Steam Permeation Research Articles

Steam permeation performance of BaCe0.7Fe0.1Sc0.2O3−δ perovskite hollow fiber membrane

This work reports the characterization and steam permeation performance of dense BaCe0.7Fe0.1Sc0.2O3−δ (BCFS) perovskite hollow fiber (HF) membrane, which was fabricated by sintering at 1400 °C with 1 wt% Co2O3 sintering aid. BCFS HF membrane could permeate steam (water vapor) in the presence of the concentration gradient of steam in feed/permeate sides at high temperature range of 700–1000 °C. The steam permeation flux through BCFS HF reached 0.077 mL cm−2 min−1 at 1000 °C, which was 189 % higher than that at 700 °C using 100 mL min−1 steam-saturated He feed gas and 100 mL min−1 N2 sweep gas. BCFS HF could maintain relatively stable yet slightly deteriorating fluxes when subjected to continuous 8 thermal cycles between 700 and 1000 °C. When external voltage (−2.0 V–2.0 V) was applied to the BCFS HF, it behaved as a steam pump and showed self-regulation behavior. Both the direction of the voltage and the wiring method for the electrode affected the steam permeation performances. In addition, steam permeation fluxes showed hysteresis profile when the applied voltage was changed. The findings reported here can essentially be used to develop HF-based electrochemical device for high temperature steam permeation and control.

Steam permeation properties of perfluorosulfonic acid/ceramic composite membranes at a high temperature under various humidity conditions

The perfluorosulfonic acid (PFSA) polymer is an important materials for dehumidification membranes and is typically used at temperatures below 70 °C. In this study, the humid gas separation performances of PFSA membranes were evaluated at temperatures ranging from 80 to 200 °C under various relative humidity (RH) conditions to enable a wide potential range of applications at high temperatures, such as in steam recovery and dehydration membrane reactors. PFSA layers with 80 nm thicknesses were prepared on ceramic supports to achieve a high water permeance of the order of 10−6–10−5 mol/(m2 s Pa) and water/nitrogen permeance ratio ranged from several tens to 100 at temperatures ranging from 150 to 200 °C. This paper discusses the detailed effect of the RH on the permeation properties at 200 °C. The thickness of the PFSA layer is approximately the same as the water cluster size in the PFSA structure, leading to the unique permeation behavior. This study provides insights into the use of PFSA membranes at high temperatures under humid conditions.

Physical, chemical, and biological characterization of biodegradable chitosan dressing for biomedical applications: Could sodium bicarbonate act as a crosslinking agent?

Chitosan, a biomaterial with properties that allows the elaboration of biocompatible and biodegradable systems, was employed to prepare dressings - 2% (w/v) in acetic acid - followed by freezing and lyophilization. Some samples were kept chemically unchanged and used as control, while others were cross-linked with Epichlorohydrin 0.01 mol L−1 for 24 h being washed, frozen and lyophilized. The neutralization procedure was performed with sodium bicarbonate, which ended up leading to a crosslinking by ionic interactions in the polymer network, and characteristics as promising as those of the chemically cross-linked with Epichlorohydrin. SEM showed that the crosslinking leads to a controlled formation of the polymeric network, conferring suitable steam permeation capacity 107 g mm.day−1.m−2.kPa−1, simulated fluid permeation between 2000 and 2500 g m−2.day-1 and porosity with interconnection which allows fluid absorption capacity above 900%. The crosslinking processes favored a better handling mechanical resistance confirmed by biodegradation assays. The dressing blocked micro-organisms permeation, forming an efficient barrier against contamination, is safe and biocompatible, allowing satisfactory cell adhesion and proliferation. These results showed that both dressings present statistically and satisfactory equivalent characteristics to be used as a functional bio dressing suitable for the treatment of different pathologies.

