Maximum Hydrogen Content Research Articles

Fermentation of Chlorella sp. for anaerobic bio-hydrogen production: Influences of inoculum–substrate ratio, volatile fatty acids and NADH

This study evaluated the influences of inoculum–substrate ratio (ISR), volatile fatty acids (VFAs) and nicotinamide adenine dinucleotide, the reduced form (NADH) on hydrogen production during the anaerobic fermentation of Chlorella sp. in batch tests at 35°C. The results indicated that the hydrogen concentration and lag time increased when ISR decreased, and the maximum hydrogen production and hydrogen content, 7.13mL/gVS and 45.3%, respectively, were obtained when ISR was equal to 0.3. On the other hand, VFAs concentrations increased with the increase of hydrogen. The NADH increased while the daily output of hydrogen decreased as the fermentation carried on. The results suggested that ISR, VFAs, and NADH were important parameters for effective anaerobic hydrogen production using Chlorella sp. as substrate.

Severe plastic deformation and hydrogenation of the titanium aluminides

Severe plastic deformation (mechanical activation in a hydrogen atmosphere and shear under pressure) effects on the hydrogenation of two titanium aluminides Ti 3Al and TiAl-type alloy (B2) have been studied. It is shown that a conventional hydrogenation of the bulk samples allows forming the hydrides with high hydrogen content and high desorption temperature: TiAl (773 K, 1.76 mass%) and Ti 3Al (1043 K, 2.94 mass%). In comparison with the conventional hydrogenation, the mechanical activation in a hydrogen atmosphere at room temperature allows one to obtain the hydrides of the TiAl (B2) and Ti 3Al alloys with the reduced desorption temperature: TiAl (453 K, 1.96 mass%) and Ti 3Al (531 K, 2.6 mass%). The shear under pressure has been applied to the sample before hydrogenation also leads to a reduction of the desorption temperature; however, it produces the phase transformation in the Ti 3Al intermetallic compounds, which lowers the observed a maximum hydrogen content.

Study of the diffusion kinetics and mechanism of electrochemical hydriding of Mg–Ni–Mm alloys

Electrochemical hydriding in a 6 M KOH solution at 20 and 80 °C for 480 min was applied on a series of as-cast binary Mg–Ni and ternary Mg–Ni–Mm alloys (Mm = mischmetal containing 45% Ce, 38% La, 12% Nd and 4% Pr) containing 11–24 wt. % Ni and 0–6 wt. % Mm. The kinetics and mechanism of the hydriding process, as well as hydrogen release temperatures, were studied by glow discharge spectrometry hydrogen profiling, scanning electron microscopy, energy dispersion analysis, X-ray diffraction and mass spectrometry. A maximum hydrogen concentration of 1.1% was achieved in the eutectic MgNi24Mm5 alloy hydrided at 80 °C. In all cases, the main hydriding product was binary MgH 2 hydride. Mass spectrometry revealed its destabilization due to Ni and Mm because its decomposition temperature was lowered by about 100 °C. Both nickel and mischmetal showed positive effects on hydriding and dehydriding kinetics. These effects are discussed in relation to the hydriding mechanism, electronic structure and atomic size of additives and structural variations of the alloys. Based on the H-concentration profiles, the diffusion coefficients of hydrogen were estimated. For the eutectic MgNi24Mm5 alloy, the H diffusion coefficient at 20 °C was 4 · 10 −10 cm 2 s −1.

