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Organic waste is generally characterized by high volume-to-weight ratios, requiring implementation of waste minimization processes. In the present study, the decomposition of high-density polyethylene (HDPE), was studied under thermal and catalytic pyrolysis conditions on two experimental systems. Firstly, pyrolytic conditions for HDPE decomposition were optimized in a laboratory-scale batch reactor. In order to maximize gas yields and minimize secondary waste, the effects of aluminosilicate catalysts, catalyst loading, and reaction temperature on decomposition efficiency were examined. Secondly, kinetics and reaction temperatures were studied on a large capacity thermobalance, especially adjusted to perform experiments under pyrolytic conditions at a larger scale (up to 20 g). The addition of catalysts was shown to enhance polymer decomposition, demonstrated by higher gas conversions. Condensable yields could be further minimized by increasing the catalyst to polymer ratio from 0.1 to 0.2. The most prominent reduction in pyrolysis temperature was obtained over ZSM-5 catalysts with low Si/Al ratios; however, this impact was accompanied by a slower reaction rate. Of the zeolites tested, the ZSM-5 catalyst with a Si/Al of 25 was found to be the most efficient catalyst for waste minimization and organic destruction, leading to high gas conversions (~90 wt%.) and a 30-fold reduction in solid waste mass.

International audience; This article presents the numerical modeling of an in-can melter containing a metallic and a glass phase. Low-frequency electromagnetic induction is used to melt and stir the metal, and the latter heats and drags the glass phase. A careful choice of operating parameters is required to prevent the solidification of the glass, and to increase the performances of the process. Numerical modeling helps in avoiding experimental trial and error method and in studying the effect of the operating parameters on the hydrodynamics. The main difficulty for the numerical modeling comes from the deformation of the interfaces, produced by the magnetic pressure. First, a theoretical estimation of this phenomenon is performed and compared with numerical and experimental results. Then, numerical results are presented for different power inputs, AC frequencies, and quantities of glass. One of the phenomena obtained numerically is air entrainment at the triple point, creating bubbles in the glass.

This study deals with the production of hydrogen from water-splitting thermochemical cycles based on mixed metal oxides. The solar synthesis of mixed oxides based on ceria was achieved by melting mixed powders of component oxides at high temperature. The reduced oxides (Ce2Ti2O7, Ce2Si2O7, CeFeO3, CeVO4, and CeNbO4) produced hydrogen in a three-step thermochemical cycle except CeVO4. The three-step cycle uses an alkali hydroxide (NaOH or KOH) in an activation reaction to improve oxidation and to facilitate water-splitting during the third step. Experimental investigations were performed to demonstrate the concept and to quantify the reactions performance for hydrogen production. The high temperature synthesis of reduced cerium-based mixed oxides was performed in a laboratory-scale solar reactor. The mixed oxides were analysed by X-ray diffraction and characterized by XPS, which identified Ce(III) species in the structure. The activation reaction with NaOH or KOH producing hydrogen was studied to determine the effect of temperature and particle diameter, and to quantify the chemical conversion for each cerium-based mixed oxide.

The production of hydrogen from a novel two-step thermochemical cycle based on SnO2/SnO redox reactions is presented. This process targets CO2-free hydrogen production by using renewable solar energy and water in a high-temperature water-splitting cycle. The cycle consists of a solar endothermic reduction of SnO2 into SnO(g) and O2 followed by a non-solar exothermic hydrolysis of SnO(s) to form H2 and SnO2(s). The objective of this study was to demonstrate this innovative concept for H2 production and to establish the potential of cycle implementation in an integrated solar chemical process. The reduction and hydrolysis reactions were experimentally tested in order to define optimal operating conditions, chemical conversion and hydrogen yield. The thermal reduction occurs under atmospheric pressure at about 1600 °C and over. The solar step encompasses the formation of SnO nanoparticles that can be hydrolysed efficiently in the temperature range 500–600 °C with a H2 yield over 90%. A preliminary process design is also proposed for cycle integration in solar chemical plants.

