PhD defense of Sabrine KARDOUS

Title: Optimization of Grade Transition in Polyethylene Polymerization in a Fluidized Bed Reactor
Summary :

The variety of PE applications requires different grade specifications to suit the market demand. Most processes used to make linear low density polyethylene (LLDPE) are gas phase processes. These processes are clean (solvent-free) and less energy consuming, but they are limited in their productivity by the high exothermicity of the reaction. In order to overcome this issue, “condensed mode cooling” is frequently employed, where induced condensing agents (ICAs) are injected in order to absorb part of the reaction heat. However, it was observed that the presence of ICA influences the absorption of monomer into the polymer and consequently the reaction rate and the polymer properties.
This work has two objectives: a) to develop an off-line dynamic optimization procedure in order to optimize the transition between different grades of LLDPE in a fluidized bed reactor. As this reactor is frequently operated under condensed mode, it is important to account for the ICA effect in the process model. Hence, a kinetic model is combined with a thermodynamic model to describe the grade transitions. The results highlight the importance of the thermodynamic model during grade transition. b) to use the developed model in predicting the melting onset temperature of polyethylene particles in a fluidized bed reactor. By this way, the model accounts for the effects of the polymer density and particle swelling by the different penetrants on the melting temperature. This model is then used within an optimization strategy to control the transition between different polymer grades while avoiding polymer melting.
Keywords: Grade transition, fluidized bed reactor; condensed mode cooling; thermodynamics; polyethylene, polymer melting temperature, off-line dynamic optimization.
In front of the jury composed of :
BENYAHIA, Brahim, Professeur Associé, Université Loughborough (Rapporteur)
LATIFI, Abderrazak, Professeur des Universités, Université de Lorraine (Rapporteur)
FONGARLAND, Pascal, Professeur des Universités, Université de Lyon  (Président du jury)
GUICHARDON, Pierrette, Professeure des Universités, École Centrale de Marseille (Examinatrice)
SHEIBAT-OTHMAN, Nida, Directrice de Recherche CNRS, Université de Lyon  (Directrice de thèse)
MCKENNA, Timothy, Directeur de Recherche CNRS, Université de Lyon  (co-encadrant de thèse)

Date(s) - 31 Mar 2021
14 h 00 min - 16 h 00 min


Filed under: Defense, PRODIS