scholarly journals Assessment of Sieverts Law Assumptions and ‘n’ Values in Palladium Membranes: Experimental and Theoretical Analyses

Membranes ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 778
Author(s):  
Abdulrahman Alraeesi ◽  
Tracy Gardner
Keyword(s):  
Concentration Polarization ◽  
Hydrogen Permeation ◽  
Pure Hydrogen ◽  
Hydrogen Purification ◽  
Hydrogen Transport ◽  
Experimental Conditions ◽  
Fixed Temperature ◽  
Hydrogen Flux ◽  
Partial Pressures ◽  
The Difference

Palladium and palladium alloy membranes are superior materials for hydrogen purification, removal, or reaction processes. Sieverts’ Law suggests that the flux of hydrogen through such membranes is proportional to the difference between the feed and permeate side partial pressures, each raised to the 0.5 power (n = 0.5). Sieverts’ Law is widely applied in analyzing the steady state hydrogen permeation through Pd-based membranes, even in some cases where the assumptions made in deriving Sieverts’ Law do not apply. Often permeation data are fit to the model allowing the pressure exponent (n) to vary. This study experimentally assessed the validity of Sieverts’ Law as hydrogen was separated from other gases and theoretically modelled the effects of pressure and temperature on the assumptions and hence the accuracy of the 0.5-power law even with pure hydrogen feed. Hydrogen fluxes through Pd and Pd-Ag alloy foils from feed mixtures (5–83% helium in hydrogen; 473–573 K; with and without a sweep gas) were measured to study the effect of concentration polarization (CP) on hydrogen permeance and the applicability of Sieverts’ Law under such conditions. Concentration polarization was found to dominate hydrogen transport under some experimental conditions, particularly when feed concentrations of hydrogen were low. All mixture feed experiments showed deviation from Sieverts’ Law. For example, the hydrogen flux through Pd foil was found to be proportional to the partial pressure difference (n ≈ 1) rather than being proportional to the difference in the square root of the partial pressures (n = 0.5), as suggested by Sieverts’ Law, indicating the high degree of concentration polarization. A theoretical model accounting for Langmuir adsorption with temperature dependent adsorption equilibrium coefficient was made and used to assess the effect of varying feed pressure from 1–136 atm at fixed temperature, and of varying temperature from 298 to 1273 K at fixed pressure. Adsorption effects, which dominate at high pressure and at low temperature, result in pressure exponents (n) values less than 0.5. With better understanding of the transport steps, a qualitative analysis of literature (n) values of 0.5, 0.5 < n < 1, and n > 1, was conducted suggesting the role of each condition or step on the hydrogen transport based on the empirically fit exponent value.

In Situ Analysis of Hydrogen Mobility during Hydrogen Permeation through Nb-Based Hydrogen Permeable Membranes

2011 ◽  
Vol 312-315 ◽  
pp. 506-512 ◽  
Author(s):  
Hiroshi Yukawa ◽  
T. Nambu ◽  
Yoshihisa Matsumoto
Keyword(s):  
Hydrogen Diffusion ◽  
Chemical Potential ◽  
Hydrogen Permeation ◽  
Hydrogen Permeability ◽  
Hydrogen Solubility ◽  
Hydrogen Flux ◽  
Pure Niobium ◽  
The Difference ◽  
Alloying Effects

The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. It is found that the hydrogen solubility decreases by the addition of ruthenium, tungsten or molybdenum into niobium. The mobility for hydrogen diffusion during hydrogen permeation is estimated from the linear relationship between the normalized hydrogen flux, , and the product of the hydrogen concentration and the difference of hydrogen chemical potential, . It is found that the mobility for hydrogen diffusion during hydrogen permeation is larger for Nb-based alloys than pure niobium, especially at low temperature. The activation energy of the mobility for hydrogen diffusion decreases by the addition of ruthenium, tungsten or molybdenum into niobium.