Effect of Plastic Strain and Preloading on Delayed Fracture Characteristics of High Strength Steel

Plastic strain takes place at the bottom of the thread, when fastening force is applied to the high strength bolts. The effect of plastic strain on the delayed fracture characteristics was studied using conventional strain rate test (CSRT). For this purpose two kinds of methods were used in the experiments: one is applying uniform plastic strain to the specimen before machining notch and the other is preloading of notched round bar (NRB) specimen. The hydrogen content increased as increasing plastic strain and in contrast, the relationship between fracture stress and hydrogen content using CSRT was independent of plastic strain, which indicates that plastic strain increases hydrogen content and results in decreasing fracture stress based on the above-mentioned relation. On the contrary, the preloading affected the fracture nominal stress obtained by CSRT of hydrogen precharged NRB specimen. Using finite element stress analysis, the maximum stress ahead of the notch tip for preloaded NRB specimen was obtained. The relationship between the fracture maximum stress and hydrogen concentration becomes unique irrespective preloading. It is concluded that the relation of local maximum stress—the hydrogen concentration at the delayed fracture initiation site is the material constant and control delayed fracture.

Effects of Cu Addition on Hydrogen Absorption and Diffusion Properties of 1470 MPa Grade Thin-walled Steel Tube under Atmospheric Corrosion

Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of Cu addition on hydrogen absorption and diffusion properties of steel under atmospheric condition, corrosion test was conducted on a 1470 MPa grade thin-walled low carbon martensite steel tube. To this end, a martensite steel tube bearing 0.18% C, 0.4% Si, 1.5% Mn, 0.15% Cu, 0.01% Nb was prepared and compared with Cu free steel tube. As a result of EPMA mapping for the rust layer, Cu accumulated discretely on the rust/steel interface, especially in the bottom of pits of 0.15% Cu bearing steel tubes after the atmospheric corrosion test over 12 years. According to x-ray absorption near-edge structure (XANES) spectra, the valence of Cu in the rust layer was mainly +2 as Cu-(O, OH, SO4). The average and maximum diffusible hydrogen content level of 0.15% Cu bearing steel was lower than that of Cu free steel after the atmospheric corrosion test. The quantity of non-diffusible hydrogen was much higher than that of diffusible hydrogen. According to diffusion calculation results, hydrogen diffusion was so rapid that the long-term corrosion hysteresis seemed to have little influence on the diffusible hydrogen content. Furthermore, the short-term corrosion hysteresis may be the main determinant of diffusible hydrogen concentration. Having regard to the fact that the valance of Cu could also be 0 as reported by Shimizu et al., an inhibition mechanism from accumulated Cu on hydrogen-induced cracking was proposed. Eluted Cuy+ ions in the rust layer may precipitate as metallic Cu at the microscopic cathode during the corrosion test. As a result, the microscopic cathode becomes inactivated as an electrochemical reaction site for hydrogen. The Cu alternates between precipitates and Cu ions depending on the relative humidity, and the condensation and pH of the water in the rust layer.

Hydrogen content in clinopyroxene phenocrysts from Salina mafic lavas (Aeolian arc, Italy)

Clinopyroxene phenocrysts from the mafic calc-alkaline lavas of Salina (Aeolian arc, southern Tyrrhenian Sea, Italy) have been analysed to determine the hydrogen content and iron oxidation state of this early crystallized phase. The volcanic activity of Salina, starting at 168 ka and developed in several centres up to 24 ka, was dominated by calc-alkaline and high-K calc-alkaline basalts and andesites, with minor dacites and rhyolites. The presence of OH vibrational bands was detected in the IR spectra of clinopyroxenes phenocrysts from Corvo, Rivi-Capo (168–87 ka), Fossa delle Felci (108–59 ka) and Monte dei Porri (57 ka) eruptions. Corvo-Rivi-Capo basalts have clinopyroxenes with the lowest water contents 75–97 ppm H2O by weight, whereas an increase in the hydrogen contents of clinopyroxenes from Fossa delle Felci centre, with 171–286 ppm H2O by weight, and Monte dei Porri with 343–390 ppm H2O by weight, was observed. Mossbauer spectroscopy showed only a limited variation on the Fe3+/Fetot ratio of the studied samples, and a very similar atomic Fe3+ content (0.042–0.047 a.p.f.u.) suggesting that only minor variation on fO2 occurred during the crystallization of these clinopyroxenes. The water content of parental melts, calculated by applying an IVAl-dependent partition coefficient to the measured hydrogen contents of clinopyroxenes, is 0.4–0.8 wt% of water in melt for the Rivi-Capo-Corvo basalts, 0.5–3.7 wt% water in melt for Fossa delle Felci lavas and 1.6–2.6 wt% of water in melt for Monte dei Porri lavas. An increase in the maximum hydrogen contents of clinopyroxenes can be recognized during the evolution of the Salina volcano, with the highest hydrogen content measured in clinopyroxenes from Monte dei Porri where the eruptions were characterized by a high degree of explosivity, suggesting a key role of volatiles.