The study deals with a dynamic modeling of a solar thermochemical reactor operating continuously to simulate its behavior during transient periods. This reactor is devoted to the thermal reduction of volatile metal oxides which are involved in water-splitting cycles for hydrogen production. Unsteady mass and energy balances are solved to determine the evolution of the reactor temperature and of the outlet gas composition versus time. The kinetics of the chemical reaction is considered in the specific case of zinc oxide dissociation for which reliable data are available. For the chosen reactor design, the thermal inertia of the reactor materials has a weak influence on zinc production during short solar flux interruptions. Energy losses by conduction through reactor walls are the highest at small scale (ranging between 30% and 40% at 1 kW scale), whereas radiative losses through the aperture become predominant at large scale (50 MW scale) and greatly depend on the solar concentration ratio. Then, simulations show that a minimum concentration ratio of 2500 is necessary to reach a sufficient temperature (above 2000 K) allowing efficient ZnO dissociation.

A novel two-step thermochemical water-splitting cycle based on SnO2/SnO is proposed from the detailed study of the whole tin oxide systems involving three redox pairs. The thermal reduction of tin(IV) oxide occurs in the temperature range 1400-1600°C following a zero order kinetic law of Arrhenius with an activation energy of 394.8 kJ mol -1 and a pre-exponential factor of 8.32 X 10 8 g s -1 at atmospheric pressure. The operating conditions that prevent gaseous stannous oxide (SnO) from recombining with O 2 are defined. The effect of a quenching device (water-cooled finger) is negligible whereas operation at low total pressure or low O 2 and SnO partial pressures leads to nearly pure SnO product. The comparison of SnO and metallic tin hydrolysis in a fixed bed reactor reveals a higher reaction rate in the case of SnO. Hydrolysis of these reduced compounds shows nearly complete conversion producing hydrogen by a solid/gas reaction proceeding at moderate temperature, thus easy to implement in a common reactor technology.

This article presents an XPS study of Ce 3d emission spectra dominated by atomic multiplet effects in core level spectroscopy of rare earth compounds (Ce oxides). Core level spectroscopy has been used to study the electronic states of Ce 3d5/2 and Ce 3d3/2 levels in Ce4+ and Ce3+ states. The well-resolved components of Ce 3d5/2 and Ce 3d3/2 spin-orbit components, due to various final states (4f0, 4f1, 4f2 configurations), were determined on 3d XPS spectra from commercial powders (CeO2, CePO4). These results were used to study the 3d spin-orbit component of mixed cerium-titanium oxide. This compound was prepared by co-melting commercial powders of CeO2 and TiO2 at 1800 K under air using a solar furnace with a flux density of 16 MW.m−2 at the focal point of the parabolic concentrator. The mixed oxide Ce2Ti2O7 was produced and contained Ce(III) species which may be reactive with water to give back the initial metal oxides and generate hydrogen, a valuable product considered as a promising energy carrier in the future in replacement of oil. The 3d photoemission spectra revealed the presence of mixed components attributed to mainly Ce(III) and Ce(IV) species. Copyright © 2008 John Wiley & Sons, Ltd.

A laboratory-scale solar reactor was designed and simulated for the thermal reduction of metal oxides involved in water-splitting thermochemical cycles for hydrogen production. This reactor features a cavity-receiver directly heated by concentrated solar energy, in which solid particles are continuously injected. A computational model was developed by coupling the fluid flow, heat and mass transfer, and the chemical reaction. The reactive particle-laden flow was simulated, accounting for a multiphase model (solid–gas flow). A discrete phase model based on a Lagrangian approach was developed. The kinetics of the chemical reaction was considered in the specific case of zinc oxide dissociation for which reliable data are available. The complete model predicts temperature and gas velocity distributions, species concentration profiles inside the reactor, particle trajectories and fates, and conversion rate assessing the reaction degree of completion. The reaction extent is highly dependent on temperature of the radiation-absorbing particles. Initial diameter of injected particles is also a key parameter because it determines the available surface area for a given particle mass feed rate. The higher the particle surface area, the higher the conversion rate. As a result, reaction completion can be achieved when particle temperature exceeds 2200 K for a 1 μ m initial particle diameter.

This paper presents a thermodynamic and experimental study of three-step thermochemical cycles for hydrogen production involving hydroxides (NaOH and KOH). Solar concentrated energy was successfull...

