Activation Energy For Permeation Research Articles

X-ray diffraction study on the effects of hydrogen on Pd60Cu40 wt% foil membranes

In-situ variable temperature X-ray diffraction analysis was performed on two as-received Pd60Cu40 wt% foil samples containing the disordered face centred cubic (FCC) phase between 30 and 700°C. One foil sample was exposed to 445kPa of flowing helium and the other foil sample was exposed to 445kPa of flowing hydrogen. Generally, it was found that 445kPa of flowing hydrogen had the effect of expanding the temperature range over which the body centred cubic (BCC) phase in the foil sample was stable when compared to testing under 445kPa of flowing helium. This is likely due to dissolved hydrogen shifting the BCC|FCC + BCC and FCC + BCC|FCC phase boundaries to relatively higher temperatures and Pd contents.An as-received Pd60Cu40 wt% foil membrane had been cycled between 50 and 450°C under a 445kPa feed pressure and 100kPa permeate pressure of hydrogen. In the third cycle, this membrane achieved a noticeably low hydrogen permeability of 5.59 × 10−9molm−1s−1Pa−0.5 at 450°C. Moreover, the partial pressure exponent was found to deviate significantly from Sieverts' law between 400 and 450°C. Subsequently, this membrane was cycled twice between 250 and 700°C achieving a much higher hydrogen permeability of 1.19 × 10−8molm−1s−1Pa−0.5 which was measured at 450°C. The activation energy for permeation reduced by more than 60% and the partial pressure exponent decreased to 0.52. The initial poor hydrogen permeability of the membrane was attributed to coring as evidenced by the presence of the disordered FCC phase in the as-received foil. The improvement in hydrogen permeability was linked to the homogenisation effect of hydrogen under the conditions used in this study.

Apparent activation energy for hydrogen permeation and its relation to the composition of homogeneous PdAu alloy thin-film membranes

Abstract PdAu alloy composite membranes are often fabricated by sequential electroless plating of Pd and Au, but this forms a layered structure that must be annealed to form a homogenous alloy. Using ex situ analysis techniques such as X-ray diffraction (XRD) or energy dispersive X-ray spectroscopy (EDS) to judge the extent of homogenization can be time-consuming as the composite membranes must be cooled to ambient temperatures prior to analysis. However, an in situ alternative is to use the apparent activation energy for H2 permeation (Eact). In this work, 27 – 41 wt% Au films were fabricated to expand upon a range of 0 – 21 wt% that has been previously reported. Homogenization (confirmed by XRD and EDS) was achieved by heat treatment in 3 MPa H2 at 550 °C for up to 120 h. The apparent Eact was found to initially decrease with increasing Au composition from 12.2 kJ mol−1 (pure Pd) to 7.5 kJ mol−1 (21 wt% Au) after which it slowly increased to 9.0 kJ mol−1 (41 wt% Au). The two distinct regimes can be explained using the relation Eact = ΔHH + ED, wherein Eact is the sum of the partial enthalpy of solution of H into the PdAu alloy (ΔHH) and the activation energy for diffusion of H in the alloy (ED). Essentially, the two components of Eact have opposite signs that counteract each other and cause a non-linear trend with increasing Au compositions.

Nanodefect-controlled permeation in AlOx/polymer gas barrier films

The permeation of water vapour through a coated polymer gas barrier film is controlled by the defects in the coating. By modelling these defects as a combination of macro-defects (in which the activation energy of permeation is that of the underlying polymer substrate) and nano-defects (in which the activation energy of permeation is something greater than that of the polymer substrate), we are able to understand the mechanisms of permeation in high gas barrier layers. Permeation is controlled by the amounts of such defects, with the observed overall activation energy informing us of the relative permeation through macro- and nano-defects. Three examples of aluminium oxide (AlOx)-coated polymers are given to illustrate this: a comparison of poly(ethylene naphthalate) and polypropylene (OPP) substrates, the role of sputter power in AlOx/OPP films and the role of oxide thickness in AlOx/OPP films. When the amount of permeation through macro-defects is quite low, and hence nano-defect permeation is a significant proportion of the overall water vapour transport, control of each of the two defect types becomes important. Contrary to what has been previously assumed, the activation energy can be observed as greater in some cases in which the overall permeation is also greater, and this can be explained by an increase in the proportion of permeation taking place through nanodefects. This model is evidenced by reference to microstructural and other characterisation, and hence gives rise to understanding of the relationship between process properties, microstructure and permeation.

