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ttractive
part of CEOS has been done not only by changing its form, but also in some cases by introducing one or even more extra param-eters [10] . On the other hand, the progresses in developing of the new alpha function were mainly started by the soave modifica-tion on RK EOS [5], in which an expression in terms of acenteric factor was introduced as a temperature dependence polynomial.
  The various alpha functions with their advantages and disadvan-tages were reviewed by the others[21,26,27] . The Soave-type alpha functions, such as Mathias and Copeman [18] , have some limita-tions as passing through minima with increasing temperature. A correct form of the alpha function behaves such that to decrease
monotonically with increasing temperature. Several investigators tried to introduce a switching function [16] , or components spe-cific parameter [19] ; however these types of alpha functions are less desirable than a generalized alpha function. Recently the alpha functions have been improved to correlation of the vapor pres-sure of the heavy hydrocarbons and polar components so that no need for switch function and correcting of the limiting value at high reduced temperatures [21] .
  The present work is a combination of the both aforementioned approaches, so in this study, first a modified attractive term is pro-posed with keeping the vdW repulsive term, and second a new alpha function is proposed, so that a new three-parameter cubic equation of state is introduced. The new alpha function has the  haracteristics of a correct behavior of an alpha function that has been explained above. In this work, the new CEOS is validated by correlation and prediction of physical properties of the pure com-ponents such as saturated vapor pressure, liquid density, vapor volume, enthalpy of vaporization, heat capacity, sound velocity and supercritical properties. Furthermore, using one-fluid vdW mixing rules, the new CEOS is applied for calculation of the bubble pressure and vapor mole fraction of several binary and ternary mixtures. n addition, the phase envelope calculation of a typical synthetic atural gas (SNG) is carried out using the new CEOS.

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