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At least 451 records · Page 25

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DOE OSTI2021

Simulation of 12-bed vacuum pressure-swing adsorption for hydrogen separation from methanol-steam reforming off-gas

This study focuses on analysis of a 12-bed vacuum pressure-swing adsorption (VPSA) process capable of purifying hydrogen from a ternary mixture (H 2 /CO 2 /CO 75/24/1 mol%) derived from methanol-steam reforming. The process produces 9 kmol H 2 /h with less than 2 ppm and 0.2 ppm of CO2 and CO, respectively, to supply a polymer electrolyte membrane fuel cell. The process model is developed in Aspen Adsorption® using the “uni-bed” approach. A parametric study of H 2 purity and recovery with respect to adsorption pressure, adsorbent height, activated carbon:zeolite ratio, feed composition, and number of beds is performed. Results show 12-bed VPSA can meet the H 2 purity goals, with H 2 recovery as high as 75.75%. Adsorption occurs at 7 bar, the column height is 1.2 m, and the adsorbent ratio is 70%:30%. Furthermore, a 4-bed VPSA can achieve the same purity goals as the 12-bed process, but H 2 recovery decreases to 61.34%.

03 NATURAL GAS↗

NASA NTRS1988

Tripropellant combustion process

The addition of small amounts of hydrogen to the combustion of LOX/hydrocarbon propellants in large rocket booster engines has the potential to enhance the system stability. Programs being conducted to evaluate the effects of hydrogen on the combustion of LOX/hydrocarbon propellants at supercritical pressures are described. Combustion instability has been a problem during the development of large hydrocarbon fueled rocket engines. At the higher combustion chamber pressures expected for the next generation of booster engines, the effect of unstable combustion could be even more destructive. The tripropellant engine cycle takes advantage of the superior cooling characteristics of hydrogen to cool the combustion chamber and a small amount of the hydrogen coolant can be used in the combustion process to enhance the system stability. Three aspects of work that will be accomplished to evaluate tripropellant combustion are described. The first is laboratory demonstration of the benefits through the evaluation of drop size, ignition delay and burning rate. The second is analytical modeling of the combustion process using the empirical relationship determined in the laboratory. The third is a subscale demonstration in which the system stability will be evaluated. The approach for each aspect is described and the analytical models that will be used are presented.

Kmiec, T. D.↗

NASA NTRS2011

Visual hydrogen detector with variable reversibility

Methods, processes and compositions are provided for a visual or chemochromic hydrogen-detector with variable or tunable reversible color change. The working temperature range for the hydrogen detector is from minus 100.degree. C. to plus 500.degree. C. A hydrogen-sensitive pigment, including, but not limited to, oxides, hydroxides and polyoxo-compounds of tungsten, molybdenum, vanadium, chromium and combinations thereof, is combined with nano-sized metal activator particles and preferably, coated on a porous or woven substrate. In the presence of hydrogen, the composition rapidly changes its color from white or light-gray or light-tan to dark gray, navy-blue or black depending on the exposure time and hydrogen concentration in the medium. After hydrogen exposure ceases, the original color of the hydrogen-sensitive pigment is restored, and the visual hydrogen detector can be used repeatedly. By changing the composition of the hydrogen-sensitive pigment, the time required for its complete regeneration is varied from a few seconds to several days.

Muradov, Nazim↗

NASA NTRS2012

Visual hydrogen detector with variable reversibilty

Muradov, Nazim Z.↗

NASA NTRS2014

Methods of Forming Visual Hydrogen Detector with Variable Reversibility

Methods, processes and compositions are provided for a visual or chemochromic hydrogen-detector with variable or tunable reversible color change. The working temperature range for the hydrogen detector is from minus 100 C to plus 500 C. A hydrogen-sensitive pigment, including, but not limited to, oxides, hydroxides and polyoxo-compounds of tungsten, molybdenum, vanadium, chromium and combinations thereof, is combined with nano-sized metal activator particles and preferably, coated on a porous or woven substrate. In the presence of hydrogen, the composition rapidly changes its color from white or light-gray or light-tan to dark gray, navy-blue or black depending on the exposure time and hydrogen concentration in the medium. After hydrogen exposure ceases, the original color of the hydrogen-sensitive pigment is restored, and the visual hydrogen detector can be used repeatedly. By changing the composition of the hydrogen-sensitive pigment, the time required for its complete regeneration is varied from a few seconds to several days.

