Desenvolvimento da equação de estado Polar SAFT-VR Mie: Medida experimental do equilíbrio de fases e da velocidade do som de sistemas contendo CO2 e hidrocarbonetos típicos das faixas da nafta ao diesel

Abstract

The recovery of oil and gas from Brazil's pre-salt layer has been associated to large quantities of carbon dioxide (CO2), which presents a high quadrupole moment. At high pressures large quantities of CO2 can be dissolved in the oil, therefore knowledge of phase equilibrium data of CO2/hydrocarbon systems is essential for understanding the thermodynamic behavior in these oil fields, as well as the knowledge of thermophysical properties of the oil at different pressures. In order to predict the behavior of hydrocarbons streams, the oil and gas industry uses different thermodynamic models, based on equations of state and mixing rules. The evaluation and improvement of these models depends on the reliability and diversity of the experimental data. The speed of sound is an important property related to the system compressibility and can be used as supporting information in comparative tests of different equations of state. Toluene and tetralin (aromatic molecules), decalin (naphthenic molecule), n-hexane, n-decane and n-hexadecane (linear alkanes) can be used as surrogate to naphtha, gasoline, kerosene and diesel fractions. In this context, the speeds of sound and densities of mixtures containing tetralin, decalin, n-decane and nhexadecane were experimentally measured. The experimental data were correlated with PFP, PHCT, PC-SAFT and SAFT-VR Mie equations of state. To evaluate the capability of the SAFT-VR Mie model to correlate equilibrium data, the phase equilibria of CO2/n-hexane, CO2/toluene, CO2/tetralin, CO2/n-decane and CO2/n-hexadecane were experimentally measured. For CO2/n-hexane, CO2/toluene and CO2/n-decane at higher temperatures the SAFT-VR Mie model predicts a critical point lower than expected. For CO2/tetralin and CO2/n-hexadecane systems the model fails to predict the liquid-liquid region observed in the lower temperatures. Aiming to improve the correlation of the phase equilibria data, the complete polar term (PSAFT-VR Mie) and truncated polar term (tPSAFT-VR Mie) from Karakatsani and Economou [J. Phys. Chem. B 2006, 110, 9252-9261] were added to the SAFT-VR Mie equation of state. The influence of using only three bodies contribution in the mixing rule of the polar term was also evaluated. The PSAFT-VR Mie model correlated the experimental speed of sound, condensed density, saturated density and saturated pressure data of pure substances with deviations close to the ones obtained with the SAFT-VR Mie model. However, the results obtained with the tPSAFT-VR Mie equation of state were better than the ones obtained with the SAFT-VR Mie model. In general, the PSAFT-VR Mie model with the modified mixing rule for the polar term presented a better performance in correlating the phase equilibria of the investigated CO2/hydrocarbon mixtures