A new equation of state applicable to both polar and nonpolar compounds has been developed. It is modeled after the nonspherical square-well potential. The repulsive pressure is approximated by contributions from the underlying hard convex molecular core and is represented by the hard convex body equation of Nezbeda. Based on the distribution function theories of liquids, the attrative part of pressure exhibited by anisotropic molecules is derived. This procedure leads to a compact, theoretically-based equation of state--a compromise between statistical mechanical rigor and engineering practicality.

The equation is applied to a variety of fluids including hydrocarbons (from methane to eicosane), natural gas components (CO(, 2), H(, 2)S, N(, 2)), alcohols, amines, ketones and coal chemicals. The accuracy in liquid density and vapor pressure prediction, in most cases, is within 1%. Comparison with similar equations of state, such as Peng-Robinson and BACK equations shows that the present equation is uniformly superior.