Methods to predict the critical constants of organic compounds

New procedures are proposed to predict the critical values of temperature, pressure and volume of pure organic compounds. They require the normal boiling temperature, the orthobaric density at 20 °C and the molecular weight as input parameters. The critical temperatures are derived through simple relations linking Trb to the above quantities while the critical pressures and volumes are evaluated by using the Rackett equation. Reliable results are obtained by evaluating the Rackett constant, Zra, as function of Tb, σ and M for several classes of compounds having similar properties. The proposed methods have been applied to 144 organic compounds, both polar and non-polar. A comparison is given with a literature method based on the group contribution procedure.