Hydrogenation of nitrogen oxide on platinum-carbon catalysts in acidic medium

1981 ◽  
Vol 46 (11) ◽  
pp. 2669-2675 ◽  
Author(s):  
Ivo Paseka
Keyword(s):  
Nitrogen Oxide ◽  
Acidic Medium ◽  
Diffusion Region ◽  
Acid Solutions ◽  
Experimental Conditions ◽  
Platinum Content ◽  
Kinetically Controlled ◽  
Partial Pressures ◽  
Carbon Catalysts

Hydrogenation of nitrogen oxide in acid solutions on Pt-C catalysts proceeds in dependence on experimental conditions either in purely diffusion region or in the diffusion and kinetically controlled region. The boundary between these two processes shifts to the higher ratio of NO to H2 partial pressures with increasing platinum content and decreasing intensity of agitation.

scholarly journals Potential Pitfalls in Membrane Fouling Evaluation: Merits of Data Representation as Resistance Instead of Flux Decline in Membrane Filtration

Membranes ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 460
Author(s):  
Bastiaan Blankert ◽  
Bart Van der Bruggen ◽  
Amy E. Childress ◽  
Noreddine Ghaffour ◽  
Johannes S. Vrouwenvelder
Keyword(s):  
Membrane Fouling ◽  
Membrane Filtration ◽  
Data Representation ◽  
Strong Impact ◽  
Experimental Conditions ◽  
Permeable Membrane ◽  
Dead End ◽  
Flux Decline ◽  
The Difference ◽  
Filtration Flux

The manner in which membrane-fouling experiments are conducted and how fouling performance data are represented have a strong impact on both how the data are interpreted and on the conclusions that may be drawn. We provide a couple of examples to prove that it is possible to obtain misleading conclusions from commonly used representations of fouling data. Although the illustrative example revolves around dead-end ultrafiltration, the underlying principles are applicable to a wider range of membrane processes. When choosing the experimental conditions and how to represent fouling data, there are three main factors that should be considered: (I) the foulant mass is principally related to the filtered volume; (II) the filtration flux can exacerbate fouling effects (e.g., concentration polarization and cake compression); and (III) the practice of normalization, as in dividing by an initial value, disregards the difference in driving force and divides the fouling effect by different numbers. Thus, a bias may occur that favors the experimental condition with the lower filtration flux and the less-permeable membrane. It is recommended to: (I) avoid relative fouling performance indicators, such as relative flux decline (J/J0); (II) use resistance vs. specific volume; and (III) use flux-controlled experiments for fouling performance evaluation.

scholarly journals Validation of a Method Based on Triglycerides for the Detection of Low Percentages of Hazelnut Oil in Olive Oil by Column Liquid Chromatography

2007 ◽  
Vol 90 (5) ◽  
pp. 1346-1353 ◽  
Author(s):  
Diego L García-González ◽  
María Viera-Macías ◽  
Ramón Aparicio-Ruiz ◽  
Maria T Morales ◽  
Ramón Aparicio
Keyword(s):  
Liquid Chromatography ◽  
Olive Oil ◽  
Carbon Number ◽  
Hazelnut Oil ◽  
Equivalent Carbon Number ◽  
Experimental Conditions ◽  
Mathematical Algorithm ◽  
Relative Standard ◽  
Triglyceride Content ◽  
The Difference

Abstract The difference between theoretical and empirical triglyceride content is a powerful tool to detect the presence of any vegetable oil in olive oil. The current drawback of the method is the separation between equivalent carbon number ECN42 compounds, which affects the reliability of the method and, hence, its cutoff limit. The determination of the triglyceride profile by liquid chromatography using propionitrile as the mobile phase has recently been proposed to improve their quantification, together with a mathematical algorithm whose binary response determines the presence or absence of hazelnut oil. Twenty-one laboratories from 9 countries participated in an interlaboratory study to evaluate the performance characteristics of the whole analytical method. Participants analyzed 12 samples in duplicate, split into 3 intercomparison studies. Statistically significant differences due to the experimental conditions were found in some laboratories, which were detected as outliers by use of Cochran's and Grubbs' tests. The relative standard deviations (RSD) for repeatability and reproducibility were determined following the AOAC Guidelines for Collaborative Studies. The analytical properties of the method were determined by means of the sensitivity (0.86), selectivity (0.94), and reliability (72) for a cutoff limit of 8 (probability 94).

