On the phenomenon of double retrograde vaporization: multi-dew point behavior in the binary system ethane + limonene

Abstract

Instead of the usual single-domed retrograde dew point curves, S-shaped dew point loci may occur in the isothermal pressure–composition diagram of the binary system methane+butane. This phenomenon has the consequence that at and immediately below the critical temperature of methane, isotherms are present showing triple-valued dew points for a fixed concentration. A similar behavior was observed in the binary system methane+pentane. However, in the latter system, in a narrow concentration range at temperatures slightly above the critical temperature of methane, isotherms were determined experimentally showing even two domes in the dew point loci, indicating quadruple-valued dew points at a given concentration. The latter behavior leads to the phenomenon of double retrograde vaporization, i.e. in a pressure–composition diagram at a fixed value of the concentration, the following sequence of phase transitions occur when going from low to high pressures: gas→liquid+gas→gas→liquid+gas→fluid. This paper presents bubble, dew and critical point data for the binary system ethane+limonene at five different compositions ranging from 99.50 to 99.93 mol% ethane. The data range within temperatures and pressures of 280–330 K and 3–6 MPa, respectively. This system also exhibits triple- and quadruple-valued dew points at certain concentrations, i.e. this binary system also shows the phenomenon of double retrograde vaporization. The results indicate that a very minor change in the concentration can vary the shape of dew point curve significantly.