Pore geometry and isosteric heat : an analysis for the carbon dioxyde adsorption on activated carbon.

International audienceThe isosteric heat of the carbon dioxide adsorption on activated carbon is determined by grand canonical Monte Carlo simulations. The results, obtained at room temperature and low pressures for an adorbent model with a slit type porosity, show that the isosteric heat depends strongly on the slit width. The maximun of the isosteric heat is reached for a pore with a width such as cooperative effects between the adsorbed molecules enhance the adsorption. The possibility to estimate the isosteric heat of a macroscopic sample, from adsorption isotherms computed for a distribution of slit pores with given sizes, is discussed

Biomolecules from olive pruning waste in Sierra Mágina - Engaging the energy transition by multi-actor and multidisciplinary analyses

Unidad de excelencia María de Maeztu MdM-2015-0552The price volatility of fossil resources, the uncertainty of their long-term availability and the environmental, climatic and societal problems posed by their operation lead to the need of an energy transition enabling the development and utilization of other alternative and sustainable resources. Acknowledging that indirect land-use change can increase greenhouse gas emission, the European Union (EU) has reshaped its biofuel policy. It has set criteria for sustainability to ensure that the use of biofuels guarantees real carbon savings and protects biodiversity. From a sustainability perspective, biofuels and bioliquids offer indeed both advantages (e.g., more secure energy supply, emission reductions, reduced air pollution and production of high added-value molecules) as well as risks (monocultures, reduced biodiversity and even higher emissions through land use change). Approaching economic, environmental and social sustainability at the local level and in an integrated way should help to maximize benefits and minimize risks. This approach has been adopted and is described in the present work that combines chemical, biological, social and territorial studies on the management of pruning waste residues from olive trees in the Sierra Mágina in Spain. The biological and social analyses helped to orientate the research towards an attractive chemical process based on extraction and pyrolysis, in which high added value molecules are recovered and in which the residual biochar may be used as pathogen-free fertilizer. In this region where farmers face declining economic margins, the new intended method may both solve greenhouse gas emission problems and provide farmers with additional revenues and convenient fertilizers. Further research with a larger partnership will consolidate the results and tackle issues such as the logistics

Combustible hydrogène - Utilisation

International audienceHydrogen has its most important application in fuel cells (FC), their powers ranging from the W (portable) to the MW (building electrical equipment). These uses require that the hydrogen be stored, transported and made available in the form of a gas compressed, liquid, or combined in solid materials. Its flammability and explosiveness require precautions set by relevant security standards. The potential role of this vector in our future energetic landscape goes hand in hand with the development of a "hydrogen economy".L'hydrogène a sa plus importante application dans les piles à combustible (PAC), leurs puissances allant du W (portables) au MW (équipements électriques d'immeubles). Ces utilisations de l'hydrogène impliquent qu'il soit stocké, transporté et mis à disposition sous forme de gaz comprimé, de liquide ou encore combiné dans des matériaux solides. Son inflammabilité et son explosivité imposent des précautions objets de normes de sécurité adaptées. Le rôle que pourrait jouer ce vecteur dans le paysage énergétique de demain va de pair avec le développement d'une «économie de l'hydrogène»

High pressure cryo-storage of hydrogen by adsorption at 77K and up to 50MPa

International audienceIn this paper, we focused on hydrogen adsorption on large surface area solids, combining optimal extreme conditions i.e. very high pressure and low temperature for gas storage process purpose. Therefore, a new volumetric device is elaborated to obtain excess adsorption isotherms at 77 K up to 500 bar. Two activated carbons with different micro-porosities are analysed in the view of hydrogen storage investigation. Also, the results are compared to zeolite adsorption properties. Based on these results, the total mass and volumetric storage capacity are calculated using the bulk density relationship. Thereby, we obtained high storage in situ capacities equal to 5.2 wt% and 54.5 kgH₂/m³. Further, we also considered practical application aspects related to hydrogen storage process in highly porous packed materials

Hydrogen storage at low temperature and high pressure for application in automobile manufacturing

International audienceA brief review of the different methods of hydrogen storage process for application in automobile manufacturing was presented and discussed. The hydrogen storage by adsorption on super activated carbon AX21 at various thermodynamic conditions wasinvestigated. In order to describe the reality of the system, we planned a brief review, adiscussion and modeling of the different EOS equations adapted to a hydrogen gas.Different characterization tools for obtaining the physical property of AX21 were used,among them SEM, BET and Helium displacement method at high temperature. Thehydrogen storage capacity of AX21 at different temperature and pressure up to 70 MPa was investigated experimentally. In order to describe the experimental hydrogen gas excess adsorption results, the model of Chilev and a modified potential theory were selected. The comparison of the two models describing adsorption isotherms and a critical discussion of their accuracy was given. Based on the models results the absolute amount adsorbed was obtained. The difference between an absolute and an excess amount adsorbed at 77 K and 293 K was discussed. A comparison between the volumetric tank capacity obtained by pure compression and the adsorption process at both temperatures were studied. The method of hydrogen storage and optimal operating conditions were investigated

Review of hydrogen storage by adsorption in carbon nanotubes

International audienceThis work deals with hydrogen adsorption in carbon nanotube materials over a wide range of pressure and temperature in order to establish the reliability of this phenomenon as a valuable storage technique of hydrogen. Our purpose is to give, discuss and compare the different results published comprising our works. Both experimental and simulation adsorption data concerning the hydrogen gas within nanotube material framework are given. A comparison between the different studies should enable to gain a better knowledge of hydrogen adsorption in nanotubes and then to answer the following questions: How and where did the gas adsorption occur? Moreover, we will consider the possibility of controlling tube diameters and lengths that will enable to optimize nanotube structure for a maximal hydrogen adsorption. Indeed, the possibility of controlling microscopic parameters will enable to control the main material macroscopic property: the gas adsorption. Finally, it is noticeable that both the material synthesis and purification will have to be optimized in order to enable the gas adsorption measurements. Indeed, the adsorbent material will have to be available in large amounts with high degree of purity to ensure the hydrogen storage by adsorption in carbon nanotubes

Multi-Compound H2, CH4, and N2 Adsorption Analysis

International audienceIn order to study the purification of hydrogen and its separation from gas mixtures by adsorption, different models describing the adsorption equilibrium of gas mixtures have been tested; seven of them have been compared with experimental multi-component data obtained from the literature. The measurements include three-component mixtures of hydrogen, nitrogen, and methane. All the models used in this study are purely predictive; such models are competitive isotherm models which use only the previously obtained coefficients of the single-component isotherms. A mathematical description of each model is developed and discussed. Based on the results of numerical experiments, an analysis of how best to apply the Sips multi-component approach and the Ideal Adsorbed Solution theory is developed. A discussion on the ability and accuracy of the different models to describe the multi-component adsorption equilibria is developed. Based on this research, the Jovanovic model, which best reproduces the experimental results of the adsorption equilibrium in all cases, can be recommended as the most appropriate to use

Molecular simulation of the selective adsorption of CO₂ in combustion effluents

International audienceThe selective adsorption of mixture components is an important property of adsorbent materials for the purification and possible capture of combustion effluents. The selectivity of an adsorbent can vary strongly with the characteristics of its pore network. This study is devoted to determine the variation of the selective adsorption between the micro and meso pores of a given adsorbent. The estimation is done by molecular simulation on the specific case of a CO₂/N₂ binary mixture adsorbed on activated carbon. The simulation results are used to evaluate the ability of a theoretical approach to predict the selectivity change with the pore size