A novel dynamic recirculating apparatus for vapour–liquid equilibrium measurements at moderate pressures and temperatures

• A novel dynamic VLE apparatus is presented.
• It has been designed for operation up to 750 kPa and 600 K.
• It is capable of both isobaric and isothermal VLE measurements.
• Operational capability demonstrated via vapour pressure and binary VLE measurements.

A novel dynamic recirculating apparatus has been constructed for the measurement of isobaric and isothermal vapour–liquid equilibrium (VLE) measurements for pressures up to 750 kPa and temperatures up to 600 K. The apparatus has been constructed from 316 stainless steel (SS) and features Pyrex sight glasses in strategic positions to allow for the observation of flow patterns and circulation rates. The capabilities of the apparatus have been demonstrated through the measurement of pure component vapour pressures and binary vapour–liquid equilibrium data. Vapour pressure measurements were undertaken for cyclohexane, n-heptane, n-octane, ethanol and 1-propanol. Isobaric VLE data have been measured for the (cyclohexane + ethanol) system at pressures of 40.00, 69.81, 97.72 and 150.0  kPa and isothermal VLE data have been obtained for the (2-propanone + 2-butanol) system at a temperature of 373.15 K. The experimental azeotropic temperatures and compositions for the cyclohexane + ethanol isobaric data sets have been determined and correlated to linear functions. The experimental VLE data were correlated to the Wilson, NRTL and UNIQUAC models using the γ − ϕ approach with the truncated two-term virial equation of state (with the Hayden and O’Connell method for second virial coefficients). Thermodynamic consistency testing for the VLE data sets was performed with the Herington area test for the isobaric data and the point test of Van Ness and Fredenslund for the isothermal data.