Hydrogen diffusion analyses of a cracked steel pipe under internal pressure

In hydrogen diffusion in metals, we have to consider not only the hydrogen flux driven by the gradient of hydrogen concentration but also the hydrogen flux driven by the gradient of hydrostatic stress. Such hydrogen diffusion is a multi-physics problem coupled hydrogen diffusion with a stress field. We performed such hydrogen diffusion analyses for a steel pipe with a crack on an inner surface under internal pressure. On the inner surface of the pipe, the hydrogen concentration calculated using the fugacity of the hydrogen molecules was used as a boundary condition for a hydrogen diffusion equation. The finite element method was employed both for a hydrogen diffusion analysis and for a stress analysis. We obtained the hydrogen concentration around a crack tip by varying the magnitude of internal pressure and the crack length, and examined the relationship between the maximum hydrogen concentration and a nonlinear fracture mechanics parameter CTOD ( Crack Tip Opening Displacement). Good correlation is found between the maximum hydrogen concentration and CTOD.

Hydrogen production by glycerol steam reforming with/without calcium oxide sorbent: A comparative study of thermodynamic and experimental work

Thermodynamic analysis and experimental tests of glycerol steam reforming with/without calcium oxide (CaO) as a carbon dioxide (CO 2) sorbent have been performed and compared in this work. Methanol, ethanol, acetaldehyde, acetone and ethylene do not exist in equilibrium conditions according to the equilibrium calculations. Without CaO present, thermodynamic predictions show that a maximum hydrogen concentration of 67% can be obtained at 925 K, with a water to glycerol ratio (WGR) of 9. In the experiments, the Ni/ZrO 2 catalyst fails to catalyze the reactions to thermodynamic equilibrium under the selected conditions as the highest hydrogen concentration obtained is 64%. With the presence of CaO, thermodynamic analysis implies hydrogen purity exceeding 95% can be achieved below 925 K at WGRs of 6 and 9. However, CaCO 3 does not exist at temperatures greater than 1025 K. In the experiments, a hydrogen purity of 95% with only 5% CH 4 as impurity can be reached at 850 K with a WGR of 9. The Ni/ZrO 2 catalyst is not active enough to convert excess CH 4 to hydrogen in glycerol steam reforming as CH 4 concentrations are usually higher than the equilibrium values. The addition of CaO to this system greatly enhances the hydrogen production while reducing the CO concentration.

ChemInform Abstract: Hydrogenation, Crystal Structure and Magnetic Ordering of R2Fe14C (R: Sm, Er, Tm).

Abstract The influence of hydrogen absorption on the magnetic properties of the compounds Sm 2 Fe 14 C, Er 2 Fe 14 C and Tm 2 Fe 14 C was studied using X-ray diffraction and measurements of the temperature dependences of the magnetization, the a.c.-susceptibility and the resistivity. The latter two compounds have a first-order spin reorientation transition close to room temperature, as confirmed by DSC measurements. It is shown that this property is largely retained upon hydrogen absorption although the corresponding Curie temperatures increase strongly with hydrogen concentration. The maximum hydrogen concentration decreases with increasing atomic number of the R component in the R 2 Fe 14 C compounds investigated.

