Selective Hydrogenation of Alkynes for Vitamin Production
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Date
2017
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Doctoral Thesis
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Abstract
Heterogeneously-catalysed hydrogenations represent key reactions for many industrial processes. In particular, selective hydrogenations of alkynes lie at the heart of pharmaceutical and fine chemicals industry for production of vitamins.
These reactions are usually carried out in batch processes in the presence of supported palladium-based catalysts modified with the addition of lead. The presence of this toxic element strongly limits the sustainability of these processes. Furthermore, the need of energy savings led, in the past decade, to a growing interest in new technologies for Process Intensification. For the aforementioned reasons, new reactor solutions need to be further investigated in order to reduce the energy consumption and to establish safe and environment-friendly process solutions.
This thesis contributes to the application and characterization of structured reactors for three-phase solvent-free continuous hydrogenation of alkynes. The proposed reactors consist of metal porous structures, with regular geometries, coated with a zinc oxide/alumina layer and impregnated with palladium nanoparticles.
The performance of this structured catalyst, in terms of reaction selectivity and activity, is found to be higher than that of Lindlar catalyst. This consideration, associated with the stringent environ-mental regulations regarding the industrial use of lead, makes this material a valuable alternative to the commercial catalysts.
Mathematical models are initially developed using a stirred slurry reactor with the aim of predicting the experimental behavior of the investigated reacting systems in the typical operating ranges of industrial processes.
The knowledge acquired during these preliminary studies is transferred to the porous structured reactor operated firstly with recirculation of the process liquid and then in fully continuous mode.
The kinetic and adsorption parameters governing the process are estimated in the kinetic regime by means of a numerical optimization procedure. The extension of the model to the mass transfer limited regime allows the estimation of an overall mass transfer coefficient under reacting conditions.
The mathematical model is successfully validated, to confirm its reliability, using the results of additional experimental runs not included in the pool used during the optimization procedure. In this case the model is used to predict the experimental results without any further adjustment of the estimated parameters.
This work enriches the understanding of three-phase selective hydrogenation of alkynes in designed structured reactors and proposes a mathematical model able to predict the performance of the experimental setup.
The model is developed in a step-by-step process and can be used to simulate the intrinsic kinetics and the mass transfer phenomena of this class of reactions in designed structured reactors. These novel reactor concepts are applied for the first time in continuous operation showing potential for Process Intensification.
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Examiner : Rudolf von Rohr, Philipp
Examiner : Morbidelli, Massimo
Examiner : Medlock, Jonathan
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ETH Zurich
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03348 - Rudolf von Rohr, Philipp (emeritus) / Rudolf von Rohr, Philipp (emeritus)