Insight into Steam Permeation through Perovskite Membrane via Transient Modeling

A dynamic model based on BaCe0.9Y0.1O3−δ (BCY10) perovskite membrane for steam permeation process is presented here to essentially investigate the internal mechanism. The transient concentration distribution and flux of the charged species and the electric potential distribution within the membrane on the steam permeation process are analyzed in detail via simulation based on this model. The results indicate that the flux of steam can be improved via elevating operating temperatures, enlarging the difference of the partial steam pressure between two sides of the membrane, increasing the membrane density, and reducing the membrane thickness. Moreover, it was found that the polarization electric potential between both sides of the membrane occurs during the steam permeation process, especially at the steady state of the steam permeation process. The polarization electric potential reaches the maximum value at about 1050 K in this membrane. The evolution of electric potential can explain the influence of the above-mentioned factors on the steam permeation process. This study advances the mechanism of steam permeation through perovskite membrane, which provides a new strategy for the fundamental investigation of related species permeation (oxygen, carbon dioxide, hydrogen, etc.) on inorganic membranes via transient modeling.

High-Temperature Membrane for Water Removal in in-Situ Process

Water is a main by-product of many chemical processes, such as the production of hydrocarbons from synthesis gas, condensation reactions, and oxidative dehydrogenation. In most cases, water must be removed before or during product purification. Current water removal technologies, including direct condensation, azeotropic distillation, and vacuum or reactive distillation, are energy intensive. We are investigating use of in-situ water removal membranes to circumvent the energy-intensive conventional approaches for separating water at low temperatures and pressures. The water removal membranes would provide a continuous flux of water at constant temperature and pressure while avoiding the energy-consuming steps of conventional separation methods. Large energy losses associated with water removal could be avoided, and process efficiency significantly improved. Water is undesirable as a primary by-product at the reaction site because it could lower the reaction rate by decreasing the catalyst activity. Removal of water at the reaction site, therefore, can prevent catalyst deactivation, and it also can increase the reaction yield by shifting the equilibrium conversion to the desired products. Because the existing polymer-based membrane technologies have a temperature limitation, we are developing ceramic membranes for separating steam under process conditions over a wide temperature range (200-900ºC). Preliminary results of the steam permeation rate measurement with dense ceramic membranes made of ionic conductor will be presented in this talk.

Modeling of steam permeation through the high temperature proton‐Conducting ceramic membranes

The BaCeO3‐based perovskite oxide can be applied as a steam‐permeable membrane due to their noticeable mixed oxygen ion and proton conducting properties. In this article, a transient model of the steam permeation through the BaCe0.9Y0.1O3‐δ perovskite membrane at elevated temperatures has been developed with the Poisson–Nernst–Planck equations for analyzing the steam permeation process, in which the distribution of charged defects in the membrane is carefully considered. The effects of the operating temperature, the membrane thickness, the steam partial pressure, and the electric potential difference between two membrane sides during the steam permeation have been simulated and discussed. The modeling results indicate there exists a maximum value of the spontaneous electric potential difference with the temperature rise and the external electric potential can obviously increase the steam flux. The model is validated using the experimental results from literature under steady state operational conditions. © 2018 American Institute of Chemical Engineers AIChE J, 65: 777–782, 2019

Failure analysis and permeation modelling of photovoltaic module sealing material in Hot and humid conditions

Hot and humid conditions are one of the most typical working environments of photovoltaic module. Studying the aging and failure mechanisms of photovoltaic module and their reactions with steam in these conditions is needed to increase the reliability of photovoltaic module products. In this paper, the IR spectrum was used to analyse ethylene-vinyl acetate in different aging states and determine the reaction process of ethylene-vinyl acetate on the aging process in hot and humid conditions. In this study, a mathematical model was developed to extrapolate the factors that influenced the steam permeation and time constant in this process. The results will benefit sealing materials selection, design and enhancement of anti-permeation abilities, decrease the risk of failure by steam permeation, and improve the reliability of photovoltaic module.

