Gas Permeation Flux Research Articles

Porous SiC ceramic obtained by spark plasma sintering of preceramic paper: Microstructure, mechanical properties and gas permeability

This paper describes the fabrication and characterization of porous SiC ceramics derived from highly-filled preceramic papers. The SiC ceramics were obtained by spark plasma sintering of stacked preceramic papers at temperatures of 2100 and 2200 °C under pressures of 5–60 MPa for 10 min. The microstructure and phase composition were analyzed by scanning electron microscopy and X-ray diffraction, respectively. Gas permeation tests were performed using hydrogen permeation cell at room temperature. It is revealed that the porosity of sintered SiC can be varied from 9 to 45 % depending on the sintering parameters. The shrinkage of the materials during spark plasma sintering occurs in four stages. The linear shrinkage value of the material increases from 7 to 47 % at 2100 °C and from 20 to 50 % for the samples sintered at 2100 and 2200 °C, respectively. Correlation dependencies between porosity and mechanical properties of the fabricated SiC were established. The obtained porous SiC ceramics exhibit high bending strength of 165 MPa and gas permeation flux of 78 molH2/m2/s at the porosity of 36 % that make it suitable for ceramic-based membranes.

Dual-phase ionic-conducting membranes: Pressure dependence of gas permeation flux

Pressure dependence of gas permeation flux for dual-phase ionic-conducting membranes is critical to the design and operation of separation or reaction processes using these membranes. However, literature on dual-phase membranes has mainly focused on temperature, rather than pressure dependence of gas permeation flux. This paper presents a theoretical approach for the development of the pressure dependence of gas permeation flux for dual-phase membranes, demonstrated with CO2 permeation for samarium-doped-ceria (SDC)/molten-carbonate (MC) dual-phase membranes. The paper presents a model showing that gas permeation through dual-phase ionic-conducting membranes is controlled not only by the intrinsic ion (or electronic) conductivity of the materials for each phase, but also by the geometric factor defined as the ratio of the volume to tortuosity of each phase. These geometric factors for both phases are determined by the topological structure of each phase. Dual-phase membranes of the same materials can have very different pressure-dependent flux equations depending on the topological structure dictated by synthesis method and conditions. CO2 permeation through SDC-MC membranes made of SDC with low porosity is controlled by carbonate conduction in the molten carbonate phase, leading to logarithmic CO2 pressure-dependent flux equation. CO2 permeation through SDC-MC membrane of SDC with intermediate porosity is controlled by oxygen ionic conduction in the SDC phase, and the CO2 permeation flux shows power-law dependence on CO2 pressures. The validity of the model is confirmed by comparison of the modeling results with experimental CO2 permeation data for SDC-MC membranes. This work provides a direction for developing pressure-dependent gas permeation flux equations for various dual-phase ionic-conducting membranes.

Structure and Properties of Porous Ti3AlC2-Doped Al2O3 Composites Obtained by Slip Casting Method for Membrane Application

In the present work, porous composites were fabricated from pure Al2O3 and mixed Ti3AlC2/Al2O3 powder by slip casting and sintering. The effect of sintering temperature and different composition ratio on microstructure, phase composition, porosity and gas permeation flux of the fabricated materials was investigated. The microstructure and phase composition of the samples were analyzed by scanning electron microscopy and X-ray diffraction, respectively. The gas permeation experiments were performed using pure hydrogen at 0.1-0.9 MPa pressure. It is shown that a decrease in sintering temperature from 1500 to 1350 °C results in an increase in hydrogen permeation flux of the alumina from 5 to 25 mol/(m2 × s), which is due to higher pore size and overall porosity of the samples. Sintering of Ti3AlC2/Al2O3 powder mixtures leads to the formation of Al2O3, Al2TiO5 and TiO2 phases as a result of oxidation of the Ti3AlC2 phase, resulting in an increased pore size in the composites compared with pure alumina. The open porosity of composites increases from 3.4 to 40% with an increasing Ti3AlC2/Al2O3 ratio from 1/10 to 1/2, respectively. The composites with the highest porosity (40%) had a maximum permeation flux of 200 mol/(m2 × s). The changes in the bending strength of the alumina and composite samples, depending on the microstructure and porosity, were also discussed. The investigated composites are considered promising materials for hydrogen separation membrane supports.