scholarly journals Alpha EEG Frontal Asymmetries during Audiovisual Perception in Cochlear Implant Users

2015 ◽  
Vol 54 (06) ◽  
pp. 500-504 ◽  
Author(s):  
A. G. Maglione ◽  
A. Scorpecci ◽  
P. Malerba ◽  
P. Marsella ◽  
S. Giannantonio ◽  
...  
Keyword(s):  
Cochlear Implant ◽  
Alpha Rhythm ◽  
Normal Hearing ◽  
Experimental Conditions ◽  
Audiovisual Perception ◽  
Audiovisual Stimuli ◽  
The Difference ◽  
Eeg Alpha ◽  
The One ◽  
Hearing Children

SummaryObjectives: The aim of the present study is to investigate the variations of the electroencephalographic (EEG) alpha rhythm in order to measure the appreciation of bilateral and unilateral young cochlear implant users during the observation of a musical cartoon. The cartoon has been modified for the generation of three experimental conditions: one with the original audio, another one with a distorted sound and, finally, a mute version.Methods: The EEG data have been recorded during the observation of the cartoons in the three experimental conditions. The frontal alpha EEG imbalance has been calculated as a measure of motivation and pleasantness to be compared across experimental populations and conditions.Results: The EEG frontal imbalance of the alpha rhythm showed significant variations during the perception of the different cartoons. In particular, the pattern of activation of normal-hearing children is very similar to the one elicited by the bilateral implanted patients. On the other hand, results related to the unilateral subjects do not present significant variations of the imbalance index across the three cartoons.Conclusion: The presented results suggest that the unilateral patients could not appreciate the difference in the audio format as well as bilaterally implanted and normal hearing subjects. The frontal alpha EEG imbalance is a useful tool to detect the differences in the appreciation of audiovisual stimuli in cochlear implant patients.

Low P50 in deer mice native to high altitude

1985 ◽  
Vol 58 (1) ◽  
pp. 193-199 ◽  
Author(s):  
L. R. Snyder
Keyword(s):  
High Altitude ◽  
Significant Negative Correlation ◽  
Deer Mice ◽  
Hypoxic Stress ◽  
Hemoglobin Saturation ◽  
Partial Pressures ◽  
Theoretical Predictions ◽  
Low Altitude ◽  
The Difference

Whereas it is widely believed that animals native to high altitude show lower O2 partial pressures at 50% hemoglobin saturation (P50) than do related animals native to low altitude, that “fact” has not been well documented. Consequently, P50 at pH 7.4, PCO2(7.4), the CO2 Bohr effect, and the buffer slope (delta log PCO2/delta pH) were determined via the mixing technique in Peromyscus maniculatus native to a range of altitudes but acclimated to 340 or 3,800 m. PCO2(7.4) and buffer slope were substantially lower at high altitude. The change in P50(7.4) between acclimation altitudes was minimal (0.8% increase at 3,800 m), because of counterbalancing changes in PCO2, 2,3-diphospho-D-glycerate concentration, and perhaps other factors. At both acclimation altitudes there was a highly significant negative correlation between P50(7.4) and native altitude. Since pH in vivo probably increases slightly at high altitude, the data on P50 corrected to pH 7.4 are probably underestimates of the difference in in vivo P50 at low vs. high altitude. Hence these results corroborate theoretical predictions that low P50 is advantageous under severe hypoxic stress.