Hydrophilic SOD and LTA membranes for membrane-supported methanol, dimethylether and dimethylcarbonate synthesis

Hydrophilic LTA and SOD membranes have been tested in the selective water removal from methanol (MeOH), dimethylcarbonate (DMC) and dimethylether (DME) thus simulating their synthesis in membrane reactors with CO2 as feed. To further improve the pervaporation selectivity of LTA membranes for an aqueous MeOH solution, Na+ ions located in the 8-membered oxygen ring of LTA were ion-exchanged with larger K+ ions in a KNO3 solution, leading to an improvement of the pervaporation separation factor of the H2O/MeOH mixture from 2.8 to 7.4 at room temperature. Furthermore, the selective removal of steam from the organic compounds MeOH, DME and DMC on supported SOD membranes was investigated at high temperatures by steam permeation. The separation performances of SOD membranes for equimolar mixtures of steam with H2, CO2, MeOH, DME or DMC, were evaluated in the temperature range from 125 to 200 °C. The mixture separation factors for steam from DME and DMC through the SOD membrane were found to be higher than 200 and 1000, respectively.

Protonic ceramic steam-permeable membranes

Yttrium-doped barium cerate is prototypical of a class of ceramic materials that incorporate water vapour into oxygen ion vacancies to produce interstitial protonic defects. At low to moderate oxygen pressures, where hole conductivity may be neglected, mixed oxygen ion/proton conduction is possible, resulting in ambipolar diffusion of protonic defects and oxygen ion vacancies. At low temperatures, protonic conduction dominates, while at high temperatures oxygen ion conduction dominates. At intermediate temperatures, however, the transport of water vapour is also possible due to chemical diffusion whenever there is a gradient in the chemical potential of steam. This mixed ionic conductivity region greatly complicates the use of protonic ceramics in electrochemical devices, but makes possible a whole new range of interesting applications as steam-permeable membranes. With such a membrane, for example, steam may be transported from moist SOFC fuel cell exhaust to dry hydrocarbon inlet fuel to aid in steam reforming. We previously reported partial conductivity measurements on BaCe 0.9Y 0.1O 3− δ in moist and dry helium [W. Grover Coors and R. Swartzlander, “Partial Conductivity Measurements in BaCe 0.9Y 0.1O 3− δ by Impedance Spectroscopy,” Proceedings of the 26th Risø International Symposium on Materials Science Solid State Electrochemistry, Linderoth, et al., Ed. (September 2005).]. With these results and the ambipolar diffusion models developed by Kreuer [K.D. Kreuer, Solid State Ionics 125, 285–302 (1999).], a steady-state steam permeation flux model is proposed for the steam flux as a function of steam pressure gradient and temperature. Using predicted steam fluxes based on empirical values for hydration enthalpy and entropy in BCY10, the model predicts a maximum in the steam flux at high temperatures, and considerable steam flux even at 800 °C, where hydrocarbon reforming is most efficient.

Charge transfer properties of BaCe 0.88Nd 0.12O 3−δ co-ionic electrolyte

Charge and mass transfer in an electrochemical cell, based on an electrolyte possessing both oxygen ion and proton conductivity (co-ionic electrolyte), under the gradient of steam partial pressure was considered from theoretical point of view. It is shown that, due to simultaneous carry of oxygen ions and protons in the same directions, steam permeation through the co-ionic electrolyte occurs. Experiments performed with the BaCe 0.88Nd 0.12O 3−δ have confirmed the existence of steam permeation through the co-ionic electrolyte.

Zeolite Membranes: From the Laboratory Scale to Technical Applications

Current trends and novel concepts in R&D of zeolite membranes like the seeding supported crystallization and the preparation of Al-containing zeolite membranes are discussed. The influences of adsorption and diffusion on the permeation properties of zeolite membranes are considered. Dehydration of ethanol by steam permeation and pervaporation as the first zeolite membrane based industrial separation is presented. Membrane supported dehydrogenation and esterification are discussed as possible applications of a catalytic membrane reactors.

