Decrease In Hydrogen Content Research Articles

Моделирование и исследование динамики адсорбционного разделения синтез-газа и концентрирования водорода

On the basis of the Dubinin theory of micropore volume filling, a mathematical model of dynamics of pressure swing adsorption processes for synthesis gas separation has been developed. The model takes into consideration the influence of the processes of mass and heat transfer in gas and solid phases on the kinetics of diffusion transfer of adsorbate (carbon dioxide, carbon monoxide, hydrogen) in the adsorbent layer and accounts for all devices included in the process diagram (adsorber, compressor, vacuum pump, valves, throttle, receiver). Numerical studies of the process of separation of synthesis gas and concentration of hydrogen in a four-adsorber unit with granulated zeolite adsorbent 13X were carried out by methods of mathematical modeling: the influence of disturbing influences (composition and temperature of the initial hydrogen-containing gas mixture), regime parameters (cycle duration, pressure at the compressor outlet, pressure at the vacuum pump inlet, backflow coefficient) and design parameters (length of the adsorbent bulk layer and inner diameter of the adsorber) on the purity of the product hydrogen, its recovery rate and productivity of the unit were studied. The most dangerous disturbances and the most effective regime parameters of pressure swing adsorption process of synthesis gas separation were determined. It is established that the increase of temperature from 298 to 323 K and decrease of hydrogen concentration from 68 to 48 % (vol.) in initial gas mixture result in ~10 % lower efficiency of the unit due to the decrease of product hydrogen recovery rate. Practical recommendations on effective choice of operation regimes of an adsorption unit to ensure the achievement of required purity of product hydrogen at the level of 99.99 % (vol.), regardless of the impact of disturbances are formulated.

Production of biomethane in a deep rock aquifer

Already in the 1990s, strong decrease of hydrogen content in town gas (45-50% H2, 20-25% CH4, 8-12% CO2, 7-11% CO and 8-10% N2) was observed in the underground gas storage. It was followed by an increase in the methane concentration. The temperature rise and the presence of unusual compounds were noted. The presence of methanogenic archaea, which appeared to be responsible for changes in gas quality, was also confirmed. A detailed survey was related to the planned switch to natural gas storage instead of town gas. At the same site where natural gas is currently stored, we and the authors of the original study conducted analyses with the aim to find out whether this natural environment could be used to the production of biomethane throughout Power to Methane technology. The observed results confirmed the occurrence of microbial methane. Water sampling has confirmed the suitable physical and chemical properties of groundwater for biomethane production.

Role of seaweeds in neutralizing the impact of seawater acidification- A laboratory study with beached shells of certain bivalves and spines of a sea urchin

Ocean acidification is one of the major impacts of climate change in sea which is manifested by the decrease in hydrogen ion concentration (pH) of seawater mainly due to increased uptake of CO2 and reduction in carbonate ions. This is a report on the dissolution rate of dead shells of four marine bivalves and spines of a sea urchin when treated with different levels of CO2 dissolved in seawater for 48 hours which was measured gravimetrically. Dissolution of dead shells expressed as reduction in shell weight was directly proportional to the concentration of dissolved CO2. Live thallus of green seaweed Chaetomorpha antennina did reduce the magnitude of dissolution rates (P<0.05) of all the shells and spines considerably as well as the change in pH of ambient seawater due to the addition of CO2. The remedial property of seaweeds was more effective at lower concentrations of dissolved CO2. The induced change in pH was restored by green seaweed only at concentrations above 250 ppm. Although we noticed strong impact of dissolved CO2 on the dead shells of Mactrinula plicataria even at 100 ppm level, the remedial action by the green seaweed was maximum in Siliqua radiata followed by Perna viridis. Results of this laboratory study shows the positive role of seaweeds in neutralizing the acidification impacts.

