Modeling Condensed Mode Operation for Ethylene Polymerization: Part I. Thermodynamics of Sorption

A process model based on the thermodynamic models of Sanchez Lacombe and PC-SAFT EoS is developed to simulate and analyze the impact of vaporized n-hexane as an induced condensing agent on the rate of gas phase ethylene polymerization on supported catalyst. The simulation results of the process model indicate that the cosolubility phenomenon (i.e., the enhancement in the equilibrium concentration of ethylene in the amorphous phase of polyethylene in the presence of n-hexane) cannot be the sole reason for the experimentally observed increase in the polymerization rate seen over the entire duration of reaction. At the beginning, the rate of ethylene polymerization is enhanced much more strongly than would be expected simply from the cosolubility effect alone. However, as the reaction proceeds, the enhancement magnitude gradually decreases and reaches a steady-state value corresponding to the promotion magnitude in the equilibrium concentration of ethylene predicted by the two thermodynamic models.