Avaliação de diferentes equações de estado cúbicas aplicadas ao equilíbrio líquido vapor de misturas binárias

Abstract

The quantitative description of separation processes that involves mass transfer, such as distillation, extraction and absorpation, is based an occurrence of thermodynamic equilibrium between the phases presents. In industry, the most commom phases coexisting are liquid and vapor and, therefore, the study of vapor liquid equilibrium (ELV), as a function of temperature, pressure and composition of substances in multicomponents systems is very important. There are two approaches to solving the problem in ELV: phi-phi (ϕ-ϕ) and gamma-phi (γ-ϕ), where the term gamma refers to the activity coefficient of the liquid phase, calculated by energy model of excess Gibbs, such as NRTL and UNIQUAC, and the term phi refers to the fugacity coefficient of the vapor phase, being calculated by a equation of state. So, this work used phi-phi approach to analyze the cubics equations of state of Peng Robinson, Soave Redlich Wong e Peng Robinson Stryjek Vera applied to the ELV of mixtures binary in the natural gas industry. The experimental data usad in this work were taken from the literature and the simulations were carried out a temperature of 230 K. In relation to the binary system methane (CH4) and ethane (C2H6), the equations showed similar results, obtaining R² near one, giving greater realiability of the results obtained. Regarding to the CH4 and CO2 system, the equations did not show satisfactory results in the region close to the critical point, which generated high mean relative error. Moreover, through the methodology adopted and computational tool, the equations were not able to simulate the C2H6 and CO2 system. Therefore, it is possible to conclude that the three equations showed satisfactories results for compounds chemically similars, as in the case of methane and ethane. For the other systems (methane + carbono dioxid and ethane + carbono dioxid), more satisfactories results would be obtained if complexs equations of state were used or a more robust tool than Excel’s Solver was used.