Modelling and numerical simulation of permeated hydrogen dispersion in a garage with adiabatic walls and still air

The dispersion of permeated hydrogen from a storage tank in a typical garage with adiabatic walls and still air is studied analytically and numerically. Numerical simulations are performed based on an original approach of a hydrogen mass source term introduction in the hydrogen conservation equation in control volumes around the tank surface. The maximum hydrogen concentration in an enclosure is always on the top surface of the tank and never reaches 100% by volume. Both the analytical analysis and numerical simulations have demonstrated that diffusion and buoyancy contributions to the hydrogen transport from the tank surface are balanced within 1 min from the start of the process. The quasi-steady state conditions within the enclosure with approximately linear distribution of hydrogen from the top to the bottom are established in about 1 h for both considered permeation rates: 1 NmL/hr/L of tank capacity and 45 NmL/hr/L the last being an equivalent to the SAE J2578 requirements. Finally, the numerical simulations demonstrated that the difference in hydrogen concentration between the garage ceiling and floor is negligible compared to the lower flammability limit of 4% by volume of hydrogen.

Evaluation of hydrogen entry into high strength steel under atmospheric corrosion

Hydrogen entry into high strength steels by atmospheric corrosion has been investigated to evaluate their susceptibility to hydrogen embrittlement. High strength steels were corroded by dry/wet cyclic corrosion after NaCl deposition. The maximum diffusible hydrogen concentration around the surface was successfully obtained by means of thermal desorption analysis after keeping the specimens at high humidity to reproduce enhanced hydrogen entry influenced by the rust layer and to homogenize the hydrogen distribution. Despite decrease in corrosion rate, hydrogen content in specimens did not decrease. Decrease of pH in inner rust layer is responsible for the enhanced hydrogen entry into steel.

Computational approach to study hydrogen storage in clathrate hydrates

This work presents collectively, analyzes and compares the results from previous Monte Carlo studies performed towards the evaluation of the hydrogen-storage capacity of clathrate hydrates. Clathrate hydrates can be regarded as a special type of nanoporous material that consists of hydrogen-bonded water molecules that form cavities where gas molecules can be entrapped. Three different hydrates structures (sI, sII, and sH) are examined where hydrogen is either the single guest component or a second substance (promoter) coexists. The storage of hydrogen in hydrates can be simulated as a process of gas adsorption in a solid material and, consequently, the Grand Canonical Monte Carlo approach seems to be the most appropriate approach. These simulations are themselves consistent and, most importantly, they are in good agreement with the available experimental data. This fact illustrates the efficiency of the specific computational approach in the study of hydrates. The comparison between the three hydrate types shows that sH hydrates can store larger amounts of hydrogen than sI or sII hydrates. In particular, the maximum hydrogen content achieved is 3.6 wt% with pure hydrogen, and 1.4 wt% with the use of a promoter (at 274 K and 500 MPa).

First-principles calculations of LaNi 5− xSn xH y intermetallics and intermediate phase

The crystal and electronic structures of LaNi4:75Sn0.25 intermetallics and LaNi4.5Sn0.5Hy (y=2.0, 2.5) intermediate phase have been investigated by the full-potential linearized augmented plane wave (FP-LAPW) method. Hydrogen occupation sites in LaNi4.5Sn0.5Hy have been determined based on Westlake's criterions: (1) the minimum hole radius is 0.04 nm; (2) the minimum H-H distance is 0.21 nm; as well as geometry optimizations and internal coordinates optimizations. We find that hydrogen atoms prefer to occupy the 12n*, 6m, 12o, 6m* sites in LaNi4.5Sn0.5H2.0 and the 6m*, 4h, 6m, 12o, 12n* sites in LaNi4.5Sn0.5H2.5. The specific coordinates of hydrogen atoms in LaNi4.5Sn0.5Hy are also determined. The results show that hydrogen atoms tend to keep away from tin atoms. The maximum hydrogen content decreases compared with LaNi5. The interactions between Sn and Ni with H play a dominate role in the stability of LaNi4.5Sn0.5-H system. Lattice expansion and increment of Fermi energy EF show that both Sn and H atoms decrease structural stability of these alloys.