Fabrication and CO2 permeation properties of amine-silica membranes using a variety of amine types

We developed a series of molecule-scale hybrid amine-silica membranes synthesized from organoalkoxysilane precursors of 3-(triethoxysilyl)propan-1-amine (PA-Si) and 3-(triethoxysilyl)-N-methylpropan-1-amine (SA-Si), and made these functional using either unhindered amines or a 3-(triethoxysilyl)-N,N-dimethylpropan-1-amine (TA-Si) that is sterically hindered. CO2 adsorption-desorption measurements of amine-silica powdered xerogels were conducted to observe the effect of amine type on CO2 adsorption and desorption/diffusion properties. The results revealed that TA-Si xerogel powders demonstrated faster kinetics for both adsorption and desorption processes compared with those of the PA-Si and SA-Si samples due to the steric hindrance effect of the amine, which reduced the CO2 binding energy and thereby boosted both the forward and reverse reaction rates of CO2-amine. In single-gas permeation performances, all the membranes exhibited excellent molecular sieving at higher temperatures and all the gases considered, except CO2, tended to permeate the membranes via activated diffusion. The effect of amine type on CO2 separation performance was compared using CO2 permeance, CO2/N2 selectivity, activation energy for permeation (Ep) of CO2 [Ep(CO2)], and differences in Ep between CO2 and N2 [Ep(CO2)-Ep(N2)]. The TA-Si membrane demonstrated superior CO2 separation performance, and achieved the highest values for both CO2 permeance and selectivity. A relatively smaller difference in CO2 separation performance was observed between PA-Si and SA-Si membranes despite some differences in basicity. This suggests that, rather than the basicity, it was the steric hindrance effect that played the greatest role in CO2 transport performance across amine-silica membranes.

The significance of entropic selectivity in carbon molecular sieve membranes derived from 6FDA/DETDA:DABA(3:2) polyimide

This study reports and analyzes gas transport and sorption properties between 35 and 50°C for polymeric and carbon molecular sieve (CMS) membranes derived from an in-house synthesized polyimide referred to as 6FDA/DETDA:DABA(3:2). The analysis of activation energies of permeation and diffusion and heats of sorption for CO2, CH4, O2, and N2 in these membrane materials provides insights regarding the permeability and selectivity changes at increasing pyrolysis temperature between 550°C and 800°C. The diffusion selectivity is factored further into “energetic” and “entropic” selectivity contributions to show that higher permselectivity of CMS membranes compared to polymeric membrane arises from a larger than unity entropic selectivity. CMS membranes pyrolyzed at 800°C are also shown to have significantly elevated entropic selectivity compared with membranes pyrolyzed at 550°C. Analysis of the selectivity factors provides fundamental insights into the importance of entropic factors as tools to tailor membrane performance.

Temperature-dependent gas transport and its correlation with kinetic diameter in polymer nanocomposite membrane

