Élimination du dioxyde de carbone atmosphérique

vignette|Planter des arbres est un moyen naturel d'éliminer temporairement le dioxyde de carbone de l'atmosphère. Lélimination du dioxyde de carbone atmosphérique, plus connue sous l'expression anglaise carbon dioxide removal (abrégé en CDR), désigne le captage et la séquestration du dioxyde de carbone () présent dans l'atmosphère par intervention humaine. Elle est également désignée sous le vocable émissions négatives. Il s'agit d'un type de séquestration du dioxyde de carbone, qui se distingue de la séquestration « naturelle » par le fait qu'elle est la conséquence d'une action volontaire de l'être humain. La CDR peut s'appuyer sur des processus de séquestration biologiques (par exemple dans les sols ou la biosphère, via la reforestation ou le changement de pratiques agricoles) ou bien sur des procédés partiellement ou totalement industriels, tels que le biochar, la bioénergie avec captage et stockage de dioxyde de carbone (BECCS) ou le captage du dioxyde de carbone dans l'air (DAC

Novel Ionic Liquids For Electrochemical Applications

Pui Shan Genevieve Lau

This thesis is organized into three main sections, and is concerned with the design and synthesis of novel ionic liquids (ILs), and their associated electrochemical applications. In the first section, a general introduction to the field of ionic liquids is presented, followed by the synthesis and characterization details of all novel compounds used in the study. The second section summarizes work done on the development of more stable dye-sensitized solar cells (DSCs). An introduction to the field of photovoltaics and DSCs is first delivered in Chapter 3, which is followed by two chapters of original work on ionic liqiud-based electrolytes for DSC applications. In Chapter 4, it is shown that novel triazolium-based ionic liquids can be used to fabricate dye-sensitized solar cells, giving power conversion efficiencies of up to 6.00 %. The ionic liquid-based electrolytes are found to be compatible with a range of organic and inorganic photosensitizers, although the ruthenium-based dye (coded C106) exhibits the best performance. A device employing one of these newly-developed electrolytes is also shown to be very stable, retaining ca. 90% of its initial performance even after 1000 hours of continuous full sun illumination at 60 âŠC. In Chapter 5, we focus on the development of stable porphyrin-sensitized solar cells, using IL-based electrolytes. Our studies reveal that the long-term stability of porphyrin-based DSCs are highly dependent on additives in the electrolyte. In particular, it is found that the additive, guanidinium thiocyanate, is essential for the preparation of long-lived devices. It is also shown that the beneficial effect of this additive originates from the thiocyanate anion, rather than the guanidinium cation. The third section of this thesis deals with the ionic liquid-catalyzed electroï¿Œchemical reduction of carbon dioxide. Following a general introduction on carbon dioxide mitigation using ionic liquids (Chapter 6), the results of our work in this area are presented in Chapter 7. Our studies reveal that not all ionic liquids are stable at the potentials required for CO2 reduction. However, the imidazolium-based salts generally perform quite well. The catalytic effect of the IL is found to mainly stem from the cation, with the anion playing a somewhat secondary role. Our results also demonstrate that substitutions on the imidazolium ring can have a huge impact on catalysis. Product analysis shows that the best-performing catalyst produces carbon monoxide as the dominant product, with Faradaic efficiencies of between 70 to 80 %.

EPFL2015

A mixture model to take into account diluted gas in liquid flow: applications to aluminium electrolysis

Emile Tryphon Pierre Soutter

Aluminium is a metal sought in the industry because of its various physical properties. It is produced by an electrolysis reduction process in large cells. In these cells, a large electric current goes through the electrolytic bath and the liquid aluminium. This electric current generates electromagnetic forces that set the bath and the aluminium into motion. Moreover, large quantities of carbon dioxide gas are produced through chemical reactions in the electrolytic bath: the presence of these gases alleviates the density of the liquid bath and changes the dynamics of the flow. Accurate knowledge of this fluid flow is essential to improve the efficiency of the whole process.The purpose of this thesis is to study and approximate the interaction of carbon dioxide with the fluid flow in the aluminium electrolysis process.In the first chapter of this work, a mixture-averaged model is developed for mixtures of gas and liquid. The model is based on the conservation of mass and momentum equations of the two phases, liquid and gas. By combining these equations, a system is established that takes into account the velocity of the liquid-gas mixture, the pressure, the gas velocity and the local gas concentration as unknowns.In the second chapter, a simplified problem is studied theoretically. It is shown that under the assumption that the gas concentration is small, the problem is well-posed. Moreover, we prove a priori error estimates of a finite element approximation of this problem.In the third chapter, we compare this liquid-gas model with a water column reactor experiment. Finally, the last chapter shows that the fluid flow is changed in aluminium electrolysis cells when we take into account the density of the bath reduced by carbon dioxide. These changes are quantified as being of the order of 30% and explain partially the differences between previous models and observations from Rio Tinto Aluminium engineers.

EPFL2022

Novel Ionic Liquids For Electrochemical Applications

Pui Shan Genevieve Lau

EPFL2015

A mixture model to take into account diluted gas in liquid flow: applications to aluminium electrolysis

Emile Tryphon Pierre Soutter

EPFL2022