ISOTHERMAL P, X, Y RELATIONS, ACTIVITY-COEFFICIENTS, AND EXCESS GIBBS FREE-ENERGIES FOR HEPTAMETHYLTRISILOXANE + TOLUENE AT 343.15, 363.15, AND 383.15K

Vapour-liquid equilibrium relations have been determined at 343.15, 363.15, and 383.15 K for heptamethyltrisiloxane + toluene. The isothermal variation of the total pressure with the composition of the equilibrium liquid and vapor phases was determined experimentally in a recirculating still over the entire composition range. Using Barker's method to calculate the vapour-phase composition, the activity coefficients and excess Gibbs free energy were calculated for each liquid composition. At 343.15 K, the curve of GE against x is asymmetric but as the temperature is increased GE decreases and passes through a minimum point in the heptamethyltrisiloxane-rich region, whereas, in the toluene-rich region, the maximum value of GE decreases and goes through a minimum. The S-shaped curves that are formed indicate an interesting variation in the intramolecular forces of the components with the temperature. Vapour pressures, the normal boiling temperature, liquid densities, and the critical properties are reported for heptamethyltrisiloxane. © 1979.