Muradov, Nazim Z.↗

NASA NTRS1975

Fractography of the high temperature hydrogen attack of a medium carbon steel

Microscopic fracture processes were studied which are associated with hydrogen attack of a medium carbon steel in a well-controlled, high-temperature, high-purity hydrogen environment. Exposure to a hydrogen pressure and temperature of 3.5 MN/m2 and 575 C was found to degrade room temperature tensile properties with increasing exposure time. After 408 hr, yield and ultimate strengths were reduced by more than 40 percent and elongation was reduced to less than 2 percent. Initial fissure formation was found to be associated with manganese rich particles, most probably manganese oxide, aligned in the microstructure during the rolling operation. Fissure growth was found to be associated with a reduction in carbide content of the microstructure and was inhibited by the depletion of carbon. The interior surfaces of sectioned fissures or bubbles exhibit both primary and secondary cracking by intergranular separation. The grain surfaces were rough and rounded, suggesting a diffusion-associated separation process. Specimens that failed at room temperature after exposure to hydrogen were found to exhibit mixed mode fracture having varying amounts of intergranular separation, dimple formation, and cleavage, depending on exposure time.

Melson, H. G.↗

NASA NTRS1991

Computational modeling of the pressurization process in a NASP vehicle propellant tank experimental simulation

A multidimensional computational model of the pressurization process in a slush hydrogen propellant storage tank was developed and its accuracy evaluated by comparison to experimental data measured for a 5 ft diameter spherical tank. The fluid mechanic, thermodynamic, and heat transfer processes within the ullage are represented by a finite-volume model. The model was shown to be in reasonable agreement with the experiment data. A parameter study was undertaken to examine the dependence of the pressurization process on initial ullage temperature distribution and pressurant mass flow rate. It is shown that for a given heat flux rate at the ullage boundary, the pressurization process is nearly independent of initial temperature distribution. Significant differences were identified between the ullage temperature and velocity fields predicted for pressurization of slush and those predicted for pressurization of liquid hydrogen. A simplified model of the pressurization process was constructed in search of a dimensionless characterization of the pressurization process. It is shown that the relationship derived from this simplified model collapses all of the pressure history data generated during this study into a single curve.

Sasmal, G. P.↗

DOE OSTI2024

Comparison of Silicon Decarbonization Methods to Reduce Process Emissions and Energy Consumption

The demand for silicon is rising due to its use in solar cells, electronics, and alloying as part of the green transition. However, these products require silicon metal (metallurgical grade silicon, >98% Si) as their main raw material before undergoing further chemical refining, usually via gas phase in methods such as the Siemens process. Silicon metal is currently produced in a submerged arc furnace via carbothermic reduction of quartz, which results in 10-12 tCO2/tSi. More than 40% of these emissions are process emissions, meaning they do not include contributions from electricity generation or transport. This talk will discuss promising methods to reduce or eliminate these process emissions. These include the use of biocarbon and carbon capture, aluminothermic reduction, electrochemical reduction with molten salts, and use of hydrogen in a modified Siemens process. Biocarbon and carbon capture is a straightforward method to reduce the net carbon emissions of the process, but long-term sustainable production of high-quality charcoal is a challenge. Aluminothermic reduction makes good use of aluminum byproducts such as dross but is perhaps limited in its applications to aluminum-silicon alloy products. Electrochemical reduction is promising as a method of producing high purity Si from quartz, without further need for the Siemens process, but is still in early stages of research and slow processing times are a concern. Finally, the use of hydrogen in a modified Siemens process would also result in a high purity Si product from quartz, however the process has considerable logistical challenges with corrosive and unstable gases at high temperatures. This talk will further expand on the potential merits and challenges of each method, while comparing their potential to reduce emissions and/or energy consumption while meeting global demand.

decarbonization↗

DOE OSTI2025

Plasma-free hydrogenation of oxygen-terminated polycrystalline diamond as determined by circular transmission line measurements (CTLM)

Here, we developed a process to fully hydrogen-terminate diamond by annealing in forming gas. The surface was characterized using circular transmission line measurements (CTLMs) to evaluate the onset and degree of hydrogen termination. No hydrogenation occurred at temperatures at or below 500 °C. Hydrogenation occurs after annealing for 5 min at temperatures between 600 and 1000 °C, with complete hydrogenation achieved at 1000 °C, which showed the same sheet resistance as diamond terminated in a hydrogen plasma. Annealing at temperatures lower than 1000 °C resulted in only partial hydrogenation but can be compensated by increasing the anneal time. At temperatures exceeding 1100 °C, the sheet resistance suddenly and drastically increases, indicating instability of a hydrogen-terminated diamond surface at elevated temperatures under forming gas. The activation energy was determined to be 1.20eV. SEM inspection showed that annealing in hydrogen produced significantly reduced surface roughness compared to diamond surfaces hydrogenated in a H 2 plasma.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Origins of hydrogen that passivates bulk defects in silicon heterojunction solar cells

