Thermal decomposition of LiAlH4 chemically mixed with Lithium amide and transition metal chlorides

Thermogravimetric analysis of LiAlH₄ chemically mixed with different additives is reported for the application of hydrogen storage. Here, we illustrated the dehydrogenation properties of combined LiAlH₄/LiNH₂ (2:1) mixture and LiAlH₄ wet-doped with different transition metals (Sc, Ti, and V) in their chloride forms. Thermal gravimetric analysis of LiAlH₄/LiNH₂ system released 7.9 wt.% of hydrogen in three decomposition steps at temperatures between 75 and 280 °C under a heating ramp of 5 °C min⁻¹. The LiAlH₄ doped with transition metals showed the decrease of decomposition temperature down to 30–40 °C for both 1st and 2nd dehydrogenation steps as compared to as-received LiAlH₄. The catalytic activity in lowering the dehydrogenation temperature of LiAlH₄ doped with transition metals increases in the order of pure LiAlH₄ < V < Ti < Sc. The X-ray diffraction analysis, field emission scanning electron microscopy, and Fourier transformation infra-red spectroscopy techniques were carried out in support of the thermogravimetric results.     

Effect of seeding on hydrogen and carbon particle production in a 10 MW solar thermal reactor for methane decomposition

Solar methane decomposition reactors are a novel technology for the production of carbon neutral hydrogen; however, the impact of this technology depends greatly on the ability to co-produce carbon black particles of commercial grade in order to offset the cost of hydrogen production and, therefore, the control of the reactor is very important. To this end, the seeding of indirect heating concept reactors using the product particles themselves could be used to control heat transfer inside the reactor. In this work, a previously developed one-dimensional reactor – particle population model was used to simulate the effect of seeding on the hydrogen and carbon particle production rates in the absorber tubes of a 10 MW indirect heating concept solar reactor. It was found that seed particle feed rates less than 10% of the methane-contained carbon feed rate allowed the hydrogen and fresh particle production rates to be doubled while keeping the rate of carbon growth on the tube walls constant. It was also found that similar seed fee rates could be used to maintain the hydrogen and particle production rates constant, given variations in the absorber tube wall temperature within a 100 °C range, for example due to cloud passage. Furthermore, it was found that the size characteristics of the freshly produced particles were not affected at these seed feed rates. Thus, seeding could be an effective means for increasing and controlling the hydrogen and carbon particle production rates in industrial scale indirect heating concept solar methane decomposition reactors, while also reducing carbon growth on the walls of the absorber tubes.     

Interaction of ZrMo2 with hydrogen at high pressure

The interaction of hydrogen with ZrMo₂ intermetallic compound at pressure up to 2500 bars has been studied. In ZrMo₂–H₂ system desorption isotherms were measured and thermodynamic parameters of hydride phase decomposition were calculated. The structure of ZrMo₂D_4.0 deuteride has been investigated by X-ray and neutron diffraction methods. It was revealed that ordering of deuterium in the cubic lattice of ZrMo₂ led to the formation of superstructure with tetragonal lattice. The occupancy of the positions of deuterium and metal atoms was determined.     

Analysis of a metal hydride reactor for hydrogen storage

In this paper a two-dimensional model of an annular cylindrical reactor filled with metal hydride suitable for hydrogen storage is presented. Comparison of the computed bed temperatures with published experimental data shows a reasonably good agreement except for the initial period. Effects of hydrogen pressure and external fluid temperatures on heat transfer and entropy generation are obtained. Results show that the time required for hydrogen charging and discharging is higher when the thermal capacity of the reactor wall is considered. The time required for absorption and desorption can be reduced significantly by varying the hydrogen gas pressure and external fluid temperatures. However, along with reduction in time the entropy generated during hydrogen storage and discharge increases significantly. Results also show that for the given input conditions, heat transfer between the external fluid and hydride bed is the main source of entropy generation.     