The diffusion of 75Se(IV) in Beishan granite – temperature, oxygen condition and ionic strength effects

2018 ◽  
Vol 107 (1) ◽  
pp. 39-54
Author(s):  
Chunli Wang ◽  
Xiaoyu Yang ◽  
Jiangang He ◽  
Fangxin Wei ◽  
Zhong Zheng ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Effective Diffusion ◽  
Aerobic Condition ◽  
Double Layers ◽  
Solution Viscosity ◽  
Formation Factor ◽  
Experimental Conditions ◽  
Beishan Granite ◽  
Oxygen Condition ◽  
The Difference

Abstract To explore the diffusion behavior of 75Se(IV) in Beishan granite (BsG), the influences of temperature, oxygen condition and ionic strength were investigated using the through-diffusion experimental method. The effective diffusion coefficient De of 75Se(IV) in BsG varied from 4.21×10−14 m2/s to 3.19×10−13 m2/s in our experimental conditions, increased with increasing temperature. The formation factor Ff of BsG was calculated to be nearly constant in the range of temperatures investigated, suggesting that the inner structure of BsG had no significant change in the temperature range of 20–55°C. Meanwhile, the De values of 75Se(IV) in BsG under anaerobic condition was significantly larger than that under aerobic condition, which may be attributed to the difference in the sorption characteristics and species distribution of Se and pH values. Moreover, the diffusion of 75Se(IV) was promoted with ionic strength increased from 0.01 M to 0.1 M, and then decreased at 0.5 M, mainly due to the combined effects of reduced double layers with increased ionic strength and increase of the solution viscosity at higher ionic strength.

scholarly journals Iodination of insulin in aqueous and organic solvents

1969 ◽  
Vol 115 (1) ◽  
pp. 11-18 ◽  
Author(s):  
A. Massaglia ◽  
U. Rosa ◽  
G. Rialdi ◽  
C. A. Rossi
Keyword(s):  
Ethylene Glycol ◽  
Organic Solvents ◽  
Molecular Conformation ◽  
Aqueous Media ◽  
Native Structure ◽  
Experimental Conditions ◽  
Polar Environment ◽  
Polar Area ◽  
The Difference ◽  
A Chain

1. The iodination of insulin was studied under various experimental conditions in aqueous media and in some organic solvents, by measuring separately the uptake of iodine by the four tyrosyl groups and the relative amounts of monoiodotyrosine and di-iodotyrosine that are formed. In aqueous media from pH1 to pH9 the iodination occurs predominantly on the tyrosyl groups of the A chain. Some organic solvents increase the iodine uptake of the B-chain tyrosyl groups. Their efficacy in promoting iodination of Tyr-B-16 and Tyr-B-26 is in the order: ethylene glycol and propylene glycol≃methanol and ethanol>dioxan>8m-urea. 2. It is suggested that each of the four tyrosyl groups in insulin has a different environment: Tyr-A-14 is fully exposed to the solvent; Tyr-A-19 is sterically influenced by the environmental structure, possibly by the vicinity of a disulphide interchain bond; Tyr-B-16 is embedded into a non-polar area whose stability is virtually independent of the molecular conformation; Tyr-B-26 is probably in a situation similar to Tyr-B-16 with the difference that its non-polar environment depends on the preservation of the native structure.

scholarly journals Flux-Reducing Tendency of Pd-Based Membranes Employed in Butane Dehydrogenation Processes

Membranes ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 291 ◽  
Author(s):  
Thijs A. Peters ◽  
Marit Stange ◽  
Rune Bredesen
Keyword(s):  
Competitive Adsorption ◽  
Prolonged Exposure ◽  
Hydrogen Permeation ◽  
State Of The Art ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Hydrogen Flux ◽  
Membrane Performance ◽  
Wide Range

We report on the effect of butane and butylene on hydrogen permeation through thin state-of-the-art Pd–Ag alloy membranes. A wide range of operating conditions, such as temperature (200–450 °C) and H2/butylene (or butane) ratio (0.5–3), on the flux-reducing tendency were investigated. In addition, the behavior of membrane performance during prolonged exposure to butylene was evaluated. In the presence of butane, the flux-reducing tendency was found to be limited up to the maximum temperature investigated, 450 °C. Compared to butane, the flux-reducing tendency in the presence of butylene was severe. At 400 °C and 20% butylene, the flux decreases by ~85% after 3 h of exposure but depends on temperature and the H2/butylene ratio. In terms of operating temperature, an optimal performance was found at 250–300 °C with respect to obtaining the highest absolute hydrogen flux in the presence of butylene. At lower temperatures, the competitive adsorption of butylene over hydrogen accounts for a large initial flux penalty.

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