Strengths and limitations of SAFT for calculating polar copolymer-solvent phase behavior

Abstract

Statistical associating fluid theory (SAFT) is used to calculate the cloud-point behavior of poly(ethylene-co-methyl acrylate) (EMA) copolymers (0–41 mol % methyl acrylate) in ethane, propane, butane, ethylene, propylene, 1-butene, chlorodifluoromethane, and dimethyl ether at temperatures to 250°C and pressures to 2,600 bar. Poor agreement is obtained between calculated and experimental data if the pure component EMA parameters used in SAFT are calculated using mixing rules that average polyethylene (PE) and poly(methyl acrylate) (PMA) parameters. Therefore, two of the three pure component parameters for all of the EMA copolymers are fixed to the values reported for PE and the third parameter, uo/k, for the copolymer containing 31 mol % methyl acrylate (EMA31) is determined by fitting the EMA31-butane cloud-point curve. The value for (uo/k)PMA is then obtained using a mixing rule and the values of uo/k for all of the EMA copolymers are calculated. A good fit of all of the copolymer–solvent cloud-point curves is obtained using a temperature-independent mixture parameter, kij. With this method of calculation it is possible to correlate cloud-point data with the SAFT equation of state if a small amount of experimental data are available. © 1996 John Wiley & Sons, Inc.