Supporting the propane dehydrogenation reactors by hydrogen permselective membrane modules to produce ultra-pure hydrogen and increasing propane conversion: Process modeling and optimization

The main aim of this research is supporting the moving bed radial flow reactors in the propane dehydrogenation unit by membrane modules to produce ultra-pure hydrogen and increasing equilibrium conversion. The propane dehydrogenation is a thermodynamically limited and endothermic reaction, which decreasing hydrogen concentration and increasing operating temperature in the system could increase equilibrium conversion. In the first step, the conventional and membrane supported reactors are heterogeneously modeled based on the mass and energy conservation laws considering catalyst decay. To verify the precision of developed model, the results of simulation are compared with the available plant data. Then, the performance of designed membrane configuration is compared with the conventional process at the same feed condition. It appears that the activity of catalyst decreases along the reactors due to coke build up on the catalyst surface, and it results in the lower propane conversion. The results show that supporting the conventional reactors by hydrogen permselective membrane module increases propane conversion up to 3.09%.

Hydrogenated diamond-like carbon film prepared by RF bias assisting magnetron sputtering

Magnetron sputtering is an efficient way to deposit hard coatings in industry. However, as for hydrogenated diamond-like carbon (DLC:H) film, the low ionization rate of reaction gases causes poor mechanical properties. Here, in order to improve the ionization rate of C2H2 during depositing DLC:H, a radio frequency (RF) bias assisting magnetron sputtering system was elaborated. With increasing the RF bias voltage, the fullerene in the amorphous carbon are disappeared, accompanied with decrease of hydrogen content and increase of the sp3 C ratio. DLC:H film with a hardness of 33 GPa is successfully deposited, and its elastic recovery is over 75%. The high mechanical properties of DLC:H is mainly due to the high sp3 C ratio, which is primarily contributed by the enhanced ionization of the RF bias. This paper suggests that the RF bias assisting magnetron sputtering is an economical and efficient method to deposit DLC:H with superior mechanical property, and it is promising for industrial mass production.

Characterization and range of kerogen properties in the Vaca Muerta Formation, Neuquén Basin, Argentina

The Vaca Muerta Formation of the Neuquén Basin, Argentina, is a prolific oil- and gas-producing resource, characterized by high organic content and a large thermal maturity gradient running east to west. Kerogen properties are expected to vary substantially across the basin because of the range in thermal maturity (immature to dry gas). A comprehensive dataset of kerogen properties comprising thermal maturity, elemental composition, skeletal density, and specific surface area was acquired on cores from six wells. Kerogen isolates were prepared using a novel combination of acid demineralization and critical point drying that preserves the chemical and microstructural characteristics of kerogen. Kerogen properties are found to differ substantially between the studied wells, with variations correlating with thermal maturity. Kerogens show decreasing hydrogen content (H/C ratio ∼0.9–0.4) and nuclear hydrogen index (∼0.75–0.45), increasing grain density (∼1.28–1.55 g/cm3), and increasing surface area (∼100–350 m2/g) during maturation. These properties can dominate the response of logging tools run in organic-rich mudrocks and are needed to properly interpret downhole logs run therein for appraisal of porosity, hydrocarbon volumes, and total hydrocarbon-in-place, for example.

Influence of deposition conditions on mechanical properties of a-C:H:SiOx films prepared by plasma-assisted chemical vapor deposition method

A series of a-C:H:SiOx films was deposited on polished silicon and glass substrates by plasma-assisted chemical vapor deposition combined with pulsed bipolar substrate bias from mixtures of argon and polyphenylmethylsiloxane vapors. Different Ar pressures and substrate bias voltages were applied for the synthesis of a-C:H:SiOx films having different mechanical properties. Detailed characterization of the mechanical properties of a-C:H:SiOx films was made using the nanoindentation. Hardness and elastic modulus were used for the evaluation of the endurance capability (H/E) and resistance to plastic deformation (H3/E2). The structural properties of the deposited films were analyzed by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. It was shown that the Ar pressure and substrate bias variation can change the film properties and the growth rate and these changes are not linear. So, depending upon application, deposition conditions are to be optimized. In all of the examined coatings, increase of Ar pressure and amplitude of negative pulse of substrate bias lead to improvement in mechanical properties. According to the results of FTIR and Raman spectroscopy; this improvement is due to an increase in the sp3 bonded carbon content and decrease of hydrogen content in the films.