Silicon heterojunction solar cell fabrication incorporates a significant amount of hydrogen into the silicon wafer bulk, and the amount of injected hydrogen is comparable to that introduced by silicon nitride films during a high-temperature firing step. In this work, the origins of the hydrogen injected during heterojunction cell processing have been identified. We demonstrate that the hydrogen plasma treatment that is routinely included to improve surface passivation considerably increases the hydrogen concentration in the wafers. We also show that the hydrogenated amorphous silicon i/p+ stack is more effective than the i/n+ stack for bulk hydrogen incorporation, and both are more effective than intrinsic films alone.

Sun, Chang (ORCID:0000000282140458)↗

DOE OSTI2021

Modeling DWPF Hydrogen Gas Retention and Release

Savannah River Remediation (SRR) currently manages the risk for retained hydrogen in the Defense Waste Processing Facility (DWPF) vessels by implementing a Retained Hydrogen Program. The current program conservatively relies on bounding assumptions concerning gas release and retention to develop allowable vessel Q-times. SRR would like to establish more realistic inputs to the Retained Hydrogen Program. To address this need, SRNL conducted a literature search on work investigating the retention and release of gas from DWPF type slurries. The search revealed that the retained hydrogen is not released instantaneously upon the start of agitation, and that hydrogen gas could be released under quiescent, non-agitated, conditions. The literature search also identified a Lattice-Boltzmann computational fluid dynamics (CFD) software that could model and predict hydrogen release from DWPF vessels. SRR requested that Savannah River National Laboratory (SRNL) personnel pursue this software and focus the model for hydrogen gas retention and release to justify relaxing these conservative assumptions. This report documents the refinement of the CFD software model and application to show its ability to describe retained hydrogen release from DWPF vessels and relax the conservativisms in the Retained Hydrogen Program.

08 HYDROGEN↗

NASA NTRS1961

Gas Requirements in Pressurized Transfer of Liquid Hydrogen

Of late, liquid hydrogen has become a very popular fuel for space missions. It is being used in such programs as Centaur and Saturn. Furthermore, hydrogen is the ideal working fluid for nuclear powered space vehicles currently under development. In these applications, liquid hydrogen fuel is generally transferred to the combustion chamber by a combination of pumping and pressurization. The pump forces the liquid propellant from the fuel tank to the combustion chamber; gaseous pressurant holds tank pressure sufficiently high to prevent cavitation at the pump inlet and to maintain the structural rigidity of the tank. The pressurizing system, composed of pressurant, tankage, and associated hardware can be a large portion of the total vehicle weight. Pressurant weight can be reduced by introducing the pressurizing gas at temperatures substantially greater than those of liquid hydrogen. Heat and mass transfer processes thereby induced complicate gas requirements during discharge. These requirements must be known to insure proper design of the pressurizing system. The aim of this paper is to develop from basic mass and energy transfer processes a general method to predict helium and hydrogen gas usage for the pressurized transfer of liquid hydrogen. This required an analytical and experimental investigation, the results of which are described in this paper.

GAS↗

DOE OSTI2025

Atomically Fine-Tuning Organic–Inorganic Carbon Molecular Sieve Membranes for Hydrogen Production

Polymeric membranes with great processability are attractive for the H 2 /CO 2 separation required for hydrogen production from renewable biomass with carbon capture for utilization and sequestration. However, it remains elusive to engineer polymer architectures to obtain desired sub-3.3 Å ultramicropores to efficiently sieve H 2 from CO 2 . Herein, we demonstrate a scalable way of carbonizing polybenzimidazole (PBI) at low temperatures, followed by vapor phase infiltration (VPI) to atomically narrow ultramicropores throughout the films, forming hybrid organic–inorganic carbon molecular sieves (CMSs). One VPI cycle (100 s) for the PBI carbonized at 500 °C remarkably increases H 2 /CO 2 selectivity from 9.6 to 83 at 100 °C, surpassing Robeson’s upper bound. The CMS demonstrates a stable H 2 /CO 2 separation performance when challenged with simulated syngas streams and can be fabricated into thin-film composite membranes, outperforming state-of-the-art membranes. Finally, the scalable approach can be ubiquitous to molecularly fine-tune ultramicropores of leading polymeric membranes to further improve their size-sieving ability and thus separation efficiency.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Studies of CO2 hydrogenation over cobalt/ceria catalysts with in situ characterization: the effect of cobalt loading and metal-support interactions on the catalytic activity

