EQUATION OF STATE MIXING RULES THAT INCORPORATE ONLY THE RESIDUAL PART OF THE UNIQUAC MODEL

New mixing rules that incorporate the residual part of the UNIQUAC act ivity coefficient model and the correct quadratic concentration depend ence of the second virial coefficient are presented. Following our rec ent approach, only the attractive part of the excess Helmholtz energy derived from the equation of state (EOS) is related to the excess Gibb s energy. It is recognized that, in the extension of this concept to t he UNIQUAC model, the interpretation of the physical contributions of the combinatorial and residual parts must be considered. We conclude t hat the attractive forces are related only to the residual part of the UNIQUAC model. This allows the formulation of a class of mixing rules that are independent of the repulsive term in the EOS and are applica ble to both cubic and noncubic EOS. The proposed mixing rules are appl ied to different low-pressure systems, exhibiting vapor-liquid and liq uid-liquid equilibria, and to two near critical and supercritical syst ems.