Production of hydrogen by partial oxidation with thermal plasma

The purpose of this paper is to investigate the characteristics and optimum operating conditions of the plasmatron-assisted CH₄ reforming reaction for the hydrogen-rich gas production. In order to increase the hydrogen production and the methane conversion rate, parametric screening study was conducted at various CH₄ flow ratio and steam flow ratio and with and without adding catalyst in the reactor. High-temperature plasma flame was made with air and arc discharge, and the air flow rate and the input power were set to 5.1  L/min and 6.4 kW, respectively.When the steam flow ratio was 30.2%, the hydrogen production was maximized and the optimal methane conversion rate was 99.7%. Under these optimal conditions, the following syngas concentrations were determined: H₂, 50.4%; CO, 5.7%; CO₂, 13.8%; and C₂H₂, 1.1%. H₂/CO ratio was 9.7 and the hydrogen yield was 93.7%.     

Development of a reaction mechanism for predicting hydrogen production from homogeneous decomposition of methane

In this paper, a reaction mechanism is developed to model the kinetics of hydrogen production from decomposition of methane. The pyrolysis of hydrocarbons from several combustion mechanisms is compared with experiment to obtain the elementary reactions of this mechanism. Some modifications are then made to reduce the large errors observed at a high residence time. Sensitivity analysis is performed to find the reactions with the highest effect on hydrogen production and their rate constants are changed by using other mechanisms to obtain the lowest error in hydrogen production compared to experimental data. This study shows that modifying the rate constants of the reactions of dissociation of methane to hydrogen and methyl radicals, and the formation of benzene from propargyl radicals have the highest effect on improving the results. The new mechanism reduces the error introduced from existing models for predicting the amount of hydrogen production up to 15%, depending on residence time and temperature levels.     

Phase field modeling of hydrogen transport and reaction in metal hydrides

The reaction of hydrogen with metals to form metal hydrides has numerous potential energy storage and management applications. The metal hydrogen system has a high volumetric energy density and is often reversible with a high cycle life. However, improving the often poor gravimetric performance of such systems through the use of lightweight metals usually comes at the cost of reduced reaction rates or the requirement of pressure and temperature conditions far from the desired operating conditions. Most studies of reaction kinetics of such systems focus on fitting low-dimensional kinetic models to measured rates and inferring the rate-limiting process based on the quality of the fit.     

Effect of nickel addition on the solubility of hydrogen in tantalum

A study of isothermal as well as isobaric P–C–T equilibrium measurements has been investigated for the solubility of hydrogen in tantalum and its alloys with nickel (1.7 and 4.9 atom % Ni) in the temperature range of 673–873 K and hydrogen pressure range of 0.60–1.20 atmospheres. The alloys were prepared by arc melting in an inert atmosphere. The dissolved hydrogen was within the solid solubility range corresponding to the temperature and followed the Sievert's law. The hydrogen solubility in tantalum decreased on the addition of nickel as an alloying element. The change in enthalpy and the change in entropy of solution for hydrogen in the tantalum metal and its alloys were calculated. The heat of reaction for hydrogen solution in all the samples was exothermic. The enthalpy of solution for hydrogen in the tantalum matrix increases on the addition of Ni as an alloying element.     

Analysis of hydrogen storage in metal hydride tanks introducing an induced phase transformation

Hydrogen absorption in a metal hydride tank is generally studied based on a heat and mass transfer analysis. The originality of this investigation is that the phase transformation from a solid (α phase) to hydride (β phase) solution is included in the hydrogen absorption mechanism. Toward this end, a modelling of the equilibrium pressure, composition (absorbed or desorbed hydrogen atoms per metal atoms), and isothermal curves of a LaNi₅ alloy is performed. Moreover, a kinetic model is developed taking into account the steps of hydrogen absorption and desorption (i.e., physisorption, chemisorption, surface penetration, nucleation and growth of the hydride phase and diffusion).     