Activation energies for permeation of polymer nanocomposite membrane have not been reported so far. A trade-off relation between permeability and selectivity shows that as permeability increases, the selectivity decreases. Attempts have been made to see this trade-off relation at relatively higher temperature. It is found that selectivity decreases drastically with increasing temperature. A polymer–matrix composite was prepared by adding silica nanoparticles using casting method. Pure gas permeability was measured using a constant volume–variable pressure method at different temperature ranges from 35 to $$70^{\circ }\hbox {C}$$ . The Van’t Hoff relation was used to estimate the activation energy for permeation. It is found to decrease as compared with virgin polycarbonate and it increases with kinetic diameter. For the first time, the permeability and selectivity for nanocomposite membrane are reported as a function of temperature. Activation energies for different gases have been calculated for nanocomposite membrane and compared with that of virgin polymer membrane. Decrease in activation energies for permeation ( $$E_\mathrm{p}$$ ) with increasing kinetic diameter has been observed for both the membranes. Selectivity reduces with temperature for both the membranes. Mechanical and thermal properties of nanocomposite membrane have been investigated using a dynamic mechanical analyser and differential scanning calorimetry, respectively. Scanning electron microscopy has been used to study surface morphology. The results show modification in physical properties due to incorporation of silica nanoparticles.

Effects of surface modification with Co3O4 nanoparticles on the oxygen permeability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ membranes

To promote the oxygen permeability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) membranes, Co3O4 nanoparticle catalysts were loaded onto the surfaces of BSCF membranes by a dip-coating process. X-ray diffraction (XRD) results reveal that Co3O4 nanoparticles crystalize in spinel phase. Scanning electron microscope (SEM) observation indicates that the mean particle size of the Co3O4 nanoparticles is about 100nm in diameter and 20μm in thickness after annealing at 500°C for 5h. Energy dispersive spectrometer (EDS) results testify that the percentage of the elements in the modified layer are in accordance with the stoichiometric ratio of Co3O4. Oxygen permeation tests were made in a laboratory self-made device, and the results show that loading Co3O4 nanoparticle catalysts onto the surfaces of BSCF membranes can significantly increase the oxygen permeability of the BSCF membranes. The unmodified BSCF membranes have an oxygen permeation flux of 0.1080mlcm−2min−1 at 600°C. This increases to 0.4302mlcm−2min−1, for the modified membranes, which is four times higher than that of the unmodified BSCF membranes. The oxygen permeation activation energy decreases from 91.42 to 50.71kJmol−1 at 600–800°C by loading Co3O4 nanoparticle catalysts on the surface of BSCF membranes.

Gas transport and characterization of poly(3 hydroxybutyrate) films

Renewable biodegradable films of poly(3-hydroxybutyrate) (PHB) were produced via thermo-compression and casting method (specimens 1 and 2). On specimens 1, gas permeability coefficients with CO2, O2, N2, and C2H4 gases were measured at 277K, 288K and 296K. The physicochemical characteristics of PHB based on calorimetric, mechanical, and thermal examination were performed for both specimens. SEM and probe ESR technique showed the dramatic differences in their surface morphology and segmental motilities in polymer bulk. In the selected temperature range, the gas permeability ranking (Pi) for the thermo-compressed films is as follows: P(CO2)>P(O2)>P(N2)≈P(C2H4). The gas diffusion coefficients were considered to be dependent on the gas critical volume, in accordance with the semi-logarithmic function, consistent with a free volume model. The activation energies of permeability, diffusivity and spin probe rotation, as well as the apparent heat of sorption equilibrium, forecast the values of PHB barrier characteristics in the range of foodstuffs stored temperatures.

Synthesis, characterization and application of PVA/ionic liquid mixed matrix membranes for pervaporation dehydration of isopropanol

Abstract In this study, polyvinyl alcohol (PVA)–ionic liquid (IL) membranes were prepared for the separation of isopropyl alcohol (IPA)–water azeotropic mixtures by pervaporation. PVA-IL composite membranes were prepared by simple solvent evaporation method using four ILs, viz. , 1- n -butyl-3-methylimidazolium chloride (BMIMCl), 1-hexyl-3-methylimidazolium chloride (HMIMCl), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF4) and 1-octyl-3-methylimidazolium chloride (OMIMCl). Three ILs were used to study the effect of alkyl chain on the pervaporation performance. The study had focused on the effect feed water concentration from 10%–40% and effect of feed temperature from 50–80 °C. Physiochemical properties of all the membranes were studied using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and contact angle measurement. The Arrhenius activation energies for permeation were estimated to be in the range 4–12 kJ·mol − 1 from the temperature dependent permeation values.

