First-principles study on the dissolution and diffusion behavior of hydrogen in carbide precipitates

To understand the hydrogen (H) behavior in the carbide precipitates, the dissolution and diffusion properties of interstitial H in the transition metal carbide (TMC; TM = Hf, Nb, Ta, Ti, V, and Zr) were studied by first-principles calculations. In these carbides, it can be seen that H tends to occupy the trigonal site (tri2-site) surrounded by three transition metal atoms and one carbon atom rather than the face center (fc-site) and the body center (bc-site) which with the larger space. We found that the bonding interaction between H atom and the nearest-neighbor (1NN) carbon atom is the dominant influence on the stability of H dissolution. Besides, we obtained the temperature-dependent solubility and diffusion coefficients of H in TMC and pure vanadium through Sievert's law and transition state theory. Compared with pure vanadium, H shows the worse solubility in TMC, and it is more difficult for hydrogen to migrate in TMC, but segregate toward the interface. Furthermore, it is interesting to note that, the diffusion barrier and the H solution energy show a linear relationship for transition metal carbides in the same period. These results can help us deepen the understanding of H behavior in vanadium alloys strengthened by carbide precipitates, and furtherly providing the theoretical guidance for the design of alloys with excellent performance.     

A comparative study on the performance of M (Rh,Ru, Ni)-promoted metallurgical waste driven catalysts for H2 production by glycerol steam reforming

A comprehensive study was conducted on the performance of M-promoted (M = 1%Ru, 1%Rh, 5%Ni) upgraded slag oxide metallurgical waste catalysts (M-UGSO) for hydrogen production by glycerol steam reforming (GSR). The results confirmed that the tendency of the incorporated metal to interact with Mg/Fe containing species within UGSO plays a key role in the surface availability of the corresponding metal, structural changes after reduction, and catalyst stability. Aside its best stability, 5% Ni-UGSO showed a performance (glycerol conversion to gaseous products of 100% and H₂ yield of 74%) comparable with 1% Rh-UGSO (100% and 78%, respectively) or even surpassing that of 1% Ru-UGSO (94% and 71%, respectively), as noble metal-based catalysts. Synergistic cooperation was achieved by incorporated metals (M) and Fe/Mg containing species within UGSO, resulting in enhanced glycerol and water activation. The weakest results of Ru-UGSO could be justified by lack of propensity for MgO–RuO₂ interaction on UGSO surface.     

Molecular dynamic investigation on sulfur migration during hydrogen production by benzothiophene gasification in supercritical water

Benzothiophene (BT) is a key sulfur-containing intermediate product in the thermal conversion process of coal and heavy oil. The migration process of the sulfur element may affect the thermal utilization design of BT. In this paper, BT was used as a model compound to simulate the supercritical water gasification (SCWG) process by molecular dynamics with a reactive force field (ReaxFF) method, and the laws of hydrogen production and sulfur migration mechanisms were obtained. Increasing the molecule number of supercritical water (SCW) and increasing the reaction temperature can enhance the generation of hydrogen and promote the conversion of organic sulfur to inorganic sulfur. Water was the main source of H₂, and H₂S was the main gaseous sulfur-containing product. SCW had a certain degree of oxidation due to a large number of hydroxyl radicals, which could increase the valence of sulfur. The conversion process of BT in SCW was mainly divided into four stages, including thiophene ring-opening; sulfur separation or carbon chain broke with sulfur retention; carbon chain cleaved, and gas generation. The lumped kinetic parameters of the conversion of sulfur in BT to inorganic sulfur were calculated, and the activation energy was 369.98 kJ/mol, which was much lower than those under pyrolysis conditions. This article aims to clarify the synergistic characteristics of hydrogen production and sulfur migration in the SCWG process of BT from the molecular perspective, which is expected to provide a theoretical basis for pollutant directional removal during hydrogen production by sulfur-containing organic matters in SCW.     

Experimental investigation on the dynamic responses of vented hydrogen explosion in a 40-foot container

To investigate the structural dynamics of a container subjected to a vented hydrogen explosion, 48 field tests were conducted in a 40-foot container with roof vents and an end vent. The effects of the hydrogen concentration, ignition position, and obstacles on the evolution of the dynamic responses were investigated. Three stages were generally observed for displacements: (1) At the stage of the vent rupture, the displacement could be approximated as a quasi-static response, and there was a linear relationship between the peaks of positive overpressure and displacement. (2) Structural deformation appeared as reciprocating vibration at the stage of Helmholtz oscillation. (3) The structure exhibited relatively weak irregular fluctuation when high-frequency acoustic oscillation occurred. Two types of the structural acceleration with low and high amplitudes resulting from Helmholtz oscillation and acoustic oscillation, respectively, were clearly observed. For the end-vented explosion, multiple peaks were observed for the displacement at the quasi-static stage due to the rupture, discharge, and external explosion. Moreover, the displacement was sensitive to hydrogen concentration, whereas the number of obstacles and the ignition position had significant influences on the peak acceleration for roof venting. This work conducted the fundamental explanation for the evolution law of structural responses induced by vented hydrogen explosions from the perspective of structural dynamics and enriched the experimental accumulation in a large-scale container with congestion in this field.     

