THE INFLUENCE OF PRESSURE AND TEMPERATURE ON THE PHASE-BEHAVIOR OF THE SYSTEM H2O+C12+C7E5 AND RELEVANT BINARY SUBSYSTEMS

The influence of pressure on the phase behaviour of the systems H2O C7E5 and C-12 + C7E5 (C7E5, n-heptylpentaoxyethylene) was studied over a temperature range of 271-358 K and a pressure range of 0.1-100 MPa. It appeared that the system H2O + C7E5 shows a miscibility gap with a n upper critical solution pressure (p(beta)) which rises with increasi ng temperature. The system C-12 + C7E5 shows a miscibility gap with a lower critical solution pressure (p(alpha)) which also rises with incr easing temperature. It was found that dp(beta)/dT is larger than dp(al pha)/dT which supports the experimental observation that in ternary wa ter + oil + non-ionic surfactant systems the region in which three liq uid phases are in equilibrium, widens and shifts to higher pressures w ith increasing temperature. The UNIQUAC equation was used to correlate the measurements at atmospheric pressure and to predict the phase beh aviour in the ternary system H2O + C-12 + C7E5. Finally, a three-phase region was measured and compared with the predicted phase behaviour i n the ternary system.