SUPERCRITICAL ANTISOLVENT FRACTIONATION OF POLYETHYLENE SIMULATED WITH MULTISTAGE ALGORITHM AND SAFT EQUATION OF STATE - STAGING LEADS TO HIGH SELECTIVITY ENHANCEMENTS FOR LIGHT FRACTIONS

A multistage algorithm coupled with the SAFT equation of state is demonstrated on supercritical antisolvent (SAS) fractionation of a model polyethylene with ethylene and 1-hexene. Staging is found to improve the overall solvent selectivities, especially for lights removal. The degree of improvement increases with decreasing size of lights: the smaller the lights the greater the sensitivity to staging. As for the single-stage fractionation, conditions that favor high solvent densities, e.g., high pressure and low ethylene concentration, usually favor high capacities but low selectivities. The temperature effect, however, is not monotonic.