Éditeur(s) : HAL CCSD
Résumé : International audience
In Biomass for sustainable applications-energy production and storage and pollution remediation.

hal-01682102
https://hal.univ-antilles.fr/hal-01682102

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Despite many studies, our understanding of silica precipitation from natural waters remains limited, in particular for geothermal waters. Here we present a detailed study on the kinetics of silica polymerization as a function of fluid temperature and pH using high-temperature (250-260 °C) seawater-derived geothermal fluids as those discharged from the Bouillante geothermal site.We monitored the on-site decrease in monomeric silica concentration(initial SiO2 concentration of about 600 mg/l)with time using the molybdenum blue spectrophotometric method on samples of separated water collected from the high-pressure separator at 167 °C and cooled to 25, 50, 75, and 90 °C and for pH values ranging from 5 to 8. During all these experiments, only silica polymerization was observed, with the formation of colloidal particles in suspension in the solutions. No scaling of amorphous silica was formed. The collected data were after modeled in order to determine the useful kinetic parameters for predicting and preventing amorphous silica precipitation in the production wells during fluid exploitation in the specific context of Bouillante. Results under the investigated experimental conditions show that the kinetics of silica precipitation is affected more strongly by pH than by temperature change. The reaction in the acidic Bouillante solution begins with a transition period that significantly decreases the kinetics of silica polymerization. Modeling the experimental data indicates that the silica polymerization up to the state of equilibrium is characterized by a 2nd-order kinetic law relative to dissolved silica; this could indicate that the polymerization is controlled mainly by the formation of dimers. However, the first hour of the experiments is better characterized by a 4th-order kinetic law, suggesting more complex polymerization reactions in the initial stage with the formation of nanocolloidal particles containing 3 to 4 monomers. In both cases, the corresponding kinetics rate constant k is linearly dependent on pH for pH between 5 and 7. The activation energy Ea for the overall reaction, calculated using the Arrhenius equation under the considered pH and temperature conditions, ranges between 41±9.8 and 54±9.6 kJ/mol. To complete this work, the colloid particles formed at the end of the kinetics experiments were extracted and analyzed by SEM and TEM microscopy, X-ray Diffraction and the BET method. Results show that the size of the colloids increase and their specific surface decrease with increasing pH and are thus dependent on pH. Globally, our work provides a reliable database for understanding silica polymerization kinetics in natural geothermal brines or geologic waters characterized by a near neutral pH and moderate dissolved silica concentrations.
ISSN: 0009-2541

hal-01403092
https://hal-brgm.archives-ouvertes.fr/hal-01403092
DOI : 10.1016/j.chemgeo.2016.08.031

Éditeur(s) : HAL CCSD
Résumé : EGU2012-6377- Geophysical Research Abstracts vol. 14
The hot geothermal fluid produced by the wells of the Bouillante power station, in Guadeloupe, contains various dissolved species such as silica or some metals (Zn, Pb, etc). During the exploitation, the geothermal fluid is flashing and cooling (from 260 to 160°C for the high-pressure steam-liquid separation and down to 110°C for the low-pressure phase separation of a part of the separated liquid at 160°C). Consequently, the dissolved species can form scale deposits such as amorphous silica or poly-metallic sulphides, according to the exploitation conditions, and cause serious scaling problems on the production and the surface installations. These minerals could also precipitate during the partial underground re-injection of the production fluids which is being set up in the Bouillante power station. In this study, in order to predict and prevent the possible silica precipitation at temperature lower than 160°C, during the partial underground reinjection of the production fluids of Bouillante or their thermal valorization down to 110°C temperatures, we propose to investigate on site the kinetics of silica precipitation as a function of temperature and pH. The experiments presented here were carried out on site on samples of separated waters collected after the steam-water separator at 160°C, containing about 600 ppm of SiO2, at four cooling temperatures: 22, 50, 75 and 90°C, and for pH ranging from 4 to 9. These experiments showed that the silica deposition was always initiated by a polymerization mechanism characterized by an order 2 kinetic law and the formation of a white colloidal gel, which slowed down the silica precipitation under solid form. This latter was observed much later, after the polymerization stage, and only in particular conditions (long time of atmospheric exposure, water stagnation,. . . ). The results also confirmed that the silica precipitation kinetics is strongly dependent on pH. In acidic solution, a transition period is observed before the beginning to the silica polymerization. At neutral-basic pH, there is no transition period and the rate of polymerization is maximal for pH close to 8. The undergoing modeling of these experimental data and specific surface area measurements on the colloidal gel will allow us to determinate the kinetics parameters useful for the prediction and prevention of silica precipitation under the specific exploitation conditions of Bouillante power station. This work is financially supported by ADEME (French Agency for Energy and Environment), BRGM and UAG.
EGU General Assembly 2012
Vienne, Austria

hal-00697627
https://hal-brgm.archives-ouvertes.fr/hal-00697627

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
Turbinaria turbinata brown seaweeds were tested as carbon electrode material in symmetric, electrochemical supercapacitors. The electrochemical properties of the carbon materials were characterised for their application as supercapacitors using cyclic voltammetry, galvanostatic charge/discharge method and electrochemical impedance spectroscopic analyses. Our initial results showed that the optimal behaviour was obtained for the sample prepared by pyrolysis at 800 degrees C. The average surface area of the carbon was 812 m(2)/g. Electrochemical tests with an organic electrolyte gave the following interesting results: a capacitance of 74.5 F/g, a specific series resistance of 0.5 Omega cm(2) and an ionic resistivity of 1.3 Omega cm(2). These results show the promising capacitive properties of carbon derived from seaweeds and their application in electrochemical supercapacitors. (C) 2013 Academie des sciences.
ISSN: 1631-0748

