SINGLE-STAGE FRACTIONATION OF POLY(ETHYLENE-CO-VINYL ACETATE) IN SUPERCRITICAL ETHYLENE WITH SAFT

Using the discrete thermodynamics approach, the single-stage fractiona tion of a poly-disperse poly(ethylene-co-vinyl acetate) in supercritic al ethylene and ethylene-vinyl acetate mixtures is modeled with an EOS rooted in statistical associating fluid theory (SAFT). The simulation results are compared to new high-pressure coexistence delta and size- exclusion chromatography data obtained on a few selected extracts. The polymer molecular-weight distribution is optimally represented by ten nearly-monodisperse pseudocomponents, determined by a nonuniform lump ing method SAFT quantitatively captures the effect of pressure, temper ature and solvent composition on the solvent capacity and the extract yield over a broad range of conditions. The ethylene capacity monotoni cally increases with increasing pressure between 200 bar and the cloud point pressure, with increasing VA concentration in the solvent mixtu re, and with increasing temperature above similar to 480 bar. At inter mediate pressure (200-480 bar), SAFT predicts that the ethylene capaci ty behaves nonmonotonically with temperature. The extract and raffinat e molecular weight and polydispersity are predicted also from SAFT as a function of pressure and solvent composition for a typical bubble- a nd dew-point-type fractionation, thereby illustrating the underlying d ifferences between those two phase disengagement mechanisms.