Selection of coals of different maturities for CO2 Storage by modelling of CH4 and CO2 adsorption isotherms

International audienceCO2 injection in unmineable coal seams could be one interesting option for both storage and methane recovery processes. The objective of this study is to compare and model pure gas sorption isotherms (CO2 and CH4) for well-characterised coals of different maturities to determine the most suitable coal for CO2 storage. Carbon dioxide and methane adsorption on several coals have been investigated using a gravimetric adsorption method. The experiments were carried out using both CO2 and CH4 pure gases at 25 °C from 0.1 to 5 MPa (1 to 50 bar). The experimental results were fitted using Temkin's approach but also with the corrected Langmuir's and the corrected Tóth's equations. The two last approaches are more accurate from a thermodynamical point of view, and have the advantage of taking into account the fact that experimental data (isotherms) correspond to excess adsorption capacities. These approaches allow better quantification of the adsorbed gas. Determined CO2 adsorption capacities are from 0.5 to 2 mmol/g of dry coal. Modelling provides also the affinity parameters of the two gases for the different coals. We have shown these parameters determined with adsorption models could be used for classification and first selection of coals for CO2 storage. The affinity ratio ranges from a value close to 1 for immature coals to 41 for high rank coals like anthracites. This ratio allows selecting coals having high CO2 adsorption capacities. In our case, the modelling study of a significant number of coals from various ranks shows that anthracites seem to have the highest CO2 storage capacities. Our study provides high quality affinity parameters and values of CO2 and CH4 adsorption capacities on various coals for the future modelling of CO2 injection in coal seams

Adsorption of rhodamine 6G and humic acids on composite bentonite-alginate in single and binary systems

In this work, the preparation, characterization, and sorption of rhodamine 6G and humic acids on a composite sodium alginate-bentonite were investigated. Their structure and morphology were analyzed by several techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, and N-2 adsorption at - 196 degrees C. A synergetic sorption mechanism was observed in binary systems; humic acids adsorption was enhanced by the presence of Rh6G in the mixture. The kinetic studies revealed that the sorption follows a pseudo-first-order kinetic model and the sorption capacities of Rh6G increased with the pH value. The Langmuir isothermal model well described the adsorption isotherm data, showing a maximum adsorption capacity for Rh6G up to 429.5 mg/g at 20 degrees C. On the basis of the data of the present investigation, it is possible to conclude that the composite exhibited excellent affinity for the dye and humic acids, and it can be applied to treat wastewater containing dye and natural organic matter.AG is grateful for financial support from Santander Bank through the Research Intensification Program

Etude de la modification du comportement thermique des brais et des mélanges brai/coke par le soufre

Coal tar Pitches (CTP) are the residues of cokefaction tar distillation. Their thermal behaviour could be modified by the utilization of additives like sulfur. This work is a systematic study of the factors which can modified the thermal behaviour of the CTP/coke blends, precursors of graphite materials, like the chemical composition of the CTP, the initial sulfur percentage, the heat law or the origin and properties of cokes. We have divided our work in two parts.In a first time we have studied the thermal behaviour of the CTP/sulfur mixtures. We have clearly shows the positive effect of sulfur on mesophase formation and in consequence on optical texture. Crieria have been defined, allowing to connect the blends thermal reactivity to the chemical composition of the CTP and more precisely, we have precised the light fraction role of CTP during thermal treatment and the role of QI on optical texture evolution. Utilization of spectoscopic and thermic methods allows us to follow evolution of sulfur structures and their stabilities in function of temperature. In the second part of this work, we have studied effect of coke addition on physical texture of CTP and thermal behaviour of CTP/coke/sulfur mixtures. Cokes have been characterized by their surface energies and morphologies. We have then tried to understand the physical phenomena on the CTP/coke interfaces using a non direct method based on selective solvant extraction of a CTP previously adsorbed on coke surface. The results show a modification of the CTP physical structure, put in evidence by an increase of the hexane yield extraction in a case of CTP/coke blends and by an evolution of the chemical composition of the hexan soluble fraction. All the results of this work is usefull for the comprehension of the sulfur role in CTP and for the adaptation to the industriel processes of graphite makingLes brais charbonniers sont les résidus de la distillation des goudrons de cokefaction. Leur comportement thermique peut être modulé par l'utilisation d'additifs comme le soufre. Ce travail est une étude systématique des facteurs pouvant modifier le comportement thermique des mélanges brai/coke, précurseurs des matériaux graphites, comme la composition chimique des brais, le pourcentage en soufre introduit, les lois de chauffe utilisées ou encore l'origine et les propriétés des cokes. Nous avons divisé notre travail en deux parties. Dans un premier temps, nous avons étudié le comportement thermique des mélanges brai/soufre. Nous avons clairement démontré l'effet bénéfique du soufre sur la formation de mésophase et donc sur les textures optiques. Nous avons défini les critères permettant de relier la réactivité thermique des mélanges à la composition chimique des brais et notamment nous avons précisé le role joue par la fraction legere du brai durant le traitement thermique et le role des qi sur l'evolution des textures optiques. L'utilisation des techniques spectroscopiques et thermiques nous a permis de suivre l'évolution des structures soufrées organiques et leurs stabilités en fonction de la température. Dans la deuxième partie de ce travail, nous avons étudié l'effet de l'addition de coke sur la texture physique du brai ainsi que le comportement thermique des mélanges brai/coke/soufre. Les cokes ont été caractérisés par leurs énergies et leurs morphologies de surface. Nous avons ensuite tente d'appréhender les phénomènes chimiques aux interfaces brai/coke en développant une méthode indirecte basée sur l'extraction aux solvants sélectifs d'un brai préalablement adsorbe sur un coke. Les résultats obtenus montrent une modification de la structure physique du brai, mise en évidence par une augmentation du rendement d'extraction à l'hexane dans le cas des mélanges brai/coke et par une modification de la composition chimique de la fraction soluble. L'ensemble des résultats de ce travail est utile, d'un point de vue fondamental pour la compréhension du rôle du soufre dans les brais et d'un point de vue des applications industrielles, pour l'adaptation des procédé