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99 GENERAL AND MISCELLANEOUS↗

NASA NTRS1974

Properties of dispersion-strengthened chromium - 4-volume-percent-thoria alloys produced by ball milling in hydrogen iodide

The effects of processing variables on the tensile properties and ductile-to-brittle transition temperature (DBTT) of Cr + 4 vol. %ThO2 alloys and of pure Cr produced by ball milling in hydrogen iodide were investigated. Hot rolled Cr + ThO2 was stronger than either hot pressed Cr + ThO2 or pure Cr at temperatures up to 1537 C. Hot pressed Cr + ThO2 had a DBTT of 501 C as compared with minus 8 to 24 C for the hot rolled Cr + ThO2 and with 139 C for pure Cr. It is postulated that the dispersoid in the hot rolled alloys lowers the DBTT by inhibiting recovery and recrystallization of the strained structure.

Arias, A.↗

NASA NTRS1975

Production of chromium base alloys by ball milling in hydrogen iodide

The effects of processing variables on the tensile properties and ductile-to-brittle transition temperature (DBTT) of Cr + 4 vol% ThO2 alloys and of pure Cr produced by ball milling in hydrogen iodide were investigated. Hot rolled Cr + ThO2 was stronger than either hot pressed Cr + ThO2 or pure Cr at temperatures up to 1540 C. Hot pressed Cr + ThO2 had a DBTT of 500 C as compared with -8 to 24 C for the hot rolled Cr + ThO2 and with 140 C for pure Cr. It is postulated that the dispersoid in the hot rolled alloys lowers the DBTT by inhibiting recovery and recrystallization of the strained structure.

Arias, A.↗

DOE OSTI2025

Manipulation of intramolecular hydrogen bonds in conjugated pseudoladder polymer for semiconductivity and solution-processability

The conformational coplanarity and local rigidity of π-conjugated backbones are critical for the semiconducting performance of organic electronic materials. The conformational coplanarity and local rigidity of π-conjugated backbones are critical for the semiconducting performance of organic electronic materials. While fusing the aromatic system into a ladder-type structure effectively enhances these properties, it also often results in poor solution processability and hence limits their transition to device application. To address this challenge, an intramolecularly hydrogen-bonded pseudoladder polymer (HPLP) system based on alternating hydrogen bond donating benzobisimidazole (BBI) and hydrogen bond accepting benzodifuran (BDF) units, is designed and synthesized. A Boc-protected precursor of HPLP allows for feasible solution processing of the polymer into thin films. Subsequently, in situ thermal Boc-deprotection generates the HPLP polymer, in which intramolecular hydrogen bonds form between each pair of neighboring repeating units, inducing coplanarity and rigidity throughout the entire backbone. This process is accompanied by a significant red-shift of the absorption spectrum, reduced bandgap, and enhanced rigidity, as confirmed by NMR, UV-Vis, and density functional theory analyses. HPLP films exhibit a three-order-of-magnitude enhancement in charge carrier mobility compared to the Boc-protected precursor and demonstrate excellent solvent resistance in organic thin-film transistors.

Miranda, Octavio↗

NASA NTRS2000

PROPULSE 980: A Hydrogen Peroxide Enrichment System

The PROPULSE 980 unit is a transportable processing plant that enriches aerospace grade hydrogen peroxide from 90% to 98% final concentration. The unit was developed by Degussa-H Is, in cooperation with Orbital, NASA Marshall Space Center, and NASA Stennis Space Center. The system is a self-contained unit that houses all of the process equipment, instrumentation and controls to perform the concentration operation nearly autonomously. It is designed to produce non-bulk quantities of 98% hydrogen peroxide. The enrichment unit design also maintains system, personnel and environmental safety during all aspects of the enrichment process and final product storage. As part of the Propulse 980 checkout and final buyoff, it will be disassembled at the Degussa-H Is Corporation plant in Theodore, AL, transported to the Stennis Space Center, reassembled and subjected to a series of checkout tests to verify design objectives have been met. This paper will summarize the basic project elements and provide an update on the present status of the project.

Boxwell, Robert↗