LIQUID-LIQUID VAPOR-PHASE EQUILIBRIA IN THE SYSTEM ETHANE- RETROGRADEBEHAVIOR OF THE HEAVY LIQUID-PHASE(PROPANE+EICOSANE )

The fluid phase behaviour of the ternary system ethane + propane + eic osane was studied experimentally with special emphasis on liquid-liqui d-vapour equilibria and retrograde condensation of the second, heavier liquid in this region. P,T-sections for mixtures of constant composit ion were determined according to the synthetic method for six constant molar ratios of ethane and eicosane and different mole fractions of p ropane. The temperature range investigated was 309-322 K and the press ure range 5.0-5.6 MPa. The liquid-liquid-vapour regions of the ternary mixtures are found at higher temperatures and pressures than the thre e-phase curve of the binary system. Addition of propane to a binary et hane + eicosane mixture of constant composition extends the three-phas e line to a region in accordance with the phase rule. This effect also gives rise to the phenomenon of retrograde condensation of the heavie r liquid phase. A description of the behaviour of ternary mixtures and a comprehensive explanation of the retrograde phenomena are given. Th e experimental results also allowed estimation of the temperature and pressure of the tricritical point.