Mont hydrothermal

Résumé

thumb|upright=0.8|Une cheminée hydrothermale dans l'océan Atlantique. Les monts hydrothermaux, cheminées hydrothermales, sources hydrothermales ou fumeurs sont des évents hydrothermaux situés sur l'axe des dorsales océaniques ainsi qu'à proximité des bassins arrière-arc. Ils sont une conséquence des mouvements des plaques tectoniques. Ils évacuent une partie de la chaleur interne de la Terre. C’est en 1977 que ces monts et la vie sous-marine luxuriante qui leur est associée ont été découverts aux îles Galápagos par le submersible américain Alvin. Cet écosystème privé de lumière est basé sur une production primaire assurée par des bactéries chimiosynthétiques qui vivent libres ou en symbiose avec les organismes. Historique right|thumb|Le submersible Alvin en 1978, un an après la découverte des monts hydrothermaux. En 1949, une étude des eaux profondes détecta des saumures anormalement chaudes dans la partie centrale de la mer Rouge. Plus tard, dans les années 1960, d'autres

Source officielle

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées

Chargement

Personnes associées

Chargement

Unités associées

Chargement

Concepts associés

Chargement

Cours associés

Chargement

Séances de cours associées

Chargement

The recycling of homogeneous acids imposes great challenges to the feasibility of lignocellulose hydrolysis processes. Although heterogeneous catalysts would offer a perspective to circumvent these challenges, conventional solid acids are instable under the hydrothermal conditions typical of hydrolysis processes. In this regard, acid functionalized carbons appear as auspicious alternatives due to the higher perseverance of carbon frameworks. The strong Brønsted acid sites in sulfonated carbons would be particularly well suited to catalyze the hydrolysis of cellulosic biomass. The utilization of these materials has so far been impeded by the controversy regarding the stability of sulfonic acid groups in carbons. Furthermore, it remains uncertain how the constraints imposed on the reaction system by the insolubility of lignocellulose influence the ability of solid acids to function as hydrolysis catalysts. This thesis shows that hydrothermally stable sulfonated carbons can be prepared by utilizing the structure-stability dependence of sulfonic acid groups in carbonaceous materials. The sulfonation of materials featuring a low degree of graphitization resulted in active solid Brønsted acid catalysts that however deactivated through the leaching of sulfonic acid groups. An in-depth physicochemical characterization of the catalysts paired with a systematic study of the stability of model sulfonic acids, revealed that the leaching-tendency is defined by substituent effects. Activating/deactivating substituents control the hydrothermal stability of aryl sulfonic acids by decreasing/increasing the tendency of the carbon-sulfur bond to undergo solvolysis. The presence of stabilizing and destabilizing substituents was found to be tunable by the temperature dependent decomposition of oxygen containing surface groups. Sulfonation of cellulose carbonized at 350°C resulted in a catalyst with 850 µmol g-1 hydrothermally (180 °C) stable sulfonic acid groups. Additionally, a hitherto unknown mode of deactivation was identified that proceeds by the ion-exchange of cationic impurities with protons of the active sites. This mode of deactivation can be fully overcome by implementing countermeasures to reverse or suppress ion-exchange processes. To tackle the limitations of homogeneous acids, the stable sulfonated carbons were used as catalysts in a semi-batch based lignocellulose hydrolysis process. It was found that the chemical recalcitrance and the insolubility of the substrate imposed strong limitations on the reaction with the catalyst and that soluble product formation occurred predominantly via auto-hydrolysis. The propensity of cellulose to undergo auto-hydrolysis could be enhanced by amorphizing its crystal structure through mechanical pretreatment in ball-mill. A heterogeneously catalyzed hydrolysis was achieved through mechanocatalytic processes facilitated by the concerted ball-milling (CBM) of the sulfonated carbon with the substrate. Sulfonic acid groups were pinpointed as active sites during the mechanocatalytic formation of soluble oligosaccharides. The secondary hydrolysis to monosaccharides in the semi-batch reactor was no longer constrained by the insolubility of the substrate. The combination of CBM pretreatment and hydrolysis in the semi-batch reactor was successfully extrapolated to the conversion of spruce fir wood to achieve yields in C5 and C6 derived products that are competitive with state-of-the-art diluted acid processes.

EPFL2019

Chargement

Life Cycle Assessment of Thermochemical Conversion of Empty Fruit Bunch of Oil Palm to Bio-Methane

Edgard Gnansounou, Paolo Montafia

The energy demand is increasing as well as the GHG emissions and the fossil fuels depletion. Public awareness on this topic significantly raised up in last decades. Nowadays conversion of residual biomasses in energy represents a real opportunity. However, the sustainability of such fuels has to be proven: Life Cycle Assessment is usually used for that purpose. Because of the increasing natural gas demand, scientists are searching for new gasification techniques and among them the hydrothermal gasification is extremely promising. In this chapter, the LCA of such a technology is presented. Contributions of land use change is highlighted. The chapter evaluates and compares effects of different allocation methods of raw material and it points out a rigorous approach for economic allocation. Furthermore, a section is devoted to the end of the plantation life and its consequence on carbon stock and GHG emissions. When the process is correctly integrated 1 MWh of heat and 16.06 kg of equivalent fertilizer are got by hydrothermal way with a significant reduction of impacts. Moreover, the climate change impact is cut down up to 91% and the fossil depletion decreases up to 96%. The study underlines the great dependency of impact reduction to allocation methods: thus, reduction percentages are 80% GHG emissions and 85% fossil depletion compared to the reference system.

Elsevier2017

Chargement

The seismic history of the Mosha fault, the largest and most active fault of Eastern Tehran metropolis, and its relation to the Damavand active volcano, the highest mountain in the Middle East, is investigated. We deduce that the central Mosha, near the Damavand, has a higher seismicity than either its western or eastern segments. On 7 May 2020, an Mw 5.1 earthquake occurred on the central Mosha, about 40 km east of Tehran and 10 km southwest of the Damavand crest, and it was felt intensely in Tehran. Its rupture is imaged and located in a region that presented a relative seismic quiescence compared to its eastern and western parts, during the last 14 years, suggesting its partial locking and heterogeneous distribution of fault frictional strength on this segment of Mosha. Its significant directivity to the west is confirmed by the mainshock rupture model, its PGA distribution, and distribution of early aftershocks. The rupture model suggests a relatively small stress drop of 2.6 bar, which is consistent with the comparatively high rupture dimension of 9 km for a Mw 5.1 earthquake, and indicates the easy rupture expansion on the central Mosha near the Damavand Volcano. The central Mosha experienced earthquakes in 1930, 1955, and 1983, as well as high microseismic activity and the 2020 seismic sequence, all of which strongly point to a possible influence of the Damavand Volcano on the seismicity of the central Mosha. This is corroborated by the observation of hydrothermal zones on the Mosha fault and the extension of a sill-like Damavand young magma chamber until central Mosha in tomography studies. We propose that the existing heat may increase the pore pressure on the fault, which lowers the effective normal stress, facilitates the nucleation-expansion of the rupture, and unclamps the fault. Damavand could act as a fuse and nucleate earthquakes, and if the rupture extends toward the west, it could have a significant directivity effect on low-frequency seismic waves that reach Tehran without attenuation and affect tall structures. In addition, high site amplification for frequencies up to 16 Hz due to the deep sedimentary basin, mainly in the mid-city of Tehran, will be remarkable for short buildings.

2022

Chargement