Effect of intercritical annealing time on hydrogen embrittlement of warm-rolled medium Mn steel

The susceptibility to hydrogen embrittlement (HE) of warm-rolled medium Mn steel (0.2C-5Mn-0.6Si-3Al) with different microstructure characteristics obtained by changing intercritical annealing time at 750 °C was investigated by carrying out slow strain rate test and hydrogen thermal analysis on electrochemically hydrogen charged samples. The results show that the increase in intercritical annealing time leads to an increase of the susceptibility to HE regardless of the decrease of both strength and diffusible hydrogen content. Unlike that of typical ductile fracture characteristic of uncharged sample, the hydrogen-charged sample shows a mixed fracture characteristic of ductile intragranular and brittle interface decohesion fracture mode in the crack initiation region. The susceptibility to HE was correlated mainly to the mechanical stability of retained austenite. These results suggest that suitable intercritical annealing treatment should be performed to ensure safety service of components made of this kind steel besides obtaining excellent combination of strength and ductility.

Giant Negative Piezoresistive Effect in Diamond-like Carbon and Diamond-like Carbon-Based Nickel Nanocomposite Films Deposited by Reactive Magnetron Sputtering of Ni Target.

Piezoresistive properties of hydrogenated diamond-like carbon (DLC) and DLC-based nickel nanocomposite (DLC:Ni) films were studied in the range of low concentration of nickel nanoparticles. The films were deposited by reactive high power pulsed magnetron sputtering (HIPIMS) of Ni target, and some samples were deposited by direct current (dc) reactive magnetron sputtering for comparison purposes. Raman scattering spectroscopy, energy-dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) were used to study the structure and chemical composition of the films. A four-point bending test was applied to study piezoresistive properties of the films. For some samples containing less than 4 at. % Ni and for the samples containing no Ni (as defined by both EDS and XPS), a giant negative piezoresistive effect was observed. The giant negative piezoresistive effect in DLC films deposited by either reactive HIPIMS or dc magnetron sputtering of Ni target was explained by possible clustering of the sp2-bonded carbon and/or formation of areas with the decreased hydrogen content. It was suggested that the tensile stress-induced rearrangements of these conglomerations have resulted in the increased conductivity paths.

Decreased hydrogen content in diamond-like carbon grown by CH4/Ar photoemission-assisted plasma chemical vapor deposition with CO2 gas

In this study, we tried to decrease the hydrogen content in diamond-like carbon (DLC) grown by photoemission-assisted plasma enhanced chemical vapor deposition (PA-PECVD) using Ar/CH4 mixed with CO2. When the CO2 flux was changed from 0 to 10 sccm with the Ar and CH4 fluxes maintained at 50 and 10 sccm, respectively, the growth rate decreased from 11 to 3 μm/h. Secondary mass spectroscopy measurements confirmed that the amount of O mixed into the DLC was increased through incorporation of CO2 into feed gas flow. The O concentration in the DLC was quantitatively evaluated by X-ray photoelectron spectroscopy (XPS) to be 0.6 atomic % at a CO2 flow ratio of 14%. Raman spectroscopy and XPS revealed that the amount of H trapped in the DLC decreased as the CO2 flow ratio was increased and the sp3/sp2 ratio remained almost unchanged. These results were interpreted by a model involving O radicals acting on the DLC surface associated with CO/CO2 and H2O, resulting in a decrease of the growth rate and H content. A portion of the O radicals also became incorporated into the DLC as COC bonds.