Defect-free PIM-1 hollow fiber membranes

A modified dual-bath method of spinning was employed to fabricate defect-free, integrally skinned, asymmetric PIM-1 hollow fiber membranes utilizing an immiscible liquid protective layer. Spinning techniques capable of addressing specific challenges presented by PIM-1 solutions are discussed. In particular, dual-bath spinning via a triple orifice spinneret circumvents the primary issue associated with spinning PIM-1, namely the lack of suitable nonvolatile solvents. The water-immiscible sheath layer coextruded with the PIM-1 polymer solution reduces evaporation of the volatile solvent (tetrahydrofuran) relative to fibers directly exposed to air, thus producing an asymmetric hollow fiber membrane structure. The work here describes the process of developing spin dopes, fabricating hollow fibers, and testing the resulting membrane modules. Ideal selectivity between various gas pairs was used to assess the quality of the membranes. Pure component permeances, selectivities, and activation energies of permeation were measured for helium, hydrogen, oxygen, nitrogen, argon, carbon dioxide, methane, ethane, and ethylene at 25, 35, and 45°C. The observed selectivities are in good agreement with previously reported PIM-1 flat sheet membrane analogs, and in fact slightly higher. Defect-free fibers with skin thicknesses from 3 to 6µm were observed with a relatively high CO2 permeance of 360 GPUs and CO2/CH4 selectivity of 23.

Blend membranes of poly(amide-6-b-ethylene oxide)/[Emim][PF6] for CO2 separation

Abstract 1-Ethyl-3-methylimidazolium hexafluorophosphate ([Emim][PF6]) was incorporated into poly(amide-6-b-ethylene oxide) (Pebax1657) to prepare blend membranes. The physical properties of Pebax1657/[Emim][PF6] blend membranes were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). For Pebax1657/[Emim][PF6] blend membranes, the melting peak of polyether (PE) segment disappeared when [Emim][PF6] content reached 10 wt%, and the melting peak of [Emim][PF6] appeared until [Emim][PF6] content came up to 60 wt%, indicating the homogeneous mixing of [Emim][PF6] and Pebax1657 for the prepared Pebax1657/[Emim][PF6] blend membranes. According to FTIR, some interactions were formed between [Emim][PF6] and PE segment. The gas transport properties of CO2, N2, CH4 and H2 for Pebax1657/[Emim][PF6] blend membranes were also investigated. The incorporation of [Emim][PF6] increased the gas solubility coefficients of CO2, N2, CH4 and H2, however the gas diffusion coefficients decreased, which led to the decrease of the permeabilities of CO2, N2, CH4 and H2. Meanwhile, the selectivity of CO2/CH4 increased slightly. With the increase of temperature (35–85 °C), the solubility coefficient of CO2 decreased, while the diffusion coefficients of CO2, N2, CH4 and H2 increased, resulting into the increase of the permeabilities of CO2, N2, CH4 and H2. Moreover, no sharp increase of gas permeability was observed at the melting point of [Emim][PF6] (60 °C). And the activation energies of permeation of CO2, N2, CH4 and H2 increased with increasing [Emim][PF6] content.

Oxygen transportation, electrical conductivity and electrochemical properties of layered perovskite SmBa0.5Sr0.5Co2O5+δ

