Local Composition Mixing Rules Research Articles

A proper theoretical basis for local composition mixing rules and a new class of activity coefficient models

A proper theoretical basis for local composition mixing rules and a new class of activity coefficient models

A molecular theory for the thermodynamic behavior of polar mixtures. II. Development of an equation of state based on the local composition mixing rules

In this study, the essential features of a molecular theory developed earlier for the local composition model in solution thermodynamics is used as the basis for more applied calculations of vapor-liquid equilibria for mixtures of molecules vastly different in size, polarity, and strength of interaction. An accurate equation of state is introduced into the method by incorporating the Helmholtz free energy through the Gibbs-Helmholtz relation. In the local composition mixing rules, the interaction energy effects are represented by a multifluid model, while molecular size effects are represented by a one-fluid model, which in spirit corresponds to a mean density approximation for the molecular pair distribution functions. Calculations of the vapor-liquid equilibria of a wide variety of binary mixtures including nonpolar hydrocarbons, hydrogen-bonding alcohols, water, ammonia , and carbon dioxide show good agreement with experimental data.

Gas solubility calculations. II. Application of a new group-contribution equation of state

A new equation of state has been developed for polar as well as nonpolar components. It is based on the generalized van der Waals partition function and uses local-composition mixing rules. The group-contribution version of this equation of state (the GC-EOS) is described and tables containing parameters for 14 solvent groups and 9 gases (H 2, N 2, CO, O 2, CH 4, C 2H 4, CO 2, C 2H 6 and H 2S) are presented. The GC-EOS predicts vapor-liquid equilibria well for all kinds of systems involving the groups considered. The method requires only information concerning readily accessible pure-component properties. Calculations for multicomponent systems show that the method suggested provides very good predictions of multicomponent high-pressure vapor-liquid equilibria and fairly good predictions of Henry's constants in mixed solvents.

Extension of the Peng-Robinson equation of state to complex mixtures: Evaluation of the various forms of the local composition concept

Density-dependent local composition (DDLC) mixing rules (Whiting and Prausnitz, 1981, 1982 and Mollerup, 1981) offer great promise to extend equations of state to highly nonideal mixtures. In this work we investigate various aspects of the DDLC concept and offer two useful forms. All development is done with the Peng-Robinson (1976) equation of state, but the results have general applicability.