This study deals with solar hydrogen production from the two-step iron oxide thermochemical cycle (Fe 3 O 4 /FeO). This cycle involves the endothermic solar-driven reduction of the metal oxide (magnetite) at high temperature followed by the exothermic steam hydrolysis of the reduced metal oxide (wustite) for hydrogen generation. Thermodynamic and experimental investigations have been performed to quantify the performances of this cycle for hydrogen production. High-temperature decomposition reaction (metal oxide reduction) was performed in a solar reactor set at the focus of a laboratory-scale solar furnace. The operating conditions for obtaining the complete reduction of magnetite into wustite were defined. An inert atmosphere is required to prevent re-oxidation of Fe(II) oxide during quenching. The water-splitting reaction with iron(II) oxide producing hydrogen was studied to determine the chemical kinetics, and the influence of temperature and particles size on the chemical conversion. A conversion of 83% was obtained for the hydrolysis reaction of non-stoichiometric solar wustite Fe (1− y ) O at 575 °C.

Hydrogen, a promising and clean energy carrier, could potentially replace the use of fossil fuels in the transportation sector. Currently, no environmentally attractive, large-scale, low-cost and high-efficiency hydrogen production process is available for commercialization. Solar-driven water-splitting thermochemical cycles may constitute one of the ultimate options for CO2-free production of hydrogen. The method is environmentally friendly since it uses only water and solar energy. First, the potentially attractive thermochemical cycles must be identified based on a set of criteria. To reach this goal, a database that contains 280 referenced cycles was established. Then, the selection and evaluation of the promising cycles was performed in the temperature range of 900–2000 °C, suitable to the use of concentrated solar energy. About 30 cycles selected for further investigations are presented in this paper. The principles and basis for a thermodynamic evaluation of the cycles are also given.

The studies carried out on the UT-3 cycle lead to propose an operating mode that was tested with the Mascot Mockup. Additional investigations, partially presented in the present paper point out that the physicochemical properties of the solid and gaseous reactants will make the running of an industrial process very difficult. For instance, the sintering of the solid, the possible reactivity of the embedding matrix, … induce additional operation and then lower very sensibly the efficiency of the cycle. Furthermore, if the toxicity of the reactants is taken into consideration, the attractivity of this cycle decreases. If other considerations than the efficiency of the cycle are taken into consideration, it is possible to investigate other cycles. The present paper shows the first results of the studies carried out on alternative cycles having either low efficiency but involving inoffensive reactants or high efficiency but without using bromine. In the first case illustrated by the iron oxide cycle, it seems that the low efficiency can be partially offset by using abundant and inexpensive energy source. In the second one illustrated by the cerium chloride cycle, the significant industrial experience regarding the chemical engineering of the chloride could make the industrial development easier.

The cold crucible technology first developed for the treatment of the high level fission products can also be used for the direct treatment of intermediate level wastes. In this case, the wastes can be under the states of liquids or solids. The first experiments carried out for the direct treatment of ionic exchange resins emphasised the requirement of very high temperature on the surface of the glass. When this surface is to cold, the unperfected oxidation lead to a glass containing inclusion such as metallic compounds coming from the reduction of species contained in the waste. Thus, the quality of the glass could be not enough to meet with some specific requirements for long term storage. For few years, the Laboratory of the Innovative Processes has been studied the capability of a cold crucible to involved plasma torches ensuring the high temperature required for a complete oxidation of a large composition of waste. The developments and the assessment of different technological ways lead to build a cold crucible fitted with a bottom inductor together with twin plasma torches above the glass bath. This is the SHIVA process. The researches carried out on this innovative technology have shown the high efficiency of the combination for the treatment of a large variety of solid wastes. The oxidation is complete and the produced glass can be easily poured in a canister. This innovative process provides new perspective of treatment for a large variety of intermediate level waste stored on the ground of nuclear facilities.

International audience; This paper presents a process analysis of ZnO/Zn, Fe3O4/FeO and Fe2O3/Fe3O4 thermochemical cycles as potential high efficiency, large scale and environmentally attractive routes to produce hydrogen by concentrated solar energy. Mass and energy balances allowed estimation of the efficiency of solar thermal energy to hydrogen conversion for current process data, accounting for chemical conversion limitations. Then, the process was optimized by taking into account possible improvements in chemical conversion and heat recoveries. Coupling of the thermochemical process with a solar tower plant providing concentrated solar energy was considered to scale up the system. An economic assessment gave a hydrogen production cost of 7.98$ kg 1 and 14.75$ kg 1 of H2 for, respectively a 55 MWth and 11 MWth solar tower plant operating 40 years.