A novel poly (4-methyl-1-pentene)/polypropylene (PMP/PP) thin film composite (TFC) artificial lung membrane for enhanced gas transport and excellent hemo-compatibility.

Extracorporeal membrane oxygenation is a technique that provides short-term supports to the heart and lungs. It removes CO2 from the blood and provides enough oxygen, which is a huge help in the fight against COVID-19. As the key component, the artificial lung membranes have evolved in three generations including silicon, polypropylene and poly (4-methyl-1-pentene). Herein, we for the first time design and fabricate a novel poly (4-methyl-1-pentene)/polypropylene (PMP/PP) thin film composite (TFC) membrane with the anticoagulant coating composed of poly (sodium 4-styrenesulfonate) and cross-linked poly (vinyl alcohol). Poly (sodium 4-styrenesulfonate) provides sulfonic acid groups to inhibit the coagulant factors (FVIII and FXII), and cross-linked poly (vinyl alcohol) increase the stability of the anticoagulant coating and further improve the hydrophilicity via abundant hydroxyl groups to depress the protein adsorption. Long-term anticoagulant property was demonstrated by whole human blood for 28 days. Blood compatibility was evaluated by hemolysis rate, anticoagulation activity (APTT, TT and PT), complement activation, platelet activation and contact activation. Pure CO2, O2 and N2 permeation rates were determined to evaluate the mass transfer properties of PMP/PP TFC membranes. Gas permeation results revealed that gas permeation flux increased in the TFC membranes because of the decrease of crystallinity. Overall, the so prepared PMP/PP membrane shows good CO2/O2 selectivity and blood compatibility as novel TFC artificial lung membrane.

Enhanced toughness and gas permeabilities of polyimide composites derived from polyimide matrix and flower‐like polyimide microparticles

AbstractThe flower‐like polyimide (PI) based on 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride and benzidine was successfully obtained via solvothermal method. Using the flower‐like PI as organic fillers, the flower‐like PI/PI composites were fabricated by using 4,4′‐diaminodiphenyl ether and 1,2,4,5‐pyromellitic dianhydride as monomers through in situ polymerization and thermal imidization. The residual amino groups on the surface of flower‐like PI microparticles easily lead to the formation of chemical linkage between the flower‐like PI and PI matrix, which are benefit for tight interface and uniform dispersion. These experimental results showed that the broken elongation of the composites was significantly improved from 9.8% (pure PI) to 33.5% (PI‐4%), but the tensile strength and Young's modules were slightly sacrificed. The glass transition temperatures were mainly concentrated at around 352°C, while the 5% and 10% thermal decomposition temperature were slightly reduced. Furthermore, the light transmittance remarkably decreased from 75.9% (pure PI) to 4.3% (PI‐5%) at 550 nm. When the incorporation of flower‐like PI was 5%, an obvious increase of water uptake from 2.05% to 2.89% was noticed, and the water surface contact angle increased from 67.5° to 89.4°, indicating the increasing hydrophobicity. Additionally, with the increase of flower‐like PI fillers, the gas permeation flux of H2, CO2, O2, and N2 enhanced by more than two times, and the selectivities of O2/N2 and CO2/N2 increased first and then decreased. Therefore, the flower‐like PI microparticles will be promising functional fillers to improve the properties of polyimide materials.

Synthesis and characterization of novel polyimide/clay nanocomposites and processing, properties and applications

Mixed matrix membranes (MMMs) with cloisite® 15A clay in polyimide (PI) matrix were matured for gas separation applications. The inorganic cations of clay were replaced with cloisite® 15A as modifier. The altered cloisite® 15A clay showed excellent dispersion in the polymer matrix as evident from TEM micrographs. Uniform dispersion of cloisite® 15A clay improved the thermal properties of MMMs. The synthesized membranes were characterized by utilizing various spectrometer including FE-SEM, XRD, DTG, and TEM. FE-SEM results showed that at 3 wt% of clay15A, the fillers were dispersed homogeneously within the PI polymer matrix. The tensile properties of PI/cloisite® 15A clay nanocomposites increased gradually according to clay content increasing. The impact strength of nanocomposites was not altered until 3 wt% of clay and decreased at 5 wt% clay loading. Layered silicate cloisite® 15A clay particle plays major several key roles in determining the gas permeation behavior of the hybrid membrane. It was no surprise that the gas permeation flux was decreasing with the addition of layered silicate cloisite® 15A clay into the PI matrix. However, it was interesting to point that the pure gas selectivity was seen to be increased by decreasing the filler loading. At 1 wt% clay loading, cloisite® 15A clay MMMs showed an increase of 55% in CO2/CH4 ideal selectivity over pristine PI membrane.