A model of hydrogen absorption by metals

The influence of the electron spectrum of transition metals on the hydrogen absorption process is considered. An absorption model is proposed where electrons, followed by protons, from adsorbed molecules or atoms of hydrogen transit into the metal. In terms of this model, the driving force of the absorption process ΔX is equal to the difference of the total electron energies in a hydrogen atom and in a metal at the Fermi level: ΔX = E H − (E F + A work). The equilibrium state in the absorption process corresponds to the equation 13.53 = E F + A work, which makes it possible to find the Fermi energy of transition metals and the valence of hydrogen absorbing metals, to define the molecular formula of hydrides, and to calculate the maximum hydrogen content in hydride phases. The hydrogen content in the composition of hydrides is shown to decrease in approaching the middle of the transition-metal rows. In groups, on the contrary, the hydrogen content grows as the atomic weight of metals increases. A good agreement of calculated and experimental compositions of hydride phases is found for the transition metals whose d band is less than half-filled with electrons.

Indications of the formation of an oversaturated solid solution during hydrogenation of Mg–Ni based nanocomposite produced by mechanical alloying

An oversaturated solid solution of H in a nanocomposite material formed mainly by nanocrystalline Mg2Ni, some residual nanocrystalline Ni and an Mg rich amorphous phase has been found for the first time. The nanocomposite was produced by mechanical alloying starting from Mg and Ni elemental powders, using a SPEX 8000D mill. The hydriding characterization of the nanocomposite was carried out by solid‐gas reaction method in a Sievert’s type apparatus. The maximum hydrogen content reached in a period of 21 Ks without prior activation was 2.00 wt.% H under hydrogen pressure of 2 MPa at 363 K. The X-ray diffraction analysis showed the presence of an oversaturated solid solution between nanocrystalline Mg2Ni and H without any sign of Mg2NiH4 hydride formation. The dehydriding behaviour was studied by differential scanning calorimetry and thermogravimetry. The results showed the existence of two desorption peaks, the first one associated with the transformation of the oversaturated solid solution into Mg2NiH4, and the second one with the Mg2NiH4 desorption.

Long-term stability of hydrogen and organic acids production in an anaerobic fluidized-bed reactor using heat treated anaerobic sludge inoculum

Abstract This study evaluates the stability of hydrogen and organic acids production in an anaerobic fluidized-bed reactor (AFBR) that contains expanded clay (2.8–3.35 mm in diameter) as a support medium and is operated on a long-term basis. The reactor was inoculated with thermally pre-treated anaerobic sludge and operated with decreasing hydraulic retention time (HRT), from 8 h to 1 h, at a controlled temperature of 30 °C and a pH of about 3.8. Glucose (2000 mg L −1 ) was used as the substrate, generating conversion rates of 92–98%. Decreasing the HRT from 8 h to 1 h led to an increase in average hydrogen-production rates, with a maximum value of 1.28 L h −1 L −1 for an HRT of 1 h. In general, hydrogen yield production increased as HRT decreased, reaching 2.29 mol of H 2 /mol glucose at an HRT of 2 h and yielding a maximum hydrogen content of 37% in the biogas. No methane was detected in the biogas throughout the period of operation. The main soluble metabolites (SMP) were acetic acid (46.94–53.84% of SMP) and butyric acid (34.51–42.16% of SMP), with less than 15.49% ethanol. The steady performance of the AFBR may be attributed to adequate thermal treatment of the inoculum, the selection of a suitable support medium for microbial adhesion, and the choice of satisfactory environmental conditions imposed on the system. The results show that stable hydrogen production and organic acids production were maintained in the AFBR over a period of 178 days.