Experimental evaluation of tritium oxidation efficiency in the room temperature recombiner

To enhance public acceptance of a nuclear fusion reactor, the realization of passive detritiation system is a technical challenge taking hypothetic extraordinary situations occurred in a nuclear fusion facility into consideration. To achieve passive tritium oxidation with a room temperature recombiner (RTR), the hydrophobic platinum catalyst has been realized and data on kinetics have been accumulated. Since the efficiency of hydrogen oxidation at room temperature decreases with a decrease in hydrogen concentration, the worst condition of the process gas for RTR is the lowest hydrogen in the process gas. To overcome this condition, we have proposed to add hydrogen intentionally to be 100 ppm at the inlet of RTR. In this study, the dynamic behavior of a tritium leakage in a 12 m3 simulated room and the detritiation with a RTR was demonstrated to confirm the effectiveness of our proposal considering the worst condition for RTR. Initial tritium concentration in the containment was 1.0 GBq/m3. The flow rate was set to 1.8 Nm3/h. The volume of the hydrophobic platinum catalyst was 1000 cm3. Tritium concentration in the containment smoothly decreased one order magnitude after processing for 900 min. We obtained a prospect that a sufficient hydrogen conversion rate can be secured by adding hydrogen of about 100 ppm. From the kinetics point of view, the required amount of catalyst for a RTR is estimated to be three times that for a heated reactor at 473 K in order to obtain the same conversion efficiency of tritium.

Empirical study of petroleum-based pitch production via pressure- and temperature-controlled thermal reactions

Three-stage thermal reactions were conducted to investigate empirical trends of petroleum-based pitch production and the chemical characteristics of pitch produced by controlling the temperature and pressure operating parameters. The softening point of pitch increased with increasing reaction temperature under atmospheric pressure, whereas the pitch yield increased with decreasing reaction temperature under a pressurized condition. Elemental analysis supported the result of decreased hydrogen content. In addition, thermogravimetric analysis revealed that higher reaction temperatures could induce the polymerization and condensation of polyaromatic hydrocarbons (PAHs) with carbon yield at 900°C. The molecular weight distribution (MWD) of pitch was analyzed by MALDI-TOF analysis according to the operating parameters during the thermal reaction. The MALDI-TOF spectrum was normalized to observe the variation in the MWD by Anthracene (178Da) as a pseudo-component. Range 2–3 and range 6–8 in the MWD coincided with the trends of the pitch yield and the softening point, respectively. The results suggested that pitch yield is related to the PAHs with 2–6 aromatic rings and that the softening point is related to highly condensed PAHs with more than 6 aromatic rings. The anisotropy/isotropy of the pitch was analyzed by polarized light microscopy. The pitch produced under the pressurized condition was isotropic. However, the pitch produced under atmospheric pressure exhibited a well-oriented domain texture. We concluded that volatile contents disturb the polymerization and condensation of PAHs because of side reactions involving the aliphatic contents.

Characterization and tribologic study in high vacuum of hydrogenated DLC films deposited using pulsed DC PECVD system for space applications

This paper focuses on diamond-like carbon (DLC) films for space applications. Specifically, it reports the structure, morphology, adhesion, and the high-vacuum tribological performance of several DLC films with different hydrogen content. DLC films have been studied as a promising solid lubricant since liquid lubricants are ineffective and undesirable for many space applications. The films were deposited by pulsed Direct Current Plasma Enhanced Chemical Vapor Deposition (DC PECVD) technique with an additional cathode. An amorphous silicon interlayer was deposited in order to guarantee the adhesion between DLC coating and substrate. For the films characterization, Raman spectroscopy, Scanning Electron Microscopy (SEM), Rockwell C indentation test, and Ion Beam analysis (IBA) were performed. Additionally, the friction coefficient was measured in high vacuum and atmospheric conditions. Results showed that the increase of the deposition voltage led to the decrease of hydrogen content of the films and the increase of DLC films hardness. Furthermore, films deposited at −200V, −300V, and −400V showed a decrease in their friction coefficients under high vacuum conditions when compared to their friction coefficients at atmospheric ambient conditions. Moreover, DLC films produced with the highest hydrogen content presented lower friction coefficients under high vacuum rather than in ambient conditions. These results demonstrated that DLC films deposited by the DC PECVD technique with additional cathode have tribological properties that enable their use in space applications. This work also validated that the use of an additional cathode represents an improvement of the DC PECVD technique. Consequently, films with higher adhesion, hardness, and hydrogen content can be produced.

