scholarly journals Membranes for Hydrogen Purification: An Important Step toward a Hydrogen-Based Economy

MRS Bulletin ◽  
2006 ◽  
Vol 31 (10) ◽  
pp. 735-744 ◽  
Author(s):  
Tina M. Nenoff ◽  
Richard J. Spontak ◽  
Christopher M. Aberg
Keyword(s):  
Chemical Reactions ◽  
Molecular Hydrogen ◽  
Glassy Polymer ◽  
Surface Flow ◽  
Pure Hydrogen ◽  
Hydrogen Purification ◽  
High Solubility ◽  
Porous Support ◽  
Basic Principles ◽  
Molecular Sieving

AbstractProduction of pure molecular hydrogen is essential to the realization of the proposed “hydrogen economy” that could ultimately provide hydrogen as a clean, renewable source of energy; eliminate the industrialized world's dependence on petroleum; and reduce the generation of greenhouse gases linked to global warming. A crucial step in obtaining pure hydrogen is separating it from other gaseous compounds—mainly CO2—that often accompany hydrogen in industrial chemical reactions. Advanced membrane technology may prove to be the key to the successful, economical production of molecular hydrogen.Size-sieving glassy polymer membranes can separate H2 on the basis of its small size. Alternatively, reverse-selective rubbery polymers can expedite the passage and, hence, removal of CO2 due to its relatively high solubility in such membranes alone or in conjunction with dissociative chemical reactions. Transition-metal membranes and their alloys can adsorb H2 molecules, dissociate the molecules into H atoms for transport through interstitial sites, and subsequently recombine the H atoms to form molecular H2 again on the opposite membrane side. Microporous amorphous silica and zeolite membranes comprising thin films on a multilayer porous support exhibit good sorption selectivity and high diffusion mobilities for H2, leading to high H2 fluxes. Finally, carbon-based membranes, including carbon nanotubes, may be viable for H2 separation on the basis of selective surface flow and molecular sieving. A wide variety of materials challenges exist in hydrogen purification, and the objective of this issue of MRS Bulletin is to address those challenges and their potential solutions from basic principles.

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.

Thermochemistry

2021 ◽  
pp. 325-343
Author(s):  
Christopher O. Oriakhi
Keyword(s):  
Chemical Reactions ◽  
Enthalpy Change ◽  
Physical Change ◽  
Bond Energies ◽  
Basic Principles ◽  
Exothermic Reactions ◽  
Bond Dissociation ◽  
Quantity Of Heat

Thermochemistry explores the basic principles of energy changes in chemical reactions. Calorimetry is described as a tool to measure the quantity of heat involved in a chemical or physical change. Quantitative overviews of enthalpy and the stoichiometry of thermochemical equations are provided, including the concepts of endothermic and exothermic reactions. Standard conditions are defined to allow comparison of enthalpies of reactions and determine how the enthalpy change for any reaction can be obtained. Hess"s Law, which allows the enthalpy change of any reaction to be calculated, is discussed with illustrative examples. A presentation of bond energies and bond dissociation enthalpies is offered along with the use of bond enthalpy to estimate heats of reactions.

scholarly journals Molecular surgical synthesis of H 2 @C 60 : recollections

2013 ◽  
Vol 371 (1998) ◽  
pp. 20110636 ◽  
Author(s):  
Koichi Komatsu
Keyword(s):  
Chemical Reactions ◽  
Molecular Hydrogen ◽  
Total Yield ◽  
Hole Size ◽  
Endohedral Fullerene ◽  
Entire Process ◽  
Surgical Method ◽  
H Nmr ◽  
Guest Species ◽  
Free Hydrogen

The first synthesis of endohedral fullerene containing molecular hydrogen, H 2 @C 60 , is briefly summarized. The synthesis was conducted according to what we call the ‘molecular surgical method’, that is, opening a hole on a C 60 surface, enlargement of the hole, insertion of a guest species and enclosure of the hole without loss of the encapsulated guest. The entire process involves three chemical reactions to open the hole and four reactions to gradually reduce the hole size and finally close the hole. The total yield of the product, H 2 @C 60 , based on consumed C 60 was 9%. The encapsulated molecule of hydrogen exhibited a 6 ppm upfield-shifted 1 H NMR signal when compared with free hydrogen, indicating the aromaticity at the inner centre of the C 60 cage.

