Transformations de l'isopropanol sur solides aluminiques : une approche mixte expérimentale / modélisation multi-échelle

Abstract : The upgrading of lignocellulosic biomass into strategic molecules for the chemical industry requires the adaptation of refining procedures to the transformation of oxygenated species. In this context, the dehydration of alcohols has seen renewed interest over the last decade. The work presented here aims at unravelling the reactivity of a model alcohol (isopropanol) over aluminic catalysts at the molecular scale. To this purpose, a study combining experiments and modelling at the molecular scale (DFT) and at the reactor scale (kinetic modelling) has been set up. By combining infrared spectroscopic experiments, kinetic measurements and molecular modelling of the adsorption and reaction pathways of isopropanol on gamma alumina, it is shown that this reactivity is mainly governed by the (100) facets of alumina. The competing formation of propene (major product) and diisopropylether (minor product) involves a common alcoolate intermediate adsorbed on a Lewis acidic aluminium atom, either by direct elimination of a water molecule (E2 mechanism) or by condensation with a second alcohol molecule adsorbed in vicinity (SN2 mechanism).A micro-kinetic model involving this single reaction site and including the transformation of the ether into isopropanol and propene allows reproducing the experimental results, provided that the effect of co-adsorbed water and alcohol molecules in the environment of the active site is taken into account, as the formation of water – intermediate dimers and the stabilization of the second alcohol molecule both contribute to an adjustment of the ether/propene ratio.
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Kim Larmier. Transformations de l'isopropanol sur solides aluminiques : une approche mixte expérimentale / modélisation multi-échelle. Chimie-Physique [physics.chem-ph]. Université Pierre et Marie Curie - Paris VI, 2015. Français. ⟨NNT : 2015PA066396⟩. ⟨tel-01282594⟩

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