Investigation of single-walled carbon nanotubes-titanium metal composite as a possible hydrogen storage medium

The present experimental work deals with the investigation of hydrogen uptake study of single-walled carbon nanotubes (SWCNTs-Ti)-titanium metal composite. The mixture containing SWCNTs and Ti powder is made into tablet by cold pressing. The composite has been prepared and hydrogenated by evaporating the tablet in hydrogen ambient on glass substrates using electron beam (EB) evaporation technique. Efficient hydrogen uptake of 4.74 wt.% is achieved with the composite and the adsorbed hydrogen posses the average hydrogen binding energy of 0.4 eV. The obtained hydrogen uptake is due to the cumulative adsorption of hydrogen by CNTs and Ti nanostructured materials. The physical properties are characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction study (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Raman analysis. Hydrogenation and dehydrogenation behavior of the composite are studied using CHN-elemental analysis and thermo gravimetric/thermal desorption spectroscopy (TG/TDS) studies, respectively. The stored hydrogen is found to be 100% reversible in the temperature range of 160–310 °C.     

Coupled hydrodynamic and kinetic model of liquid metal bubble reactor for hydrogen production by noncatalytic thermal decomposition of methane

Industrial-scale implementation of liquid metal bubble reactors (LMBRs) to produce hydrogen by methane decomposition will require large gas holdups (e.g., 20–30 vol%) and elevated gas pressures (>20 bar) to allow for practical reactor sizes. A realistic reactor design must account for the coupling between reaction kinetics and hydrodynamic effects. The gas holdup is predicted from the superficial gas velocity with a drift flux model that was experimentally corroborated in gas-molten metal mixtures. Large superficial gas velocities (>0.40 m s⁻¹) are required to achieve gas holdups of about 25 vol% in liquid metal baths (LMBs). A noncatalytic kinetic model is developed to provide thermodynamically consistent decomposition rates at methane conversions approaching equilibrium. The coupled model optimizes the LMB dimensions (diameter and length) and the inlet pressure to minimize the volume of liquid metal when the hydrogen production rate, bath temperature, methane conversion, metal composition, and maximum gas holdup are specified. For example, 200 kt a⁻¹ of hydrogen can be produced in an LMBR containing at least 96.5 m³ of molten tin held at 1100 °C in a bath measuring 3.50 m in diameter and 14.3 m in length, with an inlet methane pressure of 57.8 bar resulting in an average gas holdup of 29.7 vol% and a methane conversion of 65%.     

Phase stability and hydrogen desorption in a quinary equimolar mixture of light-metals borohydrides

The present study aims at investigating, for the first time, a quinary mixture of light-metals borohydrides. The goal is to design combinations of borohydrides with multiple cations in equimolar ratio, following the concept of high entropy alloys. The equimolar composition of the LiBH₄NaBH₄KBH₄Mg(BH₄)₂Ca(BH₄)₂ system was synthetized by ball milling. The obtained phases were analysed by X-ray diffraction and in-situ Synchrotron Radiation Powder X-ray Diffraction, in order to establish the amount of cations incorporated in the obtained crystalline phases and to study the thermal behaviour of the mixture. HP-DSC and DTA were also used to define the phase transformations and thermal decomposition reactions, leading to the release of hydrogen, that was detected by MS. The existence of a quinary liquid borohydride phase is reported for the first time. Effects of the presence of multi-cations compounds or a liquid phase on the hydrogen desorption reactions are described.     

Effect of low partial hydrogen in a mixture with methane on the mechanical properties of X70 pipeline steel

In this study, the effect of a low partial hydrogen in a mixture with natural gas on the tensile, notched tensile properties, and fracture toughness of pipeline steel X70 is investigated. An artificial HE aging is simulated by exposing the tested sample to the mixture gas condition for 720 h. In addition, a series of tests is conducted in ambient air and 10 MPa of 100% He and H₂. Overall, 10 MPa of 100% H₂ significantly degrades the mechanical properties of an X70 pipeline steel. However, it is observed that the 10 MPa gas mixture with 1% H₂ does not affect the mechanical properties when tested with a smooth tensile specimen. In the notched tensile test, a significant reduction in loss in the area is observed when tested with a notched specimen with a notch radius of 0.083 mm. It is also confirmed that a 10-MPa gas mixture with 1% H₂ causes a remarkable reduction in the toughness. The influence of the exposure time to 1% hydrogen in a mixture with natural gas was found to be minor.     