Carbon-Based Membranes

MRS Bulletin ◽  
2006 ◽  
Vol 31 (10) ◽  
pp. 765-769 ◽  
Author(s):  
Tanja Pietraß
Keyword(s):  
Gas Separation ◽  
Inorganic Carbon ◽  
Synthetic Polymer ◽  
Surface Flow ◽  
Tubular Structures ◽  
Carbon Membranes ◽  
Precursor Material ◽  
Flow Through ◽  
Molecular Sieving ◽  
Carbon Based

AbstractInorganic carbon-based membranes for gas separation comprise materials that are fabricated through pyrolysis of a precursor material (often a synthetic polymer), and the more recently discovered carbon nanotubes. Fabrication, assembly into different architectures, and mechanism of operation are summarized for precursor-based carbon membranes, with a focus on selective surface flow and molecular sieving. Only preliminary work on carbon nanotube-based membranes for gas separation has been published. Their unusual transport properties, however, promise their use in gas separation in the future. In light of this application, structural properties and results relating to flow through these tubular structures are summarized.

The Chemistry of Rubber the Interaction of Ethylenic Compounds and Rubber

1947 ◽  
Vol 20 (4) ◽  
pp. 938-948 ◽  
Author(s):  
Jean Le Bras ◽  
Patrice Compagnon
Keyword(s):  
Sulfuric Acid ◽  
Chemical Reactions ◽  
Three Dimensional ◽  
Plastic State ◽  
Macromolecular Structure ◽  
Elastic State ◽  
Fundamental Change ◽  
Important Work ◽  
Basic Principles ◽  
Dimensional Network

Abstract It is known that the hydrocarbon of rubber has an ethylenic structure; its chemical reactions, the basic principles of which were brought out in 1902 by Weber, and which were the object, in 1930, of important work by Fisher, show that it has the general properties of ethylene derivatives, including the addition of hydrogen and metalloids of the first group (chlorine and bromine in particular), the addition of hydracids, scission by ozone, autoxidation, and isomerization by means of catalysts which isomerize ethylene derivatives, such as sulfuric acid and chlorides of metalloids. However, aside from these general reactions, rubber hydrocarbon reacts in other ways which likewise depend on the unsaturation of the molecule and on the macromolecular structure, and which in this particular case are of prime importance because it is on these properties that the processing and applications of rubber depend. As a good example, a fundamental change results from the action of sulfur, viz., vulcanization, whereby rubber passes from a predominantly plastic state to a predominantly elastic state, a change which is manifest by the rubber becoming insoluble. Moreover, sulfur is not the only agent which is capable of bringing about vulcanization; in fact, it has been found that many other agents are capable of vulcanizing rubber. Although Goodyear discovered this reaction in 1839, there is still no general agreement as to the mechanism of vulcanization; however, vulcanization is at present regarded as the transformation of an agglomerate of filiform molecules into a three-dimensional network.

Impacts of H2 Blending on Capacity and Efficiency on a Gas Transport Network

2019 ◽  
Author(s):  
Francis Bainier ◽  
Rainer Kurz
Keyword(s):  
Natural Gas ◽  
Molecular Hydrogen ◽  
Gas Transport ◽  
Energy Requirement ◽  
Calorific Value ◽  
Hydrogen Gas ◽  
Transport Network ◽  
Pure Hydrogen ◽  
Pipeline Network ◽  
Methane Gas

Abstract Gas Transport System Operators (TSO1) are considering injecting hydrogen gas in their networks. Blending hydrogen into the existing natural gas pipeline network appears to be a strategy for storing and delivering renewable energy to markets [1], [2],[3]. In comparison to methane, hydrogen gas (dihydrogen or molecular hydrogen) has a higher mass calorific value than methane gas. Because of this property, molecular hydrogen is appreciated for space shuttle engines. A second property is that hydrogen gas has a lower mass density than methane gas. The result of the second property is that the volume calorific value is in favor of methane gas. The list of differences between methane and hydrogen is long. In the relevant range of pressures and temperatures, the Joule-Thomson coefficient has a different sign for hydrogen and methane, and the compressibility factor has the opposite trend when the gas is compressed. The dynamic viscosity is also significantly different, and finally, heat capacity, isentropic exponent, and the thermal conductivity are also different. What are the impacts of these hydrogen characteristics on the transport capacity and its efficiency in the case of blending in a gas transport network? The first part of the paper is a review of the differences in characteristics between Hydrogen Gas and a Typical Natural Gas in Europe and their impact on the gas flow performance in a pipeline network equipped with compressors. The second part of the paper is dedicated to pipe segments. And in the third part, compressor stations are introduced between each pipe segment. At each step, an analysis of a mixed gas from one hundred per cent pure natural gas to one hundred per cent pure hydrogen is done. The paper provides some results for 10 %, 40 %, and 100 % of hydrogen blending in an international pipeline. The study shows that the energy quantity transported at the same pressure ratio is reduced respectively by 4 %, 14 %, and 15 to 20 %, and energy requirement for compression increases respectively by 7 %, 30 %, and 210 % (i.e. it more than triples). To transport the same quantity of energy in a network, assuming the resizing to the same level of optimizations, the energy requirement increases by 11 %, 52 %, and 280 %. In other words, it takes 4 times the energy to transport a given amount of energy if the gas is pure hydrogen than it takes if the gas is pure natural gas. The paper does not address the issue of equipment or material, it only compares the influence of hydrogen gas on the network capacity and the transport efficiency. This paper doesn’t take into account the limits of the equipment. All equipment is considered as compatible with any load of hydrogen blending.

