Systematic Comparison of Slurry and Gas-Phase Polymerization of Ethylene: Part I Thermodynamic Effects

摘要

The Sanchez-Lacombe model is used to investigate the multiphase and multicomponent thermodynamic equilibrium during ethylene polymerization and ethylene/1-hexene copolymerization in slurry and gas-phase reactors. The simulation study focuses on the interactions among ethylene, polyethylene, hydrogen, 1-hexene, and n-hexane under typical polymerization conditions. When used as a diluent, n-hexane increases the concentrations of all reactants in the amorphous polymer phase due to the cosolubility effect. Moreover, n-hexane significantly swells the amorphous polyethylene. This means that a polyethylene particle with the same degree of crystallinity has a larger amorphous phase fraction in slurry than in gas-phase reactors. Consequently, if the gas phase concentration is the same in both modes of polymerization, the concentration of all reactive species in semi-crystalline polyethylene particles will be higher in slurry reactors. The thermodynamic equilibrium simulations agree with the reported experimental results and can explain why supported catalysts behave differently in slurry and gas-phase polymerizations.