A generalized alpha function of Peng-Robison equation of state for non-polar, weakly polar and polar compounds

A novel alpha function for Peng-Robinson equation of state was proposed and generalized with acentric factor and dipole moment for predicting thermodynamic properties of non-polar, weakly polar, and polar compounds. The parameters of new alpha function were fitted with vapor pressures of 70 compounds. Six different methods were investigated for the correlation of parameters of new alpha function and Heyen alpha function. The generalized new alpha function passed the consistency test. The results indicated that the predictive accuracy of generalized new alpha function and generalized Heyen alpha function was improved for the estimation of vapor pressure of 11 kinds of compounds, with the average relative deviations (ARDs) being 2.60% and 2.76%. The ARDs of the two generalized alpha functions were 2.04% and 2.09% for the enthalpy of vaporization. However, the generalized new alpha function and the other alpha functions had great deviations for the prediction of liquid volumes and isobaric heat capacities. The alpha function that was generalized with acentric factor and reduced dipole moment was more accurate than that was generalized with acentric factor, especially for the prediction of vapor pressure and enthalpy of vaporization of polar compounds.