Phase behaviour of the binary system ethane+limonene

As part of a study to assess the capacity of supercritical fluids in deterpenating citrus essential oils, high-pressure vapour–liquid equilibria of the binary system ethane+limonene were determined experimentally. Bubble and dew points were measured at ethane mole fractions ranging from 0.2 to 0.9993 and within temperature and pressure ranges of 273−372 K and 0.5–10.5 MPa, respectively. Critical points of this binary system were also determined experimentally for ethane mole fractions from 0.96 to 0.9993. The experimental results showed the interesting phenomena of double retrograde vaporisation, in which the dew point curve has a double-domed shape. In this limited region, increasing the pressure at fixed concentration results in triple- or quadruple-valued dew points. The experimental results were correlated by the Stryjek–Vera modified version of the Peng–Robinson equation of state using the Mathias–Klotz–Prausnitz mixing rule.