Ultra-small photonic crystal (PhC)-based test tool for gas permeability of polymers.

We present an ultra-small photonic crystal-based test tool for gas permeability of polymers. It features a fully-etched photonic crystal (PhC) structure occupying an area of 20 µm × 800 µm on silicon-on-insulator wafer. The light-matter interaction in the PhC cavity with deformed Polydimethylsiloxane (PDMS) under pressure difference was investigated with finite element method and finite-difference time-domain method numerically. Next, three PDMS membranes of different mixing ratios were utilized for the characterization of gas permeation flux. The feasibility and effectiveness of the proposed working mechanism are verified through clearly distinguishing the gas permeability of these three testing samples. Compared with conventional test tools, this proposed test tool has fast response while it consumes less testing gas volume in a testing system with reduced footprint. Potentially, it can be integrated into lab-on-a-chip devices to measure gas permeation in nano scale.

Tailoring the pore structure of cathode supports for improving the electrochemical performance of solid oxide fuel cells

Two types of lanthanum doped strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) composite cathodes were prepared, one with the finger-like straight open pores by the phase inversion tape casting, and the other with the randomly distributed tortuous pores by the conventional tape casting. A gas permeation flux of 42.5 × 105 Lm−2 h−1 was measured under a trans-membrane pressure of 0.6 bar for the former while only 10.6 × 105 Lm−2 h−1 for the latter. Fuel cells supported on the as-prepared LSM-YSZ composite cathodes were fabricated, comprising a 15 μm thick YSZ electrolyte layer and a 20 μm thick NiO-YSZ anode. The electrochemical performance of the fuel cells was measured using H2 as fuels and air as oxidants. The cell supported on the phase-inversion derived cathode showed a maximum power density of 362 mWcm−2 at 850 °C, while only 149 mWcm−2 for the cell supported on the cathode formed by the conventional method. The difference in the electrochemical performance between the two cells can be attributed to the pore structure of the cathode supports. It is concluded that the phase inversion tape casting provides a simple and effective approach for tailoring the pore structure of the cathode support and thus enhancing the electrochemical performance.

Optimal conditions of porous ceramic membrane synthesis based on alkali activated blast furnace slag using Taguchi method

Abstract The main purpose of this research is to synthesize porous ceramic membrane based on alkali-activated blast furnace slag and achieve optimal synthesis conditions for removing over 90% petroleum compounds and flux in the range of microfiltration (MF) and ultrafiltration (UF). The method applied for membrane synthesis is simple, environmentally friendly, and economical. The blast furnace slag as the main starting material was used to fabricate these free sintering and self-supported ceramic membranes. The L 9 orthogonal array of the Taguchi method was employed to determine the optimum conditions of three controlling factors, i.e. hydraulic pressing pressure, alkali-activated blast furnace slag drying time, and pressing time in three levels. Morphology and filtration performance of the synthesized membranes were characterized via SEM images using Image-j software, total porosity determination, and pore size study using bubble point method. Cross-flow filtration of 75 ppm gas oil in water emulsion was performed and COD analysis of permeate was then monitored. Distribution of synthesis parameters and their influences on the membrane fabrication process were investigated using analysis of variance (ANOVA). According to the results, drying time and hydraulic pressing pressure were known as the most effective parameters on COD and permeation flux. Two optimal membranes for COD removal and permeation flux were identified in hydraulic pressing pressure, drying time and pressing time of (400 bar, 6 h, 5 min) and (225 bar, 8 h, 30 min), respectively. COD optimal UF membrane with an average pore size of 0.07 µm and 100% removal of gas oil and permeation flux optimal MF membrane with an average pore size of 0.66 µm and pure water permeation flux of 1960 kg/m 2 h were introduced.

