Hydrogen Permeability Coefficient Research Articles

Molecular Simulation Study on the Hydrogen Permeation Behavior and Mechanism of Common Polymers.

This research aimed to provide an understanding of the selection and safe application of pipeline liner materials for hydrogen transport by examining the permeation properties and mechanisms of hydrogen within polymers commonly used for this purpose, such as high-density polyethylene (HDPE) and ethylene-vinyl alcohol copolymer (EVOH), through molecular simulation. The study was carried out within defined operational parameters of temperature (ranging from room temperature to 80 °C) and pressure (from 2.5 to 10 MPa) that are pertinent to hydrogen pipeline infrastructures. The results reveal that with an increase in temperature from 30 °C to 80 °C, the solubility, diffusion, and permeability coefficients of hydrogen in HDPE increase by 18.7%, 92.9%, and 129.0%, respectively. Similarly, in EVOH, these coefficients experience increments of 15.9%, 81.6%, and 112.7%. Conversely, pressure variations have a negligible effect on permeability in both polymers. HDPE exhibits significantly higher hydrogen permeability compared to EVOH. The unique chain segment configuration of EVOH leads to the formation of robust hydrogen bonds among the hydroxyl groups, thereby impeding the permeation of hydrogen. The process by which hydrogen is adsorbed in polymers involves aggregation at low potential energy levels. During diffusion, the hydrogen molecule primarily vibrates within a limited range, with intermittent occurrences of significant hole-to-hole transitions over larger distances. Hydrogen exhibits a stronger interaction with HDPE compared to EVOH, leading to a higher number of adsorption sites and increased hydrogen adsorption capacity in HDPE. Hydrogen molecules move more actively in HDPE than in EVOH, exhibiting greater hole amplitude and more holes in transition during the diffusion process.

Molecular dynamics investigations into the hydrogen permeation mechanism of polyethylene pipeline material

To avoid hydrogen embrittlement and other hydrogen damage caused during hydrogen transportation using metal pipelines, it is feasible to transport hydrogen through nonmetallic polyethylene (PE) pipelines. However, gas permeation and leakage are more obvious for hydrogen delivery using PE pipelines than those using metal pipelines. To reveal the permeation and diffusion mechanisms of hydrogen in PE pipelines, the Grand Canonical Monte Carlo simulation and molecular dynamics are conducted. The solubility and diffusion characteristics of hydrogen in amorphous PE are investigated at temperatures of 270–310 K and pressures of 0.1–0.7 MPa. The influences of temperature and pressure on hydrogen permeation are also analyzed. The results show that the solubility, diffusion, and permeability coefficients of hydrogen in amorphous PE increase with increasing temperature, and their relationships with temperature are consistent with the Arrhenius law. Pressure has a negligible effect on the permeability coefficient of hydrogen in amorphous PE, whereas temperature appreciably affects the permeability coefficient. The diffusion of hydrogen in PE conforms to the “hopping” mechanism. The hydrogen molecule vibrates in the free volume pore for a long time and then quickly hops to the adjacent pores to complete diffusion. The hydrogen molecule continues to vibrate and hop, eventually moving further away from its initial position and permeating through PE materials.

Experimental investigation of anion exchange membrane water electrolysis for a tubular microbial electrosynthesis cell design

Tubular water splitting electrolyzer was adapted to neutral pH conditions for the in-situ H2 supplying microbial electrosynthesis design. The electrolyzer was optimized to reduce ohmic losses and provide adequate gas separation. Direct membrane deposition was applied on a thin anionic exchange membrane for the membrane-electrode-assembly fabrication. Although the membrane resistance increased with the increasing membrane thickness from 55 to 165 μm, the contact resistance was reduced by applying stronger compression pressure on the membrane-electrode interface. A durability test was run for 120 h, showing a voltage increase of 134 μV/h. Moreover, the hydrogen permeability coefficient was determined at 10−14 mol/(mˑsˑPa).