Hydrogen storage behavior in C15 Laves phase compound TiCr2 by first principles

Hydrogen storage in TiCr2 alloy of AB2 type with C15 Laves phase structure has been studied using density functional theory and plane-wave pseudopotential technique. The H atom interacts stronger with Cr atoms than with Ti and tends to occupy the g (2A2B) site due to the largest interstitial space. The g sites together with e (1A3B) sites form a three-dimensional clathratelike network, providing a diffusion pathway for H atoms, and the energy barriers for the H diffusion along these paths were computed. Interaction between two interstitial H atoms inside the TiCr2 lattice can be considered as a screened Coulomb repulsion, which seems to control the maximum hydrogen content in the metal hydrides. The absorption energies and electronic structures of metal hydrides TiCr2Hx with x=0.5–12 have been computed, and the theoretical maximum hydrogen storage capacity (between 2.6 and 3.8 wt %) agrees with experiments. The effects of the lattice expansion due to hydrogen absorption of different amounts have also been investigated.

Optimization of bio-ethanol autothermal reforming and carbon monoxide removal processes

Experimental investigation of bio-ethanol autothermal reforming (ATR) and water-gas shift (WGS) processes for hydrogen production and regression analysis of the data is performed in the study. The main goal was to obtain regression relations between the most critical dependent variables such as hydrogen, carbon monoxide and methane content in the reformate gas and independent factors such as air-to-fuel ratio (λ), steam-to-carbon ratio (S/C), inlet temperature of reactants into reforming process (TATRin), pressure (p) and temperature (TATR) in the ATR reactor from the experimental data. Purpose of the regression models is to provide optimum values of the process factors that give the maximum amount of hydrogen. The experimental ATR system consisted of an evaporator, an ATR reactor and a one-stage WGS reactor. Empirical relations between hydrogen, carbon monoxide, methane content and the controlling parameters downstream of the ATR reactor are shown in the work. The optimization results show that within the considered range of the process factors the maximum hydrogen concentration of 42 dry vol. % and yield of 3.8 mol mol−1 of ethanol downstream of the ATR reactor can be achieved at S/C = 2.5, λ = 0.20–0.23, p = 0.4 bar, TATRin = 230 °C, TATR = 640 °C.

Development of Gasification and Reforming Technology using Catalyst at Lower Temperature for Effective Energy Recovery: Hydrogen Recovery Using Waste Wood

The present study was conducted as part of a series of R&D of gasification and reforming technologies aimed at creating a new energy recovery technology from biomass waste. Special emphasis was placed on the production of hydrogen-rich synthesis gas from waste wood via gasification and sequential reforming technology using catalysts. Experiments were conducted employing three types of commercially available nickel-based steam reforming catalysts. Waste wood was supplied as the raw material and the reactor temperature was set at 1023 K (750°C). The results obtained were as follows: (1) Hydrogen generation can be significantly promoted by using nickel catalysts in the reforming process, as well as by supplying steam directly to the gasification process. (2) Nickel catalysts were also found to reduce the quantities of tar and toxic materials deleterious to gas utilization, such as hydrogen sulfide. (3) A nickel catalyst containing CaO was verified to exhibit superior catalytic performance, with the synthesis gas having a maximum hydrogen content of 57vol% and the lowest tar level converted from the wood material when the catalyst was utilized at 1023 K.

Thermodynamic Analysis for the Production of Hydrogen through Sorption Enhanced Water Gas Shift (SEWGS)

A thermodynamic analysis for the process concept of hydrogen production based on the combination of the water gas shift (WGS) and CO2 capture reactions (Absorption Enhanced Water Gas Shift, SEWGS) is presented. The chemical equilibrium analysis of this reaction system was performed to select the proper CO2 absorbent among: calcined dolomite (CaO•MgO), Li4SiO4 and Na2ZrO3 to be used in the process. Results indicate that the use of Na2ZrO3 produced the highest hydrogen concentration among absorbents studied. Results also revealed that the maximum hydrogen concentration (97% mol) can be achieved with a feed molar ratio of CO/Na2ZrO3/H2/O = 1/1/2 at 500°C at atmospheric conditions. The use of a catalyst for such processes may not be needed, since the high temperature at which these reactions are proposed may promote homogeneous non-catalyzed reactions. However, if the combination of both reaction kinetics (WGS and carbonation) are not fast enough to reach equilibrium, a new non-conventional WGS catalyst may be needed.