Steam Reforming and Water-Gas Shift by Steam Permeation in a Protonic Ceramic Fuel Cell

We recently described a protonic ceramic fuel cell (PCFC) operating on dry methane that was made possible by the discovery of steam permeation reforming [W. G. Coors, J. Power Sources, 118, 150 (2003)]. This paper presents new test results from a single PCFC operated in our laboratory on four different pure fuels, hydrogen, syngas, carbon monoxide, and methane, representative of the most important anode fuel mixtures expected in a fuel cell operating on natural gas. Except for hydrogen, some combination of steam reforming and water-gas shift reactions is necessary for complete conversion to carbon dioxide. The source of water vapor at the anode for these reactions was provided by ambipolar diffusion of water vapor through the electrolyte membrane. The fuel cell used a 10% yttrium-barium cerate (BCY10) protonic ceramic electrolyte membrane with platinum electrodes, and was tested between 650 and 800°C on each gas. Clear evidence for steam permeation reforming was obtained from the I-V curves of the cell operating on each fuel. The activation energy for the rate-limiting mechanism at constant current for each fuel was determined. © 2004 The Electrochemical Society. All rights reserved.

Protonic ceramic fuel cells for high-efficiency operation with methane

A new class of fuel cells is being developed, based on ceramic electrolyte materials that exhibit high protonic conductivity at elevated temperatures. The protonic ceramic fuel cell (PCFC) is fundamentally different and unique among fuel cell types currently being developed because it relies on conduction of protons through the electrolyte at much higher temperatures than is possible with other proton-conducting fuel cells. Operating at 750 °C, the PCFC is ideal for use with hydrocarbon fuels, such as natural gas. Proton conduction implies that water vapor is produced at the cathode, where it is swept away by air, rather than at the anode (as in a solid oxide fuel cell), where it dilutes the fuel. Since carbon dioxide is the only exhaust gas produced, higher fuel utilization is possible. Ambipolar steam permeation from the cathode to the anode provides the steam for direct reforming of hydrocarbons, so external steam injection is not required. Therefore, high thermodynamic efficiency is achieved and coking is not a problem. All of these features make it possible to construct a fuel cell of unprecedented electrical efficiency when operated on hydrocarbon fuels. The principles of operation and the current status of single-cell testing on methane at Protonetics will be described.

MFI membranes of different Si/Al ratios for pervaporation and steam permeation

For pervaporation and steam permeation, in one- and two-step crystallizations, respectively, two kinds of MFI membranes of different SiO 2/Al 2O 3 ratio on a mesoporous alumina ceramic support have been prepared. In the one-step crystallization, using TPA-OH as template, a supported silicalite membrane was obtained by in situ crystallization. In the two-step crystallization, by first attaching seed crystals to the ceramic surface with electrostatic forces and then crystallizing a continuous MFI layer in a template-free synthesis, a ZSM-5 membrane was prepared. The membranes have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in combination with electron dispersive X-ray (EDX) line scan as well as by single gas and binary mixture permeation. In pervaporation and steam permeation measurements of water/iso-propanol and water/methanol mixtures, the silicalite membrane showed a hydrophobic and the ZSM-5 membrane a hydrophilic separation behavior. However, only the silicalite membrane obtained by one-step crystallization allows shape selective permeation such as the separation of n/iso-butane and methanol/MTBE mixtures. In the case of the polycrystalline ZSM-5 membrane with columnar microstructure, a superposition of mass transport through the crystal boundaries and the crystals takes place.

Development of a Demister for a Waste Evaporator Using a Hydrophobic Membrane Filter

A demister using a hydrophobic porous membrane made from polytetrafluoroethylene was developed to improve the decontamination factor (DF) of a waste evaporator. The demister removes the radioactive mist in steam generated from the evaporator.A large-scale membrane module (membrane surface area: 3 m1) for the demister was newly designed, and its steam permeation rate and DF were experimentally examined using steam containing simulated mist (5 wt% Na2SO4 solution). The steam permeation rate decreases due to adhesion of removed mist on the membrane surface, but it is maintained at ∼0.35 of the initial value through falling of the mist from the membrane surface due to the mist particles’ own weight. The DF of the demister, using a membrane having less than a 0.7-μm pore diameter, is >5 × 103. The total DF of the evaporator with the new demister is estimated to be >5 × 107.