Fast mass transport across two-dimensional graphene nanopores: Nonlinear pressure-dependent gas permeation flux

Mass transport across two-dimensional nanopores is very essential to the porous graphene and other atomically thin membranes for gas separation. Due to the contribution of gas adsorption and diffusion over the two-dimensional surfaces, mass transport across graphene nanopores cannot be described only by the kinetic theory of gases. We show that the combination of the linear pressure-dependent direct flux, governed by the kinetic motion of gas molecules, and the nonlinear pressure-dependent surface flux, caused by the Langmuir isothermal adsorption characteristics of gas molecules on the two-dimensional surfaces, results in an overall nonlinear pressure dependence of the gas permeation flux through graphene nanopores. Based on the mass transport resistance network connecting the multiple molecular transport processes in direct flux and surface flux, a theoretical model that captures the pressure dependence of permeation flux is established, offering a possible avenue to predict the mass transport rates through the two-dimensional nanopores.

Reversed thermo-switchable molecular sieving membranes composed of two-dimensional metal-organic nanosheets for gas separation

It is highly desirable to reduce the membrane thickness in order to maximize the throughput and break the trade-off limitation for membrane-based gas separation. Two-dimensional membranes composed of atomic-thick graphene or graphene oxide nanosheets have gas transport pathways that are at least three orders of magnitude higher than the membrane thickness, leading to reduced gas permeation flux and impaired separation throughput. Here we present nm-thick molecular sieving membranes composed of porous two-dimensional metal-organic nanosheets. These membranes possess pore openings parallel to gas concentration gradient allowing high gas permeation flux and high selectivity, which are proven by both experiment and molecular dynamics simulation. Furthermore, the gas transport pathways of these membranes exhibit a reversed thermo-switchable feature, which is attributed to the molecular flexibility of the building metal-organic nanosheets.

Low-cost porous mullite ceramic membrane supports fabricated from kyanite by casting and reaction sintering

Porous mullite supports are firstly fabricated by casting and reaction sintering based on kyanite with Al(OH)3 as porogenic agent. The effects of composition and sintering temperature on phase evolution, microstructure, apparent porosity, pore size distribution, linear shrinkage, gas permeation flux and mechanical property of supports are systematically investigated. Results show that the mullitization of kyanite generates needle-like mullite crystals, which form skeleton structures and improve the apparent porosity and strength of supports. Al(OH)3 addition not only promotes the formation of needle-like mullite but also enhances the apparent porosity of supports. Temperature promotes the development of mullite, from 1450 to 1500°C, the amount and size of needle-like mullite crystals increase, ≥1500°C, they reveal columnar morphology. The support prepared with kyanite+40wt%Al(OH)3 sintered at 1500–1550°C exhibits high apparent porosity, good gas permeation flux, excellent mechanical performance and interlocked network structure composed of well development needle-like mullite.

Surface monofunctionalized polymethyl pentene hollow fiber membranes by plasma treatment and hemocompatibility modification for membrane oxygenators

The hemocompatibility of polymethyl pentene (PMP) hollow fiber membranes (HFMs) was improved through surface modification for membrane oxygenator applications. The modification was performed stepwise with the following: (1) oxygen plasma treatment, (2) functionalization of monosort hydroxyl groups through NaBH4 reduction, and (3) grafting 2-methacryloyloxyethyl phosphorylcholine (MPC) or heparin. SEM, ATR-FTIR, and XPS analyses were conducted to confirm successful grafting during the modification. The hemocompatibility of PMP HFMs was analyzed and compared through protein adsorption, platelet adhesion, and coagulation tests. Pure CO2 and O2 permeation rates, as well as in vitro gas exchange rates, were determined to evaluate the mass transfer properties of PMP HFMs. SEM results showed that different nanofibril topographies were introduced on the HFM surface. ATR-FTIR and XPS spectra indicated the presence of functionalization of monosort hydroxyl group and the grafting of MPC and heparin. Hemocompatibility evaluation results showed that the modified PMP HFMs presented optimal hemocompatibility compared with pristine HFMs. Gas permeation results revealed that gas permeation flux increased in the modified HFMs because of dense surface etching during the plasma treatment. The results of in vitro gas exchange rates showed that all modified PMP HFMs presented decreased gas exchange rates because of potential surface fluid wetting. The proposed strategy exhibits a potential for fabricating membrane oxygenators for biomedical applications to prevent coagulation formation and alter plasma-induced surface topology and composition.