Oxygen transportation properties of SmBa0.5Sr0.5Co2O5+δ (SBSC55) layered perovskite has been investigated as a potential cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). This research includes the following items: (1) structural characteristics, thermogravimetric behavior, oxygen permeation, chemical bulk diffusion coefficient (Dchem), and (2) the electrochemical performance of long-term testing carried out to evaluate its electrochemical stability. The Dchem values for SBSC55 cathode are 2.6 × 10−6, 9.1 × 10−6 and 1.8 × 10−5 cm2 s−1 at 500 °C, 600 °C, and 700 °C, respectively. The oxygen permeation flux for SBSC55 membrane with 1.0 mm thickness increased from 0.143 mL min−1 cm−2 at 500 °C to 0.406 mL min−1 cm−2 at 800 °C under synthetic air at a flow rate of 50 mL min−1, helium at a rate of 25 mL min−1. The activation energies of oxygen permeation for the high temperature region (700–800 °C) and low temperature region (500–650 °C) are 23.67 and 6.96 kJ mol−1, respectively. It suggested that oxygen diffusion for high temperature range is surface exchange process, low temperature range is bulk diffusion process. The long-term test of cathodic polarization resistance for SBSC55∣SDC∣SSBSC55 half-cell at 600 °C during 96 h has been carried out with an increase rate of 0.30% h−1. Based on the impedance spectra with various oxygen partial pressure results, the rate-limiting process of ORR is determined that the oxygen ion transfer from triple-phase boundary (TPB) and/or two-phase boundary (2PB) sites of cathode is major with the minority of charger transfer reaction.

Dehydration of acetonitrile using cross-linked sodium alginate membrane containing nano-sized NaA zeolite

Pervaporation (PV) separation of water–acetonitrile mixture using sodium alginate (NaAlg) based mixed matrix membranes (MMM) comprising different amounts of nano NaA zeolite (10, 20 and 30 wt%) is investigated in various concentrations of water and temperatures. The prepared membranes are modified by sulfosuccinic acid (SSA) as a crosslinking agent. NaAlg-NaA/SSA membranes are synthesized by a solution casting technique. The process and membrane performance including separation factor, flux and activation energy of permeation are determined. Results reveal that adding of nano zeolite may lead to an increase in the flux and the separation factor of sodium alginate membrane up to 123 and 169%. In addition, using MMM in dehydration of a feed containing 30 wt% of water shows much better performance than alginate membrane. Furthermore, the activation energy of water permeation through MMM is predicted lower than sodium alginate membrane which reflects the facilitated permeation of water through MMM.

Pore morphology and temperature dependence of gas transport properties of silica membranes derived from oxidative thermolysis of polydimethylsiloxane

Transport properties of silica membranes derived from the oxidative thermolysis of crosslinked polydimethylsiloxane (PDMS) were studied between 35–100°C. Changes in pore morphology and transport properties were investigated for varying thermolysis and crosslinking treatments. Permeation and pressure-decay sorption measurements were made for CO2, H2, He, O2, N2, and CH4. Physisorption data for CO2 and N2 were also analyzed to characterize the pore size distributions of these materials. The activation energies of permeation and diffusion were measured along with the enthalpies of sorption to compare the effects of varying fabrication methods. All samples showed similar enthalpies of sorption. Regular and extended-thermolysis heat treated silica showed similar permeabilities and diffusion coefficients, but the heat treated silicas showed an average increase of 2.3kJ/mol in their activation energies of permeation. The permeation, sorption, and diffusion selectivities of various gas pairs were compared. The silicas showed high sorption selectivity in gas pairs with large differences in critical temperature, but showed low diffusion selectivity due to low entropic selectivity. Overall, the PDMS-derived silicas show promise, but require further tuning to improve the entropic selectivity of penetrants.

Surface Modification of Ba0.5Sr0.5Co0.8Fe0.2O3-d By Using Atomic Layer Deposition