Polyimides cross‐linked with amino group‐containing compounds

The commercially available linear polyimide Matrimid® 9725 was crosslinked with amino groups containing both high‐molecular‐weight and low‐molecular‐weight compounds. The multi‐functional amine‐terminated hyperbranched polyimide precursor (hyperbranched polyamic acid), based on 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride and 4,4′,4″‐triaminotriphenylmethane, and its fully imidized form (amine‐terminated hyperbranched polyimide), bifunctional amine, 4,4′‐diaminodiphenylamine and trifunctional amine, 4,4′,4″‐triaminotriphenylamine, were used as the crosslinkers. Theoretically, 10% or 20% of the Matrimid imide groups was reacted with the amino groups of the crosslinking agent during the formation of the amide groups. The insoluble content (gel) in the final materials was very low at the crosslinking temperature of 80°C and was in the 55–90% range at the crosslinking temperature of 200°. The permeability coefficients of hydrogen, carbon dioxide and methane in the self‐standing, mechanically tough film (membrane) based on the combination of Matrimid and hyperbranched polyimide were approximately 30–45% higher compared with those in the membrane made of pure Matrimid at a comparable separating ability (selectivity). POLYM. ENG. SCI., 57:1367–1373, 2017. © 2017 Society of Plastics Engineers

Mixed matrix membranes based on hyperbranched polyimide and mesoporous silica for gas separation

The novel mixed matrix membranes were prepared from the hyperbranched polyimide based on 4,4´,4´´-triaminotriphenylmethane and mesoporous silica MCM-41 (up to 16 wt.%). The permeability coefficients of hydrogen, carbon dioxide, oxygen, nitrogen and methane in the membranes increased and oxygen/nitrogen or carbon dioxide/methane selectivities decreased slightly with the silica content. The absolute values of permeability coefficients were fairly influenced by the method of additive incorporation to the polymeric matrix.

Mixed gas separation study for the hydrogen recovery from H 2/CO/N 2/CO 2 post combustion mixtures using a Matrimid membrane

In this work, the membrane separation of hydrogen from binary, ternary and quaternary mixtures of H 2, N 2, CO and CO 2 is presented. Hydrogen permeability through a polyimide Matrimid 5218 membrane was experimentally obtained using the constant pressure technique. The influence of the feed gas composition, temperature (30–100 °C), pressure range (up to 6 bar), and flow rates was experimentally analyzed. As expected, the pure gas permeability of H 2 was only slightly dependant on pressure and had an average value of 17.7 × 10 −14 m 3(STP) m m −2 s −1 kPa −1 at 30 °C. Hydrogen permeability was not affected by the presence of nitrogen and carbon monoxide, and as a result the mixed gas selectivities for the H 2/N 2/CO mixtures are very close to the selectivities calculated from pure gas permeation data. On the contrary, a strong dependency of the hydrogen permeability on CO 2 concentration was observed even at low concentrations of CO 2. A reduction of 42% of the hydrogen permeability coefficient was obtained when a mixture of 10/90 vol.% H 2/CO 2 was used as feed gas. Accordingly H 2/CO 2 selectivity decayed from a value of 4.2 calculated from pure gas permeabilities to 2.7 when permeation data were obtained in mixed gas experiments. The preferential sorption of CO 2 on the Langmuir sites of the excess free volume portion of the polymer allowed explaining and quantifying this phenomenon. The “dual-mode sorption, partial immobilization” model was used to describe H 2 and CO 2 permeation behavior of pure, binary, ternary and quaternary mixtures. The model sorption parameters for N 2 and CO 2 in the polymer Matrimid 5218 were obtained from the literature meanwhile those for H 2 and for CO were unknown and resulted from the fitting of the experimental data to the proposed model. Satisfactory agreement between predicted permeability results and experimental data with a correlation coefficient ( R) higher than 0.95 and mean squared relative error (MSRE) lower than 0.01 was attained. Thus, this work reports useful knowledge related to the intrinsic material properties, considering gas mixtures of industrial interest and essential when other membrane configurations like hollow fibers, mixed matrix membranes or polymer blends are proposed.

ChemInform Abstract: Hydrogen Permeability for Oxide-Metal Multilayered Films.

Abstract The hydrogen permeability of multilayered films consisting of various oxide and metal films, e.g. V2O5/Cu, was investigated using the colouring phenomenon of amorphous WO3 and was found to be associated with the capability of dissociation of hydrogen molecules and the hydrogen densities of the oxide layers. Hydrogen separation has been performed using V2O5/Cu multilayered films formed on a polyimide membrane. The hydrogen permeability coefficient of the films in the temperature range 343–368 K was found to be about 10 times as large as that of copper films owing to the capability of hydrogen dissociation at the V2O5/Cu double layer and owing to the large amount of hydrogen taken up by V2O5. Mixtures of H2-CO and H2-Ar with 50 mol% H2 had a concentration of H2 as high as 97 mol% after permeation through the membrane. When an LaCu5 film was formed between the copper and polyimide film, the hydrogen permeability coefficient of the film increased owing to enhanced recombination of H atoms.

