Method for computing component fugacities of binary mixtures in vapor-liquid equilibrium with results for methane-propane, methane-butane, and methane-n-pentane

Abstract

A method for computing the fugacities of components of binary mixtures at conditions of vapor-liquid equilibrium is presented. The new method utilizes coexisting phase composition and volumetric data rather than gas-phase partial volumetric data in the computations of the component fugacities. This permits an improvement in the accuracy of the computed results and increases the range of pressures for which computations can be made at isothermal vapor-liquid equilibrium conditions. Coexisting phase data published in the literature are analyzed to obtain results for methane-propane, methane-n-butane, and methane-n-pentane. Fugacity computations based on a limited quantity of gas-phase partial volumetric data are made to check the results obtained by the new method. Component fugacity data of mixtures at conditions of vapor-liquid equilibrium have practical and theoretical importance. Coexisting phase property data are required for the design of separation units in the production and refining of petroleum. In addition, compohent fugacity data may be used to evaluate and develop theories (5) for computing liquid and vapor compositions and thermodynamic properties which must be able to predict the component fugacities to establish conditions of equilibrium. A method for computing the fugacities of the components of a binary mixture at conditions of vapor-liquid equilibrium is presented. This method utilizes coexisting phase composition and volumetric data to minimize the effects of experimental errors on the computations. The data of Sage and Lacey (8) are analyzed to obtain results for methane-propane, methane-n-butane, and methane-n-pentane. Analysis . If the fugacities of the components of a mixture are known at a reference state, and sufficient experimental data exist for the mixture, the fugacities of the components at the mixture conditions can be determined by integrating the total derivatives of the fugacities from the known conditions to the mixture conditions. For a binary mixture at the temperature of the reference state,