For the application in the combustion process, oxygen permeable membrane has been gathering much attention. It requires both of bulk ionic and electronic transport to maintain the charge balance. Many perovskite-type oxides have been investigated since Teraoka et al. reported high oxygen permeability for La-Sr-Co-Fe series oxides [1]. Among many mixed conductors, Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) shows outstanding performance of oxygen permeability [2]. However, it is widely accepted that the surface exchange reaction limits the permeation rate at reducing temperature and thickness [3]. Consequently, the improved bulk property may be wasted in such regime. Thus, it is significant to understand the effects of the surface state on the oxygen transport property. Recent studies indicated the surface state takes the dominant role in the surface exchange reaction because it decides the electronic structure of the surface and availability of active sites for the reaction [4]. In this study, Atomic Layer Deposition (ALD) was employed to apply various oxide coating such as TiO2 and SrO on BSCF. Introducing gaseous precursor and oxidant alternately, ALD can grow thin film in nm order not only on a flat surface, but also on a complex shape surface such as porous structure. Applying single nm-thick oxide coating, different function can be given to the BSCF surface such as protective layer for higher chemical stability and purposely degraded terminal. BSCF substrates were synthesized by the solid state reaction method. Subsequent XRD and SEM-EDS analysis indicated that the substrates were in single phase of cubic pereovskite-type structure and in nominal cation composition. ALD was conducted on the mirror polished BSCF substrates and on quartz substrates at the table temperature of 200°C. Film thickness was determined by the spectroscopic ellipsometry for the quartz substrate. Oxygen permeation measurements were performed from 850°C to 700°C, using He for sweep gas. The thickness of TiO2 coating on BSCF was estimated to be 7.6 nm by the spectroscopic ellipsometry. In order to investigate the effect of TiO2 coating on the chemical stability of BSCF, high temperature XRD (HT-XRD) measurements were performed in N2-CO2 atmosphere at 700°C. It is reported that perovskite-type oxides containing alkaline-earth metal are critically unstable under CO2 atmosphere due to strong adsorption of CO2 molecule and / or carbonates segregation [5][6]. After applying TiO2 coating, the peak from SrCO3 was suppressed from 0 to 10%-CO2 while the sample without coating showed the same peak at the lowest CO2 content, 2.1%-CO2. This result suggests that higher tolerance of BSCF to CO2 can be given by the TiO2 coating. Moreover, it is also worth noting that very thin TiO2 coating in single nm can work as a protective layer while previous study applied much thicker coating of 250 nm [7]. Oxygen permeation measurements showed that TiO2 coating did not degrade high permeation rate of original BSCF above 775°C. Lowering the temperature, larger slope from coated BSCF resulted in lower oxygen permeation rate, and it became about 60% of that of uncoated BSCF at 700°C. The activation energy of oxygen permeation was increased by the coating, from 60.8 kJ·mol-1 to 75.9 kJ·mol-1 and from 108 kJ·mol-1 to 152 kJ·mol-1 in the temperature range of 850°C to 800°C and 775°C to 700°C, respectively. Judging from the higher activation energy for coated sample, it is suggested the TiO2 coating affects both of the diffusion and surface exchange kinetics. Much larger activation energy may imply limited area for the surface exchange reaction such as cracks in the coating, which might be introduced by the lattice mismatch between TiO2 layer and BSCF. However, permeation rate can be improved by the porous layer coating according to our previous study [8]. More details of the effects of TiO2 coating and also effects of other oxides coating will be presented along with possible mechanisms of them. [1] Y. Teraoka et al., Chem. Lett. 14 (1985) 1743-1746. [2] Z. Shao et al., J. Membr. Sci. 172 (2000) 177-188. [3] H. J. M. Bouwmeester et al., Solid State Ionics 72 (1994) 185-194. [4] Y. Chen et al., Energy Environ. Sci. 5 (2012) 7979-7988. [5] M. Arnold et al., J. Membr. Sci. 293 (2007) 44-52. [6] X. Tan et al., J. Membr. Sci. 389 (2012) 216-222. [7] I. García-Torregrosa et al., Adv. Energy Mater. 1 (2011) 618-625. [8] Y. Hayamizu et al., J. Membr. Sci. 462 (2014) 147-152.

