Double retrograde vaporization in the binary system ethane+linalool

In this study, the phenomenon of double retrograde vaporization is explained and experimental data of a binary system showing this type of behavior are presented. In double retrograde vaporization, two ‘domes’ are observed in the retrograde dew point curve of the P–x–y diagram, instead of the single-domed dew point curve in the familiar ‘single’ retrograde condensation. This results in triple- or quadruple-valued dew points at a specific composition. Double retrograde vaporization occurs within a very limited composition and temperature range very close to the critical point of the more volatile component. Even though double retrograde vaporization has been observed only a few times in literature, we believe that it is the normal behavior and always occurs in binary mixtures in which the two components differ greatly in molecular size. As a case study, experimental bubble point, dew point and critical point temperature and pressure data are presented for the binary system ethane+linalool at five different compositions ranging from 99.79 to 99.98% ethane. The data ranges within temperatures and pressures of 280–350 K and 3–6 MPa, respectively. This system exhibits quadruple-valued dew points at certain concentrations. The results indicate that a very minor change in the concentration can vary the shape of dew point curve significantly. The shapes of the multiple-dew point curves of ethane+linalool are also compared with those of the binary system ethane+limonene.