Concise dynamic model to accurately calculate the hydrogen yield during the reaction process

Estimation of hydrogen production rate and the total amount hydrogen during any reaction process require an accurate and concise dynamic model to describe the variation of hydrogen production rate with reaction time. There must be two comprehensive features of such model, the first one is that the hydrogen production rate calculated by this model is zero at the initial time is zero and the second one is that the integration of this model over time result in an explicit function. In this paper, we present a comprehensive model which meets above two requirements via amendments to the shifted logistic model. The model is validated against measured results through comparison of 25 experimental and theoretical hydrogen production rate. The experimentally validated model is used to calculate the total amount hydrogen during each reaction process. The impact of some experimental conditions on the total hydrogen production was mathematically explained for the first time, and this result reveal the excellent predictive ability of framework suggested in this paper. In addition, that is for an experimental condition history, predictions are achieved by developing a set of “secondary models” that describe some experimental conditions dependence of the “primary models” parameters. The method to obtain the parameters in “secondary models” described in this paper indicated that another major departure from the conventional models is the notion that the “secondary models” do not need to follow any preconceived formula and that they can be derived solely from the observed growth patterns. The presented framework can help the hydrogen production industry.     

Mild hydrogen production from the hydrolysis of Al–Bi–Zn composite powder

The development of mild hydrogen-generating materials is of great significance to improve the working life of hydrogen–oxygen fuel cells. In this study, Al–Bi–Zn composite powders were designed by phase diagram calculation and then prepared via the gas atomization method. The results indicated that the conversion yield of Al–12Bi–7Zn (wt.%) powder reached 98% with stable hydrogen production within 280 min at 50 °C. When composite powder reacted with NaCl solution to produce hydrogen, the dormant period of the reaction process was significantly shortened, but the conversion rate was slightly reduced. Additionally, the evolution of powder morphology during the reaction was investigated. The results showed that the continuous cracking of the powder led to the continuous exposure of fresh Al to react.     

Application of a multicriteria methodology for evaluation of energy alternatives for hydrogen production for the automotive sector – Case study

This paper presents a case study focusing on fourteen most used energy alternatives in Brazil, possible to feed large scale hydrogen production plants for the automotive sector. The evaluations are made using a Decision Making Support Method, MACBETH - Measuring Attractiveness by a Categorical Based Evaluation Technique, with the computational code M-MACBETH 3.2.0, using criteria that include economic and financial, technological, environmental and social aspects. The selected criteria that were used in the assessment, for each of the energy alternatives are capital to be invested in a plant, leveled cost of electric energy produced, CO₂ emissions, mortality rate due to the technology use and energy efficiency of technology. The main results obtained showed that photovoltaics off grid electric energy is the most attractive alternative, followed by the photovoltaic on grid alternative, for an eventual automotive hydrogen program in Brazil.     

The effect of fertilizer nitrogen input to grass-clover swards and calving date on the productivity of pasture-based dairy production

The objective of this systems-scale study was to investigate grazing season timeframes on pasture and milk production and on milk processability of dairy systems with compact spring-calving dairy cows grazing white clover (Trifolium repens L.) based grassland. Fifty-four primiparous and multiparous Holstein-Friesian dairy cows were used in a one-factor study with 3 systems (n = 18) and repeated over 2 yr (2008/09 and 2009/10). The 3 systems were: early spring calving with annual fertilizer N input of 100 kg·ha^?1 applied in spring (ES100N; 2.1 cows·ha^?1; grazing February to November), early spring calving without fertilizer N (ES0N; 1.6 cows·ha^?1; grazing February to November) and late spring calving without fertilizer N (LS0N; 1.53 cows·ha^?1; grazing April to January). Annual pasture production was affected by an interaction between grazing system and year: Mean annual pasture yields for 2008 and 2009 were ES100N; 10.35 and 9.88, ES0N; 8.88 and 8.63, LS0N; 9.18 and 10.31 t of dry matter (DM)·ha^?1 (SEM 0.39). LS0N had higher pasture DM yield in 2009 due to higher clover DM production and biological N fixation compared with the other systems. Clover stolon and root mass in the following February was correlated with stolon and root mass in the previous November with 64% of stolon mass present on LS0N in February (R² = 0.84). There were no detectable differences in per-lactation milk yield (6,335 kg·cow^?1), fat, protein and lactose yields (271, 226, 297 kg·cow^?1, respectively), cow liveweight (585 kg) or body condition score (3.02). Although winter grazing favored subsequent clover DM production, biological N fixation and pasture DM production, delaying calving date in spring and extending lactation into the following winter led to inefficient use of this pasture by the grazing herd and lowered the quality of late-lactation milk for processing purposes. Hence, a mean calving date in mid- to late-February is recommended for zero-fertilizer N input clover-based grassland.     

Comparison of thermophilic and hyperthermophilic dark fermentation with subsequent mesophilic methanogenesis in expanded granular sludge bed reactors

Herein, dark fermentation (DF, V = 5.5 L) and subsequent mesophilic methanogenesis (V = 43.5 L) are run as expanded granular sludge bed reactors (EGSB) at thermophilic (υDF = 60 °C) and hyperthermophilic (υDF = 80 °C) temperatures. A synthetic glucose wastewater is run with a 22.5 g/L chemical oxygen demand (COD) and 48–9 h hydraulic retention times (HRTs), giving organic loading rates (OLRs) of 11–60 g COD/L/d for DF. The maximum hydrogen production rate (HPR) is HPR = 3.0 m³/m³/d for HRT = 9 h with a 50 L/kg COD hydrogen yield (HY) and 40 vol% H₂. Methane production rate (MPR) reaches MPR = 2.6 m³/m³/d with 70 vol% CH₄ at HRT = 2.8 d. The highest H₂ yields are HY = 180 L/kg COD with 53 vol% H₂ (thermophilic, HRT = 48 h). Hyperthermophilic temperatures led to lower HPRs (0.7 m³/m³/d) and MPRs (1.6 m³/m³/d). 53% of Thermoanaerobacterium thermosaccharolyticum as an H₂ producer are found. Discoloration of granular sludge from black to white and granule stability was observed in DF.