Diamond-like carbon film preparation using a high-repetition nanosecond pulsed glow discharge plasma at gas pressure of 1 kPa generated by a SiC-MOSFET inverter power supply

A high-repetition nanosecond pulsed glow discharge plasma at a gas pressure of 1 kPa was generated using a SiC-MOSFET inverter power supply for diamond-like carbon (DLC) film preparation. At a high repetition frequency above 50 kHz, the period of the nanosecond voltage pulse became shorter than the decay time of the afterglow plasma, and many ions and radicals remained in the gap space. The deposition rate was 0.1 µm/min, which was 5 times higher than that of a conventional plasma CVD process. An increase in hardness to 13 GPa and a decrease in hydrogen content in the DLC film were confirmed by increasing the repetition frequency to 200 kHz.

Analysis of the Chemical Structure in a Nonpremixed H 2 /N 2 Flame Using Large Eddy Simulation with Detailed Chemistry

Abstract This paper presents numerical studies of flame structure in a well-known nonpremixed H 2 /N 2 jet flame. A detailed kinetic mechanism is implemented to large eddy simulation approach with linear eddy model as subgrid closure method. The numerical techniques are validated against experimental data in temperature profiles, specie mass fractions and mixture fractions. Reaction rates are calculated at the flame base to investigate the dominant chemistry for a variety of conditions of fuel and coflow. The results show that the decrease of hydrogen concentration leads to chemical pathways changing at the flame base that is responsible for the autoignition. Oxygen content variation in the coflow affects the reaction rates but does not change the dominant chemistry. Furthermore, water addition to the coflow is found to enhance NO x formation by promoting radical production.

Hydrogenation behaviors and characteristics of bulk Ti–6Al–4V alloy at different isothermal temperatures

The bulk Ti–6Al–4V alloy was hydrogenated at the temperature range of 723–973 K, and the hydrogen absorption characteristics and hydrogen absorption kinetics were investigated. The results show that there are two types of hydrogen absorption characteristics at different temperatures. The hydrogen content decreases, and the time reaching reaction equilibrium is shorten with the isothermal hydrogenation temperature increasing. Meanwhile, the mechanism of the hydrogen absorption kinetics is different at different temperatures. The incubation period exists at the initial hydrogen absorption stage below 823 K, and K a2 (the reaction rate constant of Stage 2) ≫ K a1 (the reaction rate constant of Stage 1). And there is no incubation period over 823 K, K a1 ≫ K a2.

Dehydrogenation-hydrogenation characteristics of nanocrystalline Mg2Ni powders compacted by high-pressure torsion

High-pressure torsion technique was applied on nanocrystalline Mg2Ni powders to produce bulk disks by simultaneous uniaxial compression and severe shear deformation. The hydrogen absorption and desorption behavior of the disks has been characterized by high-pressure calorimetry. During desorption, the decomposition of the Mg2NiH4 phase takes place, which is followed by the dehydrogenation of Mg2NiH0.3 solid solution. In order to monitor the sorption properties in details, partially dehydrogenated states of the fully absorbed disk have been performed by interrupting the desorption process at 75%, 50% and 25% hydrogen contents in a Sieverts' type apparatus. Microstructural evolution during dehydrogenation has been investigated by X-ray diffraction. The variation of average crystallite size, lattice parameters and unit cell of the competing phases has been determined by the Rietveld refinement method of X-ray diffractograms. The unit cell volume of the Mg2NiH0.3 hydride solid solution decreases with decreasing hydrogen content. Coupled differential scanning calorimetry and thermogravimetry measurements were also taken on the partially desorbed states in order to determine the activation energy of hydrogen release.

