VAPOR-LIQUID-EQUILIBRIA FOR METHANOL PLUS POLY(ETHYLENE GLYCOL) 250 DIMETHYL ETHER

Vapor-liquid equilibria P, T, x for the methanol + poly(ethylene glyco l) 250 dimethyl ether (PEGDME 250) binary system were obtained by the static method in the range of temperatures from 293.15 K to 423.15 K a t 10 K intervals. A modified Barker's method was used to accurately ca lculate the liquid and vapor composition from the overall composition of the sample, the measured pressure and temperature, and the Redlich- Kister expression for the excess Gibbs free energy of the liquid phase at each temperature. The obtained P, T, x data were correlated by the NRTL and UNIQUAC temperature-dependent activity coefficient models us ing the maximum likelihood method. This system shows nearly ideal beha vior at lower temperatures but negative deviation at higher temperatur es. Also with the increase in temperature and composition of poly(ethy lene glycol) 250 dimethyl ether, the logarithm of activity coefficient s of methanol becomes more negative. The excess molar enthalpy was cal culated using the Gibbs-Helmholtz equation and the NRTL and UNIQUAC pa rameters at 303.15 K and compared with experimental data existing in t he literature.