Comparison of transport properties of hyperbranched and linear polyimides

The non-porous, flat membranes were prepared from the novel hyperbranched polyimide based on 4,4’,4”-triaminotriphenylmethane (MTA) and 4,4’-oxydiphthalic anhydride (ODPA) and also from the linear polyimide (LPI) based on 4,4’-methylenedianiline (MDA) and ODPA. The permeability coefficients of hydrogen, carbon dioxide, oxygen, nitrogen and methane in the membrane prepared from hyperbranched polyimide were 2–3.7 times higher than those in the membrane from LPI at comparable selectivities.

The structure connectivity factor as applied to the determination of the hydrogen permeability coefficient of glasses

Glass microspheres have been used in laser physics as hydrogen microcontainers over a period of more than fifty years. However, developers of glass compositions are guided in their work only by practical experience and intuition in view of the lack of reliable data on the influence of glass components on the hydrogen permeability. There is only one expression that approximately describes the dependence of the permeability on the composition, i.e., the SiO2, B2O3, and P2O5 contents. It is advisable to complement the computational equation by the Ermolenko structure connectivity factor in order to include all glass components and the network dimensionality in the calculations.

Dependence of the Hydrogen Permeability Coefficient in Glasses of the Sodium-Silicate System on the Silica Modulus

The system Na2O – SiO2 used in designing compositions for producing gas microcontainers (microspheres) is investigated. Based on a known equation, an expression is obtained for the dependence of the hydrogen permeability coefficient of glass on its silica modulus. It is established that the alkaline modifier even in the form of an impurity can influence gas permeability. A conclusion is made on the need to apply criterial valuations in designing glasses. A nomogram is obtained for determining the silica modulus, hydrogen permeability coefficient, phase composition, and probability of glass formation in the Na2O – SiO2 system.

Hydrogen permeability for oxide-metal multilayered films

The hydrogen permeability of multilayered films consisting of various oxide and metal films, e.g. V 2O 5/Cu, was investigated using the colouring phenomenon of amorphous WO 3 and was found to be associated with the capability of dissociation of hydrogen molecules and the hydrogen densities of the oxide layers. Hydrogen separation has been performed using V 2O 5/Cu multilayered films formed on a polyimide membrane. The hydrogen permeability coefficient of the films in the temperature range 343–368 K was found to be about 10 times as large as that of copper films owing to the capability of hydrogen dissociation at the V 2O 5/Cu double layer and owing to the large amount of hydrogen taken up by V 2O 5. Mixtures of H 2-CO and H 2-Ar with 50 mol% H 2 had a concentration of H 2 as high as 97 mol% after permeation through the membrane. When an LaCu 5 film was formed between the copper and polyimide film, the hydrogen permeability coefficient of the film increased owing to enhanced recombination of H atoms.

Diffusivity and permeability of poly(α-amino acid) membranes to gases

The diffusivity and permeability characterizing transport in poly(α-amino acid) membranes have been determined for helium, hydrogen, argon, oxygen, nitrogen and carbon dioxide in the temperature range 10 to 60°C. The membranes of six poly(α-amino acid)s, namely poly(L-leucine)(PLL), poly(γ-methyl-L-glutamate)(PMLG), poly(L-methionine) (PMt), poly(γ-benzyl-L-glutamate)(PBLG), poly(N∈-carbobenzoxy-L-lysine)(PLy-Z) and poly(γ-L-glutamic acid) (PG) were synthesized. In order to elucidate the effect of the side chain on transport, membranes were used whose polymer main chain is a rigid α-helical structure. The side chains have a great influence on transport properties; for example, the permeabilities of nitrogen were distributed in the range 2 x 10 -10 to 1 x 10 −14cm 3 (STP)cm/cm 2-sec-cmHg at 20°C for PLL and PG, respectively. The ratio of the permeability coefficients of hydrogen and nitrogen was considered to be a measure of the degree of compactness between helices of poly(α-amino acid) membranes. Anomalous transient state permeation curves were observed for nitrogen in PG. The Arrhenius plots of diffusivity for various gases in the polymer with the largest side chain (PLy-Z) show an inflection and are concave to the reciprocal temperature axis.

Dependence on solution composition and temperature of the diffusion and permeability coefficients of hydrogen in solid solutions of germanium in iron

Dependence on solution composition and temperature of the diffusion and permeability coefficients of hydrogen in solid solutions of germanium in iron