Structure and mechanical properties of oxygen doped diamond-like carbon thin films

In this study, structure and mechanical properties of doped diamond-like carbon (DLC) films with oxygen were investigated. A mixture of methane (CH4), argon (Ar) and oxygen (O2) was used as feeding gas, and the RF-PECVD technique was used as a deposition method. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by Stoney equation. The XPS and ERDA-RBS results indicated that by increasing the oxygen in the feeding gas up to 5.6vol.%, the incorporation of oxygen into the films' structure was increased. The ratio of sp2 to sp3 sites was changed by the variation of oxygen content in the film structure. The sp2/sp3 ratios are 0.43 and 1.04 for un-doped and doped DLC films with 5.6vol.% oxygen in the feeding gas, respectively. The Raman spectroscopy (RS) results showed that by increasing the oxygen content in doped DLC films, the amount of sp2 CC aromatic bonds was raised and the hydrogen content reduced in the structure. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the decrease of hydrogen content and the increase the ratio of CC aromatic to olefinic bonds. Hardness and residual stress of the films were raised by increasing the oxygen content within the films' structure. The maximum hardness (19.6GPa) and residual stress (0.29GPa) were obtained for doped DLC films, which had the maximum content of oxygen in structure, while the minimum hardness (7.1GPa) and residual stress (0.16GPa) were obtained for un-doped DLC films. The increase of sp3 CC bonds between clusters and the decrease of the hydrogen content, with a simultaneous increase of oxygen in the films' structure is the reason for increase of hardness and residual stress.

Impact sensitivity of energy systems based on nanoporous silicon and oxidant: influence of the hydrogen content and specific surface

The impact sensitivity of the energy systems based on nanoporous silicon, obtained by electrochemical etching of monocrystalline silicon wafers in an HF-containing electrolyte, and calcium perchlorate was studied using a modified Weller—Ventselberg technique (estimation of the impact sensitivity of initiating explosives). The impact sensitivity of these systems is shown to be determined by both the presence of hydrogen, which is stored on the porous silicon surface during the preparation of the latter, and also the influence of other factors, including the specific surface of porous silicon. The composition, amount of the generated gas, and gas evolution rate during nonisothermal and isothermal calcination of porous silicon in a temperature range of 60—120 °С were determined using methods of thermal gravimetry (TG), measurement of the gas volume, and mass spectrometry. The generated gas almost completely consists of hydrogen, and its content in the studied samples of porous silicon achieved ~3.8 wt.%. The calculated activation energy of the hydrogen evolution process in vacuo was 103.7±3.3 kJ mol–1. The dependences of the impact sensitivity of the energy composition based on porous silicon and heat of combustion of porous silicon on oxygen on the hydrogen content were established. The impact sensitivity of the energy system decreases with a decrease in the hydrogen content in porous silicon and its specific surface.

Effects of hydrogen pressure on hydrogenated amorphous silicon thin films prepared by low‐temperature reactive pulsed laser deposition

We deposit intrinsic hydrogenated amorphous silicon (a‐Si:H) thin films by reactive pulsed laser deposition, for various hydrogen pressures in the 0–20 Pa range, at a low deposition temperature of 120 °C, and investigate the hydrogen incorporation, structural, optical, and electrical properties of the films, as a function of the ambient hydrogen pressure. The film thickness decreases linearly as the hydrogen pressure increases. The hydrogen content of the films is determined by infrared spectroscopy and the optical bandgap from UV‐Vis‐NIR transmittance and reflectance measurements. Electric measurements yield the dark conductivity of the films. The hydrogen concentration of the films lies in the 1021–1022cm–3 range and increases with the hydrogen pressure until the latter reaches 15 Pa, beyond which the hydrogen concentration decreases. The optical bandgap and dark conductivity follow the hydrogen concentration variation of the films. The dark conductivity lies in the 10–9–10–10S/cm range. An unusually wide optical bandgap of 2.2–2.6 eV is observed.