CEOS/AE mixing rules from infinite pressure to zero pressure and then to no reference pressure

A CEOS/AE mixing rule with no reference pressure is presented. An approach is developed that shows that the excess Helmholtz free energy at any pressure relative to its value for a van der Waals fluid is equivalent to the same relative value of the excess Gibbs energy at the same pressure. This approach allows the mixing rule to incorporate a GE model at any pressure and temperature without requiring any additional binary interaction parameters or causing any thermodynamic inconsistency. The methodology of developing the no-reference-pressure mixing rule avoids the common assumption of constant excess Helmholtz free energy with respect to pressure that is often made for the infinite pressure approach and extends the range of solution of the liquid volume to the critical point for the zero-pressure approach. The mixing rule is density (temperature) dependent in an explicit form. Because of this density function, the mixing rule reproduces accurately the incorporated GE model.