Fluid phase equilibria in the system dimethyl ether/water from 50 to 220 C and pressures to 500 bar

Abstract

A vapor-recirculating equilibrium system has been used to study the fluid phase behavior of the system dimethyl ether/water (DME/H 2O). This system exhibits a liquid-liquid phase separation and a mixture critical line that consists of two branches. One branch originates at the critical point of DME (T = 126.6 C, P = 53.2 bar), and ends at a critical end point (T = 157 C, P = 67.2 bar, x DME = 0.79) where it intersects the three-phase region liquid-liquid-vapor. The second branch originates at the critical point of H 2O; with decreasing temperature it passes through a minimum in pressure, and then rises sharply to higher pressures (P C = 509 bar at T = 100 C). The critical end point at 157 C is a limiting point at which the vapor and DME-rich liquid phases become identical in the presence of the H 2O-rich liquid phase. These and other qualitative features of the phase behavior are illustrated by means of PTx phase diagrams.