Solar thermal cracking of methane in a particle-flow reactor for the co-production of hydrogen and carbon

An experimental investigation on the thermal decomposition of CH₄ into C and H₂ was carried out using a 5 kW particle-flow solar chemical reactor tested in a solar furnace in the 1300–1600 K range. The reactor features a continuous flow of CH₄ laden with μm-sized carbon black particles, confined to a cavity receiver and directly exposed to concentrated solar irradiation of up to 1720 suns. The reactor performance was examined for varying operational parameters, namely the solar power input, seed particle volume fraction, gas volume flow rate, and CH₄ molar concentration. Methane conversion and hydrogen yield exceeding 95% were obtained at residence times of less than 2.0 s. A solar-to-chemical energy conversion efficiency of 16% was experimentally reached, and a maximum value of 31% was numerically predicted for a pure methane flow. SEM images revealed the formation filamentous agglomerations on the surface of the seed particles, reducing their active specific surface area.     

Analysis of hydrogen storage performance of metal hydride reactor with phase change materials

Using phase change materials (PCM) as thermal energy storage material in metal hydride reactor bed is an effective method to store the heat emitted during hydrogen charging and retrieving it later during discharging. The present work examines the effect of a PCM on the behaviour of the metal hydride in the reactor bed. A two-dimensional model was developed to describe the mass and heat transfer inside the metal hydride and the PCM as well as the interaction between them. The results were compared with other numerical simulation and experimental data. In the simulations, thermal conductivity and the latent heat were varied in order to evaluate the effect of these parameters on the kinetics of absorption, desorption and melting of the phase change material.     

Combustion characteristics of a porous media burner with partial hydrogen injection

Multiple energy sources are combined to solve the shortage due to more and more energy consumption. Hydrogen as an ideal clean and renewable energy was injected to the porous media burner to realize the utilization with methane simultaneously. The numerical model of double-layer structure imported with multi-step kinetics mechanisms was built to study the effects of hydrogen injecting position and width on the combustion characteristics of methane after the experimental validation. Results indicate that the axial temperatures during the hydrogen injection at the upstream and interface positions were obviously higher than that at the downstream position. With the increasing of hydrogen injection width, the overall temperature gradually decreased, which was corresponding to the decreasing trend of CO and NO_x emissions. However, the temperature and pollutant emissions increased as the equivalence ratio of methane and hydrogen increased. In addition, the increasing of methane and hydrogen velocity increased the CO emission and decreased the NO_x emission.     

Experimental study of hydrogen storage with reaction heat recovery using metal hydride in a totalized hydrogen energy utilization system

Experimental results for hydrogen storage tanks with metal hydrides used for load leveling of electricity in commercial buildings are described. Variability in electricity demand due to air conditioning of commercial buildings necessitates installation of on-site energy storage. Here, we propose a totalized hydrogen energy utilization system (THEUS) as an on-site energy storage system, present feasibility test results for this system with a metal hydride tank, and discuss the energy efficiency of the system. This system uses a water electrolyzer to store electricity energy via hydrogen at night and uses fuel cells to generate power during the day. The system also utilizes the cold heat of reaction heat during the hydrogen desorption process for air conditioning. The storage tank has a shell-like structure and tube heat exchangers and contains 50 kg of metal hydride. Experimental conditions were specifically designed to regulate the pressure and temperature range. Absorption and desorption of 5,400 NL of hydrogen was successfully attained when the absorption rate was 10 NL/min and desorption rate was 6.9 NL/min. A 24-h cycle experiment emulating hydrogen generation at night and power generation during the day revealed that the system achieved a ratio of recovered thermal energy to the entire reaction heat of the hydrogen storage system of 43.2% without heat loss.