal treatment of the membranes and the type of solvent were also optimized to provide good interaction between the zeolite and the polymer, limiting aggregation of the particles in the matrix, and removing all residual solvent that hinders gas permeation performance.

Influence of novel surface modifying macromolecules and coagulation media on the gas permeation properties of different polymeric gas separation membranes

AbstractIntegrally skinned asymmetric membranes for the separation of O2 and N2 were fabricated by the phase inversion technique from polysulfone, polyetherimide, and polyimide. Two types of surface modifying macromolecules (SMMs) including hydrophilic SMM (LSMM) and charged SMM (cSMM) were synthesized and blended with the casting solution to modify the membrane surface. The cast film was then immersed in the first coagulant alcohol (methanol, ethanol, or isopropanol) for a predetermined period, before being immersed in the second coagulant (water). The SMMs used in these experiments were laboratory synthesized by the two‐step process of polyurethane prepolymer synthesis and end capping, before being characterized by differential scanning calorimetry. Their molecular structure was determined from the molecular weight obtained by gel permeation chromatography. The membranes were characterized by contact angle measurement and O2 and N2 gas permeation performance. Attempts were made to interpret the gas permeation data by delayed demixing affected by solubility parameters of polymer, solvent, and nonsolvent. Furthermore, the permeation performance of cSMM membranes was interpreted by the solvation of the charged sulfonate groups present in cSMM. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Studies on gas permeation performance of asymmetric polysulfone hollow fiber mixed matrix membranes using nanosized fumed silica as fillers

This study investigated the use of nanosized fumed silica (Aerosil® R106) as fillers in the production of asymmetric hollow fiber mixed matrix membrane (HFMMM) where polysulfone was the host polymer matrix. The presence of fumed silica particles were found to stimulate the flow of CO2 as indicated by an increase (>12%) in CO2 permeability for all HFMMMs. At low loading of 0.1% (w/w), the permeability of CO2 and CH4 were 90.04 and 2.75GPU, respectively, and the calculated selectivity was higher than the neat PSf hollow fiber membrane. At higher loading of 10% (w/w), the FESEM images of the HFMMM showed severe agglomeration of fillers that contributed to nanometric defects between the aggregates, leading to higher permeation of slow gases (CH4 and N2). Hence, the selectivities of CO2/CH4 and O2/N2 were low at 7.43 and 2.02, respectively. The calculation of particle spacing within the polymer macromolecules have shown that for nanoparticles, the agglomeration was unavoidable at high loading due to sheer number of particles within the matrix. At low loading of 0.1%, the polysulfone-fumed silica HFMMM showed no visible sign of particle agglomeration. The selectivities of CO2/CH4 and O2/N2 significantly improved with an average value of 32.74 and 6.35, respectively. The HFMMM also showed an increase in glass transition temperature and has a better thermal stability as measured by DSC and TGA analyzers, respectively. The importance of filler–filler, polymer–filler and filler–gas interactions on the characteristic and permeation performance of HFMMMs are also discussed.

Silver-Doped Organic-Inorganic Hybrid Silica Membranes by Sol-Gel Method: Preparation and Hydrothermal Stability

Silver-doped methyl-modified silica membranes (Ag/M-SiO2) have been prepared using the sol-gel method by adding AgNO3 solution to a methyl-modified silica sol. The influence of silver-doping on the physical and chemical structures, thermal stability of –CH3 groups, and gas permeation performance for the silica membranes were investigated. The metallic silver results from the reduction of AgNO3 which can be completely transformed after calcined above 200°C. The Si–CH3 vibrational bands disappear completely when the calcination temperature is increased to 600°C, which mineralized when the calcination temperature is further increased to 750°C. The doping of silver nanoparticles has nearly no influence on the chemical structure of the methyl-modified silica materials and the thermal stability of –CH3 groups, but can make the mean pore size, total pore volume, H2 permeability, and H2/CO2 selectivities of the silica membranes increase. When operated at 200°C and a pressure difference of 0.35 MPa, the H2 permeance and H2/CO2 selectivity of Ag/M-SiO2 membrane with the AgNO3/tetraethylorthosilicate molar ratio of 0.08 is 8.99 × 10−6 mol · m−2 · Pa−1 · s−1 and 10.22, respectively. After hydrothermal treatment and regeneration, the Ag/M-SiO2 membranes show a smaller change in gas permeances and H2/CO2 permselectivities than the methyl-modified silica membranes without silver-doping.