hal-00817880
http://hal.upmc.fr/hal-00817880
DOI : 10.1016/j.crci.2012.12.016

Résumé : Le fluide chaud produit par les forages de la centrale géothermique de Bouillante (Guadeloupe) est enrichi en espèces dissoutes telles que la silice qui peuvent précipiter sous forme de dépôts solides lors de son refroidissement et gêner fortement la production électrique. L’un des principaux objectifs de ce travail de thèse a donc été d’améliorer l’état des connaissances sur les conditions physiques, chimiques et cinétiques de la précipitation de la silice amorphe à Bouillante. Après une étude des caractéristiques physico-chimiques des fluides et des dépôts associés au champ de Bouillante, des expériences sur la cinétique de précipitation de la silice, sur site, pour une large gamme de température (25 - 90°C) et de pH (4 - 12) ont été menées et analysées en détail.Pour l’ensemble de ces expériences, seule la polymérisation (réversible) de la silice dissoute, sous forme de suspensions colloïdales très stables en solution, a été observée. La modélisation des données expérimentales de cinétique montre que la vitesse de polymérisation de la silice suit une loi d’ordre 2 vis-à-vis de la silice dissoute jusqu’à l’équilibre en accord avec une dimérisation de la silice. Par contre, durant l’étape initiale de la réaction, une loi d’ordre 4 semble mieux adaptée, suggérant des réactions de polymérisation plus complexes avec formation de tétramères. La température a un effet limité sur la cinétique de polymérisation de la silice comparé à l’effet du pH qui est beaucoup plus important. L’énergie d’activation de la réaction globale est de 41 - 54 kJ pour des pH compris entre 5 et 8.La caractérisation de la silice précipitée a mis en évidence des différences notables entre la structure poreuse de la silice solide prélevée sur les installations de surface et celle de la silice colloïdale obtenue par polymérisation lors des expériences de cinétique, ce qui semble indiquer que des mécanismes différents interviennent dans ces deux contextes de précipitation de la silice dissoute.Le deuxième objectif de cette thèse était d’évaluer la possibilité de valoriser la silice extraite de l’eau géothermale de Bouillante dans un procédé de traitement des eaux naturelles par adsorption. Pour cela, les propriétés d’adsorption de la silice géothermale brute et fonctionnalisée par le poly(ethylèneimine) (ou PEI) ont été étudiées pour deux polluants : un colorant, le bleu de méthylène et un métal lourd, le plomb. Les résultats obtenus montrent que la silice brute possède une grande capacité d’adsorption vis-à-vis du bleu de méthylène. En outre, la fonctionnalisation de la silice par le PEI permet d’améliorer sa capacité d’adsorption vis-à-vis du plomb en solution, en accord avec un modèle cinétique du pseudo-second ordre suggérant une chimisorption. Le modèle d’isotherme de Redlich-Peterson est également en très bon accord avec les données expérimentales.
The hot geothermal fluid produced by the geothermal power plant of Bouillante (Guadeloupe) contains various dissolved components such as silica that can precipitate as solid deposits during their cooling and cause serious problems on the electricity generation. One of the aim of this study is to improve the understanding on the physical, chemical and kinetics conditions of the amorphous silica precipitation in the Bouillante geothermal field. After a study on the physical and chemical characteristics of the Bouillante fluids and deposits which can form during their exploitation, experiments on the kinetics of silica precipitation, on site, under a large range of temperature (25 – 90°C) and pH (4 – 12) have been carried out and analyzed in detail.During on site kinetics experimentations only dissolved silica polymerization (reversible) as colloidal gel, very stable in solution, was observed. Modeling of the experimental data showed that the kinetics polymerization is characterized by a 2-order kinetic law relative to dissolved silica until the equilibrium that is consistent with silica dimerization. On the other side, the initial stage of the reaction is better characterized by a 4-order kinetic law that suggested more complex polymerization reactions with tetramers formation.Temperature has a little effect on the polymerization kinetics compared with the pH which has an effect more important. The activation energy of silica precipitation calculated between 25 and 90°C, is about 41 - 54 kJ for pH ranging to 5 - 8.The characterization of the silica precipitate reveals significant differences in the porous structure of the silica collected on the surface installations and the one obtained from kinetic experiments that suggests different precipitation mechanisms. The second objective of this thesis was to evaluate the possibility to promote geothermal silica for the treatment of natural waters containing contaminants by adsorption. Adsorption properties of the untreated and functionalized by poly(ethylèneimine) (ou PEI) geothermal silica have been investigated for two pollutants: a colorant, the methylene blue and a heavy metal, the lead.Results showed that untreated silica has a great adsorption capacity concerning the methylene blue. Besides, silica functionalization by the PEI allows improving the adsorption capacity for lead in solution. The adsorption kinetics curves followed a pseudo-second order model consistent with a chimisorption. The isotherm model of Redlich-Peterson fitted well the experimental data.

http://www.theses.fr/2014AGUY0698/document