EQUATION OF STATE MODELING OF PHASE-EQUILIBRIUM IN THE LOW-DENSITY POLYETHYLENE PROCESS - THE SANCHEZ-LACOMBE, STATISTICAL ASSOCIATING FLUID THEORY, AND POLYMER-SOAVE-REDLICH-KWONG EQUATIONS OF STATE

Applicability of the equation of state models for modeling and simulat ion of phase equilibrium in polymer production processes is investigat ed. The flash separation of unreacted ethylene from polyethylene is us ed as a prototype for simulation. First, three equation of state model s (statistical associating fluid theory, Sanchez-Lacombe, and an augme nted Soave-Redlich-Kwong cubic equation of state) are comparatively us ed to correlate pure component volumetric, calorimetric, and phase equ ilibrium properties for ethylene and polyethylene. Next, they are test ed for correlation of vapor-liquid equilibrium of ethylene + low-densi ty polyethylene mixtures. Finally, a two-stage flash problem that mimi cs the separation process in the low-density polyethylene production i s simulated using the three models. Each equation of state model has s ome unique characteristics that affect the outcome of modeling pure co mponent as well as mixture behavior. The advantages and disadvantages of each model are discussed.