scholarly journals On the Star Formation in Early Stage of Galactic Evolution

1981 ◽  
Vol 93 ◽  
pp. 68-69
Author(s):  
Y. Yoshii ◽  
Y. Sabano
Keyword(s):  
Molecular Hydrogen ◽  
Thermal Instability ◽  
Heavy Element ◽  
Hydrogen Gas ◽  
Initial Mass Function ◽  
Element Abundance ◽  
Subsequent Stage ◽  
Pure Hydrogen ◽  
Wide Range ◽  
Gas Cloud

Evolution and fragmentation of a gas cloud are investigated for the primordial chemical composition which is the same as the products of the Big Bang. A pure-hydrogen gas cloud collapses isothermally at 500–1000 K when a low fraction of molecular hydrogen works as a coolant, and breaks into small subcondensations with mass less than 10 M⊙ due to thermal instability associated with molecular dissociation. On the other hand a pure-hydrogen gas cloud which contains no molecular hydrogen collapses isothermally at 6000–8000 K in a thermally stable condition, and enters the region where thermal energy exceeds radiation energy when thermal equilibrium between matter and radiation is achieved in the cloud. Consideration of energetics in the subsequent stage of the cloud evolution leads to the mass range of 0.1–20 M⊙ for the stable nuclear-burning protostars of the first generation. The thermal behavior of a gas cloud in the regime of z (the ratio of heavy element abundance to solar one) less than 10−4 is essentially similar to that in the case of no heavy element, and the heavy element cooling brings about thermal instability in a wide range of parameters in the regime of z greater than 10−3. Linear perturbation analysis gives growth time of the instability much shorter than the free-fall time, and suggests the efficient excitation of density fluctuation driven by thermal instability. Thus the possibility of the initial mass function relatively enhanced in massive star at early times is denied, and the slow rate of metal enrichment in the interstellar medium is suggested.

scholarly journals On the explosion of pure electrolytic gas

1907 ◽  
Vol 79 (529) ◽  
pp. 234-235 ◽  
Keyword(s):  
Chemical Reactions ◽  
Barium Hydroxide ◽  
Pure Hydrogen ◽  
Explosion Wave ◽  
Heated Wire ◽  
Series Of Experiments

The fact that a large number of chemical reactions have been shown to be dependent on the presence of aqueous vapour has led to many experiments being made on the union of hydrogen and oxygen. Some years ago one of us made experiments which showed that an electric spark would fire ordinary electrolytic gas, whether in the dried or the moist state; and experiments on the rate of detonation in electrolytic gas seemed to show that, once an explosion-wave was started, no influence was exerted on the propagation of the wave by aqueous vapour, except a slightly retarding one. More recently, H. B. Baker carried out a series of experiments with very pure hydrogen and oxygen obtained by the electrolysis of a solution of highly purified barium hydroxide. His results show that the initiation of the flame by a heated wire is largely influenced by the purity of the gases.

scholarly journals Plasmonic enhancement of molecular hydrogen dissociation on metallic magnesium nanoclusters

Nanoscale ◽  
2021 ◽  
Author(s):  
Oscar A. Douglas Gallardo ◽  
Connor Box ◽  
Reinhard Maurer
Keyword(s):  
Chemical Reactions ◽  
Molecular Hydrogen ◽  
Metal Catalysts ◽  
Chemical Transformations ◽  
Plasmonic Enhancement ◽  
Hydrogen Dissociation ◽  
Metallic Magnesium ◽  
Promising Strategy

Light-driven plasmonic enhancement of chemical reactions on metal catalysts is a promising strategy to achieve highly selective and efficient chemical transformations. The study of plasmonic catalyst materials has traditionally focused...

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