  Since a transcendental equation is involved in vapor liquid equilibrium (VLE)
calculations with a cubic equation of state (EoS), any exact solution has to be
carried out numerically with an iterative approach [1,2]. This causes
significant wastes of repetitive human efforts and computing resources. Based
on a recent study [3] on the Maxwell construction [4] and the van der Waals EoS
[5], here we propose a procedure for developing analytically approximate
solutions to the VLE calculation with the Soave-Redlich-Kwong (SRK) EoS [6] for
the entire coexistence curve. This procedure can be applied to any cubic EoS
and thus opens a new area for the EoS study. For industrial applications, a
simple databank can be built containing only the coefficients of a newly
defined function and other thermodynamic properties will be obtained with
analytical forms. For each system there is only a one-time effort, and
therefore, the wastes caused by the repetitive efforts can be avoided. By the
way, we also show that for exact solutions, the VLE problem with any cubic EoS
can be reduced to solving a transcendental equation with one unknown, which can
significantly simplify the methods currently employed [2,7].
