Acide acétique

L'acide éthanoïque ou acide acétique est un acide carboxylique avec une chaîne carbonée théorique en C2, analogue à l'éthane, de formule semi-développée CH3-CO-OH ou courte AcOH, où Ac signifie « CH3CO », du groupe acétyle. L'adjectif du nom courant provient du latin la, signifiant vinaigre. En effet, l'acide acétique représente le principal constituant du vinaigre après l'eau, puisqu'il lui donne son goût acide et son odeur piquante détectable à partir d'. La distillation du vinaigre, attestée dès l'époque médiévale en Europe, a permis d'obtenir l'acide acétique pur, liquide combustible incolore à forte odeur de vinaigre, de masse volumique de l'ordre d' à qui se solidifie par simple immersion dans un bain eau-glace. Il est encore connu sous le nom d'acide acétique glacial ou autrefois de vinaigre fort. C'est le premier acide industriel connu. Ce liquide très faiblement conducteur, incolore, inflammable et hygroscopique représente à température ambiante un des plu

Incremental Identification of Kinetic Models by Online Spectroscopy and Multivariate Calibration

Laurent Brandinu

Extent-based kinetic identification is a modeling technique that uses number of moles / concentrations measurements to compute extents and identify reaction kinetics (partial orders of reactions and reaction rate constant) by the integral method of parameter estimation. This project uses infrared spectroscopic data with calibration models to predict moles / concentrations via a PLS1 regression method. The calibration set (design of experiment) is constructed from a seven-level design for multivariate calibration in molar fraction with reacting material. The extent-based kinetic identification using number of moles predicted from spectroscopic data is tested through experiments in a homogeneous liquid-phase reaction system. The experiments were conducted in an RC1 calorimeter from Mettler Toledo with two inlet streams, without outlet stream, and a ReactIR 10 FT-IR probe. The reaction studied was the transesterification of methanol and hexanol with acetic anhydride producing methyl, hexyl acetate and acetic acid. No solvents or catalyst were used, only pure species at a reaction temperature of 50°C. Results in terms of calibration design and model, computation of extents and extent-based kinetic identification are discussed.

2015

Operando XAS insight in the redox dynamics of VOx species and reducible supports involved in oxidative dehydrogenation of alcohols

Anna Zabilska

Supported vanadia (VOx) belongs to some of the most versatile selective oxidation and reduction catalysts applied for many reactions in the chemical industry and pollution control. Among them, the oxidative dehydrogenation (ODH) of alcohols is particularly attractive since it is one of the main industrial methods of formaldehyde production and a possible route for the transformation of renewable bioethanol to value-added products, such as acetaldehyde and acetic acid. Despite many spectroscopic methods used to investigate the mechanism of this reaction, the details about the redox involvement of VOx species and promoting supports (CeO2 and TiO2) remain debated. In this study, we used an element-specific operando X-ray absorption spectroscopy (XAS) to probe the redox transformations of active sites in vanadia-titania and vanadia-ceria catalysts during ethanol and methanol ODH. By carefully designing the steady-state and transient operando XAS experiments and by applying advanced chemometric methods, we could discriminate specifically and often quantitatively, which role plays each redox couple during the alcohol ODH cycle and uncover hidden structure activity-relationships.Chapter 1 introduces the relevant literature and summarizes the goals and the scope of the thesis.In Chapter 2, we investigate the redox dynamics of active sites in a bilayered VOx/TiOx/SiO2 catalyst (an analog of a widely used VOx/TiO2 catalyst with comparable activity) during ODH of ethanol. Operando time-resolved V and Ti K-edge XAS coupled with a transient experimental strategy quantitatively showed that the formation of acetaldehyde over VOx/TiOx/SiO2 catalyst is kinetically coupled to the formation of a V4+ intermediate, while the formation of V3+ is delayed and its rate is 10-70 times lower. The only very weak redox activity of the Ti4+/Ti3+ couple was detected, which suggests that TiOx species promote the redox activity of VOx indirectly, either via the fast electron transport between VOx species or by changing the electronic structure of VOx species.In Chapter 3, we report on possible difficulties, which can occur during in situ XAS studies of supported vanadia (VOx) catalysts at synchrotron beamlines related to X-ray-induced photochemical reduction of vanadium. We rigorously tested this phenomenon and suggest approaches, which can help to identify and mitigate vanadium photoreduction interfering chemical speciation.In Chapter 4, we focused on the structure-activity relationships in VOx/CeO2 system. We prepared a series of VOx/CeO2 catalysts using high-surface-area CeO2 Using time-resolved operando quick XAS at V K- and Ce L3-edges, we demonstrated that during oxygen cut-off experiments vanadium and cerium change their oxidation states in concert with each other and with the production of acetaldehyde. It suggests that both reducible vanadium and cerium are parts of the same active sites. The maximum VOx/CeO2 activity per mass of catalyst observed at ca. 3 V/nm2 coincides with the maximal amount of cerium atoms, which reversibly change their oxidation state during oxygen cut-off experiments.In Chapter 5, we prove that the mechanistic findings described in Chapter 4 for ethanol ODH over VOx/CeO2 catalysts are also valid for methanol ODH. Moreover, we confirm that the VOx surface density is the main descriptor of the activity for VOx/CeO2 catalysts in alcohol ODH.

EPFL2022

Operando XAS insight in the redox dynamics of VOx species and reducible supports involved in oxidative dehydrogenation of alcohols

Anna Zabilska

EPFL2022

Acetic acid production from milk permeate in anaerobic thermophilic fermentation

Incremental Identification of Kinetic Models by Online Spectroscopy and Multivariate Calibration

Operando XAS insight in the redox dynamics of VOx species and reducible supports involved in oxidative dehydrogenation of alcohols

Operando XAS insight in the redox dynamics of VOx species and reducible supports involved in oxidative dehydrogenation of alcohols

Acetic acid production from milk permeate in anaerobic thermophilic fermentation

Incremental Identification of Kinetic Models by Online Spectroscopy and Multivariate Calibration