Water transport through short side chain perfluorosulfonic acid ionomer membranes

Liquid and water vapour transport through short side chain (SSC) perfluorosulfonic acid (PFSA) ionomer membranes are measured as a function of membrane thickness (24–96µm) and temperature (25–85°C). Three types of water permeation techniques are used in this work and are based on applied chemical potential gradients across a membrane. These are: liquid-liquid permeation (LLP) in which both sides of membrane are in contact with liquid water; liquid-vapour permeation (LVP) where one side of the membrane is exposed to liquid and the other is exposed to vapour; and vapour-vapour permeation (VVP) where both sides of the membrane are exposed to water vapour. Within the SSC series, the increase in permeance for VVP upon decreasing membrane thickness is not as significant as compared to LLP due to the larger interfacial water transport resistance (Rinterfacial) observed for membranes exposed to vapour. The study of LVP and VVP transport resistances indicates that Rinterfacial plays dominate role in determining the overall membrane resistance, even for a thick SSC membrane. It is speculated that Rinterfacial is the result of water depletion layer caused by membrane dehydration at the membrane interface. The LVP interfacial resistance for SSC membranes is similar to that found for long side chain PFSA ionomer membranes such as, Nafion®, even though SSC membranes possess significant lower internal LVP permeation resistance. Water permeance determined by LLP, LVP and VVP measurements are all found to increase with temperature, due to the increased water volume fraction (Xv) and an increase in the effective hydrophilic pore size. The activation energy of LLP, LVP and VVP water permeation are calculated to be 16.3, 40.2 and 43.1kJmol−1 respectively, which is lower than that of Nafion under similar conditions.

Rapid annealing of sequentially plated Pd-Au composite membranes using high pressure hydrogen

In this work, the time-consuming process of annealing Pd-Au alloy composite membranes, fabricated by sequential electroless plating, has been revisited. Composite Pd-Au/YSZ membranes approximately 5µm thick with compositions ranging from 8wt% to 10wt% Au were fabricated by the bi-layer fabrication technique. Using these membranes, we investigated the effect of changing the pressure of the annealing gas (H2) on annealing time at temperatures between 450°C and 550°C. X-ray diffraction (XRD) was used to study the progress of annealing, where it was observed that a ~10wt% Au membrane could be annealed in 9h at 550°C and 3MPa H2 whereas it took 120h to anneal a similar membrane at 550°C and 0.1MPa H2. Another ~10wt% Au membrane was annealed in less than 2 days at 450°C and 3MPa H2. Complete annealing was confirmed using energy dispersive x-ray spectroscopy (EDS) with multiple spot scans throughout the thickness of the membrane indicating a uniform Au composition. Additionally, it was found that the apparent activation energy for hydrogen permeation (Eact) could be used as an in situ parameter to judge the extent of annealing. In this technique, apparent Eact decreases as the membrane anneals, reaching a minimum value which is characteristic of its Au composition. Additional annealing time does not further change the apparent Eact for a membrane with a homogeneous Au distribution.

Effect of cell hydrodynamics in desalination of saline water by sweeping air pervaporation technique using innovated membrane