Incorporation of zinc for fabrication of low-cost spinel-based composite ceramic membrane support to achieve its stabilization

In order to reduce environment risk of zinc, a spinel-based porous membrane support was prepared by the high-temperature reaction of zinc and bauxite mineral. The phase evolution process, shrinkage, porosity, mechanical property, pore size distribution, gas permeation flux and microstructure were systematically studied. The XRD results, based on a Zn/Al stoichiometric composition of 1/2, show a formation of ZnAl2O4 structure starting from 1000°C and then accomplished at 1300°C. For spinel-based composite membrane, shrinkage and porosity are mainly influenced by a combination of an expansion induced by ZnAl2O4 formation and a general densification due to amorphous liquid SiO2. The highest porosity, as high as 44%, is observed in ZnAl4 membrane support among all the investigated compositions. Compared with pure bauxite (Al), ZnAl4 composite membrane support is reinforced by ZnAl2O4 phase and inter-locked mullite crystals, which is proved by the empirical strength–porosity relationships. Also, an increase in average pore diameter and gas flux can be observed in ZnAl4. A prolonged leaching experiment reveals the zinc can be successfully incorporated into ceramic membrane support via formation of ZnAl2O4, which has substantially better resistance toward acidic attack.

Environment-oriented low-cost porous mullite ceramic membrane supports fabricated from coal gangue and bauxite

Porous mullite ceramic supports for filtration membrane were successfully fabricated via recycling of coal gangue and bauxite at sintering temperatures from 1100 to 1500°C with corn starch as pore-forming agent. The dynamic sintering behaviors, phase evolution, shrinkage, porosity and pore size, gas permeation flux, microstructure and mechanical property were systematically studied. A unique volume-expansion stage was observed at increased temperatures from 1276 to 1481°C caused by a mullitization-crystal-growth process. During this stage, open porosity increases and pore size distributions broaden, which result in a maximum of nitrogen gas flux at 1400°C. The X-ray diffraction results reveal that secondary mullitization took place from 1100°C and the major phase is mullite with a content of ∼84.7wt.% at 1400°C. SEM images show that the as-fabricated mullite supports have a porous microstructure composed of sintered glassy particles embedded with inter-locked mullite crystals, which grew gradually with increasing temperature from rod-like into blocky-like morphologies. To obtain mullite membrane supports with sufficient porosity and acceptable mechanical strength, the relationship between porosity and mechanical strength was investigated, which was fitted using a parabolic equation.

Optimization of morphology and perf ormance of PVDF hollow fiber for direct contact membrane distillation using experimental design

Non-solvent induced phase inversion technology has been applied to develop porous poly (vinylidene fluoride) (PVDF) hollow fiber membranes in this study and structural characteristics of resultant membranes and their performance in direct contact membrane distillation (DCMD) were examined. Application of Taguchi experimental design with three level L9 orthogonal array (OA) and statistical analyses was attempted for identifying the relationship between the hollow fiber membrane formation conditions selected and the membrane performance and further making predictions. Membrane morphologies and microstructures were examined using FESEM, gas permeation and XRD; mechanisms for the membrane morphologies observed were discussed. Similar pattern of the plots of gas permeation and DCMD flux gave the hint that the skin resistance was not negligible in DCMD for these membranes. Analysis of variance (ANOVA) showed that among the three fabrication variables, content of non-solvent additive (i.e. glycerol) in the dope had the most significant effects on both membrane distillation coefficient Cm and thermal efficiency EE, while external coagulant composition is least influential. The observed responses at selected combination of spinning conditions were in agreement with those predicted based on the same fabrication conditions. The highest water flux achieved in the current work in desalinating 3wt% NaCl aqueous solution was higher than 20kg/m2-h at average feed temperature of 64.5°C with 99.9% rejection.

