Empirical Two-Parameter Mixing Rules for a Cubic Equation-of-State

Four two-parameter mixing rules are presented along with expressions for the fugacity coefficient and compressibility factor obtained when they are used in conjunction with the Peng-Robinson equation of state. A comparison of the forms of these expressions and results obtained in the prediction of VLE for nine systems with these temperature-, pressure-, density-, and composition-dependent rules provides a guideline for the applicability, advantages and disadvantages of each. Excellent results were obtained, especially in the near critical region, when these simple pressure- and density-dependent rules were used to describe P-x data. The density-dependent mixing rule consistently yielded better predictions of VLE over a range of temperatures (using parameters obtained at a single temperature) than the results obtained by optimizing the interaction parameter of conventional mixing rule at each temperature. The composition-dependent rule was slightly less effective for most systems, but for highly polar, asymmetric systems, this rule was superior