Scarcity of potable water nowadays, presents a serious problem all over the world. Environmental changes are taking place at a rapid pace, resulting in greenhouse effects, desertification, and lack of fresh water. Accordingly, scientists are working hard toward inventing new techniques for desalinating sea water, which presents the only alternative solution to this problem. In this regard, desalination techniques are mainly divided into thermal and membrane techniques. However, the latter are superior in that they are modular in shape, and consume less energy. In the present work, desalination by a novel recent membrane separation technique, the so-called sweeping air pervaporation (PV), which has been very sparsely applied to desalination of sea water, has been conducted in our laboratory. The technique is simple, straightforward, cost-effective and does not suffer from limitations as regards low water recovery, such as reverse osmosis. An innovated deacetylated cellulose acetate (CA) membrane was prepared by the phase inversion technique, from a specially formulated casting solution mixture composed of CA, acetone (A), dioxane (D), dimethyl formamide, dimethyl phthalate, and maleic anhydride in definite proportions, and used in all the experiments. Two PV cells of different configuration and aspect ratio (AR) were designed and constructed, in order to investigate the effect of hydrodynamics on membrane performance. Numerous variables were studied for their effect on the pervaporate flux (J) and % salt rejection (%SR), and these were: initial salt solution concentration (Ci), PV temperature (Tpv), and PV cell configuration. It was found that the flux obtained was directly proportional to Tpv, and that the J was almost independent of Ci at low Tpvs, except in the case of Tpv = 80°C for both small and large configurations, where J was inversely proportional to Ci (in the range 15–120 g/l), and that higher fluxes were obtained under the same conditions in case of the PV cell of higher AR. The activation energy (Ea) for permeation through the membrane in both the cells was computed from the Arrhenius equation, and was found to be 20.89–23.06 kJ/mol K at Ci = 120 g/l, for the cell with higher and lower AR, respectively, denoting facile permeation of water through the membrane, for the two cell designs, in particular with higher AR. The results indicate that at all concentrations tested for large cell below 70°C, the product, after a once-through operation, was exceptional potable water with very low salinity (%SR 98.9) even when Ci was 120.8 g/l, and maximum flux obtained was 5 l/m2 h at Tpv = 70°C. The separation factor (α), PV separation index (PSI), overall mass transfer coefficient (Kov), diffusion coefficient (Di), salt diffusivity (Ds), and salt permeability (P), through the membrane were all calculated and their values are stated inside the paper text. Nevertheless, α varied between 5.6 and 853.4, and PSI reached 3494.5 l/m2 h.

Testing and evaluation of microstructure of organoclay in chlorosulfunated polyethylene nanocomposites by emphasis on solvent transport properties

The present paper addresses the usefulness of a sorption gravimetric technique to assess of the compatibility and reinforcing effect of nanofiller against hazardous liquid media. The reinforcing capability of organoclay (Cloisite 30B) in chlorosulfonated polyethylene (CSM) was characterized by means of transport properties such as diffusion, sorption and permeation coefficients, activation energy, enthalpy, and entropy. The CSM/organoclay nanocomposites were prepared by melt mixing method. The transport of toluene through CSM vulcanizates were studied with special reference to the effect of organoclay concentration (0–9 parts per hundred parts of rubber) and temperature (25–55°C). The microstructure of the nanocomposites was confirmed by studying of dispersion of organoclay in CSM via transmission and scanning electron microscopy and X‐ray diffraction. The results showed that the swelling properties of nano‐filled CSMs mainly depend on the presence of organoclay and not its concentration and also the formed microstructure. A good relationship was found between the microstructure and swelling properties of CSM nanocomposites. J. VINYL ADDIT. TECHNOL., 23:E40–E50, 2017. © 2016 Society of Plastics Engineers

Iron-doping effects on the CO2 tolerance of a perovskite oxygen permeable membrane

Bao.8La0.2Co0.88−xFexNb0.12O3−δ membranes (BLCFN) with different Fe-doping were successfully prepared by solid-state reaction method. The microstructure, oxygen permeability, thermal analysis, and oxygen permeation stability using CO2 as sweep gas were systematically investigated. After being calcined under pure CO2, BLCFN membranes remain their major perovskite phase but diffraction peaks of BaCO3, CoO appeared on the membranes which Fe content is less than 0.2. Apparent activation energy of oxygen permeation are around 60–70 kJ/mol for all membranes. With the increase of Fe-doping content, the flux through BLCFN membranes decreases but the degradation of oxygen flux becomes less pronounced when CO2 is used as sweep gas at 850 °C. Enhanced CO2 resistance of the perovskite would be resulted from an increasing average binding energy due to the Fe-doping. For the membrane where the Fe-doped content equals to 0.2, the oxygen permeation flux is 0.96 mL cm−2 min−1 at 900 °C with He sweeping. When using pure CO2 as sweep gas, the oxygen permeation flux decreases slightly in the first 50 h and then reaches a steady state of ~0.31 mL cm−2 min−1 for more than 60 h in a prolonged continuous oxygen operation. The observations indicated that a stable oxygen permeation could be realized by suitable elemental doping in a single perovskite membrane.