Catalytic nitrate reduction in water

Nous avons choisi d étudier la conversion catalytique des nitrates dissous qui sont une cause majeure de contamination des eaux. C est un procédé complexe en plusieurs étapes qui suit la réaction : NO3- -> NO2- -> [NO] -> N2 + NH4+ + OH-Le but scientifique de cette thèse a été de déterminer une relation entre la structure physico-chimique des catalyseurs supportés et leur activité et leur sélectivité dans la réduction des nitrates. Les cinétiques de réaction ont également été étudiées en relation avec la structure des catalyseurs supportés Les travaux réalisés ont été axés autour des points suivants : 1. Elaboration des supports de catalyseurs : Deux groupes principaux de matériaux ont été étudiés : des matériaux carbonés et des matériaux inorganiques qui ont été modifiés par un traitement acide ou basique ou par dépôt des oxydes (Al2O3, ZrO2 seuls ou en mélange). 2. Synthèse du catalyseur : Les oxydes de métaux nobles et de transition ont été fixés sur les supports. Des systèmes monométalliques avec Pt et Pd et bimétalliques Pd-Cu ont été étudiés puis caractérisés par de nombreuses techniques. L efficacité des ces supports a été déterminée en fonction de leur activité catalytique. 3. Détermination des propriétés catalytiques : Le rôle et l effet des paramètres tels que nature du support, composition de la phase active, présence de sels inorganiques dans le milieu réactionnel, nature du réducteur sur la vitesse de réduction des nitrates et sélectivité des réactions ont été largement étudiés La discussion générale fait ressortir les combinaisons support/catalyseur les plus efficaces pour la dénitrification des eaux de consommationWe chose to study the catalytic conversion of dissolved nitrate, which are a major cause of water contamination. It is a complex process into several steps following the reaction: NO3- -> NO2-> [NO] -> N2 + NH4+ + + OH- The scientific goal of this thesis was to determine a relationship between the physico-chemical structure of catalysts and their activity and selectivity in the reduction of nitrates. The reaction kinetics were also studied in relation to the structure of catalysts. The work focused around the following points: 1. Preparation of catalyst supports: Two main groups of materials were studied: carbon materials and inorganic materials that have been modified by acid or base treatment or by deposit oxides (Al2O3, ZrO2 alone or in mixture). 2. Synthesis of catalyst: oxides of noble and transition metals have been established on the supports. Systems with monometallic Pt and Pd and bimetallic Pd-Cu have been studied and characterized by many techniques. The effectiveness of these materials was determined depending on their catalytic activity. 3. Determination of the catalytic properties: The role and effect of parameters such as support, type of medium, active phase composition, the presence of inorganic salts in the reaction medium, nature of reducing on the rate of nitrate reduction and selectivity of the reactions were widely studied. The debate highlights the combination support / most effective catalyst for denitrification of drinking waterMETZ-SCD (574632105) / SudocSudocFranceF