Removal of Organic Aerosols from Furnace Flue Gas by Ceramic Filters

Organic aerosols have severe effects on human health and climate change. In this study, a pilot-scale ceramic filter was used to remove the organic aerosols from furnace flue gas produced from industrial processes. The performance of ceramic filter and long-term stability of ceramic material were investigated. It showed that gas permeation flux fluctuated at a high level, which was the result of the surface filtration and special self-regeneration of the vertical ceramic filter. Removal efficiencies of TSP, PM10, and PM 2.5 aerosols were higher than 98.5%, and the rejection mechanisms were concluded as sieving, surface adhesion, and pore channel capture. Chemical characteristics of aerosol were analyzed based on FTIR spectra. Main organic compounds in the collected aerosols were paraffin binder, carboxylic acids, and esters. Carboxylic acids and esters were the products of the chemical reactions of paraffin and oxygen at high temperatures. After a long-term operation, ceramic membranes exhibited low flexural strength loss and slight variation in pore size distribution and the microstructure remained unchanged. Therefore, porous alumina membranes have potential for applications in the of removal organic aerosol emissions from industrial processes before reaching the atmosphere.

Separation of heavy gases from light gases using synthesized PDMS nano-composite membranes: Experimental and neural network modeling

A method for simulation of gas separation with nano-composite membranes was presented using artificial neural network (ANN). In this investigation, a number of nano-composite silica/PDMS (polydimethylsiloxane) membranes were synthesized with different amounts of silica nano-composite loaded into the polymer matrixes. The permeation behavior of pure gases including C 3H 8, CH 4, and H 2 has then been studied as functions of pressure and nano-composite loading. Experimental results were used to develop a black box model to predict gas permeability for the synthesized membranes as a function of operating pressure, nano-composite loading and one of the physical properties of the gases used. A comparison was made between three different groups of data including pressure as the first effective parameter, nano-composite loading as the second, and one out of the four variables, molecular diameter, molecular weight, boiling point, and critical temperature, as the third. It was concluded that feed pressure, nano-composite loading, and boiling point temperature in the feed neurons provides the best combination and leads to the least error in prediction of the gas permeation flux values. The results showed that, increasing pressure increases permeability of the condensable gas, C 3H 8, whereas permeabilities of the lighter gases, H 2 and CH 4, decrease with increasing pressure. In addition, nano-composite loading decreases permeability of the non-condensable gases, H 2 and CH 4, while that of C 3H 8 increases up to 2% of nano-composite loading. Ultimately, it was concluded that ANN method can be successfully used for prediction of gas separation properties of nano-composite membranes after proper network training in this case resulting in predictions of less than 4.0842 RMSE.

Reaction-sintered porous mineral-based mullite ceramic membrane supports made from recycled materials

Bulk porous mullite supports for ceramic membranes were prepared directly using a mixture of industrial waste fly ash and bauxite by dry-pressing, followed by sintering between 1200 and 1550 °C. The effects of sintering temperature on the phase composition and shrinkage percent of porous mullite were studied. The XRD results indicate that secondary mullitization reaction took place above 1200 °C, and completed at 1450 °C. During sintering, the mixture samples first shrunk, then expanded abnormally between 1326 and 1477 °C, and finally shrunk again above 1477 °C. This unique volume self-expansion is ascribed to the secondary mullitization reaction between bauxite and fly ash. More especially, the micro-structural variations induced by this self-expansion sintering were verified by SEM, porosity, pore size distribution and nitrogen gas permeation flux. During self-expansion sintering, with increasing temperature, an abnormal increase in both open porosity and pore size is observed, which also results in the increase of nitrogen gas flux. The mineral-based mullite supports with increased open porosity were obtained. Furthermore, the sintered porous mullite membrane supports were characterized in terms of thermal expansion co-efficient and mechanical strength.

Formation of a defect-free Pd–Cu–Ni ternary alloy membrane on a polished porous nickel support (PNS)

In order to decrease its resistance we enlarged the pore size of a porous nickel support (PNS) by using nickel powder with a larger particle size. The gas permeation test showed that this increased the gas permeation flux compared with the previous support. To make up for the various disadvantages, such as the enlarged surface roughness and pore size, a polishing process was introduced with sandpaper, followed by wet polishing with alumina powder. The polishing treatment was very effective in leveling off the surface of the porous nickel support, but it almost completely plugged the pores. Those pores blocked by the polishing process could be regenerated during Cu-reflow at 973 K by the upward diffusion of nickel and in this way a 12 μm defect-free Pd–Cu–Ni ternary alloy film was formed on the polished porous nickel support. Furthermore, we were able to obtain a three times higher hydrogen permeability than that reported in previous studies, because of the decreased support resistance of the porous nickel support.