Preparation of Pd-TS-1 Composite Membrane for Hydrogen Separation

Palladium composite membranes have been prepared by improved electroless plating on macroporous α-Al2O3 tubes. TS-1 zeolite layer was introduced in the palladium composite membrane to modify macroporous α-Al2O3 tubes and prevent the diffusion between Pd and alumina. The detailed microstructure and morphology of the Pd-TS-1 composite membrane were examined by SEM and XRD. Moreover, gas permeation performance was tested at the temperature range of 623~773K. Results showed that the H2 permeance and H2/N2 ideal selectivity for Pd-TS-1 composite membrane could be up to 3.7×10-7 mol·m-2·s-1·Pa-1 and 310 at 773K, respectively.

Hydrogen separation performance of CMS membranes derived from the imide-functional group of two similar types of precursors

Carbon molecular sieve (CMS) membranes derived from polyimide (PI) and polyetherimide (PEI), which have similar functional groups were fabricated for gas separation. To evaluate the effect of the functional groups of PI and PEI on the properties of their CMS membranes, the composition of the casting solution and carbonization temperatures were investigated. Thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM) were employed to characterize thermal stability, functional groups and microstructural change in the derived CMS membrane. The gas permeation performance of the CMS membranes were estimated using four gases: hydrogen, carbon dioxide, nitrogen and methane. The results show that C C stretching in imides exhibit an intense absorption peak at 1665 cm −1 with PI dominating the insignificant degradation of the imide groups at the intermediate stage. For PEI, the absorption peaks of C N stretching and C–C–C bending were intense at 1011 and 1068 cm −1 respectively, dominating the ethers and cyclic ethers of asymmetric stretching. The microstructure and gas permeation properties of the obtained CMS membranes were significantly affected by the functional group of precursors and their concentrations in the casting solution. Optimized performance for hydrogen permeation (565 Barrer) [1 Barrer = 1 × 10 −10 cm 3 (STP) cm/(cm 2 s cmHg)] was obtained with PI-10-600 CMS membrane. The best selectivity for H 2/N 2 at 33.2 was obtained from PI-10-500 CMS membrane.

EFFECT OF COAGULATION BATH TEMPERATURE ON STRUCTURE AND GAS SEPARATION PROPERTIES OF CELLULOSE HOLLOW FIBER MEMBRANES

Cellulose hollow fiber membranes (CHFMs) were prepared by a new dissolving method. The influence of coagulation bath temperature on the morphology and properties such as crystallinity degree, mechanical strength and gas permeation performance of CHFM was systematically investigated. The results showed that with the increase of coagulation bath temperature, the morphology of asymmetric cellulose hollow fiber membranes would become much looser, and more large finger-like pores could be found across the section. At the same time, crystallinity degree almost showed no change and mechanical strength became worse obviously. As a result gas permeation performance of dry CHFMs would increase dramatically with the coagulation bath temperature and show obvious "Knudson-diffusion selective" mechanism. While for wet CHFMs, permeation rates for all gases would decrease sharply and interestingly for CHFMs from coagulation bath temperature of 0 degrees C and 20 degrees C carbon dioxide became the fastest gas because of the permeation mechanism had changed to "solution selective" in wet CHFMs. While for CHFMs from coagulation bath temperature of 40 degrees C and 60 degrees C, this "solution selective" effect cannot be found because of their much looser structure.