Équilibre et cinétique d'absorption de sondes moléculaires sur charbons actifs commerciaux

Le contexte général de ce travail, réalisé dans le cadre du GDR européen "Adsorbants Carbonés et Environnement", est l'étude fondamentale du rôle joué par certaines caractéristiques physico-chimiques des charbons actifs sur leurs propriétés adsorbantes vis à vis de composés organiques volatils (COV). L'adsorption sélective pour des couples de COV, de propriétés physico-chimiques très proches a été plus particulièrement étudiée. Dans ce cas, la sélectivité est contrôlée aussi bien par les effets de diffusion rencontrés lors du transfert de matière. Dans un premier temps, nous avons étudié hétérogénéité énergétique de la surface des solides carbonés par chromatographie en phase inverse à dilution infinie et par adsorption d'argon basse pression. Les deux méthodes permettent de mettre en évidence que les énergies d'adsorption des micropores sont très différentes entre les deux classes de charbons essentiellement microporeux. Mais, il est encore difficile de préciser la nature et la localisation des centres primaires dans le réseau poreux. L'étude des isothermes et des cinétiques d'adsorption des alcools a conduit également à différencier les mécanismes d'adsorption entre les deux classes de charbons actifs[Résumé anglais]METZ-SCD (574632105) / SudocSudocFranceF

Adsorption studies of an azo dye using polyaniline coated calcined layered double hydroxides

International audienceIn this study, novel composite polyaniline/calcined layered double hydroxides was synthesized through the chemical method using the ammonium persulfate as an oxidant and investigated for its behavior in selective and high adsorption of tartrazine dye from an aqueous solution in a batch system. Scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller method and thermogravimetric analysis were carried out. The effects of solution pH, initial concentration and contact time were investigated. The adsorption processes show that the max-imum adsorption capacity of tartrazine was 487.8 mg/g, obtained for the MgAlC-PANI composite and well fitted to Langmuir isotherm model. The adsorption processes followed the pseudo-second-order kinetics model with a very high correlation coefficient of 0.998 < R2 < 1. The regeneration studies revealed that the tartrazine loaded MgAlC-PANI could be reused for four consecutive cycles

Physicochemical characterization of three natural clays used as adsorbent for the humic acid removal from aqueous solution

International audienceAdsorption behaviours of humic acid on three natural clays from Ivory Coast were studied. In order to investigate the adsorption mechanism, characterization of clays and the humic acid–clay complex was conducted by using various analytical methods (attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), specific surface area analysis (BET) and chemical composition). As a result, adsorption process showed that the maximum adsorption capacity of humic acid was achieved at pH = 3 and was found to be to 115 mg/g obtained for the best sample. For all clays, the adsorption was found to be strongly dependent on pH and well fitted by the Langmuir model. In addition, it was shown that the adsorption capacity was linked to the kaolinite content of each sample. The results showed that humic acid adsorption onto clay was made via electrostatic interactions, ligand exchange and hydrophobic interactions. This study showed that clays are valuable adsorbents for the removal of humic acid

Low pressure argon adsorption assessement of the pores connectiviries in activated carbon

Low-pressure argon adsorption has been used to study the energetic distribution of microporous activated carbons differing by their burnoff. The collected isotherms were analyzed using the derivative isotherm summation method. Some oscillations on the experimental curves for very low partial pressures were detected. The results are analyzed and discussed according to the literature and could be attributed to local overheating caused by spontaneous mass transfer of argon through constrictions between former pores and the new opening pore or deadend pores. We used the dynamic character of the experimental method and mainly the discrepancy of the quasi-equilibrium state to deduce key parameters related to the porosity topology

Coal laboratory characterisation for CO2 geological storage

International audienceGeological storage of CO2 in unmineable coal seams could be a very interesting option in the sustainable management of coal basins. However, the various chemical and physical parameters that determine the success or failure of this type of operation need to be clarified. The CHARCO project aims at developing methods and analysis techniques in order to define the major parameters enabling optimal CO2 storage conditions. In this framework, 22 coals of different ranks were sampled in different locations and systematically characterized (coal ranks, macerals, porosities, CO2 and CH4 adsorption isotherms ...). The isotherms were modelled using the classical Langmuir formalism in order to obtain their adsorption capacities and their affinity for CO2. The high number of coals and parameters considered in our study allow a statistical treatment using Principal Component Analysis. The sorption capacity can not be easily correlated with any other single parameter. On the other hand, CO2 affinity is correlated with coal rank