STRENGTHS AND LIMITATIONS OF SAFT FOR CALCULATING POLAR COPOLYMER-SOLVENT PHASE-BEHAVIOR

Statistical associating fluid theory (SAFT) is used to calculate the c loud-point behavior of poly(ethylene-co-methyl acrylate) (EMA) copolym ers (0-41 mol % methyl acrylate) in ethane, propane, butane, ethylene, propylene, 1-butene, chlorodifluoromethane, and dimethyl ether at tem peratures to 250 degrees C and pressures to 2,600 bar. Poor agreement is obtained between calculated and experimental data if the pure compo nent EMA parameters used in SAFT are calculated using mixing rules tha t 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, u(o)/k, for the copolymer containing 31 mol % methyl acryla te (EMA(31)) is determined by fitting the EMA(31)-butane cloud-point c urve. The value for (u(o)/k)(PMA) is then obtained using a mixing rule and the values of u(o)/k for all of the EMA copolymers are calculated . A good fit of all of the copolymer-solvent cloud-point curves is obt ained using a temperature-independent mixture parameter, k(ij). With t his method of calculation it is possible to correlate cloud-point data with the SAFT equation of state if a small amount of experimental dat a are available. (C) 1996 John Wiley & Sons, Inc.